diff --git a/LICENSE b/LICENSE
new file mode 100644
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,201 @@
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diff --git a/README.md b/README.md
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--- /dev/null
+++ b/README.md
@@ -0,0 +1,3 @@
+# aasam
+
+This project is a fully-extended implementation of the algorithm ℳ from Annika Aasa's "Precedences in specifications and implementations of programming languages". It provides an interface for converting distfix (mixfix) precedence grammars into unambiguous context-free grammars.
diff --git a/aasam.cabal b/aasam.cabal
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--- /dev/null
+++ b/aasam.cabal
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+cabal-version:      2.4
+name:               aasam
+version:            0.1.0.0
+license:            Apache-2.0
+license-file:       LICENSE
+maintainer:         mobotsar@protonmail.com
+author:             Alexander Lucas
+bug-reports:        https://gitlab.com/mobotsar/aasam
+synopsis:
+    Convert distfix precedence grammars to unambiguous context-free grammars.
+
+description:
+    This project is a fully-extended implementation of the algorithm ℳ from Annika Aasa's "Precedences in specifications and implementations of programming languages". It provides an interface for converting distfix (mixfix) precedence grammars into unambiguous context-free grammars.
+
+category:           parsing
+extra-source-files: README.md
+
+library
+    exposed-modules:  Aasam
+    hs-source-dirs:   lib
+    other-modules:
+        Util
+        Grammars
+
+    default-language: Haskell2010
+    build-depends:
+        base ^>=4.15.1.0,
+        containers >=0.6.4 && <0.7
+
+test-suite aasam-test
+    type:             exitcode-stdio-1.0
+    main-is:          AasamTest.hs
+    hs-source-dirs:   test
+    default-language: Haskell2010
+    build-depends:
+        base ^>=4.15.1.0,
+        HUnit ==1.6.2.0,
+        test-framework ==0.8.2.0,
+        test-framework-hunit ==0.3.0.2,
+        containers >=0.6.4 && <0.7,
+        aasam
diff --git a/lib/Aasam.hs b/lib/Aasam.hs
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--- /dev/null
+++ b/lib/Aasam.hs
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+module Aasam
+    ( m
+    , module Grammars
+    , AasamError(..)
+    ) where
+
+import Data.Function (on)
+import Data.List (groupBy)
+import qualified Data.List.NonEmpty as DLNe
+import Data.List.NonEmpty (NonEmpty((:|)))
+import Data.Set (Set, insert, union)
+import qualified Data.Set as Set
+import Grammars
+    ( CfgProduction
+    , CfgString
+    , ContextFree
+    , NonTerminal(..)
+    , Precedence
+    , PrecedenceProduction(..)
+    , Terminal(..)
+    )
+import Util ((>.), (|>), unwrapOr)
+
+import Data.Bifunctor (Bifunctor(bimap, second))
+import Data.Data (toConstr)
+import qualified Data.Foldable
+import qualified Data.List as List
+
+doGeneric :: PrecedenceProduction -> (Int -> NonEmpty String -> a) -> a
+doGeneric (Prefix prec words) f = f prec words
+doGeneric (Postfix prec words) f = f prec words
+doGeneric (Infixl prec words) f = f prec words
+doGeneric (Infixr prec words) f = f prec words
+doGeneric (Closed words) f = f 0 words
+
+getWords :: PrecedenceProduction -> [String]
+getWords = flip doGeneric (const DLNe.toList)
+
+prec :: PrecedenceProduction -> Int
+prec = flip doGeneric const
+
+nt :: Int -> Int -> Int -> NonTerminal
+nt prec p q = NonTerminal (show prec ++ show p ++ show q)
+
+-- TODO: write a proper implementation of this that doesn't depend on List
+groupSetBy :: Ord a => (a -> a -> Bool) -> Set a -> Set (Set a)
+groupSetBy projection = Set.toList >. groupBy projection >. map Set.fromList >. Set.fromList
+
+makeClasses :: Precedence -> Set Precedence
+makeClasses = groupSetBy fixeq
+  where
+    fixeq = on (==) toConstr
+        -- equivalence relation of fixity on precedence productions
+
+type UniquenessPair = (PrecedenceProduction, Precedence)
+
+-- This function returns a set of upairs. A upair contains a production of a single precedence on the left,
+-- and the set of all productions of that precedence on the right (including the one on the left).
+classToPairSet :: Precedence -> Set UniquenessPair
+classToPairSet = groupSetBy preceq >. Set.map pair
+  where
+    pair :: Precedence -> UniquenessPair
+    pair prec = (Set.elemAt 0 prec, prec)
+    preceq :: PrecedenceProduction -> PrecedenceProduction -> Bool
+    preceq a b = prec a == prec b
+
+pairifyClasses :: Set Precedence -> Set (Set UniquenessPair)
+pairifyClasses = Set.map classToPairSet
+
+type PqQuad = (Int, Int, PrecedenceProduction, Precedence)
+
+pqboundUPair :: Set UniquenessPair -> Set UniquenessPair -> UniquenessPair -> PqQuad
+pqboundUPair pre post (r, s) = (greater pre $ prec r, greater post $ prec r, r, s)
+  where
+    greater :: Set UniquenessPair -> Int -> Int
+    greater upairs n = Set.size $ Set.filter ((n <) . prec . fst) upairs
+
+pqboundClasses :: Set UniquenessPair -> Set UniquenessPair -> Set (Set UniquenessPair) -> Set (Set PqQuad)
+pqboundClasses pre post = Set.map (Set.map (pqboundUPair pre post))
+
+intersperseStart :: NonEmpty String -> CfgString
+intersperseStart = DLNe.map (Left . Terminal) >. DLNe.intersperse (Right (NonTerminal "!start")) >. DLNe.toList
+
+fill :: Precedence -> Set CfgProduction -> Set CfgProduction
+fill s cfgprods = Set.union withTerminals withoutTerminals
+  where
+    (left, withoutTerminals) = Set.partition hasTerminal cfgprods
+      where
+        hasTerminal :: CfgProduction -> Bool
+        hasTerminal (_, words) = List.any isTerminal words
+    isTerminal :: Either Terminal NonTerminal -> Bool
+    isTerminal (Right (NonTerminal _)) = False
+    isTerminal (Left (Terminal _)) = True
+    withTerminals = fill' s left
+        -- TODO: write a proper implementation of this composition that doesn't depend on List
+      where
+        fill' :: Precedence -> Set CfgProduction -> Set CfgProduction
+        fill' s = Set.toList >. repeat >. zipWith reset (Set.toList s) >. concat >. Set.fromList
+          where
+            reset :: PrecedenceProduction -> [CfgProduction] -> [CfgProduction]
+            reset pp = map (second re)
+              where
+                re :: CfgString -> CfgString
+                re str =
+                    case pp of
+                        Infixl prec words -> kansas str words
+                        Infixr prec words -> kansas str words
+                        _ ->
+                            error
+                                "This is a bug in Aasam. Somehow, I got a CfgProduction that hasn't any terminals, or a Closed production."
+                  where
+                    kansas :: CfgString -> NonEmpty String -> CfgString
+                    kansas str words = List.head str : intersperseStart words ++ [List.last str]
+
+-- The CE production on `closedrule` must go to a non-terminal.
+-- Relevant terminals in these rules are all added by `fill`. Those added immediately in the rule bodies are just to signal to fill.
+--   If an "evil" non-terminal appears anywhere in the output of a *rule fuctions, that's a bug.
+prerule :: Int -> Int -> PqQuad -> Set CfgProduction
+prerule p q (_, _, r, s) = fill s $ Set.singleton (nt (prec r) p q, [Right (nt (prec r - 1) (p + 1) q)])
+
+postrule :: Int -> Int -> PqQuad -> Set CfgProduction
+postrule p q (_, _, r, s) = fill s $ Set.singleton (nt (prec r) p q, [Right (nt (prec r - 1) p (q + 1))])
+
+inlrule :: Int -> Int -> PqQuad -> Set CfgProduction
+inlrule p q (_, _, r, s) = fill s $ Set.fromList [a, b]
+  where
+    a = (nt (prec r) p q, [Right (nt (prec r) 0 q), Left (Terminal "evil"), Right (nt (prec r - 1) p 0)])
+    b = (nt (prec r) p q, [Right (nt (prec r - 1) p q)])
+
+inrrule :: Int -> Int -> PqQuad -> Set CfgProduction
+inrrule p q (_, _, r, s) = fill s $ Set.fromList [a, b]
+  where
+    a = (nt (prec r) p q, [Right (nt (prec r - 1) 0 q), Left (Terminal "evil"), Right (nt (prec r) p 0)])
+    b = (nt (prec r) p q, [Right (nt (prec r - 1) p q)])
+
+closedrule :: Set UniquenessPair -> Set UniquenessPair -> Int -> Int -> PqQuad -> Set CfgProduction
+closedrule pres posts p q (_, _, r, s) = insert ae isets `union` jsets
+  where
+    ae :: CfgProduction
+    ae = (nt 0 p q, [Right (NonTerminal "CE")])
+    isets :: Set CfgProduction
+    isets = foldl (flip (union . ido)) Set.empty (zip (Set.toList pres) [1 .. p])
+      where
+        ido :: (UniquenessPair, Int) -> Set CfgProduction
+        ido ((r, s), i) =
+            Set.singleton
+                (nt 0 p q, intersperseStart (getWords r |> DLNe.fromList) ++ [Right (nt (prec r) (p - i) 0)])
+    jsets :: Set CfgProduction
+    jsets = foldl (flip (union . jdo)) Set.empty (zip (Set.toList posts) [1 .. q])
+      where
+        jdo :: (UniquenessPair, Int) -> Set CfgProduction
+        jdo ((r, s), j) =
+            Set.singleton
+                (nt 0 p q, Right (nt (prec r) 0 (q - j)) : intersperseStart (getWords r |> DLNe.fromList))
+
+convertClass :: (Int -> Int -> PqQuad -> Set CfgProduction) -> Set PqQuad -> Set CfgProduction
+convertClass rule = foldl (flip (union . psets)) Set.empty
+  where
+    psets (pbound, qbound, r, s) = foldl (flip (union . qsets)) Set.empty [0 .. pbound]
+      where
+        qsets p = foldl ((. flip (rule p) (pbound, qbound, r, s)) . union) Set.empty [0 .. qbound]
+
+convertClasses :: Set UniquenessPair -> Set UniquenessPair -> Set (Set PqQuad) -> Set CfgProduction
+convertClasses pres posts = Set.map convertClassBranching >. foldl union Set.empty
+  where
+    convertClassBranching :: Set PqQuad -> Set CfgProduction
+    convertClassBranching quads = convertClass rule quads
+      where
+        rule =
+            case Set.elemAt 0 quads of
+                (_, _, Infixl _ _, _) -> inlrule
+                (_, _, Infixr _ _, _) -> inrrule
+                (_, _, Prefix _ _, _) -> prerule
+                (_, _, Postfix _ _, _) -> postrule
+                (_, _, Closed _, _) -> closedrule pres posts
+-- |The type of errors. Contains a list of strings, each of which describes an error of the input grammar.
+newtype AasamError =
+    AasamError [String]
+    deriving (Show, Eq, Ord)
+
+-- |Takes a distfix precedence grammar. If there is an error, produces an 'AasamError', else produces a corresponding unambiguous context-free grammar.
+--
+-- All possible errors are enumerated in the documentation for 'Precedence'.
+m :: Precedence -> Either ContextFree AasamError
+m precg =
+    if null errors
+        then Left (nt highestPrecedence 0 0, addCes (assignStart prods))
+        else Right (AasamError errors)
+  where
+    errors :: [String]
+    errors = foldl fn [] [positive, noInitSubseq, noInitWhole, classesPrecDisjoint, precContinue]
+      where
+        fn :: [String] -> Maybe String -> [String]
+        fn a e =
+            case e of
+                Nothing -> a
+                Just err -> err : a
+        positive =
+            if all fn precg
+                then Nothing
+                else Just errstr
+          where
+            fn (Closed _) = True
+            fn x = prec x > 0
+            errstr = "All precedences must be positive integers."
+        noInitSubseq =
+            if Set.disjoint initials subsequents
+                then Nothing
+                else Just errstr
+          where
+            (initials, subsequents) = foldl fn (Set.empty, Set.empty) precg
+              where
+                fn (i, s) e = (insert (head words) i, (tail words |> Set.fromList) `union` s)
+                  where
+                    words = getWords e
+            errstr = "No initial word may also be a subsequent word of another production."
+        noInitWhole =
+            if all fx precg
+                then Nothing
+                else Just errstr
+          where
+            fx x = all fy precg
+              where
+                fy y = getWords x `notPrefixedBy` getWords y || x == y
+                  where
+                    notPrefixedBy :: Eq a => [a] -> [a] -> Bool
+                    notPrefixedBy [] [] = False
+                    notPrefixedBy (_:_) [] = False
+                    notPrefixedBy [] (_:_) = True
+                    notPrefixedBy (x:xs) (y:ys) = x /= y || notPrefixedBy xs ys
+            errstr = "No initial sequence of words may also be the whole sequence of another production."
+        classesPrecDisjoint =
+            if allDisjoint precGroups
+                then Nothing
+                else Just errstr
+          where
+            allDisjoint :: Ord a => [Set a] -> Bool
+            allDisjoint (x:xs) = all (Set.disjoint x) xs && allDisjoint xs
+            allDisjoint [] = True
+            precGroups :: [Set Int]
+            precGroups = List.map (foldl (flip (insert . prec)) Set.empty) (Set.toList classes)
+            errstr = "No precedence of a production of one fixity may also be the precedence of a production of another fixity."
+        precContinue =
+            if precedences == Set.fromList [lowestPrecedence .. highestPrecedence]
+                then Nothing
+                else Just errstr
+          where
+            errstr = "The set of precedences must be either empty or the set of integers between 1 and greatest precedence, inclusive."
+    classes = makeClasses precg
+    upairClasses = pairifyClasses classes
+    (pre, post) = (findBy isPre, findBy isPost)
+      where
+        isPre clas =
+            case Set.elemAt 0 clas of
+                (Prefix _ _, _) -> True
+                _ -> False
+        isPost clas =
+            case Set.elemAt 0 clas of
+                (Postfix _ _, _) -> True
+                _ -> False
+        findBy f = unwrapOr Set.empty $ Data.Foldable.find f upairClasses
+    prods = pqboundClasses pre post upairClasses |> convertClasses pre post
+    addCes :: Set CfgProduction -> Set CfgProduction
+    addCes = union ces
+      where
+        ces :: Set CfgProduction
+        ces =
+            Set.filter isClosed precg |>
+            Set.map (\(Closed words) -> (NonTerminal "CE", intersperseStart words))
+          where
+            isClosed :: PrecedenceProduction -> Bool
+            isClosed (Closed _) = True
+            isClosed _ = False
+    assignStart :: Set CfgProduction -> Set CfgProduction
+    assignStart = Set.map $ bimap lhsMap rhsMap
+      where
+        lhsMap :: NonTerminal -> NonTerminal
+        lhsMap lhs =
+            if lhs == NonTerminal "!start"
+                then nt highestPrecedence 0 0
+                else lhs
+        rhsMap = map submap
+          where
+            submap :: Either Terminal NonTerminal -> Either Terminal NonTerminal
+            submap (Right x) = Right $ lhsMap x
+            submap y = y
+    (highestPrecedence, lowestPrecedence, precedences) =
+        foldl
+            (\(ha, la, pa) e -> (max (prec e) ha, min (prec e) la, prec e `insert` pa))
+            (0, 0, Set.singleton 0)
+            precg
diff --git a/lib/Grammars.hs b/lib/Grammars.hs
new file mode 100644
--- /dev/null
+++ b/lib/Grammars.hs
@@ -0,0 +1,51 @@
+{-# LANGUAGE DeriveDataTypeable #-}
+
+module Grammars where
+
+import Data.Data (Data, Typeable)
+import Data.List.NonEmpty (NonEmpty)
+import Data.Set (Set)
+import qualified Data.Set as Set
+
+newtype NonTerminal =
+    NonTerminal String
+    deriving (Eq, Ord, Show)
+
+newtype Terminal =
+    Terminal String
+    deriving (Eq, Ord, Show)
+
+type CfgString = [Either Terminal NonTerminal]
+
+-- |The type of a context-free production. The left and right items correspond respectively to the left and right hand sides of a production rule.
+type CfgProduction = (NonTerminal, CfgString)
+
+-- |The type of a context-free gramar. On the left the starting non-terminal, and on the right is the set of productions in the grammar.
+type ContextFree = (NonTerminal, Set CfgProduction)
+
+-- |The type of a distfix precedence production.
+--
+-- Int parameters are precedences.
+--
+-- NonEmpty String parameters are lists of non-terminal symbols expressed as strings.
+--  The particular data constructor used implies the interspersal pattern of non-terminals in the terminal list when the production is interpreted.
+--  For example,
+--
+-- > Infixl 1 (fromList ["?", ":"])
+-- corresponds to the left-associative production, E -> E ? E : E.
+data PrecedenceProduction
+    = Prefix Int (NonEmpty String)
+    | Postfix Int (NonEmpty String)
+    | Infixl Int (NonEmpty String)
+    | Infixr Int (NonEmpty String)
+    | Closed (NonEmpty String)
+    deriving (Eq, Ord, Show, Typeable, Data)
+
+-- |The type of a distfix precedence grammar. The following must be true of any parameter to `Aasam.m`.
+--
+--      * All precedences must be positive integers.
+--      * No initial word may also be a subsequent word of another production.
+--      * No initial sequence of words may also be the whole sequence of another production.
+--      * No precedence of a production of one fixity may also be the precedence of a production of another fixity.
+--      * The set of precedences must be either empty or the set of integers between 1 and greatest precedence, inclusive.
+type Precedence = Set PrecedenceProduction
diff --git a/lib/Util.hs b/lib/Util.hs
new file mode 100644
--- /dev/null
+++ b/lib/Util.hs
@@ -0,0 +1,18 @@
+module Util where
+
+infixl 5 >.
+
+(>.) :: (a -> b) -> (b -> c) -> a -> c
+(>.) = flip (.)
+
+infixl 4 |>
+
+(|>) :: a -> (a -> b) -> b
+(|>) x f = f x
+
+unwrapOr :: a -> Maybe a -> a
+unwrapOr _ (Just x) = x
+unwrapOr y _ = y
+
+tup :: a -> b -> (a, b)
+tup a b = (a, b)
diff --git a/test/AasamTest.hs b/test/AasamTest.hs
new file mode 100644
--- /dev/null
+++ b/test/AasamTest.hs
@@ -0,0 +1,64 @@
+{-# OPTIONS_GHC -Wno-unrecognised-pragmas #-}
+
+{-# HLINT ignore "Evaluate" #-}
+module Main
+    ( main
+    ) where
+
+import Aasam
+import qualified Data.List as List
+import Data.List.NonEmpty (fromList, xor)
+import qualified Data.Set as Set
+import Test.Framework (defaultMain)
+import Test.Framework.Providers.API (Test(Test))
+import Test.Framework.Providers.HUnit (hUnitTestToTests)
+import Test.HUnit (Assertable(assert), Assertion, Test(..), assertEqual)
+
+testMap :: (Eq a, Show a) => [(String, a, a)] -> [Test.HUnit.Test]
+testMap = List.map (\(label, x, y) -> TestLabel label (TestCase (assertEqual "" x y)))
+
+tests :: [Test.Framework.Providers.API.Test]
+tests = hUnitTestToTests $ TestList labeledTests
+
+main :: IO ()
+main = defaultMain tests
+
+empt :: [a]
+empt = []
+
+labeledTests :: [Test.HUnit.Test]
+labeledTests =
+    []
+    -- ++ testMap [("okay", Just 20, Just (Set.size (snd (un (m pg0)))))]
+     ++
+    testMap [("under", Nothing, Just (m pg2))]
+
+pg0 :: Precedence
+pg0 =
+    Set.fromList
+        [ Postfix 4 (fromList ["?"])
+        , Infixl 4 (fromList ["+"])
+        , Infixl 0 (fromList ["+"])
+        , Postfix 2 (fromList ["!", "?"])
+        , Closed (fromList ["int"])
+        ]
+
+un :: Either a b -> a
+un (Left x) = x
+un _ = error "fail"
+
+pg1 :: Set.Set PrecedenceProduction
+pg1 =
+    Set.fromList
+        [ Infixr 2 (fromList ["="])
+        , Prefix 1 (fromList ["λ", "."])
+        , Closed (fromList ["x"])
+        , Closed (fromList ["(", "$", ")"])
+        ]
+
+pg2 :: Set.Set PrecedenceProduction 
+pg2 = Set.empty
+
+d :: Maybe ContextFree -> ContextFree
+d (Just x) = x
+d Nothing = (NonTerminal "String", Set.empty)
