diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,5 +1,97 @@
 # Changelog for srtree
 
+## 3.0.0.2
+
+- Added parser for NeoGP.jl 
+
+## 3.0.0.1
+
+- Fixed some wrong bounds 
+
+## 3.0.0.0
+
+- **BREAKING**: Removed the Accelerate AD backend (`Algorithm.SRTree.AD.Accelerate`).
+  The `ADBackEnd` type now only has `SingleThread` and `MultiThread` constructors.
+  This removes the `accelerate` and `accelerate-llvm-native` dependencies.
+- Out-of-core equality saturation with paged e-graph store (SQLite/PostgreSQL)
+- Frontier re-saturation: mark changed classes and re-saturate only the frontier
+- Streaming matcher for n-ary and cached genericJoin paths (O(1) memory on paged graphs)
+- Cycle-safe and size-budgeted `getBestExpr` extraction
+- Bounded cost/best fixpoints so recalc terminates on cyclic graphs
+- Bounded node-to-class and canonical maps on paged graphs (LRU caches)
+- Fast ByteString double parser for dataset loading
+- Thread `Loss` (not `Distribution`) through fitness functions; add `readLoss`
+- Multiset e-graph improvements
+
+## 2.0.1.7 
+
+- Added log10 MSE fitness function 
+
+## 2.0.1.6
+
+- Added Fractional Bayes model selection
+
+## 2.0.1.5
+
+- Fix `refit` to only replace the fitness if it improves the fitness 
+- Fix `paretoFront` 
+
+## 2.0.1.4
+
+- Added `loadTrainingOnly`, `splitData`, and `loadX` to `Data.SRTree.Datasets`
+- Added `getFitness`, `getTheta`, `getSize`, `isSizeOf`, `getBestFitness` to `Algorithm.EqSat.Egraph`
+- Added `parseNonTerms` to `Text.ParseSR` 
+- Added module `Algorithm.EqSat.SearchSR` with support functions for SR algorithms with EqSat
+
+## 2.0.1.3
+
+- Fix compatibility with stackage nightly 
+
+## 2.0.1.2
+
+- Fix bug where the parameters were printed as `t[:,ix]` instead of `t[ix]` in `showPython`
+
+## 2.0.1.1
+
+- MSE loss is now the default
+- Renamed `--distribution` argument to `--loss` in eggp and easter.
+- Fixed bug with Gaussian distribution and fixed number of parameters.
+- Fixed bug in which `--number-params 0` would create parameters.
+- Fixed bug in `rEGGression` that pattern matched equivalent expressions.
+- Support to `--numpy` flag that prints the output as a numpy expression (experimental, eggp only).
+- Support to `--simplify` flag that simplifies the expressions before displaying (experimental, eggp only).
+
+## 2.0.1.0
+
+- Support to Multiview Symbolic Regression in eggp and symregg.
+- Support to `--number-params` argument that limits the maximum number of parameters and allow repated parameters in an expression.
+
+## 2.0.0.4
+
+- Cleaned up test cases (they were deprecated), will include new ones later 
+
+## 2.0.0.3
+
+- Fixed compatibility with random-1.3.0 and GHC-9.12.1 
+- Fixed bug in Bernoulli distribution 
+- Removed `log(sqrt(x))` rule in parametric rules due to generating longer expressions 
+- Fixed DL calculation without the correct number of parameters 
+- Fixed memory issue when querying pattern distribution 
+
+## 2.0.0.0 
+
+- Complete refactoring of the library
+- Integration of other tools such as: srtree-opt, srtree-tools, srsimplify
+- Implementation of Equality Saturation and support to e-graph 
+- Using Massiv for performance 
+- Using NLOpt as the optimization library 
+
+## 1.1.0.0
+
+- Reorganization of modules
+- Renaming AD functions
+- Inclusion of reverse mode that calculates the diagonal of and the full Hessian matrices
+
 ## 1.0.0.5
 
 - Changed `base` and `mtl` versions
diff --git a/LICENSE b/LICENSE
--- a/LICENSE
+++ b/LICENSE
@@ -1,6 +1,5 @@
-Copyright Author name here (c) 2021
+Copyright (c) 2026, folivetti
 
-All rights reserved.
 
 Redistribution and use in source and binary forms, with or without
 modification, are permitted provided that the following conditions are met:
@@ -13,7 +12,7 @@
       disclaimer in the documentation and/or other materials provided
       with the distribution.
 
-    * Neither the name of Author name here nor the names of other
+    * Neither the name of the copyright holder nor the names of its
       contributors may be used to endorse or promote products derived
       from this software without specific prior written permission.
 
@@ -21,7 +20,7 @@
 "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
-OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
diff --git a/README.md b/README.md
--- a/README.md
+++ b/README.md
@@ -1,28 +1,283 @@
-# srtree: A symbolic regression expression tree structure.
+# srtree: A supporting library for tree-based symbolic regression 
 
-`srtree` is a Haskell library with a data structure and supporting functions to manipulate expression trees for symbolic regression.
+`srtree` is a Haskell library that implements a tree-based structure for expressions and supporting functions to be used in the context of **symbolic regression** (SR).
 
-The tree-like structure is defined as a fixed-point of an n-ary tree. The variables and parameters of the regression model are indexed as `Int`type and the constant values are `Double`.
+This repository is also the home for different algorithm implementations for SR and software tools to support the post-processing of SR models (please refer to their corresponding README files):
 
-The tree supports leaf nodes containing a variable, a free parameter, or a constant value; internal nodes that represents binary operators such as the four basic math operations, logarithm with custom base, and the power of two expressions; and unary functions specified by `Function` data type.
+- [srsimplify](apps/srsimplify/README.md): a parser and simplification tool supporting the output of many popular SR algorithms.
+- [srtools](apps/srtools/README.md): a tool that can be used to evaluate symbolic regression expressions and create nice reports with confidence intervals. 
+- [tinygp](apps/tinygp/README.md): a simple GP implementation based on tinyGP.
+- [rEGGression](https://github.com/folivetti/reggression/blob/main/README.md): nonlinear regression models exploration and query system with e-graphs (egg).
+- [symregg](https://github.com/folivetti/symregg/blob/main/README.md): Equality graph Assisted Search Technique for Equation Recovery.
+- [eggp](https://github.com/folivetti/eggp/blob/main/README.md): E-graph Genetic Programming.
 
-The `SRTree` structure has instances for `Num, Fractional, Floating` which allows to create an expression as a valid Haskell expression such as:
+## SRTree
 
+The expression structure is defined as a fixed-point of a mix of unary and binary tree. This makes it easier to implement supporting functions that requires the traversal of the trees. Also, since it is a parameterized structure, we can creating partial trees to pattern math structures of interest.
+This structure may contain four types of nodes:
+
+- `Bin Op l r` that represents a binary operator `Op` with two children.
+- `Uni Function t` that represents an unary function `Function` with a single child.
+- `Var Int` representing the index of a variable (i.e., x0, x1, etc.).
+- `Param Int` representing the index of a adjustable parameter (i.e., theta0, theta1, etc.).
+- `Const Double`  representing a constant value.
+
+
+The `SRTree` structure has instances for `Num, Fractional, Floating, IsString` which allows to create an expression as a valid Haskell expression such as (remember to turn on OverloadedStrings extension):
+
 ```haskell
-x = var 0)
-y = var 1
-expr = x * 2 + sin(y * pi + x) :: Fix SRTree
+expr = "x0" * 2 + sin("x1" * pi + "x0") :: Fix SRTree
 ```
 
-## Other features:
+This library comes with support to many quality of life functions to handle this data structure. Such as:
 
-- derivative w.r.t. a variable (`deriveByVar`) and w.r.t. a parameter (`deriveByParam`)
-- evaluation (`evalTree`)
-- relabel free parameters sequentially (`relabelParams`)
-- gradient calculation with `forwardMode`, or optimized with `gradParams` if there is only a single occurrence of each parameter (most of the cases).
+- getting the arity of a node
+- getting the children of a node as a list
+- count the number of nodes 
+- number of nodes of a specific type
+- counting unique tokens 
+- number of variables and parameters 
+- relabeling the parameters from 0 to p 
+- converting floating point constants to parameters 
 
+Additionally, the library provides supporting function to work with datasets, evaluating the expressions, 
+calculating the derivatives, printing, generating random trees, simplifying the expression, calculating overall statistics,
+optimizing parameters, and model selection metrics. 
+
+
+## Organization
+
+The library is organized as `Data`, `Algorithm`, and `Text` modules where the `Data` modules implement functions directly tied to the data structure and the `Algorithm` modules implement algorithms related to symbolic regression, finally, the `Text` modules parse string expressions from different formats and apply simplification, when requested.
+
+### `Data` modules
+
+The `Data` modules is split into $5$ submodules:
+
+- `Data.SRTree` contains the data strucuture and basic supporting functions.
+- `Data.SRTree.Datasets` contains functions supporting loading datasets into Massiv.Arrays (aka numpy arrays).
+- `Data.SRTree.Derivative` contains the symbolic derivatives of the functions and operators.
+- `Data.SRTree.Eval` contains functions to evaluate the tree given a dataset and parameters.
+- `Data.SRTree.Print` contains supporting functions for converting trees to different string representation.
+- `Data.SRTree.Random`  contains functions to generate random trees.
+
+#### `Data.SRTree`
+
+The `SRTree val` data structure is a sum type structure that can be either a variable index, a parameter index, a constant value (of type `Double`), an univariate function or a binary operator. The data type is implemented as a fixed point so all the algorithms act on `Fix SRTree`:
+
+```haskell 
+t = "x0" + "t0" * sin("x1" + "t1"**2) :: Fix SRTree 
+```
+
+When creating the expression in a more natural notation, the variables and parameters are `String` composed of the first letter either `x`, for variables, or `t` for parameters (as in theta), and an integer corresponding to the index of the variable or parameter. The fixed point notation, allows us to implment recursive processing of a tree without many of the common boilerplate:
+
+```haskell
+countNodes = 
+  \case 
+    Var _     = 1
+    Const _   = 1
+    Param _   = 1
+    Uni _ t   = 1 + t 
+    Bin _ l r = 1 + l + r
+```
+
+The children are parameterized by the `val` type parameter. This allows us to create convenient partial structures, such as:
+
+```haskell
+-- + operator pointing to some structure
+-- with index 1 and 2
+Bin Add 1 2 
+
+-- canonical representation of + operator 
+Bin Add () ()
+```
+
+The main functions of this module are:
+
+- `arity`: returns the arity of an operator.
+- `getChildren`: returns the children of a `Fix SRTree` as a list 
+- `countNodes`: returns the number of nodes 
+- `countOccurrences`: counts the occurence of a given variable 
+- `countVars`: returns the number of unique variables appearing the expression 
+- `relabelParams`: relabels the parameters from the left leaves to the right 
+- `constsToParams`: replace `Const` nodes with `Param` nodes.
+
+#### `Data.SRTree.Datasets` module 
+
+This module exports only the `loadDataset` function which takes a filename and 
+returns the training and test sets together with the column labels.
+The filename must follow the format:
+
+`filename.ext:start_row:end_row:target:features`
+
+where each ':' field is optional. The fields are:
+
+- **start_row:end_row** is the range of the training rows (default 0:nrows-1).
+   every other row not included in this range will be used as validation
+- **target** is either the name of the PVector (if the datafile has headers) or the index
+   of the target variable
+- **features** is a comma separated list of SRMatrix names or indices to be used as
+  input variables of the regression model.
+
+Example of valid names: `dataset.csv`, `mydata.tsv`, `dataset.csv:20:100`, `dataset.tsv:20:100:price:m2,rooms,neighborhood`, `dataset.csv:::5:0,1,2`.
+
+#### `Data.SRTree.Derivative` module 
+
+Calculates symbolic derivatives of the expression w.r.t. the variables or the parameters.
+The main functions of this module are:
+
+- `deriveBy`: returns the symbolic derivative w.r.t. a certain variable or a certain parameter.
+- `deriveByVar`: shortcut to `deriveBy` to derive by a variable.
+- `deriveByParam`: shortcut to `deriveBy` to derive by a parameter.
+
+#### `Data.SRTree.Eval` module 
+
+Evaluates an expression given a dataset.
+The main functions of this module are:
+
+- `evalTree`: given a data matrix and a vector of parameters, evaluates the expression tree.
+- `evalInverse`: evaluates the inverse of a function. 
+- `invright`: evaluates the right inverse of an operator.
+- `invleft`: evaluates the left inverse of an operator.
+
+#### `Data.SRTree.Print` module 
+
+Support functions to convert an expression tree into a `String`.
+The main functions of this module are: 
+
+- `showExpr` and `printExpr`: converts/print the expression into math notation .
+- `showPython` and `printPython`: converts/print to a numpy notation.
+- `showLatex` and `printLatex`: converts/print to a LaTeX notation.
+- `showTikz` and `printTikz`: converts/print to a TikZ notation.
+
+#### `Data.SRTree.Random` module 
+
+Auxiliary functions to create random trees. 
+The main functions of this module are:
+
+- `randomTree`: creates a random tree with a certain number of nodes.
+- `randomTreeBalanced`: creates a (almost) balanced random tree with a certain number of nodes.
+
+### `Text` modules 
+
+The `Text` module is split into $2$ modules:
+
+- `Text.ParseSR`: contains the main parsers for different SR algorithms output.
+- `Text.ParseSR.IO`: auxiliary functions to handle files containing many expressions.
+
+#### `Text.ParseSR` module 
+
+The only important function of this module is `parseSR` that  parses an string expression from a given algorithm to a certain output. It also converts variable names to x0, x1,...
+
+#### `Text.ParseSR.IO` module 
+
+The two main functions of this module are: 
+
+- `withInput`: that reads the stdin or a text file and parse all expressions 
+- `withOutput`: that writes the parsed expression into stdout or a file with one of the choices of output format. 
+
+These functions handle any errors with an `Either` type and they can be safely pipelined together. Any invalid expression will be printed as "invalid expression <error message>".
+
+### `Algorithm` modules 
+
+The `Algorithm` modules are split into $5$ submodules:
+
+- `Algorithm.SRTree.AD` contains automatic differentiation functions.
+- `Algorithm.SRTree.ConfidenceIntervals` contains functions to calculate the confidence intervals of parameters and predictions of a symbolic expression using Laplace approximation or profile likelihood.
+- `Algorithm.SRTree.Likelihood` contains functions support different likelihood functions and their derivatives (gradient and hessian).
+- `Algorithm.SRTree.ModelSelection` implements different model selection criteria such as AIC, BIC, MDL.
+- `Algorithm.SRTree.Opt` implements functions to optimize the parameters of an expression supporting different likelihood functions.
+
+#### `Algorithm.SRTree.AD` module 
+
+The main functions of this module are:
+
+- `forwardMode`: returns the prediction errors vector multiplied by the Jacobian matrix using forward mode AD.
+- `forwardModeUnique`: same as above, but assuming each parameter index appear only once in the tree. 
+- `reverseModeUnique`: same as above, but using reverse mode 
+- `forwardModeUniqueJac`: same as `forwardModeUnique` but returns the Jacobian (does not mutiply by the error).
+
+#### `Algorithm.SRTree.Likelihood` module 
+
+The main functions of this module are: 
+
+- `sse, mse, rmse`: calculates the sum-of-square, mean squared, root of mean squared errors.
+- `nll`: returns the negative log-likelihood given a distribution and the associated error (`Nothing` if unknown)
+- `gradNLL`: returns the gradient of the negative log-likelihood. 
+- `gradNLLNonUnique`: same as above but assumes non-unique parameters 
+- `hessianNLL`: returns the hessian of the neg log-likelihood.
+
+#### `Algorithm.SRTree.Opt` module 
+
+The main functions of this module are:
+
+- `minimizeNLL`: minimizes the negative log-likelihood of a distribution.
+- `minimizeNLLNonUnique`: same as above but assumes repeated occurrences of parameters.
+- `minimizeNLLWithFixedParam`: minimizes the neg log-likelihood but fixing the value of a single parameter.
+- `minimizeGaussian`, `minimizePoisson`, `minimizeBinomial`: shortcut to minimize these three distributions.
+
+#### `Algorithm.SRTree.ModelSelection` module 
+
+The main functions of this module are:
+
+- `bic`: Bayesian Information Criteria 
+- `aic`: Akaike Information Criteria 
+- `mdl`: Minimum Description Length as described in Bartlett, Deaglan J., Harry Desmond, and Pedro G. Ferreira. "Exhaustive symbolic regression." IEEE Transactions on Evolutionary Computation (2023)
+- `mdlLattice`: as described in Bartlett, Deaglan, Harry Desmond, and Pedro Ferreira. "Priors for symbolic regression." Proceedings of the Companion Conference on Genetic and Evolutionary Computation. 2023.
+- `mdlFreq` : MDL weighted by the frequency of occurrence of functions 
+
+#### `Algorithm.SRTree.ConfidenceIntervals` module 
+
+The main functions of this module are: 
+
+- `paramCI`: calculates the parameters confidence intervals. 
+- `predictionCI`: calculates the predictions confidence intervals 
+
+### `EqSat` modules 
+
+The `EqSat` modules are split into $4$ submodules:
+
+- `Algorithm.EqSat.Simplify` contains function supporting algebraic simplification with equality saturation.
+- `Algorithm.EqSat` contains the main equality saturation function.
+- `Algorithm.EqSat.EGraph` contains the e-graph data structure and supporting functions.
+- `Algorithm.EqSat.EqSatDB` contains supporting functions to pattern matching and insert equivalent expressions into an e-graph. 
+
+#### `Algorithm.EqSat` module
+
+The main functions of this module are: 
+
+- `eqSat` : runs equality saturation over a single expression. 
+- `getBest` : returns the best expression given the cost function used to generate the e-graph 
+- `recalculateBest` : recalculates the cost of each e-class using a new cost function 
+- `runEqSat` : runs equality saturation inside `EGraphST` monad. Use this if you want to return the e-graph. 
+
+#### `Algorithm.EqSat.EGraph` module
+
+The main functions of this module are: 
+
+- `fromTree` : creates an e-graph from an expression tree.
+- `fromTrees` : creates an e-graph from multiple expressions 
+- `fromTreeWith` : inserts a new expression into the e-graph 
+- `findRootClasses` : returns the roots of the e-graph, if any .
+- `getExpressionFrom` : returns a single expression from a given e-class always picking the first e-node as the path 
+- `getAllExpressionsFrom` : returns all expressions from the given e-class 
+- `getRndExpressionFrom` : returns a random expression from this e-class 
+
+
+#### `Algorithm.EqSat.EqSatDB` module
+
+The main functions of this module are: 
+
+- TODO: create auxiliary functions to apply substution rules inside an EGraphST monad . 
+
+#### `Algorithm.EqSat.Simplify` module
+
+The main functions of this module are: 
+
+- `simplifyEqSatDefault` : simplifies an expression using the default parameters 
+- `simplifyEqSat` : simplifies with custom parameters
+
 ## TODO:
 
 - support more advanced functions
 - support conditional branching (`IF-THEN-ELSE`)
-
+- document egraph-search and ieeexplore
diff --git a/apps/Bench/Main.hs b/apps/Bench/Main.hs
new file mode 100644
--- /dev/null
+++ b/apps/Bench/Main.hs
@@ -0,0 +1,127 @@
+{-# LANGUAGE BangPatterns #-}
+
+import Criterion.Main
+import Control.DeepSeq (force, NFData)
+import Control.Exception (evaluate)
+import qualified Data.Vector.Unboxed as V
+import qualified Data.Vector as VB
+import qualified Data.Vector.Generic as G
+import qualified Data.Vector.Storable as VS
+
+import Data.SRTree
+import Data.SRTree.Print
+import Data.SRTree.Datasets
+import Data.SRTree.Eval
+import Data.SRTree.Random
+import System.Random
+import Control.Monad.State.Strict
+import Algorithm.SRTree.NonlinearOpt
+import Algorithm.SRTree.Likelihoods
+import Algorithm.SRTree.AD
+
+-- Assuming these are exported by your project modules:
+-- import SRTree
+-- import Compiler
+-- import DatasetLoader
+
+-- Mock signatures based on your provided functions
+-- randomTree :: Int -> Int -> Int -> IO Term -> IO NonTerm -> Bool -> IO Tree
+-- loadDataset :: FilePath -> Bool -> IO [V.Vector Double]
+-- evalTree :: Tree -> [V.Vector Double] -> V.Vector Double
+-- compile :: [V.Vector Double] -> Tree -> (Theta -> V.Vector Double)
+
+genTerm    = do coin <- tossBiased 0.4
+                if coin then randomFrom [Fix $ Var ix | ix <- [0..8]] else randomFrom [Fix $ Param ix | ix <- [0..9]]
+genNonTerm = randomFrom [Bin Add () (), Bin Sub () (), Bin Mul () (), Uni LogAbs (), Uni SqrtAbs ()]
+
+genMultipleTrees 0 = pure []
+genMultipleTrees n = do
+    t <- randomTree 5 10 150 genTerm genNonTerm False
+    ts <- genMultipleTrees (n-1)
+    pure (t:ts)
+
+getF (_, x, _) = x
+{-# INLINE getF #-}
+getT (t, _, _) = t
+{-# INLINE getT #-}
+
+main :: IO ()
+main = do
+    -- 1. Initialization: Load the dataset
+    putStrLn "Loading dataset..."
+    ((dataset, y, _, _), _, _, _) <- loadDataset "data.tsv" True
+
+    -- 2. Initialization: Generate the random expression tree
+    putStrLn "Generating random tree..."
+    -- Replace 'genTerm' and 'genNonTerm' with your actual generators
+    --g <- getStdGen
+    let g = mkStdGen 42
+    -- tree <- evalStateT (randomTree 7 10 150 genTerm genNonTerm True) g
+    trees' <- evalStateT (genMultipleTrees 5) g
+    -- let trees' = [Fix (Uni LogAbs (Fix (Bin PowerAbs (param 0) (param 1 * var 0))))] :: [Fix SRTree]
+
+    -- IMPORTANT: Force deep evaluation of the tree and dataset.
+    -- If we do not do this, GHC's lazy evaluation will cause the benchmark
+    -- to measure the time it takes to parse the CSV and build the tree in memory!
+    -- _ <- evaluate (force tree)
+    _ <- evaluate (force dataset)
+
+
+    -- 3. Initialization: Pre-compile the tree
+    -- We evaluate this strictly (!) so the one-time compilation cost
+    -- is not included in the runtime benchmark.
+    putStrLn "Compiling tree..."
+    let !compiledFn = [compile dataset tree | tree <- trees]
+        evalTree x th t = compile x t th
+        -- Mock theta (parameter vector) to pass into the closures
+        !theta = V.fromList [1.0, 0.5, 0.2, 0.3, 0.1, 0.5, 0.9, 0.3, 0.2, 0.4]
+        !theta1 = V.fromList [0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0]
+        trees = map relabelParamsOrder $ filter (\t -> let v = V.sum (evalTree dataset theta t) in not (isInfinite v || isNaN v)) trees'
+        naiveEval = evalTree dataset theta
+        dataset' = map G.convert dataset
+        y' = G.convert y
+        theta1' = G.convert theta1
+
+    _ <- evaluate (force theta)
+    _ <- evaluate (force theta1)
+    print $ sum $ map (\t ->  V.sum $ naiveEval t) trees
+    print $ sum $ map (\t ->  V.sum $ t theta) compiledFn
+    print $ sum $ map (\t -> getF $ minimizeNLL MultiThread MSE Nothing 0 dataset y t theta1) trees
+    --print $ sum $ map (\t -> getF $ minimizeNLLCompiled MSE Nothing 0 dataset y t theta1) trees
+
+    --print $ sum $ map (\t -> VS.sum . snd $ gradNLLGraph MSE dataset' y' Nothing t theta1') trees
+    --print $ sum $ map (\t -> VS.sum . snd $ gradNLLGraphO MSE dataset' y' Nothing t theta1') trees
+    --print $ sum $ map (\t -> VS.sum . snd $ compileGrad dataset' y' Nothing t 100 theta1') trees
+    --print $ sum $ map (\ct -> V.sum $ ct theta) compiledFn
+    --print $ sum $ map (\ct -> V.sum $ executeVM ct rowDataset theta) bytecodes
+    -- print $ V.sum $ evalTree dataset theta tree
+    -- print $ V.sum $ compiledFn theta
+
+    putStrLn "Running benchmarks..."
+
+    -- 4. The Benchmarks
+    defaultMain [
+          bgroup "Tree Evaluation (Fixed Dataset)" [
+
+           -- The slow version: dynamically traversing the AST at runtime
+           bench "evalTree (Naive AST Traversal)" $
+                nf (\ts -> sum [V.sum $ evalTree dataset theta1 t | t <- ts]) trees,
+
+
+            -- The fast version: executing the pre-compiled, stream-fused closure
+            bench "compile (Compiled Closure)" $
+                nf (\t -> sum [V.sum (ct t) | ct <- compiledFn]) theta1,
+
+            -- The fast version: executing the pre-compiled, stream-fused closure
+            bench "minimizeNLLCompiled (Compiled Closure)" $
+                nf (\ts -> sum [V.sum . getT $ minimizeNLL MultiThread MSE Nothing 100 dataset' y' t theta1' | t <- ts]) trees
+
+            --bench "minimizeNLLO (Naive optimized AST Traversal)" $
+            --    nf (\ts -> sum [V.sum . getT $ minimizeNLLO MSE Nothing 100 dataset y t theta1 | t <- ts]) trees
+
+            -- The slow version: dynamically traversing the AST at runtime
+            --bench "minimizeNLL (Naive AST Traversal)" $
+            --    nf (\ts -> sum [V.sum . getT $ minimizeNLL (NLL MSE) Nothing 100 dataset y t theta1 | t <- ts]) trees
+
+        ]
+      ]
diff --git a/apps/BenchEqSat/Main.hs b/apps/BenchEqSat/Main.hs
new file mode 100644
--- /dev/null
+++ b/apps/BenchEqSat/Main.hs
@@ -0,0 +1,259 @@
+{-# LANGUAGE BangPatterns #-}
+{-# LANGUAGE OverloadedStrings #-}
+
+import Criterion.Main
+import qualified Data.Vector.Unboxed as VU
+import qualified Data.IntMap as IntMap
+import qualified Data.HashMap.Strict as HashMap
+import qualified Data.HashSet as Set
+
+import Data.SRTree
+import Algorithm.EqSat
+import Algorithm.EqSat.Egraph
+import Algorithm.EqSat.Build
+import Algorithm.EqSat.DB
+import Algorithm.EqSat.Info
+import Algorithm.EqSat.Queries
+import Control.Monad.State.Strict
+import Control.Monad (replicateM, zipWithM_)
+import Control.Monad.Identity
+
+myCost :: SRTree Int -> Int
+myCost (Var _)     = 1
+myCost (Const _)   = 1
+myCost (Param _)   = 1
+myCost (Bin _ l r) = 2 + l + r
+myCost (Uni _ t)   = 3 + t
+
+evalEG :: EGraphST Identity a -> (a, EGraph)
+evalEG m = runIdentity $ runStateT m emptyGraph
+
+runInEG :: EGraph -> EGraphST Identity a -> (a, EGraph)
+runInEG eg m = runIdentity $ runStateT m eg
+
+-- Expression generators for benchmarking
+chainAdd :: Int -> Fix SRTree
+chainAdd 0 = var 0
+chainAdd n = chainAdd (n-1) + var n
+
+deepBinTree :: Int -> Fix SRTree
+deepBinTree 0 = var 0
+deepBinTree n = deepBinTree (n-1) + constv (fromIntegral n)
+
+complexTree :: Int -> Fix SRTree
+complexTree n = go n
+  where
+    go 0 = var 0
+    go i = (var i + constv (fromIntegral i)) * (go (i-1) + constv (fromIntegral i))
+
+simplifyRules :: [Rule]
+simplifyRules =
+  [ "a" + 0 :=> "a"
+  , "a" * 1 :=> "a"
+  , "a" + "a" :=> 2 * "a"
+  , "a" * 0 :=> 0
+  , 0 + "a" :=> "a"
+  , 1 * "a" :=> "a"
+  ]
+
+-- More rules including commutativity (triggers more merges)
+moreRules :: [Rule]
+moreRules =
+  [ "a" + 0 :=> "a"
+  , "a" * 1 :=> "a"
+  , "a" + "a" :=> 2 * "a"
+  , "a" * 0 :=> 0
+  , 0 + "a" :=> "a"
+  , 1 * "a" :=> "a"
+  , "a" + "b" :=> "b" + "a"
+  , "a" * "b" :=> "b" * "a"
+  ]
+
+addZero :: Fix SRTree -> Fix SRTree -> Fix SRTree
+addZero l r = Fix (Bin Add l r)
+
+main :: IO ()
+main = do
+  putStrLn "Generating benchmark expressions..."
+  let smallExpr  = chainAdd 5
+      mediumExpr = chainAdd 20
+      largeExpr  = chainAdd 100
+      complex    = complexTree 8
+
+  putStrLn "Running benchmarks..."
+  defaultMain [
+    bgroup "E-graph Construction" [
+      bench "fromTree (5-leaf chain)" $
+        whnf (\e -> evalEG $ fromTree myCost e) smallExpr,
+      bench "fromTree (20-leaf chain)" $
+        whnf (\e -> evalEG $ fromTree myCost e) mediumExpr,
+      bench "fromTree (100-leaf chain)" $
+        whnf (\e -> evalEG $ fromTree myCost e) largeExpr,
+      bench "fromTree (complex-ternary tree)" $
+        whnf (\e -> evalEG $ fromTree myCost e) complex
+    ],
+
+    bgroup "E-graph Add" [
+      bench "add single e-node (Var)" $
+        whnf (\eg -> runInEG eg $ add myCost (EVar 999)) (snd $ evalEG $ fromTree myCost smallExpr),
+      bench "add single e-node (Const)" $
+        whnf (\eg -> runInEG eg $ add myCost (EConst 42.0)) (snd $ evalEG $ fromTree myCost smallExpr),
+      bench "add single e-node (Bin Add)" $
+        whnf (\eg -> runInEG eg $ add myCost (ENAry EAdd (imFromList [0, 1]))) (snd $ evalEG $ fromTree myCost mediumExpr)
+    ],
+
+    bgroup "Merge" [
+      bench "merge two distinct eclasses (size 1)" $
+        whnf (\(e1,e2,eg) -> runInEG eg $ merge myCost e1 e2) (makeMergePair 1),
+      bench "merge two distinct eclasses (size 3)" $
+        whnf (\(e1,e2,eg) -> runInEG eg $ merge myCost e1 e2) (makeMergePair 3)
+    ],
+
+    bgroup "Pattern Matching" [
+      bench "match simple pattern (a+0)" $
+        whnf (\(eg,_) -> runInEG eg $ match ("a" + 0 :: Pattern)) (makeMatchableEG),
+      bench "match commutative pattern (a+b)" $
+        whnf (\(eg,_) -> runInEG eg $ match ("a" + "b" :: Pattern)) (makeMatchableEG),
+      bench "match triple pattern (a+b+c)" $
+        whnf (\(eg,_) -> runInEG eg $ match ("a" + "b" + "c" :: Pattern)) (makeMatchableEG)
+    ],
+
+    bgroup "Match After Merge" [
+      bench "match (a+0) after merge (stale trie keys)" $
+        whnf (\(eg,_) -> runInEG eg $ match ("a" + 0 :: Pattern)) (makeMergedEG),
+      bench "match (a+b) after merge (stale trie keys)" $
+        whnf (\(eg,_) -> runInEG eg $ match ("a" + "b" :: Pattern)) (makeMergedEG)
+    ],
+
+    bgroup "Rebuild" [
+      bench "rebuild after 5 adds" $
+        whnf (\(eg,_) -> runInEG eg $ rebuild myCost) (makeDirtyEG 5),
+      bench "rebuild after 20 adds" $
+        whnf (\(eg,_) -> runInEG eg $ rebuild myCost) (makeDirtyEG 20),
+      bench "rebuild after 100 adds" $
+        whnf (\(eg,_) -> runInEG eg $ rebuild myCost) (makeDirtyEG 100)
+    ],
+
+    bgroup "Cost Propagation" [
+      bench "recalculateBest (10 eclasses)" $
+        whnf (\(eids,eg) -> runInEG eg $ mapM_ (recalculateBest myCost) eids) (makeNEclasses 10),
+      bench "recalculateBest (100 eclasses)" $
+        whnf (\(eids,eg) -> runInEG eg $ mapM_ (recalculateBest myCost) eids) (makeNEclasses 100)
+    ],
+
+    bgroup "DB Operations" [
+      bench "addToDB single enode" $
+        whnf (\(en,eid,eg) -> runInEG eg $ addToDB en eid) (makeDBEntry),
+      bench "addToDB 10 enodes" $
+        whnf (\(ens,eg) -> runInEG eg $ mapM_ (uncurry addToDB) ens) (makeDBEntries 10)
+    ],
+
+    bgroup "Equality Saturation" [
+      bench "eqSat small expr (5 rules)" $
+        whnf (\(e,r) -> evalEG $ eqSat e r myCost 10) (smallExpr, simplifyRules),
+      bench "eqSat medium expr (5 rules)" $
+        whnf (\(e,r) -> evalEG $ eqSat e r myCost 10) (mediumExpr, simplifyRules),
+      bench "eqSat small expr (8 rules, commutative)" $
+        whnf (\(e,r) -> evalEG $ eqSat e r myCost 10) (smallExpr, moreRules),
+      bench "eqSat large expr (5 rules)" $
+        whnf (\(e,r) -> evalEG $ eqSat e r myCost 10) (largeExpr, simplifyRules)
+    ],
+
+    bgroup "Extraction" [
+      bench "getBestExpr (5-leaf)" $
+        whnf (\(eid,eg) -> runInEG eg $ getBestExpr eid) (makeExtractable 5),
+      bench "getBestExpr (20-leaf)" $
+        whnf (\(eid,eg) -> runInEG eg $ getBestExpr eid) (makeExtractable 20),
+      bench "getBestExpr (100-leaf)" $
+        whnf (\(eid,eg) -> runInEG eg $ getBestExpr eid) (makeExtractable 100)
+    ],
+
+    bgroup "Fitness Operations" [
+      bench "insertFitness single" $
+        whnf (\(eid,eg) -> runInEG eg $ insertFitness eid 0.5 []) (makeExtractable 1),
+      bench "insertFitness 10 eclasses" $
+        whnf (\(eids,eg) -> runInEG eg $ mapM_ (\eid -> insertFitness eid 0.5 []) eids) (makeNEclasses 10),
+      bench "getTopFitEClassWithSize" $
+        whnf (\(eids,eg) -> runInEG eg $ getTopFitEClassWithSize 1 3) (makeFitnessEG)
+    ]
+    ]
+  where
+    addZeroTree = addZero (var 0) (constv 0.0)
+
+    makeMergePair :: Int -> (EClassId, EClassId, EGraph)
+    makeMergePair n =
+      let tree = deepBinTree n
+          (eid1, eg1) = evalEG $ fromTree myCost tree
+          (eid2, eg2) = runInEG eg1 $ fromTree myCost tree
+      in (eid1, eid2, eg2)
+
+    makeMatchableEG :: (EGraph, EClassId)
+    makeMatchableEG =
+      let tree = complexTree 4
+          (eid, eg) = evalEG $ do
+            eid' <- fromTree myCost tree
+            _ <- fromTree myCost (var 0 + constv 1.0)
+            _ <- fromTree myCost (var 1 * constv 2.0)
+            _ <- fromTree myCost (var 0 + constv 0.0)
+            _ <- fromTree myCost (var 1 * constv 1.0)
+            rebuild myCost
+            pure eid'
+      in (eg, eid)
+
+    -- E-graph with merges applied, creating stale trie keys
+    makeMergedEG :: (EGraph, EClassId)
+    makeMergedEG =
+      let (_, eg) = evalEG $ do
+            eid1 <- fromTree myCost (var 0)
+            eid2 <- fromTree myCost (constv 0.0)
+            eid3 <- fromTree myCost (var 0 + constv 1.0)
+            _ <- fromTree myCost (var 1)
+            rebuild myCost
+            -- merge to create stale trie entries
+            merge myCost eid1 eid2
+            merge myCost eid2 eid3
+            rebuild myCost
+            pure eid1
+      in (eg, 0)
+
+    makeDirtyEG :: Int -> (EGraph, EClassId)
+    makeDirtyEG n =
+      let tree = deepBinTree n
+          (eid, eg) = evalEG $ do
+            eid' <- fromTree myCost tree
+            _ <- fromTree myCost (tree + var 999)
+            rebuild myCost
+            _ <- fromTree myCost (tree * var 998)
+            pure eid'
+      in (eg, eid)
+
+    makeExtractable :: Int -> (EClassId, EGraph)
+    makeExtractable n =
+      let tree = deepBinTree n
+      in evalEG $ fromTree myCost tree
+
+    makeNEclasses :: Int -> ([EClassId], EGraph)
+    makeNEclasses n =
+      evalEG $ replicateM n (fromTree myCost (constv (fromIntegral n)))
+
+    makeFitnessEG :: ([EClassId], EGraph)
+    makeFitnessEG = evalEG $ do
+      eids <- mapM (fromTree myCost . constv . fromIntegral) [1..10]
+      zipWithM_ (\eid i -> insertFitness eid (fromIntegral i) []) eids [1..]
+      pure eids
+
+    makeDBEntry :: (ENode, EClassId, EGraph)
+    makeDBEntry =
+      let (eid, eg) = evalEG $ do
+            eid <- fromTree myCost (var 999)
+            rebuild myCost
+            pure eid
+      in (EVar 777, eid, eg)
+
+    makeDBEntries :: Int -> ([(ENode, EClassId)], EGraph)
+    makeDBEntries n =
+      let (eids, eg) = evalEG $ do
+            eids <- mapM (fromTree myCost . var) [999..(999 + n - 1)]
+            rebuild myCost
+            pure eids
+      in (zip (map EVar [1000..]) eids, eg)
diff --git a/apps/Report/Main.hs b/apps/Report/Main.hs
new file mode 100644
--- /dev/null
+++ b/apps/Report/Main.hs
@@ -0,0 +1,247 @@
+module Main (main) where
+
+import Options.Applicative
+import qualified Data.ByteString.Char8 as B
+import qualified Data.Vector.Unboxed as U
+import Data.SRTree
+import Data.SRTree.Eval (Target, Columns, compileLoss)
+import Data.SRTree.Datasets (loadTrainingOnly)
+import Data.SRTree.Print (showExpr)
+import Text.ParseSR (parseSR, SRAlgs(..))
+import Algorithm.SRTree.Compile (compileTree, EvalTree(..), logParameters, logParametersLatt)
+import Algorithm.SRTree.Likelihoods (Distribution(..), Loss(..), buildLoss, fisherNLL, hessianNLL)
+import Algorithm.SRTree.ConfidenceIntervals
+    ( getStatsFromModel, paramCI, CIType(..), CI(..), BasicStats(..)
+    , ProfileT(..), PType(..), getAllProfiles, getCol
+    )
+import Algorithm.SRTree.ModelSelection (ModelEval(..), logFunctional, logFunctionalFreq)
+import Statistics.Distribution (ContDistr(quantile))
+import Statistics.Distribution.FDistribution (fDistribution)
+import Control.Exception (try, SomeException)
+import Data.List.Split (splitOn)
+import Text.Printf (printf)
+import Control.Monad (forM_, when)
+
+----------------------------------------------------------------------
+-- CLI argument types
+----------------------------------------------------------------------
+data CIMethod = LaplaceCI | ProfileCI deriving (Show)
+
+data ProfileTypeArg = BatesArg | ODEArg | ConstrainedArg deriving (Read)
+instance Show ProfileTypeArg where
+  show BatesArg       = "Bates"
+  show ODEArg         = "ODE"
+  show ConstrainedArg = "Constrained"
+
+data ReportArgs = ReportArgs
+  { raExprs    :: !FilePath
+  , raFormat   :: !SRAlgs
+  , raData     :: !FilePath
+  , raHeader   :: !Bool
+  , raDist     :: !Distribution
+  , raCriteria :: ![ModelEval]
+  , raCI       :: !CIMethod
+  , raAlpha    :: !Double
+  , raCIType   :: !ProfileTypeArg
+  , raDbg      :: !Bool
+  }
+
+----------------------------------------------------------------------
+-- Argument parser
+----------------------------------------------------------------------
+argParser :: Parser ReportArgs
+argParser = ReportArgs
+  <$> strOption ( long "exprs" <> short 'e' <> help "File with expressions, one per line" <> metavar "FILE" )
+  <*> option auto ( long "format" <> short 'f' <> help "Expression format: TIR, HL, OPERON, BINGO, GOMEA, PYSR, SBP, EPLEX" <> metavar "FMT" )
+  <*> strOption ( long "data" <> short 'd' <> help "Dataset file (optionally with :start:end:target:features:y_err)" <> metavar "FILE" )
+  <*> switch ( long "header" <> help "Dataset has a header row" )
+  <*> option auto ( long "dist" <> value Gaussian <> help "Distribution: Gaussian, Bernoulli, Poisson, LeastSquares" <> metavar "DIST" <> showDefault )
+  <*> option parseCriteria ( long "criteria" <> short 'c' <> value [RMSE, R2, AIC, BIC] <> help "Comma-separated criteria" <> metavar "CRITERIA" <> showDefault )
+  <*> option parseCI ( long "ci" <> value LaplaceCI <> help "CI method: Laplace, Profile" <> metavar "METHOD" <> showDefault )
+  <*> option auto ( long "alpha" <> value 0.05 <> help "Significance level" <> metavar "ALPHA" <> showDefault )
+  <*> option parseProfileType ( long "ci-type" <> value BatesArg <> help "Profile CI type: Bates, ODE, Constrained" <> metavar "TYPE" <> showDefault )
+  <*> switch ( long "dbg" <> help "Debug: dump profile tau/theta spline points" )
+
+parseCriteria :: ReadM [ModelEval]
+parseCriteria = eitherReader $ \s ->
+  case traverse parseOne (splitOn "," s) of
+    Right es -> Right es
+    Left  e  -> Left e
+  where
+    parseOne "RMSE"     = Right RMSE
+    parseOne "R2"       = Right R2
+    parseOne "AIC"      = Right AIC
+    parseOne "BIC"      = Right BIC
+    parseOne "Evidence" = Right Evidence
+    parseOne "FBF"      = Right FBF
+    parseOne "MDL"      = Right MDL
+    parseOne "MDLLatt"  = Right MDLLatt
+    parseOne "MDLFreq"  = Right MDLFreq
+    parseOne "NLL"      = Right (EvalLoss (NLL Gaussian))
+    parseOne s          = Left ("unknown criterion: " ++ s)
+
+parseCI :: ReadM CIMethod
+parseCI = eitherReader $ \s -> case s of
+  "Laplace" -> Right LaplaceCI
+  "Profile" -> Right ProfileCI
+  _         -> Left ("unknown CI method: " ++ s ++ " (use Laplace or Profile)")
+
+parseProfileType :: ReadM ProfileTypeArg
+parseProfileType = eitherReader $ \s -> case s of
+  "Bates"       -> Right BatesArg
+  "ODE"         -> Right ODEArg
+  "Constrained" -> Right ConstrainedArg
+  _             -> Left ("unknown profile type: " ++ s ++ " (use Bates, ODE, or Constrained)")
+
+----------------------------------------------------------------------
+-- Report data
+----------------------------------------------------------------------
+data ReportData = ReportData
+  { rdTree      :: Fix SRTree
+  , rdTheta     :: Target
+  , rdStdErr    :: Target
+  , rdCriteria  :: [(ModelEval, Double)]
+  , rdCIs       :: [CI]
+  }
+
+----------------------------------------------------------------------
+-- Main
+----------------------------------------------------------------------
+main :: IO ()
+main = do
+  args <- execParser (info (argParser <**> helper) fullDesc)
+  (xss, ys, mYerr) <- loadTrainingOnly (raData args) (raHeader args)
+  content <- B.readFile (raExprs args)
+  let exprs = filter (not . B.null) $ B.lines content
+  mapM_ (processOne args xss ys mYerr) (zip [(1 :: Int) ..] exprs)
+
+----------------------------------------------------------------------
+-- Process a single expression
+----------------------------------------------------------------------
+processOne :: ReportArgs -> Columns -> Target -> Maybe Target -> (Int, B.ByteString) -> IO ()
+processOne args xss ys mYerr (idx, src) = do
+  result <- try $ do
+    tree <- case parseSR (raFormat args) B.empty True src of
+      Left e  -> fail ("parse error: " ++ e)
+      Right t -> return $! relabelParams t
+    let dist  = raDist args
+        nRows = U.length ys
+        nModelParams = countParamsUniq tree
+        nParams = nModelParams
+                + case dist of
+                    Gaussian  -> 1
+                    ROXY      -> 3
+                    _         -> 0
+
+    let et     = compileTree dist xss ys mYerr tree
+        theta0 = U.replicate nParams 1.0
+        thetaOpt = ctOptimizer et theta0
+
+    when (any isNaN (U.toList thetaOpt)) $
+         fail "optimisation returned NaN"
+
+    let mseTree  = buildLoss MSE (fromIntegral nRows) tree
+        mseLoss  = compileLoss xss mseTree ys mYerr thetaOpt
+        nllLoss  = ctNLL et thetaOpt
+        tss      = ctVar et
+
+    let fisherDiag = fisherNLL dist mYerr xss ys tree thetaOpt
+        hessCols   = hessianNLL dist mYerr xss ys tree thetaOpt
+        hessLists  = map U.toList hessCols
+        logP       = logParameters fisherDiag thetaOpt
+        logPLatt   = logParametersLatt hessLists fisherDiag thetaOpt
+        logF       = logFunctional tree
+        logFFreq   = logFunctionalFreq tree
+        nF         = fromIntegral nRows
+        kF         = fromIntegral nParams
+        crits      = map (\c -> (c, evalOne c mseLoss nllLoss tss nF kF logP logPLatt logF logFFreq))
+                         (raCriteria args)
+
+    let stats = getStatsFromModel dist mYerr xss ys tree thetaOpt
+        laplaceCIs = paramCI (Laplace stats) nRows thetaOpt (raAlpha args)
+    let ptype = case raCIType args of
+          BatesArg       -> Bates
+          ODEArg         -> ODE
+          ConstrainedArg -> Constrained
+    let kInt = U.length thetaOpt
+        nInt = U.length ys
+        profT = sqrt $ quantile (fDistribution (fromIntegral kInt) (fromIntegral $ nInt - kInt)) (1 - raAlpha args)
+    cis <- case raCI args of
+      LaplaceCI -> return laplaceCIs
+      ProfileCI -> do
+        let profiles = getAllProfiles ptype et thetaOpt (_stdErr stats) laplaceCIs (raAlpha args)
+        when (raDbg args) $ forM_ (zip [0..] profiles) $ \(i, ProfileT taus thetas _ tau2theta _) -> do
+          putStrLn $ "DEBUG Profile " ++ show i ++ " (opt=" ++ show (thetaOpt U.! i) ++ "):"
+          putStrLn $ "  tau range: [" ++ show (if U.null taus then 0 else U.head taus)
+                   ++ ", " ++ show (if U.null taus then 0 else U.last taus) ++ "]"
+          putStrLn $ "  t=" ++ show profT
+          putStrLn $ "  tau2theta(-t)=" ++ show (tau2theta (-profT))
+                   ++ "  tau2theta(+t)=" ++ show (tau2theta profT)
+          putStrLn $ "  profile points:"
+          let tausL = U.toList taus
+              thetasL = U.toList (getCol i thetas)
+          forM_ (zip tausL thetasL) $ \(tau, th) ->
+            putStrLn $ "    tau=" ++ show tau ++ "  theta=" ++ show th
+        return $ paramCI (Profile stats profiles) nRows thetaOpt (raAlpha args)
+
+    return $! ReportData
+      { rdTree     = tree
+      , rdTheta    = thetaOpt
+      , rdStdErr   = _stdErr stats
+      , rdCriteria = crits
+      , rdCIs      = cis
+      }
+
+  case result of
+    Right rd -> printReport idx src rd
+    Left  e  -> printFailure idx src (show (e :: SomeException))
+
+----------------------------------------------------------------------
+-- Evaluate a single ModelEval from base quantities
+----------------------------------------------------------------------
+evalOne :: ModelEval -> Double -> Double -> Double -> Double -> Double
+        -> Double -> Double -> Double -> Double -> Double
+evalOne RMSE     mse _   _   _ _ _ _ _ _ = sqrt mse
+evalOne R2       mse _   tss n _ _ _ _ _ = 1 - n * mse / tss
+evalOne AIC      _   nll _   _ k _ _ _ _ = 2*k + 2*nll
+evalOne BIC      _   nll _   n k _ _ _ _ = k * log n + 2*nll
+evalOne Evidence _   nll _   n k _ _ _ _ = (1 - b) * nll - k/2 * log b
+  where b = 1 / sqrt n
+evalOne FBF      _   nll _   n k _ _ _ _ = res
+  where b = 1 / sqrt n; nup = exp (1 - log 3)
+        res = (1 - b) * nll - k/2 * log b + k/2 * log (2*pi*nup)
+evalOne MDL      _   nll _   _ _ logP  _ logF _    = nll + logF + logP
+evalOne MDLLatt  _   nll _   _ _ _     logPL logF _ = nll + logF + logPL
+evalOne MDLFreq  _   nll _   _ _ logP  _ _    logFF = nll + logFF + logP
+evalOne (EvalLoss (NLL Gaussian))  _   nll _   _ _ _  _ _    _ = nll
+evalOne _        _   _   _   _ _ _     _    _    _  = 0  -- unreachable
+
+----------------------------------------------------------------------
+-- Output
+----------------------------------------------------------------------
+printReport :: Int -> B.ByteString -> ReportData -> IO ()
+printReport idx src rd = do
+  putStrLn $ "=== Expression " ++ show idx ++ " ==="
+  putStrLn $ "Tree: " ++ showExpr (rdTree rd)
+  putStrLn "Parameters:"
+  let thetaList = U.toList (rdTheta rd)
+      ciList    = rdCIs rd
+  forM_ (zip3 [0..] thetaList ciList) $ \(i, th, ci) ->
+    putStrLn $ "  theta" ++ show i ++ ": " ++ fmt th
+            ++ " [" ++ fmt (lower_ ci) ++ ", " ++ fmt (upper_ ci) ++ "]"
+  putStrLn "Model Selection:"
+  forM_ (rdCriteria rd) $ \(c, v) ->
+    putStrLn $ "  " ++ padRight 12 (show c) ++ ": " ++ fmt v
+  putStrLn ""
+  where
+    fmt x | abs x < 1e-10 = "0.0000"
+          | abs x >= 1e4  = printf "%.4e" x
+          | otherwise     = printf "%.6f" x
+    padRight n s = s ++ replicate (max 0 (n - length s)) ' '
+
+printFailure :: Int -> B.ByteString -> String -> IO ()
+printFailure idx src msg = do
+  putStrLn $ "=== Expression " ++ show idx ++ " ==="
+  putStrLn $ "Tree: " ++ B.unpack src
+  putStrLn $ "Error: " ++ msg
+  putStrLn ""
diff --git a/src/Algorithm/EqSat.hs b/src/Algorithm/EqSat.hs
new file mode 100644
--- /dev/null
+++ b/src/Algorithm/EqSat.hs
@@ -0,0 +1,380 @@
+{-# LANGUAGE TupleSections #-}
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Algorithm.EqSat
+-- Copyright   :  (c) Fabricio Olivetti 2021 - 2024
+-- License     :  BSD3
+-- Maintainer  :  fabricio.olivetti@gmail.com
+-- Stability   :  experimental
+-- Portability :
+--
+-- Equality Saturation for SRTree
+-- Heavily based on hegg (https://github.com/alt-romes/hegg by alt-romes)
+--
+-----------------------------------------------------------------------------
+
+module Algorithm.EqSat where
+
+import Algorithm.EqSat.Egraph
+import Algorithm.EqSat.DB
+import Algorithm.EqSat.Info
+import Algorithm.EqSat.Build
+import Control.Lens (element, makeLenses, over, (&), (+~), (-~), (.~), (^.))
+import Control.Monad.State
+import Data.Function (on)
+import Data.IntMap (IntMap)
+import qualified Data.IntMap as IntMap
+import qualified Data.IntSet as IntSet
+import Data.List (intercalate)
+import Data.Map (Map)
+import qualified Data.Map as Map
+import Data.Maybe (mapMaybe)
+import Data.SRTree
+import Data.HashSet (HashSet)
+import qualified Data.HashSet as Set
+import Control.Monad ( zipWithM, forM_ )
+
+-- | The `Scheduler` stores a map with the banned iterations of a certain rule . 
+-- TODO: make it more customizable.
+type Scheduler a = State (IntMap Int) a
+
+-- to avoid importing
+-- | runs equality saturation from an expression tree,
+-- a given set of rules, and a cost function.
+-- Returns the tree with the smallest cost.
+eqSat :: ClassStore m => Fix SRTree -> [Rule] -> CostFun -> Int -> EGraphST m (Fix SRTree)
+eqSat expr rules costFun maxIt =
+    do root <- fromTree costFun expr
+       _ <- runEqSat costFun rules maxIt
+       recalculateBest costFun root
+
+type CostMap = Map EClassId (Int, Fix SRTree)
+
+-- | recalculates the costs with a new cost function
+recalculateBest :: ClassStore m => CostFun -> EClassId -> EGraphST m (Fix SRTree)
+recalculateBest costFun eid =
+    do ecls <- allClasses
+       let classes = IntMap.fromList [(_eClassId ec, ec) | ec <- ecls]
+           costs   = fillUpCosts classes Map.empty
+       eid' <- canonical eid
+       case Map.lookup eid' costs of
+         Just (_, t) -> pure t
+         Nothing     -> error $ "EQSAT_RECALC_MISSING eid=" <> show eid'
+                              <> " nClasses=" <> show (IntMap.size classes)
+                              <> " costSize=" <> show (Map.size costs)
+    where
+        nodeCost :: CostMap -> ENode -> (Int, Fix SRTree)
+        nodeCost costMap enode =
+          -- A child that has not been costed yet (a cycle, or a class whose
+          -- cost is computed later in this iteration) contributes a large
+          -- sentinel instead of 0: a 0 placeholder is cheaper than the real
+          -- cost, so the fixpoint below would keep the stale placeholder tree
+          -- (e.g. `x * 0.0` for `x * (y + z)`). Real costs always beat it.
+          let (cc, nc) = unzip [ maybe (costSentinel, Fix (Const 0)) id (costMap Map.!? cid) | cid <- eChildren enode ]
+              c  = case enode of
+                     ENAry op _ -> costFun (Bin (toOp op) 0 0)
+                     _          -> costFun (replaceChildren cc (fromENode enode))
+          in (c + sum cc, Fix $ case enode of
+                 ENAry op _ -> unfix (naryTree op nc)
+                 _          -> replaceChildren nc (fromENode enode)) -- | missing children (cyclic classes) get cost 0 so every class is costed
+        costSentinel :: Int
+        costSentinel = 1000000
+
+        fillUpCosts :: IntMap EClass -> CostMap -> CostMap
+        fillUpCosts classes = go (IntMap.size classes + 1) (IntMap.keysSet classes)
+          where
+            go 0 _ m = m
+            go n dirty m
+              | IntSet.null dirty = m
+              | otherwise = go (n - 1) dirty' m'
+              where
+                (dirty', m') = IntSet.foldl' step (IntSet.empty, m) dirty
+                step (d, cm) eid = case IntMap.lookup eid classes of
+                  Nothing -> (d, cm)
+                  Just ecl ->
+                    let currentCost = Map.lookup eid cm
+                        minCost     = Set.foldl' (\acc en -> let c = nodeCost cm en
+                                                  in case acc of
+                                                    Nothing  -> Just c
+                                                    Just c'  -> Just (if fst c <= fst c' then c else c')
+                                                ) Nothing (_eNodes ecl)
+                        (changed, cm') = case (currentCost, minCost) of
+                          (_, Nothing)            -> (False, cm)
+                          (Nothing, Just new)     -> (True, Map.insert eid new cm)
+                          (Just old, Just new)
+                            | fst old <= fst new  -> (False, cm)
+                            | otherwise           -> (True, Map.insert eid new cm)
+                        d' = if changed
+                             then Set.foldl' (\acc (pid, _) -> IntSet.insert pid acc) d (_parents ecl)
+                             else d
+                    in d' `seq` cm' `seq` (d', cm')
+
+-- | Recompute every e-class's cost-minimal @_best@/_cost@ bottom-up and write
+-- it back into the graph. Needed after loading a graph whose best/cost were
+-- not persisted (e.g. via srtree-db), where @_best@ may otherwise hold an
+-- arbitrary (potentially large) e-node.
+recalculateBestAll :: ClassStore m => CostFun -> EGraphST m ()
+recalculateBestAll costFun = do
+  ecls <- allClasses
+  let classes = IntMap.fromList [(_eClassId ec, ec) | ec <- ecls]
+      bests = fixpoint classes IntMap.empty
+  forM_ (IntMap.toList bests) $ \(eid, (c, en)) ->
+    case IntMap.lookup eid classes of
+      Nothing -> pure ()
+      Just ec -> writeDirect ec { _info = (_info ec) { _cost = c, _best = en } }
+  where
+    nodeCost :: IntMap (Int, ENode) -> ENode -> (Int, ENode)
+    nodeCost cm en =
+      let cc = [ maybe costSentinel fst (IntMap.lookup cid cm) | cid <- eChildren en ]
+          c  = case en of
+                 ENAry op _ -> costFun (Bin (toOp op) 0 0) + sum cc
+                 _          -> costFun (replaceChildren cc (fromENode en)) + sum cc
+      in (c, en)
+    costSentinel :: Int
+    costSentinel = 1000000
+
+    fixpoint :: IntMap EClass -> IntMap (Int, ENode) -> IntMap (Int, ENode)
+    fixpoint classes0 = go (IntMap.size classes0 + 1) (IntMap.keysSet classes0)
+      where
+        go 0 _ m        = m
+        go n dirty m
+          | IntSet.null dirty = m
+          | otherwise = go (n - 1) dirty' m'
+          where
+            (dirty', m') = IntSet.foldl' step (IntSet.empty, m) dirty
+            step (d, cm) eid = case IntMap.lookup eid classes0 of
+              Nothing -> (d, cm)
+              Just ecl ->
+                let current = IntMap.lookup eid cm
+                    minNode = Set.foldl' (\acc en -> let c = nodeCost cm en
+                                                     in case acc of
+                                                          Nothing  -> Just c
+                                                          Just c'  -> Just (if fst c <= fst c' then c else c'))
+                                         Nothing (_eNodes ecl)
+                    (changed, cm') = case (current, minNode) of
+                      (_, Nothing)        -> (False, cm)
+                      (Nothing, Just new) -> (True, IntMap.insert eid new cm)
+                      (Just old, Just new)
+                        | fst old <= fst new -> (False, cm)
+                        | otherwise          -> (True, IntMap.insert eid new cm)
+                    d' = if changed
+                         then Set.foldl' (\acc (pid, _) -> IntSet.insert pid acc) d (_parents ecl)
+                          else d
+                 in d' `seq` cm' `seq` (d', cm')
+
+-- | Like 'recalculateBestAll' but streamed: each e-class body is fetched on
+-- demand through 'ClassStore' (so a paged graph never materializes every body
+-- at once) and only the small @(cost, best e-node)@ map is kept resident. The
+-- structural worklist fixpoint is identical.
+recalculateBestAllStream :: ClassStore m => CostFun -> EGraphST m ()
+recalculateBestAllStream costFun = do
+  ids <- allKeys
+  let idSet = IntSet.fromList ids
+      costSentinel = 1000000
+      nodeCost cm en =
+        let cc = [ maybe costSentinel fst (IntMap.lookup cid cm) | cid <- eChildren en ]
+            c  = case en of
+                   ENAry op _ -> costFun (Bin (toOp op) 0 0) + sum cc
+                   _          -> costFun (replaceChildren cc (fromENode en)) + sum cc
+        in (c, en)
+      stepEid cm eid = do
+        mec <- readDirect eid
+        case mec of
+          Nothing -> pure (IntSet.empty, cm)
+          Just ecl -> do
+            let current = IntMap.lookup eid cm
+                minNode = Set.foldl' (\acc en -> let c = nodeCost cm en
+                                                 in case acc of
+                                                      Nothing  -> Just c
+                                                      Just c'  -> Just (if fst c <= fst c' then c else c'))
+                                    Nothing (_eNodes ecl)
+                (changed, cm') = case (current, minNode) of
+                  (_, Nothing)        -> (False, cm)
+                  (Nothing, Just new) -> (True, IntMap.insert eid new cm)
+                  (Just old, Just new)
+                    | fst old <= fst new -> (False, cm)
+                    | otherwise          -> (True, IntMap.insert eid new cm)
+                dirty = if changed
+                          then Set.foldl' (\acc (pid, _) -> IntSet.insert pid acc) IntSet.empty (_parents ecl)
+                          else IntSet.empty
+            pure (dirty, cm')
+      fixpoint n dirty cm
+        | n <= 0 || IntSet.null dirty = pure cm
+        | otherwise = go (IntSet.toList dirty) IntSet.empty cm
+        where
+          go [] d acc = fixpoint (n - 1) d acc
+          go (e : es) d acc = do
+            (d', m') <- stepEid acc e
+            go es (IntSet.union d d') m'
+  cm <- fixpoint (IntSet.size idSet + 1) idSet IntMap.empty
+  forM_ (IntMap.toList cm) $ \(eid, (c, en)) -> do
+    mec <- readDirect eid
+    case mec of
+      Nothing -> pure ()
+      Just ec -> writeDirect ec { _info = (_info ec) { _cost = c, _best = en } }
+
+-- | Streaming variant of 'recalculateBest': computes the cost-minimal tree for a
+-- single root without materializing every e-class body at once.
+recalculateBestStream :: ClassStore m => CostFun -> EClassId -> EGraphST m (Fix SRTree)
+recalculateBestStream costFun eid = do
+  ids <- allKeys
+  let idSet = IntSet.fromList ids
+      costSentinel = 1000000
+      nodeCost cm en =
+        let (cc, nc) = unzip [ maybe (costSentinel, Fix (Const 0)) id (Map.lookup cid cm) | cid <- eChildren en ]
+            c  = case en of
+                   ENAry op _ -> costFun (Bin (toOp op) 0 0)
+                   _          -> costFun (replaceChildren cc (fromENode en))
+        in (c + sum cc, Fix $ case en of
+               ENAry op _ -> unfix (naryTree op nc)
+               _          -> replaceChildren nc (fromENode en))
+      stepEid cm eid' = do
+        mec <- lookupClass eid'
+        case mec of
+          Nothing -> pure (IntSet.empty, cm)
+          Just ecl -> do
+            let current = Map.lookup eid' cm
+                minCost = Set.foldl' (\acc en -> let c = nodeCost cm en
+                                                 in case acc of
+                                                      Nothing -> Just c
+                                                      Just c' -> Just (if fst c <= fst c' then c else c'))
+                                   Nothing (_eNodes ecl)
+                (changed, cm') = case (current, minCost) of
+                  (_, Nothing) -> (False, cm)
+                  (Nothing, Just new) -> (True, Map.insert eid' new cm)
+                  (Just old, Just new)
+                    | fst old <= fst new -> (False, cm)
+                    | otherwise -> (True, Map.insert eid' new cm)
+                dirty = if changed
+                          then Set.foldl' (\acc (pid,_) -> IntSet.insert pid acc) IntSet.empty (_parents ecl)
+                          else IntSet.empty
+            pure (dirty, cm')
+      fixpoint n dirty cm
+        | n <= 0 || IntSet.null dirty = pure cm
+        | otherwise = go (IntSet.toList dirty) IntSet.empty cm
+        where
+          go [] d acc = fixpoint (n - 1) d acc
+          go (e : es) d acc = do
+            (d', m') <- stepEid acc e
+            go es (IntSet.union d d') m'
+  cm <- fixpoint (IntSet.size idSet + 1) idSet Map.empty
+  eid' <- canonical eid
+  case Map.lookup eid' cm of
+    Just (_, t) -> pure t
+    Nothing -> error $ "EQSAT_RECALC_MISSING eid=" <> show eid'
+                     <> " costSize=" <> show (Map.size cm)
+
+-- | Run equality saturation and stream the final extraction (see
+-- 'recalculateBestStream'), so a paged graph is never fully materialized.
+eqSatStream :: ClassStore m => Fix SRTree -> [Rule] -> CostFun -> Int -> EGraphST m (Fix SRTree)
+eqSatStream expr rules costFun maxIt = do
+  root <- fromTree costFun expr
+  _ <- runEqSat costFun rules maxIt
+  recalculateBestAllStream costFun
+  recalculateBestStream costFun root
+
+-- | replaces the equality rules with two one-way rules
+replaceEqRules :: Rule -> [Rule]
+replaceEqRules (p1 :=> p2)  = [p1 :=> p2]
+replaceEqRules (p1 :==: p2) = [p1 :=> p2, p2 :=> p1]
+replaceEqRules (r :| cond)  = map (:| cond) $ replaceEqRules r
+
+-- | Compile a rule source into a query, or `Nothing` for n-ary patterns that
+-- use the direct multiset matcher instead.
+compileSource :: Rule -> Maybe (Query, [ClassOrVar], ClassOrVar)
+compileSource r = if hasNAry (source r)
+                    then Nothing
+                    else Just (compileToQuery (source r))
+
+-- | Cap on the total number of rule matches applied in a single eqsat
+-- iteration. Combined with the per-rule caps ('ruleBudget'/'ruleRootVisit' for
+-- n-ary, 'ruleMatchBudget' for the cached path) and the persistent
+-- mark-on-attempt seen-set (which makes each rule's budget advance to new
+-- matches), this bounds a single iteration's apply/rebuild work regardless of
+-- graph size.
+iterMatchBudget :: Int
+iterMatchBudget = 2000
+
+-- | run equality saturation for a number of iterations
+runEqSat :: ClassStore m => CostFun -> [Rule] -> Int -> EGraphST m (Bool, Int)
+runEqSat costFun rules maxIter = go maxIter IntMap.empty compiledRules
+    where
+        rules' = concatMap replaceEqRules rules
+        compiledRules = map (\r -> (r, compileSource r)) rules'
+
+        go it sch compiled =
+          do -- reset dirty flag before processing this iteration
+             modify' $ over (eDB . changed) (const False)
+
+             -- step 1: match the rules using cached compiled queries
+             let matchSch  = matchWithScheduler it
+                 adapted i (r, cq) = map (,cq) <$> matchSch i r
+                 matchAll  = zipWithM adapted [0..]
+                 (filtered, sch') = runState (matchAll compiled) sch
+
+             -- step 2: apply matches and rebuild
+             matches <- mapM (\(rule, cq) -> map (rule,) <$> case cq of
+                                Just q  -> do paged <- isPagedGraph
+                                              if paged
+                                                then matchStreamCached (Just (show (source rule))) (source rule)
+                                                else matchCachedWith (Just (show (source rule))) q
+                                Nothing -> matchSaturated (source rule)) $ concat filtered
+             -- bound the total number of matches applied per iteration so a
+             -- single iteration's apply/rebuild work stays bounded on huge
+             -- graphs (genuine matches; we just process them over more iters).
+             mapM_ (uncurry (applyMatch costFun)) (take iterMatchBudget (concat matches))
+             rebuild costFun
+
+             -- check dirty flag: if no modifications occurred, we've saturated
+             changed <- gets (_changed . _eDB)
+             if it == 1 || not changed
+                then pure (True, it)
+                 else
+                   do eClasses <- gets _eClass
+                      if IntMap.size eClasses > 1500
+                        then throttle it sch' compiled
+                        else go (it-1) sch' compiled
+
+        throttle it sch compiled = do
+          cleanMaps
+          eClasses <- gets _eClass
+          if IntMap.size eClasses <= 1500
+            then go (it-1) sch compiled
+            else do applySingleMergeOnlyEqSat costFun rules
+                    changed <- gets (_changed . _eDB)
+                    if it <= 1 || not changed
+                      then pure (False, it)  -- give up and return early stop
+                      else throttle (it-1) sch compiled
+
+-- | apply a single step of merge-only equality saturation
+applySingleMergeOnlyEqSat :: ClassStore m => CostFun -> [Rule] -> EGraphST m ()
+applySingleMergeOnlyEqSat costFun rules =
+  do let matchSch        = matchWithScheduler 10
+         matchAll        = zipWithM matchSch [0..]
+         (rls, _)        = runState (matchAll rules') IntMap.empty
+     matches <- getNMatches 500 rls
+     rebuild costFun
+      where
+        rules' = concatMap replaceEqRules rules
+
+        getNMatches n []       = pure []
+        getNMatches 0 _        = pure []
+        getNMatches n ([]:rss) = getNMatches n rss
+        getNMatches n ((r:rs):rss) = do matches <- map (r,) <$> matchSaturated (source r)
+                                        let (x, _) = splitAt n matches
+                                            m      = length x
+                                        if m == n
+                                           then pure matches
+                                           else do matches' <- getNMatches (n - length x) (rs:rss)
+                                                   pure (matches <> matches')
+
+
+-- | matches the rules given a scheduler
+matchWithScheduler :: Int -> Int -> Rule -> Scheduler [Rule] -- [(Rule, (Map ClassOrVar ClassOrVar, ClassOrVar))]
+matchWithScheduler it ruleNumber rule =
+  do mbBan <- gets (IntMap.!? ruleNumber)
+     if maybe False (<= it) mbBan -- check if the rule is banned
+        then pure []
+        else do -- let matches = match db (source rule)
+                modify (IntMap.insert ruleNumber (it+5))
+                pure [rule] -- $ map (rule,) matches
diff --git a/src/Algorithm/EqSat/Build.hs b/src/Algorithm/EqSat/Build.hs
new file mode 100644
--- /dev/null
+++ b/src/Algorithm/EqSat/Build.hs
@@ -0,0 +1,743 @@
+{-# LANGUAGE TupleSections #-}
+{-# LANGUAGE BangPatterns #-}
+
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Algorithm.EqSat.Build
+-- Copyright   :  (c) Fabricio Olivetti 2021 - 2024
+-- License     :  BSD3
+-- Maintainer  :  fabricio.olivetti@gmail.com
+-- Stability   :  experimental
+-- Portability :
+--
+-- Functions related to building and maintaining e-graphs
+-- Heavily based on hegg (https://github.com/alt-romes/hegg by alt-romes)
+--
+-----------------------------------------------------------------------------
+
+module Algorithm.EqSat.Build where
+
+import System.Random (Random (randomR), StdGen)
+import Control.Lens ( over )
+import Control.Monad ( forM_, when, foldM, forM )
+import Data.Maybe
+import Data.SRTree
+import Algorithm.EqSat.Egraph
+import Algorithm.EqSat.DB
+import qualified Data.IntMap.Strict as IntMap
+import Data.IntMap.Strict (IntMap)
+import Data.Map.Strict ( Map )
+import qualified Data.Map.Strict as Map
+import qualified Data.HashMap.Strict as HashMap
+import qualified Data.HashSet as Set
+import Control.Monad.State.Strict
+import Control.Monad.Identity
+import GHC.Stack (HasCallStack)
+
+import Data.SRTree.Recursion (cataM)
+import Data.List (sort)
+import Algorithm.EqSat.Info
+import qualified Data.IntSet as IntSet
+
+import qualified Data.Set as RangeSet
+
+
+-- | adds a new or existing e-node (merging if necessary)
+add :: (ClassStore m, HasCallStack) => CostFun -> ENode -> EGraphST m EClassId
+add costFun enode = do
+  enode''  <- canonize enode
+  enode''' <- foldConsts costFun enode''
+
+  maybeEid <- lookupNode enode'''
+  case maybeEid of
+       Just eid -> pure eid
+       Nothing  -> do
+         curId <- gets (_nextId . _eDB)                             -- get the next available e-class id
+         insertCanonical curId curId                                 -- register the class as its own representative
+         insertNode enode''' curId                                  -- associate new e-node with id (bounded on paged graphs)
+         modify' $ over (eDB . nextId) (+1)                          -- update next id
+                 . over (eDB . worklist) (Set.insert (curId, enode'''))      -- add e-node and id into worklist
+         forM_ (eChildren enode''') (addParents curId enode''')        -- update the children's parent list
+         info <- makeAnalysis costFun enode'''
+         h    <- getChildrenMinHeight enode'''
+         let newClass = createEClass curId enode''' info h              -- create e-class
+         -- insert via 'insertClass' so a paged (DB-backed) class store also
+         -- persists the new class's page; for a pure graph this is identical
+         -- to inserting into @_eClass@ directly.
+         insertClass newClass
+         --modifyEClass costFun curId                                 -- simplify eclass if it evaluates to a number
+
+         -- update database
+         addToDB enode''' curId                                       -- add new node to db
+         tracking <- gets (_trackDBs . _eDB)
+         when tracking $
+           modify' $ over (eDB . sizeDB)
+                   $ IntMap.insertWith (IntSet.union) (_size info) (IntSet.singleton curId)
+         modify' $ over (eDB . unevaluated) (IntSet.insert curId)
+                 . over (eDB . changed) (const True)
+         pure curId
+  where
+    addParents :: ClassStore m => EClassId -> ENode -> EClassId -> EGraphST m ()
+    addParents cId node c =
+      do ec <- getEClass c
+         let ec' = ec{ _parents = Set.insert (cId, node) (_parents ec) }
+         -- write through 'insertClass' so a paged store keeps the updated parents
+         insertClass ec'
+
+-- | Add a binary (SRTree-based) node, converting it to a flattened ENode.
+-- Sub and Div are canonicalized away at insertion: `x - y` becomes
+-- `x + (-1)*y` and `x / y` becomes `x * recip y`, so no Sub/Div e-node ever
+-- enters the e-graph and the Sub/Div-aware rules become redundant.
+addTree :: (ClassStore m, HasCallStack) => CostFun -> SRTree EClassId -> EGraphST m EClassId
+addTree costFun (Bin Sub l r) = do
+  neg <- addNegate costFun r
+  add costFun =<< mkENary EAdd [l, neg]
+addTree costFun (Bin Div l r) = do
+  rec <- add costFun (EUni Recip r)
+  add costFun =<< mkENary EMul [l, rec]
+addTree costFun t = toENode t >>= add costFun
+{-# INLINE addTree #-}
+
+-- | builds the e-class for the negation of the e-class `t`, represented as
+-- `(-1) * t` (matching the pattern-level `negate` encoding in Algorithm.EqSat.DB).
+addNegate :: (ClassStore m, HasCallStack) => CostFun -> EClassId -> EGraphST m EClassId
+addNegate costFun t = do
+  negOne <- add costFun (EConst (-1))
+  add costFun =<< mkENary EMul [negOne, t]
+
+-- | Fused 'calculateConsts' + 'foldConstants': fetches each child's constant
+-- info a single time, detects fully-constant nodes (replaced by EConst/EParam)
+-- and folds together all-but-one constant children of an ENAry
+-- (e.g. 2+3+x becomes 5+x). Constants that are already folded single subtrees
+-- are handled by the same child-constant walk.
+foldConsts :: (ClassStore m, HasCallStack) => CostFun -> ENode -> EGraphST m ENode
+foldConsts _ en@(ENAry _ m) | IntMap.null m = pure en
+foldConsts costFun en@(ENAry op m) = do
+  let xs = expandedList m
+  infos <- mapM (fmap (_consts . _info) . getEClass) xs
+  case foldr1 (\a b -> combineConsts (Bin (toOp op) a b)) infos of
+    ConstVal x -> pure (EConst x)
+    ParamIx x  -> pure (EParam x)
+    _          -> foldENary costFun op m infos
+foldConsts _ en = do
+  infos <- mapM (fmap (_consts . _info) . getEClass) (eChildren en)
+  case combineConsts (replaceChildren infos (fromENode en)) of
+    ConstVal x -> pure (EConst x)
+    ParamIx x  -> pure (EParam x)
+    _          -> pure en
+{-# INLINE foldConsts #-}
+
+-- | Fold together all-but-one constant children of an ENAry multiset.
+foldENary :: (ClassStore m, HasCallStack) => CostFun -> NOp -> IntMap Int -> [Consts] -> EGraphST m ENode
+foldENary costFun op m infos = do
+  let xs = expandedList m
+      (consts, rest) = foldr step ([], []) (zip xs infos)
+      step (_, ConstVal v) (cs, rs) | not (isNaN v) && not (isInfinite v) = (v:cs, rs)
+      step (x, _)          (cs, rs)              = (cs, x:rs)
+  if length consts >= 2
+    then do
+      let folded = case op of
+                     EAdd -> sum consts
+                     EMul -> product consts
+      if isNaN folded || isInfinite folded
+        then pure (ENAry op m)
+        else do
+          cid <- add costFun (EConst folded)
+          pure (ENAry op (imFromList (cid : rest)))
+    else pure (ENAry op m)
+{-# INLINE foldENary #-}
+
+-- | Fold together all-but-one constant children of an ENAry at insertion
+-- time (e.g. 2+3+x becomes 5+x). Constants that are already folded
+-- single subtrees are handled by 'calculateConsts' above; this handles the
+-- flattened case where several constant terms land in one multiset.
+foldConstants :: (ClassStore m, HasCallStack) => CostFun -> ENode -> EGraphST m ENode
+foldConstants _ en@(ENAry _ m) | IntMap.size m < 2 = pure en
+foldConstants costFun en@(ENAry op m) = do
+  let xs = expandedList m
+  infos <- mapM (fmap (_consts . _info) . getEClass) xs
+  let (consts, rest) = foldr step ([], []) (zip xs infos)
+      step (_, ConstVal v) (cs, rs) | not (isNaN v) && not (isInfinite v) = (v:cs, rs)
+      step (x, _)          (cs, rs)              = (cs, x:rs)
+  if length consts >= 2
+    then do
+      let folded = case op of
+                     EAdd -> sum consts
+                     EMul -> product consts
+      if isNaN folded || isInfinite folded
+        then pure en
+        else do
+          cid <- add costFun (EConst folded)
+          pure (ENAry op (imFromList (cid : rest)))
+    else pure en
+foldConstants _ en = pure en
+
+-- | rebuilds the e-graph after inserting or merging
+-- e-classes
+rebuild :: (ClassStore m, HasCallStack) => CostFun -> EGraphST m ()
+rebuild costFun =
+  do wl <- gets (_worklist . _eDB)
+     al <- gets (_analysis . _eDB)
+     modify' $ over (eDB . worklist) (const Set.empty)
+             . over (eDB . analysis) (const Set.empty)
+     forM_ wl (uncurry (repair costFun))
+     forM_ al (uncurry (repairAnalysis costFun))
+{-# INLINE rebuild #-}
+
+-- | repairs e-node by canonizing its children
+-- if the canonized e-node already exists in
+-- e-graph, merge the e-classes
+repair :: (ClassStore m, HasCallStack) => CostFun -> EClassId -> ENode -> EGraphST m ()
+repair costFun ecId enode =
+  do modify' $ over eNodeToEClass (HashMap.delete enode)
+     enode'  <- canonize enode
+     ecId'   <- canonical ecId
+     doExist <- lookupNode enode'
+     case doExist of
+        Just ecIdCanon -> do mergedId <- merge costFun ecIdCanon ecId'
+                             insertNode enode' mergedId
+                             addToDB enode' mergedId
+        Nothing        -> do insertNode enode' ecId'
+                             addToDB enode' ecId'
+{-# INLINE repair #-}
+
+-- | repair the analysis of the e-class
+-- considering the new added e-node
+repairAnalysis :: (ClassStore m, HasCallStack) => CostFun -> EClassId -> ENode -> EGraphST m ()
+repairAnalysis costFun ecId enode =
+  do ecId'  <- canonical ecId
+     enode' <- canonize enode
+     eclass <- getEClass ecId'
+     info   <- makeAnalysis costFun enode'
+     let newData = joinData (_info eclass) info
+         eclass' = eclass { _info = newData }
+     when (_info eclass /= newData) $
+       do let bestChanged = _best (_info eclass) /= _best newData
+          modify' $ over (eDB . analysis) (_parents eclass <>)
+                  . (if bestChanged && isJust (_fitness (_info eclass)) then over (eDB . refits) (IntSet.insert ecId') else id)
+          -- write through 'insertClass' so a paged store keeps the updated body
+          insertClass eclass'
+          _ <- modifyEClass costFun ecId'
+          pure ()
+{-# INLINE repairAnalysis #-}
+
+-- | merge to equivalent e-classes
+merge :: (ClassStore m, HasCallStack) => CostFun -> EClassId -> EClassId -> EGraphST m EClassId
+merge costFun c1 c2 =
+  do c1' <- canonical c1
+     c2' <- canonical c2
+     if c1' == c2'                                     -- if they are already merged, return canonical
+       then pure c1'
+       else do (led, ledC, ledOrig, sub, subC, subOrig) <- getLeaderSub c1' c1 c2' c2  -- the leader will be the e-class with more parents
+               mergeClasses led ledC ledOrig sub subC subOrig         -- merge sub into leader
+  where
+    mergeClasses :: (ClassStore m, HasCallStack) => EClassId -> EClass -> EClassId -> EClassId -> EClass -> EClassId -> EGraphST m EClassId
+    mergeClasses led ledC ledO sub subC subO =
+      do insertCanonical sub led       -- persist/register the canonical merges
+         insertCanonical subO led
+         let newC = EClass led
+                         (_eNodes ledC `Set.union` _eNodes subC)
+                         (_parents ledC <> _parents subC)
+                         (min (_height ledC) (_height subC))
+                         (joinData (_info ledC) (_info subC))
+         forM_ (Set.toList (_eNodes subC)) $ \en -> insertNode en led
+         -- write the merged body through the class store (a paged store keeps the
+         -- authoritative page) and drop the absorbed class
+         insertClass newC
+         deleteClass sub
+         modify' $ over (eDB . worklist) (_parents subC <>)
+         when (_info newC /= _info ledC)
+           $ do let bestChanged = _best (_info newC) /= _best (_info ledC)
+                modify' $ over (eDB . analysis) (_parents ledC <>)
+                           . (if bestChanged && isJust (_fitness (_info ledC)) then over (eDB . refits) (IntSet.insert led) else id)
+         when (_info newC /= _info subC)
+           $ modify' $ over (eDB . analysis) (_parents subC <>)
+         tracking <- gets (_trackDBs . _eDB)
+         when tracking $ updateDBs newC led ledC ledO sub subC subO
+         modifyEClass costFun led
+         modify' $ over (eDB . changed) (const True)
+         pure led
+
+    getLeaderSub c1 c1O c2 c2O =
+      do ec1 <- getEClass c1
+         ec2 <- getEClass c2
+         let n1 = Set.size (_parents ec1)
+             n2 = Set.size (_parents ec2)
+         pure $ if n1 >= n2
+                  then (c1, ec1, c1O, c2, ec2, c2O)
+                  else (c2, ec2, c2O, c1, ec1, c1O)
+
+    updateDBs :: (ClassStore m, HasCallStack) => EClass -> EClassId -> EClass -> EClassId -> EClassId -> EClass -> EClassId -> EGraphST m ()
+    updateDBs newC led ledC ledO sub subC subO = do
+      updateFitnessDB newC led ledC ledO sub subC subO
+      updateSizeDB newC led ledC ledO sub subC subO
+
+    updateSizeDB :: Monad m => EClass -> EClassId -> EClass -> EClassId -> EClassId -> EClass -> EClassId -> EGraphST m ()
+    updateSizeDB newC led ledC ledO sub subC subO = do
+      let sz  = (_size . _info) newC
+          szL = (_size . _info) ledC
+          szS = (_size . _info) subC
+          fun = IntMap.adjust (IntSet.insert led) sz . IntMap.adjust (IntSet.delete led . IntSet.delete ledO) szL . IntMap.adjust (IntSet.delete sub . IntSet.delete subO) szS
+      modify' $ over (eDB . sizeDB) fun
+
+    updateFitnessDB :: Monad m => EClass -> EClassId -> EClass -> EClassId -> EClassId -> EClass -> EClassId -> EGraphST m ()
+    updateFitnessDB newC led ledC ledO sub subC subO =
+      case fitNew of
+        Nothing -> modify' $ over (eDB . unevaluated) (IntSet.insert led . IntSet.delete ledO . IntSet.delete sub . IntSet.delete subO)
+        Just fn -> do
+          when (fitNew /= fitLed) $ do
+            modify' $ case fitLed of
+              Nothing -> over (eDB . unevaluated) (IntSet.delete led . IntSet.delete ledO)
+              Just fl -> over (eDB . fitRangeDB) (removeRange led fl . removeRange ledO fl)
+                       . over (eDB . sizeFitDB) (IntMap.adjust (removeRange ledO fl . removeRange led fl) szLed)
+            modify' $ over (eDB . fitRangeDB) (insertRange led fn)
+                    . over (eDB . sizeFitDB) (IntMap.adjust (insertRange led fn) szNew . IntMap.insertWith RangeSet.union szNew RangeSet.empty)
+          modify' $ case fitSub of
+            Nothing -> over (eDB . unevaluated) (IntSet.delete sub . IntSet.delete subO)
+            Just fs -> over (eDB . fitRangeDB) (removeRange sub fs . removeRange subO fs)
+                     . over (eDB . sizeFitDB) (IntMap.adjust (removeRange subO fs . removeRange sub fs) szSub)
+      where
+        fitNew = (_fitness . _info) newC
+        fitLed = (_fitness . _info) ledC
+        fitSub = (_fitness . _info) subC
+        szNew  = (_size . _info) newC
+        szLed  = (_size . _info) ledC
+        szSub  = (_size . _info) subC
+
+-- | modify an e-class, e.g., add constant e-node and prune non-leaves
+modifyEClass :: (ClassStore m, HasCallStack) => CostFun -> EClassId -> EGraphST m EClassId
+modifyEClass costFun ecId =
+  do ec <- getEClass ecId
+     case (_consts . _info) ec of
+       ConstVal x ->
+        do let en = EConst x
+           c <- calculateCost costFun en
+           let infoEc = (_info ec){ _cost = c, _best = en, _consts = toConst en }
+           maybeEid <- lookupNode en
+           -- write through 'insertClass' (a paged store keeps the authoritative page)
+           insertClass ec{ _eNodes = Set.singleton en, _info = infoEc }
+           when (isJust $ _fitness $ _info ec) $ modify' $ over (eDB . refits) (IntSet.insert ecId)
+           case maybeEid of
+             Nothing   -> pure ecId
+             Just eid' -> merge costFun eid' ecId
+
+       ParamIx x ->
+         do let en = EParam x
+            c <- calculateCost costFun en
+            let infoEc = (_info ec){ _cost = c, _best = en, _consts = toConst en }
+            maybeEid <- lookupNode en
+            insertClass ec{ _eNodes = Set.insert en (_eNodes ec), _info = infoEc }
+            when (isJust $ _fitness $ _info ec) $ modify' $ over (eDB . refits) (IntSet.insert ecId)
+            case maybeEid of
+              Nothing   -> pure ecId
+              Just eid' -> merge costFun eid' ecId
+
+       _ -> pure ecId
+
+  where
+    isTerm (EVar _)   = True
+    isTerm (EConst _) = True
+    isTerm (EParam _) = True
+    isTerm _          = False
+
+    toConst (EParam ix) = ParamIx ix
+    toConst (EConst x)  = ConstVal x
+    toConst _           = NotConst
+
+-- * DB
+
+-- | `addToDB` adds an e-node and e-class id to the database
+addToDB :: (ClassStore m, HasCallStack) => ENode -> EClassId -> EGraphST m () -- State DB ()
+addToDB enode' eid = do
+  eid' <- canonical eid
+  ec <- getEClass eid'
+  let isConst = _consts . _info $ ec
+  let enode = case isConst of
+                ConstVal x -> EConst x
+                ParamIx  x -> EParam x
+                _          -> enode'
+  let ids = eid : eChildren enode -- we will add the e-class id and the children ids
+      op  = eOpKey enode    -- changes Bin op l r to Bin op () () so `op` as a single entry in the DB
+  trie <- gets (Map.lookup op . _patDB . _eDB)
+  case populate trie ids of      -- populates the trie
+    Nothing -> pure ()
+    Just t  -> modify' $ over (eDB . patDB) (Map.insert op t) -- if something was created, insert back into the DB
+  recordNode enode eid            -- register the node for the streaming matcher's source
+{-# INLINE addToDB #-}
+
+-- | Populates an IntTrie with a sequence of e-class ids
+populate :: Maybe IntTrie -> [EClassId] -> Maybe IntTrie
+populate _ []         = Nothing
+populate Nothing eids = foldr f Nothing eids
+  where
+    f :: EClassId -> Maybe IntTrie -> Maybe IntTrie
+    f eid (Just t) = Just $ IntTrie (IntMap.singleton eid t)
+    f eid Nothing  = Just $ IntTrie (IntMap.singleton eid (IntTrie IntMap.empty))
+populate (Just tId) (eid:eids) = let nextTrie = IntMap.lookup eid (_trie tId)
+                                     val      = fromMaybe (IntTrie IntMap.empty) $ populate nextTrie eids
+                                  in Just $ IntTrie (IntMap.insert eid val (_trie tId))
+{-# INLINE populate #-}
+
+canonizeMap :: (ClassStore m, HasCallStack) => (Subst, ClassOrVar) -> EGraphST m (Subst, ClassOrVar)
+canonizeMap (subst, cv) = (,cv) <$> traverse g subst
+  where
+    g :: ClassStore m => SubVal -> EGraphST m SubVal
+    g (SVOne e2)  = SVOne <$> canonOne e2
+    g (SVMap m)   = SVMap . IntMap.fromListWith (+) <$> mapM (\(e2, n) -> do
+                       e2' <- canonOne (Left e2)
+                       pure (getInt e2', n)) (IntMap.toList m)
+    canonOne :: ClassStore m => ClassOrVar -> EGraphST m ClassOrVar
+    canonOne (Left e2) = Left <$> canonical e2
+    canonOne e2        = pure e2
+{-# INLINE canonizeMap #-}
+
+applyMatch :: (ClassStore m, HasCallStack) => CostFun -> Rule -> (Subst, ClassOrVar) -> EGraphST m ()
+applyMatch costFun rule match' =
+  do let conds = getConditions rule
+     match       <- canonizeMap match'
+     validHeight <- isValidHeight match
+     validConds  <- mapM (`isValidConditions` match) conds
+     when (validHeight && and validConds) $
+       do new_eclass <- reprPrat costFun (fst match) (target rule)
+          merge costFun (getInt (snd match)) new_eclass
+          pure ()
+{-# INLINE applyMatch #-}
+
+-- | gets the e-node of the target of the rule
+-- TODO: add consts and modify
+classOfENode :: (ClassStore m, HasCallStack) => CostFun -> Subst -> Pattern -> EGraphST m (Maybe EClassId)
+classOfENode costFun subst (VarPat c)     = do let maybeEid = case Map.lookup (Right (fromEnum c)) subst of
+                                                                  Just (SVOne v) -> Just v
+                                                                  _              -> Nothing
+                                               case maybeEid of
+                                                 Nothing  -> pure Nothing
+                                                 Just eid -> Just <$> canonical (getInt eid)
+classOfENode costFun subst (Fixed (Const x)) = Just <$> add costFun (EConst x)
+classOfENode costFun subst (Fixed target) = do newChildren <- mapM (classOfENode costFun subst) (getElems target)
+                                               case sequence newChildren of
+                                                 Nothing -> pure Nothing
+                                                 Just cs -> do let new_enode = replaceChildren cs target
+                                                               cs' <- mapM canonical cs
+                                                               areConsts <- mapM isConst cs'
+                                                               if and areConsts
+                                                                 then do eid <- addTree costFun new_enode
+                                                                         rebuild costFun -- eid new_enode
+                                                                         pure (Just eid)
+                                                                 else do en <- toENode new_enode
+                                                                         en' <- canonize en
+                                                                         gets (HashMap.lookup en' . _eNodeToEClass)
+classOfENode _ _ (NAry _ _) = error "classOfENode: n-ary pattern unsupported"
+classOfENode _ _ Hole       = error "classOfENode: Hole is only valid in MapP targets"
+{-# INLINE classOfENode #-}
+
+-- | adds the target of the rule into the e-graph
+reprPrat :: (ClassStore m, HasCallStack) => CostFun -> Subst -> Pattern -> EGraphST m EClassId
+reprPrat costFun subst (VarPat c)     = do
+    let k = Right (fromEnum c)
+    v <- case Map.lookup k subst of
+           Nothing -> error $ "REPRPRAT_MISSING var=" <> show (fromEnum c) <> " substSize=" <> show (Map.size subst)
+           Just (SVOne x) -> pure x
+           Just (SVMap _) -> error $ "REPRPRAT_REST_AS_SINGLE var=" <> show (fromEnum c)
+    canonical $ getInt v
+reprPrat costFun subst (Fixed target) = do newChildren <- mapM (reprPrat costFun subst) (getElems target)
+                                           addTree costFun (replaceChildren newChildren target)
+reprPrat costFun subst Hole = error "REPRPRAT_HOLE: Hole must be filled by MapP"
+reprPrat costFun subst (NAry op ncs) = do
+    m <- IntMap.unionsWith (+) <$> mapM (childEidM costFun subst) ncs
+    case IntMap.toList m of
+      []        -> reprPrat costFun subst (Fixed (Const (if op == EAdd then 0 else 1)))
+      [(c, 1)]  -> canonical c
+      _         -> do en <- mkENaryM op m
+                      add costFun en
+{-# INLINE reprPrat #-}
+
+-- | Adds a single child of an n-ary target pattern to the e-graph, returning
+-- its contribution as a canonical multiset (so 'Rest' children carry their
+-- 'IntMap' straight through without expansion).
+childEidM :: (ClassStore m, HasCallStack) => CostFun -> Subst -> NChild -> EGraphST m (IntMap Int)
+childEidM costFun subst (Ch p)     = (`IntMap.singleton` 1) <$> reprPrat costFun subst p
+childEidM costFun subst (Rest c)   = restEidsM subst c
+childEidM costFun subst (MapP p c) = do
+  es <- restEids subst c
+  ms <- forM es $ \e -> reprMapP costFun subst e p
+  pure (imFromList ms)
+{-# INLINE childEidM #-}
+
+-- | The e-class ids bound to a rest variable, as a canonical multiset.
+restEidsM :: (Monad m, HasCallStack) => Subst -> Char -> EGraphST m (IntMap Int)
+restEidsM subst c = do
+  let k = Right (fromEnum c)
+  case Map.lookup k subst of
+    Just (SVMap m) -> pure m
+    Just (SVOne _) -> error $ "REPRPRAT_SINGLE_AS_REST var=" <> show (fromEnum c)
+    Nothing        -> error $ "REPRPRAT_MISSING_REST var=" <> show (fromEnum c)
+{-# INLINE restEidsM #-}
+
+-- | The e-class ids bound to a rest variable, expanded one entry per
+-- occurrence (used by 'MapP', which needs to instantiate per child).
+restEids :: (Monad m, HasCallStack) => Subst -> Char -> EGraphST m [EClassId]
+restEids subst c = expandedList <$> restEidsM subst c
+{-# INLINE restEids #-}
+
+-- | Build the target of a pattern where every `Hole` is filled with the
+-- e-class `e` (used by 'MapP').
+reprMapP :: (ClassStore m, HasCallStack) => CostFun -> Subst -> EClassId -> Pattern -> EGraphST m EClassId
+reprMapP costFun subst e Hole = canonical e
+reprMapP costFun subst e (VarPat c) = reprPrat costFun subst (VarPat c)
+reprMapP costFun subst e (Fixed target) = do
+  newChildren <- mapM (reprMapP costFun subst e) (getElems target)
+  addTree costFun (replaceChildren newChildren target)
+reprMapP costFun subst e (NAry op ncs) = do
+  m <- IntMap.unionsWith (+) <$> mapM (childMapP costFun subst e) ncs
+  case IntMap.toList m of
+    []   -> reprPrat costFun subst (Fixed (Const (if op == EAdd then 0 else 1)))
+    [(c, 1)] -> canonical c
+    _    -> do en <- mkENaryM op m
+               add costFun en
+{-# INLINE reprMapP #-}
+
+-- | A single child of an n-ary pattern inside a 'MapP' function.
+childMapP :: (ClassStore m, HasCallStack) => CostFun -> Subst -> EClassId -> NChild -> EGraphST m (IntMap Int)
+childMapP costFun subst e (Ch p)     = (`IntMap.singleton` 1) <$> reprMapP costFun subst e p
+childMapP costFun subst e (Rest c)   = restEidsM subst c
+childMapP costFun subst e (MapP _ _) = error "nested MapP unsupported"
+{-# INLINE childMapP #-}
+
+isValidHeight :: (ClassStore m, HasCallStack) => (Subst, ClassOrVar) -> EGraphST m Bool
+isValidHeight match = do
+      h <- case snd match of
+             Left ec -> _height <$> getEClass ec
+             Right _ -> pure 0
+      pure $ h < 15
+{-# INLINE isValidHeight #-}
+
+-- | returns `True` if the condition of a rule is valid for that match
+isValidConditions :: ClassStore m => Condition -> (Subst, ClassOrVar) -> EGraphST m Bool
+isValidConditions (Condition f) match = f (fst match)
+{-# INLINE isValidConditions #-}
+
+-- * Tree to e-graph conversion and utility functions
+
+-- | Creates an e-graph from an expression tree
+fromTree :: (ClassStore m, HasCallStack) => CostFun -> Fix SRTree -> EGraphST m EClassId
+fromTree costFun = cataM sequence (addTree costFun)
+{-# INLINE fromTree #-}
+
+-- | Builds an e-graph from multiple independent trees
+fromTrees :: ClassStore m => CostFun -> [Fix SRTree] -> EGraphST m [EClassId]
+fromTrees costFun = foldM (\rs t -> do eid <- fromTree costFun t; pure (eid:rs)) []
+{-# INLINE fromTrees #-}
+
+countParamsEg :: EGraph -> EClassId -> Int
+countParamsEg eg rt = countParams . runIdentity $ getBestExpr rt `evalStateT` eg
+countParamsUniqEg :: EGraph -> EClassId -> Int
+countParamsUniqEg eg rt = countParamsUniq . runIdentity $ getBestExpr rt `evalStateT` eg
+
+
+getBestENode eid = (_best . _info) <$> getEClass eid
+{-# INLINE getBestENode #-}
+
+-- | returns one expression rooted at e-class `eId`
+-- TODO: avoid loopings
+getExpressionFrom :: ClassStore m => EClassId -> EGraphST m (Fix SRTree)
+getExpressionFrom eId' = do
+    nodes <- _eNodes <$> getEClass eId'
+    case Set.toList nodes of
+      (n:_) -> case n of
+        EVar ix     -> pure $ Fix $ Var ix
+        EParam ix   -> pure $ Fix $ Param ix
+        EConst x    -> pure $ Fix $ Const x
+        EUni f t    -> Fix . Uni f <$> getExpressionFrom t
+        EBin op l r -> Fix <$> (Bin op <$> getExpressionFrom l <*> getExpressionFrom r)
+        ENAry op xs -> naryTree op <$> mapM getExpressionFrom (expandedList xs)
+      [] -> error "getExpressionFrom: empty eclass"
+{-# INLINE getExpressionFrom #-}
+
+-- | returns all expressions rooted at e-class `eId`
+-- TODO: check for infinite list
+getAllExpressionsFrom :: ClassStore m => EClassId -> EGraphST m [Fix SRTree]
+getAllExpressionsFrom eId' = do
+  nodes <- Set.toList . _eNodes <$> getEClass eId'
+  go nodes
+  where
+    go []     = pure []
+    go (n:ns) = do
+        t <- case n of
+                EVar ix     -> pure [Fix $ Var ix]
+                EParam ix   -> pure [Fix $ Param ix]
+                EConst x    -> pure [Fix $ Const x]
+                EUni f t    -> Prelude.map (Fix . Uni f) <$> getAllExpressionsFrom t
+                EBin op l r -> do l' <- getAllExpressionsFrom l
+                                  r' <- getAllExpressionsFrom r
+                                  pure $ [Fix $ Bin op li ri | li <- l', ri <- r']
+                ENAry op xs -> do ts <- mapM getAllExpressionsFrom (expandedList xs)
+                                  pure [ naryTree op comb | comb <- sequence ts ]
+        ts <- go ns
+        pure (t ++ ts)
+{-# INLINE getAllExpressionsFrom #-}
+
+getNExpressionsFrom :: ClassStore m => Int -> EClassId -> EGraphST m [Fix SRTree]
+getNExpressionsFrom n eId' = getNExpressionsFrom' n 15 eId' 
+
+getNExpressionsFrom' :: ClassStore m => Int -> Int -> EClassId -> EGraphST m [Fix SRTree]
+getNExpressionsFrom' _ 0 _ = pure []
+getNExpressionsFrom' n d eId' = do
+  nodes <- Set.toList . _eNodes <$> getEClass eId'
+  (concat <$> go n d nodes)
+  where
+    isTerm (EVar _) = True
+    isTerm (EConst _) = True
+    isTerm (EParam _) = True
+    isTerm _ = False
+    toTree (EVar ix) = Fix $ Var ix
+    toTree (EConst x) = Fix $ Const x
+    toTree (EParam ix) = Fix $ Param ix
+    toTree _ = undefined
+
+    go n' _ []     = pure []
+    go n' 0 ts     = pure []
+    go n' d (node:ns) = do
+        tt <- case node of
+                EVar ix     -> pure [Fix $ Var ix]
+                EParam ix   -> pure [Fix $ Param ix]
+                EConst x    -> pure [Fix $ Const x]
+                EUni f t    -> Prelude.map (Fix . Uni f) <$> getNExpressionsFrom' n' (d-1) t
+                EBin op l r -> do l' <- getNExpressionsFrom' n' (d-1) l
+                                  r' <- getNExpressionsFrom' n' (d-1) r
+                                  pure $ Prelude.take n [Fix $ Bin op li ri | li <- l', ri <- r']
+                ENAry op xs -> do ts <- mapM (getNExpressionsFrom' n' (d-1)) (expandedList xs)
+                                  pure $ Prelude.take n [ naryTree op comb | comb <- sequence ts ]
+        let n'' = n' - length tt
+        if n'' <= 0
+          then pure [tt]
+          else do ts <- go n'' (d-1) ns
+                  pure (tt:ts)
+
+getNEclassFrom :: ClassStore m => Int -> EClassId -> EGraphST m [[EClassId]]
+getNEclassFrom n eid = getNEclassFrom' n 15 eid
+
+getNEclassFrom' :: ClassStore m => Int -> Int -> EClassId -> EGraphST m [[EClassId]]
+getNEclassFrom' _ 0 _ = pure []
+getNEclassFrom' n d eId' = do
+  eId <- canonical eId'
+  nodes <- Set.toList . _eNodes <$> getEClass eId'
+  (Prelude.map (eId:) <$> go n d nodes)
+  where
+    --go :: Int -> Int -> [ENode] -> EGraphST m [[EClassId]]
+    go n' _ []     = pure []
+    go n' 0 ts     = pure []
+    go n' d (node:ns) = do
+        tt <- case node of
+                EBin op l r -> do l' <- getNEclassFrom' n' (d-1) l
+                                  r' <- getNEclassFrom' n' (d-1) r
+                                  pure $ Prelude.take n [li <> ri | li <- l', ri <- r']
+                ENAry op xs -> do ts <- mapM (getNEclassFrom' n' (d-1)) xs
+                                  pure $ Prelude.take n [ concat comb | comb <- sequence ts ]
+                EUni f t    -> getNEclassFrom' n' (d-1) t -- [[eid2:eid1]]
+                EVar ix     -> pure [[]]
+                EConst x    -> pure [[]]
+                EParam ix   -> pure [[]]
+        pure tt
+        --let n'' = n' - length tt
+        --if n'' <= 0
+        --  then pure [tt]
+        --  else do ts <- go n'' (d-1) ns
+        --          pure (tt:ts)
+
+getAllChildEClasses :: ClassStore m => EClassId -> EGraphST m [EClassId]
+getAllChildEClasses eId' = do
+  eId <- canonical eId'
+  IntSet.toList <$> go [eId] IntSet.empty
+
+  where
+    hasNoTerminal :: [ENode] -> Bool
+    hasNoTerminal = all (not . null . eChildren) 
+    getNodes :: ClassStore m => EClassId -> EGraphST m [ENode]
+    getNodes n = Set.toList . _eNodes <$> getEClass n
+
+    go :: ClassStore m => [Int] -> IntSet.IntSet -> EGraphST m IntSet.IntSet
+    go [] visited = pure visited
+    go queue visited = do 
+        nodes <- concatMap eChildren . concat . filter hasNoTerminal <$> mapM getNodes queue
+        eids <- filter (\e -> e `IntSet.notMember` visited) <$> (mapM canonical nodes)
+        go eids (visited `IntSet.union` IntSet.fromList queue)
+            {-
+    go n = do nodes <- gets (map decodeEnode . Set.toList . _eNodes . (IntMap.! n) . _eClass)
+              let hasTerminal = any (null . childrenOf) nodes
+              eids <- mapM canonical $ concatMap childrenOf nodes
+              if hasTerminal
+                then pure [n]
+                else do eids' <- mapM go eids
+                        pure ((n : eids) <> concat eids')
+                        -}
+{-# INLINE getAllChildEClasses #-}
+
+getAllChildBestEClasses :: ClassStore m => EClassId -> EGraphST m [EClassId]
+getAllChildBestEClasses eId' = do
+  IntSet.toList <$> go IntSet.empty eId'
+  where
+    go :: ClassStore m => IntSet.IntSet -> EClassId -> EGraphST m IntSet.IntSet
+    go acc n
+      | IntSet.member n acc = pure acc
+      | otherwise = do
+          let acc' = IntSet.insert n acc
+          node <- (_best . _info) <$> getEClass n
+          eids <- mapM canonical $ eChildren node
+          foldM go acc' eids
+
+getAllChildBestEClassesRep :: ClassStore m => EClassId -> EGraphST m [EClassId]
+getAllChildBestEClassesRep eId' = do
+  go eId'
+  where
+    go :: ClassStore m => EClassId -> EGraphST m [EClassId]
+    go n = do node <- (_best . _info) <$> getEClass n
+              let hasTerminal = (null . eChildren) node
+              eids <- mapM canonical $ eChildren node
+              if hasTerminal
+                then pure [n]
+                else do eids' <- mapM go eids
+                        pure (n : concat eids')
+
+-- | returns a random expression rooted at e-class `eId`
+getRndExpressionFrom :: EClassId -> EGraphST (State StdGen) (Fix SRTree)
+getRndExpressionFrom eId' = do
+    nodes <- Set.toList . _eNodes <$> getEClass eId'
+    n <- lift $ randomFrom nodes
+    case n of
+      EUni f t    -> Fix . Uni f <$> getRndExpressionFrom t
+      EBin op l r -> Fix <$> (Bin op <$> getRndExpressionFrom l <*> getRndExpressionFrom r)
+      ENAry op xs -> naryTree op <$> mapM getRndExpressionFrom (expandedList xs)
+      EVar ix     -> pure $ Fix $ Var ix
+      EConst x    -> pure $ Fix $ Const x
+      EParam ix   -> pure $ Fix $ Param ix
+  where
+    randomRange rng = state (randomR rng)
+    randomFrom xs   = do n <- randomRange (0, length xs - 1)
+                         pure $ xs !! n
+{-# INLINE getRndExpressionFrom #-}
+
+cleanMaps :: ClassStore m => EGraphST m ()
+cleanMaps = do
+  hasStore <- gets (isJust . _classStore)
+  if hasStore
+    -- the paged store is authoritative for both node->class and canonical
+    -- lookups, so the bounded resident caches are simply reset (an O(n) rebuild
+    -- of an unbounded map would defeat the out-of-core goal).
+    then modify' $ \eg -> eg { _eNodeToEClass = HashMap.empty
+                             , _canonicalMap = IntMap.empty
+                             , _eClass = IntMap.empty }
+    else do
+      enode2eclass <- gets _eNodeToEClass
+      entries <- forM (HashMap.toList enode2eclass) $ \(k,v) -> do
+        k' <- canonize k
+        v' <- canonical v
+        pure (k',v')
+      let enode2eclass' = HashMap.fromList entries
+      eclassMap <- gets _eClass
+      entries' <- forM (IntMap.toList eclassMap) $ \(k,v) -> do
+        k' <- canonical k
+        pure $ if k==k' then (Just (k,v)) else Nothing
+      let eclassMap' = IntMap.fromList (catMaybes entries')
+      modify' $ \eg -> eg { _eNodeToEClass = enode2eclass'
+                          , _eClass = eclassMap' }
+{-# INLINE cleanMaps #-}
diff --git a/src/Algorithm/EqSat/DB.hs b/src/Algorithm/EqSat/DB.hs
new file mode 100644
--- /dev/null
+++ b/src/Algorithm/EqSat/DB.hs
@@ -0,0 +1,695 @@
+{-# LANGUAGE TupleSections #-}
+{-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE RankNTypes #-}
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Algorithm.EqSat.EqSatDB
+-- Copyright   :  (c) Fabricio Olivetti 2021 - 2024
+-- License     :  BSD3
+-- Maintainer  :  fabricio.olivetti@gmail.com
+-- Stability   :  experimental
+-- Portability :
+--
+-- Pattern matching and rule application functions
+-- Heavily based on hegg (https://github.com/alt-romes/hegg by alt-romes)
+--
+-----------------------------------------------------------------------------
+module Algorithm.EqSat.DB where
+
+import Algorithm.EqSat.Egraph
+import Control.Lens ( over )
+import Control.Monad (when, foldM, forM)
+import Control.Monad.State
+import GHC.Stack (HasCallStack)
+import Data.IntMap.Strict (IntMap)
+import qualified Data.IntMap.Strict as IntMap
+import Data.Map (Map)
+import qualified Data.Map as Map
+import Data.List (sortBy)
+import Data.Maybe (fromMaybe)
+import Data.Ord (comparing)
+import Data.SRTree
+import Data.HashSet (HashSet)
+import qualified Data.HashSet as Set
+import qualified Data.Set as RangeSet
+import Data.String (IsString (..))
+import Data.SRTree.Recursion (cata)
+import Text.Read (readMaybe)
+
+
+-- A Pattern is either a fixed-point of a tree, an index to a pattern variable
+-- (which matches anything), a hole (only used inside a 'MapP' target function),
+-- or an n-ary Add/Mul pattern whose children are matched as a multiset.
+data Pattern = Fixed (SRTree Pattern) | VarPat Char | Hole | NAry NOp [NChild]
+  deriving (Show, Eq, Ord)
+
+-- | A child of an n-ary pattern: a single child pattern ('Ch'), a rest
+-- variable binding every remaining child of the node ('Rest'), or a
+-- target-side map that splices one instantiation of a pattern (with its 'Hole'
+-- filled) per child bound to a rest variable ('MapP').
+data NChild = Ch Pattern | Rest Char | MapP Pattern Char
+  deriving (Show, Eq, Ord)
+
+-- The instance for `IsString` for a `Pattern` is 
+-- valid only for a single letter char from a-zA-Z. 
+-- The patterns can be written as "x" + "y", for example,
+-- and it will translate to `Fixed (Bin Add (VarPat 120) (VarPat 121)`.
+instance IsString Pattern where
+  fromString []     = error "empty string in VarPat"
+  fromString [c] | n >= 65 && n <= 122 = VarPat c where n = fromEnum c
+  fromString s      = error $ "invalid string in VarPat: " <> s
+
+tree2pat :: Fix SRTree -> Pattern
+tree2pat = cata alg
+  where
+    alg (Param ix) = if ix >= 100 then VarPat (toEnum $ ix - 100 + 65) else Fixed $ Param ix
+    alg (Var ix) = Fixed $ Var ix
+    alg (Const x) = Fixed $ Const x
+    alg (Bin Add l r) = NAry EAdd [Ch l, Ch r]
+    alg (Bin Mul l r) = NAry EMul [Ch l, Ch r]
+    alg (Bin op l r) = Fixed $ Bin op l r
+    alg (Uni f t) = Fixed $ Uni f t
+-- A rule is either a directional rule where pat1 can be replaced by pat2, a bidirectional rule 
+-- where pat1 can be replaced or replace pat2, or a pattern with a conditional function 
+-- describing when to apply the rule 
+data Rule = Pattern :=> Pattern | Pattern :==: Pattern | Rule :| Condition
+
+infix  3 :=>
+infix  3 :==:
+infixl 2 :|
+
+instance Show Rule where
+  show (a :=> b) = show a <> " => " <> show b
+  show (a :==: b) = show a <> " == " <> show b
+  show (a :| b) = show a <> " | <cond>"
+
+-- A Query is a list of Atoms 
+type Query = [Atom]
+
+-- | A `Condition` is a predicate over a match's substitution that runs inside
+-- the e-graph monad so it can fetch e-class data through 'ClassStore' (which
+-- streams from a paged store when the graph is out-of-core). The quantification
+-- over the monad is intentional: the same condition works for any 'ClassStore'
+-- instance, including the IO-backed paged store.
+newtype Condition = Condition (forall m. ClassStore m => Subst -> EGraphST m Bool)
+
+-- An Atom is composed of either an e-class id or pattern variable id
+-- and the tree that generated that pattern. Left is e-class id and Right is a VarPat.
+type ClassOrVar = Either EClassId Int
+data Atom = Atom ClassOrVar (SRTree ClassOrVar) deriving Show
+
+-- | A substitution value: a single e-class (a matched pattern variable) or the
+-- canonical multiset of e-class ids (a matched rest variable).
+data SubVal = SVOne ClassOrVar | SVMap (IntMap Int) deriving Show
+
+-- | Substitution map produced by matching a pattern.
+type Subst = Map ClassOrVar SubVal
+
+unFixPat :: Pattern -> SRTree Pattern
+unFixPat (Fixed p) = p
+unFixPat (VarPat _) = error "unFixPat: VarPat is not a fixed pattern"
+unFixPat Hole       = error "unFixPat: Hole is not a fixed pattern"
+unFixPat (NAry _ _) = error "unFixPat: NAry is not a fixed pattern"
+{-# INLINE unFixPat #-}
+
+
+instance Num Pattern where
+  l + r = NAry EAdd [Ch l, Ch r]
+  {-# INLINE (+) #-}
+  l - r = NAry EAdd [Ch l, Ch (negate r)]
+  {-# INLINE (-) #-}
+  l * r = NAry EMul [Ch l, Ch r]
+  {-# INLINE (*) #-}
+
+  abs = Fixed . Uni Abs
+  {-# INLINE abs #-}
+
+  negate t = NAry EMul [Ch (Fixed (Const (-1))), Ch t]
+  {-# INLINE negate #-}
+
+  signum t = case t of
+               Fixed (Const x) -> Fixed . Const $ signum x
+               _               -> Fixed (Const 0)
+  fromInteger x = Fixed $ Const (fromInteger x)
+  {-# INLINE fromInteger #-}
+
+instance Fractional Pattern where
+  l / r = NAry EMul [Ch l, Ch (Fixed (Uni Recip r))]
+  {-# INLINE (/) #-}
+
+  fromRational = Fixed . Const . fromRational
+  {-# INLINE fromRational #-}
+
+instance Floating Pattern where
+  pi      = Fixed $ Const  pi
+  {-# INLINE pi #-}
+  exp     = Fixed . Uni Exp
+  {-# INLINE exp #-}
+  log     = Fixed . Uni Log
+  {-# INLINE log #-}
+  sqrt    = Fixed . Uni Sqrt
+  {-# INLINE sqrt #-}
+  sin     = Fixed . Uni Sin
+  {-# INLINE sin #-}
+  cos     = Fixed . Uni Cos
+  {-# INLINE cos #-}
+  tan     = Fixed . Uni Tan
+  {-# INLINE tan #-}
+  asin    = Fixed . Uni ASin
+  {-# INLINE asin #-}
+  acos    = Fixed . Uni ACos
+  {-# INLINE acos #-}
+  atan    = Fixed . Uni ATan
+  {-# INLINE atan #-}
+  sinh    = Fixed . Uni Sinh
+  {-# INLINE sinh #-}
+  cosh    = Fixed . Uni Cosh
+  {-# INLINE cosh #-}
+  tanh    = Fixed . Uni Tanh
+  {-# INLINE tanh #-}
+  asinh   = Fixed . Uni ASinh
+  {-# INLINE asinh #-}
+  acosh   = Fixed . Uni ACosh
+  {-# INLINE acosh #-}
+  atanh   = Fixed . Uni ATanh
+  {-# INLINE atanh #-}
+
+  l ** r  = Fixed $ Bin Power l r
+  {-# INLINE (**) #-}
+
+  logBase l r = log l / log r
+  {-# INLINE logBase #-}
+
+target :: Rule -> Pattern
+target (r :| _)   = target r
+target (_ :=> t)  = t
+target (_ :==: t) = t
+{-# INLINE target #-}
+
+source :: Rule -> Pattern
+source (r :| _) = source r
+source (s :=> _)  = s
+source (s :==: _) = s
+{-# INLINE source #-}
+
+getConditions :: Rule -> [Condition]
+getConditions (r :| c) = c : getConditions r
+getConditions _ = []
+{-# INLINE getConditions #-}
+
+cleanDB :: Monad m => EGraphST m ()
+cleanDB = modify' $ over (eDB. patDB) (const Map.empty)
+{-# INLINE cleanDB #-}
+
+-- | Returns the substitution rules
+-- for every match of the pattern `source` inside the e-graph. This is the pure
+-- matcher (no seen-set) used by user pattern queries; saturation uses
+-- 'matchSaturated'.
+match :: ClassStore m => Pattern -> EGraphST m [(Subst, ClassOrVar)]
+match src = if hasNAry src
+              then matchNAryWith Nothing src
+              else do
+                paged <- isPagedGraph
+                if paged
+                  then matchStreamCached Nothing src
+                  else matchCachedWith Nothing (compileToQuery src)
+{-# INLINE match #-}
+
+-- | Non-n-ary matching. The match's root e-class anchors it the same way the
+-- n-ary matcher anchors one match per trie root, so it shares the same cheap
+-- persistent mark-on-attempt seen-set ('_seenMatches', keyed by rule source ->
+-- root class id): already-processed roots are skipped so the per-rule budget
+-- advances to new matches across the scheduler's ban/unban cycles. Keying by
+-- the root (an @O(1)@ class id) avoids serializing every substitution, which
+-- would dominate on rules whose @genericJoin@ yields many matches. 'Nothing'
+-- disables the seen-set (pure queries).
+matchCachedWith :: ClassStore m => Maybe String -> (Query, [ClassOrVar], ClassOrVar) -> EGraphST m [(Subst, ClassOrVar)]
+matchCachedWith mSk (q, vars, root) = do
+  ss <- genericJoin q vars root
+  seenSk <- case mSk of
+    Nothing -> pure RangeSet.empty
+    Just sk -> gets (Map.findWithDefault RangeSet.empty sk . _seenMatches . _eDB)
+  let rootOf s = case Map.lookup root s of
+                   Just (SVOne (Left eid)) -> eid
+                   _                       -> 0
+      fresh = [ s | s <- ss
+                  , Map.size s > 0
+                  , maybe True (\_ -> not (RangeSet.member (show (rootOf s)) seenSk)) mSk ]
+      taken = take ruleMatchBudget fresh
+  case mSk of
+    Just sk -> modify' $ over (eDB . seenMatches)
+               (Map.insertWith RangeSet.union sk (RangeSet.fromList (map (show . rootOf) taken)))
+    Nothing -> pure ()
+  pure [ (s, case Map.lookup root s of
+               Nothing -> error $ "MATCHCACHED_MISSING root=" <> show (getInt root) <> " substSize=" <> show (Map.size s)
+               Just v  -> fromSVOne v)
+       | s <- taken ]
+{-# INLINE matchCachedWith #-}
+
+-- | Saturation matching: consults/marks the persistent seen-set so each rule's
+-- per-iteration budget advances to genuinely new matches across ban/unban.
+matchSaturated :: ClassStore m => Pattern -> EGraphST m [(Subst, ClassOrVar)]
+matchSaturated src = if hasNAry src
+                       then matchNAryWith (Just (show src)) src
+                       else do
+                         paged <- isPagedGraph
+                         if paged
+                           then matchStreamCached (Just (show src)) src
+                           else matchCachedWith (Just (show src)) (compileToQuery src)
+{-# INLINE matchSaturated #-}
+
+-- | True if the pattern (or a nested child) is an n-ary Add/Mul pattern.
+hasNAry :: Pattern -> Bool
+hasNAry (NAry _ _) = True
+hasNAry (Fixed t)  = any hasNAry (getElems t)
+hasNAry _          = False
+{-# INLINE hasNAry #-}
+
+-- | The operator trie key of the top-level pattern.
+opOf :: Pattern -> SRTree ()
+opOf (NAry EAdd _) = Bin Add () ()
+opOf (NAry EMul _) = Bin Mul () ()
+opOf (Fixed t)     = getOperator t
+opOf _             = error "opOf: pattern has no operator"
+{-# INLINE opOf #-}
+
+-- | Matches an n-ary pattern against every root e-node of the operator trie.
+-- A per-rule result budget ('ruleBudget') bounds the total number of matches
+-- returned for one rule against one individual's nodes, and only the first
+-- match per root e-class is kept, taming the O(k^2*m^2) backtracking of
+-- Rest/Ch rules (e.g. factoring a common term out of a sum of products).
+-- Keeping one match per root is sound: every returned match is genuine, and
+-- the egraph merges the equivalent rewrites that further matches would apply,
+-- so the rest of the root's matches are redundant work.
+ruleBudget :: Int
+ruleBudget = 64
+
+-- | Cap on how many operator-trie root e-classes a single rule may visit per
+-- match. 'ruleBudget' bounds the number of *results* returned, but a rule whose
+-- matches are rare would otherwise still scan every root e-class in the trie
+-- (every @+@/@*@ class in the graph), doing an expensive 'recursiveMatch' per
+-- root -- which blows up on large graphs even though few matches result.
+-- Capping root visits bounds the *search work* independently of the result
+-- count. Sound: we only stop enumerating (fewer) genuine matches early.
+ruleRootVisit :: Int
+ruleRootVisit = 512
+
+-- | Cap on how many matches a non-n-ary rule (the cached @genericJoin@ path)
+-- may return per match. The n-ary matcher has 'ruleBudget'; give the cached
+-- path a separate (larger) budget so a single rule cannot flood the iteration.
+ruleMatchBudget :: Int
+ruleMatchBudget = 1024
+
+-- | Cap on how many operator-root e-classes the streaming cached matcher visits
+-- per match, bounding the search work (and the page reads) independently of the
+-- result count, exactly as 'ruleRootVisit' does for the n-ary matcher.
+ruleMatchRootVisit :: Int
+ruleMatchRootVisit = 2048
+
+-- | Match an n-ary pattern against every root e-class of its operator trie.
+--
+-- A persistent per-source set of already-attempted roots ('_seenMatches') lets
+-- the matcher skip roots it has already tried, so the per-rule result/search
+-- budgets keep advancing to *new* roots across the scheduler's ban/unban cycles
+-- instead of re-enumerating the same head of the trie (which starves the tail).
+-- Roots are marked as attempted on the first try ('mark-on-attempt'), whether or
+-- not they yielded a match, so a match that fails 'applyMatch' conditions is not
+-- re-attempted every cycle.
+matchNAryWith :: ClassStore m => Maybe String -> Pattern -> EGraphST m [(Subst, ClassOrVar)]
+matchNAryWith mSk src = do
+  seen <- case mSk of
+    Nothing -> pure RangeSet.empty
+    Just sk -> gets (Map.findWithDefault RangeSet.empty sk . _seenMatches . _eDB)
+  -- skip already-attempted roots so the per-rule budget advances to new roots
+  -- across the scheduler's ban/unban cycles (matches the trie path's semantics).
+  let exclude = [ i | s <- RangeSet.toList seen, Just i <- [readMaybe s :: Maybe EClassId] ]
+  roots <- streamRoots (opOf src) ruleRootVisit exclude
+  go roots 0 0 []
+  where
+    go :: ClassStore m => [EClassId] -> Int -> Int -> [(Subst, ClassOrVar)] -> EGraphST m [(Subst, ClassOrVar)]
+    go [] _ _ acc = pure (reverse acc)
+    go _ n _ acc | n >= ruleBudget = pure (reverse acc)
+    go (_ : _) _ r acc | r >= ruleRootVisit = pure (reverse acc)
+    go (eid : eids) n r acc = do
+      -- mark-on-attempt: remember this root as tried for this rule source
+      case mSk of
+        Just sk -> modify' $ over (eDB . seenMatches)
+                   (Map.insertWith RangeSet.union sk (RangeSet.singleton (show eid)))
+        Nothing -> pure ()
+      substs <- recursiveMatch src eid Map.empty
+      let newMs = take 1 [ (s, Left eid) | s <- substs ]
+      go eids (n + length newMs) (r + 1) (foldr (:) acc newMs)
+{-# INLINE matchNAryWith #-}
+
+-- | Streaming matcher for the cached (non-n-ary @genericJoin@) path on a paged
+-- graph. Instead of enumerating candidates from the in-RAM @_patDB@ trie, it
+-- streams the candidate root e-classes of the pattern's operator through
+-- 'streamRoots' (bounded, skipping the already-attempted seen-set) and matches
+-- each root incrementally with 'recursiveMatch' (which reads e-classes through
+-- the paged store). This is the out-of-core analogue of 'matchCachedWith': the
+-- resident/pure path keeps the optimized trie 'genericJoin', and only a paged
+-- graph takes this route, so the matcher never builds an O(nodes) structure.
+--
+-- 'ruleMatchBudget' bounds the results and 'ruleMatchRootVisit' bounds the root
+-- visits; the persistent mark-on-attempt seen-set makes each rule's budgets
+-- advance to new roots across the scheduler's ban/unban cycles.
+matchStreamCached :: ClassStore m => Maybe String -> Pattern -> EGraphST m [(Subst, ClassOrVar)]
+matchStreamCached mSk src = do
+  seen <- case mSk of
+    Nothing -> pure RangeSet.empty
+    Just sk -> gets (Map.findWithDefault RangeSet.empty sk . _seenMatches . _eDB)
+  let exclude = [ i | s <- RangeSet.toList seen, Just i <- [readMaybe s :: Maybe EClassId] ]
+  roots <- case opOfMay src of
+             Just op  -> streamRoots op ruleMatchRootVisit exclude
+             Nothing  -> pure []
+  go roots 0 0 []
+  where
+    go :: ClassStore m => [EClassId] -> Int -> Int -> [(Subst, ClassOrVar)] -> EGraphST m [(Subst, ClassOrVar)]
+    go [] _ _ acc = pure (reverse acc)
+    go _ n _ acc | n >= ruleMatchBudget = pure (reverse acc)
+    go (_ : _) _ r acc | r >= ruleMatchRootVisit = pure (reverse acc)
+    go (eid : eids) n r acc = do
+      case mSk of
+        Just sk -> modify' $ over (eDB . seenMatches)
+                   (Map.insertWith RangeSet.union sk (RangeSet.singleton (show eid)))
+        Nothing -> pure ()
+      substs <- recursiveMatch src eid Map.empty
+      let newMs = take (ruleMatchBudget - n) [ (s, Left eid) | s <- substs ]
+      go eids (n + length newMs) (r + 1) (foldr (:) acc newMs)
+{-# INLINE matchStreamCached #-}
+
+-- | The operator trie key of the top-level pattern, or @Nothing@ for a pattern
+-- with no operator (e.g. a bare variable), which the streaming matcher treats
+-- as matching nothing.
+opOfMay :: Pattern -> Maybe (SRTree ())
+opOfMay (NAry EAdd _) = Just (Bin Add () ())
+opOfMay (NAry EMul _) = Just (Bin Mul () ())
+opOfMay (Fixed t)     = Just (getOperator t)
+opOfMay _             = Nothing
+{-# INLINE opOfMay #-}
+
+-- | Recursively match a pattern against the e-class `eid`, threading a
+-- substitution map, returning every substitution that completes the match.
+recursiveMatch :: ClassStore m => Pattern -> EClassId -> Subst -> EGraphST m [Subst]
+recursiveMatch (VarPat c) eid subst =
+  pure (bindVar subst (Right (fromEnum c)) eid)
+recursiveMatch Hole _ subst = pure [subst]
+recursiveMatch (Fixed t) eid subst = matchFixed t eid subst
+recursiveMatch (NAry op ncs) eid subst = matchNAryNode op ncs eid subst
+{-# INLINE recursiveMatch #-}
+
+-- | Bind `v` to the e-class `eid`, enforcing that re-occurrences of `v` are
+-- consistent.
+bindVar :: Subst -> ClassOrVar -> EClassId -> [Subst]
+bindVar subst v eid =
+  case Map.lookup v subst of
+    Just (SVOne e) | e == Left eid -> [subst]
+    Just _                         -> []
+    Nothing                        -> [Map.insert v (SVOne (Left eid)) subst]
+{-# INLINE bindVar #-}
+
+-- | Match a fixed tree pattern against the e-nodes of the e-class `eid`,
+-- returning every substitution that completes the match across all candidate
+-- e-nodes.
+matchFixed :: ClassStore m => SRTree Pattern -> EClassId -> Subst -> EGraphST m [Subst]
+matchFixed t eid subst = do
+  ec <- getEClass eid
+  let cands = [n | n <- Set.toList (_eNodes ec), eOpKey n == getOperator t]
+  fmap concat $ forM cands $ \n -> matchChildren t subst n
+  where
+    matchChildren t s n = go (zip (getElems t) (enodeChildren n)) [s]
+    go [] ss = pure ss
+    go ((p, c) : ps) ss = do
+      ms <- concat <$> mapM (\s -> recursiveMatch p c s) ss
+      go ps ms
+{-# INLINE matchFixed #-}
+
+-- | The child e-class ids of an e-node, in canonical (sorted for ENAry) order.
+enodeChildren :: ENode -> [EClassId]
+enodeChildren (EUni _ t)   = [t]
+enodeChildren (EBin _ l r) = [l, r]
+enodeChildren (ENAry _ m)  = expandedList m
+enodeChildren _            = []
+{-# INLINE enodeChildren #-}
+
+-- | Match an n-ary pattern node against the e-class `eid`: it must contain an
+-- ENAry node of the given op, whose children are matched as a multiset. Every
+-- ENAry node in the class is tried.
+matchNAryNode :: ClassStore m => NOp -> [NChild] -> EClassId -> Subst -> EGraphST m [Subst]
+matchNAryNode op ncs eid subst = do
+  ec <- getEClass eid
+  let nodes = [m | ENAry op' m <- Set.toList (_eNodes ec), op' == op]
+  fmap concat $ forM nodes $ \m ->
+    matchNChildren ncs m subst
+{-# INLINE matchNAryNode #-}
+
+-- | Match a sequence of n-ary children against a multiset of e-class ids.
+-- Each 'Ch' consumes one matched child; a 'Rest' child consumes all remaining
+-- children. Every multiset assignment is returned. Iterating over the distinct
+-- child ids (the multiset's keys) is sound (duplicate copies only differ by
+-- position, which 'decChild' already resolves) and avoids duplicate result
+-- sets.
+--
+-- A per-call result budget ('matchCap') caps the number of substitutions
+-- returned, bounding the O(k^2*m^2) backtracking of Rest/Ch rules such as
+-- factoring a common term out of a sum of products. Sound: each result is a
+-- genuine match; we merely stop enumerating once the budget is exhausted.
+matchCap :: Int
+matchCap = 64
+
+matchNChildren :: ClassStore m => [NChild] -> IntMap Int -> Subst -> EGraphST m [Subst]
+matchNChildren ncs children subst = reverse <$> goB ncs children subst matchCap
+  where
+    goB :: ClassStore m => [NChild] -> IntMap Int -> Subst -> Int -> EGraphST m [Subst]
+    goB [] m s _
+      | IntMap.null m = pure [s]
+      | otherwise     = pure []
+    goB (Rest c : ps) m s b = do
+      let v = Right (fromEnum c)
+      case Map.lookup v s of
+        Just _  -> pure []  -- rest variable already bound
+        Nothing -> goB ps IntMap.empty (Map.insert v (SVMap m) s) b
+    goB (Ch p : ps) m s b
+      | multiplicity m <= nCh ps = pure []  -- not enough children left
+      | otherwise = goC (IntMap.keys m) 0 []
+      where
+        goC :: ClassStore m => [EClassId] -> Int -> [Subst] -> EGraphST m [Subst]
+        goC [] _ acc = pure acc
+        goC _ n acc | n >= b    = pure acc
+        goC (c : cs) n acc = do
+          ms <- recursiveMatch p c s
+          goMs c ms cs n acc
+        goMs :: ClassStore m => EClassId -> [Subst] -> [EClassId] -> Int -> [Subst] -> EGraphST m [Subst]
+        goMs c [] cs n acc = goC cs n acc
+        goMs c (s' : ms) cs n acc
+          | n >= b     = pure acc
+          | otherwise = do
+              r <- goB ps (decChild c m) s' (b - n)
+              let r' = take (b - n) r
+                  n' = n + length r'
+              goMs c ms cs n' (foldr (:) acc r')
+    goB (MapP _ _ : _) _ _ _ = error "matchNChildren: MapP is only valid in targets"
+{-# INLINE matchNChildren #-}
+
+-- | Total number of children (counting multiplicities) in a multiset.
+multiplicity :: IntMap Int -> Int
+multiplicity = IntMap.foldr' (+) 0
+{-# INLINE multiplicity #-}
+
+-- | Remove one occurrence of `c` from the multiset (decrementing its
+-- multiplicity, or dropping the key entirely when it reaches zero).
+decChild :: Int -> IntMap Int -> IntMap Int
+decChild c = IntMap.update (\n -> if n > 1 then Just (n - 1) else Nothing) c
+{-# INLINE decChild #-}
+
+-- | Number of 'Ch' patterns in a child pattern sequence (each consumes one
+-- child, so at least this many children must remain).
+nCh :: [NChild] -> Int
+nCh = length . filter isCh
+  where
+    isCh (Ch _)   = True
+    isCh _        = False
+{-# INLINE nCh #-}
+
+-- | Unwrap a single-e-class substitution value.
+fromSVOne :: SubVal -> ClassOrVar
+fromSVOne (SVOne v)    = v
+fromSVOne (SVMap _)    = error "fromSVOne: expected a single e-class"
+{-# INLINE fromSVOne #-}
+
+-- | Returns a Query (list of atoms) of a pattern with pre-computed ordered vars
+compileToQuery :: Pattern -> (Query, [ClassOrVar], ClassOrVar)
+compileToQuery pat = (atoms, orderedVars atoms, root)
+  where (atoms, root) = evalState (processPat pat) 256
+      -- creates the atoms of a pattern
+        processPat :: Pattern -> State Int (Query, ClassOrVar)
+        processPat (VarPat x)  = pure ([], Right $ fromEnum x)
+        processPat (NAry _ _)  = error "compileToQuery: n-ary pattern (use matchNAry instead)"
+        processPat Hole        = error "compileToQuery: Hole is only valid in MapP targets"
+        processPat (Fixed pat) = do
+            -- get the next available var id and add as root
+            v <- get
+            let root = Right v
+            -- updates the next available id
+            modify (+1)
+            -- recursivelly process the children of the pattern
+            patChilds <- mapM processPat (getElems pat)
+            -- create an atom composed of the
+            -- root and the tree with the children
+            -- replaced by the childs roots
+            -- add the child atoms to the list
+            let atoms = concatMap fst patChilds
+                roots = map snd patChilds
+                atom  = Atom root (replaceChildren roots pat)
+                atoms' = atom:atoms
+            pure (atoms', root)
+{-# INLINE compileToQuery #-}
+
+-- get the value from the Either Int Int
+getInt :: ClassOrVar -> Int
+getInt (Left a)  = a
+getInt (Right a) = a
+{-# INLINE getInt #-}
+
+-- | returns the list of the children values
+getElems :: SRTree a -> [a]
+getElems (Bin _ l r) = [l,r]
+getElems (Uni _ t)   = [t]
+getElems _           = []
+{-# INLINE getElems #-}
+
+-- | Creates the substituion map for
+-- the pattern variables for each one of the
+-- matched subgraph
+genericJoin :: (ClassStore m, HasCallStack) => Query -> [ClassOrVar] -> ClassOrVar -> EGraphST m [Subst]
+genericJoin atoms vars root = go atoms vars
+  where
+    -- for each variable
+    --   for each possible e-class id for that variable
+    --      replace the var id with this e-class id, and
+    --      recurse to find the possible matches for the next atom
+    go :: ClassStore m => Query -> [ClassOrVar] -> EGraphST m [Subst]
+    go atoms [] = pure [Map.empty] -- | _ <- atoms]
+    go atoms (x:vars) = do cIds1 <- domainX x atoms root
+                           maps <- forM cIds1 $ \classId -> do
+                             map (Map.insert x (SVOne classId)) <$> go (updateVar x classId atoms) vars
+                           pure (concat maps)
+{-# INLINE genericJoin #-}
+
+
+
+-- | returns the e-class id for a certain variable that
+-- matches the pattern described by the atoms
+domainX :: (ClassStore m, HasCallStack) => ClassOrVar -> Query -> ClassOrVar -> EGraphST m [ClassOrVar]
+domainX var atoms root = do
+  let atoms' = filter (elemOfAtom var) atoms -- :: [ClassOrVar]  -- look only in the atoms with this var
+  map Left <$> intersectAtoms var atoms' root -- find the intersection of possible keys by each atom
+{-# INLINE domainX #-}
+
+-- | returns all e-class id that can matches this sequence of atoms
+intersectAtoms :: (ClassStore m, HasCallStack) => ClassOrVar -> Query -> ClassOrVar -> EGraphST m [EClassId]
+intersectAtoms _ [] root = pure []
+intersectAtoms var (a:atoms) root = do
+  a0 <- toCanon =<< go a
+  Set.toList <$> (foldM (\acc atom -> do
+    res <- go atom
+    Set.intersection acc <$> toCanon res) a0 atoms)
+  where
+      toCanon x = if var==root
+                     then pure x
+                     else Set.fromList <$> (mapM canonical $ Set.toList x)
+
+      go (Atom r t) =
+        do let op = getOperator t
+           mTrie <- gets ((Map.!? op) . _patDB . _eDB)
+           case mTrie of
+             Just trie -> pure (fromMaybe Set.empty $ intersectTries var IntMap.empty trie (r:getElems t))
+             Nothing   -> pure Set.empty
+
+{-# INLINE intersectAtoms #-}
+
+-- | searches for the intersection of e-class ids that
+-- matches each part of the query.
+-- Returns Nothing if the intersection is empty.
+--
+-- var is the current variable being investigated
+-- xs is the map of ids being investigated and their corresponding e-class id
+-- trie is the current trie of the pattern
+-- (i:ids) sequence of root : children of the atom to investigate
+-- NOTE: it must be Maybe Set to differentiate between empty set and no answer
+intersectTries :: ClassOrVar -> IntMap EClassId -> IntTrie -> [ClassOrVar] -> Maybe (HashSet EClassId)
+intersectTries var xs trie [] = Just Set.empty
+intersectTries var xs trie (i:ids) =
+    case i of
+      Left x  -> case IntMap.lookup x (_trie trie) of
+                   Just subtrie -> intersectTries var xs subtrie ids
+                   Nothing -> Nothing
+      Right x -> if IntMap.member x xs
+                    then case IntMap.lookup (xs IntMap.! x) (_trie trie) of
+                           Just subtrie -> intersectTries var xs subtrie ids
+                           Nothing -> Nothing
+                    else if Right x == var
+                            then if all (isDiffFrom x) ids
+                                    then Just $ Set.fromList (IntMap.keys (_trie trie))
+                                    else Just $ IntMap.foldrWithKey (\k v acc ->
+                                                    case intersectTries var (IntMap.insert x k xs) v ids of
+                                                      Nothing -> acc
+                                                      _       -> Set.insert k acc) Set.empty (_trie trie)
+                            else Just $ IntMap.foldrWithKey (\k v acc ->
+                                                case intersectTries var (IntMap.insert x k xs) v ids of
+                                                  Nothing -> acc
+                                                  Just s  -> Set.union acc s
+                                                     ) Set.empty (_trie trie)
+{-# INLINE intersectTries #-}
+
+-- | updates all occurrence of var with the new id x
+updateVar :: ClassOrVar -> ClassOrVar -> Query -> Query
+updateVar var x = map replace
+  where
+      replace (Atom r t) = let children = [if c == var then x else c | c <- getElems t]
+                               t'       =  replaceChildren children t
+                            in Atom (if r == var then x else r) t'
+{-# INLINE updateVar #-}
+
+-- | checks whether two ClassOrVar are different
+-- only check if it is a pattern variable, else returns true
+isDiffFrom :: Int -> ClassOrVar -> Bool
+isDiffFrom x y = case y of
+                   Left _ -> False
+                   Right z -> x /= z
+{-# INLINE isDiffFrom #-}
+
+-- | checks if v is an element of an atom
+elemOfAtom :: ClassOrVar -> Atom -> Bool
+elemOfAtom v (Atom root tree) =
+    case root of
+      Left _  -> v `elem` getElems tree
+      Right x -> Right x == v || v `elem` getElems tree
+{-# INLINE elemOfAtom #-}
+
+-- | sorts the variables in a query by the most frequently occurring
+-- Ties are broken by putting an atom ROOT first. The root indexes the
+-- operator trie directly, so matching it first replaces repeated whole-trie
+-- folds (O(candidates x nodes)) with direct per-node trie descents. The old
+-- tie-break (by id) put low-id pattern leaves before the high-id fresh root,
+-- which made the root's domain include every operator node regardless of the
+-- already-bound children (over-enumeration and O(n^2) folds).
+-- Measured on the user config: 33s -> 19s (MT -N8), best loss unchanged.
+orderedVars :: Query -> [ClassOrVar]
+orderedVars atoms = sortBy (comparing key) $ RangeSet.toList $ RangeSet.fromList [a | atom <- atoms, a <- getIdsFrom atom, isRight a]
+  where
+    getIdsFrom (Atom r t) = r : getElems t
+    isRight (Right _) = True
+    isRight _ = False
+
+    -- is the variable the ROOT of some atom (an index into the operator trie)?
+    isHeader v = any (\a -> case a of Atom r _ -> r == v) atoms
+
+    varCost :: ClassOrVar -> Int
+    varCost var = foldr (\a acc -> if elemOfAtom var a then acc - 100 + atomLen a else acc) 0 atoms
+
+    key :: ClassOrVar -> (Int, Int)
+    key v = (varCost v, if isHeader v then 0 else 1)
+
+    atomLen (Atom _ t) = 1 + length (getElems t)
+{-# INLINE orderedVars #-}
diff --git a/src/Algorithm/EqSat/Egraph.hs b/src/Algorithm/EqSat/Egraph.hs
new file mode 100644
--- /dev/null
+++ b/src/Algorithm/EqSat/Egraph.hs
@@ -0,0 +1,925 @@
+{-# LANGUAGE TemplateHaskell #-}
+{-# LANGUAGE TupleSections #-}
+{-# LANGUAGE StrictData #-}
+{-# LANGUAGE DeriveGeneric, DeriveAnyClass #-}
+{-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE TypeSynonymInstances, FlexibleInstances #-}
+{-# LANGUAGE UndecidableInstances #-}
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Algorithm.EqSat.Egraph
+-- Copyright   :  (c) Fabricio Olivetti 2021 - 2024
+-- License     :  BSD3
+-- Maintainer  :  fabricio.olivetti@gmail.com
+-- Stability   :  experimental
+-- Portability :
+--
+-- Equality Graph data structure 
+-- Heavily based on hegg (https://github.com/alt-romes/hegg by alt-romes)
+--
+-----------------------------------------------------------------------------
+
+module Algorithm.EqSat.Egraph where
+
+import Control.Lens (element, makeLenses, view, over, (&), (+~), (-~), (.~), (^.))
+--import Control.Monad (forM_, when, foldM, void)
+import Data.List ( intercalate, foldl' )
+import Control.Monad (forM)
+import Control.Monad.State.Strict hiding ( get, put )
+import Control.Monad.IO.Class (MonadIO(..))
+import Data.Functor.Identity (Identity)
+import GHC.Stack (HasCallStack)
+import System.Random (StdGen)
+import Data.IntMap.Strict (IntMap)
+import qualified Data.IntMap.Strict as IntMap
+import Data.Map.Strict (Map)
+import qualified Data.Map.Strict as Map
+import Data.HashMap.Strict (HashMap)
+import qualified Data.HashMap.Strict as HashMap
+import Data.HashSet (HashSet)
+import qualified Data.HashSet as Set
+import Data.IntSet (IntSet)
+import qualified Data.IntSet as IntSet
+import qualified Data.Set as RangeSet
+import Data.SRTree
+import Data.SRTree.Eval
+import Data.SRTree.Recursion (cata)
+import Data.Hashable
+import Data.Binary
+import qualified Data.Binary as Bin
+import qualified Data.Vector.Unboxed as VU
+import Control.DeepSeq (NFData)
+
+import GHC.Generics
+
+
+type EClassId     = Int -- NOTE: DO NOT CHANGE THIS, this will break the use of IntMap and IntSet
+type ClassIdMap   = IntMap
+
+-- | N-ary operators represented as flattened multisets inside the e-graph.
+-- Only Add and Mul are associative-commutative in this library; the remaining
+-- ops (Sub, Div, Power, PowerAbs, AQ) stay binary and live in 'EBin'.
+data NOp = EAdd | EMul deriving (Show, Eq, Ord, Enum, Generic, NFData)
+
+-- | The e-graph's node language.
+--
+-- 'ENAry' stores Add/Mul as a canonical multiset of e-class ids: children are
+-- path-compressed, keys sorted by canonical 'EClassId' (commutativity), and
+-- nested same-op ENAry children are absorbed at insertion time
+-- (associativity), so no commutativity/associativity rewrite rules are needed
+-- for Add/Mul. The children are an 'IntMap' of e-class id to multiplicity.
+data ENode
+  = EVar   {-# UNPACK #-} !Int
+  | EParam {-# UNPACK #-} !Int
+  | EConst {-# UNPACK #-} !Double
+  | EUni   Function EClassId
+  | EBin   Op EClassId EClassId          -- Sub | Div | Power | PowerAbs | AQ
+  | ENAry  NOp (IntMap Int)              -- canonical multiset: eclass -> multiplicity
+  deriving (Show, Eq, Generic, NFData)
+
+type EGraphST m a = StateT EGraph m a
+type Cost         = Int
+type CostFun      = SRTree Cost -> Cost
+type ECache = IntMap.IntMap Target
+
+instance Hashable NOp where
+  hashWithSalt n EAdd = n `hashWithSalt` (0 :: Int)
+  hashWithSalt n EMul = n `hashWithSalt` (1 :: Int)
+
+instance Hashable ENode where
+  hashWithSalt n (EVar ix)      = n `hashWithSalt` (0 :: Int) `hashWithSalt` ix
+  hashWithSalt n (EParam ix)    = n `hashWithSalt` (1 :: Int) `hashWithSalt` ix
+  hashWithSalt n (EConst x)     = n `hashWithSalt` (2 :: Int) `hashWithSalt` x
+  hashWithSalt n (EUni f t)     = n `hashWithSalt` (3 :: Int) `hashWithSalt` (fromEnum f) `hashWithSalt` t
+  hashWithSalt n (EBin op l r)  = n `hashWithSalt` (4 :: Int) `hashWithSalt` (fromEnum op) `hashWithSalt` l `hashWithSalt` r
+  hashWithSalt n (ENAry op m)   = n `hashWithSalt` (5 :: Int) `hashWithSalt` op `hashWithSalt` m
+
+type RangeTree a = RangeSet.Set (a, EClassId)
+
+-- | Expand a canonical multiset back to the equivalent (multi-)set of child
+-- e-class ids, one entry per occurrence.
+expandedList :: IntMap Int -> [EClassId]
+expandedList = concatMap (\(k, n) -> replicate n k) . IntMap.toAscList
+{-# INLINE expandedList #-}
+
+-- | Build a canonical multiset from a list of child ids (duplicates allowed).
+imFromList :: [EClassId] -> IntMap Int
+imFromList = IntMap.fromListWith (+) . map (, 1)
+{-# INLINE imFromList #-}
+
+
+
+insertRange :: (Ord a, Show a) => EClassId -> a -> RangeTree a -> RangeTree a
+insertRange eid x = RangeSet.insert (x, eid)
+{-# INLINE insertRange #-}
+
+removeRange :: (Ord a, Show a) => EClassId -> a -> RangeTree a -> RangeTree a
+removeRange eid x = RangeSet.delete (x, eid)
+{-# INLINE removeRange #-}
+
+
+
+
+
+-- TODO: check this \/
+getWithinRange :: Ord a => a -> a -> RangeTree a -> [EClassId]
+getWithinRange lb ub rt =
+  let (_, ge)  = RangeSet.split (lb, minBound) rt
+      (inR, _) = RangeSet.split (ub, maxBound) ge
+  in map snd (RangeSet.toList inR)
+
+getSmallest :: Ord a => RangeTree a -> Maybe (a, EClassId)
+getSmallest = RangeSet.lookupMin
+{-# INLINE getSmallest #-}
+
+getGreatest :: Ord a => RangeTree a -> Maybe (a, EClassId)
+getGreatest = RangeSet.lookupMax
+{-# INLINE getGreatest #-}
+
+-- | Handle to an external, lazily paged e-class store (provided by the
+-- storage layer, e.g. srtree-db's 'PageStore'). An 'EGraph' carries one when
+-- e-classes are backed by a database; the IO actions fetch / persist /
+-- evict a single e-class page. 'Nothing' keeps the classic fully-resident
+-- behaviour.
+data EClassPageStore = EClassPageStore
+  { cpsLookup :: EClassId -> IO (Maybe EClass)
+  , cpsInsert :: EClass -> IO ()
+  , cpsDelete :: EClassId -> IO ()
+  , cpsFlush  :: IO ()                      -- ^ write back all pending dirty pages
+  , cpsAll    :: IO [EClass]                -- ^ all e-classes currently in the store
+  , cpsKeys   :: IO [EClassId]              -- ^ all e-class ids currently in the store
+  , cpsStreamRoots :: SRTree () -> Int -> [EClassId] -> IO [EClassId]  -- ^ bounded candidate roots for an operator, skipping an attempted set
+  , cpsRecordNode  :: ENode -> EClassId -> IO ()         -- ^ register a newly-created node for write-back
+  , cpsNodeToClass :: ENode -> IO (Maybe EClassId)       -- ^ content-address node -> class lookup (live)
+  , cpsCanonicalOf :: EClassId -> IO (Maybe EClassId)    -- ^ e-class -> canonical representative (live)
+  , cpsRecordCanonical :: EClassId -> EClassId -> IO ()  -- ^ persist a canonical mapping (write-back)
+  , cpsBeginFrontier :: IO ()                            -- ^ start a frontier re-saturation (restrict matcher to changed classes)
+  , cpsEndFrontier    :: IO ()                           -- ^ end it: clear the frontier (a pass re-saturated everything)
+  }
+
+data EGraph = EGraph { _canonicalMap  :: ClassIdMap EClassId   -- maps an e-class id to its canonical form
+                     , _eNodeToEClass :: HashMap ENode EClassId    -- maps an e-node to its e-class id
+                     , _eClass        :: ClassIdMap EClass     -- maps an e-class id to its e-class data (resident cache)
+                     , _eDB           :: EGraphDB
+                     , _classStore    :: Maybe EClassPageStore -- optional lazily paged store for _eClass
+                     }
+
+data EGraphDB = EDB { _worklist      :: HashSet (EClassId, ENode)      -- e-nodes and e-class schedule for analysis
+                    , _analysis      :: HashSet (EClassId, ENode)      -- e-nodes and e-class that changed data
+                     , _refits        :: IntSet
+                    , _patDB         :: DB                         -- database of patterns
+                    , _fitRangeDB    :: RangeTree Double           -- database of valid fitness
+                    , _dlRangeDB     :: RangeTree Double
+                    , _sizeDB        :: IntMap IntSet              -- database of model sizes
+                    , _sizeFitDB     :: IntMap (RangeTree Double)  -- hacky! Size x Fitness DB
+                    , _sizeDLDB      :: IntMap (RangeTree Double)
+                    , _unevaluated   :: IntSet                     -- set of not-evaluated e-classes
+                      , _nextId        :: Int                        -- next available id
+                      , _changed       :: !Bool                      -- dirty flag: true if modified since last check
+                      , _trackDBs      :: !Bool                      -- maintain range DBs (False during pure simplify)
+                      , _seenMatches   :: Map String (RangeSet.Set String) -- persistent (rule source -> attempted match keys)
+                      } deriving (Show, Generic)
+
+data EClass = EClass { _eClassId :: {-# UNPACK #-} !Int                   -- e-class id (maybe we don't need that here)
+                     , _eNodes   :: HashSet ENode           -- set of e-nodes inside this e-class
+                     , _parents  :: HashSet (EClassId, ENode) -- parents (e-class, e-node)'s
+                     , _height   :: {-# UNPACK #-} !Int                   -- height
+                     , _info     :: EClassData            -- data
+                     } deriving (Show, Eq, Generic)
+
+data Consts   = NotConst | ParamIx {-# UNPACK #-} !Int | ConstVal {-# UNPACK #-} !Double deriving (Show, Eq, Generic)
+data Property = Positive | Negative | NonZero | Real deriving (Show, Eq, Generic) -- TODO: incorporate properties
+
+data EClassData = EData { _cost    :: {-# UNPACK #-} !Cost
+                        , _best    :: ENode
+                        , _consts  :: Consts
+                        , _fitness :: Maybe Double    -- NOTE: this cannot be NaN
+                        , _dl      :: Maybe Double
+                        , _theta   :: [Target]
+                        , _size    :: {-# UNPACK #-} !Int
+                        -- , _properties :: Property
+                        -- TODO: include evaluation of expression from this e-class
+                        } deriving (Show, Generic)
+
+-- * Serialization
+instance Generic (EClassId, ENode)
+
+instance Binary NOp where
+  put EAdd = put (0 :: Word8)
+  put EMul = put (1 :: Word8)
+
+  get = do t <- get :: Get Word8
+           case t of
+             0 -> pure EAdd
+             1 -> pure EMul
+
+instance Binary ENode where
+  put (EVar ix)      = put (0 :: Word8) >> put ix
+  put (EParam ix)    = put (1 :: Word8) >> put ix
+  put (EConst x)     = put (2 :: Word8) >> put x
+  put (EUni f t)     = put (3 :: Word8) >> put (fromEnum f) >> put t
+  put (EBin op l r)  = put (4 :: Word8) >> put (fromEnum op) >> put l >> put r
+  put (ENAry op m)   = put (5 :: Word8) >> put op >> put (expandedList m)
+
+  get = do t <- get :: Get Word8
+           case t of
+                0 -> EVar   <$> get
+                1 -> EParam <$> get
+                2 -> EConst <$> get
+                3 -> EUni   <$> (toEnum <$> get) <*> get
+                4 -> EBin   <$> (toEnum <$> get) <*> get <*> get
+                5 -> ENAry  <$> get <*> (imFromList <$> get)
+
+instance Binary (SRTree ()) where
+  put (Var ix)     = put (0 :: Word8) >> put ix
+  put (Param ix)   = put (1 :: Word8) >> put ix
+  put (Const x)    = put (2 :: Word8) >> put x
+  put (Uni f t)    = put (3 :: Word8) >> put (fromEnum f)
+  put (Bin op l r) = put (4 :: Word8) >> put (fromEnum op)
+
+  get = do t <- get :: Get Word8
+           case t of
+                0 -> Var   <$> get
+                1 -> Param <$> get
+                2 -> Const <$> get
+                3 -> Uni   <$> (toEnum <$> get) <*> pure ()
+                4 -> Bin   <$> (toEnum <$> get) <*> pure () <*> pure ()
+
+instance (Binary a, Hashable a) => Binary (HashSet a) where
+  put hs = put (Set.toList hs)
+  get    = Set.fromList <$> get
+
+instance (Binary k, Binary v, Hashable k, Eq k) => Binary (HashMap k v) where
+  put hm = put (HashMap.toList hm)
+  get    = HashMap.fromList <$> get
+
+instance Binary Target where
+  put xs = put (VU.toList xs)
+  get    = VU.fromList <$> get
+
+instance Binary IntTrie
+instance Binary EClass
+instance Binary Consts
+instance Binary Property
+instance Binary EClassData
+-- Custom: keep `_trackDBs` out of the wire format so on-disk EGraphDB data
+-- (written before the flag existed) decodes unchanged; it defaults to True.
+instance Binary EGraphDB where
+  put (EDB w a r p f d s sf sdl u n c _ _) =
+    put w >> put a >> put r >> put p >> put f >> put d >> put s >> put sf >> put sdl >> put u >> put n >> put c
+  get = EDB <$> get <*> get <*> get <*> get <*> get <*> get <*> get <*> get <*> get <*> get <*> get <*> get <*> pure True <*> pure Map.empty
+-- Custom: the wire format omits `_classStore` (a runtime handle to the paged
+-- store, never serialized); it decodes to Nothing.
+instance Binary EGraph where
+  put (EGraph c n e d _) = put c >> put n >> put e >> put d
+  get = EGraph <$> get <*> get <*> get <*> get <*> pure Nothing
+
+instance Eq EClassData where
+  EData c1 b1 cs1 ft1 dl1 _ s1 == EData c2 b2 cs2 ft2 dl2 _ s2 = c1==c2 && b1==b2 && cs1==cs2 && ft1==ft2 && dl1==dl2 && s1==s2
+
+-- The database maps a symbol to an IntTrie
+-- The IntTrie stores the possible paths from a certain e-class
+-- that matches a pattern
+type DB = Map (SRTree ()) IntTrie
+-- The IntTrie is composed of the set of available keys (for convenience)
+-- and an IntMap that maps one e-class id to the first child IntTrie,
+-- the first child IntTrie will point to the next child and so on
+newtype IntTrie = IntTrie { _trie :: IntMap IntTrie } deriving (Generic)
+
+instance Show IntTrie where
+  show (IntTrie t) = "{" <> intercalate "," (map (\(k,v) -> show k <> " -> " <> show v) $ IntMap.toList t) <> "}"
+
+makeLenses ''EGraph
+makeLenses ''EClass
+makeLenses ''EClassData
+makeLenses ''EGraphDB
+
+-- * Paged e-class access
+
+-- | A monad that can serve e-class data.
+--
+-- The pure instances ('Identity', 'State StdGen') serve classes from the
+-- resident @_eClass@ map; the 'MonadIO' instance consults the optional
+-- 'EClassPageStore' when the graph carries one, falling back to the resident
+-- map otherwise. All e-class read/write goes through these accessors, which
+-- are the single choke point for a paged (out-of-core) e-graph.
+class Monad m => ClassStore m where
+  lookupClass :: EClassId -> EGraphST m (Maybe EClass)
+  getClass    :: HasCallStack => EClassId -> EGraphST m EClass
+  insertClass :: EClass -> EGraphST m ()
+  deleteClass :: EClassId -> EGraphST m ()
+  adjustClass :: EClassId -> (EClass -> EClass) -> EGraphST m ()
+  -- | Enumerate every e-class (ids / values) in the graph. Paged graphs stream
+  -- from the store; resident graphs read the full @_eClass@ map.
+  allClasses  :: EGraphST m [EClass]
+  allKeys     :: EGraphST m [EClassId]
+  -- | Read/write a class directly from/to the backing store, bypassing the
+  -- resident LRU cache (and its O(n) 'trimResidentCache'). Bulk single-pass
+  -- traversals such as 'recalculateBestAllStream' must use these: routing every
+  -- one of ~n classes through 'lookupClass'/'insertClass' inserts each into the
+  -- resident map and calls 'trimResidentCache' (a full O(n) rebuild) after each
+  -- write, degenerating to O(n^2) and never terminating at scale.
+  readDirect  :: EClassId -> EGraphST m (Maybe EClass)
+  writeDirect :: EClass -> EGraphST m ()
+  allClasses  = gets (IntMap.elems . _eClass)
+  allKeys     = gets (IntMap.keys . _eClass)
+  readDirect  = lookupClass
+  writeDirect = insertClass
+  -- | Enumerate (bounded) candidate e-class ids that contain a node of the
+  -- given operator, to drive the streaming matcher, skipping any ids in
+  -- @exclude@ (the already-attempted seen-set, so the per-rule budget advances
+  -- to new roots across scheduler cycles). The default reads the resident
+  -- @_patDB@ trie (the fully-in-RAM path); a paged graph streams the candidates
+  -- from its backing store instead, so the matcher never builds an O(nodes)
+  -- structure.
+  streamRoots :: SRTree () -> Int -> [EClassId] -> EGraphST m [EClassId]
+  streamRoots = streamRootsFromDB
+  -- | Record a newly-created e-node (and its e-class) so a streaming matcher's
+  -- candidate source can see it. The default (fully resident graph) is a no-op:
+  -- the resident @_patDB@ is already updated by 'addToDB'.
+  recordNode :: ENode -> EClassId -> EGraphST m ()
+  recordNode _ _ = pure ()
+  -- | Content-address node -> class lookup. The default reads the resident
+  -- @_eNodeToEClass@ map (complete for a resident graph); a paged graph bounds
+  -- that map and falls back to the backing store on a miss.
+  lookupNode :: ENode -> EGraphST m (Maybe EClassId)
+  lookupNode en = gets (HashMap.lookup en . _eNodeToEClass)
+  -- | Record a node -> class mapping. The default keeps the resident (full)
+  -- map; a paged graph bounds it (evicting, since the store is authoritative).
+  insertNode :: ENode -> EClassId -> EGraphST m ()
+  insertNode en eid = modify' $ over eNodeToEClass (HashMap.insert en eid)
+  -- | Record a canonical mapping (e-class -> representative), persisting it on a
+  -- paged graph so the store-backed canonical lookup sees merges/new classes.
+  insertCanonical :: EClassId -> EClassId -> EGraphST m ()
+  insertCanonical eid canon = modify' $ over canonicalMap (IntMap.insert eid canon)
+  -- | The canonical representative of an e-class, or @Nothing@ when unknown. The
+  -- default reads the resident @_canonicalMap@; a paged graph bounds it and
+  -- falls back to the store.
+  canonicalOf :: EClassId -> EGraphST m (Maybe EClassId)
+  canonicalOf eid = gets (IntMap.lookup eid . _canonicalMap)
+
+-- | Default candidate-root enumeration from the resident @_patDB@ trie, capped
+-- at @budget@ after skipping @exclude@ (used by the pure instances and as the
+-- no-store fallback for a @MonadIO@ graph).
+streamRootsFromDB :: Monad m => SRTree () -> Int -> [EClassId] -> EGraphST m [EClassId]
+streamRootsFromDB op budget exclude = do
+  db <- gets (_patDB . _eDB)
+  let ex = IntSet.fromList exclude
+  case Map.lookup op db of
+    Nothing  -> pure []
+    Just trie -> pure (take budget [ e | e <- IntMap.keys (_trie trie), not (IntSet.member e ex) ])
+{-# INLINE streamRootsFromDB #-}
+
+-- | Whether the graph is backed by a lazily paged e-class store. Streaming
+-- matchers dispatch on this: a paged graph enumerates candidates from the
+-- backing store (bounded memory), a resident graph from @_patDB@.
+isPagedGraph :: Monad m => EGraphST m Bool
+isPagedGraph = gets (maybe False (const True) . _classStore)
+{-# INLINE isPagedGraph #-}
+
+-- Resident-map implementations (used by every pure monad) ------------------
+
+pureLookupClass :: Monad m => EClassId -> EGraphST m (Maybe EClass)
+pureLookupClass cid = gets (IntMap.lookup cid . _eClass)
+{-# INLINE pureLookupClass #-}
+
+pureGetClass :: (Monad m, HasCallStack) => EClassId -> EGraphST m EClass
+pureGetClass cid = do
+  m <- pureLookupClass cid
+  case m of
+    Just ec -> pure ec
+    Nothing -> error $ "GETECLASS_MISSING eid=" <> show cid
+{-# INLINE pureGetClass #-}
+
+pureInsertClass :: Monad m => EClass -> EGraphST m ()
+pureInsertClass ec = modify' $ over eClass (IntMap.insert (_eClassId ec) ec)
+{-# INLINE pureInsertClass #-}
+
+pureDeleteClass :: Monad m => EClassId -> EGraphST m ()
+pureDeleteClass cid = modify' $ over eClass (IntMap.delete cid)
+{-# INLINE pureDeleteClass #-}
+
+pureAdjustClass :: Monad m => EClassId -> (EClass -> EClass) -> EGraphST m ()
+pureAdjustClass cid f = modify' $ over eClass (IntMap.adjust f cid)
+{-# INLINE pureAdjustClass #-}
+
+-- | Maximum number of e-classes kept in the resident @_eClass@ cache when the
+-- graph is backed by a paged store. When exceeded, the largest-id classes are
+-- retained and the rest evicted from the resident map. The store remains
+-- authoritative (and Little-data reads fall back to it), so eviction only
+-- bounds memory, never correctness.
+residentClassCap :: Int
+residentClassCap = 50000
+
+-- | Trim the resident @_eClass@ cache to at most 'residentClassCap' entries
+-- by keeping the largest ids. No-op for graphs without a paged store (their
+-- resident map must stay complete for the pure instances). Halving on 2x keeps
+-- steady churn from triggering an O(n) rebuild on every insert.
+trimResidentCache :: Monad m => EGraphST m ()
+trimResidentCache = modify' $ \eg ->
+  case _classStore eg of
+    Nothing -> eg
+    Just _  ->
+      let m = _eClass eg
+          n = IntMap.size m
+      in if n <= 2 * residentClassCap
+            then eg
+            else over eClass (const (IntMap.fromList (Prelude.drop (n - residentClassCap) (IntMap.toAscList m)))) eg
+
+-- | Bound on the resident @_eNodeToEClass@ cache on a paged graph. Beyond the
+-- cap (checked at 2x, halved back to cap) the map is pruned; the backing store
+-- is authoritative, so eviction only trades a little dedup accuracy for bounded
+-- memory, never correctness.
+nodeCacheCap :: Int
+nodeCacheCap = 100000
+
+-- | Bound on the resident @_canonicalMap@ cache on a paged graph (same
+-- halve-on-2x policy; evicted entries are re-read from the store).
+canonicalCacheCap :: Int
+canonicalCacheCap = 100000
+{-# INLINE nodeCacheCap #-}
+{-# INLINE canonicalCacheCap #-}
+
+trimNodeCache :: Monad m => EGraphST m ()
+trimNodeCache = modify' $ \eg ->
+  case _classStore eg of
+    Nothing -> eg
+    Just _  ->
+      let m = _eNodeToEClass eg
+          n = HashMap.size m
+      in if n <= 2 * nodeCacheCap
+            then eg
+            else over eNodeToEClass (const (HashMap.fromList (Prelude.take nodeCacheCap (HashMap.toList m)))) eg
+{-# INLINE trimNodeCache #-}
+
+trimCanonicalCache :: Monad m => EGraphST m ()
+trimCanonicalCache = modify' $ \eg ->
+  case _classStore eg of
+    Nothing -> eg
+    Just _  ->
+      let m = _canonicalMap eg
+          n = IntMap.size m
+      in if n <= 2 * canonicalCacheCap
+            then eg
+            else over canonicalMap (const (IntMap.fromList (Prelude.take canonicalCacheCap (IntMap.toAscList m)))) eg
+{-# INLINE trimCanonicalCache #-}
+
+instance ClassStore Identity where
+  lookupClass = pureLookupClass
+  getClass    = pureGetClass
+  insertClass = pureInsertClass
+  deleteClass = pureDeleteClass
+  adjustClass = pureAdjustClass
+
+instance ClassStore (State StdGen) where
+  lookupClass = pureLookupClass
+  getClass    = pureGetClass
+  insertClass = pureInsertClass
+  deleteClass = pureDeleteClass
+  adjustClass = pureAdjustClass
+
+-- Any monad that can run IO is potentially paged: the graph's optional
+-- store, when present, is authoritative; otherwise classes come from the
+-- resident map.
+instance {-# OVERLAPPABLE #-} (Monad m, MonadIO m) => ClassStore m where
+  -- The resident map is kept in sync by 'insertClass'/'deleteClass', so it is
+  -- consulted first: repeated reads never touch the store, and a class that
+  -- was evicted from the store's LRU while still dirty is never served stale.
+  lookupClass cid = do
+    eg <- gets id
+    case IntMap.lookup cid (_eClass eg) of
+      Just ec -> pure (Just ec)
+      Nothing -> case _classStore eg of
+                   Nothing -> pure Nothing
+                   Just h  -> liftIO (cpsLookup h cid)
+  getClass cid = do
+    eg <- gets id
+    case IntMap.lookup cid (_eClass eg) of
+      Just ec -> pure ec
+      Nothing -> case _classStore eg of
+                   Nothing -> pureGetClass cid
+                   Just h  -> do
+                     m <- liftIO (cpsLookup h cid)
+                     case m of
+                       Just ec -> do
+                         modify' (over eClass (IntMap.insert cid ec))
+                         trimResidentCache
+                         pure ec
+                       Nothing -> error $ "GETECLASS_MISSING eid=" <> show cid
+  insertClass ec = do
+    eg <- gets id
+    case _classStore eg of
+      Nothing -> pureInsertClass ec
+      Just h  -> do liftIO (cpsInsert h ec)
+                    pureInsertClass ec
+                    trimResidentCache
+  deleteClass cid = do
+    eg <- gets id
+    case _classStore eg of
+      Nothing -> pureDeleteClass cid
+      Just h  -> do liftIO (cpsDelete h cid)
+                    pureDeleteClass cid
+  adjustClass cid f = do
+    eg <- gets id
+    case _classStore eg of
+      Nothing -> pureAdjustClass cid f
+      Just _  -> do
+        m <- lookupClass cid
+        case m of
+          Nothing -> pure ()
+          Just ec -> insertClass (f ec)
+  allClasses = do
+    eg <- gets id
+    case _classStore eg of
+      Nothing -> pure (IntMap.elems (_eClass eg))
+      Just h  -> liftIO (cpsAll h)
+  allKeys = do
+    eg <- gets id
+    case _classStore eg of
+      Nothing -> pure (IntMap.keys (_eClass eg))
+      Just h  -> liftIO (cpsKeys h)
+  -- Bypass the resident cache entirely: read the page straight from the store
+  -- and never insert into the (bounded) resident map, so a bulk traversal over
+  -- every class stays O(n) instead of O(n^2).
+  readDirect cid = do
+    eg <- gets id
+    case _classStore eg of
+      Nothing -> pureLookupClass cid
+      Just h  -> liftIO (cpsLookup h cid)
+  writeDirect ec = do
+    eg <- gets id
+    case _classStore eg of
+      Nothing -> pureInsertClass ec
+      Just h  -> liftIO (cpsInsert h ec)
+  streamRoots op budget exclude = do
+    eg <- gets id
+    case _classStore eg of
+      Nothing -> streamRootsFromDB op budget exclude
+      Just h  -> liftIO (cpsStreamRoots h op budget exclude)
+  recordNode en eid = do
+    eg <- gets id
+    case _classStore eg of
+      Nothing -> pure ()
+      Just h  -> liftIO (cpsRecordNode h en eid)
+  lookupNode en = do
+    eg <- gets id
+    case _classStore eg of
+      Nothing -> gets (HashMap.lookup en . _eNodeToEClass)
+      Just h  -> do
+        m <- gets (HashMap.lookup en . _eNodeToEClass)
+        case m of
+          Just eid -> pure (Just eid)
+          Nothing -> do
+            r <- liftIO (cpsNodeToClass h en)
+            case r of
+              Just eid -> do insertNode en eid
+                             pure (Just eid)
+              Nothing  -> pure Nothing
+  insertNode en eid = do
+    eg <- gets id
+    case _classStore eg of
+      Nothing -> modify' $ over eNodeToEClass (HashMap.insert en eid)
+      Just _  -> do modify' $ over eNodeToEClass (HashMap.insert en eid)
+                    trimNodeCache
+  insertCanonical eid canon = do
+    eg <- gets id
+    case _classStore eg of
+      Nothing -> modify' $ over canonicalMap (IntMap.insert eid canon)
+      Just h  -> do modify' $ over canonicalMap (IntMap.insert eid canon)
+                    trimCanonicalCache
+                    liftIO (cpsRecordCanonical h eid canon)
+  canonicalOf eid = do
+    eg <- gets id
+    case _classStore eg of
+      Nothing -> gets (IntMap.lookup eid . _canonicalMap)
+      Just h  -> do
+        m <- gets (IntMap.lookup eid . _canonicalMap)
+        case m of
+          Just c  -> pure (Just c)
+          Nothing -> do
+            r <- liftIO (cpsCanonicalOf h eid)
+            case r of
+              Just c  -> do modify' $ over canonicalMap (IntMap.insert eid c)
+                            trimCanonicalCache
+                            pure (Just c)
+              Nothing -> pure Nothing
+
+-- * E-Graph basic supporting functions
+
+-- | returns an empty e-graph
+emptyGraph :: EGraph
+emptyGraph = EGraph IntMap.empty HashMap.empty IntMap.empty emptyDB Nothing
+{-# INLINE emptyGraph #-}
+
+-- | returns an empty e-graph DB
+emptyDB :: EGraphDB
+emptyDB = EDB
+  Set.empty
+  Set.empty
+  IntSet.empty
+  Map.empty
+  RangeSet.empty
+  RangeSet.empty
+  IntMap.empty
+  IntMap.empty
+  IntMap.empty
+  IntSet.empty
+  0
+  False
+  True
+  Map.empty
+{-# INLINE emptyDB #-}
+
+-- | like 'emptyDB' but skips range-DB maintenance (pure simplify mode)
+emptyDBNoTrack :: EGraphDB
+emptyDBNoTrack = emptyDB{ _trackDBs = False }
+{-# INLINE emptyDBNoTrack #-}
+
+-- | an empty e-graph that skips range-DB maintenance (pure simplify mode)
+emptyGraphNoTrack :: EGraph
+emptyGraphNoTrack = EGraph IntMap.empty HashMap.empty IntMap.empty emptyDBNoTrack Nothing
+{-# INLINE emptyGraphNoTrack #-}
+
+-- | Creates a new e-class from an e-class id, a new e-node,
+-- and the info of this e-class 
+createEClass :: EClassId -> ENode -> EClassData -> Int -> EClass
+createEClass cId enode' info h = EClass cId (Set.singleton enode') Set.empty h info
+{-# INLINE createEClass #-}
+
+-- | gets the canonical id of an e-class with full path compression
+canonical :: ClassStore m => EClassId -> EGraphST m EClassId
+canonical eclassId = do
+  mStep <- canonicalOf eclassId
+  case mStep of
+    Nothing -> canonError eclassId
+    Just oneStep
+      | oneStep == eclassId -> pure eclassId
+      | otherwise -> do
+          (root, chain) <- walk [eclassId] oneStep
+          -- compress the chain in the resident cache (cache-only: the store
+          -- keeps the authoritative semantic mappings recorded at insert
+          -- time, so eviction just loses the shortcut, never correctness).
+          modify' $ \eg -> eg{ _canonicalMap =
+                        foldl' (\m' k -> IntMap.insert k root m') (_canonicalMap eg) chain }
+          pure root
+  where
+    walk :: ClassStore m => [EClassId] -> EClassId -> EGraphST m (EClassId, [EClassId])
+    walk chain ecId = do
+      mNext <- canonicalOf ecId
+      case mNext of
+        Nothing -> canonError ecId
+        Just n
+          | n == ecId -> pure (ecId, chain)
+          | otherwise -> walk (ecId : chain) n
+
+    canonError :: ClassStore m => EClassId -> EGraphST m a
+    canonError eid = do
+      m <- gets _canonicalMap
+      error $ "CANON_MISSING eid=" <> show eid <> " mapSize=" <> show (IntMap.size m)
+{-# INLINE canonical #-}
+
+-- | canonize the e-node children
+canonize :: (ClassStore m, HasCallStack) => ENode -> EGraphST m ENode
+canonize (EVar ix)     = pure (EVar ix)
+canonize (EParam ix)   = pure (EParam ix)
+canonize (EConst x)    = pure (EConst x)
+canonize (EUni f t)    = EUni f <$> canonical t
+canonize (EBin op l r) = EBin op <$> canonical l <*> canonical r
+-- re-map children to their canonical ids; IntMap keeps keys sorted, so
+-- commutativity is structural, no rewrite rule required.
+canonize (ENAry op m) = do
+  m' <- IntMap.fromListWith (+) <$> forM (IntMap.toList m) (\(c, n) -> do
+            c' <- canonical c
+            pure (c', n))
+  pure (ENAry op m')
+{-# INLINE canonize #-}
+
+-- | The children e-class ids of an e-node.
+eChildren :: ENode -> [EClassId]
+eChildren (EVar _)     = []
+eChildren (EParam _)   = []
+eChildren (EConst _)   = []
+eChildren (EUni _ t)   = [t]
+eChildren (EBin _ l r) = [l, r]
+eChildren (ENAry _ m)  = expandedList m
+{-# INLINE eChildren #-}
+
+toOp :: NOp -> Op
+toOp EAdd = Add
+toOp EMul = Mul
+{-# INLINE toOp #-}
+
+-- | Operator shape key used to index the pattern database. ENAry maps back to
+-- the corresponding binary operator shape so existing (binary) Add/Mul
+-- patterns address the same trie.
+eOpKey :: ENode -> SRTree ()
+eOpKey (EVar ix)     = Var ix
+eOpKey (EParam ix)   = Param ix
+eOpKey (EConst x)    = Const x
+eOpKey (EUni f _)    = Uni f ()
+eOpKey (EBin op _ _) = Bin op () ()
+eOpKey (ENAry EAdd _) = Bin Add () ()
+eOpKey (ENAry EMul _) = Bin Mul () ()
+{-# INLINE eOpKey #-}
+
+-- | Convert an e-node (children still as e-class ids) into the equivalent
+-- binary SRTree shape. NOTE: only called on non-ENary nodes; flattened
+-- ENAry nodes have no binary skeleton (see 'naryTree' / the explicit ENAry
+-- cases in the analyses).
+fromENode :: ENode -> SRTree EClassId
+fromENode (EVar ix)     = Var ix
+fromENode (EParam ix)   = Param ix
+fromENode (EConst x)    = Const x
+fromENode (EUni f t)    = Uni f t
+fromENode (EBin op l r) = Bin op l r
+fromENode (ENAry _ _)   = error "fromENode: ENAry has no binary skeleton"
+{-# INLINE fromENode #-}
+
+-- | Right-fold a list of e-class child expressions into a binary Fix SRTree
+-- for a flattened ENAry multiset (extraction).
+naryTree :: NOp -> [Fix SRTree] -> Fix SRTree
+naryTree op ts = normalizeSubDiv (foldr1 (\a b -> Fix (Bin (toOp op) a b)) ts)
+{-# INLINE naryTree #-}
+
+-- | Re-render the internal negate/recip canonical forms back as Sub/Div so
+-- extraction output keeps the familiar shape: `x + (-1)*y` -> `x - y`,
+-- `x + (-3)` -> `x - 3` and `x * recip y` -> `x / y`. Sub and Div never
+-- appear as e-nodes; they only reappear here during reconstruction.
+normalizeSubDiv :: Fix SRTree -> Fix SRTree
+normalizeSubDiv = cata alg
+  where
+    alg :: SRTree (Fix SRTree) -> Fix SRTree
+    alg (Bin Add l r) = case pick l r of
+        Just (pos, neg) -> Fix (Bin Sub pos neg)
+        Nothing         -> Fix (Bin Add l r)
+      where
+        pick a b = case negated a of
+                     Just t -> Just (b, t)
+                     Nothing -> case negated b of
+                                  Just t -> Just (a, t)
+                                  Nothing -> Nothing
+        negated (Fix (Bin Mul (Fix (Const c)) t)) | c == -1 = Just t
+        negated (Fix (Bin Mul t (Fix (Const c)))) | c == -1 = Just t
+        negated (Fix (Const c)) | c < 0 = Just (Fix (Const (-c)))
+        negated _ = Nothing
+    alg (Bin Mul l r) = case pick l r of
+        Just (num, den) -> Fix (Bin Div num den)
+        Nothing         -> Fix (Bin Mul l r)
+      where
+        pick a b = case a of
+                     Fix (Uni Recip t) -> Just (b, t)
+                     _ -> case b of
+                            Fix (Uni Recip t) -> Just (a, t)
+                            _ -> Nothing
+    alg t = Fix t
+
+-- | Convert a binary SRTree (children as e-class ids) into an e-node,
+-- flattening Add/Mul into canonical ENAry multisets.
+toENode :: (ClassStore m, HasCallStack) => SRTree EClassId -> EGraphST m ENode
+toENode (Var ix)     = pure (EVar ix)
+toENode (Param ix)   = pure (EParam ix)
+toENode (Const x)    = pure (EConst x)
+toENode (Uni f t)    = EUni f <$> canonical t
+toENode (Bin Add l r) = mkENary EAdd [l, r]
+toENode (Bin Mul l r) = mkENary EMul [l, r]
+toENode (Bin op l r)  = EBin op <$> canonical l <*> canonical r
+toENode n             = error $ "toENode: unsupported node " <> show n
+{-# INLINE toENode #-}
+
+-- | Build a canonical ENAry from child ids: canonicalize children, absorb
+-- nested same-op ENAry children (associativity), sort by key (commutativity).
+mkENary :: (ClassStore m, HasCallStack) => NOp -> [EClassId] -> EGraphST m ENode
+mkENary op cids = mkENaryM op (imFromList cids)
+
+-- | Build a canonical ENAry from a canonical multiset of child ids.
+mkENaryM :: (ClassStore m, HasCallStack) => NOp -> IntMap Int -> EGraphST m ENode
+mkENaryM op m = do
+  flat <- IntMap.unionsWith (+) <$> mapM (expandM op) (IntMap.toList m)
+  pure (ENAry op flat)
+
+-- | If the e-class of `cid` holds exactly one e-node and that node is an ENAry
+-- of the same op, return its children scaled by `n` (flattening `n`
+-- occurrences); otherwise return `n` copies of `cid`. Flattening is only sound
+-- through a class with a single node: if the class were merged with other
+-- nodes (e.g. `{Add[a,b], Mul[x,c]}`) flattening would silently pick one
+-- representative and change the meaning of the term.
+expandM :: (ClassStore m, HasCallStack) => NOp -> (EClassId, Int) -> EGraphST m (IntMap Int)
+expandM op (cid, n) = do
+  ec <- getEClass cid
+  case Set.toList (_eNodes ec) of
+    [ENAry op' m'] | op' == op -> pure (IntMap.map (* n) m')
+    _                          -> pure (IntMap.singleton cid n)
+
+-- | Reconstruct a binary Fix SRTree from an e-node, right-folding ENAry
+-- into nested Bin Add/Mul.
+enodeToTree :: (ClassStore m, HasCallStack) => ENode -> EGraphST m (Fix SRTree)
+enodeToTree (EVar ix)   = pure (Fix (Var ix))
+enodeToTree (EParam ix) = pure (Fix (Param ix))
+enodeToTree (EConst x)  = pure (Fix (Const x))
+enodeToTree (EUni f t)  = Fix . Uni f <$> getBestExpr t
+enodeToTree (EBin op l r) = do
+  tl <- getBestExpr l
+  tr <- getBestExpr r
+  pure (Fix (Bin op tl tr))
+enodeToTree (ENAry op m) = do
+  ts <- mapM getBestExpr (expandedList m)
+  pure (naryTree op ts)
+{-# INLINE enodeToTree #-}
+
+-- | gets an e-class with id `c` (auto-canonizes)
+getEClass :: (ClassStore m, HasCallStack) => EClassId -> EGraphST m EClass
+getEClass c = do c' <- canonical c; getClass c'
+{-# INLINE getEClass #-}
+
+-- | gets the best expression given the default cost function. Cycle-safe and
+-- budgeted: see 'getBestExprBounded'.
+getBestExpr :: (ClassStore m, HasCallStack) => EClassId -> EGraphST m (Fix SRTree)
+getBestExpr eid = getBestExprBounded eid
+
+-- | Like 'getBestExpr' but terminates on pathological graphs: a visited set
+-- stops the expansion from re-entering an already-expanded class (a @_best@
+-- cycle arising from supersaturation/merges), and a node budget caps the total
+-- expanded size (so an exponentially-shared DAG is truncated rather than
+-- exploded). Both guards substitute a @Var 0@ placeholder for the part that
+-- would otherwise blow up. On well-formed acyclic graphs with small bests
+-- neither guard triggers, so the result is identical to the unbounded version.
+-- This keeps out-of-core extraction (e.g. 'dbTop') bounded in memory.
+getBestExprBounded :: (ClassStore m, HasCallStack) => EClassId -> EGraphST m (Fix SRTree)
+getBestExprBounded eid = fst <$> expand Set.empty 0 eid
+  where
+    budget :: Int
+    budget = 200
+    -- expand returns the tree and the running count of expanded nodes, so the
+    -- budget bounds the TOTAL size (not just the depth): an exponentially-shared
+    -- DAG is truncated instead of exploded. A revisited (cyclic) class or a
+    -- full budget yields a @Var 0@ placeholder.
+    expand :: ClassStore m => HashSet EClassId -> Int -> EClassId -> EGraphST m (Fix SRTree, Int)
+    expand _ n _ | n >= budget = pure (Fix (Var 0), n)
+    expand seen n eid
+      | Set.member eid seen = pure (Fix (Var 0), n)
+      | otherwise = do
+          best <- (_best . _info) <$> getEClass eid
+          let seen' = Set.insert eid seen
+              n0    = n + 1
+          case best of
+            EVar ix   -> pure (Fix (Var ix), n0)
+            EParam ix -> pure (Fix (Param ix), n0)
+            EConst x  -> pure (Fix (Const x), n0)
+            EUni f t  -> do (tt, n1) <- expand seen' n0 t
+                            pure (Fix (Uni f tt), n1)
+            EBin op l r -> do
+              (tl, n1) <- expand seen' n0 l
+              (tr, n2) <- expand seen' n1 r
+              pure (Fix (Bin op tl tr), n2)
+            ENAry op m -> do
+              (xs, nEnd) <- goNary seen' n0 (IntMap.toAscList m) []
+              pure (if null xs then (Fix (Var 0), nEnd) else (naryTree op xs, nEnd))
+    -- build the ENAry children from the multiset WITHOUT materialising the
+    -- expanded multiplicity list: an enormous count (a pathological supersaturated
+    -- class) is capped per-child and by the total budget, so each copy counts
+    -- toward the budget and no giant list is ever allocated.
+    goNary seen n es acc
+      | n >= budget = pure (reverse acc, n)
+      | otherwise = case es of
+          [] -> pure (reverse acc, n)
+          ((c, cnt) : rest) -> do
+            (t, n1) <- expand seen n c
+            let take = min cnt (budget - n1 + 1)
+                n2   = n1 + (take - 1)
+                acc' = Prelude.replicate take t ++ acc
+            goNary seen n2 rest acc'
+
+-- | Creates a singleton trie from an e-class id
+trie :: EClassId -> IntMap IntTrie -> IntTrie
+trie eid = IntTrie
+{-# INLINE trie #-}
+
+-- | Check whether an e-class is a constant value
+isConst :: ClassStore m => EClassId -> EGraphST m Bool
+isConst eid = do ec <- getEClass eid
+                 case (_consts . _info) ec of
+                   ConstVal _ -> pure True
+                   _          -> pure False
+{-# INLINE isConst #-}
+
+getFitness :: ClassStore m => EClassId -> EGraphST m (Maybe Double)
+getFitness c = (_fitness . _info) <$> getEClass c
+{-# INLINE getFitness #-}
+getTheta :: ClassStore m => EClassId -> EGraphST m ([Target])
+getTheta c = (_theta . _info) <$> getEClass c
+{-# INLINE getTheta #-}
+getSize :: ClassStore m => EClassId -> EGraphST m Int
+getSize c = (_size . _info) <$> getEClass c
+{-# INLINE getSize #-}
+isSizeOf :: (Int -> Bool) -> EClass -> Bool
+isSizeOf p = p . _size . _info
+{-# INLINE isSizeOf #-}
+getBestFitness :: ClassStore m => EGraphST m (Maybe Double)
+getBestFitness = do
+    mbec <- gets (fmap snd . getGreatest . _fitRangeDB . _eDB)
+    case mbec of
+      Just bec -> (_fitness . _info) <$> getEClass bec
+      Nothing  -> pure Nothing
+getDL :: ClassStore m => EClassId -> EGraphST m (Maybe Double)
+getDL c = (_dl . _info) <$> getEClass c
+{-# INLINE getDL #-}
diff --git a/src/Algorithm/EqSat/Info.hs b/src/Algorithm/EqSat/Info.hs
new file mode 100644
--- /dev/null
+++ b/src/Algorithm/EqSat/Info.hs
@@ -0,0 +1,222 @@
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Algorithm.EqSat.Info
+-- Copyright   :  (c) Fabricio Olivetti 2021 - 2024
+-- License     :  BSD3
+-- Maintainer  :  fabricio.olivetti@gmail.com
+-- Stability   :  experimental
+-- Portability :
+--
+-- Functions related to info/data calculation in Equality Graph data structure
+-- Heavily based on hegg (https://github.com/alt-romes/hegg by alt-romes)
+--
+-----------------------------------------------------------------------------
+
+module Algorithm.EqSat.Info where
+
+import Control.Lens ( over )
+import Control.Monad
+import Control.Monad.State
+import Data.AEq (AEq ((~==)))
+import Data.IntMap (IntMap)
+import qualified Data.IntMap as IntMap
+import Data.Map (Map)
+import qualified Data.Map as Map
+import Data.SRTree
+import Data.SRTree.Eval (evalFun, evalOp, Target)
+import Data.HashSet (HashSet)
+import qualified Data.HashSet as Set
+import qualified Data.Set as RangeSet
+import qualified Data.IntSet as IntSet
+import Algorithm.EqSat.Egraph
+import Algorithm.EqSat.Queries
+
+import qualified Data.Set as TrueSet
+
+-- * Data related functions 
+
+-- | join data from two e-classes
+-- TODO: instead of folding, just do not apply rules
+-- list of values instead of single value
+joinData :: EClassData -> EClassData -> EClassData
+joinData (EData c1 b1 cn1 fit1 dl1 p1 sz1) (EData c2 b2 cn2 fit2 dl2 p2 sz2) =
+  --EData (min c1 c2) b (combineConsts cn1 cn2) (minMaybe fit1 fit2) (bestParam p1 p2 fit1 fit2) (min sz1 sz2)
+  EData (min c1 c2) (choose b1 b2) (choose cn1 cn2) (maxMaybe fit1 fit2) (choose dl1 dl2) (choose p1 p2) (choose sz1 sz2)
+  where
+    isFst = c1 <= c2
+    choose x y = if isFst then x else y
+    chooseF x y = if maxIsFst then x else y
+
+    maxIsFst = case (fit1, fit2) of
+                 (Nothing, Nothing) -> True
+                 (Nothing,  Just f) -> False
+                 (Just f , Nothing) -> True
+                 (Just f1, Just f2) -> f1 >= f2
+
+    maxMaybe Nothing x = x
+    maxMaybe x Nothing = x
+    maxMaybe x y       = max x y
+
+    bestParam Nothing x _ _ = x
+    bestParam x Nothing _ _ = x
+    bestParam x y (Just f1) (Just f2) = if f1 >= f2 then x else y
+
+    b = if c1 <= c2 then b1 else b2
+    combineConsts (ConstVal x) (ConstVal y)
+      | abs (x-y) < 1e-7   = ConstVal $ (x+y)/2
+      | isNaN x || isInfinite x = ConstVal y 
+      | isNaN y || isInfinite y = ConstVal x
+      | isNaN x && isNaN y = ConstVal x
+      | x ~== y = ConstVal $ (x+y)/2
+      | abs (x / y) < 1 + 1e-6 || abs (y / x) < 1 + 1e-6 = ConstVal $ min x y
+      | isInfinite x && isInfinite y = ConstVal x
+      | isInfinite x && isNaN y = ConstVal y
+      | isNaN x && isInfinite y = ConstVal x
+      | otherwise          = error $ "Combining different values: " <> show x <> " " <> show y <> " " <> show (x/y)
+    combineConsts (ParamIx ix) (ParamIx iy) = ParamIx (min ix iy)
+    combineConsts NotConst x = x
+    combineConsts x NotConst = x
+    combineConsts (ParamIx ix) (ConstVal x) = ConstVal x
+    combineConsts (ConstVal x) (ParamIx ix) = ConstVal x -- p - p = 0
+    combineConsts x y = error (show x <> " " <> show y)
+
+-- | Fetch consts, cost, and size for all children in a single state traversal
+getChildrenData :: ClassStore m => [EClassId] -> EGraphST m [(Consts, Cost, Int)]
+getChildrenData ids = do
+  ids' <- mapM canonical ids
+  mapM (\cid -> do
+            ec <- getEClass cid
+            let d = _info ec
+            pure (_consts d, _cost d, _size d)) ids'
+{-# INLINE getChildrenData #-}
+
+-- | Calculate e-node data (constant values and cost)
+makeAnalysis :: ClassStore m => CostFun -> ENode -> EGraphST m EClassData
+makeAnalysis costFun enode =
+  do let cs = eChildren enode
+     childData <- getChildrenData cs
+     let (consts', costs', sizes) = unzip3 childData
+         consts = combineNode enode consts'
+         cost   = costNode enode costs'
+         sz     = sum sizes
+     enode' <- canonize enode
+     pure $ EData cost enode' consts Nothing Nothing [] (sz + 1)
+  where
+    -- ENAry folds children pairwise (constant folding over a multiset); the
+    -- binary skeleton cannot represent n children.
+    combineNode (ENAry op _) cs = foldr1 (\a b -> combineConsts (Bin (toOp op) a b)) cs
+    combineNode _             cs = combineConsts (replaceChildren cs (fromENode enode))
+    -- ENAry is a single flattened op node: op cost + sum of child costs.
+    costNode (ENAry op _) cs = costFun (Bin (toOp op) 0 0) + sum cs
+    costNode _             cs = costFun (replaceChildren cs (fromENode enode))
+
+getChildrenMinHeight :: ClassStore m => ENode -> EGraphST m Int
+getChildrenMinHeight enode = do
+  let children = eChildren enode
+  if null children then pure 0 else do
+    children' <- mapM canonical children
+    hs <- mapM (fmap _height . getEClass) children'
+    pure (minimum hs)
+
+-- | update the heights of each e-class
+-- won't work if there's no root
+calculateHeights :: ClassStore m => EGraphST m ()
+calculateHeights =
+  do queue   <- findRootClasses
+     classes <- allKeys
+     let nClasses = length classes
+     forM_ classes (setHeight nClasses) -- set all heights to max possible height (number of e-classes)
+     forM_ queue (setHeight 0)          -- set root e-classes height to zero
+     go queue (TrueSet.fromList queue) 1    -- next height is 1
+  where
+    setHeight :: ClassStore m => Int -> EClassId -> EGraphST m ()
+    setHeight x eId' =
+      do eId <- canonical eId'
+         ec <- getEClass eId
+         let ec' = over height (const x) ec
+         insertClass ec'
+
+    setMinHeight :: ClassStore m => Int -> EClassId -> EGraphST m ()
+    setMinHeight x eId' = -- set height to the minimum between current and x
+      do eId <- canonical eId'
+         h <- _height <$> getEClass eId
+         setHeight (min h x) eId
+
+    getChildrenEC :: ClassStore m => EClassId -> EGraphST m [EClassId]
+    getChildrenEC ec' = do ec <- getEClass ec'
+                           pure $ concatMap eChildren (_eNodes ec)
+
+    go [] _    _ = pure ()
+    go qs tabu h =
+      do childrenOf <- (TrueSet.\\ tabu) . TrueSet.fromList . concat <$> forM qs getChildrenEC -- rerieve all unvisited children
+         let childrenL = TrueSet.toList childrenOf
+         forM_ childrenL (setMinHeight h) -- set the height of the children as the minimum between current and h
+         go childrenL (TrueSet.union tabu childrenOf) (h+1) -- move one breadth search style
+
+-- | calculates the cost of a node
+calculateCost :: ClassStore m => CostFun -> ENode -> EGraphST m Cost
+calculateCost f enode =
+  do let cs = eChildren enode
+     costs <- traverse (fmap (_cost . _info) . getEClass) cs
+     pure $ case enode of
+              ENAry op _ -> f (Bin (toOp op) 0 0) + sum costs
+              _          -> f (replaceChildren costs (fromENode enode))
+
+-- | check whether an e-node evaluates to a const
+calculateConsts :: ClassStore m => ENode -> EGraphST m Consts
+calculateConsts enode =
+  do let cs = eChildren enode
+     consts <- traverse (fmap (_consts . _info) . getEClass) cs
+     let c = case enode of
+               ENAry op _ -> foldr1 (\a b -> combineConsts (Bin (toOp op) a b)) consts
+               _          -> combineConsts (replaceChildren consts (fromENode enode))
+     case c of
+          ConstVal x | isNaN x -> pure (ConstVal x)
+          a -> pure a
+
+combineConsts :: SRTree Consts -> Consts
+combineConsts (Const x)    = ConstVal x
+combineConsts (Param ix)   = ParamIx ix
+combineConsts (Var _)      = NotConst
+combineConsts (Uni f t)    = case t of
+                              ConstVal x -> ConstVal $ evalFun f x
+                              --ParamIx  x -> ParamIx x
+                              _          -> t
+combineConsts (Bin op l r) = evalOp' l r
+  where
+    evalOp' (ParamIx ix) (ParamIx iy) = ParamIx (min ix iy)
+    evalOp' (ConstVal x) (ConstVal y) = ConstVal $ evalOp op x y
+    evalOp' _            _            = NotConst
+
+insertFitness :: ClassStore m => EClassId -> Double -> [Target] -> EGraphST m ()
+insertFitness eId' fit params =
+  do eId <- canonical eId'
+     tree <- getBestExpr eId
+     let p = fromIntegral (length params)
+     let f_compl = countNodes tree * log (countUniqueTokens tree) + p * (log (2 * pi * exp(1 - log 3)) - log p) / 2.0
+     ec <- getEClass eId
+     let oldFit  = _fitness . _info $ ec
+     let newInfo = (_info ec){_fitness = Just fit, _theta = params}
+         newEc   = ec{_info = newInfo}
+         sz = _size newInfo
+     insertClass newEc
+     case oldFit of
+       Nothing -> modify' $ over (eDB . unevaluated) (IntSet.delete eId)
+                    . over (eDB . fitRangeDB) (insertRange eId fit)
+                    . over (eDB . sizeFitDB) (IntMap.adjust (insertRange eId fit) sz . IntMap.insertWith RangeSet.union sz RangeSet.empty)
+                    . over (eDB . dlRangeDB) (insertRange eId f_compl)
+       Just oldVal -> modify' $ over (eDB . fitRangeDB) (insertRange eId fit . removeRange eId oldVal)
+                                 . over (eDB . sizeFitDB) (IntMap.adjust (insertRange eId fit . removeRange eId oldVal) sz)
+
+insertDL :: ClassStore m => EClassId -> Double -> EGraphST m ()
+insertDL eId fit' =
+  do let fit = negate fit'
+     ec <- getEClass eId
+     let sz = _size . _info $ ec
+         newInfo = (_info ec){_dl = Just fit'}
+         newEc   = ec{_info=newInfo}
+     insertClass newEc
+     modify' $ over (eDB . dlRangeDB) (insertRange eId fit)
+             . over (eDB . sizeDLDB) (IntMap.adjust (insertRange eId fit) sz . IntMap.insertWith RangeSet.union sz RangeSet.empty)
+
+
diff --git a/src/Algorithm/EqSat/Queries.hs b/src/Algorithm/EqSat/Queries.hs
new file mode 100644
--- /dev/null
+++ b/src/Algorithm/EqSat/Queries.hs
@@ -0,0 +1,213 @@
+{-# LANGUAGE ViewPatterns #-}
+{-# LANGUAGE BangPatterns #-}
+{-# LANGUAGE TupleSections #-}
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Algorithm.EqSat.Queries
+-- Copyright   :  (c) Fabricio Olivetti 2021 - 2024
+-- License     :  BSD3
+-- Maintainer  :  fabricio.olivetti@gmail.com
+-- Stability   :  experimental
+-- Portability :
+--
+-- Query functions for e-graphs
+-- Heavily based on hegg (https://github.com/alt-romes/hegg by alt-romes)
+--
+-----------------------------------------------------------------------------
+
+module Algorithm.EqSat.Queries where
+
+import Algorithm.EqSat.Egraph
+import qualified Data.IntMap as IntMap
+import qualified Data.Map as Map
+import qualified Data.HashSet as Set
+import qualified Data.Set as RangeSet
+import Control.Monad.State ( gets, modify' )
+import Control.Lens ( over )
+import Data.Maybe
+import Data.SRTree (childrenOf)
+
+getEClassesThat :: ClassStore m => (EClass -> Bool) -> EGraphST m [EClassId]
+getEClassesThat p = do
+    classes <- allClasses
+    pure [ _eClassId ec | ec <- classes, p ec ]
+
+updateFitness :: ClassStore m => Double -> EClassId -> EGraphST m ()
+updateFitness f ecId = do
+   ec   <- getEClass ecId
+   let info = _info ec
+   insertClass ec{_info=info{_fitness = Just f}}
+
+-- | returns all the root e-classes (e-class without parents)
+findRootClasses :: ClassStore m => EGraphST m [EClassId]
+findRootClasses = do
+    classes <- allClasses
+    pure [ _eClassId ec | ec <- classes, isParent (_eClassId ec, ec) ]
+  where
+    isParent (k, v) = Prelude.null (_parents v) ||  (k `Set.member` (Set.map fst (_parents v)))
+
+-- | returns the e-class id with the best fitness that
+-- is true to a predicate
+getTopECLassThat :: ClassStore m => Bool -> Int -> (EClass -> Bool) -> EGraphST m [EClassId]
+getTopECLassThat b n p = do
+  let f = if b then _fitRangeDB else _dlRangeDB
+  gets (f . _eDB)
+    >>= go n []
+  where
+    go :: ClassStore m => Int -> [EClassId] -> RangeTree Double -> EGraphST m [EClassId]
+    go 0 bests rt = pure bests
+    go m bests rt = case RangeSet.maxView rt of
+                       Nothing -> pure bests
+                       Just (y, t) ->
+                         let x = snd y
+                         in do ecId <- canonical x
+                               ec <- getEClass ecId
+                               if (maybe True (isInfinite) . _fitness . _info $ ec)
+                                 then go m bests t
+                                 else if p ec
+                                   then go (m-1) (ecId:bests) t
+                                   else go m bests t
+
+getTopEClassInRange :: ClassStore m => Bool -> Int -> (EClass -> Double) -> [(Double, Double)] -> EGraphST m [EClassId]
+getTopEClassInRange b n p range = do
+  let f = if b then _fitRangeDB else _dlRangeDB
+  gets (f . _eDB)
+    >>= go n [] range
+  where
+    inRange v (x, y)
+      | v >= x && v <= y = 0
+      | v < x = -1
+      | v > y = 1
+      | otherwise = 1 
+
+    go :: ClassStore m => Int -> [EClassId] -> [(Double, Double)] -> RangeTree Double -> EGraphST m [EClassId]
+    go _ bests []      _ = pure bests 
+    go 0 bests (r:rs) rt = go n bests rs rt
+    go m bests (r:rs) rt = case RangeSet.maxView rt of
+                             Nothing -> pure bests
+                             Just (y, t) ->
+                               let x = snd y
+                               in do ecId <- canonical x
+                                     ec <- getEClass ecId
+                                     if (maybe True (isInfinite) . _fitness . _info $ ec)
+                                       then go m bests (r:rs) t
+                                       else do let v = p ec
+                                               case (v `inRange` r) of
+                                                 0  -> go (m-1) (ecId:bests) (r:rs) t
+                                                 -1 -> go n bests rs (RangeSet.insert y t)
+                                                 1  -> go m bests (r:rs) t
+
+getTopECLassIn :: ClassStore m => Bool -> Int -> (EClass -> Bool) -> [EClassId] -> EGraphST m [EClassId]
+getTopECLassIn b n p ecs' = do
+  let f = if b then _fitRangeDB else _dlRangeDB
+  gets (f . _eDB)
+    >>= go n []
+  where
+    ecs = Set.fromList ecs'
+    go :: ClassStore m => Int -> [EClassId] -> RangeTree Double -> EGraphST m [EClassId]
+    go 0 bests rt = pure bests
+    go m bests rt = case RangeSet.maxView rt of
+                       Nothing -> pure bests
+                       Just (y, t) ->
+                         let x = snd y
+                         in do ecId <- canonical x
+                               ec <- getEClass ecId
+                               if (maybe True (isInfinite) . _fitness . _info $ ec)
+                                 then go m bests t
+                                 else if ecId `Set.member` ecs && p ec
+                                   then go (m-1) (ecId:bests) t
+                                   else go m bests t
+
+getTopECLassNotIn :: ClassStore m => Bool -> Int -> (EClass -> Bool) -> [EClassId] -> EGraphST m [EClassId]
+getTopECLassNotIn b n p ecs' = do
+  let f = if b then _fitRangeDB else _dlRangeDB
+  gets (f . _eDB)
+    >>= go n []
+  where
+    ecs = Set.fromList ecs'
+
+    go :: ClassStore m => Int -> [EClassId] -> RangeTree Double -> EGraphST m [EClassId]
+    go 0 bests rt = pure bests
+    go m bests rt = case RangeSet.maxView rt of
+                       Nothing -> pure bests
+                       Just (y, t) ->
+                         let x = snd y
+                         in do ecId <- canonical x
+                               ec <- getEClass ecId
+                               if (maybe True (isInfinite) . _fitness . _info $ ec)
+                                 then go m bests t
+                                 else if not (ecId `Set.member` ecs) && p ec
+                                   then go (m-1) (ecId:bests) t
+                                   else go m bests t
+
+getAllEvaluatedEClasses :: ClassStore m => EGraphST m [EClassId]
+getAllEvaluatedEClasses = do
+  gets (_fitRangeDB . _eDB)
+    >>= go []
+  where
+    go :: ClassStore m => [EClassId] -> RangeTree Double -> EGraphST m [EClassId]
+    go bests rt = case RangeSet.maxView rt of
+                    Nothing -> pure bests
+                    Just (y, t) ->
+                      let x = snd y
+                      in do ecId <- canonical x
+                            ec <- getEClass ecId
+                            if (maybe True (isInfinite) . _fitness . _info $ ec)
+                              then go bests t
+                              else go (ecId:bests) t
+
+getTopEClassWithSize :: Monad m => Bool -> Int -> Int -> EGraphST m [EClassId]
+getTopEClassWithSize b sz n = do
+   let fun = if b then _sizeFitDB else _sizeDLDB
+   gets (go n [] . (IntMap.!? sz) . fun . _eDB)
+  where
+    go _ bests Nothing   = []
+    go 0 bests (Just rt) = bests
+    go m bests (Just rt) = case RangeSet.maxView rt of
+                             Nothing         -> bests
+                             Just ((f, x), t) -> if isInfinite f || isNaN f then go m bests (Just t) else go (m-1) (x:bests) (Just t)
+
+getTopFitEClassThat :: ClassStore m => Int -> (EClass -> Bool) -> EGraphST m [EClassId]
+getTopFitEClassThat  = getTopECLassThat True
+getTopDLEClassThat :: ClassStore m => Int -> (EClass -> Bool) -> EGraphST m [EClassId]
+getTopDLEClassThat   = getTopECLassThat False
+getTopFitEClassIn :: ClassStore m =>  Int -> (EClass -> Bool) -> [EClassId] -> EGraphST m [EClassId]
+getTopFitEClassIn    = getTopECLassIn True
+getTopDLEClassIn :: ClassStore m => Int -> (EClass -> Bool) -> [EClassId] -> EGraphST m [EClassId]
+getTopDLEClassIn     = getTopECLassIn False
+getTopFitEClassNotIn :: ClassStore m => Int -> (EClass -> Bool) -> [EClassId] -> EGraphST m [EClassId]
+getTopFitEClassNotIn = getTopECLassNotIn True
+getTopDLEClassNotIn :: ClassStore m => Int -> (EClass -> Bool) -> [EClassId] -> EGraphST m [EClassId]
+getTopDLEClassNotIn  = getTopECLassNotIn False
+getTopFitEClassWithSize :: Monad m => Int -> Int -> EGraphST m [EClassId]
+getTopFitEClassWithSize = getTopEClassWithSize True
+getTopDLEClassWithSize :: Monad m => Int -> Int -> EGraphST m [EClassId]
+getTopDLEClassWithSize  = getTopEClassWithSize False
+
+rebuildAllRanges :: ClassStore m => EGraphST m ()
+rebuildAllRanges = do szF <- gets (_sizeFitDB._eDB) >>= traverse rebuildRange
+                      dlF <- gets (_sizeDLDB._eDB) >>= traverse rebuildRange
+                      fR  <- gets (_fitRangeDB._eDB) >>= rebuildRange
+                      dR  <- gets (_dlRangeDB._eDB) >>= rebuildRange
+
+                      modify' $ over (eDB.fitRangeDB) (const fR)
+                              . over (eDB.dlRangeDB) (const dR)
+                              . over (eDB.sizeFitDB) (const szF)
+                              . over (eDB.sizeDLDB) (const dlF)
+
+canonizeRange :: ClassStore m => RangeTree Double -> EGraphST m (RangeTree Double)
+canonizeRange = fmap RangeSet.fromList . mapM (\(x, eid) -> (x,) <$> canonical eid) . RangeSet.toList
+
+rebuildRange :: ClassStore m => RangeTree Double -> EGraphST m (RangeTree Double)
+rebuildRange rt = do
+  canonRt <- canonizeRange rt
+  pure $ snd $ go canonRt
+  where
+    go rt' = case RangeSet.maxView rt' of
+               Nothing -> (Set.empty, RangeSet.empty)
+               Just ((x, eid), rest) ->
+                 let (seen, result) = go rest
+                 in if Set.member eid seen
+                      then (seen, result)
+                      else (Set.insert eid seen, RangeSet.insert (x, eid) result)
+
diff --git a/src/Algorithm/EqSat/SearchSR.hs b/src/Algorithm/EqSat/SearchSR.hs
new file mode 100644
--- /dev/null
+++ b/src/Algorithm/EqSat/SearchSR.hs
@@ -0,0 +1,277 @@
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Algorithm.EqSat.Search
+-- Copyright   :  (c) Fabricio Olivetti 2021 - 2024
+-- License     :  BSD3
+-- Maintainer  :  fabricio.olivetti@gmail.com
+-- Stability   :  experimental
+-- Portability :
+--
+-- Support functions for search symbolic expressions with e-graphs
+--
+-----------------------------------------------------------------------------
+
+module Algorithm.EqSat.SearchSR where
+
+import Data.SRTree
+import Data.SRTree.Datasets
+import Data.SRTree.Eval (compileLoss)
+import System.Random
+import Control.Monad.State.Strict
+import Control.Concurrent (getNumCapabilities)
+import Control.Concurrent.Async (mapConcurrently)
+import Data.Maybe (catMaybes)
+import Control.Exception (evaluate)
+import qualified Control.DeepSeq as DeepSeq
+import Algorithm.EqSat.Egraph
+import Algorithm.SRTree.Likelihoods
+import Algorithm.SRTree.AD (ADBackEnd(..))
+import Algorithm.SRTree.AD.Unboxed (setMTPopParallel)
+import qualified Data.IntMap as IM
+import qualified Data.IntSet as IntSet
+import qualified Data.SRTree.Random as Random
+import Data.Function ( on )
+import Algorithm.SRTree.NonlinearOpt
+import Control.Monad ( when, replicateM, forM, forM_ )
+import Numeric.Optimization.NLOPT
+import Algorithm.EqSat.Info
+import Algorithm.EqSat.Build
+import Data.SRTree.Random
+import Algorithm.EqSat.Queries
+import Data.List ( maximumBy )
+import qualified Data.List as Data.List
+import qualified Data.HashMap.Strict as HashMap
+import qualified Data.Vector.Unboxed as V
+
+-- Environment of an e-graph with support to random generator and IO
+type RndEGraph a = EGraphST (StateT StdGen IO) a
+
+io :: IO a -> RndEGraph a
+io = lift . lift
+{-# INLINE io #-}
+rnd :: StateT StdGen IO a -> RndEGraph a
+rnd = lift
+{-# INLINE rnd #-}
+
+-- | Run an 'RndEGraph' action against a read-only egraph snapshot with the given
+-- generator (for concurrent workers that do not mutate the shared egraph).
+runRndEGraph :: EGraph -> StdGen -> RndEGraph a -> IO a
+runRndEGraph eg g m = do
+  ((a, _), _) <- runStateT (runStateT m eg) g
+  pure a
+{-# INLINE runRndEGraph #-}
+
+-- | Fit a batch of e-classes in parallel, then insert the results serially.
+-- Semantics mirror 'updateIfNothing' (skip already-fitted) unless 'force' is
+-- True. The shared 'StdGen' is split once; each worker gets its own generator,
+-- so the global draw sequence differs from the serial search (acceptable).
+-- While the batch runs, the MultiThread backend is switched to single-chunk so
+-- cores go to the batch rather than oversubscribing the inner per-tree split.
+fitBatch :: Bool
+         -> (Fix SRTree -> RndEGraph (Double, [Target]))
+         -> [EClassId]
+         -> RndEGraph ()
+fitBatch force fitFun ecs0 = do
+  ecs <- Prelude.mapM canonical ecs0
+  jobs <- fmap catMaybes $ forM ecs $ \ec -> do
+            mf <- getFitness ec
+            if force || mf == Nothing
+               then do tree <- getBestExpr ec
+                       pure (Just (ec, tree))
+               else pure Nothing
+  case jobs of
+    [] -> pure ()
+    _  -> do
+      nCaps <- io getNumCapabilities
+      g0 <- rnd get
+      let (seed, g1) = random g0 :: (Int, StdGen)
+          gs    = [ mkStdGen (seed + fromIntegral i) | i <- [0 .. length jobs - 1] ]
+          jobsG = [ (ec, tree, g) | ((ec, tree), g) <- zip jobs gs ]
+          chunk k xs = [ [ xs !! j | j <- [i, i + k .. length xs - 1] ] | i <- [0 .. k - 1] ]
+      rnd (put g1)
+      eg <- get
+      io (setMTPopParallel True)
+      results <- io $ fmap concat (mapConcurrently (mapM (runJob eg fitFun)) (chunk nCaps jobsG))
+      io (setMTPopParallel False)
+      forM_ results $ \(ec0, f, p) -> insertFitness ec0 f p
+  where
+    runJob :: EGraph -> (Fix SRTree -> RndEGraph (Double, [Target])) -> (EClassId, Fix SRTree, StdGen) -> IO (EClassId, Double, [Target])
+    runJob eg fit' (ec, tree, g) = do
+      (f, p) <- runRndEGraph eg g (fit' tree)
+      f' <- evaluate (DeepSeq.force f)
+      p' <- evaluate (DeepSeq.force p)
+      pure (ec, f', p')
+
+myCost :: SRTree Int -> Int
+myCost (Var _)     = 1
+myCost (Const _)   = 1
+myCost (Param _)   = 1
+myCost (Bin _ l r) = 2 + l + r
+myCost (Uni _ t)   = 3 + t
+
+while :: Monad f => (t -> Bool) -> t -> (t -> f t) -> f t
+while p arg prog = do if (p arg)
+                      then do arg' <- prog arg
+                              while p arg' prog
+                      else pure arg
+
+fitnessFun :: ADBackEnd -> Bool -> Int -> Loss -> DataSet -> DataSet -> Fix SRTree -> Target -> (Double, Target)
+fitnessFun backend skipVal nIter loss (x, y, mYErr) (x_val, y_val, mYErr_val) tree thetaOrig =
+  if isNaN val
+    then (-(1/0), theta)
+    else (val, theta)
+  where
+    nParams       = countParamsUniq tree + if loss == NLL ROXY then 3 else if loss == NLL Gaussian then 1 else 0
+    (theta, lossVal, _) = minimizeNLL' VAR1 backend loss mYErr nIter x y tree thetaOrig
+    evalF a b c   = negate $ compileLoss a (buildLoss loss (fromIntegral (V.length b)) tree) b c $ if nParams == 0 then thetaOrig else theta
+    -- at folds=1 the validation split is the training data itself, so the
+    -- train loss returned by minimizeNLL' already is the val loss; skipping
+    -- the separate compileLoss below avoids re-evaluating every expression.
+    val           = if skipVal then negate lossVal else evalF x_val y_val mYErr_val
+
+--{-# INLINE fitnessFun #-}
+
+fitnessFunRep :: ADBackEnd -> Bool -> Int -> Int -> Loss -> DataSet -> DataSet -> Fix SRTree -> RndEGraph (Double, Target)
+fitnessFunRep backend skipVal nRep nIter loss dataTrain dataVal tree = do
+    let nParams = countParamsUniq tree + if loss == NLL ROXY then 3 else if loss == NLL Gaussian then 1 else 0
+    thetaOrigs <- replicateM nRep (rnd $ randomVec nParams)
+    pure $ maximumBy (\(x, _) (y, _) -> compare x y) $ Prelude.map (fitnessFun backend skipVal nIter loss dataTrain dataVal tree) thetaOrigs
+--{-# INLINE fitnessFunRep #-}
+
+
+fitnessMV :: ADBackEnd -> Bool -> Bool -> Int -> Int -> Loss -> [(DataSet, DataSet)] -> Fix SRTree -> RndEGraph (Double, [Target])
+fitnessMV backend skipVal shouldReparam nRep nIter loss dataTrainsVals _tree = do
+  let tree = if shouldReparam then relabelParams _tree else relabelParamsOrder _tree
+  response <- forM dataTrainsVals $ \(dt, dv) -> fitnessFunRep backend skipVal nRep nIter loss dt dv tree
+  pure (minimum (Prelude.map fst response), Prelude.map snd response)
+
+
+
+
+
+-- RndEGraph utils
+-- fitFun fitnessFunRep rep iter distribution x y mYErr x_val y_val mYErr_val
+insertExpr :: Fix SRTree -> (Fix SRTree -> RndEGraph (Double, [Target])) -> RndEGraph EClassId
+insertExpr t fitFun = do
+    ecId <- fromTree myCost t >>= canonical
+    (f, p) <- fitFun t
+    insertFitness ecId f p
+    pure ecId
+  where powabs l r  = Fix (Bin PowerAbs l r)
+
+updateIfNothing fitFun ec = do
+      mf <- getFitness ec
+      case mf of
+        Nothing -> do
+          t <- getBestExpr ec
+          (f, p) <- fitFun t
+          insertFitness ec f p
+          pure True
+        Just _ -> pure False
+
+pickRndSubTree :: RndEGraph (Maybe EClassId)
+pickRndSubTree = do ecIds <- gets (IntSet.toList . _unevaluated . _eDB)
+                    if not (null ecIds)
+                      then do rndId' <- rnd $ randomFrom ecIds
+                              rndId  <- canonical rndId'
+                              constType <- (_consts . _info) <$> getEClass rndId
+                              case constType of
+                                NotConst -> pure $ Just rndId
+                                _        -> pure Nothing
+                      else pure Nothing
+
+getParetoEcsUpTo n maxSize = concat <$> forM [1..maxSize] (\i -> getTopFitEClassWithSize i n)
+getParetoDLEcsUpTo n maxSize = concat <$> forM [1..maxSize] (\i -> getTopDLEClassWithSize i n)
+
+getBestExprWithSize n =
+        do ec <- getTopFitEClassWithSize n 1 >>= traverse canonical
+           case ec of
+             (x:_) -> do bestFit <- getFitness x
+                         bestP   <- (_theta . _info) <$> getEClass x
+                         pure [(x, bestFit)]
+             []    -> pure []
+
+insertRndExpr maxSize rndTerm rndNonTerm =
+      do grow <- rnd toss
+         n <- rnd (randomFrom [if maxSize > 4 then 4 else 1 .. max 1 maxSize])
+         t <- rnd $ Random.randomTree 3 8 n rndTerm rndNonTerm grow
+         fromTree myCost t >>= canonical
+
+refit fitFun ec = do
+  t <- getBestExpr ec
+  (f, p) <- fitFun t
+  mf <- getFitness ec
+  case mf of
+    Nothing -> insertFitness ec f p
+    Just f' -> when (f > f') $ insertFitness ec f p
+
+--printBest :: (Int -> EClassId -> RndEGraph ()) -> RndEGraph ()
+printBest fitFun printExprFun = do
+      mbec <- gets (fmap snd . getGreatest . _fitRangeDB . _eDB)
+      case mbec of
+        Just bec -> do bestFit <- (_fitness . _info) <$> getEClass bec
+                       printExprFun 0 bec
+        Nothing  -> pure ()
+
+--paretoFront :: Int -> (Int -> EClassId -> RndEGraph ()) -> RndEGraph ()
+paretoFront fitFun maxSize printExprFun = go 1 0 (-(1.0/0.0))
+    where
+    go :: Int -> Int -> Double -> RndEGraph [[String]]
+    go n ix f
+        | n > maxSize = pure []
+        | otherwise   = do
+            ecList <- getBestExprWithSize n
+            case ecList of
+              ((ec, Just f'):_) -> do
+                let improved = f' >= f && (not . isNaN) f' && (not . isInfinite) f'
+                ec' <- canonical ec
+                if improved
+                  then do refit fitFun ec'
+                          t <- printExprFun ix ec'
+                          ts <- go (n+1) (ix + if improved then 1 else 0) (max f f')
+                          pure (t:ts)
+                  else go (n+1) (ix + if improved then 1 else 0) (max f f')
+              _ -> go (n+1) ix f
+
+evaluateUnevaluated fitFun = do
+          ec <- gets (IntSet.toList . _unevaluated . _eDB)
+          forM_ ec $ \c -> do
+              t <- getBestExpr c
+              (f, p) <- fitFun t
+              insertFitness c f p
+
+evaluateRndUnevaluated fitFun = do
+          ec <- gets (IntSet.toList . _unevaluated . _eDB)
+          c <- rnd . randomFrom $ ec
+          t <- getBestExpr c
+          (f, p) <- fitFun t
+          insertFitness c f p
+          pure c
+
+-- | check whether an e-node exists or does not exist in the e-graph
+doesExist, doesNotExist :: ENode -> RndEGraph Bool
+doesExist en = gets ((HashMap.member en) . _eNodeToEClass)
+doesNotExist en = gets ((not . HashMap.member en) . _eNodeToEClass)
+
+-- | check whether the partial tree defined by a list of ancestors will create
+-- a non-existent expression when combined with a certain e-node.
+doesNotExistGens :: [Maybe (EClassId -> ENode)] -> ENode -> RndEGraph Bool
+doesNotExistGens []              en = gets ((not . HashMap.member en) . _eNodeToEClass)
+doesNotExistGens (mGrand:grands) en = do  b <- gets ((not . HashMap.member en) . _eNodeToEClass)
+                                          if b
+                                            then pure True
+                                            else case mGrand of
+                                                Nothing -> pure False
+                                                Just gf -> do ec  <- gets ((HashMap.! en) . _eNodeToEClass)
+                                                              en' <- canonize (gf ec)
+                                                              doesNotExistGens grands en'
+
+-- | check whether combining a partial tree `parent` with the e-node `en'`
+-- will create a new expression
+checkToken parent en' = do  en <- canonize en'
+                            mEc <- gets (HashMap.lookup en . _eNodeToEClass)
+                            case mEc of
+                                Nothing -> pure True
+                                Just ec -> do ec' <- canonical ec
+                                              ec'' <- canonize (parent ec')
+                                              not <$> doesExist ec''
diff --git a/src/Algorithm/EqSat/Simplify.hs b/src/Algorithm/EqSat/Simplify.hs
new file mode 100644
--- /dev/null
+++ b/src/Algorithm/EqSat/Simplify.hs
@@ -0,0 +1,284 @@
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE LambdaCase #-}
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Algorithm.EqSat.Simplify
+-- Copyright   :  (c) Fabricio Olivetti 2021 - 2024
+-- License     :  BSD3
+-- Maintainer  :  fabricio.olivetti@gmail.com
+-- Stability   :  experimental
+-- Portability :
+--
+-- Module containing the algebraic rules and simplification function.
+--
+-----------------------------------------------------------------------------
+module Algorithm.EqSat.Simplify ( Rule(..), simplifyEqSatDefault, applyMergeOnlyDftl, rewrites, rewritesParams, rewriteBasic, rewritesFun, rewritesSimple, rewritesWithConstant, myCost ) where
+
+import Algorithm.EqSat (eqSat, applySingleMergeOnlyEqSat)
+import Algorithm.EqSat.Egraph
+import Algorithm.EqSat.DB
+  ( ClassOrVar,
+    Condition (Condition),
+    NChild (Ch, MapP, Rest),
+    Pattern (Fixed, Hole, NAry, VarPat),
+    Rule (..),
+    Subst,
+    SubVal (SVMap, SVOne),
+    getInt,
+  )
+import Control.Monad.State.Strict (evalState)
+import Data.IntMap.Strict (IntMap)
+import qualified Data.IntMap.Strict as IM
+import Data.Map (Map)
+import qualified Data.Map as Map
+import Data.SRTree
+
+-- | A constraint over a match's substitution: when applied to a substitution it
+-- runs in the e-graph monad and fetches e-class data through 'ClassStore', so it
+-- works on a paged (out-of-core) graph whose resident cache is bounded/empty.
+type ConstrFun = Pattern -> Condition
+
+constrainOnVal :: (Consts -> Bool) -> Pattern -> Condition
+constrainOnVal f (VarPat c) = Condition $ \subst -> do
+    let cid = getInt $ case Map.lookup (Right (fromEnum c)) subst of
+                        Nothing -> error $ "CONSTRAINVAL_MISSING var=" <> show (fromEnum c) <> " substSize=" <> show (Map.size subst)
+                        Just (SVOne v) -> v
+                        Just (SVMap _) -> error $ "CONSTRAINVAL_REST_AS_SINGLE var=" <> show (fromEnum c)
+    ec <- getEClass cid
+    pure (f (_consts . _info $ ec))
+constrainOnVal _ _ = Condition $ \_ -> pure False
+
+-- TODO: aux functions to avoid repeated pattern in constraint creation 
+--
+-- check if a matched pattern contains constant 
+isConstPt :: ConstrFun
+isConstPt = constrainOnVal $ 
+    \case
+       ConstVal _ -> True 
+       _          -> False
+
+-- check if the matched pattern is a positive constant 
+isConstPos :: ConstrFun
+isConstPos = constrainOnVal $
+    \case
+      ConstVal x -> x > 0 
+      _          -> False
+
+isNotParam :: ConstrFun
+isNotParam = constrainOnVal $
+   \case
+      ParamIx _ -> False
+      _         -> True
+
+-- check if the matched pattern is nonzero
+isNotZero :: ConstrFun
+isNotZero = constrainOnVal $
+    \case
+       ConstVal x -> abs x > 1e-9
+       _          -> True
+
+-- check if the matched pattern is even 
+isEven :: ConstrFun
+isEven = constrainOnVal $
+    \case
+       ConstVal x -> ceiling x == floor x && even (round x) 
+       _          -> True
+
+-- check if the matched pattern is integer
+isInteger :: ConstrFun
+isInteger = constrainOnVal $
+    \case
+       ConstVal x -> ceiling x == floor x
+       _          -> True
+
+-- check if the matched pattern is positive
+isPositive :: ConstrFun
+isPositive = constrainOnVal $
+    \case
+       ConstVal x -> x > 0
+       _          -> True
+
+-- check if the matched pattern is valid
+isValid :: ConstrFun
+isValid = constrainOnVal $
+    \case
+       ConstVal x -> not (isNaN x || isInfinite x)
+       _          -> True
+
+-- | e-class ids bound to a rest variable
+restEidsOf :: Char -> Subst -> [EClassId]
+restEidsOf c subst = case Map.lookup (Right (fromEnum c)) subst of
+                       Just (SVMap m) -> expandedList m
+                       _              -> []
+
+-- | every e-class bound to a rest variable holds a valid value
+allValidRest :: Char -> Condition
+allValidRest c = Condition $ \subst -> do
+    let eids = restEidsOf c subst
+        validEid eid = getEClass eid >>= \ec ->
+            pure $ case _consts . _info $ ec of
+                     ConstVal x -> not (isNaN x || isInfinite x)
+                     _          -> True
+    and <$> mapM validEid eids
+
+-- basic algebraic rules
+rewriteBasic :: [Rule]
+rewriteBasic =
+    [
+      -- B7/B8/C5: factor a common term out of a sum of products, and the
+      -- reverse (distribute), which make x*(y+z) and x*y+x*z equivalent.
+      NAry EAdd [ Ch (NAry EMul [Ch "x", Rest '1'])
+                , Ch (NAry EMul [Ch "x", Rest '2'])
+                , Rest '3' ]
+        :=>
+      NAry EAdd [ Ch (NAry EMul [ Ch "x"
+                                , Ch (NAry EAdd [Rest '1', Rest '2'])
+                                ])
+                , Rest '3' ]
+    , NAry EAdd [ Ch (NAry EMul [ Ch "x"
+                                , Ch (NAry EAdd [Rest '1'])
+                                ])
+                , Rest '2' ]
+        :=>
+      NAry EAdd [ MapP (NAry EMul [Ch "x", Ch Hole]) '1'
+                , Rest '2' ]
+    -- C5: x*y - z*x = x*(y - z)
+    , NAry EAdd [ Ch (NAry EMul [Ch "x", Rest '1'])
+                , Ch (NAry EMul [Ch (Fixed (Const (-1))), Ch "x", Ch "z"])
+                , Rest '3' ]
+        :=>
+      NAry EAdd [ Ch (NAry EMul [ Ch "x"
+                                , Ch (NAry EAdd [Rest '1', Ch (negate (VarPat 'z'))])
+                                ])
+                , Rest '3' ]
+    -- B1: group duplicate factors into a power (x*x = x^2)
+    , NAry EMul [Ch "x", Ch "x"] :=> "x" ** 2
+    -- C9: binomial expansion of a closed 2-ary square
+    , ("x" + "y") ** 2 :=> "x" ** 2 + 2 * "x" * "y" + "y" ** 2
+    -- C10: x^2 + x*y + ... = x*(x + y) + ...
+    , NAry EAdd [ Ch (Fixed (Bin Power (VarPat 'x') (Fixed (Const 2))))
+                , Ch (NAry EMul [Ch "x", Rest '1'])
+                , Rest '2' ]
+        :=>
+      NAry EAdd [ Ch (NAry EMul [ Ch "x"
+                                , Ch (NAry EAdd [Ch "x", Rest '1'])
+                                ])
+                , Rest '2' ]
+    ]
+
+-- rules for nonlinear functions 
+rewritesFun :: [Rule]
+rewritesFun =
+    [
+      log (exp "x")  :=> "x"
+    -- C11: log(x*y*z*...) = log x + log y + ...
+    , log (NAry EMul [Rest '1']) :=> NAry EAdd [MapP (Fixed (Uni Log Hole)) '1']
+    , log ("x" ** "y") :=> "y" * log "x"
+    , log (powabs "x" "y") :=> "y" * log (abs "x")
+    -- C12: abs(x*y*z*...) = abs x * abs y * ...
+    , abs (NAry EMul [Rest '1']) :=> NAry EMul [MapP (Fixed (Uni Abs Hole)) '1']
+    , abs ("x" ** "y") :=> abs "x" ** "y"
+    , recip (recip "x") :=> "x" :| isNotZero "x"
+    -- C13: (x*y*z*...)^w = x^w * y^w * ...   [was disabled: combinatorial blowup on (x*x)^t; the multiset matcher + matchCap bound that]
+    , (NAry EMul [Rest '1']) ** "z" :=> NAry EMul [MapP (Hole ** VarPat 'z') '1']
+    , abs "x" ** "y" :=> "x" ** "y" :| isEven "y"
+    -- C14: sqrt(x*x) = abs x
+    , sqrt (NAry EMul [Ch "x", Ch "x"]) :=> abs "x"
+    ]
+
+-- Rules that reduces redundant parameters
+constReduction :: [Rule]
+constReduction =
+    [
+      -- B3: 0 + rest = rest
+      NAry EAdd [Ch (Fixed (Const 0)), Rest '1'] :=> NAry EAdd [Rest '1']
+    , "x" ** 1 :=> "x"
+    , powabs "x" 1 :=> abs "x"
+
+    -- B9: x^y * x^z = x^(y+z)
+    , NAry EMul [Ch (Fixed (Bin Power (VarPat 'x') (VarPat 'y'))), Ch (Fixed (Bin Power (VarPat 'x') (VarPat 'z')))]
+        :==:
+      Fixed (Bin Power (VarPat 'x') (NAry EAdd [Ch (VarPat 'y'), Ch (VarPat 'z')]))
+        :| isPositive "x"
+    -- B10: |x|^y * |x|^z = |x|^(y+z)  (fixed: target used "y+x" instead of "y+z")
+    , NAry EMul [Ch (Fixed (Bin PowerAbs (VarPat 'x') (VarPat 'y'))), Ch (Fixed (Bin PowerAbs (VarPat 'x') (VarPat 'z')))]
+        :=>
+      Fixed (Bin PowerAbs (VarPat 'x') (NAry EAdd [Ch (VarPat 'y'), Ch (VarPat 'z')]))
+    -- B11: (x^y)^z = x^(y*z)
+    , Fixed (Bin Power (Fixed (Bin Power (VarPat 'x') (VarPat 'y'))) (VarPat 'z'))
+        :==:
+      Fixed (Bin Power (VarPat 'x') (NAry EMul [Ch (VarPat 'y'), Ch (VarPat 'z')]))
+        :| isPositive "x"
+    , powabs (powabs "x" "y") "z" :=> powabs "x" ("y" * "z")
+    ]
+
+rewritesWithConstant :: [Rule]
+rewritesWithConstant =
+    [
+      "x" - "x" :=> 0
+    , "x" / "x" :=> 1 :| isNotZero "x"
+    , "x" ** "y" * "x" :=> "x" ** ("y" + 1) :| isPositive "x"
+    , 1 ** "x" :=> 1
+    , powabs 1 "x" :=> 1
+    , log (sqrt "x") :=> 0.5 * log "x" :| isNotParam "x"
+    , "x" ** (1/2)   :==: sqrt "x"
+    , powabs "x" (1/2) :=> sqrt (abs "x")
+    , "x" ** (1/3) :==: Fixed (Uni Cbrt "x")
+    -- B4: 0 * rest = 0 (provided every factor is valid)
+    , NAry EMul [Ch (Fixed (Const 0)), Rest '1'] :=> 0 :| allValidRest '1'
+    , 0 ** "x" :=> 0 :| isPositive "x"
+    , powabs 0 "x" :=> 0
+    -- n-ary cancellation: x + y - x = y
+    , NAry EAdd [ Ch "a"
+                , Ch (NAry EMul [ Ch (Fixed (Const (-1.0))), Ch "a" ])
+                , Rest 'r' ]
+        :=> NAry EAdd [Rest 'r']
+    -- combining like terms: x + x = 2*x
+    , NAry EAdd [ Ch "a", Ch "a", Rest 'r' ]
+        :=> NAry EAdd [ Ch (2 * "a"), Rest 'r' ]
+    ]
+rewritesWithParam :: [Rule]
+rewritesWithParam =
+    [
+      "x" - "x" :=> Fixed (Param 0)
+    , "x" / "x" :=> Fixed (Param 0) :| isNotZero "x"
+    , 1 ** "x" :=> Fixed (Param 0)
+    , powabs 1 "x" :=> Fixed (Param 0)
+    ]
+
+rewritesSimple :: [Rule]
+rewritesSimple = rewriteBasic <> constReduction <> rewritesFun
+powabs l r = Fixed (Bin PowerAbs l r)
+
+-- | default cost function for simplification
+-- TODO:
+-- num_params:
+--   length:
+--      terminal < nonterminal:
+--        symbol comparison (constants, parameters, variables x0, x10, x2)
+--          op priorities (+, -, *, inv_div, pow, abs, exp, log, log10, sqrt)
+--            univariates
+myCost :: SRTree Int -> Int
+myCost (Var _)      = 1
+myCost (Const _)    = 3
+myCost (Param _)    = 3
+myCost (Bin op l r) = 2 + l + r
+myCost (Uni _ t)    = 3 + t
+
+-- all rewrite rules
+rewrites :: [Rule]
+rewrites = rewriteBasic <> constReduction <> rewritesFun <> rewritesWithConstant
+rewritesParams :: [Rule]
+rewritesParams = rewriteBasic <> constReduction <> rewritesFun <> rewritesWithParam
+
+-- | simplify using the default parameters
+simplifyEqSatDefault :: Fix SRTree -> Fix SRTree
+simplifyEqSatDefault t = eqSat t rewrites myCost 30 `evalState` emptyGraphNoTrack
+
+-- | simplifies with custom parameters
+simplifyEqSat :: [Rule] -> CostFun -> Int -> Fix SRTree -> Fix SRTree
+simplifyEqSat rwrts costFun it t = eqSat t rwrts costFun it `evalState` emptyGraph
+
+-- | apply a single step of merge-only using default rules
+applyMergeOnlyDftl :: ClassStore m => CostFun -> EGraphST m ()
+applyMergeOnlyDftl costFun = applySingleMergeOnlyEqSat costFun rewrites
diff --git a/src/Algorithm/EqSat/Store.hs b/src/Algorithm/EqSat/Store.hs
new file mode 100644
--- /dev/null
+++ b/src/Algorithm/EqSat/Store.hs
@@ -0,0 +1,243 @@
+{-# LANGUAGE TupleSections #-}
+{-# LANGUAGE DeriveGeneric #-}
+{-# LANGUAGE DeriveDataTypeable #-}
+
+module Algorithm.EqSat.Store
+  ( GraphRows(..)
+  , EClassRow(..)
+  , exportEGraph
+  , importEGraph
+  , mergeEGraph
+  , rebuildDBs
+  ) where
+
+import Control.Lens ( over )
+import Control.Monad ( forM, forM_, foldM )
+import Control.Monad.Identity ( Identity, runIdentity )
+import Control.Monad.State.Strict ( StateT, execStateT, modify', gets )
+import GHC.Generics ( Generic )
+import GHC.Stack ( HasCallStack )
+
+import qualified Data.HashMap.Strict as HashMap
+import Data.HashMap.Strict ( HashMap )
+import qualified Data.HashSet as Set
+import qualified Data.IntMap.Strict as IntMap
+import Data.IntMap.Strict ( IntMap )
+import qualified Data.IntSet as IntSet
+import qualified Data.Set as RangeSet
+import Data.List ( sortOn )
+
+import Data.SRTree
+import Algorithm.EqSat.Egraph
+import Algorithm.EqSat.Build
+
+-- | Row representation of the core (structural) state of an e-graph,
+-- normalized for external storage (e.g. a relational DB).
+data GraphRows = GraphRows
+  { _grCanonical     :: IntMap EClassId                    -- ^ eid -> canonical representative (self-loop for roots)
+  , _grENodeToEClass :: HashMap ENode EClassId             -- ^ canonical e-node -> its e-class
+  , _grEClasses      :: IntMap EClassRow                   -- ^ canonical e-class id -> data row
+  , _grNextId        :: Int                                -- ^ next free e-class id
+  , _grTrackDBs      :: Bool                               -- ^ whether range DBs are maintained
+  } deriving (Show, Eq, Generic)
+
+-- | Per-e-class data row.
+data EClassRow = EClassRow
+  { _rcNodes   :: Set.HashSet ENode
+  , _rcParents :: Set.HashSet (EClassId, ENode)
+  , _rcHeight  :: Int
+  , _rcInfo    :: EClassData
+  } deriving (Show, Eq, Generic)
+
+-- | Export the core structural state of an e-graph into a normalised row format.
+exportEGraph :: EGraph -> GraphRows
+exportEGraph eg = GraphRows
+  { _grCanonical     = _canonicalMap eg
+  , _grENodeToEClass = _eNodeToEClass eg
+  , _grEClasses      = IntMap.map toRow (_eClass eg)
+  , _grNextId        = _nextId (_eDB eg)
+  , _grTrackDBs      = _trackDBs (_eDB eg)
+  }
+  where
+    toRow ec = EClassRow (_eNodes ec) (_parents ec) (_height ec) (_info ec)
+
+-- | Reconstruct an e-graph from normalised rows, rebuilding all derived indexes.
+--
+-- Real e-graphs may carry stale @_eNodeToEClass@ entries left behind by
+-- merges (a node pointing at a class whose canonical representative is
+-- another class). Such entries are canonicalized at import: node -> class
+-- values are routed through the canonical map and any non-root class rows
+-- are dropped. Parent pointers are recomputed from the canonicalized node
+-- map so they never reference dead classes.
+importEGraph :: GraphRows -> Either String EGraph
+importEGraph rows
+  | not (validate rows) = Left (validationMsg rows)
+  | otherwise           = Right (runIdentity $ execStateT rebuildDBs (buildCore (canonicalize rows)))
+
+-- | Normalize stale rows: route node->class values through the canonical map
+-- and drop non-root class rows.
+--
+-- Parent pointers come from the stored @_rcParents@ when a class has any
+-- (e.g. after a storage-layer round-trip through the @parent@ table); parent
+-- class ids are routed through the canonical map so they never reference dead
+-- classes. Classes without stored parents (legacy rows, hand-built rows) fall
+-- back to recomputing parents from the canonicalized node map.
+canonicalize :: GraphRows -> GraphRows
+canonicalize rows =
+  let canon    = _grCanonical rows
+      rep eid  = IntMap.findWithDefault eid eid canon
+      nodeMap' = HashMap.map rep (_grENodeToEClass rows)
+      classes' = IntMap.filterWithKey
+                   (\eid _ -> IntMap.lookup eid canon == Just eid)
+                   (_grEClasses rows)
+      parents' = IntMap.fromListWith Set.union
+        [ (c, Set.singleton (eid, en))
+        | (en, eid) <- HashMap.toList nodeMap'
+        , c <- eChildren en ]
+      stored'  = IntMap.mapWithKey
+                   (\_ r -> Set.map (\(pEid, pEn) -> (rep pEid, pEn)) (_rcParents r))
+                   classes'
+      fixRow eid r =
+        let stored = IntMap.findWithDefault Set.empty eid stored'
+        in r { _rcParents = if Set.null stored
+                              then IntMap.findWithDefault Set.empty eid parents'
+                              else stored }
+  in rows { _grENodeToEClass = nodeMap'
+          , _grEClasses      = IntMap.mapWithKey fixRow classes' }
+
+buildCore :: GraphRows -> EGraph
+buildCore rows = EGraph
+  { _canonicalMap     = _grCanonical rows
+  , _eNodeToEClass    = _grENodeToEClass rows
+  , _eClass           = IntMap.mapWithKey mkEClass (_grEClasses rows)
+  , _eDB              = (emptyDB){ _nextId = _grNextId rows, _trackDBs = _grTrackDBs rows }
+  , _classStore       = Nothing
+  }
+  where
+    mkEClass eid r = EClass eid (_rcNodes r) (_rcParents r) (_rcHeight r) (_rcInfo r)
+
+rebuildDBs :: EGraphST Identity ()
+rebuildDBs = do
+  -- Rebuild the pattern database from the canonical e-node -> class mapping
+  nodes <- gets _eNodeToEClass
+  forM_ (HashMap.toList nodes) $ \(en, eid) -> addToDB en eid
+
+  -- Rebuild range/size indexes from class info
+  classes <- gets _eClass
+  forM_ (IntMap.toList classes) $ \(eid, ec) -> do
+    let info = _info ec
+        sz   = _size info
+        fit  = _fitness info
+        dl   = _dl info
+    modify' $ over (eDB . sizeDB) (IntMap.insertWith IntSet.union sz (IntSet.singleton eid))
+    case fit of
+      Nothing -> modify' $ over (eDB . unevaluated) (IntSet.insert eid)
+      Just fn -> modify' $ over (eDB . fitRangeDB) (insertRange eid fn)
+                        . over (eDB . sizeFitDB) (IntMap.insertWith RangeSet.union sz (RangeSet.singleton (fn, eid)))
+    case dl of
+      Nothing -> pure ()
+      Just dn -> modify' $ over (eDB . dlRangeDB) (insertRange eid dn)
+                        . over (eDB . sizeDLDB) (IntMap.insertWith RangeSet.union sz (RangeSet.singleton (dn, eid)))
+
+-- | Validate that the exported rows form a consistent graph.
+--
+-- All referenced ids must be present in the canonical map. Node -> class
+-- values and class rows may reference classes that are not their own
+-- canonical representative (stale entries left behind by merges); those are
+-- repaired by 'canonicalize' during import.
+validate :: GraphRows -> Bool
+validate rows =
+  let canon      = _grCanonical rows
+      classes    = _grEClasses rows
+      nodeIds    = HashMap.keys (_grENodeToEClass rows)
+      extraIds   = IntMap.keys classes
+                   ++ HashMap.elems (_grENodeToEClass rows)
+                   ++ concatMap eChildren nodeIds
+      inCanon    = all (`IntMap.member` canon) extraIds
+      nextOk     = _grNextId rows >= 0
+  in inCanon && nextOk
+
+validationMsg :: GraphRows -> String
+validationMsg rows
+  | not inCanon = "some e-node/e-class id is not present in the canonical map"
+  | not nextOk  = "next id is negative"
+  | otherwise   = "invalid GraphRows"
+  where
+    canon      = _grCanonical rows
+    classes    = _grEClasses rows
+    nodeIds    = HashMap.keys (_grENodeToEClass rows)
+    extraIds   = IntMap.keys classes
+                 ++ HashMap.elems (_grENodeToEClass rows)
+                 ++ concatMap eChildren nodeIds
+    inCanon    = all (`IntMap.member` canon) extraIds
+    nextOk     = _grNextId rows >= 0
+
+-- | Return canonical e-class ids ordered children-before-parents (ascending height).
+classOrder :: GraphRows -> Either String [EClassId]
+classOrder rows =
+  Right $ map fst $ sortOn (_rcHeight . snd) $ IntMap.toAscList (_grEClasses rows)
+
+-- | Remap a B-e-graph's e-node into A's id-space using the correspondence map.
+remapNode
+  :: GraphRows               -- ^ rows of graph B (source)
+  -> IntMap EClassId         -- ^ corr: B canonical id -> A id
+  -> ENode
+  -> Either String ENode
+remapNode rowsB corr = go
+  where
+    canonB :: EClassId -> EClassId
+    canonB cid = IntMap.findWithDefault cid cid (_grCanonical rowsB)
+
+    toA :: EClassId -> Either String EClassId
+    toA cid =
+      case IntMap.lookup (canonB cid) corr of
+        Just eidA -> Right eidA
+        Nothing   -> Left ("child " <> show cid <> " of graph B not yet merged")
+
+    go (EVar ix)     = Right (EVar ix)
+    go (EParam ix)   = Right (EParam ix)
+    go (EConst x)    = Right (EConst x)
+    go (EUni f t)    = EUni f <$> toA t
+    go (EBin op l r) = EBin op <$> toA l <*> toA r
+    go (ENAry op m)  = do
+      m' <- foldM step IntMap.empty (IntMap.toList m)
+      Right (ENAry op m')
+      where
+        step acc (cid, n) = do
+          cidA <- toA cid
+          pure (IntMap.insertWith (+) cidA n acc)
+
+-- | Merge class ids by unioning their e-classes under the given cost function.
+mergeClass :: HasCallStack => CostFun -> EClassId -> EClassId -> EGraphST Identity EClassId
+mergeClass costFun x y =
+  if x == y then pure x else merge costFun x y
+
+-- | Structurally merge graph @b@ into a copy of graph @a@.
+--
+-- The e-nodes of @b@ are canonicalized under @a@'s id space, deduplicated
+-- against @a@'s existing content, and equivalent classes are unioned. Cost and
+-- best of newly introduced content are computed with @costFun@ (i.e. merging
+-- adopts @a@'s cost function). Dataset-specific values (fitness/DL/theta) are
+-- NOT transferred: they are per-dataset data managed by the storage layer.
+mergeEGraph :: HasCallStack => CostFun -> EGraph -> EGraph -> Either String EGraph
+mergeEGraph costFun a b =
+  let rowsB = exportEGraph b
+  in case classOrder rowsB of
+       Left err -> Left err
+       Right order -> Right (runIdentity $ execStateT (step IntMap.empty order) a)
+  where
+    step :: IntMap EClassId -> [EClassId] -> EGraphST Identity ()
+    step _ [] = rebuild costFun
+    step corr (bCanon : rest) = do
+      let ec = _grEClasses rowsB IntMap.! bCanon
+      resolved <- forM (Set.toList (_rcNodes ec)) $ \en ->
+        case remapNode rowsB corr en of
+          Left err  -> pure (Left err)
+          Right enA -> Right <$> add costFun enA
+      case sequence resolved of
+        Left err  -> error ("mergeEGraph: " <> err)  -- pre-validated
+        Right []  -> step corr rest
+        Right (x : xs) -> do
+          rep <- foldM (mergeClass costFun) x xs
+          step (IntMap.insert bCanon rep corr) rest
+    rowsB = exportEGraph b
diff --git a/src/Algorithm/SRTree/AD.hs b/src/Algorithm/SRTree/AD.hs
new file mode 100644
--- /dev/null
+++ b/src/Algorithm/SRTree/AD.hs
@@ -0,0 +1,32 @@
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Data.SRTree.AD 
+-- Copyright   :  (c) Fabricio Olivetti 2021 - 2024
+-- License     :  BSD3
+-- Maintainer  :  fabricio.olivetti@gmail.com
+-- Stability   :  experimental
+-- Portability :  FlexibleInstances, DeriveFunctor, ScopedTypeVariables
+--
+-- Automatic Differentiation for Expression trees
+--
+-----------------------------------------------------------------------------
+
+module Algorithm.SRTree.AD
+         ( compileFunAndGrad
+         , ADBackEnd(..)
+         ) where
+
+import qualified Data.Vector.Unboxed  as VU
+import qualified Data.Vector.Storable as V
+import Data.SRTree
+import Algorithm.SRTree.AD.Unboxed
+
+data ADBackEnd = SingleThread | MultiThread deriving (Read, Show)
+
+compileFunAndGrad :: ADBackEnd -> [VU.Vector Double] -> VU.Vector Double -> Maybe (VU.Vector Double) -> Fix SRTree -> V.Vector Double -> (Double, V.Vector Double)
+compileFunAndGrad SingleThread xss ys mYerr tree =
+    let ct = compileTree xss ys mYerr tree
+    in \theta -> evalGradVec ct theta
+compileFunAndGrad MultiThread xss ys mYerr tree =
+    let cts = compileTreeMulti xss ys mYerr tree
+    in \theta -> evalGradMulti cts theta
diff --git a/src/Algorithm/SRTree/AD/CompiledAD.hs b/src/Algorithm/SRTree/AD/CompiledAD.hs
new file mode 100644
--- /dev/null
+++ b/src/Algorithm/SRTree/AD/CompiledAD.hs
@@ -0,0 +1,39 @@
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Data.SRTree.AD.CompiledAD
+-- Copyright   :  (c) Fabricio Olivetti 2021 - 2024
+-- License     :  BSD3
+-- Maintainer  :  fabricio.olivetti@gmail.com
+-- Stability   :  experimental
+-- Portability :  FlexibleInstances, DeriveFunctor, ScopedTypeVariables
+--
+-- Automatic Differentiation for Expression trees
+--
+-----------------------------------------------------------------------------
+
+module Algorithm.SRTree.AD.CompiledAD
+         ( CompiledTree(..)
+         ) where
+
+import Data.SRTree.Internal
+import qualified Data.Vector.Unboxed          as VU
+import qualified Data.Vector as VB
+
+-- ---------------------------------------------------------------------
+-- Public entry point -- same signature/behaviour as before.
+-- ---------------------------------------------------------------------
+data CompiledTree = CompiledTree
+  { ctNodes  :: !(VB.Vector (SRTree Int))            -- id -> node, children already resolved to ids
+  , ctRoot   :: !Int
+  , ctDyn    :: !(VU.Vector Bool)                    -- id -> depends on theta?
+  , ctStatic :: VU.Vector Double                     -- flat [staticSlot * m + row]; only static nodes
+  , ctStaticBase :: !(VU.Vector Int)                 -- id -> staticSlot * m (0 for dynamic ids and Var leaves)
+  , ctM      :: !Int
+  , ctNPred  :: !Int                                 -- root + 1 (stride for flat static)
+  , ctKind   :: !(VU.Vector Int)                     -- id -> node kind: 0 Var, 1 Param, 2 Const, 3 Uni, 4 Bin
+  , ctArg    :: !(VU.Vector Int)                     -- id -> Param: param ix; Var: var ix (-1 = y, -2 = yErr); Uni: child id; Bin: left id
+  , ctArg2   :: !(VU.Vector Int)                     -- id -> Bin: right id; else 0
+  , ctFcode  :: !(VU.Vector Int)                     -- id -> Uni: fromEnum Function
+  , ctOcode  :: !(VU.Vector Int)                     -- id -> Bin: fromEnum Op
+  , ctVars   :: !(VB.Vector (VU.Vector Double))      -- leaf source columns xss ++ [y, yErr] (referenced, not copied)
+  }
diff --git a/src/Algorithm/SRTree/AD/Unboxed.hs b/src/Algorithm/SRTree/AD/Unboxed.hs
new file mode 100644
--- /dev/null
+++ b/src/Algorithm/SRTree/AD/Unboxed.hs
@@ -0,0 +1,965 @@
+{-# language FlexibleInstances, DeriveFunctor #-}
+{-# language ScopedTypeVariables #-}
+{-# language RankNTypes #-}
+{-# language ViewPatterns #-}
+{-# language FlexibleContexts #-}
+{-# language BangPatterns #-}
+{-# language TypeApplications #-}
+{-# language MultiWayIf #-}
+{-# LANGUAGE LambdaCase #-}
+
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Data.SRTree.AD 
+-- Copyright   :  (c) Fabricio Olivetti 2021 - 2024
+-- License     :  BSD3
+-- Maintainer  :  fabricio.olivetti@gmail.com
+-- Stability   :  experimental
+-- Portability :  FlexibleInstances, DeriveFunctor, ScopedTypeVariables
+--
+-- Automatic Differentiation for Expression trees
+--
+-----------------------------------------------------------------------------
+
+module Algorithm.SRTree.AD.Unboxed
+         ( compileTree
+         , compileTreeMulti
+         , evalGradMulti
+         , evalGrad
+         , evalGradVec
+         , evalLossVec
+         , CompiledTree(..)
+         , setMTPopParallel
+         ) where
+
+import Control.Monad (forM_, foldM, when, unless)
+import Control.Monad.ST
+import Data.STRef (newSTRef, readSTRef, modifySTRef')
+import Data.Bifunctor (bimap, first, second)
+import Data.SRTree.Derivative ( derivative )
+import Data.SRTree.Eval
+    ( Target, Theta, Columns, evalFun, evalOp, replicateAs )
+import Data.SRTree.Internal
+import Data.SRTree.Print (showExpr)
+import Data.SRTree.Recursion ( cataM, cata, accu )
+import qualified Data.Vector.Storable as V
+import qualified Data.Vector.Storable.Mutable as VM
+import qualified Data.Vector.Unboxed          as VU
+import qualified Data.Vector.Unboxed.Mutable  as VUM
+import qualified Data.Vector as VB
+import qualified Data.Vector.Mutable as VMB
+import Debug.Trace (trace, traceShow)
+import qualified Data.IntMap.Strict as IntMap
+import Data.List ( foldl', foldl1' )
+import Data.Maybe (isJust, fromMaybe)
+
+import Control.Monad.State.Strict
+import Control.Monad.Identity
+
+
+import Data.List (transpose)
+import System.IO.Unsafe (unsafePerformIO)
+import Control.Concurrent (getNumCapabilities)
+import Control.Concurrent.Async (forConcurrently)
+import Control.Exception (evaluate)
+import Data.IORef (IORef, newIORef, writeIORef, readIORef)
+
+import qualified Data.Map.Strict as Map
+import Algorithm.SRTree.AD.CompiledAD
+
+compileTree :: [VU.Vector Double] -> VU.Vector Double -> Maybe (VU.Vector Double) -> Fix SRTree -> CompiledTree
+compileTree xss ys mYErr tree =
+    CompiledTree { ctNodes = nodes, ctRoot = root, ctDyn = dynArr, ctStatic = staticArr, ctStaticBase = staticBaseArr, ctM = m, ctNPred = root + 1
+                 , ctKind = kindArr, ctArg = argArr, ctArg2 = arg2Arr, ctFcode = fcodeArr, ctOcode = ocodeArr, ctVars = vars }
+  where
+    -- yErr is only defined when mYErr is present (a tree referencing Var -2
+    -- always pairs with mYErr = Just e, see the likelihood loss wrappers). The
+    -- ctVars list must stay well-defined for every column even when mYErr is
+    -- Nothing -- the Accelerate leaf array concatenates the whole list -- so a
+    -- missing yErr is represented by a zero column rather than the bottom
+    -- `fromJust mYErr` (which the old static-array copy path could keep lazy).
+    yErr = case mYErr of
+             Just e  -> e
+             Nothing -> VU.replicate m 0
+    m    = VU.length ys
+    -- Leaf source columns, referenced (never copied per tree): a static Var
+    -- leaf reads feature column ix (arg), y (arg = -1), or yErr (arg = -2)
+    -- straight from these run-fixed vectors instead of a materialized copy in
+    -- staticArr. ctVars ix = xss !! ix, ctVars nFeats = y, ctVars (nFeats+1)
+    -- = yErr.
+    vars   = VB.fromList (xss <> [ys, yErr])
+    nFeats = VB.length vars - 2
+
+    -- Rewrite x ** 2.0 into the unary Square kernel (x*x, fcode 17):
+    -- the loss wrap ((tree - y) ** 2) / m is the single hottest subgraph in
+    -- every NLopt call, and replacing the per-element pow with a multiply
+    -- avoids the slow ** (x**2.0 == x*x exactly, and the derivative 2x
+    -- matches), so no numerical semantics change.
+    tree' = rewritePowSq tree
+
+    -- state: (structural CSE map, id -> node, id -> isDynamic, counter)
+    (_, int2key, dynMap, (subtract 1) -> root) =
+        cataM leftToRight alg tree'
+          `execState` (Map.empty, IntMap.empty, IntMap.empty, 0)
+
+    nodes     = VB.fromList (IntMap.elems int2key)
+    dynArr    = VU.fromList (IntMap.elems dynMap)
+    stride    = root + 1
+    -- static nodes in ascending (topological) id order, so a single bottom-up
+    -- sweep fills every column before its parent. Dynamic nodes are omitted
+    -- entirely, and so are Var leaves (their values are read directly from the
+    -- run-fixed `vars` columns, see the eval kernels): their static slots were
+    -- zeros that evalGrad*/forwardPassRange never read, so the flat array
+    -- shrinks from stride * m to #static * m (a handful of feature/const
+    -- columns per tree instead of all nodes).
+    staticKeys = [k | k <- [0 .. root], not (VU.unsafeIndex dynArr k), not (isVarLeaf k)]
+    nStatic    = length staticKeys
+    isVarLeaf k = case VB.unsafeIndex nodes k of { Var _ -> True; _ -> False }
+    -- id -> static slot base (slot * m); 0 for dynamic ids (never read)
+    staticBaseArr = VU.create $ do
+        arr <- VUM.replicate (root + 1) 0
+        forM_ (zip staticKeys [0 ..]) $ \(k, slot) ->
+            VUM.write arr k (slot * m)
+        pure arr
+    -- flat [slot * m + row]; computed in a single bottom-up sweep over the
+    -- static ids (a child always gets a smaller id than its parent, since
+    -- cataM assigns the id only after both children are built), writing each
+    -- static node's column directly into the flat array. This fuses the old
+    -- per-node VU.map/VU.zipWith intermediates into the array.
+    staticArr = VU.create $ do
+        arr <- VUM.replicate (nStatic * m) 0
+        let slice slot = VUM.slice (slot * m) m arr
+            slotOf k   = VU.unsafeIndex staticBaseArr k `div` m
+            -- Resolve a static child @c@ to its source column ONCE per
+            -- column (hoisted out of the row loop): Var leaves are not
+            -- materialized in staticArr, so their column is the run-fixed
+            -- `vars` vector; every other static node is a column already
+            -- written into the (mutable) arr (children always have smaller
+            -- ids). `Left` = pure vector (Var leaf), `Right` = mutable slice.
+            staticSrc c
+              | isVarLeaf c = Left (VB.unsafeIndex vars (leafSrcIdx nFeats (VU.unsafeIndex argArr c)))
+              | otherwise   = Right (slice (slotOf c))
+            -- Read row @i from a hoisted source (see staticSrc). Called per
+            -- element, but the Left/Right tag is fixed per column, so GHC
+            -- keeps the dispatch cheap and no slice/leaf lookup is repeated.
+            readSrc s i = case s of
+                Left v  -> pure (VU.unsafeIndex v i)
+                Right m -> VUM.unsafeRead m i
+            mapStatic f t k = go 0
+              where
+                dst = slice (slotOf k)
+                src = staticSrc t
+                go !i | i >= m    = pure ()
+                      | otherwise = do
+                          x <- readSrc src i
+                          VUM.unsafeWrite dst i (evalFun f x)
+                          go (i + 1)
+            zipStatic op l r k = go 0
+              where
+                dst = slice (slotOf k)
+                srcL = staticSrc l
+                srcR = staticSrc r
+                go !i | i >= m    = pure ()
+                      | otherwise = do
+                          xl <- readSrc srcL i
+                          xr <- readSrc srcR i
+                          VUM.unsafeWrite dst i (evalOp op xl xr)
+                          go (i + 1)
+        forM_ (zip staticKeys [0 ..]) $ \(k, slot) ->
+            case VB.unsafeIndex nodes k of
+                -- Var leaves are excluded from staticKeys (their columns live
+                -- in `vars`), so they never reach this sweep.
+                Const v    -> VUM.set (slice slot) v
+                Uni f t    -> mapStatic f t k
+                Bin op l r -> zipStatic op l r k
+                Param _    -> pure ()
+                Var _      -> pure ()
+        pure arr
+
+    -- compact unboxed per-id code arrays (length root+1) so the hot row loop
+    -- never touches the boxed `nodes` vector nor dispatches through the
+    -- function-returning evalOp/evalFun
+    kindArr  = VU.generate (root + 1) $ \k -> case int2key IntMap.! k of
+        Var _     -> 0
+        Param _   -> 1
+        Const _   -> 2
+        Uni _ _   -> 3
+        Bin _ _ _ -> 4
+    argArr   = VU.generate (root + 1) $ \k -> case int2key IntMap.! k of
+        Var ix    -> ix
+        Param ix  -> ix
+        Uni _ t   -> t
+        Bin _ l _ -> l
+        Const _   -> 0
+    arg2Arr  = VU.generate (root + 1) $ \k -> case int2key IntMap.! k of
+        Bin _ _ r -> r
+        _         -> 0
+    fcodeArr = VU.generate (root + 1) $ \k -> case int2key IntMap.! k of
+        Uni f _   -> fromEnum f
+        _         -> 0
+    ocodeArr = VU.generate (root + 1) $ \k -> case int2key IntMap.! k of
+        Bin op _ _ -> fromEnum op
+        _          -> 0
+
+    leftToRight (Uni f mt)    = Uni f <$> mt
+    leftToRight (Bin f ml mr) = Bin f <$> ml <*> mr
+    leftToRight (Var ix)      = pure (Var ix)
+    leftToRight (Param ix)    = pure (Param ix)
+    leftToRight (Const c)     = pure (Const c)
+
+    alg = insertKey
+
+    graph      (a, _, _, _) = a
+    isDynSt  k (_, _, d, _) = d IntMap.! k
+
+    insEntry key isD (a, b, d, c) =
+        ( Map.insert key c a
+        , IntMap.insert c key b
+        , IntMap.insert c isD d
+        , c + 1 )
+
+    -- a node depends on theta iff it IS a Param, or any child does
+    nodeIsDynamic (Param _)   = pure True
+    nodeIsDynamic (Var _)     = pure False
+    nodeIsDynamic (Const _)   = pure False
+    nodeIsDynamic (Uni _ t)   = gets (isDynSt t)
+    nodeIsDynamic (Bin _ l r) = (||) <$> gets (isDynSt l) <*> gets (isDynSt r)
+
+    -- Data.Map is unreliable with NaN-valued keys (Ord Double is not a valid
+    -- total order for NaN: insert(Const NaN) then member/lookup can disagree),
+    -- and eqsat constant folding can yield Const NaN nodes. So do a single
+    -- direct lookup; on a miss, return the fresh id that insEntry assigns
+    -- instead of looking the key back up. Repeated NaN nodes simply get
+    -- separate ids (no CSE), which is harmless since their static value is
+    -- recomputed identically.
+    insertKey key = do
+        cached <- gets (Map.lookup key . graph)
+        case cached of
+          Just v  -> pure v
+          Nothing -> do
+            d  <- nodeIsDynamic key
+            fresh <- state $ \st@(_, _, _, c) -> let st' = insEntry key d st in (c, st')
+            pure fresh
+
+-- Rewrite (a) Bin Power t (Const 2.0) into the unary Square kernel and
+-- (b) Bin Div t (Const c) into Bin Mul t (Const (1/c)). Both are exact at
+-- the Double level (x ** 2.0 == x * x; x / c == x * (1/c) up to one ulp)
+-- and replace the slow per-element pow()/div with a multiply. The loss
+-- wrap ((tree - y) ** 2) / m appears in every NLopt objective/gradient
+-- call, so these two rewrites are worth a measurable fraction of the AD
+-- time.
+rewritePowSq :: Fix SRTree -> Fix SRTree
+rewritePowSq = cata alg
+  where
+    alg :: SRTree (Fix SRTree) -> Fix SRTree
+    alg (Bin Power t (Fix (Const 2.0))) = Fix (Uni Square t)
+    alg (Bin Div t (Fix (Const c)))     | c /= 0 = Fix (Bin Mul t (Fix (Const (recip c))))
+    alg n                                = Fix n
+
+-- ---------------------------------------------------------------------
+-- Static-child source resolution. A static Var leaf is NOT materialized
+-- into ctStatic anymore: its value column lives in ctVars (= xss ++ [y,
+-- yErr]) and is read directly at the absolute row (base 0, so the chunk
+-- start s0 positions the read). Every other static node is a computed
+-- column inside ctStatic at ctStaticBase k.
+-- ---------------------------------------------------------------------
+
+-- | Map a Var leaf's arg (feature ix, or -1 = y, -2 = yErr) to an index
+-- into ctVars = xss ++ [y, yErr].
+leafSrcIdx :: Int -> Int -> Int
+leafSrcIdx nFeats a | a >= 0   = a
+                    | a == -1  = nFeats
+                    | otherwise = nFeats + 1
+{-# INLINE leafSrcIdx #-}
+
+-- | Resolve the (source vector, base) of a static child node @k@, where the
+-- row value is read at @src (base + i)@.
+resolveStatic :: VU.Vector Double
+              -> VB.Vector (VU.Vector Double)
+              -> VU.Vector Int
+              -> VU.Vector Int
+              -> VU.Vector Int
+              -> Int -> Int -> Int
+              -> (VU.Vector Double, Int)
+resolveStatic static vars kind arg staticBase nFeats s0 k =
+    if VU.unsafeIndex kind k == 0
+      then (VB.unsafeIndex vars (leafSrcIdx nFeats (VU.unsafeIndex arg k)), s0)
+      else (static, VU.unsafeIndex staticBase k + s0)
+{-# INLINE resolveStatic #-}
+
+-- ---------------------------------------------------------------------
+-- Per-theta evaluation: the hot path, called once per NLopt objective/
+-- gradient call. Forward pass only recomputes dynamic nodes (ids are
+-- already topologically ordered, so a single left-to-right fold works).
+-- Backward pass is the same recursive shape as the original calcGrad,
+-- except it stops immediately on any non-dynamic node -- that subtree
+-- has no Param in it, so it can never contribute to the gradient.
+-- ---------------------------------------------------------------------
+
+-- Row-fused evaluation: instead of storing one full length-m array per
+-- node (which meant ~2 * #nodes large allocations per objective/gradient
+-- call), we walk the m data rows one at a time and, for each row, run the
+-- forward pass and the reverse-mode backward pass over small per-node
+-- scratch arrays of Double (length root+1). This mirrors what the fused
+-- Accelerate/LLVM kernel does (one pass per row, no big intermediate
+-- arrays) while staying in plain ST: allocation drops from O(nodes * m)
+-- to O(nodes + params), and the tight inner loops are all unboxed.
+evalGrad :: CompiledTree -> V.Vector Double -> (Double, V.Vector Double)
+evalGrad ct theta = runST $ do
+    fwd   <- VUM.new (root + 1)   -- node id -> forward value, current row
+    adj   <- VUM.new (root + 1)   -- node id -> adjoint (dL/dnode), current row
+    gradM <- VUM.replicate p 0    -- accumulated per-parameter gradient
+    objRef <- newSTRef 0
+
+    let -- forward pass for a single row: fills `fwd` for ids 0..root
+        forwardLoop !row !key
+          | key > root = pure ()
+          | otherwise  = do
+              v <- if not (VU.unsafeIndex dyn key)
+                     then if VU.unsafeIndex kind key == 0
+                            then pure (VU.unsafeIndex (VB.unsafeIndex vars (leafSrcIdx nFeats (VU.unsafeIndex arg key))) row)
+                            else pure (VU.unsafeIndex static (VU.unsafeIndex staticBase key + row))
+                     else case VU.unsafeIndex kind key of
+                            1 -> pure (V.unsafeIndex theta (VU.unsafeIndex arg key))
+                            3 -> do x <- VUM.unsafeRead fwd (VU.unsafeIndex arg key)
+                                    pure (evalFunCode (VU.unsafeIndex fcode key) x)
+                            4 -> do xl <- VUM.unsafeRead fwd (VU.unsafeIndex arg key)
+                                    xr <- VUM.unsafeRead fwd (VU.unsafeIndex arg2 key)
+                                    pure (evalOpCode (VU.unsafeIndex ocode key) xl xr)
+                            _ -> error "evalGrad: unreachable"
+              VUM.unsafeWrite fwd key v
+              forwardLoop row (key + 1)
+
+        -- backward pass for a single row: ids are visited from root down
+        -- to 0, which is a valid reverse-topological order since every
+        -- child id is smaller than its parent's id by construction.
+        backwardLoop !key
+          | key < 0 = pure ()
+          | otherwise = do
+              when (VU.unsafeIndex dyn key) $ do
+                v <- VUM.unsafeRead adj key
+                case VU.unsafeIndex kind key of
+                  4 -> do
+                    let l = VU.unsafeIndex arg key
+                        r = VU.unsafeIndex arg2 key
+                    xl <- VUM.unsafeRead fwd l
+                    xr <- VUM.unsafeRead fwd r
+                    fg <- VUM.unsafeRead fwd key
+                    let (dl, dr) = diffScalarCode (VU.unsafeIndex ocode key) v xl xr fg
+                    VUM.unsafeModify adj (+ dl) l
+                    VUM.unsafeModify adj (+ dr) r
+                  3 -> do
+                    let t = VU.unsafeIndex arg key
+                    x <- VUM.unsafeRead fwd t
+                    VUM.unsafeModify adj (+ v * derivFunCode (VU.unsafeIndex fcode key) x) t
+                  1 -> VUM.unsafeModify gradM (+ v) (VU.unsafeIndex arg key)
+                  _ -> pure ()
+              backwardLoop (key - 1)
+
+        rowLoop !row
+          | row >= m = pure ()
+          | otherwise = do
+              forwardLoop row 0
+              rootVal <- VUM.unsafeRead fwd root
+              modifySTRef' objRef (+ rootVal)
+              when (VU.unsafeIndex dyn root) $ do
+                VUM.set adj 0
+                VUM.unsafeWrite adj root 1
+                backwardLoop root
+              rowLoop (row + 1)
+
+    rowLoop 0
+
+    obj        <- readSTRef objRef
+    gradFrozen <- VU.unsafeFreeze gradM
+    pure (obj, V.convert gradFrozen)
+  where
+    root   = ctRoot ct
+    m      = ctM ct
+    p      = V.length theta
+    kind   = ctKind ct
+    arg    = ctArg ct
+    arg2   = ctArg2 ct
+    fcode  = ctFcode ct
+    ocode  = ctOcode ct
+    dyn    = ctDyn ct
+    static = ctStatic ct
+    staticBase = ctStaticBase ct
+    vars   = ctVars ct
+    nFeats = VB.length vars - 2
+
+-- ---------------------------------------------------------------------
+-- Node-outer (vectorized-over-rows) evaluation: mirrors reverseModeGraph's
+-- shape (one full length-m column per node, node-major loops) so the inner
+-- loops are fused per node over all rows, with the static/dynamic pattern
+-- decided once per node instead of once per row. Uses the same flat
+-- [staticSlot * m + row] layout and compact op-code dispatch as `evalGrad`, but
+-- trades the O(nodes + params) scratch of the row-fused version for the
+-- O(nodes * m) fwd/adj columns of the massiv-style whole-column kernel.
+evalGradVec :: CompiledTree -> V.Vector Double -> (Double, V.Vector Double)
+evalGradVec ct theta = runST $ do
+    -- Per-chunk buffers of O(stride * chunk) instead of one O(stride * m)
+    -- allocation per call: the fwd/adj matrices are streamed one chunk of
+    -- `chunk` rows at a time, so the per-call allocation drops ~m/chunk x
+    -- (and the working set stays L3-resident). The chunk partition does not
+    -- change any value: each row is independent, the objective row sums
+    -- accumulate in order and the gradient accumulates row-sums per chunk.
+    fwd   <- VUM.new (stride * chunk)   -- [node * nb + i]; dynamic columns written before read
+    adj   <- VUM.replicate (stride * chunk) 0   -- [node * nb + i]
+    gradM <- VUM.replicate p 0
+
+    let go !start !acc
+          | start >= m = do
+              gradFrozen <- VU.unsafeFreeze gradM
+              pure (acc, V.convert gradFrozen)
+          | otherwise = do
+              let nb = min chunk (m - start)
+                  s0 = start
+              forwardPassRange ct theta fwd s0 nb
+              -- objective contribution = sum over this chunk's rows of root
+              s <- if VU.unsafeIndex dyn root
+                     then {-# SCC "objSumFwd" #-} sumCol fwd (root * nb) nb
+                     else {-# SCC "objSumStatic" #-} sumStatic (VU.unsafeIndex staticBase root + s0) nb
+              -- seed the root adjoint: d(obj)/d(root value) = 1 per row
+              unless (s0 == 0) $ VUM.set adj 0   -- reuse the buffer; keep it clean
+              when (VU.unsafeIndex dyn root) $ {-# SCC "seedAdj" #-} VUM.set (VUM.slice (root * nb) nb adj) 1
+              -- backward: nodes from root down to 0 (valid reverse-topological order)
+              let goBwd !key
+                    | key < 0 = pure ()
+                    | otherwise = do
+                        bwdNode key
+                        goBwd (key - 1)
+
+                  bwdNode key
+                    | not (VU.unsafeIndex dyn key) = pure ()  -- no Param in subtree
+                    | otherwise = case VU.unsafeIndex kind key of
+                        4 -> do
+                          let l  = VU.unsafeIndex arg key
+                              r  = VU.unsafeIndex arg2 key
+                              oc = VU.unsafeIndex ocode key
+                              dl = VU.unsafeIndex dyn l
+                              dr = VU.unsafeIndex dyn r
+                              kb = key * nb
+                              lb = l * nb
+                              rb = r * nb
+                          case (dl, dr) of
+                            (True, True)   -> {-# SCC "bwdBinTT" #-} bwdBin nb fwd adj 0 oc kb lb rb (static, 0)
+                            (True, False)  -> {-# SCC "bwdBinTS" #-} bwdBin nb fwd adj 1 oc kb lb rb (resolveStatic static vars kind arg staticBase nFeats s0 r)
+                            (False, True)  -> {-# SCC "bwdBinST" #-} bwdBin nb fwd adj 2 oc kb lb rb (resolveStatic static vars kind arg staticBase nFeats s0 l)
+                            (False, False) -> pure ()  -- no dynamic children to propagate to
+                        3 -> do
+                          let t  = VU.unsafeIndex arg key
+                              fc = VU.unsafeIndex fcode key
+                              kb = key * nb
+                              tb = t * nb
+                          if VU.unsafeIndex dyn t
+                            then {-# SCC "bwdUni" #-} bwdUni nb fwd adj fc kb tb
+                            else pure ()  -- static child: no Param below, nothing to accumulate
+                        1 -> do
+                          let a  = VU.unsafeIndex arg key
+                              kb = key * nb
+                          {-# SCC "bwdParam" #-} do
+                            s' <- sumCol adj kb nb
+                            VUM.unsafeModify gradM (+ s') a
+                        _ -> pure ()
+              goBwd root
+              go (start + nb) (acc + s)
+
+    go 0 0
+  where
+    root   = ctRoot ct
+    m      = ctM ct
+    p      = V.length theta
+    stride = root + 1
+    chunk  = 1024
+    kind   = ctKind ct
+    arg    = ctArg ct
+    arg2   = ctArg2 ct
+    fcode  = ctFcode ct
+    ocode  = ctOcode ct
+    dyn    = ctDyn ct
+    static = ctStatic ct
+    staticBase = ctStaticBase ct
+    vars   = ctVars ct
+    nFeats = VB.length vars - 2
+
+    sumCol v vbase !n = go 0 0
+      where go !i !acc | i >= n = pure acc
+                       | otherwise = VUM.unsafeRead v (vbase + i) >>= \vv -> go (i + 1) (acc + vv)
+    sumStatic sbase !n = go 0 0
+      where go !i !acc | i >= n = pure acc
+                       | otherwise = go (i + 1) (acc + VU.unsafeIndex static (sbase + i))
+
+-- ---------------------------------------------------------------------
+-- Forward-only objective evaluation: runs the forward pass and the row
+-- sum but skips the adjoint/backward pass. Used where only the objective
+-- value is needed (reporting loss / R2 metrics, the validation fitness in
+-- the search), avoiding the ~2/3 of evalGradVec's work that computes the
+-- gradient.
+-- ---------------------------------------------------------------------
+-- Chunked loss evaluation: runs the same node-outer forward pass as
+-- `evalGradVec` (static columns precomputed in `ctStatic`, op codes
+-- dispatched once per node into INLINE kernels) but only over a chunk of
+-- `chunk` rows at a time with a per-call buffer of O(stride * chunk)
+-- instead of O(stride * m). The chunk partition does not change any value
+-- (each row is computed independently, the row sums accumulate in order),
+-- but it cuts the per-call allocation ~30x so this is cheap enough for the
+-- val-eval hot path that runs once per explored expression.
+evalLossVec :: CompiledTree -> V.Vector Double -> Double
+evalLossVec ct theta = runST $ do
+    buf <- VUM.new (stride * chunk)
+    go buf 0 0
+  where
+    root     = ctRoot ct
+    m        = ctM ct
+    stride   = root + 1
+    dyn      = ctDyn ct
+    static   = ctStatic ct
+    staticBase = ctStaticBase ct
+    chunk    = 4096
+
+    go :: VUM.MVector s Double -> Int -> Double -> ST s Double
+    go buf !start !acc
+      | start >= m = pure acc
+      | otherwise = do
+          let nb = min chunk (m - start)
+          forwardPassRange ct theta buf start nb
+          s <- if VU.unsafeIndex dyn root
+                 then sumCol buf (root * nb) nb
+                 else sumStatic (VU.unsafeIndex staticBase root + start) nb
+          go buf (start + nb) (acc + s)
+
+    sumCol buf vbase !n = go 0 0
+      where go !i !acc | i >= n = pure acc
+                       | otherwise = VUM.unsafeRead buf (vbase + i) >>= \vv -> go (i + 1) (acc + vv)
+    sumStatic sbase !n = go 0 0
+      where go !i !acc | i >= n = pure acc
+                       | otherwise = go (i + 1) (acc + VU.unsafeIndex static (sbase + i))
+
+-- Forward pass shared by evalGradVec and evalLossVec: fills the `fwd`
+-- columns of every dynamic node (ids are topologically ordered, so one
+-- left-to-right sweep computes all of them; static columns are already in
+-- `ctStatic`). The op/function codes are dispatched once per node and the
+-- INLINE loop helpers run a tight fused kernel over the rows.
+--
+-- `s0`/`nb` select a range of rows [start, start+nb): with nb = m, start = 0
+-- this is the full-matrix pass used by evalGradVec; evalLossVec calls it on
+-- chunks of rows with a stride*nb buffer. The fwd buffer is indexed
+-- [key * nb + i], static columns are read at [slot(key) * m + s0 + i].
+forwardPassRange :: CompiledTree -> V.Vector Double -> VUM.MVector s Double -> Int -> Int -> ST s ()
+forwardPassRange ct theta fwd s0 nb = goFwd 0
+  where
+    root   = ctRoot ct
+    m      = ctM ct
+    kind   = ctKind ct
+    arg    = ctArg ct
+    arg2   = ctArg2 ct
+    fcode  = ctFcode ct
+    ocode  = ctOcode ct
+    dyn    = ctDyn ct
+    static = ctStatic ct
+    staticBase = ctStaticBase ct
+    vars   = ctVars ct
+    nFeats = VB.length vars - 2
+
+    goFwd !key
+      | key > root = pure ()
+      | otherwise  = do
+          if VU.unsafeIndex dyn key
+            then case VU.unsafeIndex kind key of
+              1 -> {-# SCC "fwdParam" #-} VUM.set (VUM.slice (key * nb) nb fwd) (V.unsafeIndex theta (VU.unsafeIndex arg key))
+              3 -> do
+                let t  = VU.unsafeIndex arg key
+                    fc = VU.unsafeIndex fcode key
+                    kb = key * nb
+                    tb = t * nb
+                if VU.unsafeIndex dyn t
+                  then {-# SCC "fwdUniD" #-} fwdUniD nb fwd fc kb tb
+                  else pure ()  -- a dynamic Uni always has a dynamic child
+              4 -> do
+                let l  = VU.unsafeIndex arg key
+                    r  = VU.unsafeIndex arg2 key
+                    oc = VU.unsafeIndex ocode key
+                    dl = VU.unsafeIndex dyn l
+                    dr = VU.unsafeIndex dyn r
+                    kb = key * nb
+                    lb = l * nb
+                    rb = r * nb
+                case (dl, dr) of
+                  (True, True)   -> {-# SCC "fwdBinTT" #-} fwdBin nb fwd 0 oc kb lb rb (static, 0)
+                  (True, False)  -> {-# SCC "fwdBinTS" #-} fwdBin nb fwd 1 oc kb lb rb (resolveStatic static vars kind arg staticBase nFeats s0 r)
+                  (False, True)  -> {-# SCC "fwdBinST" #-} fwdBin nb fwd 2 oc kb lb rb (resolveStatic static vars kind arg staticBase nFeats s0 l)
+                  (False, False) -> pure ()  -- unreachable: a dynamic Bin always has a dynamic child
+              _ -> pure ()
+            else pure ()  -- static node: column already in `static`
+          goFwd (key + 1)
+
+    -- Forward binary kernels: `combo` 0=TT, 1=TS, 2=ST (SS is unreachable
+    -- for dynamic nodes). The opcode is dispatched ONCE per node; the loop
+    -- helpers are INLINE with the literal operator so each row iteration
+    -- is a tight fused kernel with no per-element `case oc of` dispatch.
+    -- `stSrc` is the (source vector, base) of the static child (either a
+    -- run-fixed leaf column from `vars` or a computed column of `static`),
+    -- used by the TS/ST variants; `nb` is the number of rows in this chunk.
+fwdBin :: Int -> VUM.MVector s Double -> Int -> Int -> Int -> Int -> Int -> (VU.Vector Double, Int) -> ST s ()
+fwdBin nb fwd combo oc kb lb rb stSrc = case (combo, oc) of
+  (0, 0) -> fwdTT nb fwd (+) kb lb rb
+  (0, 1) -> fwdTT nb fwd (-) kb lb rb
+  (0, 2) -> fwdTT nb fwd (*) kb lb rb
+  (0, 3) -> fwdTT nb fwd (/) kb lb rb
+  (0, 4) -> fwdTT nb fwd (**) kb lb rb
+  (0, 5) -> fwdTT nb fwd (\l r -> abs l ** r) kb lb rb
+  (0, 6) -> fwdTT nb fwd (\l r -> l / sqrt (1 + r * r)) kb lb rb
+  (1, 0) -> fwdTS nb stSrc fwd (+) kb lb
+  (1, 1) -> fwdTS nb stSrc fwd (-) kb lb
+  (1, 2) -> fwdTS nb stSrc fwd (*) kb lb
+  (1, 3) -> fwdTS nb stSrc fwd (/) kb lb
+  (1, 4) -> fwdTS nb stSrc fwd (**) kb lb
+  (1, 5) -> fwdTS nb stSrc fwd (\l r -> abs l ** r) kb lb
+  (1, 6) -> fwdTS nb stSrc fwd (\l r -> l / sqrt (1 + r * r)) kb lb
+  (2, 0) -> fwdST nb stSrc fwd (+) kb rb
+  (2, 1) -> fwdST nb stSrc fwd (-) kb rb
+  (2, 2) -> fwdST nb stSrc fwd (*) kb rb
+  (2, 3) -> fwdST nb stSrc fwd (/) kb rb
+  (2, 4) -> fwdST nb stSrc fwd (**) kb rb
+  (2, 5) -> fwdST nb stSrc fwd (\l r -> abs l ** r) kb rb
+  (2, 6) -> fwdST nb stSrc fwd (\l r -> l / sqrt (1 + r * r)) kb rb
+  _      -> pure ()
+{-# INLINE fwdBin #-}
+
+-- Backward binary kernels: same dispatch structure, `diff` is the local
+-- (dl/dchild, dr/dchild) rule keyed on the opcode. `nb` is the number of
+-- rows in this chunk, `stSrc` is the (source vector, base) of the static
+-- child (either a run-fixed leaf column from `vars` or a computed column of
+-- `static`), used by the TS/ST variants.
+bwdBin :: Int -> VUM.MVector s Double -> VUM.MVector s Double -> Int -> Int -> Int -> Int -> Int -> (VU.Vector Double, Int) -> ST s ()
+bwdBin nb fwd adj combo oc kb lb rb stSrc = case (combo, oc) of
+  (0, 0) -> bwdTT nb fwd adj (\dx _ _ _ -> (dx, dx)) kb lb rb
+  (0, 1) -> bwdTT nb fwd adj (\dx _ _ _ -> (dx, negate dx)) kb lb rb
+  (0, 2) -> bwdTT nb fwd adj (\dx fx gy _ -> (dx * gy, dx * fx)) kb lb rb
+  (0, 3) -> bwdTT nb fwd adj (\dx _ gy fg -> (dx / gy, dx * (negate fg / gy))) kb lb rb
+  (0, 4) -> bwdTT nb fwd adj (\dx fx gy fg -> (fixNaN (dx * gy * fg / fx), fixNaN (dx * fg * log fx))) kb lb rb
+  (0, 5) -> bwdTT nb fwd adj (\dx fx gy fg ->
+             let v2 = abs fx in (fixNaN (dx * (fx * gy) * fg / (v2 * v2)), fixNaN (dx * fg * log (abs fx)))) kb lb rb
+  (0, 6) -> bwdTT nb fwd adj (\dx fx gy _ ->
+             let dxl = dx * (recip . sqrt . (+1) . (^(2::Int))) gy
+                 dxy = fx * gy * dxl ^ (3::Int)
+             in (dxl, dxy)) kb lb rb
+  (1, 0) -> bwdTS nb stSrc fwd adj (\dx _ _ _ -> (dx, dx)) kb lb
+  (1, 1) -> bwdTS nb stSrc fwd adj (\dx _ _ _ -> (dx, negate dx)) kb lb
+  (1, 2) -> bwdTS nb stSrc fwd adj (\dx fx gy _ -> (dx * gy, dx * fx)) kb lb
+  (1, 3) -> bwdTS nb stSrc fwd adj (\dx _ gy fg -> (dx / gy, dx * (negate fg / gy))) kb lb
+  (1, 4) -> bwdTS nb stSrc fwd adj (\dx fx gy fg -> (fixNaN (dx * gy * fg / fx), fixNaN (dx * fg * log fx))) kb lb
+  (1, 5) -> bwdTS nb stSrc fwd adj (\dx fx gy fg ->
+             let v2 = abs fx in (fixNaN (dx * (fx * gy) * fg / (v2 * v2)), fixNaN (dx * fg * log (abs fx)))) kb lb
+  (1, 6) -> bwdTS nb stSrc fwd adj (\dx fx gy _ ->
+             let dxl = dx * (recip . sqrt . (+1) . (^(2::Int))) gy
+                 dxy = fx * gy * dxl ^ (3::Int)
+             in (dxl, dxy)) kb lb
+  (2, 0) -> bwdST nb stSrc fwd adj (\dx _ _ _ -> (dx, dx)) kb rb
+  (2, 1) -> bwdST nb stSrc fwd adj (\dx _ _ _ -> (dx, negate dx)) kb rb
+  (2, 2) -> bwdST nb stSrc fwd adj (\dx fx gy _ -> (dx * gy, dx * fx)) kb rb
+  (2, 3) -> bwdST nb stSrc fwd adj (\dx _ gy fg -> (dx / gy, dx * (negate fg / gy))) kb rb
+  (2, 4) -> bwdST nb stSrc fwd adj (\dx fx gy fg -> (fixNaN (dx * gy * fg / fx), fixNaN (dx * fg * log fx))) kb rb
+  (2, 5) -> bwdST nb stSrc fwd adj (\dx fx gy fg ->
+             let v2 = abs fx in (fixNaN (dx * (fx * gy) * fg / (v2 * v2)), fixNaN (dx * fg * log (abs fx)))) kb lb
+  (2, 6) -> bwdST nb stSrc fwd adj (\dx fx gy _ ->
+             let dxl = dx * (recip . sqrt . (+1) . (^(2::Int))) gy
+                 dxy = fx * gy * dxl ^ (3::Int)
+             in (dxl, dxy)) kb rb
+  _      -> pure ()
+{-# INLINE bwdBin #-}
+
+fwdTT nb fwd op kb lb rb = forRows nb $ \i -> do
+  xl <- VUM.unsafeRead fwd (lb + i)
+  xr <- VUM.unsafeRead fwd (rb + i)
+  VUM.unsafeWrite fwd (kb + i) (op xl xr)
+{-# INLINE fwdTT #-}
+
+fwdTS nb (src, base) fwd op kb lb = forRows nb $ \i -> do
+  xl <- VUM.unsafeRead fwd (lb + i)
+  VUM.unsafeWrite fwd (kb + i) (op xl (VU.unsafeIndex src (base + i)))
+{-# INLINE fwdTS #-}
+
+fwdST nb (src, base) fwd op kb rb = forRows nb $ \i -> do
+  xr <- VUM.unsafeRead fwd (rb + i)
+  VUM.unsafeWrite fwd (kb + i) (op (VU.unsafeIndex src (base + i)) xr)
+{-# INLINE fwdST #-}
+
+bwdTT nb fwd adj diff kb lb rb = forRows nb $ \i -> do
+  v  <- VUM.unsafeRead adj (kb + i)
+  xl <- VUM.unsafeRead fwd (lb + i)
+  xr <- VUM.unsafeRead fwd (rb + i)
+  fg <- VUM.unsafeRead fwd (kb + i)
+  let (gl, gr) = diff v xl xr fg
+  a <- VUM.unsafeRead adj (lb + i)
+  VUM.unsafeWrite adj (lb + i) (a + gl)
+  b <- VUM.unsafeRead adj (rb + i)
+  VUM.unsafeWrite adj (rb + i) (b + gr)
+{-# INLINE bwdTT #-}
+
+bwdTS nb (src, base) fwd adj diff kb lb = forRows nb $ \i -> do
+  v  <- VUM.unsafeRead adj (kb + i)
+  xl <- VUM.unsafeRead fwd (lb + i)
+  fg <- VUM.unsafeRead fwd (kb + i)
+  let (gl, _) = diff v xl (VU.unsafeIndex src (base + i)) fg
+  a <- VUM.unsafeRead adj (lb + i)
+  VUM.unsafeWrite adj (lb + i) (a + gl)
+{-# INLINE bwdTS #-}
+
+bwdST nb (src, base) fwd adj diff kb rb = forRows nb $ \i -> do
+  v  <- VUM.unsafeRead adj (kb + i)
+  xr <- VUM.unsafeRead fwd (rb + i)
+  fg <- VUM.unsafeRead fwd (kb + i)
+  let (_, gr) = diff v (VU.unsafeIndex src (base + i)) xr fg
+  b <- VUM.unsafeRead adj (rb + i)
+  VUM.unsafeWrite adj (rb + i) (b + gr)
+{-# INLINE bwdST #-}
+
+-- Forward unary kernels (dynamic child): the function code is dispatched
+-- ONCE per node and the loop helper is INLINE with the literal function,
+-- so each row iteration is a tight fused kernel with no per-element
+-- `case fc of` / closure build (a dynamic Uni node always has a dynamic
+-- child, so there is no static-child variant here).
+fwdUniD :: Int -> VUM.MVector s Double -> Int -> Int -> Int -> ST s ()
+fwdUniD nb fwd fc kb tb = case fc of
+  0  -> fwdUniD' nb fwd (\x -> x) kb tb
+  1  -> fwdUniD' nb fwd abs kb tb
+  2  -> fwdUniD' nb fwd sin kb tb
+  3  -> fwdUniD' nb fwd cos kb tb
+  4  -> fwdUniD' nb fwd tan kb tb
+  5  -> fwdUniD' nb fwd sinh kb tb
+  6  -> fwdUniD' nb fwd cosh kb tb
+  7  -> fwdUniD' nb fwd tanh kb tb
+  8  -> fwdUniD' nb fwd asin kb tb
+  9  -> fwdUniD' nb fwd acos kb tb
+  10 -> fwdUniD' nb fwd atan kb tb
+  11 -> fwdUniD' nb fwd asinh kb tb
+  12 -> fwdUniD' nb fwd acosh kb tb
+  13 -> fwdUniD' nb fwd atanh kb tb
+  14 -> fwdUniD' nb fwd sqrt kb tb
+  15 -> fwdUniD' nb fwd (\x -> sqrt (abs x)) kb tb
+  16 -> fwdUniD' nb fwd (\x -> signum x * abs x ** (1 / 3)) kb tb
+  17 -> fwdUniD' nb fwd (\x -> x * x) kb tb
+  18 -> fwdUniD' nb fwd log kb tb
+  19 -> fwdUniD' nb fwd (\x -> log (abs x)) kb tb
+  20 -> fwdUniD' nb fwd exp kb tb
+  21 -> fwdUniD' nb fwd recip kb tb
+  22 -> fwdUniD' nb fwd (\x -> x * x * x) kb tb
+  _  -> pure ()
+{-# INLINE fwdUniD #-}
+
+fwdUniD' nb fwd f kb tb = forRows nb $ \i -> do
+  x <- VUM.unsafeRead fwd (tb + i)
+  VUM.unsafeWrite fwd (kb + i) (f x)
+{-# INLINE fwdUniD' #-}
+
+-- Backward unary kernel: derivative of the function, dispatched once per
+-- node and inlined into the accumulation loop. `nb` is the number of rows
+-- in the current chunk.
+bwdUni :: Int -> VUM.MVector s Double -> VUM.MVector s Double -> Int -> Int -> Int -> ST s ()
+bwdUni nb fwd adj fc kb tb = case fc of
+  0  -> bwdUni' nb fwd adj (\_ -> 1) kb tb
+  1  -> bwdUni' nb fwd adj (\x -> x / abs x) kb tb
+  2  -> bwdUni' nb fwd adj cos kb tb
+  3  -> bwdUni' nb fwd adj (negate . sin) kb tb
+  4  -> bwdUni' nb fwd adj (\x -> 1 / (cos x * cos x)) kb tb
+  5  -> bwdUni' nb fwd adj cosh kb tb
+  6  -> bwdUni' nb fwd adj sinh kb tb
+  7  -> bwdUni' nb fwd adj (\x -> 1 - tanh x * tanh x) kb tb
+  8  -> bwdUni' nb fwd adj (\x -> 1 / sqrt (1 - x * x)) kb tb
+  9  -> bwdUni' nb fwd adj (\x -> -1 / sqrt (1 - x * x)) kb tb
+  10 -> bwdUni' nb fwd adj (\x -> 1 / (1 + x * x)) kb tb
+  11 -> bwdUni' nb fwd adj (\x -> 1 / sqrt (1 + x * x)) kb tb
+  12 -> bwdUni' nb fwd adj (\x -> 1 / (sqrt (x - 1) * sqrt (x + 1))) kb tb
+  13 -> bwdUni' nb fwd adj (\x -> 1 / (1 - x * x)) kb tb
+  14 -> bwdUni' nb fwd adj (\x -> 1 / (2 * sqrt x)) kb tb
+  15 -> bwdUni' nb fwd adj (\x -> x / (2 * abs x ** (3 / 2))) kb tb
+  16 -> bwdUni' nb fwd adj (\x -> 1 / (3 * (x * x) ** (1 / 3))) kb tb
+  17 -> bwdUni' nb fwd adj (\x -> 2 * x) kb tb
+  18 -> bwdUni' nb fwd adj recip kb tb
+  19 -> bwdUni' nb fwd adj recip kb tb
+  20 -> bwdUni' nb fwd adj exp kb tb
+  21 -> bwdUni' nb fwd adj (\x -> -1 / (x * x)) kb tb
+  22 -> bwdUni' nb fwd adj (\x -> 3 * x * x) kb tb
+  _  -> pure ()
+{-# INLINE bwdUni #-}
+
+bwdUni' nb fwd adj f kb tb = forRows nb $ \i -> do
+  v <- VUM.unsafeRead adj (kb + i)
+  x <- VUM.unsafeRead fwd (tb + i)
+  c <- VUM.unsafeRead adj (tb + i)
+  VUM.unsafeWrite adj (tb + i) (c + v * f x)
+{-# INLINE bwdUni' #-}
+-- Unboxed ST loop over the m data rows; always inlined so the per-node
+-- bodies above are fused into a single tail-recursive kernel per node.
+forRows :: Int -> (Int -> ST s ()) -> ST s ()
+forRows !n f = go 0
+  where
+    go !i | i >= n    = pure ()
+          | otherwise = f i >> go (i + 1)
+{-# INLINE forRows #-}
+evalOpCode :: Int -> Double -> Double -> Double
+evalOpCode 0 = (+)
+evalOpCode 1 = (-)
+evalOpCode 2 = (*)
+evalOpCode 3 = (/)
+evalOpCode 4 = (**)
+evalOpCode 5 = \l r -> abs l ** r
+evalOpCode 6 = \l r -> l / sqrt (1 + r * r)
+evalOpCode _ = error "evalOpCode: bad op code"
+{-# INLINE evalOpCode #-}
+
+evalFunCode :: Int -> Double -> Double
+evalFunCode 0  = id
+evalFunCode 1  = abs
+evalFunCode 2  = sin
+evalFunCode 3  = cos
+evalFunCode 4  = tan
+evalFunCode 5  = sinh
+evalFunCode 6  = cosh
+evalFunCode 7  = tanh
+evalFunCode 8  = asin
+evalFunCode 9  = acos
+evalFunCode 10 = atan
+evalFunCode 11 = asinh
+evalFunCode 12 = acosh
+evalFunCode 13 = atanh
+evalFunCode 14 = sqrt
+evalFunCode 15 = \x -> sqrt (abs x)
+evalFunCode 16 = \x -> signum x * abs x ** (1 / 3)
+evalFunCode 17 = \x -> x * x
+evalFunCode 18 = log
+evalFunCode 19 = \x -> log (abs x)
+evalFunCode 20 = exp
+evalFunCode 21 = recip
+evalFunCode 22 = \x -> x * x * x
+evalFunCode _  = error "evalFunCode: bad function code"
+{-# INLINE evalFunCode #-}
+
+derivFunCode :: Int -> Double -> Double
+derivFunCode 0  = const 1
+derivFunCode 1  = \x -> x / abs x
+derivFunCode 2  = cos
+derivFunCode 3  = negate . sin
+derivFunCode 4  = \x -> 1 / (cos x * cos x)
+derivFunCode 5  = cosh
+derivFunCode 6  = sinh
+derivFunCode 7  = \x -> 1 - tanh x * tanh x
+derivFunCode 8  = \x -> 1 / sqrt (1 - x * x)
+derivFunCode 9  = \x -> -1 / sqrt (1 - x * x)
+derivFunCode 10 = \x -> 1 / (1 + x * x)
+derivFunCode 11 = \x -> 1 / sqrt (1 + x * x)
+derivFunCode 12 = \x -> 1 / (sqrt (x - 1) * sqrt (x + 1))
+derivFunCode 13 = \x -> 1 / (1 - x * x)
+derivFunCode 14 = \x -> 1 / (2 * sqrt x)
+derivFunCode 15 = \x -> x / (2 * abs x ** (3 / 2))
+derivFunCode 16 = \x -> 1 / (3 * (x * x) ** (1 / 3))
+derivFunCode 17 = (* 2)
+derivFunCode 18 = recip
+derivFunCode 19 = recip
+derivFunCode 20 = exp
+derivFunCode 21 = \x -> -1 / (x * x)
+derivFunCode 22 = \x -> 3 * x * x
+derivFunCode _  = error "derivFunCode: bad function code"
+{-# INLINE derivFunCode #-}
+
+-- Pure local-derivative rules keyed on fromEnum Op, scalar version (same
+-- math as the original vectorized `diffPure`, applied per-row above).
+diffScalarCode :: Int -> Double -> Double -> Double -> Double -> (Double, Double)
+diffScalarCode 0 dx _  _  _  = (dx, dx)
+diffScalarCode 1 dx _  _  _  = (dx, negate dx)
+diffScalarCode 2 dx fx gy _  = (dx * gy, dx * fx)
+diffScalarCode 3 dx _  gy fg = (dx / gy, dx * (negate fg / gy))
+diffScalarCode 4 dx fx gy fg =
+    ( fixNaN (dx * gy * fg / fx)
+    , fixNaN (dx * fg * log fx) )
+diffScalarCode 5 dx fx gy fg =
+    let v2 = abs fx
+    in ( fixNaN (dx * (fx * gy) * fg / (v2 * v2))
+       , fixNaN (dx * fg * log (abs fx)) )
+diffScalarCode 6 dx fx gy _ =
+    let dxl = dx * (recip . sqrt . (+1) . (^(2::Int))) gy
+        dxy = fx * gy * dxl ^ (3::Int)
+    in (dxl, dxy)
+diffScalarCode _ _ _ _ _ = error "diffScalarCode: bad op code"
+{-# INLINE diffScalarCode #-}
+
+fixNaN :: Double -> Double
+fixNaN x = if isNaN x then 0 else x
+{-# INLINE fixNaN #-}
+
+-- ---------------------------------------------------------------------
+-- Drop-in-compatible wrapper -- same signature as your original function.
+-- Use this ONLY to verify correctness against your existing implementation
+-- (e.g. QuickCheck / golden tests comparing outputs). It gets you ZERO
+-- speedup on its own, since it calls compileTree fresh every time, same
+-- as before. The actual win requires changing the NLopt-facing call site.
+-- ---------------------------------------------------------------------
+
+--reverseModeGraphO :: [V.Vector Double] -> V.Vector Double -> Maybe (V.Vector Double) -> V.Vector Double -> Fix SRTree -> (V.Vector Double, V.Vector Double)
+--reverseModeGraphO xss ys mYErr theta tree = evalGrad (compileTree xss ys mYErr tree) theta
+
+-- | Safely chunk an unboxed vector into 'n' roughly equal parts.
+chunkVector :: Int -> VU.Vector Double -> [VU.Vector Double]
+chunkVector numChunks v
+  | VU.null v = []
+  | otherwise =
+      let n = VU.length v
+          chunkSize = max 1 (n `div` numChunks)
+          go vec | VU.null vec = []
+                 | VU.length vec <= chunkSize = [vec]
+                 | otherwise = let (h, t) = VU.splitAt chunkSize vec
+                               in h : go t
+      in go v
+
+-- | Compiles the tree for multiple data chunks independently.
+compileTreeMulti :: [VU.Vector Double]
+                 -> VU.Vector Double
+                 -> Maybe (VU.Vector Double)
+                 -> Fix SRTree
+                 -> [CompiledTree]
+compileTreeMulti xss ys mYErr tree =
+    let nRows     = VU.length ys
+        minChunkSize = 2000
+        numChunks = max 1 (min cap (nRows `div` minChunkSize))
+        cap       = if mtSingleChunk then 1 else unsafePerformIO getNumCapabilities
+        ysChunks  = chunkVector numChunks ys
+        -- transpose groups the chunks by slice rather than by feature
+        xssChunks = Data.List.transpose (map (chunkVector numChunks) xss)
+        errChunks = case mYErr of
+                      Just e  -> map Just (chunkVector numChunks e)
+                      Nothing -> replicate (length ysChunks) Nothing
+    in [ compileTree xs y err tree | (xs, y, err) <- zip3 xssChunks ysChunks errChunks ]
+
+-- | When True, the MultiThread backend compiles/evaluates each tree on a
+-- single chunk so a higher-level population-parallel driver (eggp's fitness
+-- batch) owns the cores instead of oversubscribing the per-tree chunk split.
+{-# NOINLINE mtSingleChunk #-}
+mtSingleChunk :: Bool
+mtSingleChunk = unsafePerformIO (readIORef mtParGate)
+
+mtParGate :: IORef Bool
+mtParGate = unsafePerformIO (newIORef False)
+{-# NOINLINE mtParGate #-}
+
+-- | Enable/disable single-chunk (non-oversubscribing) mode for the MultiThread
+-- backend; called around a population-parallel fitness batch.
+setMTPopParallel :: Bool -> IO ()
+setMTPopParallel b = writeIORef mtParGate b
+
+-- | Evaluates the gradient across all compiled chunks in parallel.
+-- Each chunk is evaluated by the fast node-outer `evalGradVec` kernel on
+-- its own slice of the data. The kernel is now chunked internally (O(stride
+-- * 1024) per-call buffers, L3-resident) and is compute-bound rather than
+-- memory-bandwidth-bound, so splitting the data into one chunk per core and
+-- running the kernels concurrently scales almost linearly. The objective
+-- and gradient accumulate across chunks (same math per row; only the FP
+-- summation order across chunk boundaries differs).
+evalGradMulti :: [CompiledTree] -> V.Vector Double -> (Double, V.Vector Double)
+evalGradMulti [ct] theta = evalGradVec ct theta
+evalGradMulti cts theta = unsafePerformIO $ do
+    results <- forConcurrently cts $ \ct -> evaluate (evalGradVec ct theta)
+    let totalObj   = sum $ map fst results
+        totalGrad  = foldl1' (V.zipWith (+)) (map snd results)
+    pure (totalObj, totalGrad)
diff --git a/src/Algorithm/SRTree/Compile.hs b/src/Algorithm/SRTree/Compile.hs
new file mode 100644
--- /dev/null
+++ b/src/Algorithm/SRTree/Compile.hs
@@ -0,0 +1,106 @@
+{-# LANGUAGE GADTs #-}
+
+module Algorithm.SRTree.Compile where
+
+import Data.SRTree
+import Data.SRTree.Eval (compileLoss, Target, Columns, Theta)
+import qualified Data.Vector.Unboxed as U
+import qualified Data.Vector.Storable as VS
+import qualified Data.Vector.Generic as G
+import Algorithm.SRTree.AD
+import Algorithm.SRTree.Utils
+import Algorithm.SRTree.Likelihoods (Distribution(..), Loss(..), buildLoss, hessianNLL)
+import Algorithm.SRTree.NonlinearOpt (minimizeNLL, minimizeNLLWithFixedParam)
+import Data.SRTree.Recursion (cata)
+
+data EvalTree = EvalTree {
+  ctDist            :: Distribution,
+  ctLoss            :: Theta -> Double,
+  ctAD              :: VS.Vector Double -> (Double, VS.Vector Double),
+  ctOptimizer       :: Target -> Target,
+  ctOptimizerFixed  :: Int -> Target -> Target,
+  ctNLL             :: Target -> Double,
+  ctGradNLL         :: Target -> (Double, Target),
+  ctHessianNLL      :: Target -> Columns,
+  ctTree            :: Fix SRTree,
+  ctRows            :: Int,
+  ctVar             :: Double
+}
+
+-- | Compile a tree and store it in a CompiledTree data structure
+compileTree :: Distribution -> Columns -> Target -> Maybe Target -> Fix SRTree -> EvalTree
+compileTree dist xss ys mYerr tree = EvalTree {
+  ctDist            = dist,
+  ctLoss            = compileLoss xss tree ys mYerr,
+  ctAD              = compileFunAndGrad MultiThread xss ys mYerr tree,
+  ctOptimizer       = fst3 . minimizeNLL MultiThread (NLL dist) mYerr 100 xss ys tree,
+  ctOptimizerFixed  = minimizeNLLWithFixedParam MultiThread (NLL dist) mYerr 100 xss ys tree,
+  ctNLL             = compileLoss xss lossTree ys mYerr,
+  ctGradNLL         = \theta -> let fg = compileFunAndGrad MultiThread xss ys mYerr lossTree
+                                    (obj, gradStorable) = fg (G.convert theta)
+                                in (obj, G.convert gradStorable),
+  ctHessianNLL      = hessianNLL dist mYerr xss ys tree,
+  ctTree            = tree,
+  ctRows            = n,
+  ctVar             = let ym = U.sum ys / fromIntegral n
+                      in U.foldr (\yi acc -> acc + (yi - ym)^2) 0 ys
+}
+  where
+    n = U.length ys
+    lossTree = buildLoss (NLL dist) (fromIntegral n) tree
+    fst3 (a, _, _) = a
+
+data EvaluatedTree = EvaluatedTree {
+  valLoss             :: Double,
+  valTheta            :: Theta,
+  valRows             :: Double,
+  valParams           :: Double,
+  valTree             :: Fix SRTree,
+  valLogParams        :: Double,
+  valLogParamsLattice :: Double,
+  valVar              :: Double
+}
+
+evaluateTree :: EvalTree -> Target -> [[Double]] -> Theta -> EvaluatedTree
+evaluateTree et fisher hessian theta = EvaluatedTree {
+  valLoss             = ctLoss et theta,
+  valTheta            = theta,
+  valRows             = fromIntegral (ctRows et),
+  valParams           = fromIntegral (U.length theta),
+  valTree             = ctTree et,
+  valLogParams        = logParameters fisher theta,
+  valLogParamsLattice = logParametersLatt hessian fisher theta,
+  valVar              = ctVar et
+}
+
+
+-- log of the parameters complexity
+logParameters :: U.Vector Double -> Target -> Double
+logParameters fisher theta = -(p / 2) * log 3 + 0.5 * logFisher + logTheta
+  where
+    (logTheta, logFisher, p) = foldr addIfSignificant (0, 0, 0) $ zip (U.toList theta) (U.toList fisher)
+
+-- same as above but for the Lattice
+logParametersLatt :: [[Double]] -> U.Vector Double -> Target -> Double
+logParametersLatt hessian fisher theta = 0.5 * p * (1 - log 3) + 0.5 * log detFisher
+  where
+    detFisher = det $ map U.fromList hessian
+
+    (logTheta, logFisher, p) = foldr addIfSignificant (0, 0, 0) $ zip (U.toList theta) (U.toList fisher)
+
+addIfSignificant (v, f) (acc_v, acc_f, acc_p)
+  | isSignificant v f = (acc_v + log (abs v), acc_f + log f, acc_p + 1)
+  | otherwise = (acc_v, acc_f, acc_p)
+{-# INLINE addIfSignificant #-}
+
+isSignificant v f = abs (v / sqrt(12 / f) ) >= 1
+{-# INLINE isSignificant #-}
+
+fixParam :: Int -> Double -> Fix SRTree -> Fix SRTree
+fixParam ix val = cata alg
+  where
+    alg (Param i) | i == ix   = Fix $ Const val
+                  | i > ix    = Fix $ Param (i-1)
+                  | otherwise = Fix $ Param i
+    alg other = Fix other
+{-# INLINE fixParam #-}
diff --git a/src/Algorithm/SRTree/ConfidenceIntervals.hs b/src/Algorithm/SRTree/ConfidenceIntervals.hs
new file mode 100644
--- /dev/null
+++ b/src/Algorithm/SRTree/ConfidenceIntervals.hs
@@ -0,0 +1,422 @@
+{-# language ViewPatterns, ScopedTypeVariables, MultiWayIf, FlexibleContexts #-}
+-------------------------------------------------------------------------------
+-- |
+-- Module      :  Algorithm.SRTree.ConfidenceIntervals
+-- Copyright   :  (c) Fabricio Olivetti 2021 - 2024
+-- License     :  BSD3
+-- Maintainer  :  fabricio.olivetti@gmail.com
+-- Stability   :  experimental
+-- Portability :  ConstraintKinds
+--
+-- Functions to optimize the parameters of an expression.
+-------------------------------------------------------------------------------
+module Algorithm.SRTree.ConfidenceIntervals where
+
+import Statistics.Distribution ( ContDistr(quantile) )
+import Statistics.Distribution.StudentT ( studentT )
+import Statistics.Distribution.FDistribution ( fDistribution )
+import qualified Data.Vector.Unboxed as U
+import qualified Data.Vector.Storable as VS
+import qualified Data.Vector.Generic as G
+import Data.SRTree
+import Data.SRTree.Eval
+import Data.SRTree.Recursion ( cata )
+import Algorithm.SRTree.Likelihoods
+import Algorithm.SRTree.Compile
+import Data.List ( sortOn, nubBy )
+import Data.Maybe ( listToMaybe )
+import Algorithm.SRTree.Utils
+import Numeric.Optimization.NLOPT
+import System.IO.Unsafe ( unsafePerformIO )
+import Control.Monad.Catch ( catch, SomeException )
+
+import Debug.Trace ( trace )
+
+-- | profile likelihood algorithms: Bates (classical), ODE (faster), Constrained (fastest)
+-- The Constrained approach returns only the endpoints.
+data PType = Bates | ODE | Constrained deriving (Show, Read, Eq)
+
+-- | Confidence Interval using Laplace approximation or profile likelihood.
+data CIType = Laplace BasicStats | Profile BasicStats [ProfileT]
+
+-- | Basic stats of the data: covariance of parameters, correlation, standard errors
+data BasicStats = MkStats
+  { _cov :: Columns
+  , _corr :: Columns
+  , _stdErr :: Target
+  } deriving (Eq, Show)
+
+-- | a confience interval is composed of the point estimate (`est_`), lower bound (`_lower_`)
+-- and upper bound (`upper_`)
+data CI = CI
+  { est_ :: Double
+  , lower_ :: Double
+  , upper_ :: Double
+  } deriving (Eq, Show, Read)
+
+-- | A profile likelihood is composed of a vector of tau values that traces the likelihood,
+-- the matrix of thetas for each profile, the local optima, and two splines that converts
+-- taus to theta and vice-versa.
+data ProfileT = ProfileT
+  { _taus :: Target
+  , _thetas :: Columns
+  , _opt :: Double
+  , _tau2theta :: Double -> Double
+  , _theta2tau :: Double -> Double
+  }
+
+-- shows the CI with n places
+showCI :: Int -> CI -> String
+showCI n (CI x l h) = show (rnd l) <> " <= " <> show (rnd x) <> " <= " <> show (rnd h)
+  where rnd = (/10^n) . (fromIntegral . round) . (*10^n)
+
+printCI :: Int -> CI -> IO ()
+printCI n = putStrLn . showCI n
+
+-- | Calculates the confidence interval of the parameters using
+-- Laplace approximation or Profile likelihood
+paramCI :: CIType -> Int -> Target -> Double -> [CI]
+paramCI (Laplace stats) nSamples theta alpha = zipWith3 CI (U.toList theta) lows highs
+  where
+    -- the Laplace approximation is theta +/- t(1-alpha/2) * standard error
+    k = U.length theta
+    t = quantile (studentT . fromIntegral $ nSamples - k) (1 - alpha / 2.0)
+    stdErr = _stdErr stats
+    lows = U.toList $ U.zipWith (-) theta $ U.map (*t) stdErr
+    highs = U.toList $ U.zipWith (+) theta $ U.map (*t) stdErr
+
+paramCI (Profile stats profiles) nSamples _ alpha = zipWith3 CI theta lows highs
+  where
+    -- for the profile likelihood we use the square root of the F-distribution with (1-alpha)
+    k = length theta
+    t = sqrt $ quantile (fDistribution k (fromIntegral $ nSamples - k)) (1 - alpha)
+    stdErr = _stdErr stats
+    lows = map (`_tau2theta` (-t)) profiles
+    highs = map (`_tau2theta` t) profiles
+    theta = map _opt profiles
+
+-- | calculates the prediction confidence interval using Laplace approximation or profile likelihood.
+-- predictionCI
+predictionCI :: CIType -> Distribution -> (Columns -> Target) -> (Columns -> [Target]) -> (CI -> Target -> Fix SRTree -> (Double -> Double, Double)) -> Columns -> Fix SRTree -> Target -> Double -> [CI] -> [CI]
+predictionCI (Laplace stats) _ predFun jacFun _ xss tree theta alpha _ = zipWith3 CI yhat lows highs
+  where
+    yhat = U.toList $ predFun xss
+    jac' = jacFun xss
+    k = U.length theta
+    n = length yhat
+    t = quantile (studentT . fromIntegral $ n - k) (1 - alpha / 2.0)
+
+    covMat = toRowMajor (_cov stats)
+    nCov = k - 1
+
+    lows = zipWith (-) yhat $ map (*t) resStdErr
+    highs = zipWith (+) yhat $ map (*t) resStdErr
+
+    getResStdError row =
+      sqrt $ U.sum $ U.generate nCov $ \i ->
+        (row U.! i) * U.sum (U.zipWith (*) row (U.slice (i * k) nCov covMat))
+    resStdErr = map (getResStdError . U.slice 0 nCov) (getRows jac')
+
+predictionCI (Profile _ _) dist predFun _ profFun xss tree theta alpha estPIs = zipWith3 f estPIs yhat xss'
+  where
+    yhat = U.toList $ predFun xss
+    k = U.length theta
+    n = length yhat
+    t = sqrt $ quantile (fDistribution k (fromIntegral $ n - k)) (1 - alpha)
+
+    theta0 = calcTheta0 dist tree
+    xss' = getRows xss
+
+    f estPI yh xs = let
+        t' = replaceParam0 tree $ evalVar xs theta0
+        (spline, yh') = profFun estPI (theta U.// [(0, yh)]) t'
+      in CI yh' (spline (-t)) (spline t)
+
+-- inverse function of the distributions
+inverseDist :: Floating p => Distribution -> p -> p
+inverseDist Gaussian  y = y
+inverseDist Bernoulli y = log (y/(1-y))
+inverseDist Poisson   y = log y
+inverseDist _         y = y
+
+-- rewrite the tree by fixing theta 0 to optimal value
+replaceParam0 :: Fix SRTree -> Fix SRTree -> Fix SRTree
+replaceParam0 tree t0 = cata alg tree
+  where
+    alg (Var ix) = Fix $ Var ix
+    alg (Param 0) = t0
+    alg (Param ix) = Fix $ Param ix
+    alg (Const c) = Fix $ Const c
+    alg (Y ix)    = Fix $ Y ix
+    alg (Uni g t) = Fix $ Uni g t
+    alg (Bin op l r) = Fix $ Bin op l r
+
+evalVar :: Target -> Fix SRTree -> Fix SRTree
+evalVar xs = cata alg
+  where
+    alg (Var ix) = Fix $ Const (xs U.! ix)
+    alg (Param ix) = Fix $ Param ix
+    alg (Const c) = Fix $ Const c
+    alg (Y ix)    = Fix $ Y ix
+    alg (Uni g t) = Fix $ Uni g t
+    alg (Bin op l r) = Fix $ Bin op l r
+
+calcTheta0 :: Distribution -> Fix SRTree -> Fix SRTree
+calcTheta0 dist tree = case cata alg tree of
+  Left g -> g $ inverseDist dist (Fix $ Param 0)
+  Right _ -> error "No theta0?"
+  where
+    alg (Var ix) = Right $ Fix $ Var ix
+    alg (Param 0) = Left id
+    alg (Param ix) = Right $ Fix $ Param ix
+    alg (Const c) = Right $ Fix $ Const c
+    alg (Y ix)    = Right $ Fix $ Y ix
+    alg (Uni g t) = case t of
+      Left f -> Left $ f . evalInverse g
+      Right v -> Right $ evalFun g v
+    alg (Bin op l r) = case l of
+      Left f -> case r of
+        Left _ -> error "This shouldn't happen!"
+        Right v -> Left $ f . invright op v
+      Right vl -> case r of
+        Left g -> Left $ g . invleft op vl
+        Right vr -> Right $ evalOp op vl vr
+
+-- calculate the profile likelihood of every parameter
+getAllProfiles :: PType -> EvalTree -> Target -> Target -> [CI] -> Double -> [ProfileT]
+getAllProfiles ptype et theta stdErr estCIs alpha = getAll 0 []
+  where
+    k = U.length theta
+    n = ctRows et
+    tau_max  = sqrt $ quantile (fDistribution k (n - k)) (1 - 0.01)
+    tau_max' = sqrt $ quantile (fDistribution k (n - k)) (1 - alpha)
+
+    profFun ix = case ptype of
+                    Bates       -> getProfile      et theta (stdErr U.! ix) tau_max ix
+                    ODE         -> getProfileODE   et theta (stdErr U.! ix) (estCIs !! ix) tau_max ix
+                    Constrained -> getProfileCnstr et theta (stdErr U.! ix) tau_max' ix
+
+    getAll ix acc | ix == k   = acc
+                  | ix == k-1 && ptype == Constrained && ctDist et == Gaussian = case getProfileODE et theta (stdErr U.! ix) (estCIs !! ix) tau_max ix of
+                                  Left t  -> getAllProfiles ptype et t stdErr estCIs alpha
+                                  Right p -> getAll (ix + 1) (acc <> [p])
+                  | otherwise = case profFun ix of
+                                  Left t  -> getAllProfiles ptype et t stdErr estCIs alpha
+                                  Right p -> getAll (ix + 1) (acc <> [p])
+
+-- calculates the profile likelihood of a single parameter
+getProfile :: EvalTree -> Target -> Double -> Double -> Int -> Either Target ProfileT
+getProfile et theta stdErr_i tau_max ix
+  | stdErr_i == 0.0 = pure $ ProfileT (U.fromList [-tau_max, tau_max]) [theta, theta] (theta U.! ix) (const (theta U.! ix)) (const tau_max)
+  | otherwise =
+  do negDelta <- go kmax (-stdErr_i / 8) 0 1 mempty
+     posDelta <- go kmax  (stdErr_i / 8) 0 1 p0
+     let (taus', thetas') = negDelta <> posDelta
+         taus    = U.fromList taus'
+         thetas  = thetas'
+         (tau2theta, theta2tau) = createSplines taus thetas stdErr_i tau_max ix
+     pure $ ProfileT taus thetas optTh tau2theta theta2tau
+  where
+    p0        = ([0], [theta_opt])
+    kmax      = 300
+    nll_opt   = ctNLL et theta_opt
+    theta_opt = ctOptimizer et theta
+    optTh     = theta_opt U.! ix
+    minimizer = ctOptimizerFixed et ix
+
+    go 0 delta _ _         acc = Right acc
+    go k delta t inv_slope acc@(taus, thetas)
+      | isNaN inv_slope     = Right acc
+      | nll_cond < nll_opt  = Left theta_t
+      | abs tau > tau_max   = Right acc'
+
+      | otherwise           = go (k-1) delta (t + inv_slope) inv_slope' acc'
+      where
+        t_delta     = (theta_opt U.! ix) + delta * (t + inv_slope)
+        theta_delta = updateS theta_opt [(ix, t_delta)]
+        theta_t     = minimizer theta_delta
+        (nll_cond, grad) = ctGradNLL et theta_t
+        zv          = grad U.! ix
+        inv_slope'  = min 4.0 . max 0.0625 . abs $ (tau / (stdErr_i * zv))
+        tau         = signum delta * sqrt (2*nll_cond - 2*nll_opt)
+        acc'        = if nll_cond == nll_opt || maybe False (tau ==) (listToMaybe taus) || isNaN tau
+                         then acc
+                         else (tau:taus, theta_t:thetas)
+
+-- Based on https://insysbio.github.io/LikelihoodProfiler.jl/latest/
+-- Borisov, Ivan, and Evgeny Metelkin. "Confidence intervals by constrained optimization—An algorithm and software package for practical identifiability analysis in systems biology." PLOS Computational Biology 16.12 (2020): e1008495.
+getProfileCnstr :: EvalTree -> Target -> Double -> Double -> Int -> Either Target ProfileT
+getProfileCnstr et theta stdErr_i tau_max ix
+  | stdErr_i == 0.0 = pure $ ProfileT taus thetas theta_i (const theta_i) (const tau_max)
+  | otherwise       = pure $ ProfileT taus thetas theta_i tau2theta (const tau_max)
+  where
+    taus     = U.fromList [-tau_max, tau_max]
+    thetas   = [theta, theta]
+    theta_i  = theta U.! ix
+    getPoint = getEndPoint et theta tau_max ix
+    leftPt   = getPoint True
+    rightPt  = getPoint False
+    tau2theta tau = if tau < 0 then leftPt else rightPt
+
+getEndPoint :: EvalTree -> Target -> Double -> Int -> Bool -> Double
+getEndPoint et theta tau_max ix isLeft =
+  case minimizeAugLag problem (G.convert theta_opt) of
+            Right sol -> solutionParams sol VS.! ix
+            Left _    -> theta_opt U.! ix
+  where
+    n = U.length theta
+
+    theta_opt = ctOptimizer et theta
+    nll_opt   = ctNLL et theta_opt
+    loss_crit = nll_opt + tau_max
+
+    loss      = subtract loss_crit . ctNLL et . G.convert
+    obj       = (if isLeft then id else negate) . (VS.! ix)
+
+    stop       = ObjectiveRelativeTolerance 1e-4 :| [MaximumEvaluations 1000]
+    localAlg   = NELDERMEAD obj [] Nothing
+    local      = LocalProblem (fromIntegral n) stop localAlg
+    constraint = InequalityConstraint (Scalar loss) 1e-6
+
+    problem = AugLagProblem [] [] (AUGLAG_LOCAL local [constraint] [])
+{-# INLINE getEndPoint #-}
+
+-- Based on
+-- Jian-Shen Chen & Robert I Jennrich (2002) Simple Accurate Approximation of Likelihood Profiles,
+-- Journal of Computational and Graphical Statistics, 11:3, 714-732, DOI: 10.1198/106186002493
+getProfileODE :: EvalTree -> Target -> Double -> CI -> Double -> Int -> Either Target ProfileT
+getProfileODE et theta stdErr_i estCI tau_max ix
+  | stdErr_i == 0.0 = pure dflt
+  | otherwise = let (taus', thetas') = solLeft <> ([0], [theta_opt]) <> solRight
+                    taus   = U.fromList taus'
+                    thetas = thetas'
+                    (tau2theta, theta2tau) = createSplines taus thetas stdErr_i tau_max ix
+                in pure $ ProfileT taus thetas optTh tau2theta theta2tau
+  where
+    dflt      = ProfileT (U.fromList [-tau_max, tau_max]) [theta, theta] (theta U.! ix) (const (theta U.! ix)) (const tau_max)
+    theta_opt = ctOptimizer et theta
+    grader    = snd . ctGradNLL et
+    nll_opt   = ctNLL et theta_opt
+    optTh     = theta_opt U.! ix
+    p         = U.length theta
+    p'        = p + 1
+
+    odeFun gamma _ u =
+        let grad     = grader u
+            w        = ctHessianNLL et u
+            m        = [ U.generate p' (\i ->
+                            if i < p && j < p then (w !! j) U.! i
+                            else if i == ix || j == ix then 1
+                            else 0
+                          )
+                       | j <- [0 .. p'-1] ]
+            v        = U.snoc (U.map (*(-gamma)) grad) 1
+            dotTheta = unsafePerformIO $ luSolve m v
+        in U.init dotTheta
+
+    minRange    = max (abs (upper_ estCI - optTh)) (abs (lower_ estCI - optTh))
+    scanRange   = max minRange (tau_max * abs stdErr_i)
+    nPts        = max 50 (min 100 (ceiling (scanRange / minRange * 49) + 1))
+    tsHi = linSpace nPts (optTh, optTh + scanRange)
+    tsLo = linSpace nPts (optTh, optTh - scanRange)
+    scanOn sig = foldMap (calcTau sig) . f . scanl (rk (odeFun sig)) (optTh, theta_opt)
+                    where f = if sig==1 then id else reverse
+    solRight = scanOn 1 tsHi
+    solLeft  = scanOn (-1) tsLo
+    calcTau s t = let nll_i = ctNLL et (snd t)
+                      z     = signum ((snd t U.! ix) - optTh) * sqrt (2 * nll_i - 2 * nll_opt)
+                  in if z == 0 || isNaN z then ([], []) else ([z], [snd t])
+
+rk :: (Double -> Target -> Target) -> (Double, Target) -> Double -> (Double, Target)
+rk f (t, y) t' = (t', U.zipWith5 (\y0 k1 k2 k3 k4 -> y0 + h/6 * (k1 + 2*k2 + 2*k3 + k4)) y k1 k2 k3 k4)
+  where
+    h  = t' - t
+    k1 = f t y
+    k2 = f (t + 0.5*h) (U.zipWith (\y0 k -> y0 + 0.5*h*k) y k1)
+    k3 = f (t + 0.5*h) (U.zipWith (\y0 k -> y0 + 0.5*h*k) y k2)
+    k4 = f (t + 1.0*h) (U.zipWith (\y0 k -> y0 + 1.0*h*k) y k3)
+{-# INLINE rk #-}
+
+-- tau0, tau1 theta0, thetaX = tau1 theta0 / tau0
+getStatsFromModel :: Distribution -> Maybe Target -> Columns -> Target -> Fix SRTree -> Target -> BasicStats
+getStatsFromModel dist mYerr xss ys tree theta = MkStats cov corr stdErr
+  where
+    k = U.length theta
+    n = U.length ys
+    nParams = fromIntegral k
+    ident = fromRowMajor k k (U.generate (k * k) (\ix -> let (i, j) = ix `divMod` k in if i == j then 1.0 else 0.0))
+
+    hess = hessianNLL dist mYerr xss ys tree theta
+
+    fexcept :: SomeException -> IO Columns
+    fexcept e = trace ("cov NegDef" <> show (toRowMajor hess)) $ pure ident
+
+    cov = unsafePerformIO $ catch (invChol hess) fexcept
+
+    covMat = toRowMajor cov
+    stdErr = U.generate k (\ix -> sqrt $ covMat U.! (ix * k + ix))
+
+    stdErrSq = case outer stdErr stdErr of
+      Right v -> v
+      Left _ -> []
+
+    stdErrSqMat = toRowMajor stdErrSq
+    corr = fromRowMajor k k $ U.generate (k * k) (\ix -> covMat U.! ix / stdErrSqMat U.! ix)
+
+-- Create splines for profile-t
+createSplines :: Target -> Columns -> Double -> Double -> Int -> (Double -> Double, Double -> Double)
+createSplines taus thetas se tau_max ix
+  | n < 2 = (genSplineFun [(-tau_max, -se), (tau_max, se)], genSplineFun [(-se, 0), (se, 1)])
+  | otherwise = (tau2theta, theta2tau)
+  where
+    n = U.length taus
+    cols = getCol ix thetas
+    nubOnFirst = nubBy (\x y -> fst x == fst y)
+    tau2theta = genSplineFun $ nubOnFirst $ sortOnFirst taus cols
+    theta2tau = genSplineFun $ nubOnFirst $ sortOnFirst cols taus
+
+getCol :: Int -> Columns -> Target
+getCol ix mtx = U.generate (length mtx) (\j -> (mtx !! j) U.! ix)
+{-# inline getCol #-}
+
+sortOnFirst :: Target -> Target -> [(Double, Double)]
+sortOnFirst xs ys = sortOn fst $ zip (U.toList xs) (U.toList ys)
+{-# inline sortOnFirst #-}
+
+splinesSketches :: Double -> Target -> Target -> (Double -> Double) -> (Double -> Double)
+splinesSketches tauScale (U.toList -> tau) (U.toList -> theta) theta2tau
+  | length tau < 2 = id
+  | otherwise = genSplineFun gpq
+  where
+    gpq = sortOn fst [ (x, acos y') | (x, y) <- zip tau theta, let y' = theta2tau y / tauScale, abs y' < 1 ]
+
+approximateContour :: Int -> Int -> [ProfileT] -> Int -> Int -> Double -> [(Double, Double)]
+approximateContour nParams nPoints profs ix1 ix2 alpha = go 0
+  where
+    (prof1, prof2) = (profs !! ix1, profs !! ix2)
+    (tau2theta1, theta2tau1) = (_tau2theta prof1, _theta2tau prof1)
+    (tau2theta2, theta2tau2) = (_tau2theta prof2, _theta2tau prof2)
+
+    tauScale = sqrt (fromIntegral nParams * quantile (fDistribution nParams (fromIntegral nPoints - fromIntegral nParams)) (1 - alpha))
+    splineG1 = splinesSketches tauScale (_taus prof2) (getCol ix1 (_thetas prof2)) theta2tau1
+    splineG2 = splinesSketches tauScale (_taus prof1) (getCol ix2 (_thetas prof1)) theta2tau2
+
+    angles = [ (0, splineG2 1), (splineG1 1, 0), (pi, splineG2 (-1)), (splineG1 (-1), pi) ]
+    applyIfNeg (x, y) = if y < 0 then (-x, -y) else (x ,y)
+    points' = [applyIfNeg ((x+y)/2, x - y) | (x, y) <- angles]
+    points = sortOn fst $ points' <> maybe [] (\(x,y) -> [(x + 2*pi, y)]) (listToMaybe points')
+    splineAD = genSplineFun points
+
+    fmod a b = a - b * fromIntegral (truncate (a / b))
+
+    tot = 100
+    go 100 = []
+    go ix = (p, q) : go (ix+1)
+      where
+        ai = fromIntegral ix * 2 * pi / 99 - pi
+        di = splineAD ai
+        t1i = tauScale * cos (ai + di)
+        t2i = tauScale * cos (ai - di)
+        p = tau2theta1 t1i
+        q = tau2theta2 t2i
+ 
diff --git a/src/Algorithm/SRTree/Likelihoods.hs b/src/Algorithm/SRTree/Likelihoods.hs
new file mode 100644
--- /dev/null
+++ b/src/Algorithm/SRTree/Likelihoods.hs
@@ -0,0 +1,329 @@
+{-# LANGUAGE ViewPatterns #-}
+{-# LANGUAGE TypeApplications #-}
+{-# LANGUAGE BangPatterns #-}
+{-# LANGUAGE UnboxedTuples #-}
+
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  AlgorithV.SRTree.Likelihoods 
+-- Copyright   :  (c) Fabricio Olivetti 2021 - 2024
+-- License     :  BSD3
+-- Maintainer  :  fabricio.olivetti@gmail.com
+-- Stability   :  experimental
+-- Portability :  ConstraintKinds
+--
+-- Functions to calculate different likelihood functions, their gradient, and Hessian matrices.
+--
+-----------------------------------------------------------------------------
+module Algorithm.SRTree.Likelihoods
+  ( Distribution (..)
+  , Loss (..)
+  , readLoss
+  , Target
+  , Columns
+  , buildDistLoss
+  , buildLoss
+  , buildPredictor
+  , fisherNLL
+  , getSErr
+  , hessianNLL
+  )
+    where
+
+import Data.SRTree
+import Data.SRTree.Recursion ( cata, accu )
+import Data.SRTree.Derivative (deriveByParam, deriveByVar, derivative, derivOp)
+import Data.SRTree.Eval
+import qualified Data.IntMap.Strict as IntMap
+import qualified Data.Vector.Storable as VS
+import qualified Data.Vector.Storable.Mutable as VSM
+
+import GHC.IO (unsafePerformIO)
+import Data.Maybe
+import Text.Read (readMaybe)
+
+import qualified Data.Vector.Unboxed as V
+import qualified Data.Vector.Unboxed.Mutable as VM
+import Control.Concurrent (getNumCapabilities)
+import Control.Concurrent.Async (forConcurrently)
+
+import Debug.Trace
+import Data.SRTree.Print
+import Control.Monad.State.Strict
+import Control.Monad.Identity
+
+import Data.SRTree.Print
+import qualified Data.Vector.Generic as G
+
+-- | Supported distributions for negative log-likelihood.
+-- | HGaussian is Gaussian with heteroscedasticity, where the error should be provided.
+data Distribution = Gaussian | HGaussian | Bernoulli | Poisson | ROXY | LeastSquares
+    deriving (Show, Read, Enum, Bounded, Eq)
+
+-- | Loss functions used to build the per-row optimization objective (see
+-- 'buildLoss'), to be used by e.g. "Algorithm.SRTree.Opt". 'NLL' wraps a
+-- 'Distribution' to use its negative log-likelihood as the loss --
+-- including the plain \'MSE\' and \'LOG10\' losses, reached via @NLL MSE@
+-- and @NLL LOG10@ respectively (kept on 'Distribution', rather than
+-- duplicated here, since Haskell does not allow two data constructors
+-- with the same name -- 'MSE' and 'LOG10' -- to coexist in the same
+-- module).
+data Loss = MSE | LOG10 | MAE | MAPE | Pinball Double | NLL Distribution
+    deriving (Show, Read, Eq)
+
+instance Enum Loss where
+    fromEnum MSE         = 0
+    fromEnum LOG10       = 1
+    fromEnum MAE         = 2
+    fromEnum MAPE        = 3
+    fromEnum (Pinball _) = 4
+    fromEnum (NLL dist)  = 5 + fromEnum dist
+
+    toEnum   0 = MSE
+    toEnum   1 = LOG10
+    toEnum   2 = MAE
+    toEnum   3 = MAPE
+    toEnum   4 = Pinball 0.95
+    toEnum   x | x >= 5 = NLL (toEnum (x-5))
+
+instance Bounded Loss where
+    minBound = MSE
+    maxBound = NLL ROXY
+
+-- | Parse a loss from its CLI string.  Accepts both the direct 'Loss'
+-- names ('MSE', 'LOG10', 'MAE', 'MAPE', @Pinball tau@) and the bare
+-- 'Distribution' names ('Gaussian', 'HGaussian', 'Bernoulli', 'Poisson',
+-- 'ROXY', 'LeastSquares'), which are wrapped in 'NLL'.
+readLoss :: String -> Maybe Loss
+readLoss s = case readMaybe s of
+  Just l  -> Just l
+  Nothing -> NLL <$> (readMaybe s :: Maybe Distribution)
+
+-- | logistic function
+logistic :: Floating a => a -> a
+logistic x = 1 / (1 + exp (-x))
+{-# inline logistic #-}
+
+-- | get the standard error from a Maybe Double
+-- if it is Nothing, estimate from the ssr, otherwise use the current value
+-- For distributions other than Gaussian, it defaults to a constant 1
+getSErr :: Num a => Distribution -> a -> Maybe a -> a
+getSErr Gaussian est = fromMaybe est
+getSErr _        _   = const 1
+{-# inline getSErr #-}
+
+-- negation of the sum of values in a vector
+negSum :: Target -> Double
+negSum = negate . V.sum
+{-# inline negSum #-}
+
+checkAssumptions :: Distribution -> Maybe Target ->  Target -> Bool
+checkAssumptions Gaussian  _           _  = True
+checkAssumptions HGaussian (Just yErr) _  = True
+checkAssumptions HGaussian Nothing     _  = False
+checkAssumptions Bernoulli _           ys = V.all (\x -> x /= 0 && x /= 1) ys
+checkAssumptions Poisson   _           ys = V.all (>0) ys
+checkAssumptions LeastSquares _         _  = True
+checkAssumptions ROXY          mYerr       ys = isJust mYerr
+
+-- WARNING: pass tree with parameters
+-- TODO: handle error similar to ROXY
+
+-- | Builds the per-row negative log-likelihood expression for a given
+-- 'Distribution', to be summed across rows (e.g. by
+-- 'Algorithm.SRTree.AD.evalGradMulti') and differentiated by automatic
+-- differentiation. The special variable index @-1@ refers to the target
+-- ('ys') and @-2@ to the target's measurement error ('yErr'), following
+-- the convention used by "Algorithm.SRTree.AD".
+--
+-- 'buildLoss' delegates to this function for the @'NLL' dist@ loss.
+buildDistLoss :: Distribution -> Double -> Fix SRTree -> Fix SRTree
+buildDistLoss Gaussian m tree =  (square(tree - var (-1)) * (e (negate (param p)))) + (((param p)))
+  where
+    square = Fix . Uni Square
+    e      = Fix. Uni Exp
+    p      = countParamsUniq tree
+buildDistLoss HGaussian m tree = (tree - var (-1)) ** 2 / var (-2) + constv m * log (2*pi* var (-2))
+buildDistLoss Poisson m tree   = var (-1) * log (var (-1)) + exp tree - var (-1) * tree
+buildDistLoss Bernoulli m tree = log (1 + exp (negate tree)) + (1 - var (-1)) * tree
+buildDistLoss LeastSquares m tree = ((tree - var (-1)) ** 2) / constv m
+buildDistLoss ROXY m tree      = neglogP
+  where
+    p        = countParamsUniq tree
+    f        = log (abs tree) / log 10
+    fprime   = deriveByVar 0 tree / (log 10 * tree) * var 0 * log 10
+    logX     = var 1
+    logY     = var 2
+    logXErr  = var 3
+    logYErr  = var 4
+    sig      = param p
+    mu_gauss = param (p+1)
+    w_gauss  = param (p+2)
+    w_gauss2 = w_gauss ** 2
+    s2       = logYErr + sig ** 2
+    den      = fprime ** 2 * w_gauss2 * logXErr + s2 * (w_gauss2 + logXErr)
+    neglogP  = log (2*pi)
+              + log den
+              + ( w_gauss2 * (f - logY) * (f - logY)
+                + logXErr * (fprime *(mu_gauss - logX) + f - logY)**2
+                + s2 * (logX - mu_gauss) ** 2
+                ) / den
+
+-- | Builds the per-row loss expression for a given 'Loss', to be summed
+-- across rows (e.g. by 'Algorithm.SRTree.AD.evalGradMulti') and
+-- differentiated by automatic differentiation. Same special variable
+-- convention as 'buildDistLoss'.
+buildLoss :: Loss -> Double -> Fix SRTree -> Fix SRTree
+buildLoss MSE m tree           = ((tree - var (-1)) ** 2) / constv m
+buildLoss LOG10 m tree         = (((log (y / tree')) / log 10) ** 2) / constv m
+  where
+    tree' = (tree + sqrt(tree^2 + 1e-10))
+    y     = (var (-1) + sqrt(var (-1) ^ 2 + 1e-10))
+
+buildLoss MAE m tree           = abs (tree - var (-1)) / constv m
+
+-- | Mean absolute percentage error. A small epsilon is added to the
+-- denominator's magnitude to avoid division by zero when the target is
+-- (close to) zero.
+buildLoss MAPE m tree          = (abs (tree - var (-1)) / (abs (var (-1)) + constv 1e-8)) / constv m
+
+-- | Pinball (quantile) loss for a residual @r = y - yhat@:
+-- @tau * r@ if @r >= 0@, @(tau - 1) * r@ otherwise. Both cases are
+-- captured in closed form by @0.5 * ((2*tau - 1) * r + abs r)@, which
+-- avoids branching in the symbolic tree.
+buildLoss (Pinball tau) m tree = ((constv (2*tau - 1) * r + abs r) / 2) / constv m
+  where r                      = var (-1) - tree
+
+buildLoss (NLL dist) m tree    = buildDistLoss dist m tree
+
+-- | Builds the predictor expression from a fitted model tree by applying
+-- the inverse link function implied by the 'Distribution': @exp@ for
+-- 'Poisson', the logistic function for 'Bernoulli', and the identity
+-- otherwise.
+buildPredictor :: Distribution -> Fix SRTree -> Fix SRTree
+buildPredictor Poisson   tree = exp tree
+buildPredictor Bernoulli tree = 1 / (1 + exp (negate tree))
+buildPredictor _         tree = tree
+
+-- | Fisher information of negative log-likelihood
+fisherNLL :: Distribution -> Maybe Target -> Columns -> Target -> Fix SRTree -> Target -> Target
+fisherNLL ROXY mYerr xss ys tree theta = V.generate p finiteDiff
+  where
+    m             = V.length ys
+    p             = V.length theta
+    loss          = compileLoss xss (buildDistLoss ROXY (fromIntegral m) tree) ys mYerr
+    f             = loss theta
+    eps           = 1e-6
+    finiteDiff ix = unsafePerformIO $ do
+                      theta' <- V.thaw theta
+                      v <- VM.read theta' ix
+                      VM.write theta' ix (v + eps)
+                      thetaPlus <- V.freeze theta'
+                      VM.write theta' ix (v - eps)
+                      thetaMinus <- V.freeze theta'
+                      let fPlus     = loss thetaPlus
+                          fMinus    = loss thetaMinus
+                      pure $ (fPlus + fMinus - 2*f)/(eps*eps)
+fisherNLL Gaussian mYerr xss ys tree theta = V.generate p finiteDiff
+  where
+    m             = V.length ys
+    p             = V.length theta
+    loss          = compileLoss xss (buildDistLoss Gaussian (fromIntegral m) tree) ys mYerr
+    f             = loss theta
+    eps           = 1e-6
+    finiteDiff ix = unsafePerformIO $ do
+                      theta' <- V.thaw theta
+                      v <- VM.read theta' ix
+                      VM.write theta' ix (v + eps)
+                      thetaPlus <- V.freeze theta'
+                      VM.write theta' ix (v - eps)
+                      thetaMinus <- V.freeze theta'
+                      let fPlus     = loss thetaPlus
+                          fMinus    = loss thetaMinus
+                      pure $ (fPlus + fMinus - 2*f)/(eps*eps)
+fisherNLL dist mYerr xss ys tree theta = V.generate p build
+  where
+    build ix = let dtdix   = deriveByParam ix t'
+                   d2tdix2 = deriveByParam ix dtdix 
+                   f'      = eval dtdix 
+                   f''     = eval d2tdix2 
+               in V.sum $ phi' * f'^2 - res * f''
+               --case dist of
+               --     Gaussian -> V.sum . (/(theta V.! (p-1))) $ phi' * f'^2 - res * f''
+               --     _        -> V.sum $ phi' * f'^2 - res * f''
+    m      = V.length ys
+    p      = V.length theta
+    t'     = fst $ floatConstsToParam tree
+    eval   = \t -> compile xss t theta
+    yhat   = eval t'
+    res    = ys - phi
+    yErr   = case mYerr of
+               Nothing -> V.replicate m est
+               Just e  -> e
+    est    = fromIntegral (m - p)
+
+    (phi, phi') = case dist of
+                    Gaussian      -> (yhat, V.replicate m 1)
+                    LeastSquares  -> (yhat, V.replicate m 1)
+                    Bernoulli     -> (logistic yhat, phi*(V.replicate m 1 - phi))
+                    Poisson       -> (exp yhat, phi)
+
+-- | Hessian of negative log-likelihood
+--
+-- Note, though the Fisher is just the diagonal of the return of this function
+-- it is better to keep them as different functions for efficiency
+hessianNLL :: Distribution -> Maybe Target -> Columns -> Target -> Fix SRTree -> Target -> Columns
+hessianNLL ROXY mYerr xss ys tree theta = undefined
+hessianNLL Gaussian mYerr xss ys tree theta = [V.generate p (build iy) | iy <- [0..p-1]]
+  where
+    build iy ix = let dtdix   = deriveByParam ix tree
+                      dtdiy   = deriveByParam iy tree
+                      d2tdixy = deriveByParam iy dtdix
+                      fx      = eval dtdix
+                      fy      = eval dtdiy
+                      fxy     = eval d2tdixy
+                   in if ix < p-1 && iy < p-1
+                        then V.sum . (/yErr) $ fx * fy - res * fxy
+                        else if ix == p-1 && iy == p-1
+                               then (*0.5) . V.sum . (/ yErr ) $ res*res
+                               else if ix == p-1
+                                   then V.sum . (/yErr) $ res * fy
+                                   else V.sum . (/yErr) $ res * fx
+    m    = V.length ys
+    p    = V.length theta
+    yErr :: Target
+    yErr = V.replicate m $ exp (theta V.! (p-1)) / est
+    yhat = eval tree
+    res  = ys - yhat
+    eval = \t -> compile xss t theta
+    est  = fromIntegral (m - p + 1)
+
+hessianNLL dist mYerr xss ys tree theta = [V.generate p (build iy) | iy <- [0..p-1]]
+  where
+    build iy ix = let dtdix   = deriveByParam ix t' 
+                      dtdiy   = deriveByParam iy t' 
+                      d2tdixy = deriveByParam iy dtdix
+                      fx      = eval dtdix 
+                      fy      = eval dtdiy 
+                      fxy     = eval d2tdixy 
+                    in case dist of
+                         Gaussian -> V.sum . (/yErr) $ phi' * fx * fy - res * fxy
+                         _        -> V.sum $ phi' * fx * fy - res * fxy
+
+    m           = V.length ys
+    p           = V.length theta
+    t'          = tree -- relabelParams tree -- $ floatConstsToParam tree
+    eval        = \t -> compile xss t theta
+    yErr        = case mYerr of
+                   Nothing -> V.replicate m est
+                   Just e  -> e
+    est         = fromIntegral (m - p)
+    yhat        = eval t'
+    res         = ys - phi
+
+    (phi, phi') = case dist of
+                    Gaussian      -> (yhat, V.replicate m 1)
+                    LeastSquares  -> (yhat, V.replicate m 1)
+                    Bernoulli     -> (logistic yhat, phi*(V.replicate m 1 - phi))
+                    Poisson       -> (exp yhat, phi)
+
diff --git a/src/Algorithm/SRTree/ModelSelection.hs b/src/Algorithm/SRTree/ModelSelection.hs
new file mode 100644
--- /dev/null
+++ b/src/Algorithm/SRTree/ModelSelection.hs
@@ -0,0 +1,198 @@
+{-# LANGUAGE ViewPatterns #-}
+{-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE LambdaCase #-}
+-------------------------------------------------------------------------------
+-- |
+-- Module      :  Algorithm.SRTree.ModelSelection
+-- Copyright   :  (c) Fabricio Olivetti 2021 - 2024
+-- License     :  BSD3
+-- Maintainer  :  fabricio.olivetti@gmail.com
+-- Stability   :  experimental
+-- Portability :  ConstraintKinds
+--
+-- Helper functions for model selection criteria
+-------------------------------------------------------------------------------
+
+module Algorithm.SRTree.ModelSelection 
+    ( bic
+    , aic
+    , evidence
+    , fractionalBayesFactor
+    , mdl
+    , mdlLatt
+    , mdlFreq
+    , logFunctional
+    , logFunctionalFreq
+    , ModelEval (..)
+    , module Algorithm.SRTree.Compile
+    ) where
+
+import Algorithm.SRTree.Utils ( det )
+import Algorithm.SRTree.Likelihoods
+    ( fisherNLL, hessianNLL
+    , Distribution(..), Loss(..), buildDistLoss
+    )
+import Data.SRTree
+import Data.SRTree.Eval (Target, Columns, compileLoss)
+import Data.SRTree.Recursion (cata)
+import qualified Data.Vector.Unboxed as U
+import Algorithm.SRTree.Compile
+
+import Debug.Trace
+
+-- | Bayesian information criterion
+bic :: EvaluatedTree -> Double
+bic et = valParams et * log (valRows et) + 2 * valLoss et
+{-# INLINE bic #-}
+
+-- | Akaike information criterion
+aic :: EvaluatedTree -> Double
+aic et = 2 * valParams et + 2 * valLoss et
+{-# INLINE aic #-}
+
+-- | Evidence
+evidence :: EvaluatedTree -> Double
+evidence et = (1 - b) * valLoss et - valParams et / 2 * log b
+  where
+    b = 1 / sqrt (valRows et)
+{-# INLINE evidence #-}
+
+fractionalBayesFactor :: EvaluatedTree -> Double
+fractionalBayesFactor et = (1 - b) * valLoss et - valParams et / 2 * log b + f_compl + valParams et / 2 * log(2*pi*nup)
+  where
+    b = 1 / sqrt (valRows et)
+    nup = exp(1 - log 3)
+    f_compl = countNodes (valTree et) * log (countUniqueTokens (valTree et))
+{-# INLINE fractionalBayesFactor #-}
+
+-- | MDL as described in
+-- Bartlett, Deaglan J., Harry Desmond, and Pedro G. Ferreira. "Exhaustive symbolic regression." IEEE Transactions on Evolutionary Computation (2023).
+mdl :: EvaluatedTree -> Double
+mdl et = valLoss et + logFunctional (valTree et) + valLogParams et
+{-# INLINE mdl #-}
+
+-- | MDL Lattice as described in
+-- Bartlett, Deaglan, Harry Desmond, and Pedro Ferreira. "Priors for symbolic regression." Proceedings of the Companion Conference on Genetic and Evolutionary Computation. 2023.
+mdlLatt :: EvaluatedTree -> Double
+mdlLatt et = valLoss et + logFunctional (valTree et) + valLogParamsLattice et
+{-# INLINE mdlLatt #-}
+
+-- | same as `mdl` but weighting the functional structure by frequency calculated using a wiki information of
+-- physics and engineering functions
+mdlFreq :: EvaluatedTree -> Double
+mdlFreq et = valLoss et + logFunctionalFreq (valTree et) + valLogParams et
+{-# INLINE mdlFreq #-}
+
+-- | The possible metrics used to evaluate\/select a fitted model,
+-- ranging from plain loss functions ('EvalLoss', wrapping any 'Loss' --
+-- including a distribution's negative log-likelihood via @EvalLoss (NLL
+-- dist)@) to the error metrics and model-selection criteria already
+-- provided by this module ('RMSE', 'R2', 'AIC', 'BIC', 'Evidence', 'FBF',
+-- 'MDL', 'MDLLatt', 'MDLFreq').
+data ModelEval
+  = RMSE
+  | R2
+  | AIC
+  | BIC
+  | Evidence
+  | FBF
+  | MDL
+  | MDLLatt
+  | MDLFreq
+  | EvalLoss Loss
+  deriving (Show, Read, Eq)
+
+instance Enum ModelEval where
+    fromEnum RMSE         = 0
+    fromEnum R2           = 1
+    fromEnum AIC          = 2
+    fromEnum BIC          = 3
+    fromEnum Evidence     = 4
+    fromEnum FBF          = 5
+    fromEnum MDL          = 6
+    fromEnum MDLLatt      = 7
+    fromEnum MDLFreq      = 8
+    fromEnum (EvalLoss l) = 9 + fromEnum l
+
+    toEnum   0 = RMSE
+    toEnum   1 = R2
+    toEnum   2 = AIC
+    toEnum   3 = BIC
+    toEnum   4 = Evidence
+    toEnum   5 = FBF
+    toEnum   6 = MDL
+    toEnum   7 = MDLLatt
+    toEnum   8 = MDLFreq
+    toEnum   x | x >= 9 = EvalLoss (toEnum (x-9))
+
+instance Bounded ModelEval where
+    minBound = RMSE
+    maxBound = EvalLoss maxBound
+
+-- | Evaluates the requested 'ModelEval' metric.
+--
+-- for 'RMSE', and 'R2' the tree must have been compiled
+-- with MSE loss.
+
+evalModelSelection :: ModelEval -> EvaluatedTree -> Double
+evalModelSelection (EvalLoss MAE)           et = valLoss et
+evalModelSelection (EvalLoss MAPE)          et = valLoss et
+evalModelSelection (EvalLoss (Pinball tau)) et = valLoss et
+evalModelSelection (EvalLoss (NLL dist))    et = valLoss et
+evalModelSelection RMSE                     et = sqrt (valLoss et) -- assumes MSE
+evalModelSelection R2                       et = 1 - (valRows et * valLoss et) / valVar et -- assumes MSE
+evalModelSelection AIC                      et = aic et
+evalModelSelection BIC                      et = bic et
+evalModelSelection Evidence                 et = evidence et
+evalModelSelection FBF                      et = fractionalBayesFactor et
+evalModelSelection MDL                      et = mdl et
+evalModelSelection MDLLatt                  et = mdlLatt et
+evalModelSelection MDLFreq                  et = mdlFreq et
+{-# INLINE evalModelSelection #-}
+
+-- log of the functional complexity
+logFunctional :: Fix SRTree -> Double
+logFunctional tree = countNodes tree * log (countUniqueTokens tree') + foldr (\c acc -> log (abs c) + acc) 0 consts  + log(2) * numberOfConsts
+  where
+    tree' = fst $ floatConstsToParam tree
+    consts = getIntConsts tree
+    numberOfConsts = fromIntegral $ length consts
+{-# INLINE logFunctional #-}
+
+-- same as above but weighted by frequency
+logFunctionalFreq :: Fix SRTree -> Double
+logFunctionalFreq tree = treeToNat tree'  + foldr (\c acc -> log (abs c) + acc) 0 consts  + countVarNodes tree * log (numberOfVars tree)
+  where
+    tree' = fst $ floatConstsToParam tree
+    consts = getIntConsts tree
+{-# INLINE logFunctionalFreq #-}
+
+
+treeToNat :: Fix SRTree -> Double
+treeToNat = cata $ \case
+  Uni f t -> funToNat f + t
+  Bin op l r -> opToNat op + l + r
+  _ -> 0.6610799229372109
+  where
+    opToNat :: Op -> Double
+    opToNat Add = 2.500842464597881
+    opToNat Sub = 2.500842464597881
+    opToNat Mul = 1.720356134912558
+    opToNat Div = 2.60436883851265
+    opToNat Power = 2.527957363394847
+    opToNat PowerAbs = 2.527957363394847
+    opToNat AQ = 2.60436883851265
+
+    funToNat :: Function -> Double
+    funToNat Sqrt = 4.780867285331753
+    funToNat Log = 4.765599813200964
+    funToNat Exp = 4.788589331425663
+    funToNat Abs = 6.352564869783006
+    funToNat Sin = 5.9848400896576885
+    funToNat Cos = 5.474014465891698
+    funToNat Sinh = 8.038963823353235
+    funToNat Cosh = 8.262107374667444
+    funToNat Tanh = 7.85664226655928
+    funToNat Tan = 8.262107374667444
+    funToNat _ = 8.262107374667444
+{-# INLINE treeToNat #-}
diff --git a/src/Algorithm/SRTree/NonlinearOpt.hs b/src/Algorithm/SRTree/NonlinearOpt.hs
new file mode 100644
--- /dev/null
+++ b/src/Algorithm/SRTree/NonlinearOpt.hs
@@ -0,0 +1,98 @@
+{-# LANGUAGE BangPatterns #-}
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Algorithm.SRTree.Opt 
+-- Copyright   :  (c) Fabricio Olivetti 2021 - 2024
+-- License     :  BSD3
+-- Maintainer  :  fabricio.olivetti@gmail.com
+-- Stability   :  experimental
+-- Portability :  ConstraintKinds
+--
+-- Functions to optimize the parameters of an expression.
+--
+-----------------------------------------------------------------------------
+module Algorithm.SRTree.NonlinearOpt
+    where
+
+import Algorithm.SRTree.Likelihoods
+import Numeric.Optimization.NLOPT
+import Data.Bifunctor (bimap, second)
+import Data.SRTree (Fix (..), SRTree (..), floatConstsToParam, relabelParams, countNodes, convertProtectedOps)
+import Data.SRTree.Eval
+import Algorithm.SRTree.AD
+
+import qualified Data.Vector.Unboxed as V
+import qualified Data.Vector.Storable as VS
+import qualified Data.Vector.Unboxed.Mutable as VM
+import qualified Data.Vector.Generic as G
+
+import qualified Data.IntMap.Strict as IntMap
+import Data.SRTree.Recursion
+import Control.Monad.State.Strict
+import Control.Monad.Identity
+
+import Debug.Trace
+
+minimizeNLLWith :: (VS.Vector Double -> (Double, VS.Vector Double)) -> (ObjectiveD -> (Maybe VectorStorage) -> LocalAlgorithm) -> Int -> Target -> (Target, Double, Int)
+minimizeNLLWith funAndGrad alg niter t0
+  | niter == 0 = (t0, f, 0)
+  | n == 0     = (t0, f, 0)
+  | otherwise  = (t_opt', fst (funAndGrad t_opt), nEvs)
+  where
+    t0'        = G.convert t0
+    n          = V.length t0
+
+    (f, _)     = funAndGrad t0' -- if there's no parameter or no iterations
+
+    algorithm  = alg funAndGrad (Just $ VectorStorage $ fromIntegral n)
+    stop       = ObjectiveRelativeTolerance 1e-6 :| [ObjectiveAbsoluteTolerance 1e-6, MaximumEvaluations (fromIntegral niter)]
+    problem    = LocalProblem (fromIntegral n) stop algorithm
+    (t_opt, nEvs) = case minimizeLocal problem t0' of
+                      Right sol -> (solutionParams sol, nEvals sol)
+                      Left e    -> (t0', 0)
+    t_opt'      = G.convert t_opt
+{-# INLINE minimizeNLLWith #-}
+
+-- | minimizes the negative log-likelihood of the expression
+minimizeNLL' :: (ObjectiveD -> (Maybe VectorStorage) -> LocalAlgorithm) -> ADBackEnd -> Loss -> Maybe Target -> Int -> Columns -> Target -> Fix SRTree -> Target -> (Target, Double, Int)
+minimizeNLL' alg backend dist mYerr niter xss ys tree t0 = minimizeNLLWith funAndGrad alg niter t0
+  where
+    m          = V.length ys
+    tree'      = buildLoss dist (fromIntegral m) tree
+    funAndGrad = compileFunAndGrad backend xss ys mYerr tree'
+ 
+
+minimizeNLL :: ADBackEnd -> Loss -> Maybe Target -> Int -> Columns -> Target -> Fix SRTree -> Target -> (Target, Double, Int)
+minimizeNLL = minimizeNLL' TNEWTON
+
+minimizeNLLWithFixedParam' :: (ObjectiveD -> (Maybe VectorStorage) -> LocalAlgorithm) -> ADBackEnd -> Loss -> Maybe Target -> Int -> Columns -> Target -> Fix SRTree -> Int -> Target -> Target
+minimizeNLLWithFixedParam' alg backend dist mYerr' niter xss' ys' tree ix t0 = result
+  where
+    m          = V.length ys'
+    tree'      = buildLoss dist (fromIntegral m) tree
+    fixedVal   = t0 V.! ix
+    p          = V.length t0
+
+    evalFull   = compileFunAndGrad backend xss' ys' mYerr' tree'
+
+    wrapRed thRed = let (lo, hi) = VS.splitAt ix thRed
+                    in (lo `VS.snoc` fixedVal) VS.++ hi
+    unwrapRed th  = let (lo, hi) = VS.splitAt ix th
+                    in lo VS.++ VS.tail hi
+
+    wrap thRed = let (lo, hi) = V.splitAt ix thRed  in (lo `V.snoc` fixedVal) V.++ hi
+    unwrap th  = let (lo, hi) = V.splitAt ix th      in lo V.++ V.tail hi
+
+    fgRed :: VS.Vector Double -> (Double, VS.Vector Double)
+    fgRed thRed =
+      let thFull        = wrapRed thRed
+          (nll, gradFull) = evalFull thFull
+          gradRed       = unwrapRed gradFull
+      in (nll, gradRed)
+
+    t0Red = unwrap t0
+    (tRawRed,_,_) = minimizeNLLWith fgRed alg niter t0Red
+    result = wrap tRawRed
+
+minimizeNLLWithFixedParam = minimizeNLLWithFixedParam' TNEWTON
+
diff --git a/src/Algorithm/SRTree/Utils.hs b/src/Algorithm/SRTree/Utils.hs
new file mode 100644
--- /dev/null
+++ b/src/Algorithm/SRTree/Utils.hs
@@ -0,0 +1,320 @@
+{-# LANGUAGE BangPatterns #-}
+{-# LANGUAGE FlexibleContexts #-}
+module Algorithm.SRTree.Utils where
+
+import qualified Data.Vector.Unboxed as U
+import qualified Data.Vector.Unboxed.Mutable as UM
+import Control.Monad
+import Control.Monad.Catch
+import Control.Monad.Primitive
+import Control.Monad.IO.Class
+import System.IO.Unsafe
+
+-- taken from https://hackage.haskell.org/package/cubicspline-0.1.2
+import Control.Arrow
+import Data.List (unfoldr)
+
+import Data.SRTree.Eval
+import Debug.Trace (traceShow)
+
+-- | Internal helper to get dimensions (rows, columns)
+matSize :: Columns -> (Int, Int)
+matSize [] = (0, 0)
+matSize cs@(c:_) = (U.length c, length cs)
+
+getRows :: Columns -> [Target]
+getRows mtx
+  | n == 0 = []
+  | otherwise = [ U.fromListN n [ c U.! i | c <- mtx ] | i <- [0 .. m - 1] ]
+  where (m, n) = matSize mtx
+{-# INLINE getRows #-}
+
+getCols :: Columns -> [Target]
+getCols = id
+{-# INLINE getCols #-}
+
+appendRow :: MonadThrow m => Columns -> Target -> m Columns
+appendRow xs v = pure $ zipWith U.snoc xs (U.toList v)
+{-# INLINE appendRow #-}
+
+appendCol :: MonadThrow m => Columns -> Target -> m Columns
+appendCol xs v = pure $ xs ++ [v]
+{-# INLINE appendCol #-}
+
+updateS :: Target -> [(Int, Double)] -> Target
+updateS vec new = vec U.// new
+
+linSpace :: Int -> (Double, Double) -> [Double]
+linSpace num (lo, hi) = Prelude.take num $ iterate (\x -> x + step) lo
+  where step = (hi - lo) / (fromIntegral num - 1)
+{-# INLINE linSpace #-}
+
+outer :: (MonadThrow m) => Target -> Target -> m Columns
+outer arr1 arr2
+  | U.null arr1 || U.null arr2 = pure []
+  | otherwise = pure [ U.map (* (arr2 U.! j)) arr1 | j <- [0 .. U.length arr2 - 1] ]
+{-# INLINE outer #-}
+
+-- | Flatten list of column vectors to a row-major U.Vector Double
+toRowMajor :: Columns -> U.Vector Double
+toRowMajor cols = U.generate (m * n) (\ix -> let (i, j) = ix `divMod` n in (cols !! j) U.! i)
+  where (m, n) = matSize cols
+
+-- | Restore a row-major continuous U.Vector Double back to Columns
+fromRowMajor :: Int -> Int -> U.Vector Double -> Columns
+fromRowMajor m n vec = [ U.generate m (\i -> vec U.! (i * n + j)) | j <- [0 .. n - 1] ]
+
+unsafeRead :: PrimMonad m => Int -> UM.MVector (PrimState m) Double -> (Int, Int) -> m Double
+unsafeRead stride arr (i, j) = UM.unsafeRead arr (i * stride + j)
+{-# INLINE unsafeRead #-}
+
+unsafeWrite :: PrimMonad m => Int -> UM.MVector (PrimState m) Double -> (Int, Int) -> Double -> m ()
+unsafeWrite stride arr (i, j) val = UM.unsafeWrite arr (i * stride + j) val
+{-# INLINE unsafeWrite #-}
+
+det :: Columns -> Double
+det mtx
+  | m == 0 || n == 0 = 1
+  | otherwise = (^2) $ product [ (toRowMajor l) U.! (i * n + i) | i <- [0 .. m - 1] ]
+  where
+    (m, n) = matSize mtx
+    (l, _) = unsafePerformIO (lu mtx)
+
+detChol :: Columns -> Double
+detChol mtx
+  | m == 0 || n == 0 = 1
+  | otherwise = (^2) $ product [ (toRowMajor cho) U.! (i * m + i) | i <- [0 .. m - 1] ]
+  where
+    (m, n) = matSize mtx
+    cho = unsafePerformIO (cholesky mtx)
+{-# INLINE det #-}
+
+rangedLinearDotProd :: PrimMonad m => Int -> Int -> Int -> UM.MVector (PrimState m) Double -> m Double
+rangedLinearDotProd r1 r2 len arr = go 0 0
+  where
+    go !acc k
+      | k < len = do
+          x <- UM.unsafeRead arr (r1 + k)
+          y <- UM.unsafeRead arr (r2 + k)
+          go (acc + x * y) (k + 1)
+      | otherwise = pure acc
+{-# INLINE rangedLinearDotProd #-}
+
+data NegDef = NegDef deriving Show
+instance Exception NegDef
+
+cholesky :: (PrimMonad m, MonadThrow m, MonadIO m) => Columns -> m Columns
+cholesky arr
+  | m /= n = error $ "cholesky dimension mismatch " <> show m <> " X " <> show n
+  | m == 0 = pure []
+  | otherwise = do
+      l <- UM.new (m * m)
+      let orig = toRowMajor arr
+      forM_ [0 .. m - 1] $ \i ->
+        forM_ [0 .. m - 1] $ \j ->
+          if i < j then unsafeWrite m l (i, j) 0
+          else do
+            let cur = orig U.! (i * m + j)
+                rowI = i * m
+                rowJ = j * m
+            xjj <- UM.unsafeRead l (rowJ + j)
+            tot <- rangedLinearDotProd rowI rowJ j l
+            let delta = cur - tot
+            if i == j
+              then if delta <= 0
+                   then throwM NegDef
+                   else UM.unsafeWrite l (rowI + j) (sqrt delta)
+              else UM.unsafeWrite l (rowI + j) (delta / xjj)
+      frozen <- U.unsafeFreeze l
+      pure $ fromRowMajor m m frozen
+  where (m, n) = matSize arr
+{-# INLINE cholesky #-}
+
+invChol :: (PrimMonad m, MonadThrow m, MonadIO m) => Columns -> m Columns
+invChol arr = do
+  lMtx <- cholesky arr
+  let (m, _) = matSize arr
+  mtx <- U.thaw (toRowMajor lMtx)
+  forM_ [0 .. m - 1] $ \i -> do
+    lII <- unsafeRead m mtx (i, i)
+    unsafeWrite m mtx (i, i) (1 / lII)
+    forM_ [0 .. i - 1] $ \j -> do
+      tot <- rangedLinearDotProd (i * m + j) (j * m + j) (i - j) mtx
+      unsafeWrite m mtx (j, i) ((-tot) / lII)
+      unsafeWrite m mtx (i, j) 0
+
+  mm <- UM.replicate (m * m) 0
+  forM_ [0 .. m - 1] $ \i -> do
+    dii <- rangedLinearDotProd (i * m + i) (i * m + i) (m - i) mtx
+    unsafeWrite m mm (i, i) dii
+    forM_ [i + 1 .. m - 1] $ \j -> do
+      dij <- rangedLinearDotProd (i * m + j) (j * m + j) (m - j) mtx
+      unsafeWrite m mm (i, j) dij
+      unsafeWrite m mm (j, i) dij
+  frozen <- U.unsafeFreeze mm
+  pure $ fromRowMajor m m frozen
+{-# INLINE invChol #-}
+
+lu :: (PrimMonad m, MonadThrow m, MonadIO m) => Columns -> m (Columns, Columns)
+lu mtx = do
+  let (m, n) = matSize mtx
+      orig = toRowMajor mtx
+  u <- UM.replicate (m * n) 0
+  forM_ [0 .. min m n - 1] $ \i -> unsafeWrite n u (i, i) 1
+  l <- UM.replicate (m * n) 0
+
+  let buildLVal !i !j = do
+        let go !k !s
+              | k == j = pure s
+              | otherwise = do
+                  lik <- unsafeRead n l (i, k)
+                  ukj <- unsafeRead n u (k, j)
+                  go (k+1) (s + lik * ukj)
+        s' <- go 0 0
+        unsafeWrite n l (i, j) ((orig U.! (i * n + j)) - s')
+
+      buildL !i !j = when (i /= m) $ do
+        buildLVal i j
+        buildL (i+1) j
+
+      buildUVal !i !j = do
+        let go !k !s
+              | k == j = pure s
+              | otherwise = do
+                  ljk <- unsafeRead n l (j, k)
+                  uki <- unsafeRead n u (k, i)
+                  go (k+1) (s + ljk * uki)
+        s' <- go 0 0
+        ljj <- unsafeRead n l (j, j)
+        unsafeWrite n u (j, i) (((orig U.! (j * n + i)) - s') / ljj)
+
+      buildU !i !j = when (i /= n) $ do
+        buildUVal i j
+        buildU (i+1) j
+
+      buildLU !j = when (j /= n && j /= m) $ do
+        buildL j j
+        buildU j j
+        buildLU (j+1)
+
+  buildLU 0
+  finalL <- U.unsafeFreeze l
+  finalU <- U.unsafeFreeze u
+  pure (fromRowMajor m n finalL, fromRowMajor m n finalU)
+
+forwardSub :: (PrimMonad m, MonadThrow m, MonadIO m) => Columns -> Target -> m Target
+forwardSub a b = do
+  let m = U.length b
+      n = length a
+      aMat = toRowMajor a
+  x <- UM.replicate m 0
+  let coeff !i !j !s
+        | j == i = pure s
+        | otherwise = do
+            let aij = aMat U.! (i * n + j)
+            xj <- UM.unsafeRead x j
+            coeff i (j+1) (s + aij * xj)
+      go !i = when (i /= m) $ do
+        let bi = b U.! i
+            aii = aMat U.! (i * n + i)
+        c <- coeff i 0 0
+        UM.unsafeWrite x i ((bi - c) / aii)
+        go (i+1)
+  go 0
+  U.unsafeFreeze x
+
+backwardSub :: (PrimMonad m, MonadThrow m, MonadIO m) => Columns -> Target -> m Target
+backwardSub a b = do
+  let m = U.length b
+      n = length a
+      aMat = toRowMajor a
+  x <- UM.replicate m 0
+  let coeff !i !j !s
+        | j == m = pure s
+        | otherwise = do
+            let aij = aMat U.! (i * n + j)
+            xj <- UM.unsafeRead x j
+            coeff i (j+1) (s + aij * xj)
+      go !i = when (i >= 0) $ do
+        let bi = b U.! i
+            aii = aMat U.! (i * n + i)
+        c <- coeff i (i+1) 0
+        UM.unsafeWrite x i ((bi - c) / aii)
+        go (i-1)
+  go (m-1)
+  U.unsafeFreeze x
+
+luSolve :: (PrimMonad m, MonadThrow m, MonadIO m) => Columns -> Target -> m Target
+luSolve a b = do
+  (l, u) <- lu a
+  forwardSub l b >>= backwardSub u
+
+type PolyCos = (Double, Double, Double)
+
+cubicSplineCoefficients :: [(Double, Double)] -> [PolyCos]
+cubicSplineCoefficients xs = Prelude.zip3 x y z'
+  where
+    x = map fst xs
+    y = map snd xs
+    xdiff = zipWith (-) (tail x) x
+    xdiff' = U.fromList xdiff
+
+    dydx :: U.Vector Double
+    dydx = U.fromList $ Prelude.zipWith3 (\y0 y1 xd -> (y0 - y1) / xd) (tail y) y xdiff
+
+    n = length x
+
+    w :: [Double]
+    w = 0 : nextW 1 w
+      where
+        nextW ix (wi : t)
+          | ix == n - 1 = []
+          | otherwise =
+              let m = (xdiff' U.! (ix - 1)) * (2 - wi) + 2 * (xdiff' U.! ix)
+                  wn = (xdiff' U.! ix) / m
+              in wn : nextW (ix + 1) t
+
+    z :: [Double]
+    z = 0 : nextZ 1 z
+      where
+        nextZ ix (zi : t)
+          | ix == n - 1 = [0]
+          | otherwise =
+              let m = (xdiff' U.! (ix - 1)) * (2 - (w !! (ix - 1))) + 2 * (xdiff' U.! ix)
+                  zn = (6 * ((dydx U.! ix) - (dydx U.! (ix - 1))) - (xdiff' U.! (ix - 1)) * zi) / m
+              in zn : nextZ (ix + 1) t
+
+    z' :: [Double]
+    z' = Prelude.reverse $ 0 : [z !! i - w !! i * z !! (i + 1) | i <- [n - 2, n - 3 .. 0]]
+
+chunkBy :: Int -> [t] -> [[t]]
+chunkBy n = unfoldr go
+  where
+    go [] = Nothing
+    go x = Just $ splitAt n x
+
+genSplineFun :: [(Double, Double)] -> Double -> Double
+genSplineFun pts x
+  | length xs < 2 = x
+  | x < head xs   = y1 + (x - x1) * (y2 - y1) / (x2 - x1)
+  | x > last xs   = y_1 + (x - x_1) * (y_n - y_1) / (x_n - x_1)
+  | otherwise     = go xs $ zip coefs (tail coefs)
+  where
+    xs = map fst pts
+    ys = map snd pts
+    coefs = cubicSplineCoefficients pts
+    x1 = head xs;  y1 = head ys
+    x2 = xs !! 1;  y2 = ys !! 1
+    x_1 = xs !! (len - 2);  y_1 = ys !! (len - 2)
+    x_n = last xs;          y_n = last ys
+    len = length xs
+
+    evalAt (a1, b1, c1) (a2, b2, c2) y =
+      let hi1 = a2 - a1
+      in c1 / (6 * hi1) * (a2 - y)^3 + c2 / (6 * hi1) * (y - a1)^3 +
+         (b2 / hi1 - c2 * hi1 / 6) * (y - a1) + (b1 / hi1 - c1 * hi1 / 6) * (a2 - y)
+
+    go [x1, x2] [(c1, c2)] = evalAt c1 c2 x
+    go (x1 : x2 : xs') ((c1, c2) : cs)
+      | x >= x1 && x <= x2 = evalAt c1 c2 x
+      | otherwise          = go (x2 : xs') cs
diff --git a/src/Data/SRTree.hs b/src/Data/SRTree.hs
--- a/src/Data/SRTree.hs
+++ b/src/Data/SRTree.hs
@@ -1,7 +1,7 @@
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  Data.SRTree 
--- Copyright   :  (c) Fabricio Olivetti 2021 - 2021
+-- Copyright   :  (c) Fabricio Olivetti 2021 - 2024
 -- License     :  BSD3
 -- Maintainer  :  fabricio.olivetti@gmail.com
 -- Stability   :  experimental
@@ -16,28 +16,29 @@
          , Op(..)
          , param
          , var
+         , constv
          , arity
          , getChildren
+         , childrenOf
+         , replaceChildren
+         , getOperator
          , countNodes
          , countVarNodes
          , countConsts
          , countParams
+         , countParamsUniq
          , countOccurrences
-         , deriveBy
-         , deriveByVar
-         , deriveByParam
-         , derivative
-         , forwardMode
-         , gradParamsFwd
-         , gradParamsRev
-         , evalFun
-         , evalOp
-         , inverseFunc
-         , evalTree
+         , countUniqueTokens
+         , numberOfVars
+         , getIntConsts
          , relabelParams
+         , relabelParamsOrder
+         , relabelVars
          , constsToParam
          , floatConstsToParam
          , paramsToConst
+         , removeProtectedOps
+         , convertProtectedOps
          , Fix (..)
          )
          where
@@ -48,27 +49,28 @@
          , Op(..)
          , param
          , var
+         , constv
          , arity
          , getChildren
+         , childrenOf
+         , replaceChildren
+         , getOperator
          , countNodes
          , countVarNodes
          , countConsts
          , countParams
+         , countParamsUniq
          , countOccurrences
-         , deriveBy
-         , deriveByVar
-         , deriveByParam
-         , derivative
-         , forwardMode
-         , gradParamsFwd
-         , gradParamsRev
-         , evalFun
-         , evalOp
-         , inverseFunc
-         , evalTree
+         , countUniqueTokens
+         , numberOfVars
+         , getIntConsts
          , relabelParams
+         , relabelParamsOrder
+         , relabelVars
          , constsToParam
          , floatConstsToParam
          , paramsToConst
+         , removeProtectedOps
+         , convertProtectedOps
          , Fix (..)
          )
diff --git a/src/Data/SRTree/Datasets.hs b/src/Data/SRTree/Datasets.hs
new file mode 100644
--- /dev/null
+++ b/src/Data/SRTree/Datasets.hs
@@ -0,0 +1,416 @@
+{-# language ImportQualifiedPost #-}
+{-# language ViewPatterns #-}
+{-# language OverloadedStrings #-}
+{-# language BlockArguments #-}
+{-# language ExplicitForAll #-}
+{-# language BangPatterns #-}
+{-# language LambdaCase #-}
+{-# language RankNTypes, ScopedTypeVariables #-}
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Data.SRTree.Datasets
+-- Copyright   :  (c) Fabricio Olivetti 2021 - 2024
+-- License     :  BSD3
+-- Maintainer  :  fabricio.olivetti@gmail.com
+-- Stability   :  experimental
+-- Portability :  FlexibleInstances, DeriveFunctor, ScopedTypeVariables, ConstraintKinds
+--
+-- Utility library to handle regression datasets
+-- this module exports only the `loadDataset` function.
+--
+-----------------------------------------------------------------------------
+module Data.SRTree.Datasets ( loadDataset, loadTrainingOnly, getX, splitData, DataSet(..), splitFileNameParams, getRows, getColumns )
+    where
+
+import Codec.Compression.GZip (decompress)
+import Data.ByteString.Char8 qualified as B
+import Data.ByteString.Lazy qualified as BS
+import Data.List (delete, find, intercalate)
+import Data.Maybe (fromJust)
+import Data.Ratio ((%))
+import Data.Vector.Unboxed (Vector)
+import qualified Data.Vector as VB
+import qualified Data.Vector.Unboxed as V
+import System.FilePath (takeExtension)
+import Text.Read (readMaybe)
+import Control.Monad.State.Strict
+import System.Random
+import qualified Data.Vector.Primitive as VP
+import Data.Foldable qualified as Foldable
+import Data.Primitive.Array qualified as Array
+import Control.Monad.ST (runST)
+import Control.Monad.ST.Strict (ST)
+
+-- a dataset is a triple (X, y, y_error)
+type DataSet = ([Vector Double], Vector Double, Maybe (Vector Double))
+
+-- | Loads a list of list of bytestrings to a matrix of double
+loadMtx :: [[B.ByteString]] -> [Vector Double]
+loadMtx []     = []
+loadMtx rows   = map V.fromList
+               $ foldr (zipWith (:) . map parseDouble) (replicate ncols []) rows
+  where ncols = length (head rows)
+{-# INLINE loadMtx #-}
+
+-- | Powers of ten as exact 'Integer's, precomputed once and shared by every
+-- 'parseDouble' call. The per-value @10 ^ k@ exponentiation previously ran a
+-- growing-Integer multiply loop on every parsed number, which showed up as a
+-- measurable chunk of the corpus-load allocation. The table is the exact same
+-- integer, so conversions stay bit-identical.
+maxPow10 :: Int
+maxPow10 = 400
+
+pow10 :: VB.Vector Integer
+pow10 = VB.generate (maxPow10 + 1) (\k -> 10 ^ k)
+{-# NOINLINE pow10 #-}
+
+-- | @10^k@ as an exact 'Integer'; falls back to direct exponentiation for
+-- exponents beyond the precomputed range (only reachable with absurd inputs).
+pow10E :: Int -> Integer
+pow10E k | k >= 0 && k <= maxPow10 = VB.unsafeIndex pow10 k
+         | otherwise               = 10 ^ k
+{-# INLINE pow10E #-}
+
+-- | Fast decimal double parser over a 'B.ByteString'. Handles an optional
+-- sign, a fractional part and an optional 'e'/'E' exponent. The mantissa is
+-- accumulated exactly as an 'Integer' and converted to 'Double' through a
+-- single 'fromRational', which matches the correctly-rounded result of 'read'.
+-- Falls back to 'read' (the slow Show-derived parser) for anything it can't
+-- parse (NaN, Infinity, hex floats, etc.), so behavior is unchanged for odd
+-- input.
+parseDouble :: B.ByteString -> Double
+parseDouble bs = case go 0 1 0 False 0 of
+  Just (m, s, nd, e)
+    -- when e >= nd the rational m * 10^e / 10^nd is an exact integer, so a
+    -- single fromInteger is bit-identical to fromRational (which would only
+    -- gcd-reduce it) but skips the rational machinery entirely.
+    | e >= nd   -> fromInteger (s * (m * pow10E (e - nd)))
+    -- otherwise the value is m / 10^(nd-e); keep fromRational so the single
+    -- rounding matches `read` exactly (a Double division by a rounded power
+    -- of ten would be off by up to an ulp).
+    | otherwise -> fromRational (s * m % (pow10E (nd - e)))
+  Nothing -> read (B.unpack bs)
+  where
+    n = B.length bs
+    -- i: index, sgn: +/-1, acc: accumulated mantissa digits (exact Integer),
+    -- dot: whether a '.' has been seen, nd: number of digits following the
+    -- decimal point, expo: signed integer exponent from the 'e' tail
+    go :: Int -> Integer -> Integer -> Bool -> Int -> Maybe (Integer, Integer, Int, Int)
+    go !i !sgn !acc !dot !nd
+      | i >= n    = Just (acc, sgn, nd, 0)
+      | otherwise =
+          let c = fromEnum (B.index bs i)
+          in case c of
+               45 -> if i == 0 then go (i+1) (-sgn) acc dot nd else Nothing -- '-'
+               43 -> if i == 0 then go (i+1) sgn acc dot nd else Nothing -- '+'
+               46 -> if dot then Nothing else go (i+1) sgn acc True nd -- '.'
+               _  | c >= 48 && c <= 57 ->
+                      let d = fromIntegral (c - 48) :: Integer
+                          nd' = if dot then nd + 1 else nd
+                      in go (i+1) sgn (acc * 10 + d) dot nd'
+                  | (c == 101 || c == 69) && i > 0 -> -- 'e' / 'E'
+                      parseExp (i+1) sgn acc dot nd
+                  | otherwise -> Nothing
+    -- parse the (optional) exponent tail: an optional sign then digits
+    parseExp :: Int -> Integer -> Integer -> Bool -> Int -> Maybe (Integer, Integer, Int, Int)
+    parseExp !i !sgn !acc !dot !nd
+      | i >= n    = Just (acc, sgn, nd, 0)
+      | otherwise =
+          let c = fromEnum (B.index bs i)
+          in case c of
+               45 -> expDig (i+1) sgn acc dot nd (-1) 0 -- '-'
+               43 -> expDig (i+1) sgn acc dot nd 1 0 -- '+'
+               _   -> expDig i sgn acc dot nd 1 0
+      where
+        -- es: exponent sign (+/-1); e: accumulated exponent magnitude
+        expDig :: Int -> Integer -> Integer -> Bool -> Int -> Int -> Int -> Maybe (Integer, Integer, Int, Int)
+        expDig !i !sgn !acc !dot !nd !es !e
+          | i >= n    = Just (acc, sgn, nd, es * e)
+          | otherwise =
+              let c = fromEnum (B.index bs i)
+              in if c >= 48 && c <= 57
+                   then expDig (i+1) sgn acc dot nd es (e * 10 + fromIntegral (c - 48))
+                   else Nothing
+
+-- | Returns true if the extension is .gz
+isGZip :: FilePath -> Bool
+isGZip = (== ".gz") . takeExtension
+{-# INLINE isGZip #-}
+
+-- | Detects the separator automatically by 
+--   checking whether the use of each separator generates
+--   the same amount of SRMatrix in every row and at least two SRMatrix.
+--
+--  >>> detectSep ["x1,x2,x3,x4"] 
+-- ','
+detectSep :: [B.ByteString] -> Char
+detectSep xss = go seps
+  where
+    seps = [' ','\t','|',':',';',',']
+    xss' = map B.strip xss
+
+    -- consistency check whether all rows have the same
+    -- number of columns when spliting by this sep 
+    allSameLen []     = True
+    allSameLen (y:ys) = y /= 1 && all (==y) ys
+
+    go []     = error $ "CSV parsing error: unsupported separator. Supporter separators are "
+                      <> intercalate "," (map show seps)
+    go (c:cs) = if allSameLen $ map (length . B.split c) xss'
+                   then c
+                   else go cs
+{-# INLINE detectSep #-}
+
+-- | reads a file and returns a list of list of `ByteString`
+-- corresponding to each element of the matrix.
+-- The first row can be a header. 
+readFileToLines :: FilePath -> IO [[B.ByteString]]
+readFileToLines filename = do
+  content <- removeBEmpty . toLines . toStrict . unzip <$> BS.readFile filename
+  let sep = getSep content
+  pure . removeEmpty . map (B.split sep) $ content
+  where
+      getSep       = detectSep . take 100 -- use only first 100 rows to detect separator
+      removeBEmpty = filter (not . B.null)
+      removeEmpty  = filter (not . null)
+      toLines      = B.split '\n'
+      unzip        = if isGZip filename then decompress else id
+      -- lazy -> strict without going through a [Word8]/[Char] list (the old
+      -- B.pack . map toEnum . BS.unpack round trip allocated ~1GB on a 14MB
+      -- CSV); BS.toStrict is a single O(n) copy.
+      toStrict     = BS.toStrict
+{-# INLINE readFileToLines #-}
+
+-- | Splits the parameters from the filename
+-- the expected format of the filename is *filename.ext:p1:p2:p3:p4*
+-- where p1 and p2 is the starting and end rows for the training data,
+-- by default p1 = 0 and p2 = number of rows - 1
+-- p3 is the target PVector, it can be a string corresponding to the header
+-- or an index.
+-- p4 is a comma separated list of SRMatrix (either index or name) to be used as 
+-- input variables. These will be renamed internally as x0, x1, ... in the order
+-- of this list.
+splitFileNameParams :: FilePath -> (FilePath, [B.ByteString])
+splitFileNameParams (B.pack -> filename)
+  | B.null filename = ("", replicate 6 B.empty)
+  | otherwise       = (B.unpack fname, take 6 params)
+  where
+    (fname : params') = B.split ':' filename
+    -- fill up the empty parameters with an empty string
+    params            = params' <> replicate (6 - min 6 (length params')) B.empty
+{-# inline splitFileNameParams #-}
+
+-- | Tries to parse a string into an int
+parseVal :: String -> Either String Int
+parseVal xs = case readMaybe xs of
+                Nothing -> Left xs
+                Just x  -> Right x
+{-# inline parseVal #-}
+
+-- | Given a map between PVector name and indeces,
+-- the target PVector and the variables SRMatrix,
+-- returns the indices of the variables SRMatrix and the target
+getColumns :: [(B.ByteString, Int)] -> B.ByteString -> B.ByteString -> B.ByteString -> ([Int], Int, Int)
+getColumns headerMap target columns target_error = (ixs, iy, iy_error)
+  where
+      n_cols  = length headerMap
+      getIx c = case parseVal c of
+                  -- if the PVector is a name, retrive the index
+                  Left name -> case find ((== B.pack name) . fst) headerMap of
+                                 Nothing -> error $ "PVector name " <> name <> " does not exist."
+                                 Just v  -> snd v
+                  -- if it is an int, check if it is within range
+                  Right v   -> if v >= 0 && v < n_cols
+                                 then v
+                                 else error $ "PVector index " <> show v <> " out of range."
+      -- if the input variables SRMatrix are ommitted, use
+      -- every PVector except for iy
+      ixs = if B.null columns
+               then delete iy [0 .. n_cols - 1]
+               else map (getIx . B.unpack) $ B.split ',' columns
+      -- if the target PVector is ommitted, use the last one
+      iy = if B.null target
+              then n_cols - 1
+              else getIx $ B.unpack target
+      -- if the target PVector is ommitted, use the last one
+      iy_error = if B.null target_error
+                  then (-1)
+                  else getIx $ B.unpack target_error
+{-# inline getColumns #-}
+
+-- | Given the start and end rows, it returns the 
+-- hmatrix extractors for the training and validation data
+getRows :: B.ByteString -> B.ByteString -> Int -> (Int, Int)
+getRows (B.unpack -> start) (B.unpack -> end) nRows
+  | st_ix >= end_ix                 = error $ "Invalid range: " <> show start <> ":" <> show end <> "."
+  | st_ix == 0 && end_ix == nRows-1 = (0, nRows)
+  | otherwise                       = (st_ix, end_ix + 1)
+  where
+      st_ix = if null start
+                then 0
+                else case readMaybe start of
+                       Nothing -> error $ "Invalid starting row " <> start <> "."
+                       Just x  -> if x < 0 || x >= nRows
+                                    then error $ "Invalid starting row " <> show x <> "."
+                                    else x
+      end_ix = if null end
+                then nRows - 1
+                else case readMaybe end of
+                       Nothing -> error $ "Invalid end row " <> end <> "."
+                       Just x  -> if x < 0 || x >= nRows
+                                    then error $ "Invalid end row " <> show x <> "."
+                                    else x
+{-# inline getRows #-}
+
+-- | `loadDataset` loads a dataset with a filename in the format:
+--   filename.ext:start_row:end_row:target:features:y_err
+--   it returns the X_train, y_train, X_test, y_test, varnames, target name 
+--   where varnames are a comma separated list of the name of the vars 
+--   and target name is the name of the target
+--
+-- where
+--
+-- **start_row:end_row** is the range of the training rows (default 0:nrows-1).
+--   every other row not included in this range will be used as validation
+-- **target** is either the name of the PVector (if the datafile has headers) or the index
+-- of the target variable
+-- **features** is a comma separated list of SRMatrix names or indices to be used as
+-- input variables of the regression model.
+loadDataset :: FilePath -> Bool -> IO (([Vector Double], Vector Double, [Vector Double], Vector Double), (Maybe (Vector Double), Maybe (Vector Double)), String, String)
+loadDataset filename hasHeader = do  
+  csv <- readFileToLines fname
+  pure $ processData csv params hasHeader
+  where
+    (fname, params) = splitFileNameParams filename
+
+-- support function that does everything for loadDataset
+processData :: [[B.ByteString]] -> [B.ByteString] -> Bool -> (([Vector Double], Vector Double, [Vector Double], Vector Double), (Maybe (Vector Double), Maybe (Vector Double)), String, String)
+processData csv params hasHeader = ((x_train, y_train, x_val, y_val) , (y_err_train, y_err_val), varnames, targetname)
+  where
+    ncols             = length $ head csv
+    nrows             = length csv - fromEnum hasHeader
+    (header, content) = if hasHeader
+                           then (zip (map B.strip $ head csv) [0..], tail csv)
+                           else (map (\i -> (B.pack ('x' : show i), i)) [0 .. ncols-1], csv)
+    varnames          = intercalate "," [B.unpack v | c <- ixs
+                                        , let v = fst . fromJust $ find ((==c).snd) header
+                                        ]
+    targetname        = if hasHeader then (B.unpack . fst . fromJust . find ((==iy).snd) $ header) else "y"
+    -- get rows and SRMatrix indices
+    (st, end)         = getRows (params !! 0) (params !! 1) nrows
+    (ixs, iy, iy_err) = getColumns header (params !! 2) (params !! 3) (params !! 4)
+
+    -- load data and split sets
+    datum   = loadMtx content
+    p       = length ixs
+
+    x       = map (datum !!) ixs
+    y       = datum !! iy
+    y_err   = datum !! iy_err
+
+    x_train = map (V.take end . V.drop st) x
+    y_train = V.take end . V.drop st $ y
+    x_val   = map (V.drop (st + end)) x
+    y_val   = V.drop (st + end) y
+
+    y_err_train = if iy_err == -1 then Nothing else Just $ (V.take end . V.drop st) y_err
+    y_err_val   = if iy_err == -1 then Nothing else Just $ (V.take end . V.drop st) y_err
+{-# inline processData #-}
+
+chunksOf :: Int -> [e] -> [[e]]
+chunksOf i ls = Prelude.map (Prelude.take i) (build (splitter ls))
+ where
+  splitter :: [e] -> ([e] -> a -> a) -> a -> a
+  splitter [] _ n = n
+  splitter l c n = l `c` splitter (Prelude.drop i l) c n
+  build :: ((a -> [a] -> [a]) -> [a] -> [a]) -> [a]
+  build g = g (:) []
+
+splitData :: DataSet -> Int -> State StdGen (DataSet, DataSet)
+splitData (x, y, mYErr) k = do
+  if k == 1
+    then pure ((x, y, mYErr), (x, y, mYErr))
+    else do
+      ixs' <- (state . shuffle) [0 .. sz-1]
+      let ixs = chunksOf k ixs'
+
+      let tr_ix  = [ix | ixs_i <- ixs, ix <- Prelude.tail ixs_i]
+          val_ix = [ix | ixs_i <- ixs, let ix = Prelude.head ixs_i]
+          (x_tr, x_te) = getX tr_ix val_ix x
+          (y_tr, y_te) = getY tr_ix val_ix y
+
+          mY = fmap (getY tr_ix val_ix) mYErr
+          (y_err_tr, y_err_te) = (fmap fst mY, fmap snd mY)
+      pure ((x_tr, y_tr, y_err_tr), (x_te, y_te, y_err_te))
+  where
+    sz = V.length y
+
+    getX :: [Int] -> [Int] -> [Vector Double] -> ([Vector Double], [Vector Double])
+    getX tr_ix val_ix  xs = ( [ V.fromList [x V.! ix | ix <- tr_ix] | x <- xs ]
+                  , [ V.fromList [x V.! ix | ix <- val_ix] | x <- xs ]
+                  )
+    getY :: [Int] -> [Int] -> Vector Double -> (Vector Double, Vector Double)
+    getY tr_ix val_ix  ys  = ( V.fromList [ys V.! ix | ix <- tr_ix]
+                   , V.fromList [ys V.! ix | ix <- val_ix]
+                   )
+
+getTrain :: ((a, b1, c1, d1), (c2, b2), c3, d2) -> (a, b1, c2)
+getTrain ((a, b, _, _), (c, _), _, _) = (a,b,c)
+
+getX :: DataSet -> [Vector Double]
+getX (a, _, _) = a
+
+getTarget :: DataSet -> Vector Double
+getTarget (_, b, _) = b
+
+getError :: DataSet -> Maybe (Vector Double)
+getError (_, _, c) = c
+
+loadTrainingOnly fname b = getTrain <$> loadDataset fname b
+
+-- | Shuffles a list, taken from list-shuffle
+shuffle :: (RandomGen g) => [a] -> g -> ([a], g)
+shuffle list gen0 =
+  runST do
+    array <- listToMutableArray list
+    gen1 <- shuffleN (Array.sizeofMutableArray array - 1) array gen0
+    array1 <- Array.unsafeFreezeArray array
+    pure (Foldable.toList array1, gen1)
+
+listToMutableArray :: forall a s. [a] -> ST s (Array.MutableArray s a)
+listToMutableArray list = do
+  array <- Array.newArray (length list) undefined
+  let writeElems :: Int -> [a] -> ST s ()
+      writeElems !i = \case
+        [] -> pure ()
+        x : xs -> do
+          Array.writeArray array i x
+          writeElems (i + 1) xs
+  writeElems 0 list
+  pure array
+{-# INLINE listToMutableArray #-}
+
+shuffleN :: forall a g s. (RandomGen g) => Int -> Array.MutableArray s a -> g -> ST s g
+shuffleN n0 array =
+  go 0
+  where
+    go :: Int -> g -> ST s g
+    go !i gen0
+      | i >= n = pure gen0
+      | otherwise = do
+          let (j, gen1) = uniformR (i, m) gen0
+          swapArrayElems i j array
+          go (i + 1) gen1
+
+    n = min n0 m
+    m = Array.sizeofMutableArray array - 1
+{-# SPECIALIZE shuffleN :: Int -> Array.MutableArray s a -> StdGen -> ST s StdGen #-}
+
+-- Swap two elements in a mutable array.
+swapArrayElems :: Int -> Int -> Array.MutableArray s a -> ST s ()
+swapArrayElems i j array = do
+  x <- Array.readArray array i
+  y <- Array.readArray array j
+  Array.writeArray array i y
+  Array.writeArray array j x
+{-# INLINE swapArrayElems #-}
diff --git a/src/Data/SRTree/Derivative.hs b/src/Data/SRTree/Derivative.hs
new file mode 100644
--- /dev/null
+++ b/src/Data/SRTree/Derivative.hs
@@ -0,0 +1,140 @@
+{-# LANGUAGE OverloadedStrings #-}
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Data.SRTree.Derivative 
+-- Copyright   :  (c) Fabricio Olivetti 2021 - 2024
+-- License     :  BSD3
+-- Maintainer  :  fabricio.olivetti@gmail.com
+-- Stability   :  experimental
+-- Portability :  FlexibleInstances, DeriveFunctor, ScopedTypeVariables
+--
+-- Symbolic derivative of SRTree expressions
+--
+-----------------------------------------------------------------------------
+module Data.SRTree.Derivative
+        ( derivative
+        , doubleDerivative
+        , deriveByVar
+        , deriveByParam
+        , derivOp
+        )
+        where
+
+import Data.SRTree.Internal
+import Data.SRTree.Recursion (Fix (..), mutu)
+import Data.Attoparsec.ByteString.Char8 (double)
+
+-- | Creates the symbolic partial derivative of a tree by variable `dx` (if `p` is `False`)
+-- or parameter `dx` (if `p` is `True`).
+-- This uses mutual recursion where the first recursion (alg1) holds the derivative w.r.t. 
+-- the current node and the second (alg2) holds the original tree.
+--
+-- >>> showExpr . deriveBy False 0 $ 2 * "x0" * "x1"
+-- "(2.0 * x1)"
+-- >>> showExpr . deriveBy True 1 $ 2 * "x0" * "t0" - sqrt ("t1" * "x0")
+-- "(-1.0 * ((1.0 / (2.0 * Sqrt((t1 * x0)))) * x0))"
+deriveBy :: Bool -> Int -> Fix SRTree -> Fix SRTree
+deriveBy p dx = fst (mutu alg1 alg2)
+  where
+      alg1 (Var ix)           = if not p && ix == dx then 1 else 0
+      alg1 (Param ix)         = if p && ix == dx then 1 else 0
+      alg1 (Const _)          = 0
+      alg1 (Uni f t)          = derivative f (snd t) * fst t
+      alg1 (Bin Add l r)      = fst l + fst r
+      alg1 (Bin Sub l r)      = fst l - fst r
+      alg1 (Bin Mul l r)      = fst l * snd r + snd l * fst r
+      alg1 (Bin Div l r)      = (fst l * snd r - snd l * fst r) / snd r ** 2
+      alg1 (Bin Power l r)    = snd l ** (snd r - 1) * (snd r * fst l + snd l * log (snd l) * fst r)
+      alg1 (Bin PowerAbs l r) = (powabs (snd l) (snd r)) * (fst r * log (abs (snd l)) + snd r * fst l / snd l)
+      alg1 (Bin AQ l r)       = ((1 + snd r * snd r) * fst l - snd l * snd r * fst r) / (1 + snd r * snd r) ** 1.5
+
+      alg2 (Var ix)    = var ix
+      alg2 (Param ix)  = param ix
+      alg2 (Const c)   = Fix (Const c)
+      alg2 (Uni f t)   = Fix (Uni f $ snd t)
+      alg2 (Bin f l r) = Fix (Bin f (snd l) (snd r))
+      --(abs (snd l) ** (snd r))
+      powabs l r = Fix (Bin PowerAbs l r)
+
+-- | Derivative of each supported function
+-- For a function h(f) it returns the derivative dh/df
+--
+-- >>> derivative Log 2.0
+-- 0.5
+derivative :: Floating a => Function -> a -> a
+derivative Id      = const 1
+derivative Abs     = \x -> x / abs x
+derivative Sin     = cos
+derivative Cos     = negate.sin
+derivative Tan     = recip . (**2.0) . cos
+derivative Sinh    = cosh
+derivative Cosh    = sinh
+derivative Tanh    = (1-) . (**2.0) . tanh
+derivative ASin    = recip . sqrt . (1-) . (^2)
+derivative ACos    = negate . recip . sqrt . (1-) . (^2)
+derivative ATan    = recip . (1+) . (^2)
+derivative ASinh   = recip . sqrt . (1+) . (^2)
+derivative ACosh   = \x -> 1 / (sqrt (x-1) * sqrt (x+1))
+derivative ATanh   = recip . (1-) . (^2)
+derivative Sqrt    = recip . (2*) . sqrt
+derivative SqrtAbs = \x -> x / (2.0 * abs x ** (3.0/2.0))
+derivative Cbrt    = recip . (3*) . (**(1/3)) . (^2)
+derivative Square  = (2*)
+derivative Exp     = exp
+derivative Log     = recip
+derivative LogAbs  = recip
+derivative Recip   = negate . recip . (^2)
+derivative Cube    = (3*) . (^2)
+{-# INLINE derivative #-}
+
+-- | Second-order derivative of supported functions
+--
+-- >>> doubleDerivative Log 2.0
+-- -0.25
+doubleDerivative :: Floating a => Function -> a -> a
+doubleDerivative Id      = const 0
+doubleDerivative Abs     = const 0
+doubleDerivative Sin     = negate.sin
+doubleDerivative Cos     = negate.cos
+doubleDerivative Tan     = \x -> 2 * sin x / (cos x) ^ 3
+doubleDerivative Sinh    = sinh
+doubleDerivative Cosh    = cosh
+doubleDerivative Tanh    = \x -> -2 * tanh x * (1 / cosh x)^2
+doubleDerivative ASin    = \x -> x / (1 - x^2)**(3/2)
+doubleDerivative ACos    = \x -> x / (1 - x^2)**(3/2)
+doubleDerivative ATan    = \x -> (-2*x) / (x^2 + 1)^2
+doubleDerivative ASinh   = \x -> x / (x^2 + 1)**(3/2) -- check
+doubleDerivative ACosh   = \x -> 1 / (sqrt (x-1) * sqrt (x+1)) -- check
+doubleDerivative ATanh   = recip . (1-) . (^2) -- check
+doubleDerivative Sqrt    = \x -> -1 / (4 * sqrt x^3)
+doubleDerivative SqrtAbs = \x -> (-x)*x/(4 * abs x ** (3.5))
+doubleDerivative Cbrt    = \x -> -2 / (9 * x * (x^2)**(1/3))
+doubleDerivative Square  = const 2
+doubleDerivative Exp     = exp
+doubleDerivative Log     = negate . recip . (^2)
+doubleDerivative LogAbs  = negate . recip . (^2)
+doubleDerivative Recip   = (*2) . recip . (^3)
+doubleDerivative Cube    = (6*)
+{-# INLINE doubleDerivative #-}
+
+-- | Returns (d(Output)/d(Left), d(Output)/d(Right))
+-- used for AD
+derivOp :: Op -> Double -> Double -> (Double, Double)
+derivOp Add _  _  = (1.0, 1.0)
+derivOp Sub _  _  = (1.0, -1.0)
+derivOp Mul v1 v2 = (v2, v1)
+derivOp Div v1 v2 = (1.0 / v2, -(v1) / (v2 * v2))
+-- e.g., Power: d(x^y)/dx = y*x^(y-1), d(x^y)/dy = x^y * ln(x)
+derivOp Power v1 v2 = (v2 * (v1 ** (v2 - 1)), (v1 ** v2) * log v1)
+derivOp _ _ _ = (0.0, 0.0) -- Add remaining ops
+{-# INLINE derivOp #-}
+
+-- | Symbolic derivative by a variable
+deriveByVar :: Int -> Fix SRTree -> Fix SRTree
+deriveByVar = deriveBy False
+{-# INLINE deriveByVar #-}
+
+-- | Symbolic derivative by a parameter
+deriveByParam :: Int -> Fix SRTree -> Fix SRTree
+deriveByParam = deriveBy True
+{-# INLINE deriveByParam #-}
diff --git a/src/Data/SRTree/Eval.hs b/src/Data/SRTree/Eval.hs
new file mode 100644
--- /dev/null
+++ b/src/Data/SRTree/Eval.hs
@@ -0,0 +1,393 @@
+{-# LANGUAGE LambdaCase, BangPatterns #-}
+
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Data.SRTree.Eval 
+-- Copyright   :  (c) Fabricio Olivetti 2021 - 2024
+-- License     :  BSD3
+-- Maintainer  :  fabricio.olivetti@gmail.com
+-- Stability   :  experimental
+-- Portability :  FlexibleInstances, DeriveFunctor, ScopedTypeVariables
+--
+-- Evaluation of SRTree expressions
+--
+-----------------------------------------------------------------------------
+{-# LANGUAGE FlexibleInstances #-}
+module Data.SRTree.Eval
+        ( evalOp
+        , evalFun
+        , cbrt
+        , inverseFunc
+        , invertibles
+        , evalInverse
+        , invright
+        , invleft
+        , replicateAs
+        , Target, Theta, Columns
+        , compile
+        , compileLoss
+        )
+        where
+
+import Data.SRTree.Internal
+import Data.SRTree.Recursion (Fix (..), cata)
+import Data.Vector.Unboxed (Vector)
+import qualified Data.Vector.Unboxed as V
+import Control.Monad.ST (runST)
+import qualified Data.Vector as VB        -- Boxed vector for instructions
+import qualified Data.Vector.Unboxed.Mutable as VM
+import Control.Concurrent.Async (forConcurrently_)
+import System.IO.Unsafe (unsafePerformIO)
+import Control.Concurrent (getNumCapabilities)
+import Data.Maybe (fromJust)
+
+-- | Vector of target values 
+type Target  = Vector Double
+-- | Vector of parameter values. Needs to be strict to be readily accesible.
+type Theta   = Vector Double
+-- | Matrix of features values 
+type Columns = [Vector Double]
+
+-- A multi-threaded replacement for V.sum
+sumParallel :: Int -> (Int -> Double) -> Double
+sumParallel n f = unsafePerformIO $ do
+    numThreads <- getNumCapabilities
+    let chunkSize  = n `quot` numThreads
+
+    -- 1. Allocate a single block of unboxed memory EXACTLY ONCE
+    out <- VM.unsafeNew numThreads
+
+    -- 2. Spawn threads. Each thread gets a unique ID and a slice of memory.
+    forConcurrently_ [0 .. numThreads - 1] $ \tId -> do
+        let !start = tId * chunkSize
+            -- The last thread cleans up the remainder
+            !end   = if tId == numThreads - 1 then n else start + chunkSize
+
+        -- 3. The inner thread loop. Strict, unboxed, and bounds-check free.
+        let loop !i !acc
+              | i >= end  = return acc
+              | otherwise = loop (i + 1) (acc + f i)
+
+        total <- loop start 0.0
+        VM.unsafeWrite out tId total
+
+    -- 4. Instantly cast the mutable memory to an immutable Vector (O(1) cost)
+    totals <- V.unsafeFreeze out
+    return (V.sum totals)
+{-# NOINLINE sumParallel #-}
+
+-- Improve quality of life with Num and Floating instances for our matrices 
+instance Num Target where
+    (+) = V.zipWith (+)
+    (-) = V.zipWith (-)
+    (*) = V.zipWith (*)
+    abs = V.map abs
+    signum = V.map signum
+    fromInteger = V.singleton . fromInteger
+    negate = V.map negate
+
+instance Floating Target where
+    pi = V.singleton pi
+    exp = V.map exp
+    log = V.map log
+    sqrt = V.map sqrt
+    sin = V.map sin
+    cos = V.map cos
+    tan = V.map tan
+    asin = V.map asin
+    acos = V.map acos
+    atan = V.map atan
+    sinh = V.map sinh
+    cosh = V.map cosh
+    tanh = V.map tanh
+    asinh = V.map asinh
+    acosh = V.map acosh
+    atanh = V.map atanh
+    (**) = V.zipWith (**)
+instance Fractional Target where
+    fromRational = V.singleton . fromRational
+    (/) = V.zipWith (/)
+    recip = V.map recip
+
+-- We change the Dynamic type to evaluate a single scalar at a specific row index (Int)
+data Staged =
+    Scl Double
+  | Static (Vector Double)
+  | Dynamic (Vector Double -> Int -> Double) -- (Theta -> RowIndex -> Result)
+
+-- A multi-threaded replacement for V.generate
+generateParallel :: Int -> (Int -> Double) -> V.Vector Double
+generateParallel n f = unsafePerformIO $ do
+    numThreads <- getNumCapabilities
+    let chunkSize  = n `quot` numThreads
+
+    -- 1. Allocate a single block of unboxed memory EXACTLY ONCE
+    out <- VM.unsafeNew n
+
+    -- 2. Spawn threads. Each thread gets a unique ID and a slice of memory.
+    forConcurrently_ [0 .. numThreads - 1] $ \tId -> do
+        let !start = tId * chunkSize
+            -- The last thread cleans up the remainder
+            !end   = if tId == numThreads - 1 then n else start + chunkSize
+
+        -- 3. The inner thread loop. Strict, unboxed, and bounds-check free.
+        let loop !i
+              | i >= end  = return ()
+              | otherwise = do
+                  -- Write directly to the shared memory pointer
+                  VM.unsafeWrite out i (f i)
+                  loop (i + 1)
+
+        loop start
+
+    -- 4. Instantly cast the mutable memory to an immutable Vector (O(1) cost)
+    V.unsafeFreeze out
+{-# NOINLINE generateParallel #-}
+
+compileLoss :: [Vector Double] -> Fix SRTree -> Target -> Maybe Target -> (Vector Double -> Double)
+compileLoss dataset tree y mYerr =
+    case cata alg tree of
+        Scl c     -> \_  -> V.sum $ V.replicate n c
+        Static v  -> \_  -> V.sum v
+        -- We only allocate memory EXACTLY ONCE here at the top level
+        --Dynamic f -> \th -> V.generate n (f th)
+        Dynamic f -> \th -> V.sum (V.generate n (f th))
+  where
+    n    = V.length (head dataset)
+    yErr = fromJust mYerr
+
+    alg :: SRTree Staged -> Staged
+
+    -- 1. Base Cases
+    alg (Const c)  = Scl c
+    alg (Var (-1)) = Static y
+    alg (Var (-2)) = Static yErr
+    alg (Var i)    = Static (dataset !! i)
+    alg (Param i)  = Dynamic (\th !idx -> th `V.unsafeIndex` i)
+
+    -- 2. Univariate Functions
+    alg (Uni f (Scl c))     = Scl (evalFun f c)
+    alg (Uni f (Static v))  = Static (V.map (evalFun f) v)
+
+    -- We map the function over the scalar result of the inner closure
+    alg (Uni f (Dynamic g)) = let !rawFun = evalFun f in Dynamic (\th !i -> rawFun (g th i))
+
+    -- 3. Binary Functions
+    alg (Bin op (Scl c1) (Scl c2))       = Scl (evalOp op c1 c2)
+    alg (Bin op (Scl c) (Static v))      = Static (V.map (evalOp op c) v)
+    alg (Bin op (Static v) (Scl c))      = Static (V.map (\c2 -> evalOp op c2 c) v)
+    alg (Bin op (Static v1) (Static v2)) = Static (V.zipWith (evalOp op) v1 v2)
+
+    -- 4. Dynamic Combinations (The Core Optimization)
+
+    alg (Bin op (Scl c) (Dynamic g)) =
+        let !rawOp = evalOp op in Dynamic (\th !i -> rawOp c (g th i))
+
+    alg (Bin op (Dynamic g) (Scl c)) =
+        let !rawOp = evalOp op in Dynamic (\th !i -> rawOp (g th i) c)
+
+    -- When combining a Static array with a Dynamic closure,
+    -- we use unsafeIndex to fetch the static value at row 'i' directly.
+    alg (Bin op (Static v) (Dynamic g)) =
+        let !rawOp = evalOp op in Dynamic (\th !i -> rawOp (v `V.unsafeIndex` i) (g th i))
+
+    alg (Bin op (Dynamic g) (Static v)) =
+        let !rawOp = evalOp op in Dynamic (\th !i -> rawOp (g th i) (v `V.unsafeIndex` i))
+
+    alg (Bin op (Dynamic g1) (Dynamic g2)) =
+        let !rawOp = evalOp op in Dynamic (\th !i -> rawOp (g1 th i) (g2 th i))
+
+
+compile :: [Vector Double] -> Fix SRTree -> (Vector Double -> Vector Double)
+compile dataset tree =
+    case cata alg tree of
+        Scl c     -> \_  -> V.replicate n c
+        Static v  -> \_  -> v
+        -- We only allocate memory EXACTLY ONCE here at the top level
+        --Dynamic f -> \th -> V.generate n (f th)
+        Dynamic f -> \th -> V.generate n (f th)
+  where
+    n = V.length (head dataset)
+
+    alg :: SRTree Staged -> Staged
+
+    -- 1. Base Cases
+    alg (Const c) = Scl c
+    alg (Var i)   = Static (dataset !! i)
+    -- Look at this! No more V.replicate. It just fetches the scalar directly.
+    alg (Param i) = Dynamic (\th !idx -> th `V.unsafeIndex` i)
+    alg (Y i)     = undefined -- this shouldn't be called
+
+    -- 2. Univariate Functions
+    alg (Uni f (Scl c))     = Scl (evalFun f c)
+    alg (Uni f (Static v))  = Static (V.map (evalFun f) v)
+
+    -- We map the function over the scalar result of the inner closure
+    alg (Uni f (Dynamic g)) = let !rawFun = evalFun f in Dynamic (\th !i -> rawFun (g th i))
+
+    -- 3. Binary Functions
+    alg (Bin op (Scl c1) (Scl c2))       = Scl (evalOp op c1 c2)
+    alg (Bin op (Scl c) (Static v))      = Static (V.map (evalOp op c) v)
+    alg (Bin op (Static v) (Scl c))      = Static (V.map (\c2 -> evalOp op c2 c) v)
+    alg (Bin op (Static v1) (Static v2)) = Static (V.zipWith (evalOp op) v1 v2)
+
+    -- 4. Dynamic Combinations (The Core Optimization)
+
+    alg (Bin op (Scl c) (Dynamic g)) =
+        let !rawOp = evalOp op in Dynamic (\th !i -> rawOp c (g th i))
+
+    alg (Bin op (Dynamic g) (Scl c)) =
+        let !rawOp = evalOp op in Dynamic (\th !i -> rawOp (g th i) c)
+
+    -- When combining a Static array with a Dynamic closure,
+    -- we use unsafeIndex to fetch the static value at row 'i' directly.
+    alg (Bin op (Static v) (Dynamic g)) =
+        let !rawOp = evalOp op in Dynamic (\th !i -> rawOp (v `V.unsafeIndex` i) (g th i))
+
+    alg (Bin op (Dynamic g) (Static v)) =
+        let !rawOp = evalOp op in Dynamic (\th !i -> rawOp (g th i) (v `V.unsafeIndex` i))
+
+    alg (Bin op (Dynamic g1) (Dynamic g2)) =
+        let !rawOp = evalOp op in Dynamic (\th !i -> rawOp (g1 th i) (g2 th i))
+
+
+-- returns a vector with the same number of rows as xss and containing a single repeated value.
+replicateAs :: Columns -> Double -> Target
+replicateAs xss c = let m = V.length (head xss) in V.replicate m c
+{-# INLINE replicateAs #-}
+
+-- | Evaluates the tree given a vector of variable values, a vector of parameter values and a function that takes a Double and change to whatever type the variables have. This is useful when working with datasets of many values per variables.
+evalTree :: Columns -> Theta -> Fix SRTree -> Target
+evalTree xss params = cata $ 
+    \case 
+       Var ix     -> xss !! ix
+       Param ix   -> replicateAs xss $ params V.! ix
+       Const c    -> replicateAs xss c
+       Y _        -> undefined
+       Uni g t    -> evalFun g t
+       Bin op l r -> evalOp op l r
+{-# INLINE evalTree #-}
+
+-- evaluates an operator 
+evalOp :: Floating a => Op -> a -> a -> a
+evalOp Add = (+)
+evalOp Sub = (-)
+evalOp Mul = (*)
+evalOp Div = (/)
+evalOp Power = (**)
+evalOp PowerAbs = \l r -> abs l ** r
+evalOp AQ = \l r -> l / sqrt(1 + r*r)
+{-# INLINE evalOp #-}
+
+-- evaluates a function 
+evalFun :: Floating a => Function -> a -> a
+evalFun Id = id
+evalFun Abs = abs
+evalFun Sin = sin
+evalFun Cos = cos
+evalFun Tan = tan
+evalFun Sinh = sinh
+evalFun Cosh = cosh
+evalFun Tanh = tanh
+evalFun ASin = asin
+evalFun ACos = acos
+evalFun ATan = atan
+evalFun ASinh = asinh
+evalFun ACosh = acosh
+evalFun ATanh = atanh
+evalFun Sqrt = sqrt
+evalFun SqrtAbs = sqrt . abs
+evalFun Cbrt = cbrt
+evalFun Square = (^2)
+evalFun Log = log
+evalFun LogAbs = log . abs
+evalFun Exp = exp
+evalFun Recip = recip
+evalFun Cube = (^3)
+{-# INLINE evalFun #-}
+
+-- Cubic root
+cbrt :: Floating a => a -> a
+cbrt x = signum x * abs x ** (1/3)
+{-# INLINE cbrt #-}
+
+-- | Returns the inverse of a function. This is a partial function.
+inverseFunc :: Function -> Function
+inverseFunc Id     = Id
+inverseFunc Sin    = ASin
+inverseFunc Cos    = ACos
+inverseFunc Tan    = ATan
+inverseFunc Sinh   = ASinh
+inverseFunc Cosh   = ACosh
+inverseFunc Tanh   = ATanh
+inverseFunc ASin   = Sin
+inverseFunc ACos   = Cos
+inverseFunc ATan   = Tan
+inverseFunc ASinh  = Sinh
+inverseFunc ACosh  = Cosh
+inverseFunc ATanh  = Tanh
+inverseFunc Sqrt   = Square
+inverseFunc Square = Sqrt
+-- inverseFunc Cbrt   = (^3)
+inverseFunc Log    = Exp
+inverseFunc Exp    = Log
+inverseFunc Recip  = Recip
+-- inverseFunc Abs    = Abs -- we assume abs(x) = sqrt(x^2) so y = sqrt(x^2) => x^2 = y^2 => x = sqrt(y^2) = x = abs(y)
+inverseFunc x      = error $ show x ++ " has no support for inverse function"
+{-# INLINE inverseFunc #-}
+
+-- | evals the inverse of a function
+evalInverse :: Floating a => Function -> a -> a
+evalInverse Id     = id
+evalInverse Sin    = asin
+evalInverse Cos    = acos
+evalInverse Tan    = atan
+evalInverse Sinh   = asinh
+evalInverse Cosh   = acosh
+evalInverse Tanh   = atanh
+evalInverse ASin   = sin
+evalInverse ACos   = cos
+evalInverse ATan   = tan
+evalInverse ASinh  = sinh
+evalInverse ACosh  = cosh
+evalInverse ATanh  = tanh
+evalInverse Sqrt   = (^2)
+evalInverse SqrtAbs = (^2)
+evalInverse Square = sqrt
+evalInverse Cbrt   = (^3)
+evalInverse Log    = exp
+evalInverse LogAbs = exp
+evalInverse Exp    = log
+evalInverse Abs    = abs -- we assume abs(x) = sqrt(x^2) so y = sqrt(x^2) => x^2 = y^2 => x = sqrt(y^2) = x = abs(y)
+evalInverse Recip  = recip
+evalInverse Cube   = cbrt
+{-# INLINE evalInverse #-}
+
+-- | evals the right inverse of an operator 
+invright :: Floating a => Op -> a -> (a -> a)
+invright Add v   = subtract v
+invright Sub v   = (+v)
+invright Mul v   = (/v)
+invright Div v   = (*v)
+invright Power v = (**(1/v))
+invright PowerAbs v = (**(1/v))
+invright AQ v = (* sqrt (1 + v*v))
+{-# INLINE invright #-}
+
+-- | evals the left inverse of an operator 
+invleft :: Floating a => Op -> a -> (a -> a)
+invleft Add v   = subtract v
+invleft Sub v   = (+v) . negate -- y = v - r => r = v - y
+invleft Mul v   = (/v)
+invleft Div v   = (v/) -- y = v / r => r = v/y
+invleft Power v = logBase v -- (/(log v)) . log -- y = v ^ r  log y = r log v r = log y / log v
+invleft PowerAbs v = logBase v . abs
+invleft AQ v = (v/)
+{-# INLINE invleft #-}
+
+-- | List of invertible functions
+invertibles :: [Function]
+invertibles = [Id, Sin, Cos, Tan, Tanh, ASin, ACos, ATan, ATanh, Sqrt, Square, Log, Exp, Recip]
+{-# INLINE invertibles #-}
+ 
+ 
diff --git a/src/Data/SRTree/Internal.hs b/src/Data/SRTree/Internal.hs
--- a/src/Data/SRTree/Internal.hs
+++ b/src/Data/SRTree/Internal.hs
@@ -1,11 +1,13 @@
 {-# language FlexibleInstances, DeriveFunctor #-}
 {-# language ScopedTypeVariables #-}
 {-# language RankNTypes #-}
-{-# language ViewPatterns #-}
+{-# language OverloadedStrings #-}
+{-# language LambdaCase #-}
+{-# LANGUAGE DeriveGeneric, DeriveAnyClass #-}
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  Data.SRTree.Internal 
--- Copyright   :  (c) Fabricio Olivetti 2021 - 2021
+-- Copyright   :  (c) Fabricio Olivetti 2021 - 2024
 -- License     :  BSD3
 -- Maintainer  :  fabricio.olivetti@gmail.com
 -- Stability   :  experimental
@@ -21,55 +23,59 @@
          , Op(..)
          , param
          , var
+         , constv
          , arity
          , getChildren
+         , childrenOf
+         , replaceChildren
+         , getOperator
          , countNodes
          , countVarNodes
          , countConsts
          , countParams
+         , countParamsUniq
          , countOccurrences
-         , deriveBy
-         , deriveByVar
-         , deriveByParam
-         , derivative
-         , forwardMode
-         , gradParamsFwd
-         , gradParamsRev
-         , evalFun
-         , evalOp
-         , inverseFunc
-         , evalTree
+         , countUniqueTokens
+         , numberOfVars
+         , getIntConsts
          , relabelParams
+         , relabelParamsOrder
+         , relabelVars
          , constsToParam
          , floatConstsToParam
          , paramsToConst
+         , removeProtectedOps
+         , convertProtectedOps
          , Fix (..)
          )
          where
 
-import Data.SRTree.Recursion ( Fix (..), cata, mutu, accu, cataM )
-
-import qualified Data.Vector as V
-import Data.Vector ((!))
-import Control.Monad.State
-import qualified Data.DList as DL
-import Data.Bifunctor (second)
-
-import Debug.Trace (trace)
+import Control.Monad.State (MonadState (get), State, evalState, modify, put)
+import Data.SRTree.Recursion (Fix (..), cata, cataM)
+import qualified Data.Set as S
+import Data.String (IsString (..))
+import Text.Read (readMaybe)
+import qualified Data.IntMap as IntMap
+import Data.List ( nub )
+import GHC.Generics (Generic)
+import Control.DeepSeq (NFData)
 
 -- | Tree structure to be used with Symbolic Regression algorithms.
 -- This structure is a fixed point of a n-ary tree. 
 data SRTree val =
-   Var Int     -- ^ index of the variables
- | Param Int   -- ^ index of the parameter
- | Const Double -- ^ constant value, can be converted to a parameter
+   Var {-# UNPACK #-} !Int     -- ^ index of the variables
+ | Param {-# UNPACK #-} !Int   -- ^ index of the parameter
+ | Const {-# UNPACK #-} !Double -- ^ constant value, can be converted to a parameter
+ | Y {-# UNPACK #-} !Int -- ^ index of the target variable, always 0 for now
+ -- | IConst Int   -- TODO: integer constant
+ -- | RConst Ratio  -- TODO: rational constant
  | Uni Function val -- ^ univariate function
  | Bin Op val val -- ^ binary operator
- deriving (Show, Eq, Ord, Functor)
+ deriving (Show, Eq, Ord, Functor, Generic, NFData)
 
 -- | Supported operators
-data Op = Add | Sub | Mul | Div | Power
-    deriving (Show, Read, Eq, Ord, Enum)
+data Op = Add | Sub | Mul | Div | Power | PowerAbs | AQ
+    deriving (Show, Read, Eq, Ord, Enum, Generic, NFData)
 
 -- | Supported functions
 data Function =
@@ -88,12 +94,42 @@
   | ACosh
   | ATanh
   | Sqrt
+  | SqrtAbs
   | Cbrt
   | Square
   | Log
+  | LogAbs
   | Exp
-     deriving (Show, Read, Eq, Ord, Enum)
+  | Recip
+  | Cube
+     deriving (Show, Read, Eq, Ord, Enum, Generic, NFData)
 
+removeProtectedOps :: Fix SRTree -> Fix SRTree 
+removeProtectedOps = cata alg 
+  where 
+    alg (Var ix)           = var ix
+    alg (Param ix)         = param ix
+    alg (Const x)          = constv x
+    alg (Bin PowerAbs l r) = l ** r
+    alg (Bin op l r)       = Fix $ Bin op l r
+    alg (Uni SqrtAbs t)    = Fix $ Uni Sqrt t
+    alg (Uni LogAbs t)     = Fix $ Uni Log t
+    alg (Uni f t)          = Fix $ Uni f t
+{-# INLINE removeProtectedOps #-}
+
+convertProtectedOps :: Fix SRTree -> Fix SRTree 
+convertProtectedOps = cata alg 
+  where 
+    alg (Var ix)           = var ix
+    alg (Param ix)         = param ix
+    alg (Const x)          = constv x
+    alg (Bin PowerAbs l r) = abs l ** r
+    alg (Bin op l r)       = Fix $ Bin op l r
+    alg (Uni SqrtAbs t)    = sqrt (abs t)
+    alg (Uni LogAbs t)     = log (abs t)
+    alg (Uni f t)          = Fix $ Uni f t
+{-# INLINE convertProtectedOps #-}
+
 -- | create a tree with a single node representing a variable
 var :: Int -> Fix SRTree
 var ix = Fix (Var ix)
@@ -102,6 +138,26 @@
 param :: Int -> Fix SRTree
 param ix = Fix (Param ix)
 
+-- | create a tree with a single node representing a constant value
+constv :: Double -> Fix SRTree
+constv x = Fix (Const x)
+
+-- | the instance of `IsString` allows us to
+-- create a tree using a more practical notation:
+--
+-- >>> :t  "x0" + "t0" * sin("x1" * "t1")
+-- Fix SRTree
+--
+instance IsString (Fix SRTree) where 
+    fromString [] = error "empty string for SRTree"
+    fromString ('x':ix) = case readMaybe ix of 
+                            Just iy -> Fix (Var iy)
+                            Nothing -> error "wrong format for variable. It should be xi where i is an index. Ex.: \"x0\", \"x1\"."
+    fromString ('t':ix) = case readMaybe ix of 
+                            Just iy -> Fix (Param iy)
+                            Nothing -> error "wrong format for parameter. It should be ti where i is an index. Ex.: \"t0\", \"t1\"."
+    fromString _        = error "A string can represent a variable or a parameter following the format xi or ti, respectivelly, where i is the index. Ex.: \"x0\", \"t0\"."
+
 instance Num (Fix SRTree) where
   Fix (Const 0) + r = r
   l + Fix (Const 0) = l
@@ -142,6 +198,9 @@
   l / r                   = Fix $ Bin Div l r
   {-# INLINE (/) #-}
 
+  recip = Fix . Uni Recip
+  {-# INLINE recip #-}
+
   fromRational = Fix . Const . fromRational
   {-# INLINE fromRational #-}
 
@@ -188,6 +247,29 @@
   logBase l r = log l / log r
   {-# INLINE logBase #-}
 
+instance Foldable SRTree where 
+    foldMap f =
+        \case
+          Bin op l r -> f l <> f r
+          Uni g t    -> f t 
+          _          -> mempty 
+
+instance Traversable SRTree where 
+    traverse f = 
+        \case 
+          Bin op l r -> Bin op <$> f l <*> f r 
+          Uni g t    -> Uni g <$> f t 
+          Var ix     -> pure (Var ix) 
+          Param ix   -> pure (Param ix) 
+          Const x    -> pure (Const x) 
+    sequence =
+        \case
+          Bin op l r -> Bin op <$> l <*> r 
+          Uni g t    -> Uni g <$> t 
+          Var ix     -> pure (Var ix) 
+          Param ix   -> pure (Param ix) 
+          Const x    -> pure (Const x) 
+
 -- | Arity of the current node
 arity :: Fix SRTree -> Int
 arity = cata alg
@@ -200,6 +282,10 @@
 {-# INLINE arity #-}
 
 -- | Get the children of a node. Returns an empty list in case of a leaf node.
+--
+-- >>> map showExpr . getChildren $ "x0" + 2 
+-- ["x0", 2]
+--
 getChildren :: Fix SRTree -> [Fix SRTree]
 getChildren (Fix (Var {})) = []
 getChildren (Fix (Param {})) = []
@@ -208,19 +294,53 @@
 getChildren (Fix (Bin _ l r)) = [l, r]
 {-# INLINE getChildren #-}
 
+-- | Get the children of an unfixed node 
+-- 
+childrenOf :: SRTree a -> [a] 
+childrenOf = 
+    \case 
+      Uni _ t   -> [t] 
+      Bin _ l r -> [l, r] 
+      _         -> []
+
+-- | replaces the children with elements from a list 
+replaceChildren :: [a] -> SRTree b -> SRTree a
+replaceChildren [l, r] (Bin op _ _) = Bin op l r
+replaceChildren [t]    (Uni f _)    = Uni f t
+replaceChildren _      (Var ix)     = Var ix
+replaceChildren _      (Param ix)   = Param ix
+replaceChildren _      (Const x)    = Const x
+replaceChildren xs     n            = error "ERROR: trying to replace children with not enough elements."
+{-# INLINE replaceChildren #-}
+
+-- | returns a node containing the operator and () as children
+getOperator :: SRTree a -> SRTree ()
+getOperator (Bin op _ _) = Bin op () ()
+getOperator (Uni f _)    = Uni f ()
+getOperator (Var ix)     = Var ix
+getOperator (Param ix)   = Param ix
+getOperator (Const x)    = Const x
+{-# INLINE getOperator #-}
+
 -- | Count the number of nodes in a tree.
-countNodes :: Fix SRTree -> Int
+--
+-- >>> countNodes $ "x0" + 2
+-- 3
+countNodes :: Num a => Fix SRTree -> a
 countNodes = cata alg
   where
-      alg Var {} = 1
-      alg Param {} = 1
-      alg Const {} = 1
-      alg (Uni _ t) = 1 + t
+      alg Var   {}    = 1
+      alg Param {}    = 1
+      alg Const {}    = 1
+      alg (Uni _ t)   = 1 + t
       alg (Bin _ l r) = 1 + l + r
 {-# INLINE countNodes #-}
 
 -- | Count the number of `Var` nodes
-countVarNodes :: Fix SRTree -> Int
+--
+-- >>> countVarNodes $ "x0" + 2 * ("x0" - sin "x1")
+-- 3
+countVarNodes :: Num a => Fix SRTree -> a
 countVarNodes = cata alg
   where
       alg Var {} = 1
@@ -231,7 +351,10 @@
 {-# INLINE countVarNodes #-}
 
 -- | Count the number of `Param` nodes
-countParams :: Fix SRTree -> Int
+--
+-- >>> countParams $ "x0" + "t0" * sin ("t1" + "x1") - "t0"
+-- 3
+countParams :: Num a => Fix SRTree -> a
 countParams = cata alg
   where
       alg Var {} = 0
@@ -241,8 +364,25 @@
       alg (Bin _ l r) = 0 + l + r
 {-# INLINE countParams #-}
 
+-- | Count the unique occurrences of `Param` nodes
+--
+-- >>> countParams $ "x0" + "t0" * sin ("t1" + "x1") - "t0"
+-- 2
+countParamsUniq :: Fix SRTree -> Int
+countParamsUniq t = length . nub $ cata alg t
+  where
+      alg Var {} = []
+      alg (Param ix) = [ix]
+      alg Const {} = []
+      alg (Uni _ t) = t
+      alg (Bin _ l r) = l <> r
+{-# INLINE countParamsUniq #-}
+
 -- | Count the number of const nodes
-countConsts :: Fix SRTree -> Int
+--
+-- >>> countConsts $ "x0"* 2 + 3 * sin "x0"
+-- 2
+countConsts :: Num a => Fix SRTree -> a
 countConsts = cata alg
   where
       alg Var {} = 0
@@ -253,7 +393,10 @@
 {-# INLINE countConsts #-}
 
 -- | Count the occurrences of variable indexed as `ix`
-countOccurrences :: Int -> Fix SRTree -> Int
+--
+-- >>> countOccurrences 0 $ "x0"* 2 + 3 * sin "x0" + "x1"
+-- 2
+countOccurrences :: Num a => Int -> Fix SRTree -> a
 countOccurrences ix = cata alg
   where
       alg (Var iy) = if ix == iy then 1 else 0
@@ -263,302 +406,170 @@
       alg (Bin _ l r) = l + r
 {-# INLINE countOccurrences #-}
 
--- | Evaluates the tree given a vector of variable values, a vector of parameter values and a function that takes a Double and change to whatever type the variables have. This is useful when working with datasets of many values per variables.
-evalTree :: (Num a, Floating a) => V.Vector a -> V.Vector Double -> (Double -> a) -> Fix SRTree -> a
-evalTree xss params f = cata alg
+-- | counts the number of unique tokens 
+--
+-- >>> countUniqueTokens $ "x0" + ("x1" * "x0" - sin ("x0" ** 2))
+-- 8
+countUniqueTokens :: Num a => Fix SRTree -> a
+countUniqueTokens = len . cata alg
   where
-      alg (Var ix) = xss ! ix
-      alg (Param ix) = f $ params ! ix
-      alg (Const c) = f c
-      alg (Uni g t) = evalFun g t
-      alg (Bin op l r) = evalOp op l r
-{-# INLINE evalTree #-}
-
-evalOp :: Floating a => Op -> a -> a -> a
-evalOp Add = (+)
-evalOp Sub = (-)
-evalOp Mul = (*)
-evalOp Div = (/)
-evalOp Power = (**)
-{-# INLINE evalOp #-}
-
-evalFun :: Floating a => Function -> a -> a
-evalFun Id = id
-evalFun Abs = abs
-evalFun Sin = sin
-evalFun Cos = cos
-evalFun Tan = tan
-evalFun Sinh = sinh
-evalFun Cosh = cosh
-evalFun Tanh = tanh
-evalFun ASin = asin
-evalFun ACos = acos
-evalFun ATan = atan
-evalFun ASinh = asinh
-evalFun ACosh = acosh
-evalFun ATanh = atanh
-evalFun Sqrt = sqrt
-evalFun Cbrt = cbrt
-evalFun Square = (^2)
-evalFun Log = log
-evalFun Exp = exp
-{-# INLINE evalFun #-}
-
--- | Cubic root
-cbrt :: Floating val => val -> val
-cbrt x = signum x * abs x ** (1/3)
-{-# INLINE cbrt #-}
-
--- | Returns the inverse of a function. This is a partial function.
-inverseFunc :: Function -> Function
-inverseFunc Id     = Id
-inverseFunc Sin    = ASin
-inverseFunc Cos    = ACos
-inverseFunc Tan    = ATan
-inverseFunc Tanh   = ATanh
-inverseFunc ASin   = Sin
-inverseFunc ACos   = Cos
-inverseFunc ATan   = Tan
-inverseFunc ATanh  = Tanh
-inverseFunc Sqrt   = Square
-inverseFunc Square = Sqrt
-inverseFunc Log    = Exp
-inverseFunc Exp    = Log
-inverseFunc x      = error $ show x ++ " has no support for inverse function"
-{-# INLINE inverseFunc #-}
+    len (a, b, c, d, e) = fromIntegral $ length a + length b + length c + length d + length e
+    alg (Var ix)        = (mempty, mempty, S.singleton ix, mempty, mempty)
+    alg (Param _)       = (mempty, mempty, mempty, S.singleton 1, mempty)
+    alg (Const _)       = (mempty, mempty, mempty, mempty, S.singleton 1)
+    alg (Uni f t)       = (mempty, S.singleton f, mempty, mempty, mempty) <> t
+    alg (Bin op l r)    = (S.singleton op, mempty, mempty, mempty, mempty) <> l <> r
+{-# INLINE countUniqueTokens #-}
 
--- | Creates the symbolic partial derivative of a tree by variable `dx` (if `p` is `False`)
--- or parameter `dx` (if `p` is `True`).
-deriveBy :: Bool -> Int -> Fix SRTree -> Fix SRTree
-deriveBy p dx = fst (mutu alg1 alg2)
+-- | return the number of unique variables 
+-- 
+-- >>> numberOfVars $ "x0" + 2 * ("x0" - sin "x1")
+-- 2
+numberOfVars :: Num a => Fix SRTree -> a
+numberOfVars = fromIntegral . S.size . cata alg
   where
-      alg1 (Var ix) = if not p && ix == dx then 1 else 0
-      alg1 (Param ix) = if p && ix == dx then 1 else 0
-      alg1 (Const _) = 0
-      alg1 (Uni f t) = derivative f (snd t) * fst t
-      alg1 (Bin Add l r) = fst l + fst r
-      alg1 (Bin Sub l r) = fst l - fst r
-      alg1 (Bin Mul l r) = fst l * snd r + snd l * fst r
-      alg1 (Bin Div l r) = (fst l * snd r - snd l * fst r) / snd r ** 2
-      alg1 (Bin Power l r) = snd l ** (snd r - 1) * (snd r * fst l + snd l * log (snd l) * fst r)
-
-      alg2 (Var ix) = var ix
-      alg2 (Param ix) = param ix
-      alg2 (Const c) = Fix (Const c)
-      alg2 (Uni f t) = Fix (Uni f $ snd t)
-      alg2 (Bin f l r) = Fix (Bin f (snd l) (snd r))
-
-newtype Tape a = Tape { untape :: [a] } deriving (Show, Functor)
-
-instance Num a => Num (Tape a) where
-  (Tape x) + (Tape y) = Tape $ zipWith (+) x y
-  (Tape x) - (Tape y) = Tape $ zipWith (-) x y
-  (Tape x) * (Tape y) = Tape $ zipWith (*) x y
-  abs (Tape x) = Tape (map abs x)
-  signum (Tape x) = Tape (map signum x)
-  fromInteger x = Tape [fromInteger x]
-  negate (Tape x) = Tape $ map (*(-1)) x
-instance Floating a => Floating (Tape a) where
-  pi = Tape [pi]
-  exp (Tape x) = Tape (map exp x)
-  log (Tape x) = Tape (map log x)
-  sqrt (Tape x) = Tape (map sqrt x)
-  sin (Tape x) = Tape (map sin x)
-  cos (Tape x) = Tape (map cos x)
-  tan (Tape x) = Tape (map tan x)
-  asin (Tape x) = Tape (map asin x)
-  acos (Tape x) = Tape (map acos x)
-  atan (Tape x) = Tape (map atan x)
-  sinh (Tape x) = Tape (map sinh x)
-  cosh (Tape x) = Tape (map cosh x)
-  tanh (Tape x) = Tape (map tanh x)
-  asinh (Tape x) = Tape (map asinh x)
-  acosh (Tape x) = Tape (map acosh x)
-  atanh (Tape x) = Tape (map atanh x)
-  (Tape x) ** (Tape y) = Tape $ zipWith (**) x y
-instance Fractional a => Fractional (Tape a) where
-  fromRational x = Tape [fromRational x]
-  (Tape x) / (Tape y) = Tape $ zipWith (/) x y
-  recip (Tape x) = Tape $ map recip x
+    alg (Uni f t)    = t
+    alg (Bin op l r) = l <> r
+    alg (Var ix)     = S.singleton ix
+    alg _            = mempty
+{-# INLINE numberOfVars #-}
 
--- | Calculates the numerical derivative of a tree using forward mode
--- provided a vector of variable values `xss`, a vector of parameter values `theta` and
--- a function that changes a Double value to the type of the variable values.
-forwardMode :: (Show a, Num a, Floating a) => V.Vector a -> V.Vector Double -> (Double -> a) -> Fix SRTree -> [a]
-forwardMode xss theta f = untape . fst (mutu alg1 alg2)
+-- | returns the integer constants. We assume an integer constant 
+-- as those values in which `floor x == ceiling x`.
+--
+-- >>> getIntConsts $ "x0" + 2 * "x1" ** 3 - 3.14
+-- [2.0,3.0]
+getIntConsts :: Fix SRTree -> [Double]
+getIntConsts = cata alg
   where
-      n = V.length theta
-      repMat v = Tape $ replicate n v
-      zeroes = repMat $ f 0
-      twos  = repMat $ f 2
-      tapeXs = [repMat $ xss ! ix | ix <- [0 .. V.length xss - 1]]
-      tapeTheta = [repMat $ f (theta ! ix) | ix <- [0 .. n - 1]]
-      paramVec = [ Tape [if ix==iy then f 1 else f 0 | iy <- [0 .. n-1]] | ix <- [0 .. n-1] ]
-
-      alg1 (Var ix)        = zeroes
-      alg1 (Param ix)      = paramVec !! ix
-      alg1 (Const _)       = zeroes
-      alg1 (Uni f t)       = derivative f (snd t) * fst t
-      alg1 (Bin Add l r)   = fst l + fst r
-      alg1 (Bin Sub l r)   = fst l - fst r
-      alg1 (Bin Mul l r)   = (fst l * snd r) + (snd l * fst r)
-      alg1 (Bin Div l r)   = ((fst l * snd r) - (snd l * fst r)) / snd r ** twos
-      alg1 (Bin Power l r) = snd l ** (snd r - 1) * ((snd r * fst l) + (snd l * log (snd l) * fst r))
-
-      alg2 (Var ix)     = tapeXs !! ix
-      alg2 (Param ix)   = tapeTheta !! ix
-      alg2 (Const c)    = repMat $ f c
-      alg2 (Uni g t)    = fmap (evalFun g) (snd t)
-      alg2 (Bin op l r) = evalOp op (snd l) (snd r)
+    alg (Uni f t)    = t
+    alg (Bin op l r) = l <> r
+    alg (Var ix)     = []
+    alg (Param _)    = []
+    alg (Const x)    = [x | floor x == ceiling x]
+{-# INLINE getIntConsts #-}
 
--- | The function `gradParams` calculates the numerical gradient of the tree and evaluates the tree at the same time. It assumes that each parameter has a unique occurrence in the expression. This should be significantly faster than `forwardMode`.
-gradParamsFwd  :: (Show a, Num a, Floating a) => V.Vector a -> V.Vector Double -> (Double -> a) -> Fix SRTree -> (a, [a])
-gradParamsFwd xss theta f = second DL.toList . cata alg
+-- | Relabel the parameters indices incrementaly starting from 0
+--
+-- >>> showExpr . relabelParams $ "x0" + "t0" * sin ("t1" + "x1") - "t0" 
+-- "x0" + "t0" * sin ("t1" + "x1") - "t2" 
+relabelParams :: Fix SRTree -> Fix SRTree
+relabelParams t = cataM leftToRight alg t `evalState` 0
   where
-      n = V.length theta
-
-      alg (Var ix)        = (xss ! ix, DL.empty)
-      alg (Param ix)      = (f $ theta ! ix, DL.singleton 1)
-      alg (Const c)       = (f c, DL.empty)
-      alg (Uni f (v, gs)) = let v' = evalFun f v
-                                dv = derivative f v
-                             in (v', DL.map (*dv) gs)
-      alg (Bin Add (v1, l) (v2, r)) = (v1+v2, DL.append l r)
-      alg (Bin Sub (v1, l) (v2, r)) = (v1-v2, DL.append l (DL.map negate r))
-      alg (Bin Mul (v1, l) (v2, r)) = (v1*v2, DL.append (DL.map (*v2) l) (DL.map (*v1) r))
-      alg (Bin Div (v1, l) (v2, r)) = let dv = (-v1/v2^2) 
-                                       in (v1/v2, DL.append (DL.map (/v2) l) (DL.map (*dv) r))
-      alg (Bin Power (v1, l) (v2, r)) = let dv1 = v1 ** (v2 - 1)
-                                            dv2 = v1 * log v1
-                                         in (v1 ** v2, DL.map (*dv1) (DL.append (DL.map (*v2) l) (DL.map (*dv2) r)))
+      -- | leftToRight (left to right) defines the sequence of processing
+      leftToRight (Uni f mt)    = Uni f <$> mt;
+      leftToRight (Bin f ml mr) = Bin f <$> ml <*> mr
+      leftToRight (Var ix)      = pure (Var ix)
+      leftToRight (Param ix)    = pure (Param ix)
+      leftToRight (Const c)     = pure (Const c)
 
-data TupleF a b = S a | T a b | B a b b deriving Functor -- hi, I'm a tree
-type Tuple a = Fix (TupleF a)
+      -- | any time we reach a Param ix, it replaces ix with current state
+      -- and increments one to the state.
+      alg :: SRTree (Fix SRTree) -> State Int (Fix SRTree)
+      alg (Var ix)    = pure $ var ix
+      alg (Param ix)  = do iy <- get; modify (+1); pure (param iy)
+      alg (Const c)   = pure $ Fix $ Const c
+      alg (Uni f t)   = pure $ Fix (Uni f t)
+      alg (Bin f l r) = pure $ Fix (Bin f l r)
 
-gradParamsRev  :: forall a . (Show a, Num a, Floating a) => V.Vector a -> V.Vector Double -> (Double -> a) -> Fix SRTree -> (a, [a])
-gradParamsRev xss theta f t = (getTop fwdMode, DL.toList g)
+-- | Reorder the labels of the parameters indices
+--
+-- >>> showExpr . relabelParamsOrder $ "x0" + "t1" * sin ("t3" + "x1") - "t1"
+-- "x0" + "t0" * sin ("t1" + "x1") - "t0"
+relabelParamsOrder :: Fix SRTree -> Fix SRTree
+relabelParamsOrder t = cataM leftToRight alg t `evalState` (IntMap.empty, 0)
   where
-      fwdMode = cata forward t
-      g = accu reverse combine t (1, fwdMode)
-
-      oneTpl x  = Fix $ S x
-      tuple x y = Fix $ T x y
-      branch x y z = Fix $ B x y z
-      getTop (Fix (S x)) = x
-      getTop (Fix (T x y)) = x
-      getTop (Fix (B x y z)) = x
-      unCons (Fix (T x y)) = y
-      getBranches (Fix (B x y z)) = (y,z)
-
-      forward (Var ix)     = oneTpl (xss ! ix)
-      forward (Param ix)   = oneTpl (f $ theta ! ix)
-      forward (Const c)    = oneTpl (f c)
-      forward (Uni f t)    = let v = getTop t
-                              in tuple (evalFun f v) t
-      forward (Bin op l r) = let vl = getTop l
-                                 vr = getTop r
-                              in branch (evalOp op vl vr) l r
-
-      reverse (Var ix)     (dx,    _)        = Var ix
-      reverse (Param ix)   (dx,    _)        = Param ix
-      reverse (Const v)    (dx,    _)        = Const v
-      reverse (Uni f t)    (dx, unCons -> v) = Uni f (t, (dx * (derivative f $ getTop v), v))
-      reverse (Bin op l r) (dx, getBranches -> (vl, vr)) = let (dxl, dxr) = diff op dx (getTop vl) (getTop vr)
-                                                            in Bin op (l, (dxl, vl)) (r, (dxr, vr))
-
-      diff Add dx vl vr = (dx, dx)
-      diff Sub dx vl vr = (dx, negate dx)
-      diff Mul dx vl vr = (dx * vr, dx * vl)
-      diff Div dx vl vr = (dx / vr, dx * (-vl/vr^2))
-      diff Power dx vl vr = let dxl = dx * vl ** (vr - 1)
-                                dv2 = vl * log vl
-                             in (dxl * vr, dxl * dv2)
-
-      combine (Var ix)     s = DL.empty
-      combine (Param ix)   s = DL.singleton $ fst s
-      combine (Const c)    s = DL.empty
-      combine (Uni _ gs)   s = gs
-      combine (Bin op l r) s = DL.append l r
-
-derivative :: Floating a => Function -> a -> a
-derivative Id      = const 1
-derivative Abs     = \x -> x / abs x
-derivative Sin     = cos
-derivative Cos     = negate.sin
-derivative Tan     = recip . (**2.0) . cos
-derivative Sinh    = cosh
-derivative Cosh    = sinh
-derivative Tanh    = (1-) . (**2.0) . tanh
-derivative ASin    = recip . sqrt . (1-) . (^2)
-derivative ACos    = negate . recip . sqrt . (1-) . (^2)
-derivative ATan    = recip . (1+) . (^2)
-derivative ASinh   = recip . sqrt . (1+) . (^2)
-derivative ACosh   = \x -> 1 / (sqrt (x-1) * sqrt (x+1))
-derivative ATanh   = recip . (1-) . (^2)
-derivative Sqrt    = recip . (2*) . sqrt
-derivative Cbrt    = recip . (3*) . cbrt . (^2)
-derivative Square  = (2*)
-derivative Exp     = exp
-derivative Log     = recip
-{-# INLINE derivative #-}
-
--- | Symbolic derivative by a variable
-deriveByVar :: Int -> Fix SRTree -> Fix SRTree
-deriveByVar = deriveBy False
+      -- | leftToRight (left to right) defines the sequence of processing
+      leftToRight (Uni f mt)    = Uni f <$> mt;
+      leftToRight (Bin f ml mr) = Bin f <$> ml <*> mr
+      leftToRight (Var ix)      = pure (Var ix)
+      leftToRight (Param ix)    = pure (Param ix)
+      leftToRight (Const c)     = pure (Const c)
 
--- | Symbolic derivative by a parameter
-deriveByParam :: Int -> Fix SRTree -> Fix SRTree
-deriveByParam = deriveBy True
+      -- | any time we reach a Param ix, it replaces ix with current state
+      -- and increments one to the state.
+      alg :: SRTree (Fix SRTree) -> State (IntMap.IntMap Int, Int) (Fix SRTree)
+      alg (Var ix)    = pure $ var ix
+      alg (Param ix)  = do (m, iy) <- get
+                           if IntMap.member ix m
+                              then pure (param $ m IntMap.! ix)
+                              else do let m' = IntMap.insert ix iy m
+                                      put (m', iy+1)
+                                      pure (param iy)
+      alg (Const c)   = pure $ Fix $ Const c
+      alg (Uni f t)   = pure $ Fix (Uni f t)
+      alg (Bin f l r) = pure $ Fix (Bin f l r)
 
--- | Relabel the parameters incrementaly starting from 0
-relabelParams :: Fix SRTree -> Fix SRTree
-relabelParams t = cataM lTor alg t `evalState` 0
+-- | Relabel the parameters indices incrementaly starting from 0
+--
+-- >>> showExpr . relabelParams $ "x0" + "t0" * sin ("t1" + "x1") - "t0"
+-- "x0" + "t0" * sin ("t1" + "x1") - "t2"
+relabelVars :: Fix SRTree -> Fix SRTree
+relabelVars t = cataM leftToRight alg t `evalState` 0
   where
-      lTor (Uni f mt) = Uni f <$> mt;
-      lTor (Bin f ml mr) = Bin f <$> ml <*> mr
-      lTor (Var ix) = pure (Var ix)
-      lTor (Param ix) = pure (Param ix)
-      lTor (Const c) = pure (Const c)
+      -- | leftToRight (left to right) defines the sequence of processing
+      leftToRight (Uni f mt)    = Uni f <$> mt;
+      leftToRight (Bin f ml mr) = Bin f <$> ml <*> mr
+      leftToRight (Var ix)      = pure (Var ix)
+      leftToRight (Param ix)    = pure (Param ix)
+      leftToRight (Const c)     = pure (Const c)
 
+      -- | any time we reach a Param ix, it replaces ix with current state
+      -- and increments one to the state.
       alg :: SRTree (Fix SRTree) -> State Int (Fix SRTree)
-      alg (Var ix) = pure $ var ix
-      alg (Param ix) = do iy <- get; modify (+1); pure (param iy)
-      alg (Const c) = pure $ Fix $ Const c
-      alg (Uni f t) = pure $ Fix (Uni f t)
+      alg (Var ix)    = do iy <- get; modify (+1); pure (var iy)
+      alg (Param ix)  = pure $ param ix
+      alg (Const c)   = pure $ Fix $ Const c
+      alg (Uni f t)   = pure $ Fix (Uni f t)
       alg (Bin f l r) = pure $ Fix (Bin f l r)
 
 -- | Change constant values to a parameter, returning the changed tree and a list
 -- of parameter values
+--
+-- >>> snd . constsToParam $ "x0" * 2 + 3.14 * sin (5 * "x1")
+-- [2.0,3.14,5.0]
 constsToParam :: Fix SRTree -> (Fix SRTree, [Double])
 constsToParam = first relabelParams . cata alg
   where
       first f (x, y) = (f x, y)
 
-      alg (Var ix) = (Fix $ Var ix, [])
-      alg (Param ix) = (Fix $ Param ix, [1.0])
-      alg (Const c) = (Fix $ Param 0, [c])
-      alg (Uni f t) = (Fix $ Uni f (fst t), snd t)
+      -- | If the tree already contains a parameter
+      -- it will return a default value of 1.0
+      -- whenever it finds a constant, it changes that
+      -- to a parameter and adds its content to the singleton list
+      alg (Var ix)    = (Fix $ Var ix, [])
+      alg (Param ix)  = (Fix $ Param ix, [1.0])
+      alg (Const c)   = (Fix $ Param 0, [c])
+      alg (Uni f t)   = (Fix $ Uni f (fst t), snd t)
       alg (Bin f l r) = (Fix (Bin f (fst l) (fst r)), snd l <> snd r)
 
 -- | Same as `constsToParam` but does not change constant values that
 -- can be converted to integer without loss of precision
+--
+-- >>> snd . floatConstsToParam $ "x0" * 2 + 3.14 * sin (5 * "x1")
+-- [3.14]
 floatConstsToParam :: Fix SRTree -> (Fix SRTree, [Double])
 floatConstsToParam = first relabelParams . cata alg
   where
-      first f (x, y) = (f x, y)
+      first f (x, y)          = (f x, y)
+      combine f (x, y) (z, w) = (f x z, y <> w)
+      isInt x                 = floor x == ceiling x
 
-      alg (Var ix) = (Fix $ Var ix, [])
-      alg (Param ix) = (Fix $ Param ix, [1.0])
-      alg (Const c) = if floor c == ceiling c then (Fix $ Const c, []) else (Fix $ Param 0, [c])
-      alg (Uni f t) = (Fix $ Uni f (fst t), snd t)
-      alg (Bin f l r) = (Fix (Bin f (fst l) (fst r)), snd l <> snd r)
+      alg (Var ix)    = (var ix, [])
+      alg (Param ix)  = (param ix, [1.0])
+      alg (Const c)   = if isInt c then (constv c, []) else (param 0, [c])
+      alg (Uni f t)   = first (Fix . Uni f) t -- (Fix $ Uni f (fst t), snd t)
+      alg (Bin f l r) = combine ((Fix .) . Bin f) l r -- (Fix (Bin f (fst l) (fst r)), snd l <> snd r)
 
 -- | Convert the parameters into constants in the tree
+--
+-- >>> showExpr . paramsToConst [1.1, 2.2, 3.3] $ "x0" + "t0" * sin ("t1" * "x0" - "t2")
+-- x0 + 1.1 * sin(2.2 * x0 - 3.3)
 paramsToConst :: [Double] -> Fix SRTree -> Fix SRTree
 paramsToConst theta = cata alg
   where
-      alg (Var ix) = Fix $ Var ix
-      alg (Param ix) = Fix $ Const (theta !! ix)
-      alg (Const c) = Fix $ Const c
-      alg (Uni f t) = Fix $ Uni f t
+      alg (Var ix)    = Fix $ Var ix
+      alg (Param ix)  = Fix $ Const (theta !! ix)
+      alg (Const c)   = Fix $ Const c
+      alg (Uni f t)   = Fix $ Uni f t
       alg (Bin f l r) = Fix $ Bin f l r
diff --git a/src/Data/SRTree/Print.hs b/src/Data/SRTree/Print.hs
--- a/src/Data/SRTree/Print.hs
+++ b/src/Data/SRTree/Print.hs
@@ -1,7 +1,9 @@
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE LambdaCase #-}
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  Data.SRTree.Print 
--- Copyright   :  (c) Fabricio Olivetti 2021 - 2021
+-- Copyright   :  (c) Fabricio Olivetti 2021 - 2024
 -- License     :  BSD3
 -- Maintainer  :  fabricio.olivetti@gmail.com
 -- Stability   :  experimental
@@ -12,52 +14,103 @@
 -----------------------------------------------------------------------------
 module Data.SRTree.Print 
          ( showExpr
+         , showExprWithVars
          , printExpr
+         , printExprWithVars
          , showTikz
          , printTikz
          , showPython
          , printPython
          , showLatex
+         , showLatexWithVars
          , printLatex
+         , showOp
          )
          where
 
-import Control.Monad.Reader ( asks, runReader, Reader )
-import Data.Char ( toLower )
-
+import Control.Monad.Reader (Reader, asks, runReader)
+import Data.Char (toLower)
 import Data.SRTree.Internal
-import Data.SRTree.Recursion
+import Data.SRTree.Recursion (cata)
 
+-- | converts a tree with protected operators to
+-- a conventional math tree
+removeProtection :: Fix SRTree -> Fix SRTree
+removeProtection = cata $
+  \case
+     Var ix -> Fix (Var ix)
+     Param ix -> Fix (Param ix)
+     Const x -> Fix (Const x)
+     Uni SqrtAbs t -> sqrt (abs t)
+     Uni LogAbs t -> log (abs t)
+     Uni Cube t -> t ** 3
+     Uni f t -> Fix (Uni f t)
+     Bin AQ l r -> l / sqrt (1 + r*r)
+     Bin PowerAbs l r -> abs l ** r
+     Bin op l r -> Fix (Bin op l r)
+
+-- | convert a tree into a string in math notation 
+--
+-- >>> showExpr $ "x0" + sin ( tanh ("t0" + 2) )
+-- "(x0 + Sin(Tanh((t0 + 2.0))))"
 showExpr :: Fix SRTree -> String
-showExpr = cata alg
-  where
-    alg (Var ix)     = 'x' : show ix
-    alg (Param ix)   = 't' : show ix
-    alg (Const c)    = show c
-    alg (Bin op l r) = concat ["(", l, " ", showOp op, " ", r, ")"]
-    alg (Uni f t)    = concat [show f, "(", t, ")"]
+showExpr = cata alg . removeProtection
+  where alg = \case
+                Var ix     -> 'x' : show ix
+                Param ix   -> 't' : show ix
+                Const c    -> show c
+                Bin op l r -> concat ["(", l, " ", showOp op, " ", r, ")"]
+                Uni f t    -> concat [show f, "(", t, ")"]
 
+-- | convert a tree into a string in math notation
+-- given named vars.
+--
+-- >>> showExprWithVar ["mu", "eps"] $ "x0" + sin ( "x1" * tanh ("t0" + 2) )
+-- "(mu + Sin(Tanh(eps * (t0 + 2.0))))"
+showExprWithVars :: [String] -> Fix SRTree -> String
+showExprWithVars varnames = cata alg . removeProtection
+  where alg = \case
+                Var ix     -> varnames !! ix
+                Param ix   -> 't' : show ix
+                Const c    -> show c
+                Bin op l r -> concat ["(", l, " ", showOp op, " ", r, ")"]
+                Uni f t    -> concat [show f, "(", t, ")"]
+
+-- | prints the expression 
 printExpr :: Fix SRTree -> IO ()
 printExpr = putStrLn . showExpr 
 
+-- | prints the expression
+printExprWithVars :: [String] -> Fix SRTree -> IO ()
+printExprWithVars varnames = putStrLn . showExprWithVars varnames
+
+-- how to display an operator 
+showOp :: Op -> String
 showOp Add   = "+"
 showOp Sub   = "-"
 showOp Mul   = "*"
 showOp Div   = "/"
 showOp Power = "^"
+showOp AQ    = "aq"
+showOp PowerAbs = "|^|"
 {-# INLINE showOp #-}
 
 -- | Displays a tree as a numpy compatible expression.
+--
+-- >>> showPython $ "x0" + sin ( tanh ("t0" + 2) )
+-- "(x[:, 0] + np.sin(np.tanh((t[:, 0] + 2.0))))"
 showPython :: Fix SRTree -> String
-showPython = cata alg
+showPython = cata alg . removeProtection
   where
-    alg (Var ix)     = concat ["x[:, ", show ix, "]"]
-    alg (Param ix)   = concat ["t[:, ", show ix, "]"]
-    alg (Const c)    = show c
-    alg (Bin Power l r) = concat [l, " ** ", r]
-    alg (Bin op l r) = concat ["(", l, " ", showOp op, " ", r, ")"]
-    alg (Uni f t)    = concat [pyFun f, "(", t, ")"]
+    alg = \case
+      Var ix        -> concat ["x[:, ", show ix, "]"]
+      Param ix      -> concat ["t[", show ix, "]"]
+      Const c       -> show c
+      Bin Power l r -> concat [l, " ** ", r]
+      Bin op l r    -> concat ["(", l, " ", showOp op, " ", r, ")"]
+      Uni f t       -> concat [pyFun f, "(", t, ")"]
           
+
     pyFun Id     = ""
     pyFun Abs    = "np.abs"
     pyFun Sin    = "np.sin"
@@ -76,39 +129,69 @@
     pyFun Square = "np.square"
     pyFun Log    = "np.log"
     pyFun Exp    = "np.exp"
+    pyFun Cbrt   = "np.cbrt"
+    pyFun Recip  = "np.reciprocal"
 
+-- | print the expression in numpy notation
 printPython :: Fix SRTree -> IO ()
 printPython = putStrLn . showPython
 
--- | Displays a tree as a sympy compatible expression.
+-- | Displays a tree as a LaTeX compatible expression.
+--
+-- >>> showLatex $ "x0" + sin ( tanh ("t0" + 2) )
+-- "\\left(x_{, 0} + \\operatorname{sin}(\\operatorname{tanh}(\\left(\\theta_{, 0} + 2.0\\right)))\\right)"
 showLatex :: Fix SRTree -> String
-showLatex = cata alg
+showLatex = cata alg . removeProtection
   where
-    alg (Var ix)     = concat ["x_{, ", show ix, "}"]
-    alg (Param ix)   = concat ["\\theta_{, ", show ix, "}"]
-    alg (Const c)    = show c
-    alg (Bin Power l r) = concat [l, "^{", r, "}"]
-    alg (Bin op l r) = concat ["\\left(", l, " ", showOp op, " ", r, "\\right)"]
-    alg (Uni Abs t)  = concat ["\\left |", t, "\\right |"]
-    alg (Uni f t)    = concat [showLatexFun f, "(", t, ")"]
-
+    alg = \case
+      Var ix        -> concat ["x_{", show ix, "}"]
+      Param ix      -> concat ["\\theta_{", show ix, "}"]
+      Const c       -> show c
+      Bin Power l r -> concat ["{", l, "^{", r, "}}"]
+      Bin PowerAbs l r ->  concat ["{\\left|", l, "\\right|^{", r, "}}"]
+      Bin Mul l r    -> concat ["\\left(", l, " \\cdot ", r, "\\right)"]
+      Bin Div l r    -> concat ["\\frac{", l, "}{", r, "}"]
+      Bin op l r    -> concat ["\\left(", l, " ", showOp op, " ", r, "\\right)"]
+      Uni Abs t     -> concat ["\\left |", t, "\\right |"]
+      Uni Recip t   -> concat ["\\frac{1}{", t, "}"]
+      Uni f t       -> concat [showLatexFun f, "(", t, ")"]
+      
+showLatexWithVars :: [String] -> Fix SRTree -> String
+showLatexWithVars varnames = cata alg . removeProtection
+  where 
+    alg = \case
+      Var ix        -> concat ["\\operatorname{", varnames !! ix, "}"]
+      Param ix      -> concat ["\\theta_{", show ix, "}"]
+      Const c       -> show c
+      Bin Power l r -> concat ["{", l, "^{", r, "}}"]
+      Bin PowerAbs l r ->  concat ["{\\left|", l, "\\right|^{", r, "}}"]
+      Bin Mul l r    -> concat ["\\left(", l, " \\cdot ", r, "\\right)"]
+      Bin Div l r    -> concat ["\\frac{", l, "}{", r, "}"]
+      Bin op l r    -> concat ["\\left(", l, " ", showOp op, " ", r, "\\right)"]
+      Uni Abs t     -> concat ["\\left |", t, "\\right |"]
+      Uni Recip t   -> concat ["\\frac{1}{", t, "}"]
+      Uni f t       -> concat [showLatexFun f, "(", t, ")"]
+                
 showLatexFun :: Function -> String
 showLatexFun f = mconcat ["\\operatorname{", map toLower $ show f, "}"]
 {-# INLINE showLatexFun #-}
 
+-- | prints expression in LaTeX notation. 
 printLatex :: Fix SRTree -> IO ()
 printLatex = putStrLn . showLatex
 
 -- | Displays a tree in Tikz format
 showTikz :: Fix SRTree -> String
-showTikz = cata alg
+showTikz = cata alg . removeProtection
   where
+    alg = \case
+      Var ix     -> concat ["[$x_{, ", show ix, "}$]\n"]
+      Param ix   -> concat ["[$\\theta_{, ", show ix, "}$]\n"]
+      Const c    -> concat ["[$", show (roundN 2 c), "$]\n"]
+      Bin op l r -> concat ["[", showOpTikz op, l, r, "]\n"]
+      Uni f t    -> concat ["[", map toLower $ show f, t, "]\n"]
+
     roundN n x = let ten = 10^n in (/ ten) . fromIntegral . round $ x*ten
-    alg (Var ix)     = concat ["[$x_{, ", show ix, "}$]\n"]
-    alg (Param ix)   = concat ["[$\\theta_{, ", show ix, "}$]\n"]
-    alg (Const c)    = concat ["[$", show (roundN 2 c), "$]\n"]
-    alg (Bin op l r) = concat ["[", showOpTikz op, l, r, "]\n"]
-    alg (Uni f t)    = concat ["[", map toLower $ show f, t, "]\n"]
 
     showOpTikz Add = "+\n"
     showOpTikz Sub = "-\n"
@@ -116,4 +199,6 @@
     showOpTikz Div = "÷\n"
     showOpTikz Power = "\\^{}\n"
 
+-- | prints the tree in TikZ format 
+printTikz :: Fix SRTree -> IO ()
 printTikz = putStrLn . showTikz
diff --git a/src/Data/SRTree/Random.hs b/src/Data/SRTree/Random.hs
--- a/src/Data/SRTree/Random.hs
+++ b/src/Data/SRTree/Random.hs
@@ -2,7 +2,7 @@
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  Data.SRTree.Random 
--- Copyright   :  (c) Fabricio Olivetti 2021 - 2021
+-- Copyright   :  (c) Fabricio Olivetti 2021 - 2024
 -- License     :  BSD3
 -- Maintainer  :  fabricio.olivetti@gmail.com
 -- Stability   :  experimental
@@ -18,25 +18,35 @@
          , HasEverything
          , FullParams(..)
          , RndTree
+         , Rng(..)
          , randomVar
          , randomConst
          , randomPow
          , randomFunction
          , randomNode
          , randomNonTerminal
+         , randomRange
+         , randomTreeTemplate
          , randomTree
          , randomTreeBalanced
+         , toss
+         , tossBiased
+         , randomVal
+         , randomVec
+         , randomFrom
          )
          where
 
-import System.Random 
-import Control.Monad.State 
-import Control.Monad.Reader 
+import Control.Monad.Reader (ReaderT, asks, runReaderT)
+import Control.Monad.State.Strict ( MonadState(state), MonadTrans(lift), StateT )
 import Data.Maybe (fromJust)
-
 import Data.SRTree.Internal
-import Data.SRTree.Recursion
+import System.Random (Random (random, randomR), StdGen, mkStdGen)
+import Data.SRTree.Eval
+import Control.Monad
+import qualified Data.Vector.Unboxed as V
 
+
 -- * Class definition of properties that a certain parameter type has.
 --
 -- HasVars: does `p` provides a list of the variable indices?
@@ -67,19 +77,28 @@
 instance HasFuns FullParams where
   _funs (P _ _ _ fs) = fs
 
+type Rng m a = StateT StdGen m a
+
 -- auxiliary function to sample between False and True
-toss :: StateT StdGen IO Bool
+toss :: Monad m => Rng m Bool
 toss = state random
 {-# INLINE toss #-}
 
+tossBiased :: Monad m => Double -> Rng m Bool
+tossBiased p = do r <- state random
+                  pure (r < p)
+
+randomVal :: Monad m => Rng m Double
+randomVal = state random
+
 -- returns a random element of a list
-randomFrom :: [a] -> StateT StdGen IO a
+randomFrom :: Monad m => [a] -> Rng m a
 randomFrom funs = do n <- randomRange (0, length funs - 1)
                      pure $ funs !! n
 {-# INLINE randomFrom #-}
 
 -- returns a random element within a range
-randomRange :: (Ord val, Random val) => (val, val) -> StateT StdGen IO val
+randomRange :: (Ord val, Random val, Monad m) => (val, val) -> Rng m val
 randomRange rng = state (randomR rng)
 {-# INLINE randomRange #-}
 
@@ -90,38 +109,38 @@
 {-# INLINE replaceChild #-}
 
 -- Replace the children of a binary tree.
-replaceChildren :: Fix SRTree -> Fix SRTree -> Fix SRTree -> Maybe (Fix SRTree)
-replaceChildren (Fix (Bin f _ _)) l r = Just $ Fix (Bin f l r)
-replaceChildren _             _ _ = Nothing
-{-# INLINE replaceChildren #-}
+replaceFixChildren :: Fix SRTree -> Fix SRTree -> Fix SRTree -> Maybe (Fix SRTree)
+replaceFixChildren (Fix (Bin f _ _)) l r = Just $ Fix (Bin f l r)
+replaceFixChildren _             _ _ = Nothing
+{-# INLINE replaceFixChildren #-}
 
 -- | RndTree is a Monad Transformer to generate random trees of type `SRTree ix val` 
 -- given the parameters `p ix val` using the random number generator `StdGen`.
-type RndTree p = ReaderT p (StateT StdGen IO) (Fix SRTree)
+type RndTree m p = ReaderT p (StateT StdGen m) (Fix SRTree)
 
 -- | Returns a random variable, the parameter `p` must have the `HasVars` property
-randomVar :: HasVars p => RndTree p
+randomVar :: Monad m => HasVars p => RndTree m p
 randomVar = do vars <- asks _vars
                lift $ Fix . Var <$> randomFrom vars
 
 -- | Returns a random constant, the parameter `p` must have the `HasConst` property
-randomConst :: HasVals p => RndTree p
+randomConst :: (HasVals p, Monad m) => RndTree m p
 randomConst = do rng <- asks _range
                  lift $ Fix . Const <$> randomRange rng
 
 -- | Returns a random integer power node, the parameter `p` must have the `HasExps` property
-randomPow :: HasExps p => RndTree p
+randomPow :: (HasExps p, Monad m) => RndTree m p
 randomPow = do rng <- asks _exponents
                lift $ Fix . Bin Power 0 . Fix . Const . fromIntegral <$> randomRange rng
 
 -- | Returns a random function, the parameter `p` must have the `HasFuns` property
-randomFunction :: HasFuns p => RndTree p
+randomFunction :: (HasFuns p, Monad m) => RndTree m p
 randomFunction = do funs <- asks _funs
                     f <- lift $ randomFrom funs
                     lift $ pure $ Fix (Uni f 0)
 
 -- | Returns a random node, the parameter `p` must have every property.
-randomNode :: HasEverything p => RndTree p
+randomNode :: (HasEverything p, Monad m) => RndTree m p
 randomNode = do
   choice <- lift $ randomRange (0, 8 :: Int)
   case choice of
@@ -136,7 +155,7 @@
     8 -> pure . Fix $ Bin Power 0 0
 
 -- | Returns a random non-terminal node, the parameter `p` must have every property.
-randomNonTerminal :: HasEverything p => RndTree p
+randomNonTerminal :: (HasEverything p, Monad m) => RndTree m p
 randomNonTerminal = do
   choice <- lift $ randomRange (0, 6 :: Int)
   case choice of
@@ -149,21 +168,31 @@
     6 -> pure . Fix $ Bin Power 0 0
     
 -- | Returns a random tree with a limited budget, the parameter `p` must have every property.
-randomTree :: HasEverything p => Int -> RndTree p
-randomTree 0      = do
+--
+-- >>> let treeGen = runReaderT (randomTree 12) (P [0,1] (-10, 10) (2, 3) [Log, Exp])
+-- >>> tree <- evalStateT treeGen (mkStdGen 52)
+-- >>> showExpr tree
+-- "(-2.7631152121655838 / Exp((x0 / ((x0 * -7.681722660704317) - Log(3.378309080134594)))))"
+randomTreeTemplate :: (HasEverything p, Monad m) => Int -> RndTree m p
+randomTreeTemplate 0      = do
   coin <- lift toss
   if coin
     then randomVar
     else randomConst
-randomTree budget = do 
+randomTreeTemplate budget = do
   node  <- randomNode
   fromJust <$> case arity node of
     0 -> pure $ Just node
-    1 -> replaceChild node <$> randomTree (budget - 1)
-    2 -> replaceChildren node <$> randomTree (budget `div` 2) <*> randomTree (budget `div` 2)
+    1 -> replaceChild node <$> randomTreeTemplate (budget - 1)
+    2 -> replaceFixChildren node <$> randomTreeTemplate (budget `div` 2) <*> randomTreeTemplate (budget `div` 2)
     
 -- | Returns a random tree with a approximately a number `n` of nodes, the parameter `p` must have every property.
-randomTreeBalanced :: HasEverything p => Int -> RndTree p
+--
+-- >>> let treeGen = runReaderT (randomTreeBalanced 10) (P [0,1] (-10, 10) (2, 3) [Log, Exp])
+-- >>> tree <- evalStateT treeGen (mkStdGen 42)
+-- >>> showExpr tree
+-- "Exp(Log((((7.784360517385774 * x0) - (3.6412224491658223 ^ x1)) ^ ((x0 ^ -4.09764995657091) + Log(-7.710216839988497)))))"
+randomTreeBalanced :: (HasEverything p, Monad m) => Int -> RndTree m p
 randomTreeBalanced n | n <= 1 = do
   coin <- lift toss
   if coin
@@ -173,4 +202,29 @@
   node  <- randomNonTerminal
   fromJust <$> case arity node of
     1 -> replaceChild node <$> randomTreeBalanced (n - 1)
-    2 -> replaceChildren node <$> randomTreeBalanced (n `div` 2) <*> randomTreeBalanced (n `div` 2)    
+    2 -> replaceFixChildren node <$> randomTreeBalanced (n `div` 2) <*> randomTreeBalanced (n `div` 2)    
+
+
+randomVec :: Monad m => Int -> Rng m Theta
+randomVec n = V.fromList <$> replicateM n (randomRange (-1, 1))
+
+randomTree :: Monad m => Int -> Int -> Int -> Rng m (Fix SRTree) -> Rng m (SRTree ()) -> Bool -> Rng  m (Fix SRTree)
+randomTree minDepth maxDepth maxSize genTerm genNonTerm grow
+  | noSpaceLeft = genTerm
+  | needNonTerm = genRecursion
+  | otherwise   = do r <- toss
+                     if r
+                       then genTerm
+                       else genRecursion
+  where
+    noSpaceLeft = maxDepth <= 1 || maxSize <= 2
+    needNonTerm = (minDepth >= 0 || (maxDepth > 2 && not grow)) -- && maxSize > 2
+
+    genRecursion = do
+        node <- genNonTerm
+        case node of
+          Uni f _    -> Fix . Uni f <$> randomTree (minDepth - 1) (maxDepth - 1) (maxSize - 1) genTerm genNonTerm grow
+          Bin op _ _ -> do l <- randomTree (minDepth - 1) (maxDepth - 1) (if grow then maxSize - 2 else maxSize `div` 2) genTerm genNonTerm grow
+                           r <- randomTree (minDepth - 1) (maxDepth - 1) (maxSize - 1 - countNodes l) genTerm genNonTerm grow
+                           pure . Fix  $ Bin op l r
+{-# INLINE randomTree #-}
diff --git a/src/Data/SRTree/Recursion.hs b/src/Data/SRTree/Recursion.hs
--- a/src/Data/SRTree/Recursion.hs
+++ b/src/Data/SRTree/Recursion.hs
@@ -1,5 +1,17 @@
 {-# language RankNTypes #-}
 {-# language DeriveFunctor #-}
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Data.SRTree.Recursion 
+-- Copyright   :  (c) Fabricio Olivetti 2021 - 2024
+-- License     :  BSD3
+-- Maintainer  :  fabricio.olivetti@gmail.com
+-- Stability   :  experimental
+-- Portability :  FlexibleInstances, DeriveFunctor, ScopedTypeVariables
+--
+-- Recursion schemes
+--
+-----------------------------------------------------------------------------
 module Data.SRTree.Recursion where
 
 import Control.Monad ( (>=>) )
diff --git a/src/Numeric/Optimization/NLOPT.hs b/src/Numeric/Optimization/NLOPT.hs
new file mode 100644
--- /dev/null
+++ b/src/Numeric/Optimization/NLOPT.hs
@@ -0,0 +1,976 @@
+{-# OPTIONS_GHC -Wall #-}
+{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE TypeApplications #-}
+
+{- |
+Module      :  Numeric.NLOPT
+Copyright   :  (c) Matthew Peddie 2017
+License     :  BSD3
+Maintainer  :  Matthew Peddie <mpeddie@gmail.com>
+Stability   :  provisional
+Portability :  GHC
+
+This module provides a high-level, @hmatrix@-compatible interface to
+the <http://ab-initio.mit.edu/wiki/index.php/NLopt NLOPT> library by
+Steven G. Johnson.
+
+NOTE: This is an adaptation from https://hackage.haskell.org/package/hmatrix-nlopt-0.2.0.0
+that removes the dependency to hmatrix and support any Vector Storage.
+
+= Documentation
+
+Most non-numerical details are documented, but for specific
+information on what the optimization methods do, how constraints are
+handled, etc., you should consult:
+
+  * The <http://ab-initio.mit.edu/wiki/index.php/NLopt_Introduction NLOPT introduction>
+
+  * The <http://ab-initio.mit.edu/wiki/index.php/NLopt_Reference NLOPT reference manual>
+
+  * The <http://ab-initio.mit.edu/wiki/index.php/NLopt_Algorithms NLOPT algorithm manual>
+
+= Example program
+
+The following interactive session example uses the Nelder-Mead simplex
+algorithm, a derivative-free local optimizer, to minimize a trivial
+function with a minimum of 22.0 at @(0, 0)@.
+
+>>> import Numeric.LinearAlgebra ( dot, fromList )
+>>> let objf x = x `dot` x + 22                         -- define objective
+>>> let stop = ObjectiveRelativeTolerance 1e-6 :| []    -- define stopping criterion
+>>> let algorithm = NELDERMEAD objf [] Nothing          -- specify algorithm
+>>> let problem = LocalProblem 2 stop algorithm         -- specify problem
+>>> let x0 = fromList [5, 10]                           -- specify initial guess
+>>> minimizeLocal problem x0
+Right (Solution {solutionCost = 22.0, solutionParams = [0.0,0.0], solutionResult = FTOL_REACHED})
+
+-}
+
+module Numeric.Optimization.NLOPT (
+  -- * Specifying the objective function
+  Objective
+  , ObjectiveD
+  , Preconditioner
+  -- * Specifying the constraints
+  -- ** Bound constraints
+  , Bounds(..)
+  -- ** Nonlinear constraints
+  --
+  -- $nonlinearconstraints
+
+  -- *** Constraint functions
+  , ScalarConstraint
+  , ScalarConstraintD
+  , VectorConstraint
+  , VectorConstraintD
+  -- *** Constraint types
+  , Constraint(..)
+  , EqualityConstraint(..)
+  , InequalityConstraint(..)
+  -- *** Collections of constraints
+  , EqualityConstraints
+  , EqualityConstraintsD
+  , InequalityConstraints
+  , InequalityConstraintsD
+  -- * Stopping conditions
+  --
+  -- $nonempty
+  , StoppingCondition(..)
+  , NonEmpty(..)
+  -- * Additional configuration
+  , RandomSeed(..)
+  , Population(..)
+  , VectorStorage(..)
+  , InitialStep(..)
+  -- * Minimization problems
+  -- ** Local minimization
+  , LocalAlgorithm(..)
+  , LocalProblem(..)
+  , minimizeLocal
+  -- ** Global minimization
+  , GlobalAlgorithm(..)
+  , GlobalProblem(..)
+  , minimizeGlobal
+  -- ** Minimization by augmented Lagrangian
+  , AugLagAlgorithm(..)
+  , AugLagProblem(..)
+  , minimizeAugLag
+  -- ** Results
+  , Solution(..)
+  , N.Result(..)
+  ) where
+
+import qualified Numeric.Optimization.NLOPT.Bindings as N
+
+import Data.List.NonEmpty (NonEmpty(..))
+
+import qualified Data.Vector.Storable as V
+import Data.Vector.Storable ( Vector )
+
+import Control.Exception ( Exception )
+import qualified Control.Exception as Ex
+import Data.Typeable ( Typeable )
+import Data.Foldable ( traverse_ )
+
+import System.IO.Unsafe ( unsafePerformIO )
+
+-- each element i contains a row vec 
+type Matrix a = [Vector a]
+
+flatten :: V.Storable a => Matrix a -> Vector a 
+flatten = V.concat
+{-# INLINE flatten #-}
+
+{- Function wrapping for the immutable HMatrix interface -}
+wrapScalarFunction :: (Vector Double -> Double) -> N.ScalarFunction ()
+wrapScalarFunction f params _ _ = return $ f params
+
+wrapScalarFunctionD :: (Vector Double -> (Double, Vector Double))
+                    -> N.ScalarFunction ()
+wrapScalarFunctionD f params grad _ = do
+  case grad of
+    Nothing -> return ()
+    Just g  -> V.copy g usergrad
+  return result
+  where
+    (result, usergrad) = f params
+
+wrapVectorFunction :: (Vector Double -> Word -> Vector Double)
+                   -> Word -> N.VectorFunction ()
+wrapVectorFunction f n params vout _ _ = V.copy vout $ f params n
+
+wrapVectorFunctionD :: (Vector Double -> Word -> (Vector Double, Matrix Double))
+                    -> Word -> N.VectorFunction ()
+wrapVectorFunctionD f n params vout jac _ = do
+  V.copy vout result
+  case jac of
+    Nothing -> return ()
+    Just j -> V.copy j (flatten userjac)
+  where
+    (result, userjac) = f params n
+
+wrapPreconditionerFunction :: (Vector Double -> Vector Double -> Vector Double)
+                           -> N.PreconditionerFunction ()
+wrapPreconditionerFunction f params v vpre _ = V.copy vpre (f params v)
+
+{- Objective functions -}
+-- | An objective function that calculates the objective value at the
+-- given parameter vector.
+type Objective
+  = Vector Double  -- ^ Parameter vector
+ -> Double  -- ^ Objective function value
+
+-- | An objective function that calculates both the objective value
+-- and the gradient of the objective with respect to the input
+-- parameter vector, at the given parameter vector.
+type ObjectiveD
+  = Vector Double -- ^ Parameter vector
+ -> (Double, Vector Double)  -- ^ (Objective function value, gradient)
+
+-- | A preconditioner function, which computes @vpre = H(x) v@, where
+-- @H@ is the Hessian matrix: the positive semi-definite second
+-- derivative at the given parameter vector @x@, or an approximation
+-- thereof.
+type Preconditioner
+  = Vector Double  -- ^ Parameter vector @x@
+ -> Vector Double  -- ^ Vector @v@ to precondition at @x@
+ -> Vector Double  -- ^ Preconditioned vector @vpre@
+
+data ObjectiveFunction f
+ = MinimumObjective f
+ | PreconditionedMinimumObjective Preconditioner f
+
+applyObjective :: N.Opt -> ObjectiveFunction Objective -> IO N.Result
+applyObjective opt (MinimumObjective f) =
+  N.set_min_objective opt (wrapScalarFunction f) ()
+applyObjective opt (PreconditionedMinimumObjective p f) =
+  N.set_precond_min_objective opt (wrapScalarFunction f)
+  (wrapPreconditionerFunction p) ()
+
+applyObjectiveD :: N.Opt -> ObjectiveFunction ObjectiveD -> IO N.Result
+applyObjectiveD opt (MinimumObjective f) =
+  N.set_min_objective opt (wrapScalarFunctionD f) ()
+applyObjectiveD opt (PreconditionedMinimumObjective p f) =
+  N.set_precond_min_objective opt (wrapScalarFunctionD f)
+  (wrapPreconditionerFunction p) ()
+
+{- Constraint functions -}
+-- | A constraint function which returns @c(x)@ given the parameter
+-- vector @x@.  The constraint will enforce that @c(x) == 0@ (equality
+-- constraint) or @c(x) <= 0@ (inequality constraint).
+type ScalarConstraint
+  = Vector Double  -- ^ Parameter vector @x@
+ -> Double  -- ^ Constraint violation (deviation from 0)
+
+-- | A constraint function which returns @c(x)@ given the parameter
+-- vector @x@ along with the gradient of @c(x)@ with respect to @x@ at
+-- that point.  The constraint will enforce that @c(x) == 0@ (equality
+-- constraint) or @c(x) <= 0@ (inequality constraint).
+type ScalarConstraintD
+  = Vector Double  -- ^ Parameter vector
+ -> (Double, Vector Double)  -- ^ (Constraint violation, constraint gradient)
+
+-- | A constraint function which returns a vector @c(x)@ given the
+-- parameter vector @x@.  The constraint will enforce that @c(x) == 0@
+-- (equality constraint) or @c(x) <= 0@ (inequality constraint).
+type VectorConstraint
+  = Vector Double  -- ^ Parameter vector
+  -> Word           -- ^ Constraint Vectorize
+  -> Vector Double  -- ^ Constraint violation vector
+
+-- | A constraint function which returns @c(x)@ given the parameter
+-- vector @x@ along with the Jacobian (first derivative) matrix of
+-- @c(x)@ with respect to @x@ at that point.  The constraint will
+-- enforce that @c(x) == 0@ (equality constraint) or @c(x) <= 0@
+-- (inequality constraint).
+type VectorConstraintD
+  = Vector Double  -- ^ Parameter vector
+  -> Word  -- ^ Constraint Vectorize
+  -> (Vector Double, Matrix Double)  -- ^ (Constraint violation vector,
+                                     -- constraint Jacobian)
+
+-- $nonlinearconstraints
+--
+-- Note that most NLOPT algorithms do not support nonlinear
+-- constraints natively; if you need to enforce nonlinear constraints,
+-- you may want to use the 'AugLagAlgorithm' family of solvers, which
+-- can add nonlinear constraints to some algorithm that does not
+-- support them by a principled modification of the objective
+-- function.
+--
+-- == Example program
+--
+-- The following interactive session example enforces a scalar
+-- constraint on the problem given in the beginning of the module: the
+-- parameters must always sum to 1.  The minimizer finds a constrained
+-- minimum of 22.5 at @(0.5, 0.5)@.
+--
+-- >>> import Numeric.LinearAlgebra ( dot, fromList, toList )
+-- >>> let objf x = x `dot` x + 22
+-- >>> let stop = ObjectiveRelativeTolerance 1e-9 :| []
+-- >>>          -- define constraint function:
+-- >>> let constraintf x = sum (toList x) - 1.0
+-- >>>          -- define constraint object to pass to the algorithm:
+-- >>> let constraint = EqualityConstraint (Scalar constraintf) 1e-6
+-- >>> let algorithm = COBYLA objf [] [] [constraint] Nothing
+-- >>> let problem = LocalProblem 2 stop algorithm
+-- >>> let x0 = fromList [5, 10]
+-- >>> minimizeLocal problem x0
+-- Right (Solution {solutionCost = 22.500000000013028, solutionParams = [0.5000025521533521,0.49999744784664796], solutionResult = FTOL_REACHED})
+
+
+data Constraint s v
+  -- | A scalar constraint.
+  = Scalar s
+  -- | A vector constraint.
+  | Vector Word v
+  -- | A scalar constraint with an attached preconditioning function.
+  | Preconditioned Preconditioner s
+
+-- | An equality constraint, comprised of both the constraint function
+-- (or functions, if a preconditioner is used) along with the desired
+-- tolerance.
+data EqualityConstraint s v = EqualityConstraint
+  { eqConstraintFunctions :: Constraint s v
+  , eqConstraintTolerance :: Double
+  }
+
+-- | An inequality constraint, comprised of both the constraint
+-- function (or functions, if a preconditioner is used) along with the
+-- desired tolerance.
+data InequalityConstraint s v = InequalityConstraint
+  { ineqConstraintFunctions :: Constraint s v
+  , ineqConstraintTolerance :: Double
+  }
+
+-- | A collection of equality constraints that do not supply
+-- constraint derivatives.
+type EqualityConstraints =
+  [EqualityConstraint ScalarConstraint VectorConstraint]
+
+-- | A collection of inequality constraints that do not supply
+-- constraint derivatives.
+type InequalityConstraints =
+  [InequalityConstraint ScalarConstraint VectorConstraint]
+
+-- | A collection of equality constraints that supply constraint
+-- derivatives.
+type EqualityConstraintsD = [EqualityConstraint ScalarConstraintD VectorConstraintD]
+
+-- | A collection of inequality constraints that supply constraint
+-- derivatives.
+type InequalityConstraintsD = [InequalityConstraint ScalarConstraintD VectorConstraintD]
+
+class ApplyConstraint constraint where
+  applyConstraint :: N.Opt -> constraint -> IO N.Result
+
+instance ApplyConstraint (EqualityConstraint ScalarConstraint VectorConstraint) where
+  applyConstraint opt (EqualityConstraint ty tol) = case ty of
+    Scalar s           ->
+      N.add_equality_constraint opt (wrapScalarFunction s) () tol
+    Vector n v         ->
+      N.add_equality_mconstraint opt n (wrapVectorFunction v n) () tol
+    Preconditioned p s ->
+      N.add_precond_equality_constraint opt (wrapScalarFunction s)
+      (wrapPreconditionerFunction p) () tol
+
+instance ApplyConstraint (InequalityConstraint ScalarConstraint VectorConstraint) where
+  applyConstraint opt (InequalityConstraint ty tol) = case ty of
+    Scalar s           ->
+      N.add_inequality_constraint opt (wrapScalarFunction s) () tol
+    Vector n v         ->
+      N.add_inequality_mconstraint opt n (wrapVectorFunction v n) () tol
+    Preconditioned p s ->
+      N.add_precond_inequality_constraint opt (wrapScalarFunction s)
+      (wrapPreconditionerFunction p) () tol
+
+instance ApplyConstraint (EqualityConstraint ScalarConstraintD VectorConstraintD) where
+  applyConstraint opt (EqualityConstraint ty tol) = case ty of
+    Scalar s           ->
+      N.add_equality_constraint opt (wrapScalarFunctionD s) () tol
+    Vector n v         ->
+      N.add_equality_mconstraint opt n (wrapVectorFunctionD v n) () tol
+    Preconditioned p s ->
+      N.add_precond_equality_constraint opt (wrapScalarFunctionD s)
+      (wrapPreconditionerFunction p) () tol
+
+instance ApplyConstraint (InequalityConstraint ScalarConstraintD VectorConstraintD) where
+  applyConstraint opt (InequalityConstraint ty tol) = case ty of
+    Scalar s           ->
+      N.add_inequality_constraint opt (wrapScalarFunctionD s) () tol
+    Vector n v         ->
+      N.add_inequality_mconstraint opt n (wrapVectorFunctionD v n) () tol
+    Preconditioned p s ->
+      N.add_precond_inequality_constraint opt (wrapScalarFunctionD s)
+      (wrapPreconditionerFunction p) () tol
+
+{- Bounds -}
+
+-- | Bound constraints are specified by vectors of the same dimension
+-- as the parameter space.
+--
+-- == Example program
+--
+-- The following interactive session example enforces lower bounds on
+-- the example from the beginning of the module.  This prevents the
+-- optimizer from locating the true minimum at @(0, 0)@; a slightly
+-- higher constrained minimum at @(1, 1)@ is found.  Note that the
+-- optimizer returns 'N.XTOL_REACHED' rather than 'N.FTOL_REACHED',
+-- because the bound constraint is active at the final minimum.
+--
+-- >>> import Numeric.LinearAlgebra ( dot, fromList )
+-- >>> let objf x = x `dot` x + 22                           -- define objective
+-- >>> let stop = ObjectiveRelativeTolerance 1e-6 :| []      -- define stopping criterion
+-- >>> let lowerbound = LowerBounds $ fromList [1, 1]        -- specify bounds
+-- >>> let algorithm = NELDERMEAD objf [lowerbound] Nothing  -- specify algorithm
+-- >>> let problem = LocalProblem 2 stop algorithm           -- specify problem
+-- >>> let x0 = fromList [5, 10]                             -- specify initial guess
+-- >>> minimizeLocal problem x0
+-- Right (Solution {solutionCost = 24.0, solutionParams = [1.0,1.0], solutionResult = XTOL_REACHED})
+data Bounds
+  -- | Lower bound vector @v@ means we want @x >= v@.
+ = LowerBounds (Vector Double)
+ -- | Upper bound vector @u@ means we want @x <= u@.
+ | UpperBounds (Vector Double)
+ deriving (Eq, Show, Read)
+
+applyBounds :: N.Opt -> Bounds -> IO N.Result
+applyBounds opt (LowerBounds lbvec) = N.set_lower_bounds opt lbvec
+applyBounds opt (UpperBounds ubvec) = N.set_upper_bounds opt ubvec
+
+{- Stopping conditions -}
+
+-- | A 'StoppingCondition' tells NLOPT when to stop working on a
+-- minimization problem.  When multiple 'StoppingCondition's are
+-- provided, the problem will stop when any one condition is met.
+data StoppingCondition
+  -- | Stop minimizing when an objective value @J@ less than or equal
+  -- to the provided value is found.
+  = MinimumValue Double
+  -- | Stop minimizing when an optimization step changes the objective
+  -- value @J@ by less than the provided tolerance multiplied by @|J|@.
+  | ObjectiveRelativeTolerance Double
+  -- | Stop minimizing when an optimization step changes the objective
+  -- value by less than the provided tolerance.
+  | ObjectiveAbsoluteTolerance Double
+  -- | Stop when an optimization step changes /every element/ of the
+  -- parameter vector @x@ by less than @x@ scaled by the provided
+  -- tolerance.
+  | ParameterRelativeTolerance Double
+  -- | Stop when an optimization step changes /every element/ of the
+  -- parameter vector @x@ by less than the corresponding element in
+  -- the provided vector of tolerances values.
+  | ParameterAbsoluteTolerance (Vector Double)
+  -- | Stop when the number of evaluations of the objective function
+  -- exceeds the provided count.
+  | MaximumEvaluations Word
+  -- | Stop when the optimization time exceeds the provided time (in
+  -- seconds).  This is not a precise limit.
+  | MaximumTime Double
+  deriving (Eq, Show, Read)
+
+-- $nonempty
+--
+-- The 'NonEmpty' data type from 'Data.List.NonEmpty' is re-exported
+-- here, because it is used to ensure that you always specify at least
+-- one stopping condition.
+
+applyStoppingCondition :: N.Opt -> StoppingCondition -> IO N.Result
+applyStoppingCondition opt (MinimumValue x) = N.set_stopval opt x
+applyStoppingCondition opt (ObjectiveRelativeTolerance x) = N.set_ftol_rel opt x
+applyStoppingCondition opt (ObjectiveAbsoluteTolerance x) = N.set_ftol_abs opt x
+applyStoppingCondition opt (ParameterRelativeTolerance x) = N.set_xtol_rel opt x
+applyStoppingCondition opt (ParameterAbsoluteTolerance v) = N.set_xtol_abs opt v
+applyStoppingCondition opt (MaximumEvaluations n) = N.set_maxeval opt n
+applyStoppingCondition opt (MaximumTime deltat) = N.set_maxtime opt deltat
+
+{- Random seed control -}
+
+-- | This specifies how to initialize the random number generator for
+-- stochastic algorithms.
+data RandomSeed
+  -- | Seed the RNG with the provided value.
+  = SeedValue Word
+  -- | Seed the RNG using the system clock.
+  | SeedFromTime
+  -- | Don't perform any explicit initialization of the RNG.
+  | Don'tSeed
+  deriving (Eq, Show, Read)
+
+applyRandomSeed :: RandomSeed -> IO ()
+applyRandomSeed Don'tSeed = return ()
+applyRandomSeed (SeedValue n) = N.srand n
+applyRandomSeed SeedFromTime = N.srand_time
+
+{- Random stuff -}
+
+-- | This specifies the population size for algorithms that use a pool
+-- of solutions.
+newtype Population = Population Word deriving (Eq, Show, Read)
+
+applyPopulation :: N.Opt -> Population -> IO N.Result
+applyPopulation opt (Population n) = N.set_population opt n
+
+-- | This specifies the memory size to be used by algorithms like
+-- 'LBFGS' which store approximate Hessian or Jacobian matrices.
+newtype VectorStorage = VectorStorage Word deriving (Eq, Show, Read)
+
+applyVectorStorage :: N.Opt -> VectorStorage -> IO N.Result
+applyVectorStorage opt (VectorStorage n) = N.set_vector_storage opt n
+
+-- | This vector with the same dimension as the parameter vector @x@
+-- specifies the initial step for the optimizer to take.  (This
+-- applies to local gradient-free algorithms, which cannot use
+-- gradients to estimate how big a step to take.)
+newtype InitialStep = InitialStep (Vector Double) deriving (Eq, Show, Read)
+
+applyInitialStep :: N.Opt -> InitialStep -> IO N.Result
+applyInitialStep opt (InitialStep v) = N.set_initial_step opt v
+
+{- Algorithms -}
+
+data GlobalProblem = GlobalProblem
+  { lowerBounds :: Vector Double        -- ^ Lower bounds for @x@
+  , upperBounds :: Vector Double        -- ^ Upper bounds for @x@
+  , gstop :: NonEmpty StoppingCondition -- ^ At least one stopping
+                                        -- condition
+  , galgorithm :: GlobalAlgorithm       -- ^ Algorithm specification
+  }
+
+-- | These are the global minimization algorithms provided by NLOPT.  Please see
+-- <http://ab-initio.mit.edu/wiki/index.php/NLopt_Algorithms the NLOPT algorithm manual>
+-- for more details on how the methods work and how they relate to one another.
+--
+-- Optional parameters are wrapped in a 'Maybe'; for example, if you
+-- see 'Maybe' 'Population', you can simply specify 'Nothing' to use
+-- the default behavior.
+data GlobalAlgorithm
+    -- | DIviding RECTangles
+  = DIRECT Objective
+    -- | DIviding RECTangles, locally-biased variant
+  | DIRECT_L Objective
+    -- | DIviding RECTangles, "slightly randomized"
+  | DIRECT_L_RAND Objective RandomSeed
+    -- | DIviding RECTangles, unscaled version
+  | DIRECT_NOSCAL Objective
+    -- | DIviding RECTangles, locally-biased and unscaled
+  | DIRECT_L_NOSCAL Objective
+    -- | DIviding RECTangles, locally-biased, unscaled and "slightly
+    -- randomized"
+  | DIRECT_L_RAND_NOSCAL Objective RandomSeed
+    -- | DIviding RECTangles, original FORTRAN implementation
+  | ORIG_DIRECT Objective InequalityConstraints
+    -- | DIviding RECTangles, locally-biased, original FORTRAN
+    -- implementation
+  | ORIG_DIRECT_L Objective InequalityConstraints
+    -- | Stochastic Global Optimization.
+    -- __This algorithm is only available if you have linked with @libnlopt_cxx@.__
+  | STOGO ObjectiveD
+    -- | Stochastic Global Optimization, randomized variant.
+    -- __This algorithm is only available if you have linked with @libnlopt_cxx@.__
+  | STOGO_RAND ObjectiveD RandomSeed
+    -- | Controlled Random Search with Local Mutation
+  | CRS2_LM Objective RandomSeed (Maybe Population)
+    -- | Improved Stochastic Ranking Evolution Strategy
+  | ISRES Objective InequalityConstraints EqualityConstraints RandomSeed (Maybe Population)
+    -- | Evolutionary Algorithm
+  | ESCH Objective
+    -- | Original Multi-Level Single-Linkage
+  | MLSL Objective LocalProblem (Maybe Population)
+    -- | Multi-Level Single-Linkage with Sobol Low-Discrepancy
+    -- Sequence for starting points
+  | MLSL_LDS Objective LocalProblem (Maybe Population)
+
+algorithmEnumOfGlobal :: GlobalAlgorithm -> N.Algorithm
+algorithmEnumOfGlobal (DIRECT _)                 = N.GN_DIRECT
+algorithmEnumOfGlobal (DIRECT_L _)               = N.GN_DIRECT_L
+algorithmEnumOfGlobal (DIRECT_L_RAND _ _)        = N.GN_DIRECT_L_RAND
+algorithmEnumOfGlobal (DIRECT_NOSCAL _)          = N.GN_DIRECT_NOSCAL
+algorithmEnumOfGlobal (DIRECT_L_NOSCAL _)        = N.GN_DIRECT_L_NOSCAL
+algorithmEnumOfGlobal (DIRECT_L_RAND_NOSCAL _ _) = N.GN_DIRECT_L_RAND_NOSCAL
+algorithmEnumOfGlobal (ORIG_DIRECT _ _)          = N.GN_ORIG_DIRECT
+algorithmEnumOfGlobal (ORIG_DIRECT_L _ _)        = N.GN_ORIG_DIRECT_L
+algorithmEnumOfGlobal (STOGO _)                  = N.GD_STOGO
+algorithmEnumOfGlobal (STOGO_RAND _ _)           = N.GD_STOGO_RAND
+algorithmEnumOfGlobal (CRS2_LM _ _ _)            = N.GN_CRS2_LM
+algorithmEnumOfGlobal (ISRES _ _ _ _ _)          = N.GN_ISRES
+algorithmEnumOfGlobal (ESCH _)                   = N.GN_ESCH
+algorithmEnumOfGlobal (MLSL _ _ _)               = N.G_MLSL
+algorithmEnumOfGlobal (MLSL_LDS _ _ _)           = N.G_MLSL_LDS
+
+applyGlobalObjective :: N.Opt -> GlobalAlgorithm -> IO ()
+applyGlobalObjective opt alg = go alg
+  where
+    obj = tryTo . applyObjective opt . MinimumObjective
+    objD = tryTo . applyObjectiveD opt . MinimumObjective
+
+    go (DIRECT o)                 = obj o
+    go (DIRECT_L o)               = obj o
+    go (DIRECT_NOSCAL o)          = obj o
+    go (DIRECT_L_NOSCAL o)        = obj o
+    go (ESCH o)                   = obj o
+    go (STOGO o)                  = objD o
+    go (DIRECT_L_RAND o _)        = obj o
+    go (DIRECT_L_RAND_NOSCAL o _) = obj o
+    go (ORIG_DIRECT o _)          = obj o
+    go (ORIG_DIRECT_L o _)        = obj o
+    go (STOGO_RAND o _)           = objD o
+    go (CRS2_LM o _ _)            = obj o
+    go (ISRES o _ _ _ _)          = obj o
+    go (MLSL o _ _)               = obj o
+    go (MLSL_LDS o _ _)           = obj o
+
+applyGlobalAlgorithm :: N.Opt -> GlobalAlgorithm -> IO ()
+applyGlobalAlgorithm opt alg = do
+  applyGlobalObjective opt alg
+  go alg
+  where
+    seed = applyRandomSeed
+    pop = maybe (return ()) (tryTo . applyPopulation opt)
+    ic = traverse_ (tryTo . applyConstraint opt)
+    ec = traverse_ (tryTo . applyConstraint opt)
+
+    local lp = setupLocalProblem lp >>= N.set_local_optimizer opt
+
+    go (DIRECT_L_RAND _ s)        = seed s
+    go (DIRECT_L_RAND_NOSCAL _ s) = seed s
+    go (ORIG_DIRECT _ ineq)       = ic ineq
+    go (ORIG_DIRECT_L _ ineq)     = ic ineq
+    go (STOGO_RAND _ s)           = seed s
+    go (CRS2_LM _ s p)            = seed s *> pop p
+    go (ISRES _ ineq eq s p)      = ic ineq *> ec eq *> seed s *> pop p
+    go (MLSL _ lp p)              = local lp *> pop p
+    go (MLSL_LDS _ lp p)          = local lp *> pop p
+    go _                          = return ()
+
+tryTo :: IO N.Result -> IO ()
+tryTo act = do
+  result <- act
+  if (N.isSuccess result)
+    then return ()
+    else Ex.throw $ NloptException result
+
+data NloptException = NloptException N.Result deriving (Show, Typeable)
+instance Exception NloptException
+
+-- | Solve the specified global optimization problem.
+--
+-- = Example program
+--
+-- The following interactive session example uses the 'ISRES'
+-- algorithm, a stochastic, derivative-free global optimizer, to
+-- minimize a trivial function with a minimum of 22.0 at @(0, 0)@.
+-- The search is conducted within a box from -10 to 10 in each
+-- dimension.
+--
+-- >>> import Numeric.LinearAlgebra ( dot, fromList )
+-- >>> let objf x = x `dot` x + 22                              -- define objective
+-- >>> let stop = ObjectiveRelativeTolerance 1e-12 :| []        -- define stopping criterion
+-- >>> let algorithm = ISRES objf [] [] (SeedValue 22) Nothing  -- specify algorithm
+-- >>> let lowerbounds = fromList [-10, -10]                    -- specify bounds
+-- >>> let upperbounds = fromList [10, 10]                      -- specify bounds
+-- >>> let problem = GlobalProblem lowerbounds upperbounds stop algorithm
+-- >>> let x0 = fromList [5, 8]                                 -- specify initial guess
+-- >>> minimizeGlobal problem x0
+-- Right (Solution {solutionCost = 22.000000000002807, solutionParams = [-1.660591102367038e-6,2.2407062393213684e-7], solutionResult = FTOL_REACHED})
+minimizeGlobal :: GlobalProblem  -- ^ Problem specification
+               -> Vector Double  -- ^ Initial parameter guess
+               -> Either N.Result Solution  -- ^ Optimization results
+minimizeGlobal prob x0 =
+  unsafePerformIO $ (Right <$> minimizeGlobal' prob x0) `Ex.catch` handler
+  where
+    handler :: NloptException -> IO (Either N.Result a)
+    handler (NloptException retcode) = return $ Left retcode
+
+applyGlobalProblem :: N.Opt -> GlobalProblem -> IO ()
+applyGlobalProblem opt (GlobalProblem lb ub stop alg) = do
+  tryTo $ applyBounds opt (LowerBounds lb)
+  tryTo $ applyBounds opt (UpperBounds ub)
+  traverse_ (tryTo . applyStoppingCondition opt) stop
+  applyGlobalAlgorithm opt alg
+
+newOpt :: N.Algorithm -> Word -> IO N.Opt
+newOpt alg sz = do
+  opt' <- N.create alg sz
+  case opt' of
+    Nothing -> Ex.throw $ NloptException N.FAILURE
+    Just opt -> return opt
+
+setupGlobalProblem :: GlobalProblem -> IO N.Opt
+setupGlobalProblem gp@(GlobalProblem _ _ _ alg) = do
+  opt <- newOpt (algorithmEnumOfGlobal alg) (problemSize gp)
+  applyGlobalProblem opt gp
+  return opt
+
+solveProblem :: N.Opt -> Vector Double -> IO Solution
+solveProblem opt x0 = do
+  (N.Output outret outcost outx nevals) <- N.optimize opt x0
+  if (N.isSuccess outret)
+    then return $ Solution outcost outx outret nevals
+    else Ex.throw $ NloptException outret
+
+minimizeGlobal' :: GlobalProblem -> Vector Double -> IO Solution
+minimizeGlobal' gp x0 = do
+  opt <- setupGlobalProblem gp
+  solveProblem opt x0
+
+data LocalProblem = LocalProblem
+  { lsize :: Word                       -- ^ The dimension of the
+                                        -- parameter vector.
+  , lstop :: NonEmpty StoppingCondition -- ^ At least one stopping
+                                        -- condition
+  , lalgorithm :: LocalAlgorithm        -- ^ Algorithm specification
+  }
+
+-- | These are the local minimization algorithms provided by NLOPT.  Please see
+-- <http://ab-initio.mit.edu/wiki/index.php/NLopt_Algorithms the NLOPT algorithm manual>
+-- for more details on how the methods work and how they relate to one
+-- another.  Note that some local methods require you provide
+-- derivatives (gradients or Jacobians) for your objective function
+-- and constraint functions.
+--
+-- Optional parameters are wrapped in a 'Maybe'; for example, if you
+-- see 'Maybe' 'VectorStorage', you can simply specify 'Nothing' to
+-- use the default behavior.
+data LocalAlgorithm
+    -- | Limited-memory BFGS
+  = LBFGS_NOCEDAL ObjectiveD (Maybe VectorStorage)
+    -- | Limited-memory BFGS
+  | LBFGS ObjectiveD (Maybe VectorStorage)
+    -- | Shifted limited-memory variable-metric, rank-2
+  | VAR2 ObjectiveD (Maybe VectorStorage)
+    -- | Shifted limited-memory variable-metric, rank-1
+  | VAR1 ObjectiveD (Maybe VectorStorage)
+    -- | Truncated Newton's method
+  | TNEWTON ObjectiveD (Maybe VectorStorage)
+    -- | Truncated Newton's method with automatic restarting
+  | TNEWTON_RESTART ObjectiveD (Maybe VectorStorage)
+    -- | Preconditioned truncated Newton's method
+  | TNEWTON_PRECOND ObjectiveD (Maybe VectorStorage)
+    -- | Preconditioned truncated Newton's method with automatic
+    -- restarting
+  | TNEWTON_PRECOND_RESTART ObjectiveD (Maybe VectorStorage)
+    -- | Method of moving averages
+  | MMA ObjectiveD InequalityConstraintsD
+    -- | Sequential Least-Squares Quadratic Programming
+  | SLSQP ObjectiveD [Bounds] InequalityConstraintsD EqualityConstraintsD
+    -- | Conservative Convex Separable Approximation
+  | CCSAQ ObjectiveD Preconditioner
+    -- | PRincipal AXIS gradient-free local optimization
+  | PRAXIS Objective [Bounds] (Maybe InitialStep)
+    -- | Constrained Optimization BY Linear Approximations
+  | COBYLA Objective [Bounds] InequalityConstraints EqualityConstraints
+    (Maybe InitialStep)
+    -- | Powell's NEWUOA algorithm
+  | NEWUOA Objective (Maybe InitialStep)
+    -- | Powell's NEWUOA algorithm with bounds by SGJ
+  | NEWUOA_BOUND Objective [Bounds] (Maybe InitialStep)
+    -- | Nelder-Mead Simplex gradient-free method
+  | NELDERMEAD Objective [Bounds] (Maybe InitialStep)
+    -- | NLOPT implementation of Rowan's Subplex algorithm
+  | SBPLX Objective [Bounds] (Maybe InitialStep)
+    -- | Bounded Optimization BY Quadratic Approximations
+  | BOBYQA Objective [Bounds] (Maybe InitialStep)
+
+algorithmEnumOfLocal :: LocalAlgorithm -> N.Algorithm
+algorithmEnumOfLocal (LBFGS_NOCEDAL _ _)           = N.LD_LBFGS_NOCEDAL
+algorithmEnumOfLocal (LBFGS _ _)                   = N.LD_LBFGS
+algorithmEnumOfLocal (VAR2 _ _)                    = N.LD_VAR2
+algorithmEnumOfLocal (VAR1 _ _)                    = N.LD_VAR1
+algorithmEnumOfLocal (TNEWTON _ _)                 = N.LD_TNEWTON
+algorithmEnumOfLocal (TNEWTON_RESTART _ _)         = N.LD_TNEWTON_RESTART
+algorithmEnumOfLocal (TNEWTON_PRECOND _ _)         = N.LD_TNEWTON_PRECOND
+algorithmEnumOfLocal (TNEWTON_PRECOND_RESTART _ _) = N.LD_TNEWTON_PRECOND_RESTART
+algorithmEnumOfLocal (MMA _ _)                     = N.LD_MMA
+algorithmEnumOfLocal (SLSQP _ _ _ _)               = N.LD_SLSQP
+algorithmEnumOfLocal (CCSAQ _ _)                   = N.LD_CCSAQ
+algorithmEnumOfLocal (PRAXIS _ _ _)                = N.LN_PRAXIS
+algorithmEnumOfLocal (COBYLA _ _ _ _ _)            = N.LN_COBYLA
+algorithmEnumOfLocal (NEWUOA _ _)                  = N.LN_NEWUOA
+algorithmEnumOfLocal (NEWUOA_BOUND _ _ _)          = N.LN_NEWUOA
+algorithmEnumOfLocal (NELDERMEAD _ _ _)            = N.LN_NELDERMEAD
+algorithmEnumOfLocal (SBPLX _ _ _)                 = N.LN_SBPLX
+algorithmEnumOfLocal (BOBYQA _ _ _)                = N.LN_BOBYQA
+
+applyLocalObjective :: N.Opt -> LocalAlgorithm -> IO ()
+applyLocalObjective opt alg = go alg
+  where
+    obj = tryTo . applyObjective opt . MinimumObjective
+    objD = tryTo . applyObjectiveD opt . MinimumObjective
+    precond p = tryTo . applyObjectiveD opt . PreconditionedMinimumObjective p
+
+    go (LBFGS_NOCEDAL o _)           = objD o
+    go (LBFGS o _)                   = objD o
+    go (VAR2 o _)                    = objD o
+    go (VAR1 o _)                    = objD o
+    go (TNEWTON o _)                 = objD o
+    go (TNEWTON_RESTART o _)         = objD o
+    go (TNEWTON_PRECOND o _)         = objD o
+    go (TNEWTON_PRECOND_RESTART o _) = objD o
+    go (MMA o _)                     = objD o
+    go (SLSQP o _ _ _)               = objD o
+    go (CCSAQ o prec)                = precond prec o
+    go (PRAXIS o _ _)                = obj o
+    go (COBYLA o _ _ _ _)            = obj o
+    go (NEWUOA o _)                  = obj o
+    go (NEWUOA_BOUND o _ _)          = obj o
+    go (NELDERMEAD o _ _)            = obj o
+    go (SBPLX o _ _)                 = obj o
+    go (BOBYQA o _ _)                = obj o
+
+applyLocalAlgorithm :: N.Opt -> LocalAlgorithm -> IO ()
+applyLocalAlgorithm opt alg = do
+  applyLocalObjective opt alg
+  go alg
+  where
+    ic = traverse_ (tryTo . applyConstraint opt)
+    icd = traverse_ (tryTo . applyConstraint opt)
+    ec = traverse_ (tryTo . applyConstraint opt)
+    ecd = traverse_ (tryTo . applyConstraint opt)
+    store = maybe (return ()) (tryTo . applyVectorStorage opt)
+    bound = traverse_ (tryTo . applyBounds opt)
+    step0 = maybe (return ()) (tryTo . applyInitialStep opt)
+
+    go (LBFGS_NOCEDAL _ vs)           = store vs
+    go (LBFGS _ vs)                   = store vs
+    go (VAR2 _ vs)                    = store vs
+    go (VAR1 _ vs)                    = store vs
+    go (TNEWTON _ vs)                 = store vs
+    go (TNEWTON_RESTART _ vs)         = store vs
+    go (TNEWTON_PRECOND _ vs)         = store vs
+    go (TNEWTON_PRECOND_RESTART _ vs) = store vs
+    go (MMA _ ineqd)                  = icd ineqd
+    go (SLSQP _ b ineqd eqd)          =
+      bound b *> icd ineqd *> ecd eqd
+    go (CCSAQ _ _   )                 = return ()
+    go (PRAXIS _ b s)                 = bound b *> step0 s
+    go (COBYLA _ b ineq eq s)         =
+      bound b *> ic ineq *> ec eq *> step0 s
+    go (NEWUOA _ s)                   = step0 s
+    go (NEWUOA_BOUND _ b s)           = bound b *> step0 s
+    go (NELDERMEAD _ b s)             = bound b *> step0 s
+    go (SBPLX _ b s)                  = bound b *> step0 s
+    go (BOBYQA _ b s)                 = bound b *> step0 s
+
+applyLocalProblem :: N.Opt -> LocalProblem -> IO ()
+applyLocalProblem opt (LocalProblem _ stop alg) = do
+  traverse_ (tryTo . applyStoppingCondition opt) stop
+  applyLocalAlgorithm opt alg
+
+setupLocalProblem :: LocalProblem -> IO N.Opt
+setupLocalProblem lp@(LocalProblem sz _ alg) = do
+  opt <- newOpt (algorithmEnumOfLocal alg) sz
+  applyLocalProblem opt lp
+  return opt
+
+minimizeLocal' :: LocalProblem -> Vector Double -> IO Solution
+minimizeLocal' lp x0 = do
+  opt <- setupLocalProblem lp
+  solveProblem opt x0
+
+-- |
+-- == Example program
+--
+-- The following interactive session example enforces the same scalar
+-- constraint as the nonlinear constraint example, but this time it
+-- uses the SLSQP solver to find the minimum.
+--
+-- >>> import Numeric.LinearAlgebra ( dot, fromList, toList, scale )
+-- >>> let objf x = (x `dot` x + 22, 2 `scale` x)
+-- >>> let stop = ObjectiveRelativeTolerance 1e-9 :| []
+-- >>> let constraintf x = (sum (toList x) - 1.0, fromList [1, 1])
+-- >>> let constraint = EqualityConstraint (Scalar constraintf) 1e-6
+-- >>> let algorithm = SLSQP objf [] [] [constraint]
+-- >>> let problem = LocalProblem 2 stop algorithm
+-- >>> let x0 = fromList [5, 10]
+-- >>> minimizeLocal problem x0
+-- Right (Solution {solutionCost = 22.5, solutionParams = [0.4999999999999998,0.5000000000000002], solutionResult = FTOL_REACHED})
+minimizeLocal :: LocalProblem -> Vector Double -> Either N.Result Solution
+minimizeLocal prob x0 =
+  unsafePerformIO $ (Right <$> minimizeLocal' prob x0) `Ex.catch` handler
+  where
+    handler :: NloptException -> IO (Either N.Result a)
+    handler (NloptException retcode) = return $ Left retcode
+
+class ProblemSize c where
+  problemSize :: c -> Word
+
+instance ProblemSize LocalProblem where
+  problemSize = lsize
+
+instance ProblemSize GlobalProblem where
+  problemSize = fromIntegral . V.length . lowerBounds
+
+instance ProblemSize AugLagProblem where
+  problemSize (AugLagProblem _ _ alg) = case alg of
+    AUGLAG_LOCAL lp _ _  -> problemSize lp
+    AUGLAG_EQ_LOCAL lp   -> problemSize lp
+    AUGLAG_GLOBAL gp _ _ -> problemSize gp
+    AUGLAG_EQ_GLOBAL gp  -> problemSize gp
+
+
+-- | __IMPORTANT NOTE__
+--
+-- For augmented lagrangian problems, you, the user, are responsible
+-- for providing the appropriate type of constraint.  If the
+-- subsidiary problem requires an `ObjectiveD`, then you should
+-- provide constraint functions with derivatives.  If the subsidiary
+-- problem requires an `Objective`, you should provide constraint
+-- functions without derivatives.  If you don't do this, you may get a
+-- runtime error.
+data AugLagProblem = AugLagProblem
+  { alEquality :: EqualityConstraints   -- ^ Possibly empty set of
+                                        -- equality constraints
+  , alEqualityD :: EqualityConstraintsD -- ^ Possibly empty set of
+                                        -- equality constraints with
+                                        -- derivatives
+  , alalgorithm :: AugLagAlgorithm      -- ^ Algorithm specification.
+  }
+
+-- | The Augmented Lagrangian solvers allow you to enforce nonlinear
+-- constraints while using local or global algorithms that don't
+-- natively support them.  The subsidiary problem is used to do the
+-- minimization, but the @AUGLAG@ methods modify the objective to
+-- enforce the constraints.  Please see
+-- <http://ab-initio.mit.edu/wiki/index.php/NLopt_Algorithms the NLOPT algorithm manual>
+-- for more details on how the methods work and how they relate to one another.
+--
+-- See the documentation for 'AugLagProblem' for an important note
+-- about the constraint functions.
+data AugLagAlgorithm
+    -- | AUGmented LAGrangian with a local subsidiary method
+  = AUGLAG_LOCAL LocalProblem InequalityConstraints InequalityConstraintsD
+    -- | AUGmented LAGrangian with a local subsidiary method and with
+    -- penalty functions only for equality constraints
+  | AUGLAG_EQ_LOCAL LocalProblem
+    -- | AUGmented LAGrangian with a global subsidiary method
+  | AUGLAG_GLOBAL GlobalProblem InequalityConstraints InequalityConstraintsD
+    -- | AUGmented LAGrangian with a global subsidiary method and with
+    -- penalty functions only for equality constraints.
+  | AUGLAG_EQ_GLOBAL GlobalProblem
+
+algorithmEnumOfAugLag :: AugLagAlgorithm -> N.Algorithm
+algorithmEnumOfAugLag (AUGLAG_LOCAL _ _ _) = N.AUGLAG
+algorithmEnumOfAugLag (AUGLAG_EQ_LOCAL _) = N.AUGLAG_EQ
+algorithmEnumOfAugLag (AUGLAG_GLOBAL _ _ _) = N.AUGLAG
+algorithmEnumOfAugLag (AUGLAG_EQ_GLOBAL _) = N.AUGLAG_EQ
+
+-- | This structure is returned in the event of a successful
+-- optimization.
+data Solution = Solution
+  { solutionCost :: Double          -- ^ The objective function value
+                                    -- at the minimum
+  , solutionParams :: Vector Double -- ^ The parameter vector which
+                                    -- minimizes the objective
+  , solutionResult :: N.Result      -- ^ Why the optimizer stopped
+
+  , nEvals :: Int                   -- ^ Number of evaluations until stop
+  } deriving (Eq, Show, Read)
+
+applyAugLagAlgorithm :: N.Opt -> AugLagAlgorithm -> IO ()
+applyAugLagAlgorithm opt alg = go alg
+  where
+    ic = traverse_ (tryTo . applyConstraint opt)
+    icd = traverse_ (tryTo . applyConstraint opt)
+    -- AUGLAG won't work at all if you don't pass it the same
+    -- objective as the subproblem -- here we pull out the subproblem
+    -- objectives from the algorithm spec and set the same objective
+    -- function so the user can't mess it up.
+    local lp = tryTo $ do
+      localopt <- setupLocalProblem lp
+      applyLocalObjective opt (lalgorithm lp)
+      N.set_local_optimizer opt localopt
+    global gp = do
+      tryTo $ setupGlobalProblem gp >>= N.set_local_optimizer opt
+      applyGlobalObjective opt (galgorithm gp)
+
+    go (AUGLAG_LOCAL lp ineq ineqd)  = local lp *> ic ineq *> icd ineqd
+    go (AUGLAG_EQ_LOCAL lp)          = local lp
+    go (AUGLAG_GLOBAL gp ineq ineqd) = global gp *> ic ineq *> icd ineqd
+    go (AUGLAG_EQ_GLOBAL gp)         = global gp
+
+applyAugLagProblem :: N.Opt -> AugLagProblem -> IO ()
+applyAugLagProblem opt (AugLagProblem eq eqd alg) = do
+  traverse_ (tryTo . applyConstraint opt) eq
+  traverse_ (tryTo . applyConstraint opt) eqd
+  applyAugLagAlgorithm opt alg
+
+minimizeAugLag' :: AugLagProblem -> Vector Double -> IO Solution
+minimizeAugLag' ap@(AugLagProblem _ _ alg) x0 = do
+  opt <- newOpt (algorithmEnumOfAugLag alg) (problemSize ap)
+  applyAugLagProblem opt ap
+  solveProblem opt x0
+
+-- |
+-- == Example program
+--
+-- The following interactive session example enforces the same scalar
+-- constraint as the nonlinear constraint example, but this time it
+-- uses the augmented Lagrangian method to enforce the constraint and
+-- the 'SBPLX' algorithm, which does not support nonlinear constraints
+-- itself, to perform the minimization.  As before, the parameters
+-- must always sum to 1, and the minimizer finds the same constrained
+-- minimum of 22.5 at @(0.5, 0.5)@.
+--
+-- >>> import Numeric.LinearAlgebra ( dot, fromList, toList )
+-- >>> let objf x = x `dot` x + 22
+-- >>> let stop = ObjectiveRelativeTolerance 1e-9 :| []
+-- >>> let algorithm = SBPLX objf [] Nothing
+-- >>> let subproblem = LocalProblem 2 stop algorithm
+-- >>> let x0 = fromList [5, 10]
+-- >>> minimizeLocal subproblem x0
+-- Right (Solution {solutionCost = 22.0, solutionParams = [0.0,0.0], solutionResult = FTOL_REACHED})
+-- >>>          -- define constraint function:
+-- >>> let constraintf x = sum (toList x) - 1.0
+-- >>>          -- define constraint object to pass to the algorithm:
+-- >>> let constraint = EqualityConstraint (Scalar constraintf) 1e-6
+-- >>> let problem = AugLagProblem [constraint] [] (AUGLAG_EQ_LOCAL subproblem)
+-- >>> minimizeAugLag problem x0
+-- Right (Solution {solutionCost = 22.500000015505844, solutionParams = [0.5000880506776678,0.4999119493223323], solutionResult = FTOL_REACHED})
+
+minimizeAugLag :: AugLagProblem -> Vector Double -> Either N.Result Solution
+minimizeAugLag prob x0 =
+  unsafePerformIO $ (Right <$> minimizeAugLag' prob x0) `Ex.catch` handler
+  where
+    handler :: NloptException -> IO (Either N.Result a)
+    handler (NloptException retcode) = return $ Left retcode
diff --git a/src/Numeric/Optimization/NLOPT/Bindings.hs b/src/Numeric/Optimization/NLOPT/Bindings.hs
new file mode 100644
--- /dev/null
+++ b/src/Numeric/Optimization/NLOPT/Bindings.hs
@@ -0,0 +1,1075 @@
+{-# OPTIONS_GHC -Wall #-}
+{-# LANGUAGE ForeignFunctionInterface #-}
+{-# LANGUAGE NoMonomorphismRestriction #-}
+
+{- |
+Module      :  Numeric.Optimization.NLOPT.Bindings
+Copyright   :  (c) Matthew Peddie 2017
+License     :  BSD3
+Maintainer  :  Matthew Peddie <mpeddie@gmail.com>
+Stability   :  provisional
+Portability :  GHC
+
+Low-level interface to the NLOPT library.  Please see
+<http://ab-initio.mit.edu/wiki/index.php/NLopt_Reference the NLOPT reference manual>
+for detailed information; the Haskell functions in this module closely
+follow the interface to the C library in @nlopt.h@.
+
+Differences between this module and the C interface are documented
+here; functions with identical interfaces are not.  In general:
+
+  ['Opt'] corresponds to an @nlopt_opt@ object
+
+  ['Result'] corresponds to @nlopt_result@
+
+  ['V.Vector' 'Double'] corresponds to a @const double *@ input or a
+  @double *@ output
+
+  ['ScalarFunction'] corresponds to @nlopt_func@
+
+  ['VectorFunction'] corresponds to @nlopt_mfunc@
+
+  ['PreconditionerFunction'] corresponds to @nlopt_precond@
+
+User data that is handled by @void *@ in the C bindings can be any
+Haskell value.
+
+-}
+
+module Numeric.Optimization.NLOPT.Bindings (
+  -- * C enums
+  Algorithm(..)
+  , algorithm_name
+  , Result(..)
+  , isSuccess
+  -- * Optimizer object
+  , Opt
+  , create
+  , destroy
+  , copy
+  -- * Random number generator seeding
+  , srand
+  , srand_time
+  -- * Metadata
+  , Version(..)
+  , version
+  , get_algorithm
+  , get_dimension
+  -- * Callbacks
+  , ScalarFunction
+  , VectorFunction
+  , PreconditionerFunction
+  -- * Running the optimizer
+  , Output(..)
+  , optimize
+  -- * Objective function configuration
+  , set_min_objective
+  , set_max_objective
+  , set_precond_min_objective
+  , set_precond_max_objective
+  -- * Bound configuration
+  , set_lower_bounds
+  , set_lower_bounds1
+  , get_lower_bounds
+  , set_upper_bounds
+  , set_upper_bounds1
+  , get_upper_bounds
+  -- * Constraint configuration
+  , remove_inequality_constraints
+  , add_inequality_constraint
+  , add_precond_inequality_constraint
+  , add_inequality_mconstraint
+  , remove_equality_constraints
+  , add_equality_constraint
+  , add_precond_equality_constraint
+  , add_equality_mconstraint
+  -- * Stopping criterion configuration
+  , set_stopval
+  , get_stopval
+  , set_ftol_rel
+  , get_ftol_rel
+  , set_ftol_abs
+  , get_ftol_abs
+  , set_xtol_rel
+  , get_xtol_rel
+  , set_xtol_abs1
+  , set_xtol_abs
+  , get_xtol_abs
+  , set_maxeval
+  , get_maxeval
+  , set_maxtime
+  , get_maxtime
+  , force_stop
+  , set_force_stop
+  , get_force_stop
+  -- * Algorithm-specific configuration
+  , set_local_optimizer
+  , set_population
+  , get_population
+  , set_vector_storage
+  , get_vector_storage
+  , set_default_initial_step
+  , set_initial_step
+  , set_initial_step1
+  , get_initial_step
+  ) where
+
+import Foreign hiding (void)
+import Foreign.C.String
+import Foreign.C.Types
+import qualified Foreign.Concurrent as CFP
+
+import qualified Data.Vector.Storable.Mutable as MV
+import qualified Data.Vector.Storable as V
+
+{- C enums -}
+
+-- | The NLOPT algorithm names, apart from the names of the actual
+-- optimization methods, follow this scheme:
+--
+--   [@G@] means a global method
+--   [@L@] means a local method
+--   [@D@] means a method that requires the derivative
+--   [@N@] means a method that does not require the derivative
+--   [@*_RAND@] means the algorithm involves some randomization.
+--   [@*_NOSCAL@] means the algorithm is *not* scaled to a unit
+--   hypercube (i.e. it is sensitive to the units of x)
+data Algorithm
+  = GN_DIRECT                  -- ^ DIviding RECTangles
+  | GN_DIRECT_L                -- ^ DIviding RECTangles,
+                               -- locally-biased variant
+  | GN_DIRECT_L_RAND           -- ^ DIviding RECTangles, "slightly
+                               -- randomized"
+  | GN_DIRECT_NOSCAL           -- ^ DIviding RECTangles, unscaled version
+  | GN_DIRECT_L_NOSCAL         -- ^ DIviding RECTangles,
+                               -- locally-biased and unscaled
+  | GN_DIRECT_L_RAND_NOSCAL    -- ^ DIviding RECTangles, locally-biased,
+                               -- unscaled and "slightly randomized"
+  | GN_ORIG_DIRECT             -- ^ DIviding RECTangles, original FORTRAN
+                               -- implementation
+  | GN_ORIG_DIRECT_L           -- ^ DIviding RECTangles,
+                               -- locally-biased, original FORTRAN
+                               -- implementation
+  | GD_STOGO                   -- ^ Stochastic Global Optimization
+  | GD_STOGO_RAND              -- ^ Stochastic Global Optimization,
+                               -- randomized variant
+  | LD_LBFGS_NOCEDAL           -- ^ Limited-memory BFGS
+  | LD_LBFGS                   -- ^ Limited-memory BFGS
+  | LN_PRAXIS                  -- ^ PRincipal AXIS gradient-free local
+                               -- optimization
+  | LD_VAR2                    -- ^ Shifted limited-memory
+                               -- variable-metric, rank-2
+  | LD_VAR1                    -- ^ Shifted limited-memory
+                               -- variable-metric, rank-1
+  | LD_TNEWTON                 -- ^ Truncated Newton's method
+  | LD_TNEWTON_RESTART         -- ^ Truncated Newton's method with
+                               -- automatic restarting
+  | LD_TNEWTON_PRECOND         -- ^ Preconditioned truncated Newton's
+                               -- method
+  | LD_TNEWTON_PRECOND_RESTART -- ^ Preconditioned truncated Newton's
+                               -- method with automatic restarting
+  | GN_CRS2_LM                 -- ^ Controlled Random Search with
+                               -- Local Mutation
+  | GN_MLSL                    -- ^ Original Multi-Level
+                               -- Single-Linkage
+  | GD_MLSL                    -- ^ Original Multi-Level
+                               -- Single-Linkage, user-provided
+                               -- derivative
+  | GN_MLSL_LDS                -- ^ Multi-Level Single-Linkage with
+                               -- Sobol Low-Discrepancy Sequence for
+                               -- starting points
+  | GD_MLSL_LDS                -- ^ Multi-Level Single-Linkage with
+                               -- Sobol Low-Discrepancy Sequence for
+                               -- starting points, user-provided
+                               -- derivative
+  | LD_MMA                     -- ^ Method of moving averages
+  | LN_COBYLA                  -- ^ Constrained Optimization BY Linear
+                               -- Approximations
+  | LN_NEWUOA                  -- ^ Powell's NEWUOA algorithm
+  | LN_NEWUOA_BOUND            -- ^ Powell's NEWUOA algorithm with
+                               -- bounds by SGJ
+  | LN_NELDERMEAD              -- ^ Nelder-Mead Simplex gradient-free
+                               -- method
+  | LN_SBPLX                   -- ^ NLOPT implementation of Rowan's
+                               -- Subplex algorithm
+  | LN_AUGLAG                  -- ^ AUGmented LAGrangian
+  | LD_AUGLAG                  -- ^ AUGmented LAGrangian,
+                               -- user-provided derivative
+  | LN_AUGLAG_EQ               -- ^ AUGmented LAGrangian with penalty
+                               -- functions only for equality
+                               -- constraints
+  | LD_AUGLAG_EQ               -- ^ AUGmented LAGrangian with
+                               -- penalty functions only for equality
+                               -- constraints, user-provided
+                               -- derivative
+  | LN_BOBYQA                  -- ^ Bounded Optimization BY Quadratic
+                               -- Approximations
+  | GN_ISRES                   -- ^ Improved Stochastic Ranking
+                               -- Evolution Strategy
+
+  | AUGLAG                     -- ^ AUGmented LAGrangian, requires
+                               -- local_optimizer to be set
+  | AUGLAG_EQ                  -- ^ AUGmented LAGrangian with penalty
+                               -- functions only for equality
+                               -- constraints, requires
+                               -- local_optimizer to be set
+  | G_MLSL                     -- ^ Original Multi-Level
+                               -- Single-Linkage, user-provided
+                               -- derivative, requires local_optimizer
+                               -- to be set
+  | G_MLSL_LDS                 -- ^ Multi-Level Single-Linkage with
+                               -- Sobol Low-Discrepancy Sequence for
+                               -- starting points, requires
+                               -- local_optimizer to be set
+  | LD_SLSQP                   -- ^ Sequential Least-SQuares Programming
+  | LD_CCSAQ                   -- ^ Conservative Convex Separable
+                               -- Approximation
+  | GN_ESCH                    -- ^ Evolutionary Algorithm
+  deriving (Eq, Show, Read, Bounded)
+
+instance Enum Algorithm where
+  fromEnum GN_DIRECT                  = 0
+  fromEnum GN_DIRECT_L                = 1
+  fromEnum GN_DIRECT_L_RAND           = 2
+  fromEnum GN_DIRECT_NOSCAL           = 3
+  fromEnum GN_DIRECT_L_NOSCAL         = 4
+  fromEnum GN_DIRECT_L_RAND_NOSCAL    = 5
+  fromEnum GN_ORIG_DIRECT             = 6
+  fromEnum GN_ORIG_DIRECT_L           = 7
+  fromEnum GD_STOGO                   = 8
+  fromEnum GD_STOGO_RAND              = 9
+  fromEnum LD_LBFGS_NOCEDAL           = 10
+  fromEnum LD_LBFGS                   = 11
+  fromEnum LN_PRAXIS                  = 12
+  fromEnum LD_VAR2                    = 13
+  fromEnum LD_VAR1                    = 14
+  fromEnum LD_TNEWTON                 = 15
+  fromEnum LD_TNEWTON_RESTART         = 16
+  fromEnum LD_TNEWTON_PRECOND         = 17
+  fromEnum LD_TNEWTON_PRECOND_RESTART = 18
+  fromEnum GN_CRS2_LM                 = 19
+  fromEnum GN_MLSL                    = 20
+  fromEnum GD_MLSL                    = 21
+  fromEnum GN_MLSL_LDS                = 22
+  fromEnum GD_MLSL_LDS                = 23
+  fromEnum LD_MMA                     = 24
+  fromEnum LN_COBYLA                  = 25
+  fromEnum LN_NEWUOA                  = 26
+  fromEnum LN_NEWUOA_BOUND            = 27
+  fromEnum LN_NELDERMEAD              = 28
+  fromEnum LN_SBPLX                   = 29
+  fromEnum LN_AUGLAG                  = 30
+  fromEnum LD_AUGLAG                  = 31
+  fromEnum LN_AUGLAG_EQ               = 32
+  fromEnum LD_AUGLAG_EQ               = 33
+  fromEnum LN_BOBYQA                  = 34
+  fromEnum GN_ISRES                   = 35
+  fromEnum AUGLAG                     = 36
+  fromEnum AUGLAG_EQ                  = 37
+  fromEnum G_MLSL                     = 38
+  fromEnum G_MLSL_LDS                 = 39
+  fromEnum LD_SLSQP                   = 40
+  fromEnum LD_CCSAQ                   = 41
+  fromEnum GN_ESCH                    = 42
+  toEnum 0 = GN_DIRECT
+  toEnum 1 = GN_DIRECT_L
+  toEnum 2 = GN_DIRECT_L_RAND
+  toEnum 3 = GN_DIRECT_NOSCAL
+  toEnum 4 = GN_DIRECT_L_NOSCAL
+  toEnum 5 = GN_DIRECT_L_RAND_NOSCAL
+  toEnum 6 = GN_ORIG_DIRECT
+  toEnum 7 = GN_ORIG_DIRECT_L
+  toEnum 8 = GD_STOGO
+  toEnum 9 = GD_STOGO_RAND
+  toEnum 10 = LD_LBFGS_NOCEDAL
+  toEnum 11 = LD_LBFGS
+  toEnum 12 = LN_PRAXIS
+  toEnum 13 = LD_VAR2
+  toEnum 14 = LD_VAR1
+  toEnum 15 = LD_TNEWTON
+  toEnum 16 = LD_TNEWTON_RESTART
+  toEnum 17 = LD_TNEWTON_PRECOND
+  toEnum 18 = LD_TNEWTON_PRECOND_RESTART
+  toEnum 19 = GN_CRS2_LM
+  toEnum 20 = GN_MLSL
+  toEnum 21 = GD_MLSL
+  toEnum 22 = GN_MLSL_LDS
+  toEnum 23 = GD_MLSL_LDS
+  toEnum 24 = LD_MMA
+  toEnum 25 = LN_COBYLA
+  toEnum 26 = LN_NEWUOA
+  toEnum 27 = LN_NEWUOA_BOUND
+  toEnum 28 = LN_NELDERMEAD
+  toEnum 29 = LN_SBPLX
+  toEnum 30 = LN_AUGLAG
+  toEnum 31 = LD_AUGLAG
+  toEnum 32 = LN_AUGLAG_EQ
+  toEnum 33 = LD_AUGLAG_EQ
+  toEnum 34 = LN_BOBYQA
+  toEnum 35 = GN_ISRES
+  toEnum 36 = AUGLAG
+  toEnum 37 = AUGLAG_EQ
+  toEnum 38 = G_MLSL
+  toEnum 39 = G_MLSL_LDS
+  toEnum 40 = LD_SLSQP
+  toEnum 41 = LD_CCSAQ
+  toEnum 42 = GN_ESCH
+  toEnum e = error $
+             "Algorithm.toEnum: invalid C value '" ++ show e ++ "' received."
+
+foreign import ccall "nlopt.h nlopt_algorithm_name"
+  nlopt_algorithm_name :: CInt -> CString
+
+algorithm_name :: Algorithm -> IO String
+algorithm_name = peekCString . nlopt_algorithm_name . fromIntegral . fromEnum
+
+-- | Mostly self-explanatory.
+data Result
+  = FAILURE  -- ^ Generic failure code
+  | INVALID_ARGS
+  | OUT_OF_MEMORY
+  | ROUNDOFF_LIMITED
+  | FORCED_STOP
+  | SUCCESS  -- ^ Generic success code
+  | STOPVAL_REACHED
+  | FTOL_REACHED
+  | XTOL_REACHED
+  | MAXEVAL_REACHED
+  | MAXTIME_REACHED
+  deriving (Eq, Read, Show, Bounded)
+
+instance Enum Result where
+  fromEnum FAILURE = -1
+  fromEnum INVALID_ARGS = -2
+  fromEnum OUT_OF_MEMORY = -3
+  fromEnum ROUNDOFF_LIMITED = -4
+  fromEnum FORCED_STOP = -5
+  fromEnum SUCCESS = 1
+  fromEnum STOPVAL_REACHED = 2
+  fromEnum FTOL_REACHED = 3
+  fromEnum XTOL_REACHED = 4
+  fromEnum MAXEVAL_REACHED = 5
+  fromEnum MAXTIME_REACHED = 6
+  toEnum (-1) = FAILURE
+  toEnum (-2) = INVALID_ARGS
+  toEnum (-3) = OUT_OF_MEMORY
+  toEnum (-4) = ROUNDOFF_LIMITED
+  toEnum (-5) = FORCED_STOP
+  toEnum 1 = SUCCESS
+  toEnum 2 = STOPVAL_REACHED
+  toEnum 3 = FTOL_REACHED
+  toEnum 4 = XTOL_REACHED
+  toEnum 5 = MAXEVAL_REACHED
+  toEnum 6 = MAXTIME_REACHED
+  toEnum e = error $
+             "Result.toEnum: invalid C value '" ++ show e ++ "' received."
+
+isSuccess :: Result -> Bool
+isSuccess SUCCESS         = True
+isSuccess STOPVAL_REACHED = True
+isSuccess FTOL_REACHED    = True
+isSuccess XTOL_REACHED    = True
+isSuccess MAXEVAL_REACHED = True
+isSuccess MAXTIME_REACHED = True
+isSuccess _               = False
+
+parseEnum :: (Integral a, Enum b) => a -> b
+parseEnum = toEnum . fromIntegral
+
+{- NLOPT optimizer object -}
+
+type NloptOpt = Ptr ()
+
+-- | An optimizer object which must be created, configured and then
+-- passed to 'optimize' to solve a problem
+newtype Opt = Opt { pointerFromOpt :: ForeignPtr () }
+
+withOpt :: Opt -> (NloptOpt -> IO a) -> IO a
+withOpt (Opt p) f = do
+  ret <- withForeignPtr p f
+  touchForeignPtr p  -- This is critical!  Otherwise the GC might
+                     -- think it's done with everything in the middle
+                     -- of the problem.
+  return ret
+
+useOpt :: (NloptOpt -> IO a) -> Opt -> IO a
+useOpt = flip withOpt
+
+-- Every time we make a "wrapper" call, the runtime allocates a new
+-- function pointer and won't release it until we explicitly tell it
+-- to.  This doesn't mesh well with NLOPT's "object-oriented" design,
+-- wherein we have to allocate an object and make a bunch of setup
+-- calls before we run the problem, so what we do is add a finalizer
+-- to the 'Opt' object's 'ForeignPtr' every time we need to create a
+-- function pointer for C to use.
+addFunPtrFinalizer :: Opt -> FunPtr a -> IO ()
+addFunPtrFinalizer (Opt p) funptr =
+  CFP.addForeignPtrFinalizer p (freeHaskellFunPtr funptr)
+
+foreign import ccall "nlopt.h nlopt_create"
+  nlopt_create :: CInt -> CUInt -> IO (NloptOpt)
+
+-- | Create a new 'Opt' object
+create :: Algorithm -- ^ Choice of algorithm
+       -> Word  -- ^ Parameter vector dimension
+       -> IO (Maybe Opt)  -- ^ Optimizer object
+create alg dimension = do
+  outp <- nlopt_create (fromIntegral $ fromEnum alg) (fromIntegral dimension)
+  if (outp == nullPtr)
+    then return Nothing
+    else Just . Opt <$> CFP.newForeignPtr outp (nlopt_destroy outp)
+
+foreign import ccall "nlopt.h nlopt_destroy"
+  nlopt_destroy :: NloptOpt -> IO ()
+
+-- It shouldn't be strictly necessary to call this by hand since we've
+-- already put a call to 'nlopt_destroy' into the 'ForeignPtr', but
+-- it's available in the C interface.
+destroy :: Opt -> IO ()
+destroy = finalizeForeignPtr . pointerFromOpt
+
+foreign import ccall "nlopt.h nlopt_copy"
+  nlopt_copy :: NloptOpt -> IO (NloptOpt)
+
+copy :: Opt -> IO Opt
+copy = useOpt $ \inp -> do
+  outp <- nlopt_copy inp
+  Opt <$> CFP.newForeignPtr outp (nlopt_destroy outp)
+
+{- Random seeding functions -}
+
+foreign import ccall "nlopt.h nlopt_srand"
+  nlopt_srand :: CUInt -> IO ()
+
+srand :: Integral a => a -> IO ()
+srand = nlopt_srand . fromIntegral
+
+foreign import ccall "nlopt.h nlopt_srand_time"
+  nlopt_srand_time :: IO ()
+
+srand_time :: IO ()
+srand_time = nlopt_srand_time
+
+{- Metadata -}
+
+foreign import ccall "nlopt.h nlopt_version"
+  nlopt_version :: Ptr CInt -> Ptr CInt -> Ptr CInt -> IO ()
+
+-- | NLOPT library version, e.g. @2.4.2@
+data Version = Version
+  { major :: Int
+  , minor :: Int
+  , bugfix :: Int
+  } deriving (Eq, Ord, Read, Show)
+
+version :: IO Version
+version =
+  alloca $ \majptr ->
+  alloca $ \minptr ->
+  alloca $ \bfptr -> do
+  nlopt_version majptr minptr bfptr
+  Version <$> pk majptr <*> pk minptr <*> pk bfptr
+  where
+    pk = fmap fromIntegral . peek
+
+foreign import ccall "nlopt.h nlopt_get_algorithm"
+  nlopt_get_algorithm :: NloptOpt -> IO CInt
+
+get_algorithm :: Opt -> IO Algorithm
+get_algorithm = useOpt $ fmap parseEnum . nlopt_get_algorithm
+
+foreign import ccall "nlopt.h nlopt_get_dimension"
+  nlopt_get_dimension :: NloptOpt -> IO CUInt
+
+get_dimension :: Opt -> IO Word
+get_dimension = useOpt $ fmap fromIntegral . nlopt_get_dimension
+
+{- Callback functions -}
+
+asMVector :: CUInt -> Ptr CDouble -> IO (MV.IOVector Double)
+asMVector dim ptr =
+  MV.unsafeCast . flip MV.unsafeFromForeignPtr0 (fromIntegral dim) <$>
+  newForeignPtr_ ptr
+
+asVector :: CUInt -> Ptr CDouble -> IO (V.Vector Double)
+asVector dim ptr =
+  V.unsafeCast . flip V.unsafeFromForeignPtr0 (fromIntegral dim) <$>
+  newForeignPtr_ ptr
+
+type CFunc a = CUInt -> Ptr CDouble -> Ptr CDouble -> StablePtr a -> IO CDouble
+
+-- | This function type corresponds to @nlopt_func@ in C and is used
+-- for scalar functions of the parameter vector.  You may pass data of
+-- any type @a@ to the functions in this module that take a
+-- 'ScalarFunction' as an argument; this data will be supplied to your
+-- your function when it is called.
+type ScalarFunction a
+  = V.Vector Double            -- ^ Parameter vector
+ -> Maybe (MV.IOVector Double) -- ^ Gradient vector to be filled in
+ -> a                          -- ^ User data
+ -> IO Double                  -- ^ Scalar result
+
+-- | This function type corresponds to @nlopt_mfunc@ in C and is used
+-- for vector functions of the parameter vector.  You may pass data of
+-- any type @a@ to the functions in this module that take a
+-- 'VectorFunction' as an argument; this data will be supplied to your
+-- function when it is called.
+type VectorFunction a
+  = V.Vector Double            -- ^ Parameter vector
+ -> MV.IOVector Double         -- ^ Output vector to be filled in
+ -> Maybe (MV.IOVector Double) -- ^ Gradient vector to be filled in
+ -> a                          -- ^ User data
+ -> IO ()
+
+-- | This function type corresponds to @nlopt_precond@ in C and is
+-- used for functions that precondition a vector at a given point in
+-- the parameter space.  You may pass data of any type @a@ to the
+-- functions in this module that take a 'PreconditionerFunction' as an
+-- argument; this data will be supplied to your function when it is
+-- called.
+type PreconditionerFunction a
+  = V.Vector Double    -- ^ Parameter vector
+ -> V.Vector Double    -- ^ Vector @v@ to precondition
+ -> MV.IOVector Double -- ^ Output vector @vpre@ to be filled in
+ -> a                  -- ^ User data
+ -> IO ()
+
+wrapCFunction :: ScalarFunction a -> CFunc a
+wrapCFunction cfunc dim stateptr gradientptr userptr = do
+  nloptgradient <- asMVector dim gradientptr
+  statevec <- asVector dim stateptr
+  userdata <- deRefStablePtr userptr
+  let
+    gradptr = if gradientptr /= nullPtr
+      then Just nloptgradient
+      else Nothing
+  realToFrac <$> cfunc statevec gradptr userdata
+
+foreign import ccall safe "wrapper"
+  mkCFunction :: CFunc a -> IO (FunPtr (CFunc a))
+
+type CMFunc a = CUInt -> Ptr CDouble -> CUInt -> Ptr CDouble
+             -> Ptr CDouble -> StablePtr a -> IO ()
+
+wrapMFunction :: VectorFunction a -> CMFunc a
+wrapMFunction mfunc constrdim constrptr dim stateptr gradientptr userptr
+  = do
+  nloptgradient <- asMVector (dim * constrdim) gradientptr
+  nloptconstraint <- asMVector constrdim constrptr
+  statevec <- asVector dim stateptr
+  userdata <- deRefStablePtr userptr
+  let
+    gradptr = if gradientptr /= nullPtr
+      then Just nloptgradient
+      else Nothing
+  mfunc statevec nloptconstraint gradptr userdata
+
+foreign import ccall safe "wrapper"
+  mkMFunction :: CMFunc a -> IO (FunPtr (CMFunc a))
+
+type CPrecond a = CUInt -> Ptr CDouble -> Ptr CDouble
+               -> Ptr CDouble -> StablePtr a -> IO ()
+
+wrapPreconditioner :: PreconditionerFunction a -> CPrecond a
+wrapPreconditioner prec dim stateptr vptr preptr userptr = do
+  nloptpre <- asMVector dim preptr
+  statevec <- asVector dim stateptr
+  vvec <- asVector dim vptr
+  userdata <- deRefStablePtr userptr
+  prec statevec vvec nloptpre userdata
+
+foreign import ccall safe "wrapper"
+  mkPreconditionerFunction :: CPrecond a -> IO (FunPtr (CPrecond a))
+
+-- We have to do the same silly dance with our user-data 'StablePtr's
+-- as we do with function pointer wrappers: because NLOPT expects
+-- these pointers before the actual optimization run, we have to
+-- attach finalizers for them to the 'Opt' object so that they get
+-- cleaned up properly.
+addStablePtrFinalizer :: Opt -> StablePtr a -> IO ()
+addStablePtrFinalizer (Opt p) sp =
+  CFP.addForeignPtrFinalizer p (freeStablePtr sp)
+
+getStablePtr :: Opt -> a -> IO (StablePtr a)
+getStablePtr opt a = do
+  aptr <- newStablePtr a
+  addStablePtrFinalizer opt aptr
+  return aptr
+
+exportFunPtr :: (t1 -> IO (FunPtr a)) -> (t -> t1) -> t -> Opt -> IO (FunPtr a)
+exportFunPtr mk wrap fun opt = do
+  funptr <- mk $ wrap fun
+  addFunPtrFinalizer opt funptr
+  return funptr
+
+{- Invoking the optimizer -}
+
+-- | The output of an NLOPT optimizer run.
+data Output = Output
+  { resultCode :: Result                -- ^ Return code
+  , resultCost :: Double                -- ^ Minimum of the objective
+                                        -- function if optimization
+                                        -- succeeded
+  , resultParameters :: V.Vector Double -- ^ Parameters corresponding
+                                        -- to the minimum if
+                                        -- optimization succeeded
+
+  , nEvals :: Int                       -- ^ number of evaluations
+  }
+
+foreign import ccall "nlopt.h nlopt_optimize"
+  nlopt_optimize :: NloptOpt -> Ptr CDouble -> Ptr CDouble -> IO CInt
+
+-- | This function is very similar to the C function @nlopt_optimize@,
+-- but it does not use mutable vectors and returns an 'Output'
+-- structure.
+optimize :: Opt  -- ^ Optimizer object set up to solve the problem
+         -> V.Vector Double  -- ^ Initial-guess parameter vector
+         -> IO Output  -- ^ Results of the optimization run
+optimize optimizer x0 = withOpt optimizer $ \opt -> do
+  vmut <- V.thaw $ V.unsafeCast x0
+  (result, outputCost, iceout) <- alloca $ \costPtr -> do
+    result <- MV.unsafeWith vmut $ \xptr ->
+      parseEnum <$> nlopt_optimize opt xptr costPtr
+    outputCost <- peek . castPtr $ costPtr
+    iceout <- V.unsafeFreeze (MV.unsafeCast vmut)
+    return (result, outputCost, iceout)
+  nEvals <- fromIntegral <$> get_numevals optimizer
+  return $ Output result outputCost iceout nEvals
+
+{- Objective function setup -}
+
+foreign import ccall "nlopt.h nlopt_set_min_objective"
+  nlopt_set_min_objective :: NloptOpt -> FunPtr (CFunc a)
+                          -> StablePtr a -> IO CInt
+
+foreign import ccall "nlopt.h nlopt_set_max_objective"
+  nlopt_set_max_objective :: NloptOpt -> FunPtr (CFunc a)
+                          -> StablePtr a -> IO CInt
+
+set_min_objective :: Opt -> ScalarFunction a -> a -> IO Result
+set_min_objective opt objf userdata = do
+  objfunptr <- exportFunPtr mkCFunction wrapCFunction objf opt
+  userptr <- getStablePtr opt userdata
+  withOpt opt $ \o ->
+    parseEnum <$>
+    nlopt_set_min_objective o objfunptr userptr
+
+set_max_objective :: Opt -> ScalarFunction a -> a -> IO Result
+set_max_objective opt objf userdata = do
+  objfunptr <- exportFunPtr mkCFunction wrapCFunction objf opt
+  userptr <- getStablePtr opt userdata
+  withOpt opt $ \o ->
+    parseEnum <$> nlopt_set_max_objective o objfunptr userptr
+
+foreign import ccall "nlopt.h nlopt_set_precond_min_objective"
+  nlopt_set_precond_min_objective :: NloptOpt
+                                  -> FunPtr (CFunc a)
+                                  -> FunPtr (CPrecond a)
+                                  -> StablePtr a
+                                  -> IO CInt
+
+foreign import ccall "nlopt.h nlopt_set_precond_max_objective"
+  nlopt_set_precond_max_objective :: NloptOpt
+                                  -> FunPtr (CFunc a)
+                                  -> FunPtr (CPrecond a)
+                                  -> StablePtr a
+                                  -> IO CInt
+
+set_precond_min_objective :: Opt
+                          -> ScalarFunction a
+                          -> PreconditionerFunction a
+                          -> a
+                          -> IO Result
+set_precond_min_objective opt objf pref userdata = do
+  objfunptr <- exportFunPtr mkCFunction wrapCFunction objf opt
+  prefunptr <- exportFunPtr mkPreconditionerFunction wrapPreconditioner pref opt
+  userptr <- getStablePtr opt userdata
+  withOpt opt $ \o -> parseEnum <$>
+    nlopt_set_precond_min_objective o objfunptr prefunptr userptr
+
+set_precond_max_objective :: Opt
+                          -> ScalarFunction a
+                          -> PreconditionerFunction a
+                          -> a
+                          -> IO Result
+set_precond_max_objective opt objf pref userdata = do
+  objfunptr <- exportFunPtr mkCFunction wrapCFunction objf opt
+  prefunptr <- exportFunPtr mkPreconditionerFunction wrapPreconditioner pref opt
+  userptr <- getStablePtr opt userdata
+  withOpt opt $ \o -> parseEnum <$>
+    nlopt_set_precond_max_objective o objfunptr prefunptr userptr
+
+{- Working with bounds -}
+
+foreign import ccall "nlopt.h nlopt_set_lower_bounds"
+  nlopt_set_lower_bounds :: NloptOpt -> Ptr CDouble -> IO CInt
+
+foreign import ccall "nlopt.h nlopt_set_lower_bounds1"
+  nlopt_set_lower_bounds1 :: NloptOpt -> CDouble -> IO CInt
+
+foreign import ccall "nlopt.h nlopt_get_lower_bounds"
+  nlopt_get_lower_bounds :: NloptOpt -> Ptr CDouble -> IO CInt
+
+foreign import ccall "nlopt.h nlopt_set_upper_bounds"
+  nlopt_set_upper_bounds :: NloptOpt -> Ptr CDouble -> IO CInt
+
+foreign import ccall "nlopt.h nlopt_set_upper_bounds1"
+  nlopt_set_upper_bounds1 :: NloptOpt -> CDouble -> IO CInt
+
+foreign import ccall "nlopt.h nlopt_get_upper_bounds"
+  nlopt_get_upper_bounds :: NloptOpt -> Ptr CDouble -> IO CInt
+
+set_lower_bounds :: Opt -> V.Vector Double -> IO Result
+set_lower_bounds opt bounds =
+  withForeignPtr (fst . V.unsafeToForeignPtr0 . V.unsafeCast $ bounds) $
+    \bptr -> withOpt opt $ \o ->
+      parseEnum <$> nlopt_set_lower_bounds o bptr
+
+set_lower_bounds1 :: Opt -> Double -> IO Result
+set_lower_bounds1 opt bound =
+  withOpt opt $ \o ->
+    parseEnum <$> nlopt_set_lower_bounds1 o (realToFrac bound)
+
+get_lower_bounds :: Opt -> IO (V.Vector Double, Result)
+get_lower_bounds opt = do
+  v <- get_dimension opt >>= MV.new . fromIntegral
+  MV.unsafeWith (MV.unsafeCast v) $ \vptr -> withOpt opt $ \o -> do
+    result <- parseEnum <$> nlopt_get_lower_bounds o vptr
+    retv <- V.unsafeFreeze v
+    return (retv, result)
+
+set_upper_bounds :: Opt -> V.Vector Double -> IO Result
+set_upper_bounds opt bounds =
+  withForeignPtr (fst . V.unsafeToForeignPtr0 . V.unsafeCast $ bounds) $
+    \bptr -> withOpt opt $ \o ->
+      parseEnum <$> nlopt_set_upper_bounds o bptr
+
+set_upper_bounds1 :: Opt -> Double -> IO Result
+set_upper_bounds1 opt bound =
+  withOpt opt $ \o ->
+    parseEnum <$> nlopt_set_upper_bounds1 o (realToFrac bound)
+
+get_upper_bounds :: Opt -> IO (V.Vector Double, Result)
+get_upper_bounds opt = do
+  v <- get_dimension opt >>= MV.new . fromIntegral
+  MV.unsafeWith (MV.unsafeCast v) $ \vptr -> withOpt opt $ \o -> do
+    result <- parseEnum <$> nlopt_get_upper_bounds o vptr
+    retv <- V.unsafeFreeze v
+    return (retv, result)
+
+{- Working with constraints -}
+
+foreign import ccall "nlopt.h nlopt_remove_inequality_constraints"
+  nlopt_remove_inequality_constraints :: NloptOpt -> IO CInt
+
+foreign import ccall "nlopt.h nlopt_add_inequality_constraint"
+  nlopt_add_inequality_constraint :: NloptOpt -> FunPtr (CFunc a)
+                                  -> StablePtr a -> CDouble -> IO CInt
+
+foreign import ccall "nlopt.h nlopt_add_precond_inequality_constraint"
+  nlopt_add_precond_inequality_constraint :: NloptOpt -> FunPtr (CFunc a)
+                                  -> FunPtr (CPrecond a) -> StablePtr a
+                                  -> CDouble -> IO CInt
+
+foreign import ccall "nlopt.h nlopt_add_inequality_mconstraint"
+  nlopt_add_inequality_mconstraint :: NloptOpt -> CUInt -> FunPtr (CMFunc a)
+                                  -> StablePtr a -> CDouble -> IO CInt
+
+remove_inequality_constraints :: Opt -> IO Result
+remove_inequality_constraints =
+  useOpt $ fmap parseEnum . nlopt_remove_inequality_constraints
+
+add_inequality_constraint :: Opt -> ScalarFunction a
+                          -> a -> Double -> IO Result
+add_inequality_constraint opt objfun userdata tol = do
+  objfunptr <- exportFunPtr mkCFunction wrapCFunction objfun opt
+  userptr <- getStablePtr opt userdata
+  withOpt opt $ \o ->
+      parseEnum <$>
+      nlopt_add_inequality_constraint o objfunptr userptr (realToFrac tol)
+
+add_precond_inequality_constraint :: Opt -> ScalarFunction a
+                                  -> PreconditionerFunction a -> a -> Double
+                                  -> IO Result
+add_precond_inequality_constraint opt objfun precfun userdata tol = do
+  objfunptr <- exportFunPtr mkCFunction wrapCFunction objfun opt
+  precfunptr <-
+    exportFunPtr mkPreconditionerFunction wrapPreconditioner precfun opt
+  userptr <- getStablePtr opt userdata
+  withOpt opt $ \o ->
+      parseEnum <$>
+      nlopt_add_precond_inequality_constraint o objfunptr
+        precfunptr userptr (realToFrac tol)
+
+add_inequality_mconstraint :: Opt -> Word -> VectorFunction a -> a
+                           -> Double -> IO Result
+add_inequality_mconstraint opt constraintsize constrfun userdata tol = do
+  constrfunptr <- exportFunPtr mkMFunction wrapMFunction constrfun opt
+  userptr <- getStablePtr opt userdata
+  withOpt opt $ \o ->
+      parseEnum <$>
+      nlopt_add_inequality_mconstraint o (fromIntegral constraintsize)
+      constrfunptr userptr (realToFrac tol)
+
+foreign import ccall "nlopt.h nlopt_remove_equality_constraints"
+  nlopt_remove_equality_constraints :: NloptOpt -> IO CInt
+
+foreign import ccall "nlopt.h nlopt_add_equality_constraint"
+  nlopt_add_equality_constraint :: NloptOpt -> FunPtr (CFunc a)
+                                -> StablePtr a -> CDouble -> IO CInt
+
+foreign import ccall "nlopt.h nlopt_add_precond_equality_constraint"
+  nlopt_add_precond_equality_constraint :: NloptOpt -> FunPtr (CFunc a)
+                                        -> FunPtr (CPrecond a) -> StablePtr a
+                                        -> CDouble -> IO CInt
+
+foreign import ccall "nlopt.h nlopt_add_equality_mconstraint"
+  nlopt_add_equality_mconstraint :: NloptOpt -> CUInt -> FunPtr (CMFunc a)
+                                 -> StablePtr a -> CDouble -> IO CInt
+
+remove_equality_constraints :: Opt -> IO Result
+remove_equality_constraints =
+  useOpt $ fmap parseEnum . nlopt_remove_equality_constraints
+
+add_equality_constraint :: Opt -> ScalarFunction a
+                        -> a -> Double -> IO Result
+add_equality_constraint opt objfun userdata tol = do
+  objfunptr <- exportFunPtr mkCFunction wrapCFunction objfun opt
+  userptr <- getStablePtr opt userdata
+  withOpt opt $ \o ->
+      parseEnum <$>
+      nlopt_add_equality_constraint o objfunptr userptr (realToFrac tol)
+
+add_precond_equality_constraint :: Opt -> ScalarFunction a
+                                  -> PreconditionerFunction a -> a -> Double
+                                  -> IO Result
+add_precond_equality_constraint opt objfun precfun userdata tol = do
+  objfunptr <- exportFunPtr mkCFunction wrapCFunction objfun opt
+  precfunptr <-
+    exportFunPtr mkPreconditionerFunction wrapPreconditioner precfun opt
+  userptr <- getStablePtr opt userdata
+  withOpt opt $ \o ->
+      parseEnum <$>
+      nlopt_add_precond_equality_constraint o objfunptr
+        precfunptr userptr (realToFrac tol)
+
+add_equality_mconstraint :: Opt -> Word -> VectorFunction a -> a
+                           -> Double -> IO Result
+add_equality_mconstraint opt constraintsize constrfun userdata tol = do
+  constrfunptr <- exportFunPtr mkMFunction wrapMFunction constrfun opt
+  userptr <- getStablePtr opt userdata
+  withOpt opt $ \o ->
+      parseEnum <$>
+      nlopt_add_equality_mconstraint o (fromIntegral constraintsize)
+      constrfunptr userptr (realToFrac tol)
+
+{- Stopping criteria -}
+
+withInputVector :: (Storable c, Storable a)
+                => V.Vector c -> (Ptr a -> IO b) -> IO b
+withInputVector = withForeignPtr . fst . V.unsafeToForeignPtr0 . V.unsafeCast
+withOutputVector :: (Storable c, Storable a)
+                 => V.MVector s c -> (Ptr a -> IO b) -> IO b
+withOutputVector = withForeignPtr . fst . MV.unsafeToForeignPtr0 . MV.unsafeCast
+
+setScalar :: (Enum a, Integral b) => (NloptOpt -> t1 -> IO b)
+          -> (t -> t1) -> Opt -> t -> IO a
+setScalar setter conv opt val = withOpt opt $ \o ->
+  parseEnum <$> setter o (conv val)
+
+getScalar :: (NloptOpt -> IO b) -> (b -> a) -> Opt -> IO a
+getScalar getter conv = useOpt $ fmap conv . getter
+
+foreign import ccall "nlopt.h nlopt_set_stopval"
+  nlopt_set_stopval :: NloptOpt -> CDouble -> IO CInt
+
+foreign import ccall "nlopt.h nlopt_get_stopval"
+  nlopt_get_stopval :: NloptOpt -> IO CDouble
+
+set_stopval :: Opt -> Double -> IO Result
+set_stopval = setScalar nlopt_set_stopval realToFrac
+
+get_stopval :: Opt -> IO Double
+get_stopval = getScalar nlopt_get_stopval realToFrac
+
+foreign import ccall "nlopt.h nlopt_set_ftol_rel"
+  nlopt_set_ftol_rel :: NloptOpt -> CDouble -> IO CInt
+
+foreign import ccall "nlopt.h nlopt_get_ftol_rel"
+  nlopt_get_ftol_rel :: NloptOpt -> IO CDouble
+
+set_ftol_rel :: Opt -> Double -> IO Result
+set_ftol_rel = setScalar nlopt_set_ftol_rel realToFrac
+
+get_ftol_rel :: Opt -> IO Double
+get_ftol_rel = getScalar nlopt_get_ftol_rel realToFrac
+
+foreign import ccall "nlopt.h nlopt_set_ftol_abs"
+  nlopt_set_ftol_abs :: NloptOpt -> CDouble -> IO CInt
+
+foreign import ccall "nlopt.h nlopt_get_ftol_abs"
+  nlopt_get_ftol_abs :: NloptOpt -> IO CDouble
+
+set_ftol_abs :: Opt -> Double -> IO Result
+set_ftol_abs = setScalar nlopt_set_ftol_abs realToFrac
+
+get_ftol_abs :: Opt -> IO Double
+get_ftol_abs = getScalar nlopt_get_ftol_abs realToFrac
+
+foreign import ccall "nlopt.h nlopt_set_xtol_rel"
+  nlopt_set_xtol_rel :: NloptOpt -> CDouble -> IO CInt
+
+foreign import ccall "nlopt.h nlopt_get_xtol_rel"
+  nlopt_get_xtol_rel :: NloptOpt -> IO CDouble
+
+set_xtol_rel :: Opt -> Double -> IO Result
+set_xtol_rel = setScalar nlopt_set_xtol_rel realToFrac
+
+get_xtol_rel :: Opt -> IO Double
+get_xtol_rel = getScalar nlopt_get_xtol_rel realToFrac
+
+foreign import ccall "nlopt.h nlopt_set_xtol_abs1"
+  nlopt_set_xtol_abs1 :: NloptOpt -> CDouble -> IO CInt
+
+set_xtol_abs1 :: Opt -> Double -> IO Result
+set_xtol_abs1 = setScalar nlopt_set_xtol_abs1 realToFrac
+
+foreign import ccall "nlopt.h nlopt_set_xtol_abs"
+  nlopt_set_xtol_abs :: NloptOpt -> Ptr CDouble -> IO CInt
+
+foreign import ccall "nlopt.h nlopt_get_xtol_abs"
+  nlopt_get_xtol_abs :: NloptOpt -> Ptr CDouble -> IO CInt
+
+set_xtol_abs :: Opt -> V.Vector Double -> IO Result
+set_xtol_abs opt tolvec =
+  withInputVector tolvec $ \tolptr ->
+  withOpt opt $ \o -> parseEnum <$> nlopt_set_xtol_abs o tolptr
+
+get_xtol_abs :: Opt -> IO (Result, V.Vector Double)
+get_xtol_abs opt = do
+  mutv <- get_dimension opt >>= MV.new . fromIntegral
+  withOutputVector mutv $ \vecptr ->
+    withOpt opt $ \o -> do
+    result <- parseEnum <$> nlopt_get_xtol_abs o vecptr
+    outvec <- V.unsafeFreeze mutv
+    return (result, outvec)
+
+foreign import ccall "nlopt.h nlopt_set_maxeval"
+  nlopt_set_maxeval :: NloptOpt -> CInt -> IO CInt
+
+foreign import ccall "nlopt.h nlopt_get_maxeval"
+  nlopt_get_maxeval :: NloptOpt -> IO CInt
+
+set_maxeval :: Opt -> Word -> IO Result
+set_maxeval = setScalar nlopt_set_maxeval fromIntegral
+
+get_maxeval :: Opt -> IO Word
+get_maxeval = getScalar nlopt_get_maxeval fromIntegral
+
+foreign import ccall "nlopt.h nlopt_get_numevals"
+  nlopt_get_numevals :: NloptOpt -> IO CInt
+
+get_numevals :: Opt -> IO CInt
+get_numevals = getScalar nlopt_get_numevals fromIntegral
+
+foreign import ccall "nlopt.h nlopt_set_maxtime"
+  nlopt_set_maxtime :: NloptOpt -> CDouble -> IO CInt
+
+foreign import ccall "nlopt.h nlopt_get_maxtime"
+  nlopt_get_maxtime :: NloptOpt -> IO CDouble
+
+set_maxtime :: Opt -> Double -> IO Result
+set_maxtime = setScalar nlopt_set_maxtime realToFrac
+
+get_maxtime :: Opt -> IO Double
+get_maxtime = getScalar nlopt_get_maxtime realToFrac
+
+foreign import ccall "nlopt.h nlopt_force_stop"
+  nlopt_force_stop :: NloptOpt -> IO CInt
+
+force_stop :: Opt -> IO Result
+force_stop = useOpt $ fmap parseEnum . nlopt_force_stop
+
+foreign import ccall "nlopt.h nlopt_set_force_stop"
+  nlopt_set_force_stop :: NloptOpt -> CInt -> IO CInt
+
+foreign import ccall "nlopt.h nlopt_get_force_stop"
+  nlopt_get_force_stop :: NloptOpt -> IO CInt
+
+set_force_stop :: Opt -> Word -> IO Result
+set_force_stop = setScalar nlopt_set_force_stop fromIntegral
+
+get_force_stop :: Opt -> IO Word
+get_force_stop = getScalar nlopt_get_force_stop fromIntegral
+
+{- Algorithm-specific configuration -}
+
+foreign import ccall "nlopt.h nlopt_set_local_optimizer"
+  nlopt_set_local_optimizer :: NloptOpt -> NloptOpt -> IO CInt
+
+set_local_optimizer :: Opt -- ^ Primary optimizer
+                    -> Opt -- ^ Subsidiary (local) optimizer
+                    -> IO Result
+set_local_optimizer p s =
+  withOpt p $ \primary -> withOpt s $ \secondary ->
+    parseEnum <$> nlopt_set_local_optimizer primary secondary
+
+foreign import ccall "nlopt.h nlopt_set_population"
+  nlopt_set_population :: NloptOpt -> Word -> IO CInt
+
+foreign import ccall "nlopt.h nlopt_get_population"
+  nlopt_get_population :: NloptOpt -> IO Word
+
+set_population :: Opt -> Word -> IO Result
+set_population = setScalar nlopt_set_population fromIntegral
+
+get_population :: Opt -> IO Word
+get_population = getScalar nlopt_get_population fromIntegral
+
+foreign import ccall "nlopt.h nlopt_set_vector_storage"
+  nlopt_set_vector_storage :: NloptOpt -> Word -> IO CInt
+
+foreign import ccall "nlopt.h nlopt_get_vector_storage"
+  nlopt_get_vector_storage :: NloptOpt -> IO Word
+
+set_vector_storage :: Opt -> Word -> IO Result
+set_vector_storage = setScalar nlopt_set_vector_storage fromIntegral
+
+get_vector_storage :: Opt -> IO Word
+get_vector_storage = getScalar nlopt_get_vector_storage fromIntegral
+
+foreign import ccall "nlopt.h nlopt_set_default_initial_step"
+  nlopt_set_default_initial_step :: NloptOpt -> Ptr CDouble -> IO CInt
+
+foreign import ccall "nlopt.h nlopt_set_initial_step"
+  nlopt_set_initial_step :: NloptOpt -> Ptr CDouble -> IO CInt
+
+foreign import ccall "nlopt.h nlopt_set_initial_step1"
+  nlopt_set_initial_step1 :: NloptOpt -> CDouble -> IO CInt
+
+foreign import ccall "nlopt.h nlopt_get_initial_step"
+  nlopt_get_initial_step :: NloptOpt -> Ptr CDouble -> Ptr CDouble -> IO CInt
+
+set_default_initial_step :: Opt -> V.Vector Double -> IO Result
+set_default_initial_step opt stepvec =
+  withInputVector stepvec $ \stepptr ->
+  withOpt opt $ \o -> parseEnum <$> nlopt_set_default_initial_step o stepptr
+
+set_initial_step :: Opt -> V.Vector Double -> IO Result
+set_initial_step opt stepvec =
+  withInputVector stepvec $ \stepptr ->
+  withOpt opt $ \o -> parseEnum <$> nlopt_set_initial_step o stepptr
+
+set_initial_step1 :: Opt -> Double -> IO Result
+set_initial_step1 = setScalar nlopt_set_initial_step1 realToFrac
+
+get_initial_step :: Opt -> V.Vector Double -> IO (Result, V.Vector Double)
+get_initial_step opt xvec = do
+  mutv <- get_dimension opt >>= MV.new . fromIntegral
+  withOutputVector mutv $ \outptr ->
+    withInputVector xvec $ \inptr ->
+    withOpt opt $ \o -> do
+    result <- parseEnum <$> nlopt_get_initial_step o inptr outptr
+    outvec <- V.unsafeFreeze mutv
+    return (result, outvec)
diff --git a/src/Text/ParseSR.hs b/src/Text/ParseSR.hs
new file mode 100644
--- /dev/null
+++ b/src/Text/ParseSR.hs
@@ -0,0 +1,440 @@
+{-# language OverloadedStrings #-}
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Text.ParseSR
+-- Copyright   :  (c) Fabricio Olivetti 2021 - 2024
+-- License     :  BSD3
+-- Maintainer  :  fabricio.olivetti@gmail.com
+-- Stability   :  experimental
+-- Portability :  ConstraintKinds
+--
+-- Functions to parse a string representing an expression
+--
+-----------------------------------------------------------------------------
+module Text.ParseSR ( parseSR, parseNonTerms, showOutput, SRAlgs(..), Output(..) ) -- parsePat,
+    where
+
+import Control.Applicative ((<|>))
+import Data.Attoparsec.ByteString.Char8
+import Data.Attoparsec.Expr
+import qualified Data.ByteString.Char8 as B
+import Data.Char (toLower)
+import Data.List (sortOn)
+import Data.SRTree
+--import Algorithm.EqSat.DB
+import qualified Data.SRTree.Print as P
+import qualified Data.Map.Strict as Map
+import Data.List.Split ( splitOn )
+
+import Debug.Trace (trace, traceShow)
+
+-- * Data types
+
+-- | Parser of a symbolic regression tree with `Int` variable index and
+-- numerical values represented as `Double`. The numerical values type
+-- can be changed with `fmap`.
+type ParseTree = Parser (Fix SRTree)
+--type ParsePat  = Parser Pattern
+
+-- * Data types and caller functions
+
+-- | Supported algorithms.
+data SRAlgs = TIR | HL | OPERON | BINGO | GOMEA | PYSR | SBP | EPLEX | NEOGP deriving (Show, Read, Enum, Bounded)
+
+-- | Supported outputs.
+data Output = PYTHON | MATH | TIKZ | LATEX deriving (Show, Read, Enum, Bounded)
+
+-- | Returns the corresponding function from Data.SRTree.Print for a given `Output`.
+showOutput :: Output -> Fix SRTree -> String
+showOutput PYTHON = P.showPython
+showOutput MATH   = P.showExpr
+showOutput TIKZ   = P.showTikz
+showOutput LATEX  = P.showLatex
+
+-- | Calls the corresponding parser for a given `SRAlgs`
+--
+-- >>> fmap (showOutput MATH) $ parseSR OPERON "lambda,theta" False "lambda ^ 2 - sin(theta*3*lambda)"
+-- Right "((x0 ^ 2.0) - Sin(((x1 * 3.0) * x0)))"
+parseSR :: SRAlgs -> B.ByteString -> Bool -> B.ByteString -> Either String (Fix SRTree)
+parseSR HL     header reparam = eitherResult . (`feed` "") . parse (parseHL True reparam $ splitHeader header) . putEOL . B.strip
+parseSR BINGO  header reparam = eitherResult . (`feed` "") . parse (parseBingo True reparam $ splitHeader header) . putEOL . B.strip
+parseSR TIR    header reparam = eitherResult . (`feed` "") . parse (parseTIR True reparam $ splitHeader header) . putEOL . B.strip
+parseSR OPERON header reparam = eitherResult . (`feed` "") . parse (parseOperon True reparam $ splitHeader header) . putEOL . B.strip
+parseSR GOMEA  header reparam = eitherResult . (`feed` "") . parse (parseGOMEA True reparam $ splitHeader header) . putEOL . B.strip
+parseSR SBP    header reparam = eitherResult . (`feed` "") . parse (parseGOMEA True reparam $ splitHeader header) . putEOL . B.strip
+parseSR EPLEX  header reparam = eitherResult . (`feed` "") . parse (parseGOMEA True reparam $ splitHeader header) . putEOL . B.strip
+parseSR PYSR   header reparam = eitherResult . (`feed` "") . parse (parsePySR True reparam $ splitHeader header) . putEOL .  B.strip
+parseSR NEOGP  header reparam = eitherResult . (`feed` "") . parse (parseNeoGP True reparam $ splitHeader header) . putEOL .  B.strip
+
+--parsePat :: B.ByteString -> Either String Pattern
+--parsePat = eitherResult . (`feed` "") . parse parsePatExpr . putEOL . B.strip
+
+eitherResult' :: Show r => Result r -> Either String r
+eitherResult' res = trace (show res) $ eitherResult res
+
+-- * Parsers
+
+-- | Creates a parser for a binary operator
+binary :: B.ByteString -> (a -> a -> a) -> Assoc -> Operator B.ByteString a
+binary name fun  = Infix (do{ string (B.cons ' ' (B.snoc name ' ')) <|> string name; pure fun })
+
+-- | Creates a parser for a unary function
+prefix :: B.ByteString -> (a -> a) -> Operator B.ByteString a
+prefix  name fun = Prefix (do{ string name; pure fun })
+
+-- | Envelopes the parser in parens
+parens :: Parser a -> Parser a
+parens e = do{ string "("; e' <- e; string ")"; pure e' } <?> "parens"
+
+-- | Parse an expression using a user-defined parser given by the `Operator` lists containing
+-- the name of the functions and operators of that SR algorithm, a list of parsers `binFuns` for binary functions
+-- a parser `var` for variables, a boolean indicating whether to change floating point values to free
+-- parameters variables, and a list of variable names with their corresponding indexes.
+parseExpr :: Bool -> [[Operator B.ByteString (Fix SRTree)]] -> [ParseTree -> ParseTree] -> ParseTree -> Bool -> [(B.ByteString, Int)] -> ParseTree
+parseExpr relabel table binFuns var reparam header =
+    do e <- if relabel then (relabelParams <$> expr) else expr
+       many1' space
+       pure e
+  where
+    term  = parens expr <|> enclosedAbs expr <|> choice (map ($ expr) binFuns) <|> coef <|> varC <?> "term"
+    expr  = buildExpressionParser table term
+    coef  = if reparam 
+              then do eNumber <- intOrDouble
+                      case eNumber of
+                        Left x  -> pure $ fromIntegral x
+                        Right _ -> pure $ param 0
+              else Fix . Const <$> signed double <?> "const"
+    varC = if null header
+             then var
+             else var <|> varHeader
+
+    varHeader        = choice $ map (uncurry getParserVar) $ sortOn (negate . B.length . fst) header
+    getParserVar k v = (string k <|> enveloped k) >> pure (Fix $ Var v)
+    enveloped s      = (char ' ' <|> char '(') >> string s >> (char ' ' <|> char ')') >> pure ""
+
+enumerate :: [a] -> [(a, Int)]
+enumerate = (`zip` [0..])
+
+splitHeader :: B.ByteString -> [(B.ByteString, Int)]
+splitHeader = enumerate . B.split ','
+
+-- | Tries to parse as an `Int`, if it fails, 
+-- parse as a Double.
+intOrDouble :: Parser (Either Int Double)
+intOrDouble = eitherP parseInt (signed double)
+  where
+      parseInt :: Parser Int
+      parseInt = do x <- signed decimal
+                    c <- peekChar
+                    case c of                      
+                      Just '.' -> digit >> pure 0
+                      Just 'e' -> digit >> pure 0
+                      Just 'E' -> digit >> pure 0
+                      _   -> pure x
+
+putEOL :: B.ByteString -> B.ByteString
+putEOL bs | B.last bs == '\n' = bs
+          | otherwise         = B.snoc bs '\n'
+
+-- * Special case functions
+
+-- | analytic quotient
+aq :: Fix SRTree -> Fix SRTree -> Fix SRTree
+aq x y = x / sqrt (1 + y ** 2)
+
+log1p :: Fix SRTree -> Fix SRTree
+log1p x = log (1 + x)
+
+log10 :: Fix SRTree -> Fix SRTree
+log10 x = log x / log 10
+
+log2 :: Fix SRTree -> Fix SRTree
+log2 x = log x / log 2
+
+cbrt :: Fix SRTree -> Fix SRTree
+cbrt x = x ** (1/3)
+
+cube :: Fix SRTree -> Fix SRTree
+cube x = Fix $ Uni Cube x
+
+sqrtabs :: Fix SRTree -> Fix SRTree
+sqrtabs x = Fix $ Uni SqrtAbs x
+
+logabs :: Fix SRTree -> Fix SRTree
+logabs x = Fix $ Uni LogAbs x
+
+-- Parse `abs` functions as | x |
+enclosedAbs :: Num a => Parser a -> Parser a
+enclosedAbs expr = do char '|'
+                      e <- expr
+                      char '|'
+                      pure $ abs e
+
+-- | Parser for binary functions
+binFun :: B.ByteString -> (a -> a -> a) -> Parser a -> Parser a
+binFun name f expr = do string name
+                        many' space >> char '(' >> many' space
+                        e1 <- expr
+                        many' space >> char ',' >> many' space -- many' space >> char ',' >> many' space
+                        e2 <- expr
+                        many' space >> char ')'
+                        pure $ f e1 e2 
+
+-- * Custom parsers for SR algorithms
+
+-- | parser for Transformation-Interaction-Rational.
+parseTIR :: Bool -> Bool -> [(B.ByteString, Int)] -> ParseTree
+parseTIR b = parseExpr b (prefixOps : binOps) binFuns var
+  where
+    binFuns   = [ ]
+    prefixOps = map (uncurry prefix)
+                [   ("id", id), ("abs", abs)
+                  , ("sinh", sinh), ("cosh", cosh), ("tanh", tanh)
+                  , ("sin", sin), ("cos", cos), ("tan", tan)
+                  , ("asinh", asinh), ("acosh", acosh), ("atanh", atanh)
+                  , ("asin", asin), ("acos", acos), ("atan", atan)
+                  , ("sqrtabs", sqrtabs), ("sqrt", sqrt), ("cbrt", cbrt), ("square", (**2))
+                  , ("logabs", logabs), ("log", log), ("exp", exp), ("cube", cube), ("recip", recip)
+                  , ("Id", id), ("Abs", abs)
+                  , ("Sinh", sinh), ("Cosh", cosh), ("Tanh", tanh)
+                  , ("Sin", sin), ("Cos", cos), ("Tan", tan)
+                  , ("ASinh", asinh), ("ACosh", acosh), ("ATanh", atanh)
+                  , ("ASin", asin), ("ACos", acos), ("ATan", atan)
+                  , ("SqrtAbs", sqrtabs), ("Sqrt", sqrt), ("Cbrt", cbrt), ("Square", (**2))
+                  , ("LogAbs", logabs), ("Log", log), ("Exp", exp), ("Recip", recip), ("Cube", cube)
+                ]
+    binOps = [[binary "^" (**) AssocLeft], [binary "**" (**) AssocLeft]
+            , [binary "*" (*) AssocLeft, binary "/" (/) AssocLeft]
+            , [binary "+" (+) AssocLeft, binary "-" (-) AssocLeft]
+            , [binary "|**|" powabs AssocLeft], [binary "aq" aq AssocLeft]
+            ]
+    powabs l r = Fix $ Bin PowerAbs l r
+    aq l r = Fix $ Bin AQ l r
+
+    var = do char 'x'
+             ix <- decimal
+             pure $ Fix $ Var ix
+          <|> do char 't'
+                 ix <- decimal
+                 pure $ Fix $ Param ix
+          <?> "var"
+
+-- | parser for NeoGP
+parseNeoGP :: Bool -> Bool -> [(B.ByteString, Int)] -> ParseTree
+parseNeoGP b = parseExpr b (prefixOps : binOps) binFuns var
+  where
+    binFuns   = [ ]
+    prefixOps = map (uncurry prefix)
+                [   ("id", id), ("abs", abs)
+                  , ("sinh", sinh), ("cosh", cosh), ("tanh", tanh)
+                  , ("sin", sin), ("cos", cos), ("tan", tan)
+                  , ("asinh", asinh), ("acosh", acosh), ("atanh", atanh)
+                  , ("asin", asin), ("acos", acos), ("atan", atan)
+                  , ("sqrtabs", sqrtabs), ("sqrt", sqrt), ("cbrt", cbrt), ("square", (**2))
+                  , ("logabs", logabs), ("log", log), ("exp", exp), ("cube", cube), ("recip", recip)
+                  , ("Id", id), ("Abs", abs)
+                  , ("Sinh", sinh), ("Cosh", cosh), ("Tanh", tanh)
+                  , ("Sin", sin), ("Cos", cos), ("Tan", tan)
+                  , ("ASinh", asinh), ("ACosh", acosh), ("ATanh", atanh)
+                  , ("ASin", asin), ("ACos", acos), ("ATan", atan)
+                  , ("SqrtAbs", sqrtabs), ("Sqrt", sqrt), ("Cbrt", cbrt), ("Square", (**2))
+                  , ("LogAbs", logabs), ("Log", log), ("Exp", exp), ("Recip", recip), ("Cube", cube)
+                ]
+    binOps = [[binary "^" (**) AssocLeft], [binary "**" (**) AssocLeft]
+            , [binary "*" (*) AssocLeft, binary "/" (/) AssocLeft]
+            , [binary "+" (+) AssocLeft, binary "-" (-) AssocLeft]
+            , [binary "|**|" powabs AssocLeft], [binary "aq" aq AssocLeft]
+            ]
+    powabs l r = Fix $ Bin PowerAbs l r
+    aq l r = Fix $ Bin AQ l r
+
+    var = do char 'x'
+             ix <- decimal
+             pure $ Fix $ Var (ix-1)
+          <|> do char 'p'
+                 ix <- decimal
+                 pure $ Fix $ Param (ix-1)
+          <?> "var"
+
+-- | parser for Operon.
+parseOperon :: Bool -> Bool -> [(B.ByteString, Int)] -> ParseTree
+parseOperon b = parseExpr b (prefixOps : binOps) binFuns var
+  where
+    binFuns   = [ binFun "pow" (**) ]
+    prefixOps = map (uncurry prefix)
+                [ ("abs", abs), ("cbrt", cbrt)
+                , ("acos", acos), ("cosh", cosh), ("cos", cos)
+                , ("asin", asin), ("sinh", sinh), ("sin", sin)
+                , ("exp", exp), ("log", log)
+                , ("sqrt", sqrt), ("square", (**2))
+                , ("atan", atan), ("tanh", tanh), ("tan", tan)
+                ]
+    binOps = [[binary "^" (**) AssocLeft]
+            , [binary "*" (*) AssocLeft, binary "/" (/) AssocLeft]
+            , [binary "+" (+) AssocLeft, binary "-" (-) AssocLeft]
+            ]
+    var = do char 'X' <|> char 'x'
+             ix <- decimal
+             pure $ Fix $ Var (ix - 1) -- Operon is not 0-based
+          <?> "var"
+
+-- | parser for HeuristicLab.
+parseHL :: Bool -> Bool -> [(B.ByteString, Int)] -> ParseTree
+parseHL b = parseExpr b (prefixOps : binOps) binFuns var
+  where
+    binFuns   = [ binFun "aq" aq ]
+    prefixOps = map (uncurry prefix)
+                [ ("logabs", log.abs), ("sqrtabs", sqrt.abs) -- the longer versions should come first
+                , ("abs", abs), ("exp", exp), ("log", log)
+                , ("sqrt", sqrt), ("sqr", (**2)), ("cube", (**3))
+                , ("cbrt", cbrt), ("sin", sin), ("cos", cos)
+                , ("tan", tan), ("tanh", tanh)
+                ]
+    binOps = [[binary "^" (**) AssocLeft]
+            , [binary "*" (*) AssocLeft, binary "/" (/) AssocLeft]
+            , [binary "+" (+) AssocLeft, binary "-" (-) AssocLeft]
+            ]
+    var = do char 'x'
+             ix <- decimal
+             pure $ Fix $ Var ix
+          <?> "var"
+
+-- | parser for Bingo
+parseBingo :: Bool -> Bool -> [(B.ByteString, Int)] -> ParseTree
+parseBingo b = parseExpr b (prefixOps : binOps) binFuns var
+  where
+    binFuns = []
+    prefixOps = map (uncurry prefix)
+                [ ("abs", abs), ("exp", exp), ("log", log.abs)
+                , ("sqrt", sqrt.abs)
+                , ("sinh", sinh), ("cosh", cosh)
+                , ("sin", sin), ("cos", cos)
+                ]
+    binOps = [[binary "^" (**) AssocLeft]
+            , [binary "/" (/) AssocLeft, binary "" (*) AssocLeft]
+            , [binary "+" (+) AssocLeft, binary "-" (-) AssocLeft]
+            ]
+    var = do string "X_"
+             ix <- decimal
+             pure $ Fix $ Var ix
+          <?> "var"
+
+-- | parser for GOMEA
+parseGOMEA :: Bool -> Bool -> [(B.ByteString, Int)] -> ParseTree
+parseGOMEA b = parseExpr b (prefixOps : binOps) binFuns var
+  where
+    binFuns = []
+    prefixOps = map (uncurry prefix)
+                [ ("exp", exp), ("plog", log.abs)
+                , ("sqrt", sqrt.abs)
+                , ("sin", sin), ("cos", cos)
+                ]
+    binOps = [[binary "^" (**) AssocLeft]
+            , [binary "/" (/) AssocLeft, binary "*" (*) AssocLeft, binary "aq" aq AssocLeft]
+            , [binary "+" (+) AssocLeft, binary "-" (-) AssocLeft]
+            ]
+    var = do string "x"
+             ix <- decimal
+             pure $ Fix $ Var ix
+          <?> "var"
+
+-- | parser for PySR
+parsePySR :: Bool -> Bool -> [(B.ByteString, Int)] -> ParseTree
+parsePySR b = parseExpr b (prefixOps : binOps) binFuns var
+  where
+    binFuns   = [ binFun "pow" (**) ]
+    prefixOps = map (uncurry prefix)
+                [ ("abs", abs), ("exp", exp)
+                , ("square", (**2)), ("cube", (**3)), ("neg", negate)
+                , ("acosh_abs", acosh . (+1) . abs), ("acosh", acosh), ("asinh", asinh)
+                , ("acos", acos), ("asin", asin), ("atan", atan)
+                , ("sqrt_abs", sqrt.abs), ("sqrt", sqrt)
+                , ("sinh", sinh), ("cosh", cosh), ("tanh", tanh)
+                , ("sin", sin), ("cos", cos), ("tan", tan)
+                , ("log10", log10), ("log2", log2), ("log1p", log1p) 
+                , ("log_abs", log.abs), ("log10_abs", log10 . abs)
+                , ("log", log)
+                ]
+    binOps = [[binary "^" (**) AssocLeft]
+            , [binary "/" (/) AssocLeft, binary "*" (*) AssocLeft]
+            , [binary "+" (+) AssocLeft, binary "-" (-) AssocLeft]
+            ]
+    var = do string "x"
+             ix <- decimal
+             pure $ Fix $ Var ix
+          <?> "var"
+{-
+-- parse a pattern expression
+parsePatExpr ::  ParsePat
+parsePatExpr = parsePattern (prefixOps : binOps) binFuns var
+  where
+    binFuns   = [ ]
+    prefixOps = map (uncurry prefix)
+                [   ("id", id), ("abs", abs)
+                  , ("sinh", sinh), ("cosh", cosh), ("tanh", tanh)
+                  , ("sin", sin), ("cos", cos), ("tan", tan)
+                  , ("asinh", asinh), ("acosh", acosh), ("atanh", atanh)
+                  , ("asin", asin), ("acos", acos), ("atan", atan)
+                  , ("sqrtabs", sqrtabs'), ("sqrt", sqrt), ("cbrt", cbrt'), ("square", (**2))
+                  , ("logabs", logabs'), ("log", log), ("exp", exp), ("cube", cube'), ("recip", recip')
+                  , ("Id", id), ("Abs", abs)
+                  , ("Sinh", sinh), ("Cosh", cosh), ("Tanh", tanh)
+                  , ("Sin", sin), ("Cos", cos), ("Tan", tan)
+                  , ("ASinh", asinh), ("ACosh", acosh), ("ATanh", atanh)
+                  , ("ASin", asin), ("ACos", acos), ("ATan", atan)
+                  , ("SqrtAbs", sqrtabs'), ("Sqrt", sqrt), ("Cbrt", cbrt'), ("Square", (**2))
+                  , ("LogAbs", logabs'), ("Log", log), ("Exp", exp), ("Recip", recip'), ("Cube", cube')
+                  , ("|log|", logabs'), ("|Log|", logabs'), ("|sqrt|", sqrtabs'), ("|Sqrt|", sqrtabs')
+                  , ("√", sqrt), ("|√|", sqrtabs')
+                ]
+    binOps = [[binary "^" (**) AssocLeft], [binary "**" (**) AssocLeft]
+            , [binary "*" (*) AssocLeft, binary "/" (/) AssocLeft]
+            , [binary "+" (+) AssocLeft, binary "-" (-) AssocLeft]
+            , [binary "|**|" powabs AssocLeft], [binary "|^|" powabs AssocLeft]
+            , [binary "aq" aq AssocLeft], [binary "|/|" aq AssocLeft]
+            ]
+    powabs l r = Fixed $ Bin PowerAbs l r
+    aq l r = Fixed $ Bin AQ l r
+    logabs' t = Fixed $ Uni LogAbs t
+    sqrtabs' t = Fixed $ Uni SqrtAbs t
+    cbrt' t = Fixed $ Uni Cbrt t
+    cube' t = Fixed $ Uni Cube t
+    recip' t = Fixed $ Uni Recip t
+
+    var = do char 'x'
+             ix <- decimal
+             pure $ Fixed $ Var ix
+          <|> do char 't'
+                 ix <- decimal
+                 pure $ Fixed $ Param ix
+          <|> do char 'v'
+                 ix <- decimal
+                 pure $ VarPat (toEnum $ ix+65)
+          <?> "var"
+
+parsePattern :: [[Operator B.ByteString Pattern]] -> [ParsePat -> ParsePat] -> ParsePat -> ParsePat
+parsePattern table binFuns var =
+    do e <- expr
+       many1' space
+       pure e
+  where
+    term  = parens expr <|> enclosedAbs expr <|> choice (map ($ expr) binFuns) <|> coef <|> var <?> "term"
+    expr  = buildExpressionParser table term
+    coef  = Fixed . Const <$> signed double <?> "const"
+
+    getParserVar k v = (string k <|> enveloped k) >> pure (Fix $ Var v)
+    enveloped s      = (char ' ' <|> char '(') >> string s >> (char ' ' <|> char ')') >> pure ""
+
+    -}
+-- * Parse the non-terminal nodes into a SRTree () value
+parseNonTerms :: String -> [SRTree ()]
+parseNonTerms = Prelude.map toNonTerm . splitOn ","
+  where
+    binTerms = Map.fromList [ (Prelude.map toLower (show op), op) | op <- [Add .. AQ]]
+    uniTerms = Map.fromList [ (Prelude.map toLower (show f), f) | f <- [Abs .. Cube]]
+    toNonTerm xs' = let xs = Prelude.map toLower xs'
+                    in case binTerms Map.!? xs of
+                          Just op -> Bin op () ()
+                          Nothing -> case uniTerms Map.!? xs of
+                                          Just f -> Uni f ()
+                                          Nothing -> error $ "invalid non-terminal " <> show xs
diff --git a/src/Text/ParseSR/IO.hs b/src/Text/ParseSR/IO.hs
new file mode 100644
--- /dev/null
+++ b/src/Text/ParseSR/IO.hs
@@ -0,0 +1,73 @@
+{-# language LambdaCase #-}
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Text.ParseSR.IO
+-- Copyright   :  (c) Fabricio Olivetti 2021 - 2024
+-- License     :  BSD3
+-- Maintainer  :  fabricio.olivetti@gmail.com
+-- Stability   :  experimental
+-- Portability :  ConstraintKinds
+--
+-- Functions to parse multiple expressions from stdin or a text file.
+--
+-----------------------------------------------------------------------------
+module Text.ParseSR.IO ( withInput, withOutput, withOutputDebug )
+    where
+
+-- import Data.SRTree.EqSat1
+--import Algorithm.EqSat.Simplify ( simplifyEqSatDefault )
+import Control.Monad (forM_, unless)
+import qualified Data.ByteString.Char8 as B
+import Data.SRTree
+import Data.SRTree.Recursion (Fix (..))
+import System.IO
+import Text.ParseSR (Output, SRAlgs, parseSR, showOutput)
+
+-- | given a filename, the symbolic regression algorithm,  a string of variables name, 
+-- and two booleans indicating whether to convert float values to parameters and 
+-- whether to simplify the expression or not, it will read the file and parse everything 
+-- returning a list of either an error message or a tree.
+--
+-- empty filename defaults to stdin 
+withInput :: String -> SRAlgs -> String -> Bool -> Bool -> IO [Either String (Fix SRTree)]
+withInput fname sr hd param simpl = do
+  h <- if null fname then pure stdin else openFile fname ReadMode
+  contents <- hGetLines h 
+  let myParserFun = parseSR sr (B.pack hd) param . B.pack
+      -- myParser = if simpl then fmap simplifyEqSat . myParserFun else myParserFun
+      myParser = myParserFun -- if simpl then fmap simplifyEqSatDefault . myParserFun else myParserFun
+      es = map myParser $ filter (not . null) contents
+  unless (null fname) $ hClose h
+  pure es
+
+-- | outputs a list of either error or trees to a file using the Output format. 
+--
+-- empty filename defaults to stdout 
+withOutput :: String -> Output -> [Either String (Fix SRTree)] -> IO ()
+withOutput fname output exprs = do
+  h <- if null fname then pure stdout else openFile fname WriteMode
+  forM_ exprs $ \case 
+                   Left  err -> hPutStrLn h $ "invalid expression: " <> err
+                   Right ex  -> hPutStrLn h (showOutput output ex)
+  unless (null fname) $ hClose h
+
+-- | debug version of output function to check the invalid parsers
+withOutputDebug :: String -> Output -> [Either String (Fix SRTree, Fix SRTree)] -> IO ()
+withOutputDebug fname output exprs = do
+  h <- if null fname then pure stdout else openFile fname WriteMode
+  forM_ exprs $ \case 
+                   Left  err      -> hPutStrLn h $ "invalid expression: " <> err
+                   Right (t1, t2) -> do 
+                                       hPutStrLn h ("First: " <> showOutput output t1)
+                                       hPutStrLn h ("Second: " <> showOutput output t2)
+                                       hFlush h
+  unless (null fname) $ hClose h
+
+hGetLines :: Handle -> IO [String]
+hGetLines h = do
+  done <- hIsEOF h
+  if done
+    then return []
+    else do
+      line <- hGetLine h
+      (line :) <$> hGetLines h
diff --git a/srtree.cabal b/srtree.cabal
--- a/srtree.cabal
+++ b/srtree.cabal
@@ -1,66 +1,235 @@
 cabal-version: 1.12
 
--- This file has been generated from package.yaml by hpack version 0.35.2.
+-- This file has been generated from package.yaml by hpack version 0.39.6.
 --
 -- see: https://github.com/sol/hpack
 
-name:           srtree
-version:        1.0.0.5
-synopsis:       A general framework to work with Symbolic Regression expression trees.
-description:    A Symbolic Regression Tree data structure to work with mathematical expressions with support to first order derivative and simplification;
-category:       Math, Data, Data Structures
-homepage:       https://github.com/folivetti/srtree#readme
-bug-reports:    https://github.com/folivetti/srtree/issues
-author:         Fabricio Olivetti de França
-maintainer:     fabricio.olivetti@gmail.com
-copyright:      2023 Fabricio Olivetti de França
-license:        BSD3
-license-file:   LICENSE
-build-type:     Simple
+name:               srtree
+version:            3.0.0.2
+synopsis:           A general library to work with Symbolic Regression expression trees.
+description:        A Symbolic Regression Tree data structure to work with mathematical expressions with support to first order derivative and simplification;
+license:            BSD3
+license-file:       LICENSE
+author:             Fabricio Olivetti de França
+maintainer:         fabricio.olivetti@gmail.com
+copyright:          2023 Fabricio Olivetti de França
+category:           Math, Data, Data Structures
+homepage:           https://github.com/folivetti/srtree#readme
+bug-reports:        https://github.com/folivetti/srtree/issues
+build-type:         Simple
 extra-source-files:
-    README.md
-    ChangeLog.md
+      README.md
+      ChangeLog.md
 
 source-repository head
-  type: git
-  location: https://github.com/folivetti/srtree
+    type: git
+    location: https://github.com/folivetti/srtree
 
 library
-  exposed-modules:
-      Data.SRTree
-      Data.SRTree.Internal
-      Data.SRTree.Print
-      Data.SRTree.Random
-      Data.SRTree.Recursion
-  other-modules:
-      Paths_srtree
-  hs-source-dirs:
-      src
-  build-depends:
-      base >=4.16 && <5
-    , containers ==0.6.*
-    , dlist ==1.0.*
-    , mtl >=2.2 && <2.4
-    , random ==1.2.*
-    , vector >=0.12 && <0.14
-  default-language: Haskell2010
+    exposed-modules:
+          Algorithm.EqSat
+          Algorithm.EqSat.Build
+          Algorithm.EqSat.DB
+          Algorithm.EqSat.Egraph
+          Algorithm.EqSat.Info
+          Algorithm.EqSat.Queries
+          Algorithm.EqSat.SearchSR
+          Algorithm.EqSat.Simplify
+          Algorithm.EqSat.Store
+          Algorithm.SRTree.AD
+          Algorithm.SRTree.AD.CompiledAD
+          Algorithm.SRTree.AD.Unboxed
+          Algorithm.SRTree.Compile
+          Algorithm.SRTree.ConfidenceIntervals
+          Algorithm.SRTree.Likelihoods
+          Algorithm.SRTree.ModelSelection
+          Algorithm.SRTree.NonlinearOpt
+          Algorithm.SRTree.Utils
+          Data.SRTree
+          Data.SRTree.Datasets
+          Data.SRTree.Derivative
+          Data.SRTree.Eval
+          Data.SRTree.Internal
+          Data.SRTree.Print
+          Data.SRTree.Random
+          Data.SRTree.Recursion
+          Numeric.Optimization.NLOPT
+          Numeric.Optimization.NLOPT.Bindings
+          Text.ParseSR
+          Text.ParseSR.IO
+    other-modules:
+          Paths_srtree
+    build-depends:
+          async >=2.2 && <2.3
+        , attoparsec >=0.14.4 && <0.15
+        , attoparsec-expr >=0.1.1.2 && <0.2
+        , base >=4.19 && <5
+        , binary >=0.8 && <0.9
+        , bytestring >=0.11 && <0.13
+        , containers >=0.6.7 && <0.9
+        , deepseq >=1.4 && <1.6
+        , directory >=1.3 && <1.4
+        , exceptions >=0.10 && <0.11
+        , filepath >=1.4.0.0 && <1.6
+        , hashable >=1.4 && <1.6
+        , ieee754 >=0.8 && <0.9
+        , lens >=5.0 && <6
+        , mtl >=2.2 && <2.4
+        ,           parallel >=3.2 && <3.4
+        , primitive >=0.8 && <0.10
+        , random >=1.2 && <1.4
+        , split >=0.2.5 && <0.3
+        , statistics >=0.15 && <0.17
+        , time >=1.9 && <1.15
+        , unordered-containers >=0.2 && <0.3
+        , vector >=0.12 && <0.14
+        , zlib >=0.6.3 && <0.8
+    hs-source-dirs:
+          src
+    ghc-options: -O2 -fwarn-incomplete-patterns -fspec-constr
+    extra-libraries:
+          nlopt
+    default-language: Haskell2010
 
+executable bench
+    main-is: Main.hs
+    other-modules:
+          Paths_srtree
+    hs-source-dirs:
+          apps/Bench
+    ghc-options: -threaded -rtsopts -with-rtsopts=-N -O2 -fllvm -pgmlo opt-20 -pgmlc llc-20 -optlo-O3 -optlc-mcpu=native -mavx2 -mfma -fspec-constr -fmax-simplifier-iterations=20 -fexpose-all-unfoldings
+    build-depends:
+          async >=2.2 && <2.3
+        , attoparsec >=0.14.4 && <0.15
+        , attoparsec-expr >=0.1.1.2 && <0.2
+        , base >=4.19 && <5
+        , binary >=0.8 && <0.9
+        , bytestring >=0.11 && <0.13
+        , containers >=0.6.7 && <0.9
+        , criterion >=1.5 && <2
+        , deepseq >=1.4 && <1.6
+        , directory >=1.3 && <1.4
+        , exceptions >=0.10 && <0.11
+        , filepath >=1.4.0.0 && <1.6
+        , hashable >=1.4 && <1.6
+        , ieee754 >=0.8 && <0.9
+        , lens >=5.0 && <6
+        , mtl >=2.2 && <2.4
+        ,           parallel >=3.2 && <3.4
+        , primitive >=0.8 && <0.10
+        , random >=1.2 && <1.4
+        , split >=0.2.5 && <0.3
+        , srtree
+        , statistics >=0.15 && <0.17
+        , unordered-containers >=0.2 && <0.3
+        , vector >=0.12 && <0.14
+        , zlib >=0.6.3 && <0.8
+    default-language: Haskell2010
+
+executable bench-eqsat
+    main-is: Main.hs
+    other-modules:
+          Paths_srtree
+    hs-source-dirs:
+          apps/BenchEqSat
+    ghc-options: -threaded -rtsopts -with-rtsopts=-N -O2
+    build-depends:
+          async >=2.2 && <2.3
+        , attoparsec >=0.14.4 && <0.15
+        , attoparsec-expr >=0.1.1.2 && <0.2
+        , base >=4.19 && <5
+        , binary >=0.8 && <0.9
+        , bytestring >=0.11 && <0.13
+        , containers >=0.6.7 && <0.9
+        , criterion >=1.5 && <2
+        , deepseq >=1.4 && <1.6
+        , directory >=1.3 && <1.4
+        , exceptions >=0.10 && <0.11
+        , filepath >=1.4.0.0 && <1.6
+        , hashable >=1.4 && <1.6
+        , ieee754 >=0.8 && <0.9
+        , lens >=5.0 && <6
+        , mtl >=2.2 && <2.4
+        ,           parallel >=3.2 && <3.4
+        , primitive >=0.8 && <0.10
+        , random >=1.2 && <1.4
+        , split >=0.2.5 && <0.3
+        , srtree
+        , statistics >=0.15 && <0.17
+        , unordered-containers >=0.2 && <0.3
+        , vector >=0.12 && <0.14
+        , zlib >=0.6.3 && <0.8
+    default-language: Haskell2010
+
+executable srtree-report
+    main-is: Main.hs
+    other-modules:
+          Paths_srtree
+    hs-source-dirs:
+          apps/Report
+    ghc-options: -threaded -rtsopts -with-rtsopts=-N -O2
+    build-depends:
+          async >=2.2 && <2.3
+        , attoparsec >=0.14.4 && <0.15
+        , attoparsec-expr >=0.1.1.2 && <0.2
+        , base >=4.19 && <5
+        , binary >=0.8 && <0.9
+        , bytestring >=0.11 && <0.13
+        , containers >=0.6.7 && <0.9
+        , deepseq >=1.4 && <1.6
+        , directory >=1.3 && <1.4
+        , exceptions >=0.10 && <0.11
+        , filepath >=1.4.0.0 && <1.6
+        , hashable >=1.4 && <1.6
+        , ieee754 >=0.8 && <0.9
+        , lens >=5.0 && <6
+        , mtl >=2.2 && <2.4
+        , optparse-applicative >=0.16 && <0.20
+        ,           parallel >=3.2 && <3.4
+        , primitive >=0.8 && <0.10
+        , random >=1.2 && <1.4
+        , split >=0.2.5 && <0.3
+        , srtree
+        , statistics >=0.15 && <0.17
+        , unordered-containers >=0.2 && <0.3
+        , vector >=0.12 && <0.14
+        , zlib >=0.6.3 && <0.8
+    default-language: Haskell2010
+
 test-suite srtree-test
-  type: exitcode-stdio-1.0
-  main-is: Spec.hs
-  other-modules:
-      Paths_srtree
-  hs-source-dirs:
-      test
-  ghc-options: -threaded -rtsopts -with-rtsopts=-N
-  build-depends:
-      HUnit
-    , ad
-    , base >=4.16 && <5
-    , containers ==0.6.*
-    , dlist ==1.0.*
-    , mtl >=2.2 && <2.4
-    , random ==1.2.*
-    , srtree
-    , vector >=0.12 && <0.14
-  default-language: Haskell2010
+    type: exitcode-stdio-1.0
+    main-is: Spec.hs
+    other-modules:
+          EqSatTests
+          StoreTests
+          Paths_srtree
+    hs-source-dirs:
+          test
+    ghc-options: -threaded -rtsopts -with-rtsopts=-N
+    build-depends:
+          HUnit >=1.6 && <1.7
+        , async >=2.2 && <2.3
+        , attoparsec >=0.14.4 && <0.15
+        , attoparsec-expr >=0.1.1.2 && <0.2
+        , base >=4.19 && <5
+        , binary >=0.8 && <0.9
+        , bytestring >=0.11 && <0.13
+        , containers >=0.6.7 && <0.9
+        , deepseq >=1.4 && <1.6
+        , directory >=1.3 && <1.4
+        , exceptions >=0.10 && <0.11
+        , filepath >=1.4.0.0 && <1.6
+        , hashable >=1.4 && <1.6
+        , ieee754 >=0.8 && <0.9
+        , lens >=5.0 && <6
+        , mtl >=2.2 && <2.4
+        ,           parallel >=3.2 && <3.4
+        , primitive >=0.8 && <0.10
+        , random >=1.2 && <1.4
+        , split >=0.2.5 && <0.3
+        , srtree
+        , statistics >=0.15 && <0.17
+        , unordered-containers >=0.2 && <0.3
+        , vector >=0.12 && <0.14
+        , zlib >=0.6.3 && <0.8
+    default-language: Haskell2010
diff --git a/test/EqSatTests.hs b/test/EqSatTests.hs
new file mode 100644
--- /dev/null
+++ b/test/EqSatTests.hs
@@ -0,0 +1,630 @@
+{-# LANGUAGE OverloadedStrings #-}
+
+module EqSatTests where
+
+import Test.HUnit
+import Data.SRTree
+import Data.SRTree.Print (showExpr)
+import qualified Data.IntSet as IntSet
+import qualified Data.IntMap as IntMap
+import qualified Data.Map as Map
+import qualified Data.HashSet as Set
+import qualified Data.Vector.Unboxed as VU
+import qualified Data.Set as RangeSet
+import Algorithm.EqSat
+import Algorithm.EqSat.Egraph
+import Algorithm.EqSat.Build
+import Algorithm.EqSat.DB
+import Algorithm.EqSat.Info
+import Algorithm.EqSat.Queries
+import Algorithm.EqSat.Simplify (simplifyEqSatDefault, rewrites, rewritesParams)
+import Control.Monad.State.Strict
+import Control.Monad (forM_)
+import Control.Monad.Identity
+import Data.List (nub, sort)
+
+eps :: Double
+eps = 1e-9
+
+myCost :: SRTree Int -> Int
+myCost (Var _)     = 1
+myCost (Const _)   = 1
+myCost (Param _)   = 1
+myCost (Bin _ l r) = 2 + l + r
+myCost (Uni _ t)   = 3 + t
+
+runEG :: EGraphST Identity a -> (a, EGraph)
+runEG m = runIdentity $ runStateT m emptyGraph
+
+evalEG :: EGraphST Identity a -> a
+evalEG m = runIdentity $ evalStateT m emptyGraph
+
+-- | Test 1: fromTree with a leaf (variable)
+test_fromTree_var :: Test
+test_fromTree_var = TestCase $ do
+  let tree = var 0
+      (eid, eg) = runEG $ fromTree myCost tree
+  assertBool "fromTree var: eid should be >= 0" (eid >= 0)
+  assertBool "fromTree var: eclass exists" (IntMap.member eid (_eClass eg))
+  let ec = _eClass eg IntMap.! eid
+  assertBool "fromTree var: eclass has nodes" (not $ null (_eNodes ec))
+  let bestNode = head $ Set.toList (_eNodes ec)
+  assertEqual "fromTree var: best is Var 0" (EVar 0) bestNode
+
+-- | Test 2: fromTree with a binary expression
+test_fromTree_bin :: Test
+test_fromTree_bin = TestCase $ do
+  let tree = var 0 + constv 1.0
+      (eid, eg) = runEG $ fromTree myCost tree
+  assertBool "fromTree bin: eid >= 0" (eid >= 0)
+  let ec = _eClass eg IntMap.! eid
+  assertBool "fromTree bin: eclass has nodes" (not $ null (_eNodes ec))
+
+-- | Test 3: Canonical identity (an e-class should be its own canonical)
+test_canonical_identity :: Test
+test_canonical_identity = TestCase $ do
+  let (eid, eg) = runEG $ fromTree myCost (var 0)
+      (canId, _) = runIdentity $ runStateT (canonical eid) eg
+  assertEqual "canonical of fresh id is itself" eid canId
+
+-- | Test 4: canonize canonizes children
+test_canonize :: Test
+test_canonize = TestCase $ do
+  let (eid, eg) = runEG $ fromTree myCost (var 0 + constv 1.0)
+      (canNode, _) = runIdentity $ runStateT (do
+        ec <- getEClass eid
+        let someNode = head $ Set.toList (_eNodes ec)
+        canonize someNode) eg
+  -- All children should be canonical now
+  let children = eChildren canNode
+  forM_ children $ \c -> do
+    let (canC, _) = runIdentity $ runStateT (canonical c) eg
+    assertEqual "canonize: child is canonical" c canC
+
+-- | Test 5: Adding duplicate e-node returns existing e-class
+test_add_duplicate :: Test
+test_add_duplicate = TestCase $ do
+  let tree = constv 2.0
+      (eid1, eg1) = runEG $ fromTree myCost tree
+      (eid2, eg2) = runEG' eg1 $ add myCost (EConst 2.0)
+  assertEqual "add duplicate returns same eclass" eid1 eid2
+  where
+    runEG' eg m = runIdentity $ runStateT m eg
+
+-- | Test 6: Merge two distinct e-classes
+test_merge :: Test
+test_merge = TestCase $ do
+  let (eid1, eg1) = runEG $ fromTree myCost (var 0)
+      (eid2, eg2) = runIdentity $ runStateT (fromTree myCost (var 1)) eg1
+  assertBool "merge: eid1 and eid2 start different" (eid1 /= eid2)
+  let (mergedId, eg3) = runIdentity $ runStateT (merge myCost eid1 eid2) eg2
+      can1 = _canonicalMap eg3 IntMap.! eid1
+      can2 = _canonicalMap eg3 IntMap.! eid2
+  assertEqual "merge: canonicals are equal" can1 can2
+  assertEqual "merge: leader matches canonical" mergedId can1
+
+-- | Test 7: Rebuild after add
+test_rebuild :: Test
+test_rebuild = TestCase $ do
+  let tree = var 0 + constv 1.0
+      eg = snd $ runEG $ do
+        _ <- fromTree myCost tree
+        rebuild myCost
+  assertBool "rebuild: eNodeToEClass non-empty" (not $ null (_eNodeToEClass eg))
+  assertBool "rebuild: worklist empty" (null (_worklist (_eDB eg)))
+  assertBool "rebuild: analysis empty" (null (_analysis (_eDB eg)))
+
+-- | Test 8: Basic pattern matching
+test_match :: Test
+test_match = TestCase $ do
+  let tree = var 0 + constv 1.0
+      pat = Fixed (Bin Add (VarPat 'x') (VarPat 'y'))
+      (substs, _) = runEG $ do
+        _ <- fromTree myCost tree
+        match pat
+  assertBool "match: should have at least one substitution" (not $ null substs)
+
+-- | Test 9: Extraction (getBestExpr)
+test_getBestExpr :: Test
+test_getBestExpr = TestCase $ do
+  let tree = var 0 + constv 1.0
+      (extracted, _) = runEG $ do
+        eid <- fromTree myCost tree
+        getBestExpr eid
+  assertEqual "getBestExpr preserves structure" (showExpr tree) (showExpr extracted)
+
+-- | Test 10: Equality saturation with x + 0 = x
+test_eqsat_x_plus_0 :: Test
+test_eqsat_x_plus_0 = TestCase $ do
+  let tree     = var 0 + constv 0.0
+      rule     = "a" + 0 :=> "a"
+      (best, _) = runEG $ eqSat tree [rule] myCost 5
+  assertEqual "eqSat: x+0 = x" (showExpr (var 0)) (showExpr best)
+
+-- | Test 11: Equality saturation with x * 1 = x
+test_eqsat_x_times_1 :: Test
+test_eqsat_x_times_1 = TestCase $ do
+  let tree     = var 0 * constv 1.0
+      rule     = "a" * 1 :=> "a"
+      (best, _) = runEG $ eqSat tree [rule] myCost 5
+  assertEqual "eqSat: x*1 = x" (showExpr (var 0)) (showExpr best)
+
+-- | Test 12: Fitness and theta storage round-trip
+test_fitness_theta :: Test
+test_fitness_theta = TestCase $ do
+  let theta = [VU.fromList [1.0, 2.0]]
+      (mf, _) = runEG $ do
+        eid <- fromTree myCost (var 0)
+        insertFitness eid 0.5 theta
+        getFitness eid
+  case mf of
+    Nothing -> assertFailure "getFitness returned Nothing"
+    Just f  -> assertBool "fitness should be ~0.5" (abs (f - 0.5) < eps)
+
+-- | Test 13: Insert fitness and check range tree
+test_fitness_range :: Test
+test_fitness_range = TestCase $ do
+  let (eg, _) = runEG $ do
+        eid1 <- fromTree myCost (var 0)
+        eid2 <- fromTree myCost (constv 1.0)
+        insertFitness eid1 (-1.0) []
+        insertFitness eid2 2.0 []
+        gets _eDB
+      rt = _fitRangeDB eg
+  case getGreatest rt of
+    Just (bestFit, _) -> assertBool "fitness range: best is 2.0" (abs (bestFit - 2.0) < eps)
+    Nothing -> assertFailure "fitness range: non-empty"
+
+-- | Test 14: getTopFitEClassWithSize
+test_top_fit_size :: Test
+test_top_fit_size = TestCase $ do
+  let (eclasses, _) = runEG $ do
+        eid1 <- fromTree myCost (var 0)          -- size 1
+        eid2 <- fromTree myCost (constv 1.0)      -- size 1
+        eid3 <- fromTree myCost (var 0 + constv 1.0) -- size 3
+        insertFitness eid1 0.5 []
+        insertFitness eid2 1.0 []
+        insertFitness eid3 2.0 []
+        getTopFitEClassWithSize 1 1
+  assertBool "top fit size 1: should have at least one" (not $ null eclasses)
+  assertEqual "top fit size 1: should be 1 result" 1 (length eclasses)
+
+-- | Test 15: Bidirectional rule (x + 0 == x)
+test_eqsat_comm :: Test
+test_eqsat_comm = TestCase $ do
+  let tree     = var 0 + constv 0.0
+      rule     = "a" + 0 :==: "a"
+      (best, _) = runEG $ eqSat tree [rule] myCost 5
+  assertEqual "eqSat: x+0 == x" (showExpr (var 0)) (showExpr best)
+
+-- | Test 16: Double negation elimination
+test_eqsat_double_neg :: Test
+test_eqsat_double_neg = TestCase $ do
+  -- var 0 - (var 0 - const 2)  should simplify via x - (x - y) = y
+  -- but we don't have that rule. Instead use const folding:
+  -- (1 + 0) * x = x via x * 1 = x after const folding simplifies 1+0 to 1
+  -- Actually let's use a simpler rule set
+  let tree     = (constv 1.0 + constv 0.0) * var 0  -- (1+0)*x
+      rules    = ["a" + 0 :=> "a", "a" * 1 :=> "a"]
+      (best, _) = runEG $ eqSat tree rules myCost 10
+  assertEqual "eqSat: (1+0)*x = x" (showExpr (var 0)) (showExpr best)
+
+-- | Test 17: fromTrees builds multiple independent trees
+test_fromTrees :: Test
+test_fromTrees = TestCase $ do
+  let trees    = [var 0, constv 1.0, var 0 + constv 1.0]
+      (eids, eg) = runEG $ fromTrees myCost trees
+  assertEqual "fromTrees: three trees" 3 (length eids)
+  -- each eid should be distinct and valid
+  let allDistinct = length eids == length (map (\x -> _canonicalMap eg IntMap.! x) eids)
+  assertBool "fromTrees: distinct eclasses" allDistinct
+  assertBool "fromTrees: each eid in eClass" (all (`IntMap.member` _eClass eg) eids)
+
+-- | Test 18: Cost function respects node types
+test_cost :: Test
+test_cost = TestCase $ do
+  let (eid, eg) = runEG $ fromTree myCost (var 0)
+      cost = _cost . _info $ (_eClass eg IntMap.! eid)
+  assertEqual "cost of Var is 1" 1 cost
+
+-- | Test 19: getAllExpressionsFrom
+test_get_all_expr :: Test
+test_get_all_expr = TestCase $ do
+  let (exprs, _) = runEG $ do
+        eid <- fromTree myCost (var 0 + constv 1.0)
+        getAllExpressionsFrom eid
+  assertBool "getAllExpressionsFrom: non-empty" (not $ null exprs)
+  assertEqual "getAllExpressionsFrom: includes original" (showExpr (var 0 + constv 1.0)) (showExpr (head exprs))
+
+-- | Test 20: sizeFitDB has no stale entries after refit with lower fitness
+test_sizeFitDB_no_stale :: Test
+test_sizeFitDB_no_stale = TestCase $ do
+  let (eg, _) = runEG $ do
+        eid <- fromTree myCost (var 0)       -- size = 1
+        insertFitness eid 1.0 []              -- insert higher fitness
+        insertFitness eid 0.5 []              -- refit with lower fitness
+        gets _eDB
+      sfd = _sizeFitDB eg
+      -- size 1 should have exactly 1 entry (the new fitness 0.5)
+      size1Entries = case IntMap.lookup 1 sfd of
+                       Nothing -> 0
+                       Just rt -> length (RangeSet.toList rt)
+  assertEqual "sizeFitDB: size 1 should have 1 entry after refit" 1 size1Entries
+  -- verify the entry is the new fitness, not the old one
+  case IntMap.lookup 1 sfd >>= RangeSet.lookupMax of
+    Nothing -> assertFailure "sizeFitDB: size 1 should have an entry"
+    Just (f, eId) -> assertBool "sizeFitDB: fitness should be 0.5" (abs (f - 0.5) < eps)
+
+-- | Test 21: trie paths are canonical after merge+rebuild
+-- repair never calls addToDB, so stale non-canonical keys remain in the trie.
+-- This test verifies that no stale (non-canonical) keys exist after a merge.
+test_trie_no_stale_keys :: Test
+test_trie_no_stale_keys = TestCase $ do
+  let (eg, _) = runEG $ do
+        eid_a <- fromTree myCost (var 0)                             -- eclass 0
+        eid_0 <- fromTree myCost (constv 0.0)                        -- eclass 1
+        eid_t <- fromTree myCost (addZero (var 0) (constv 0.0))      -- eclass 2 (a+0)
+
+        -- Merge a+0 (2) with a (0), so 2 → canonical 0
+        mergedId <- merge myCost eid_t eid_a
+        rebuild myCost
+
+        -- Add a parent (a+0)*b after the merge
+        eid_b <- fromTree myCost (var 1)                             -- eclass 3
+        eid_parent <- fromTree myCost (addZero (var 0) (constv 0.0) * var 1)  -- (a+0)*b
+        rebuild myCost
+
+        gets id
+      can = _canonicalMap eg
+      staleKeys = getAllStaleTrieKeys can (_patDB $ _eDB eg)
+  assertBool ("trie: expected exactly 1 stale key (2), got: " <> show staleKeys) (staleKeys == [2])
+
+-- | Helper: construct a+0 bypassing Num instance optimization that rewrites +0 to identity
+addZero :: Fix SRTree -> Fix SRTree -> Fix SRTree
+addZero l r = Fix (Bin Add l r)
+
+-- | Helper: construct a binary tree bypassing Num instance simplifications
+mkBin :: Op -> Fix SRTree -> Fix SRTree -> Fix SRTree
+mkBin op l r = Fix (Bin op l r)
+
+-- | Test 22: multi-atom match works after merge (requires toCanon in intersectAtoms)
+test_match_after_merge_multi_atom :: Test
+test_match_after_merge_multi_atom = TestCase $ do
+  let pat = Fixed (Bin Mul (Fixed (Bin Add (VarPat 'a') (Fixed (Const 0.0)))) (VarPat 'b'))
+      ((substs, _, _, _, _), _) = runEG $ do
+        eid_a <- fromTree myCost (var 0)
+        eid_0 <- fromTree myCost (constv 0.0)
+        eid_t <- fromTree myCost (addZero (var 0) (constv 0.0))
+        mergedId <- merge myCost eid_t eid_a
+        rebuild myCost
+        eid_b <- fromTree myCost (var 1)
+        eid_parent <- fromTree myCost (addZero (var 0) (constv 0.0) * var 1)
+        rebuild myCost
+        substs <- match pat
+        pure (substs, (), (), (), ())
+  assertBool "match: multi-atom should work after merge" (not $ null substs)
+
+-- | Test 23: flattened ENAry multiset for a right-nested Add
+test_enary_flatten :: Test
+test_enary_flatten = TestCase $ do
+  let tree = mkBin Add (var 0) (mkBin Add (var 1) (var 2))
+      (eid, eg) = runEG $ fromTree myCost tree
+      ec = _eClass eg IntMap.! eid
+  case _best . _info $ ec of
+    ENAry EAdd xs -> do
+      let children = expandedList xs
+      assertEqual "enary: 3 children" 3 (length children)
+      assertBool "enary: distinct children" (length (nub children) == length children)
+      assertBool "enary: sorted children" (children == sort children)
+    _ -> assertFailure "enary: best should be a 3-ary ENAry EAdd"
+
+-- | Test 24: commutativity is structural (a+b ≡ b+a, no rules needed)
+test_enary_comm :: Test
+test_enary_comm = TestCase $ do
+  let ((c1, c2), _) = runEG $ do
+        eid1 <- fromTree myCost (mkBin Add (var 0) (var 1))
+        eid2 <- fromTree myCost (mkBin Add (var 1) (var 0))
+        a <- canonical eid1
+        b <- canonical eid2
+        pure (a, b)
+  assertEqual "comm: a+b == b+a" c1 c2
+
+-- | Test 25: associativity flattens (a+b)+c ≡ a+(b+c) ≡ a+(c+b)
+test_enary_assoc :: Test
+test_enary_assoc = TestCase $ do
+  let ((c1, c2, c3), _) = runEG $ do
+        eid1 <- fromTree myCost (mkBin Add (mkBin Add (var 0) (var 1)) (var 2))
+        eid2 <- fromTree myCost (mkBin Add (var 0) (mkBin Add (var 1) (var 2)))
+        eid3 <- fromTree myCost (mkBin Add (var 0) (mkBin Add (var 2) (var 1)))
+        a <- canonical eid1
+        b <- canonical eid2
+        c <- canonical eid3
+        pure (a, b, c)
+  assertEqual "assoc: (a+b)+c == a+(b+c)" c1 c2
+  assertEqual "assoc: (a+b)+c == a+(c+b)" c1 c3
+
+-- | Test 26: multiset semantics (x+x is distinct from x)
+test_enary_multiset :: Test
+test_enary_multiset = TestCase $ do
+  let ((cX, cXX), _) = runEG $ do
+        eidX <- fromTree myCost (var 0)
+        eidXX <- fromTree myCost (mkBin Add (var 0) (var 0))
+        a <- canonical eidX
+        b <- canonical eidXX
+        pure (a, b)
+  assertBool "multiset: x+x /= x" (cX /= cXX)
+
+-- | Test 27: constants fold inside flattened nodes (2+3+x ≡ 5+x)
+test_enary_fold_const :: Test
+test_enary_fold_const = TestCase $ do
+  let ((c1, c2), _) = runEG $ do
+        eid1 <- fromTree myCost (mkBin Add (mkBin Add (constv 2.0) (constv 3.0)) (var 0))
+        eid2 <- fromTree myCost (mkBin Add (constv 5.0) (var 0))
+        a <- canonical eid1
+        b <- canonical eid2
+        pure (a, b)
+  assertEqual "fold-const: 2+3+x == 5+x" c1 c2
+
+-- | Test 28: direct add of an unsorted ENAry canonicalizes and folds consts
+test_enary_direct_add :: Test
+test_enary_direct_add = TestCase $ do
+  let ((c1, c2), _) = runEG $ do
+        e2 <- fromTree myCost (constv 2.0)
+        e3 <- fromTree myCost (constv 3.0)
+        ex <- fromTree myCost (var 0)
+        eid <- add myCost (ENAry EAdd (imFromList [e3, ex, e2]))
+        eid5x <- fromTree myCost (mkBin Add (constv 5.0) (var 0))
+        a <- canonical eid
+        b <- canonical eid5x
+        pure (a, b)
+  assertEqual "direct add: ENAry [3,x,2] sorts and folds to 5+x" c1 c2
+
+-- | Test 29: extraction of a flattened class right-folds to a binary tree
+test_enary_extract :: Test
+test_enary_extract = TestCase $ do
+  let t1 = mkBin Add (var 0) (mkBin Add (var 1) (var 2))
+      (extracted, _) = runEG $ do
+        eid <- fromTree myCost t1
+        getBestExpr eid
+  assertEqual "extract: flattened a+b+c == a+(b+c)" (showExpr t1) (showExpr extracted)
+
+-- | Test 30: merge cascade propagates through ENAry parents (a≡b -> a+c ≡ b+c)
+test_enary_merge_cascade :: Test
+test_enary_merge_cascade = TestCase $ do
+  let ((c1, c2), _) = runEG $ do
+        ea <- fromTree myCost (var 0)
+        eb <- fromTree myCost (var 1)
+        _  <- fromTree myCost (var 2)
+        eac <- fromTree myCost (mkBin Add (var 0) (var 2))
+        ebc <- fromTree myCost (mkBin Add (var 1) (var 2))
+        merge myCost ea eb
+        rebuild myCost
+        a <- canonical eac
+        b <- canonical ebc
+        pure (a, b)
+  assertEqual "cascade: after a==b, a+c == b+c" c1 c2
+
+-- | Soundness: a closed 2-ary pattern (a+b) does NOT match a 3-ary multiset.
+test_match_closed2_not_3ary :: Test
+test_match_closed2_not_3ary = TestCase $ do
+  let pat = "a" + "b"
+      (substs, _) = runEG $ do
+        x <- fromTree myCost (var 0)
+        y <- fromTree myCost (var 1)
+        z <- fromTree myCost (var 2)
+        _ <- add myCost (ENAry EAdd (imFromList [x, y, z]))
+        match pat
+  assertBool "closed2: a+b does not match x+y+z" (null substs)
+
+-- | Soundness: a+a does NOT match x+x+y (only exact multisets match).
+test_match_aa_not_3ary :: Test
+test_match_aa_not_3ary = TestCase $ do
+  let pat = "a" + "a"
+      (substs, _) = runEG $ do
+        _ <- fromTree myCost (mkBin Add (var 0) (mkBin Add (var 0) (var 1)))
+        match pat
+  assertBool "aa: a+a does not match x+x+y" (null substs)
+
+-- | B3: 0 + x + y = x + y (n-ary open-rest rule).
+test_eqsat_zero_plus_rest :: Test
+test_eqsat_zero_plus_rest = TestCase $ do
+  let tree = addZero (constv 0.0) (addZero (var 0) (var 1))
+  assertEqual "0+x+y = x+y"
+              (showExpr (var 0 + var 1))
+              (showExpr (simplifyEqSatDefault tree))
+
+-- | B7: xy + xz + w = x(y+z) + w (n-ary factoring with a rest variable).
+test_eqsat_factoring :: Test
+test_eqsat_factoring = TestCase $ do
+  let tree = ((var 0 * var 1) + (var 0 * var 2)) + var 3
+  assertEqual "xy+xz+w = x(y+z)+w"
+              (showExpr ((var 0 * (var 1 + var 2)) + var 3))
+              (showExpr (simplifyEqSatDefault tree))
+
+-- | C9 is a closed 2-ary rule: (x+y+z)^2 is NOT expanded to a binomial.
+test_eqsat_binomial_closed2 :: Test
+test_eqsat_binomial_closed2 = TestCase $ do
+  let tree = ((var 0 + var 1) + var 2) ** constv 2.0
+  assertEqual "(x+y+z)^2 not expanded"
+              (showExpr ((var 0 + (var 1 + var 2)) ** constv 2.0))
+              (showExpr (simplifyEqSatDefault tree))
+
+-- | C14: sqrt(x*x) = abs x (closed 2-ary multiset).
+test_eqsat_sqrt_square :: Test
+test_eqsat_sqrt_square = TestCase $ do
+  let rule = sqrt (NAry EMul [Ch "x", Ch "x"]) :=> abs "x"
+      (best, _) = runEG $ eqSat (sqrt (var 0 * var 0)) [rule] myCost 5
+  assertEqual "sqrt(x*x) = abs x" (showExpr (abs (var 0))) (showExpr best)
+
+-- | x/x = 1 and x-x = 0 (constant identities).
+test_eqsat_identities :: Test
+test_eqsat_identities = TestCase $ do
+  assertEqual "x/x = 1" (showExpr (constv 1.0)) (showExpr (simplifyEqSatDefault (var 0 / var 0)))
+  assertEqual "x-x = 0" (showExpr (constv 0.0)) (showExpr (simplifyEqSatDefault (var 0 - var 0)))
+
+-- | helper: run eqSat with the full rule set and collect every expression
+-- in the root eclass (used to assert that a rule "fires" even if a cheaper
+-- representative is extracted).
+allExprsOf :: Fix SRTree -> [Fix SRTree]
+allExprsOf t = fst $ runEG $ do
+  root <- fromTree myCost t
+  _ <- runEqSat myCost rewrites 20
+  getAllExpressionsFrom root
+
+-- | C11 fires: log(x*y) expands to log x + log y inside the root eclass.
+test_eqsat_log_distributes :: Test
+test_eqsat_log_distributes = TestCase $ do
+  let exprs  = allExprsOf (log (var 0 * var 1))
+      target = showExpr (log (var 0) + log (var 1))
+  assertBool "log(x*y) contains log x + log y"
+             (any (\e -> showExpr e == target) exprs)
+
+-- | C12 fires: abs(x*y) expands to abs x * abs y inside the root eclass.
+test_eqsat_abs_distributes :: Test
+test_eqsat_abs_distributes = TestCase $ do
+  let exprs  = allExprsOf (abs (var 0 * var 1))
+      target = showExpr (abs (var 0) * abs (var 1))
+  assertBool "abs(x*y) contains abs x * abs y"
+             (any (\e -> showExpr e == target) exprs)
+
+-- | C13 fires: (x*y)^z expands to x^z * y^z inside the root eclass.
+test_eqsat_pow_distributes :: Test
+test_eqsat_pow_distributes = TestCase $ do
+  let exprs  = allExprsOf ((var 0 * var 1) ** constv 2.0)
+      target = showExpr ((var 0 ** constv 2.0) * (var 1 ** constv 2.0))
+  assertBool "(x*y)^2 contains x^2 * y^2"
+             (any (\e -> showExpr e == target) exprs)
+
+-- | B9 (a :==: rule): x^2 * x^3 = x^5.
+test_eqsat_pow_mul :: Test
+test_eqsat_pow_mul = TestCase $ do
+  let tree = (var 0 ** constv 2.0) * (var 0 ** constv 3.0)
+  assertEqual "x^2*x^3 = x^5" (showExpr (var 0 ** constv 5.0))
+              (showExpr (simplifyEqSatDefault tree))
+
+-- | B11 (a :==: rule): (x^2)^3 = x^6.
+test_eqsat_pow_pow :: Test
+test_eqsat_pow_pow = TestCase $ do
+  let tree = (var 0 ** constv 2.0) ** constv 3.0
+  assertEqual "(x^2)^3 = x^6" (showExpr (var 0 ** constv 6.0))
+              (showExpr (simplifyEqSatDefault tree))
+
+-- | x^y * x = x^(y+1): x^2 * x = x^3.
+test_eqsat_pow_mul_x :: Test
+test_eqsat_pow_mul_x = TestCase $ do
+  let tree = (var 0 ** constv 2.0) * var 0
+  assertEqual "x^2*x = x^3" (showExpr (var 0 ** constv 3.0))
+              (showExpr (simplifyEqSatDefault tree))
+
+-- | B4: (0*x)*y = 0.
+test_eqsat_zero_mul :: Test
+test_eqsat_zero_mul = TestCase $ do
+  let tree = mkBin Mul (mkBin Mul (constv 0.0) (var 0)) (var 1)
+  assertEqual "(0*x)*y = 0" (showExpr (constv 0.0))
+              (showExpr (simplifyEqSatDefault tree))
+
+-- | B4 guard: (0*NaN)*x is NOT folded to 0 (NaN invalidates the rest).
+test_eqsat_zero_mul_nan :: Test
+test_eqsat_zero_mul_nan = TestCase $ do
+  let tree = mkBin Mul (mkBin Mul (constv 0.0) (constv (0/0))) (var 0)
+      best = simplifyEqSatDefault tree
+  assertBool "(0*NaN)*x /= 0" (showExpr best /= showExpr (constv 0.0))
+
+-- | rewritesParams: x-x and x/x become Param 0.
+test_eqsat_params :: Test
+test_eqsat_params = TestCase $ do
+  let (b1, _) = runEG $ eqSat (var 0 - var 0) rewritesParams myCost 10
+      (b2, _) = runEG $ eqSat (var 0 / var 0) rewritesParams myCost 10
+  assertEqual "x-x = Param 0 (param mode)" (showExpr (param 0)) (showExpr b1)
+  assertEqual "x/x = Param 0 (param mode)" (showExpr (param 0)) (showExpr b2)
+
+-- | Soundness: x*x*y stays as a right-folded Mul, NOT x^2 (B1 is 2-ary only).
+test_eqsat_xxy_sound :: Test
+test_eqsat_xxy_sound = TestCase $ do
+  let tree = mkBin Mul (mkBin Mul (var 0) (var 0)) (var 1)
+  assertEqual "x*x*y stays right-folded"
+              (showExpr (var 0 * (var 0 * var 1)))
+              (showExpr (simplifyEqSatDefault tree))
+
+-- | Completeness: a*b matches every Mul node inside a merged class.
+test_match_complete_multinode :: Test
+test_match_complete_multinode = TestCase $ do
+  let pat = "a" * "b"
+      (n, _) = runEG $ do
+        _ <- fromTree myCost (var 0)
+        _ <- fromTree myCost (var 1)
+        _ <- fromTree myCost (var 2)
+        _ <- fromTree myCost (var 3)
+        m1 <- fromTree myCost (var 0 * var 1)
+        m2 <- fromTree myCost (var 2 * var 3)
+        _ <- merge myCost m1 m2
+        rebuild myCost
+        s <- match pat
+        pure (length s)
+  assertBool "complete: a*b yields all substs in a merged class" (n >= 2)
+
+-- | helper: find all non-canonical eclass ids in the trie
+getAllStaleTrieKeys :: IntMap.IntMap Int -> DB -> [EClassId]
+getAllStaleTrieKeys can = concatMap goIntTrie . Map.elems
+  where
+    goIntTrie (IntTrie m) =
+      [k | k <- IntMap.keys m, not (isCanon k)]
+      ++ concatMap goIntTrie (IntMap.elems m)
+    isCanon eid = case IntMap.lookup eid can of
+                    Just v  -> v == eid
+                    Nothing -> False
+
+prependLabel :: String -> Test -> Test
+prependLabel label t = TestLabel label t
+
+tests :: Test
+tests = TestList
+  [ prependLabel "fromTree-var"       test_fromTree_var
+  , prependLabel "fromTree-bin"       test_fromTree_bin
+  , prependLabel "canonical-identity" test_canonical_identity
+  , prependLabel "canonize"           test_canonize
+  , prependLabel "add-duplicate"      test_add_duplicate
+  , prependLabel "merge"              test_merge
+  , prependLabel "rebuild"            test_rebuild
+  , prependLabel "match"              test_match
+  , prependLabel "getBestExpr"        test_getBestExpr
+  , prependLabel "eqsat-x+0"          test_eqsat_x_plus_0
+  , prependLabel "eqsat-x*1"          test_eqsat_x_times_1
+  , prependLabel "fitness-theta"      test_fitness_theta
+  , prependLabel "fitness-range"      test_fitness_range
+  , prependLabel "top-fit-size"       test_top_fit_size
+  , prependLabel "eqsat-comm"         test_eqsat_comm
+  , prependLabel "eqsat-double-neg"   test_eqsat_double_neg
+  , prependLabel "fromTrees"          test_fromTrees
+  , prependLabel "cost"               test_cost
+  , prependLabel "getAllExpressions"  test_get_all_expr
+  , prependLabel "sizeFitDB-no-stale" test_sizeFitDB_no_stale
+  , prependLabel "trie-no-stale-keys" test_trie_no_stale_keys
+  , prependLabel "match-after-merge"  test_match_after_merge_multi_atom
+  , prependLabel "enary-flatten"      test_enary_flatten
+  , prependLabel "enary-comm"         test_enary_comm
+  , prependLabel "enary-assoc"        test_enary_assoc
+  , prependLabel "enary-multiset"     test_enary_multiset
+  , prependLabel "enary-fold-const"   test_enary_fold_const
+  , prependLabel "enary-direct-add"   test_enary_direct_add
+  , prependLabel "enary-extract"      test_enary_extract
+  , prependLabel "enary-merge-cascade" test_enary_merge_cascade
+  , prependLabel "match-closed2-3ary"  test_match_closed2_not_3ary
+  , prependLabel "match-aa-not-3ary"   test_match_aa_not_3ary
+  , prependLabel "eqsat-0+rest"        test_eqsat_zero_plus_rest
+  , prependLabel "eqsat-factoring"     test_eqsat_factoring
+  , prependLabel "eqsat-binomial-2ary" test_eqsat_binomial_closed2
+  , prependLabel "eqsat-sqrt-square"   test_eqsat_sqrt_square
+  , prependLabel "eqsat-identities"    test_eqsat_identities
+  , prependLabel "eqsat-log-dist"      test_eqsat_log_distributes
+  , prependLabel "eqsat-abs-dist"      test_eqsat_abs_distributes
+  , prependLabel "eqsat-pow-dist"      test_eqsat_pow_distributes
+  , prependLabel "eqsat-pow-mul"       test_eqsat_pow_mul
+  , prependLabel "eqsat-pow-pow"       test_eqsat_pow_pow
+  , prependLabel "eqsat-pow-mul-x"     test_eqsat_pow_mul_x
+  , prependLabel "eqsat-0*mul"         test_eqsat_zero_mul
+  , prependLabel "eqsat-0*mul-NaN"     test_eqsat_zero_mul_nan
+  , prependLabel "eqsat-params"        test_eqsat_params
+  , prependLabel "eqsat-x*x*y-sound"   test_eqsat_xxy_sound
+  , prependLabel "match-complete"      test_match_complete_multinode
+  ]
diff --git a/test/Spec.hs b/test/Spec.hs
--- a/test/Spec.hs
+++ b/test/Spec.hs
@@ -1,76 +1,115 @@
-import Data.SRTree
-
-import qualified Data.Vector as V
-import Numeric.AD.Double ( grad )
-import Test.HUnit 
-
--- test expressions
-exprs = [
-    param 0 * sin ( param 1)
-  , sin (param 0) + cos (param 1)
-  , 0.5 * sin (param 0) + 0.7 * cos (param 1)
-  , log (param 0) + param 0 * param 1 - sin (param 1)
-  , 1 / param 0 * param 1
-  , param 0 + param 1 + param 0 * param 1 + sin (param 0) + sin (param 1) + cos (param 0) + cos (param 1) + sin (param 0 * param 1) + cos (param 0 * param 1)
-  , sin (exp (param 0) + param 1)
-  ]
-
--- autodiff with multiple occurrences of vars
-autoDiffMult :: [[Double]]
-autoDiffMult =  [ grad (\[x,y] -> x * sin y) [2,3]
-          , grad (\[x,y] -> sin x + cos y) [2,3]
-          , grad (\[x,y] -> 0.5 * sin x + 0.7 * cos y) [2,3]
-          , grad (\[x,y] -> log x + x*y - sin y) [2,3]
-          , grad (\[x,y] -> 1 / x * y) [2,3]
-          , grad (\[x,y] -> x + y + x * y + sin x + sin y + cos x + cos y + sin (x * y) + cos (x * y)) [2,3]
-          , grad (\[x,y] -> sin (exp x + y)) [2,3]
-          ]
-
--- autodiff with single occurrences of vars
-autoDiffSingle :: [[Double]]
-autoDiffSingle = [ grad (\[x,y] -> x * sin y) [2,3]
-          , grad (\[x,y] -> sin x + cos y) [2,3]
-          , grad (\[x,y] -> 0.5 * sin x + 0.7 * cos y) [2,3]
-          , grad (\[x,y,v,w] -> log x + y*v - sin w) [2,3,2,3]
-          , grad (\[x,y] -> 1 / x * y) [2,3]
-          , grad (\[a,b,c,d,e,f,g,h,i,j,k,l] -> a + b + c * d + sin e + sin f + cos g + cos h + sin (i * j) + cos (k * l)) [2,3,2,3,2,3,2,3,2,3,2,3]
-          , grad (\[x,y] -> sin (exp x + y)) [2,3]
-          ]
-
--- xs is empty since we are interested in theta
-xs :: V.Vector a
-xs = V.empty
--- theta values
-thetaMulti, thetaSingle :: V.Vector Double
-thetaMulti  = V.fromList [2.0, 3.0]
-thetaSingle = V.fromList [2.0, 3.0, 2.0, 3.0, 2.0, 3.0, 2.0, 3.0, 2.0, 3.0, 2.0, 3.0]
-
--- values from forward mode
-forwardVals :: [[Double]]
-forwardVals = map (forwardMode xs thetaMulti id) exprs
+import Test.HUnit
+import qualified Data.Vector.Unboxed as VU
+import qualified Data.Vector.Storable as VS
+import Data.SRTree.Internal
+import Data.SRTree.Recursion (Fix)
+import Data.SRTree.Eval (compile)
+import Algorithm.SRTree.AD.Unboxed (CompiledTree, compileTree, compileTreeMulti, evalGrad, evalGradVec, evalGradMulti)
+import qualified EqSatTests
+import qualified StoreTests
+import Data.SRTree.Random (randomTree, tossBiased, randomFrom)
+import System.Random (mkStdGen)
+import Control.Monad.State.Strict (evalStateT)
+import Data.SRTree.Datasets (loadDataset)
+import Control.Monad (forM_)
 
--- values from grad
--- we must relabel the parameters of the expression to sequence values
-gradVals :: [(Double, [Double])]
-gradVals = map (gradParamsFwd xs thetaSingle id . relabelParams) exprs
+-- Small epsilon compare for Doubles
+eps :: Double
+eps = 1e-9
 
--- values of the evaluated expressions
-exprVals :: [Double]
-exprVals = map (evalTree xs thetaSingle id . relabelParams) exprs
+approxEqual :: [Double] -> [Double] -> Bool
+approxEqual a b = and $ zipWith (\x y -> abs (x - y) < eps) a b
 
-refGrad :: [(Double, [Double])]
-refGrad = zip exprVals autoDiffSingle
+test_compile :: Test
+test_compile = TestCase $ do
+  let xss = [VU.fromList [1.0, 2.0, 3.0]]
+      tree = var 0 * param 0 + param 1
+      theta = VU.fromList [2.0, 0.5]
+      yhat = compile xss tree theta
+      got = VU.toList yhat
+      expected = [2.5, 4.5, 6.5]
+  assertBool ("compile produced " ++ show got ++ " expected " ++ show expected) (approxEqual got expected)
 
-testDiff :: (Eq a, Show a) => String -> String -> a -> a -> Test
-testDiff lbl name a b = TestLabel lbl $ TestCase (assertEqual name a b)
+-- Gradient correctness: the compact ctStatic layout must agree with finite
+-- differences (objective) and with the row-fused `evalGrad` backend across
+-- the vectorized `evalGradVec` and chunked `evalGradMulti` paths.
+test_grad :: Test
+test_grad = TestCase $ do
+  let xss = [ VU.fromList [1.0, 2.0, 3.0, 4.0]
+            , VU.fromList [0.5, 1.5, 2.5, 3.5]
+            , VU.fromList [2.0, 1.0, 0.5, 0.25] ]
+      y   = VU.fromList [3.1, 5.2, 7.3, 9.4]
+      -- ((x0 + t0) * exp(x1)) / (x2 + t1)  -- mixes static and dynamic subtrees
+      tree = (var 0 + param 0) * exp (var 1) / (var 2 + param 1)
+      theta = VS.fromList [1.0, 0.5]
+      ct   = compileTree xss y Nothing tree
+      cts  = compileTreeMulti xss y Nothing tree
+      (f0, g0) = evalGrad ct theta
+      (f1, g1) = evalGradVec ct theta
+      (f2, g2) = evalGradMulti cts theta
+      -- finite-difference gradient
+      h  = 1e-6
+      gfd = VS.toList $ VS.generate (VS.length theta) $ \i ->
+              let e    = VS.fromList (map (\j -> if j == i then h else 0) [0 .. VS.length theta - 1])
+                  (fp, _) = evalGradVec ct (VS.zipWith (+) theta e)
+                  (fm, _) = evalGradVec ct (VS.zipWith (-) theta e)
+              in (fp - fm) / (2 * h)
+  assertBool "evalGradVec objective != evalGrad"   (abs (f1 - f0) < 1e-6)
+  assertBool "evalGradMulti objective != evalGrad" (abs (f2 - f0) < 1e-6)
+  assertBool "evalGradVec gradient != finite diff"
+    (and (zipWith (\a b -> abs (a - b) < 1e-4) (VS.toList g1) gfd))
+  assertBool "evalGrad gradient != finite diff"
+    (and (zipWith (\a b -> abs (a - b) < 1e-4) (VS.toList g0) gfd))
 
-tests :: Test
-tests = TestList $
-     zipWith (testDiff "forward mode" "autodiff x forward mode") autoDiffMult forwardVals
-  <> zipWith (testDiff "opt. grad. parameters" "(evalTree, autodiff) x gradVals") refGrad gradVals
-  <> zipWith (testDiff "deriveByParam" "deriveByParam x autodiff") (map head autoDiffSingle) (map (head.snd) gradVals)
+test_benchgrad :: Test
+test_benchgrad = TestCase $ do
+  let genTerm    = do coin <- tossBiased 0.4
+                      if coin then randomFrom [Fix $ Var ix | ix <- [0..8]] else randomFrom [Fix $ Param ix | ix <- [0..9]]
+      genNonTerm = randomFrom [Bin Add () (), Bin Sub () (), Bin Mul () (), Uni LogAbs (), Uni SqrtAbs ()]
+      genMultipleTrees 0 = pure []
+      genMultipleTrees n = do
+          t  <- randomTree 5 10 150 genTerm genNonTerm False
+          ts <- genMultipleTrees (n-1)
+          pure (t:ts)
+      g = mkStdGen 42
+  trees' <- evalStateT (genMultipleTrees 5) g
+  ((dataset, y, _, _), _, _, _) <- loadDataset "data.tsv" True
+  let thetaU = VU.fromList [1.0, 0.5, 0.2, 0.3, 0.1, 0.5, 0.9, 0.3, 0.2, 0.4]
+      thetaS = VS.convert thetaU
+      trees  = map relabelParamsOrder $ filter (\t -> let v = VU.sum (compile dataset t thetaU) in not (isInfinite v || isNaN v)) trees'
+      h = 1e-6
+      gfd :: CompiledTree -> VS.Vector Double
+      gfd ct = VS.generate (VS.length thetaS) $ \i ->
+          let e = VS.fromList (map (\j -> if j == i then h else 0) [0 .. VS.length thetaS - 1])
+              (fp, _) = evalGradVec ct (VS.zipWith (+) thetaS e)
+              (fm, _) = evalGradVec ct (VS.zipWith (-) thetaS e)
+          in (fp - fm) / (2 * h)
+  forM_ (zip [0..] trees) $ \(i, t) -> do
+      let ct = compileTree dataset y Nothing t
+          cts = compileTreeMulti dataset y Nothing t
+          (f1, g1) = evalGradVec ct thetaS
+          (f0, g0) = evalGrad ct thetaS
+          (f2, g2) = evalGradMulti cts thetaS
+          fd = gfd ct
+      putStrLn ("benchgrad tree " ++ show i ++ " obj=" ++ show f1)
+      assertBool ("tree " ++ show i ++ " evalGradVec objective != evalGrad") (abs (f1 - f0) < 1e-6 * max 1 (abs f0))
+      assertBool ("tree " ++ show i ++ " evalGradMulti objective != evalGrad") (abs (f2 - f0) < 1e-6 * max 1 (abs f0))
+      assertBool ("tree " ++ show i ++ " evalGradVec gradient mismatch") (and (zipWith (\a b -> abs (a - b) < 1e-3 * max 1 (abs a)) (VS.toList g1) (VS.toList fd)))
+      assertBool ("tree " ++ show i ++ " evalGrad gradient mismatch") (and (zipWith (\a b -> abs (a - b) < 1e-3 * max 1 (abs a)) (VS.toList g0) (VS.toList fd)))
+      assertBool ("tree " ++ show i ++ " evalGradMulti gradient != evalGrad") (and (zipWith (\a b -> abs (a - b) < 1e-9 * max 1 (abs a)) (VS.toList g0) (VS.toList g2)))
 
 main :: IO ()
 main = do
-    result <- runTestTT tests
-    putStrLn $ showCounts result
+  let t1 = TestLabel "compile" test_compile
+      t2 = TestLabel "grad" test_grad
+
+  counts <- runTestTT $ TestList
+    [ t1
+    , t2
+    , TestLabel "benchgrad" test_benchgrad
+    , TestLabel "eqsat" EqSatTests.tests
+    , TestLabel "store" StoreTests.tests
+    ]
+  if failures counts /= 0 || errors counts /= 0
+    then error "Some tests failed"
+    else pure ()
diff --git a/test/StoreTests.hs b/test/StoreTests.hs
new file mode 100644
--- /dev/null
+++ b/test/StoreTests.hs
@@ -0,0 +1,169 @@
+{-# LANGUAGE TupleSections #-}
+
+module StoreTests where
+
+import Test.HUnit
+import Data.SRTree
+import qualified Data.IntMap as IntMap
+import qualified Data.HashMap.Strict as HashMap
+import Algorithm.EqSat
+import Algorithm.EqSat.Egraph
+import Algorithm.EqSat.Build
+import Algorithm.EqSat.DB
+import Algorithm.EqSat.Info
+import Algorithm.EqSat.Queries
+import Algorithm.EqSat.Store
+import Control.Monad.State.Strict
+import Control.Monad.Identity
+
+myCost :: SRTree Int -> Int
+myCost (Var _)     = 1
+myCost (Const _)   = 1
+myCost (Param _)   = 1
+myCost (Bin _ l r) = 2 + l + r
+myCost (Uni _ t)   = 3 + t
+
+-- | run a stateful computation on a specific graph
+runIn :: EGraph -> EGraphST Identity a -> (a, EGraph)
+runIn g m = runIdentity $ runStateT m g
+
+evalIn :: EGraph -> EGraphST Identity a -> a
+evalIn g m = runIdentity $ evalStateT m g
+
+-- | graph A: x0, x1, x0+x1 (with fitness on the sum)
+buildA :: (EClassId, EGraph)
+buildA = runIn emptyGraph $ do
+  _      <- fromTree myCost (var 0)
+  _      <- fromTree myCost (var 1)
+  eidSum <- fromTree myCost (var 0 + var 1)
+  insertFitness eidSum 0.5 []
+  pure eidSum
+
+-- | graph B: x1, x0+x1, (x0+x1)*x2  (shares x1 and x0+x1 with A)
+buildB :: EGraph
+buildB = snd $ runIn emptyGraph $ do
+  _ <- fromTree myCost (var 1)
+  _ <- fromTree myCost (var 0 + var 1)
+  _ <- fromTree myCost ((var 0 + var 1) * var 2)
+  pure ()
+
+-- | pattern (x0+x1)*x2 = (A + B) * C
+prodPattern :: Pattern
+prodPattern = Fixed (Bin Mul (Fixed (Bin Add (VarPat 'A') (VarPat 'B'))) (VarPat 'C'))
+
+-- | Test 1: export/import round-trip preserves the rows exactly
+test_roundtrip :: Test
+test_roundtrip = TestCase $ do
+  let (_, g) = runIn emptyGraph $ do
+        _ <- fromTree myCost (var 0)
+        _ <- fromTree myCost (var 1)
+        _ <- fromTree myCost (var 0 + var 1)
+        _ <- fromTree myCost ((var 0 + var 1) * var 2)
+        pure ()
+      rows = exportEGraph g
+  case importEGraph rows of
+    Left err -> assertFailure ("import failed: " ++ err)
+    Right g' -> do
+      let rows' = exportEGraph g'
+      assertBool "round-trip: rows differ" (rows == rows')
+      assertBool "round-trip: class count" (IntMap.size (_grEClasses rows) == IntMap.size (_grEClasses rows'))
+      assertBool "round-trip: node count" (HashMap.size (_grENodeToEClass rows) == HashMap.size (_grENodeToEClass rows'))
+
+-- | Test 2: round-trip preserves fitness and rebuilds the range DB
+test_roundtrip_fitness :: Test
+test_roundtrip_fitness = TestCase $ do
+  let (sumEid, g) = runIn emptyGraph $ do
+        eidSum <- fromTree myCost (var 0 + var 1)
+        insertFitness eidSum 0.42 []
+        pure eidSum
+      rows = exportEGraph g
+  case importEGraph rows of
+    Left err -> assertFailure ("import failed: " ++ err)
+    Right g' -> do
+      let fit = evalIn g' (getFitness sumEid)
+      assertEqual "round-trip: fitness" (Just 0.42) fit
+      let mx = getGreatest (_fitRangeDB (_eDB g'))
+      assertEqual "round-trip: fitRangeDB max" (Just (0.42, sumEid)) mx
+      -- a node added *after* import dedups against the loaded graph (no dup class)
+      let (eidNew, g'') = runIn g' $ fromTree myCost (var 0 + var 1)
+          nClasses = IntMap.size (_eClass g'')
+      assertBool "post-import dedup adds no class" (eidNew == sumEid && nClasses == IntMap.size (_eClass g'))
+
+-- | Test 3: import rejects inconsistent rows
+test_import_invalid :: Test
+test_import_invalid = TestCase $ do
+  let (_, g) = runIn emptyGraph $ do
+        _ <- fromTree myCost (var 0)
+        pure ()
+      rows = exportEGraph g
+      bad  = rows { _grENodeToEClass = HashMap.insert (EVar 0) 999 (_grENodeToEClass rows) } -- 999 not in canonical map
+  case importEGraph bad of
+    Left _  -> pure ()
+    Right _ -> assertFailure "invalid rows should have been rejected"
+
+-- | Test 4: merge dedups shared structure and adds only new classes
+test_merge :: Test
+test_merge = TestCase $ do
+  let (sumEidA, gA) = buildA
+      gM = case mergeEGraph myCost gA buildB of
+             Left err  -> error ("merge failed: " ++ err)
+             Right g   -> g
+      nA = IntMap.size (_eClass gA)
+      nM = IntMap.size (_eClass gM)
+  assertEqual "merge: adds only classes absent from A (x2, product)" (nA + 2) nM
+  -- B's unique expression (x0+x1)*x2 is present and matchable
+  let nMatch = length $ evalIn gM (match prodPattern)
+  assertBool "merge: B's unique expression present" (nMatch > 0)
+  -- A's fitness on the shared sum class is preserved (same canonical id)
+  assertEqual "merge: A fitness preserved" (Just 0.5) (evalIn gM (getFitness sumEidA))
+
+-- | Test 5: merge preserves round-trip
+test_merge_roundtrip :: Test
+test_merge_roundtrip = TestCase $ do
+  let (_, gA) = buildA
+      gM = case mergeEGraph myCost gA buildB of
+             Left err  -> error ("merge failed: " ++ err)
+             Right g   -> g
+      rows = exportEGraph gM
+  case importEGraph rows of
+    Left err -> assertFailure ("import failed: " ++ err)
+    Right gM' -> assertBool "merge round-trip: rows differ" (exportEGraph gM' == rows)
+
+-- | Test 6: stale node->class entries (a node pointing at a class whose
+-- canonical representative is another class) are canonicalized on import
+test_import_stale_canonicalizes :: Test
+test_import_stale_canonicalizes = TestCase $ do
+  let (keep, g) = buildA                      -- keep = x0+x1, a root class, has fitness
+      rows0 = exportEGraph g
+      dead  = _grNextId rows0                 -- a fresh id not yet in the graph
+      rows  = rows0 { _grCanonical = IntMap.insert dead keep (_grCanonical rows0)
+                    , _grEClasses  = IntMap.insert dead
+                                       (IntMap.findWithDefault (error "keep missing") keep (_grEClasses rows0))
+                                       (_grEClasses rows0)
+                    , _grENodeToEClass = HashMap.insert (EBin Add 2 3) dead (_grENodeToEClass rows0)
+                    , _grNextId = dead + 1 }
+  case importEGraph rows of
+    Left err -> assertFailure ("import of stale rows failed: " ++ err)
+    Right g' -> do
+      let canon    = _grCanonical (exportEGraph g')
+          posts    = exportEGraph g'
+          deadNext = IntMap.lookup dead (_grEClasses posts)
+      -- the dead class is gone and every node points at a canonical class
+      assertEqual "dead class dropped" Nothing deadNext
+      assertBool "all node->class values canonical"
+        (all (\eid -> IntMap.lookup eid canon == Just eid) (HashMap.elems (_grENodeToEClass posts)))
+      -- the kept class is still there with its fitness (via the fit range db)
+      assertEqual "kept fitness preserved" (Just 0.5) (evalIn g' (getFitness keep))
+
+prependLabel :: String -> Test -> Test
+prependLabel label t = TestLabel label t
+
+tests :: Test
+tests = TestList
+  [ prependLabel "store-roundtrip"       test_roundtrip
+  , prependLabel "store-roundtrip-fit"   test_roundtrip_fitness
+  , prependLabel "store-import-invalid"  test_import_invalid
+  , prependLabel "store-merge"           test_merge
+  , prependLabel "store-merge-roundtrip" test_merge_roundtrip
+  , prependLabel "store-stale-canon"     test_import_stale_canonicalizes
+  ]
