nix-eval (empty) → 0.1.0.0
raw patch · 7 files changed
+987/−0 lines, 7 filesdep +QuickCheckdep +basedep +nix-evalsetup-changed
Dependencies added: QuickCheck, base, nix-eval, process, tasty, tasty-quickcheck
Files
- LICENSE +674/−0
- README.md +73/−0
- Setup.hs +2/−0
- nix-eval.cabal +38/−0
- src/Language/Eval.hs +32/−0
- src/Language/Eval/Internal.hs +109/−0
- tests/Main.hs +59/−0
+ LICENSE view
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Of course, your program's commands+might be different; for a GUI interface, you would use an "about box".++ You should also get your employer (if you work as a programmer) or school,+if any, to sign a "copyright disclaimer" for the program, if necessary.+For more information on this, and how to apply and follow the GNU GPL, see+<http://www.gnu.org/licenses/>.++ The GNU General Public License does not permit incorporating your program+into proprietary programs. If your program is a subroutine library, you+may consider it more useful to permit linking proprietary applications with+the library. If this is what you want to do, use the GNU Lesser General+Public License instead of this License. But first, please read+<http://www.gnu.org/philosophy/why-not-lgpl.html>.
+ README.md view
@@ -0,0 +1,73 @@+# Dependency-Injecting Eval for Haskell++This Haskell package is a crude implementation of `eval`, as found in dynamic+languages like Lisp, Python, Javascript, etc. It lets us construct Haskell+code programatically (either at run time, or in Template Haskell), and attempt+to evaluate it.++What sets this package apart from other `eval` implementations, is the ability+to control which packages and modules are available during evaluation. This is+achieved by calling out to the [Nix package manager](http://nix.nixos.org).++# Implementation Details++`Expr` is the type of expressions, which contains a list of package names, a+list of modules to import and a `String` of Haskell code. All of these are just+`String`s internally, but the wrappers prevent accidentally using package as+modules, etc. A few combinators are provided for common manipulations, and the+`OverloadedStrings` extension allows packages, modules and expressions to be+written as literals. Note that literal expressions are given an empty context;+you will have to specify any required modules or packages separately.++When evaluated, the Haskell code is prefixed by an import of each module and+wrapped in `main = putStr (..)`, then piped into `runhaskell`. That process is+invoked via the `nix-shell` command, using Nix's standard+`haskellPackages.ghcWithPackages` function to ensure the GHC instance has all of+the given packages available.++If the process exits successfully, its stdout will be returned wrapped in+`Just`; otherwise `Nothing` is returned.++This implementation is a little rough; for example, you may prefer to use `Text`+rather than `String`; use a better representation like the syntax trees from+TemplateHaskell or `haskell-src-exts` instead; or accumulate packages and+modules monadically.++The intention of this library is to provide a simple, minimal base to support+such design choices, and `String` is the lowest common denominator. You're+welcome, and encouraged, to build more sophisticated APIs; as long as you can+pretty-print to a `String`, they should work out of the box.++This is also why we return the contents of stdout, rather than trying to parse+it into a more appropriate type: it's not our place to choose how the result+should be parsed, so we avoid the problem; by that point, our job is done.++# Limitations++ - Since evaluation takes place in a separate GHC process, there can be no+ sharing of data (unless you provide a separate mechanism like a FIFO)+ - Expressions are wrapped in `putStr`, so the expression must be a `String`.+ You may need to marshall your data into a form which is more amenable to+ serialising/deserialising via `String`.+ - Evaluation is **SLOW**! More specifically, `eval` has a very high latency, so+ it's *much* more efficient to `eval` one big collection of values than it is+ to `eval` each individually.+ - Evaluation time is highly variable, since the required packages may need to+ be compiled. Nix caches build products, so subsequent calls using the same+ packages will be quicker; however, my machine still takes about 2 seconds to+ instantiate a cached environment.+ - Output is captured from stdout, so if your expression triggers side-effects+ they'll appear in your result (this may be desirable, but keep it in mind).+ - Evaluation doesn't always compose, ie. just because `x` and `y` evaluate+ successfully doesn't mean that some combination of them will. Obviously an+ ill-typed combination will fail, but other reasons include:+ - Combining both import lists can make names ambiguous. For this reason you+ should always try to qualify your expressions.+ - Global properties may conflict between modules, like overlapping typeclass+ instances.+ - Combining both package lists can make modules ambiguous.+ - If the dependencies of two packages conflict, evaluation will fail.+ - Language extensions aren't handled yet. I'll add them as and when the need+ arises.+ - As with any kind of `eval`, there is absolutely no security. Do not pass+ potentially-malicious user input to this library.
+ Setup.hs view
@@ -0,0 +1,2 @@+import Distribution.Simple+main = defaultMain
+ nix-eval.cabal view
@@ -0,0 +1,38 @@+-- Initial nix-eval.cabal generated by cabal init. For further documentation, +-- see http://haskell.org/cabal/users-guide/++name: nix-eval+version: 0.1.0.0+synopsis: Evaluate Haskell expressions using Nix to get packages+description: Evaluate Haskell expressions using Nix to get packages+homepage: http://chriswarbo.net/git/nix-eval+license: GPL+license-file: LICENSE+author: Chris Warburton+maintainer: chriswarbo@gmail.com+-- copyright: +category: Language+build-type: Simple+extra-source-files: README.md+cabal-version: >=1.10++library+ exposed-modules: Language.Eval.Internal+ , Language.Eval+ -- other-modules: + -- other-extensions: + build-depends: base >=4.8 && <4.9+ , process+ hs-source-dirs: src+ default-language: Haskell2010++test-suite tests+ default-language: Haskell2010+ type: exitcode-stdio-1.0+ hs-source-dirs: tests+ main-is: Main.hs+ build-depends: base >= 4.7+ , QuickCheck+ , tasty >= 0.7+ , tasty-quickcheck+ , nix-eval
+ src/Language/Eval.hs view
@@ -0,0 +1,32 @@+{-+nix-eval: Dependency-injecting Haskell evaluator++Copyright (C) 2015 Chris Warburton++This program is free software: you can redistribute it and/or modify+it under the terms of the GNU General Public License as published by+the Free Software Foundation, either version 3 of the License, or+(at your option) any later version.++This program is distributed in the hope that it will be useful,+but WITHOUT ANY WARRANTY; without even the implied warranty of+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the+GNU General Public License for more details.++You should have received a copy of the GNU General Public License+along with this program. If not, see <http://www.gnu.org/licenses/>.+-}++module Language.Eval (+ Pkg(..)+ , Mod(..)+ , Expr(..)+ , eval+ , raw+ , ($$)+ , asString+ , qualified+ , withMods+ , withPkgs) where++import Language.Eval.Internal
+ src/Language/Eval/Internal.hs view
@@ -0,0 +1,109 @@+{-+nix-eval: Dependency-injecting Haskell evaluator++Copyright (C) 2015 Chris Warburton++This program is free software: you can redistribute it and/or modify+it under the terms of the GNU General Public License as published by+the Free Software Foundation, either version 3 of the License, or+(at your option) any later version.++This program is distributed in the hope that it will be useful,+but WITHOUT ANY WARRANTY; without even the implied warranty of+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the+GNU General Public License for more details.++You should have received a copy of the GNU General Public License+along with this program. If not, see <http://www.gnu.org/licenses/>.+-}++module Language.Eval.Internal where++import Data.Char+import Data.List+import Data.String+import System.Exit+import System.IO+import System.Process++-- We're stringly typed, with a veneer of safety++newtype Pkg = Pkg String deriving (Eq, Ord, Show)+newtype Mod = Mod String deriving (Eq, Ord, Show)+newtype Expr = Expr ([Pkg], [Mod], String) deriving (Show)++-- Allow permutations of package and module lists+instance Eq Expr where+ (Expr (p1, m1, e1)) == (Expr (p2, m2, e2)) = e1 == e2 &&+ perm p1 p2 &&+ perm m1 m2+ where perm xs ys = allIn xs ys && allIn ys xs+ allIn xs ys = all (`elem` ys) xs++-- For convenience++instance IsString Expr where+ fromString = raw++instance IsString Pkg where+ fromString = Pkg++instance IsString Mod where+ fromString = Mod++-- Evaluation via `nix-shell`++-- | Evaluate an `Expr`; this is where the magic happens! If successful, returns+-- `Just` a `String`, which you can do what you like with.+eval :: Expr -> IO (Maybe String)+eval x@(Expr (pkgs, mods, expr)) = do+ (code, out, err) <- let (cmd, args) = mkCmd x+ in readProcessWithExitCode cmd args (mkHs x)+ hPutStr stderr err+ return $ case code of+ ExitSuccess -> Just (trim out)+ ExitFailure _ -> Nothing++mkCmd :: Expr -> (String, [String])+mkCmd (Expr (ps, _, _)) = ("nix-shell", ["--run", "runhaskell",+ "-p", mkGhcPkg ps])++-- The prefix "h." is arbitrary, as long as it matches the argument "h:"+mkGhcPkg ps = let pkgs = map (\(Pkg p) -> "(h." ++ p ++ ")") ps+ in concat ["haskellPackages.ghcWithPackages ",+ "(h: [", unwords pkgs, "])"]++mkHs :: Expr -> String+mkHs (Expr (_, ms, e)) = unlines (imports ++ [main])+ where imports = map (\(Mod m) -> "import " ++ m) ms+ main = "main = putStr (" ++ e ++ ")"++trim :: String -> String+trim = reverse . dropWhile isSpace . reverse . dropWhile isSpace++-- User-facing combinators++-- | A raw String of Haskell code, with no packages or modules. You can use+-- OverloadedStrings to call this automatically.+raw :: String -> Expr+raw s = Expr ([], [], s)++-- | Apply the first Expr to the second, eg. `f $$ x` ==> `f x`+($$) :: Expr -> Expr -> Expr+(Expr (p1, m1, e1)) $$ (Expr (p2, m2, e2)) = Expr+ (nub (p1 ++ p2),+ nub (m1 ++ m2),+ concat ["((", e1, ") (", e2, "))"])++-- | Convert the argument to a String, then send to `raw`+asString :: (Show a) => a -> Expr+asString = raw . show++qualified :: Mod -> String -> Expr+qualified (Mod m) e = Expr ([], [Mod m], m ++ "." ++ e)++withMods :: [Mod] -> Expr -> Expr+withMods ms (Expr (ps, ms', e)) = Expr (ps, ms' ++ ms, e)++withPkgs :: [Pkg] -> Expr -> Expr+withPkgs ps (Expr (ps', ms, e)) = Expr (ps' ++ ps, ms, e)
+ tests/Main.hs view
@@ -0,0 +1,59 @@+{-# LANGUAGE OverloadedStrings #-}++{-+nix-eval: Dependency-injecting Haskell evaluator++Copyright (C) 2015 Chris Warburton++This program is free software: you can redistribute it and/or modify+it under the terms of the GNU General Public License as published by+the Free Software Foundation, either version 3 of the License, or+(at your option) any later version.++This program is distributed in the hope that it will be useful,+but WITHOUT ANY WARRANTY; without even the implied warranty of+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the+GNU General Public License for more details.++You should have received a copy of the GNU General Public License+along with this program. If not, see <http://www.gnu.org/licenses/>.+-}++module Main where++import Language.Eval+import Test.QuickCheck.Monadic+import Test.Tasty (defaultMain, testGroup)+import Test.Tasty.QuickCheck++main = defaultMain $ testGroup "All tests" [+ testProperty "Can eval unit" unitEval+ , testProperty "Can eval sums" sumEval+ , testProperty "Can import modules" modulesImport+ , testProperty "Can import packages" packagesImport+ ]++unitEval = checkIO "()" (Just "()")++sumEval :: [Int] -> Property+sumEval s = checkIO ("sum" $$ asString s)+ (Just (show (sum s)))++modulesImport =+ checkIO (qualified "Data.Maybe" "isNothing" $$ "Nothing")+ (Just "True")++packagesImport :: String -> Property+packagesImport s = let expr = len $$ (pack $$ asString s)+ len = qualified "Data.Text" "length"+ pack = qualified "Data.Text" "pack"+ in checkIO (withPkgs ["text"] expr)+ (Just (show (length s)))+++-- Helpers++checkIO :: Expr -> Maybe String -> Property+checkIO i o = once $ ioProperty $ do+ result <- eval ("show" $$ i)+ return (result === o)