@@ -0,0 +1,882 @@
1+-----------------------------------------------------------------------------
2+--
3+-- Module : Language.PureScript.TypeChecker.Types
4+-- Copyright : (c) Phil Freeman 2013
5+-- License : MIT
6+--
7+-- Maintainer : Phil Freeman <paf31@cantab.net>
8+-- Stability : experimental
9+-- Portability :
10+--
11+-- |
12+-- This module implements the type checker
13+--
14+-----------------------------------------------------------------------------
15+
16+{-# OPTIONS_GHC -fno-warn-orphans #-}
17+{-# LANGUAGE DeriveDataTypeable #-}
18+{-# LANGUAGE FlexibleContexts #-}
19+{-# LANGUAGE MultiParamTypeClasses #-}
20+
21+module Language.PureScript.TypeChecker.Types (
22+ typesOf
23+) where
24+
25+{-
26+ The following functions represent the corresponding type checking judgements:
27+
28+ infer
29+ Synthesize a type for a value
30+
31+ check
32+ Check a value has a given type
33+
34+ checkProperties
35+ Check an object with a given type contains specified properties
36+
37+ checkFunctionApplication
38+ Check a function of a given type returns a value of another type when applied to its arguments
39+
40+ subsumes
41+ Check a type subsumes another type
42+-}
43+
44+import Data.List
45+import Data.Maybe (maybeToList, isNothing, isJust, fromMaybe)
46+import qualified Data.Data as D
47+import Data.Generics
48+ (mkM, everywhereM, everything, mkT, something, everywhere, mkQ)
49+
50+import Language.PureScript.Values
51+import Language.PureScript.Types
52+import Language.PureScript.Kinds
53+import Language.PureScript.Names
54+import Language.PureScript.TypeChecker.Monad
55+import Language.PureScript.TypeChecker.Kinds
56+import Language.PureScript.TypeChecker.Synonyms
57+import Language.PureScript.Pretty
58+
59+import Control.Monad.State
60+import Control.Monad.Error
61+import Control.Monad.Reader
62+import Control.Monad.Unify
63+
64+import Control.Applicative
65+import Control.Arrow (Arrow(..))
66+
67+import qualified Data.Map as M
68+import Data.Function (on)
69+
70+instance Partial Type where
71+ unknown = TUnknown
72+ isUnknown (TUnknown u) = Just u
73+ isUnknown _ = Nothing
74+
75+instance Unifiable Check Type where
76+ (=?=) = unifyTypes
77+
78+-- |
79+-- Unify two types, updating the current substitution
80+--
81+unifyTypes :: Type -> Type -> UnifyT Type Check ()
82+unifyTypes t1 t2 = rethrow (\e -> "Error unifying type " ++ prettyPrintType t1 ++ " with type " ++ prettyPrintType t2 ++ ":\n" ++ e) $ do
83+ unifyTypes' t1 t2
84+ where
85+ unifyTypes' (TUnknown u1) (TUnknown u2) | u1 == u2 = return ()
86+ unifyTypes' (TUnknown u) t = u =:= t
87+ unifyTypes' t (TUnknown u) = u =:= t
88+ unifyTypes' (SaturatedTypeSynonym name args) ty = do
89+ ty1 <- expandTypeSynonym name args
90+ ty1 `unifyTypes` ty
91+ unifyTypes' ty s@(SaturatedTypeSynonym _ _) = s `unifyTypes` ty
92+ unifyTypes' (ForAll ident1 ty1) (ForAll ident2 ty2) = do
93+ sk <- skolemize ident1 ty1
94+ replaced <- replaceVarWithUnknown ident2 ty2
95+ sk `unifyTypes` replaced
96+ unifyTypes' (ForAll ident ty1) ty2 = do
97+ sk <- skolemize ident ty1
98+ sk `unifyTypes` ty2
99+ unifyTypes' ty f@(ForAll _ _) = f `unifyTypes` ty
100+ unifyTypes' (Object row1) (Object row2) = row1 =?= row2
101+ unifyTypes' (TypeVar v1) (TypeVar v2) | v1 == v2 = return ()
102+ unifyTypes' (TypeConstructor c1) (TypeConstructor c2) = do
103+ env <- getEnv
104+ Just moduleName <- checkCurrentModule <$> get
105+ guardWith ("Cannot unify " ++ show c1 ++ " with " ++ show c2 ++ ".") (typeConstructorsAreEqual env moduleName c1 c2)
106+ unifyTypes' (TypeApp t3 t4) (TypeApp t5 t6) = do
107+ t3 `unifyTypes` t5
108+ t4 `unifyTypes` t6
109+ unifyTypes' (Skolem s1) (Skolem s2) | s1 == s2 = return ()
110+ unifyTypes' r1@(RCons _ _ _) r2 = unifyRows r1 r2
111+ unifyTypes' r1 r2@(RCons _ _ _) = unifyRows r1 r2
112+ unifyTypes' r1@REmpty r2 = unifyRows r1 r2
113+ unifyTypes' r1 r2@REmpty = unifyRows r1 r2
114+ unifyTypes' t3 t4 = throwError $ "Cannot unify " ++ prettyPrintType t3 ++ " with " ++ prettyPrintType t4 ++ "."
115+
116+-- |
117+-- Unify two rows, updating the current substitution
118+--
119+-- Common labels are first identified, and unified. Remaining labels and types are unified with a
120+-- trailing row unification variable, if appropriate, otherwise leftover labels result in a unification
121+-- error.
122+--
123+unifyRows :: Type -> Type -> UnifyT Type Check ()
124+unifyRows r1 r2 =
125+ let
126+ (s1, r1') = rowToList r1
127+ (s2, r2') = rowToList r2
128+ int = [ (t1, t2) | (name, t1) <- s1, (name', t2) <- s2, name == name' ]
129+ sd1 = [ (name, t1) | (name, t1) <- s1, name `notElem` map fst s2 ]
130+ sd2 = [ (name, t2) | (name, t2) <- s2, name `notElem` map fst s1 ]
131+ in do
132+ forM_ int (uncurry (=?=))
133+ unifyRows' sd1 r1' sd2 r2'
134+ where
135+ unifyRows' :: [(String, Type)] -> Type -> [(String, Type)] -> Type -> UnifyT Type Check ()
136+ unifyRows' [] (TUnknown u) sd r = u =:= rowFromList (sd, r)
137+ unifyRows' sd r [] (TUnknown u) = u =:= rowFromList (sd, r)
138+ unifyRows' ((name, ty):row) r others u@(TUnknown un) = do
139+ occursCheck un ty
140+ forM_ row $ \(_, t) -> occursCheck un t
141+ u' <- fresh
142+ u =?= RCons name ty u'
143+ unifyRows' row r others u'
144+ unifyRows' [] REmpty [] REmpty = return ()
145+ unifyRows' [] (TypeVar v1) [] (TypeVar v2) | v1 == v2 = return ()
146+ unifyRows' [] (Skolem s1) [] (Skolem s2) | s1 == s2 = return ()
147+ unifyRows' sd3 r3 sd4 r4 = throwError $ "Cannot unify " ++ prettyPrintRow (rowFromList (sd3, r3)) ++ " with " ++ prettyPrintRow (rowFromList (sd4, r4)) ++ "."
148+
149+-- |
150+-- Ensure type constructors are equal after canonicalization
151+--
152+typeConstructorsAreEqual :: Environment -> ModuleName -> Qualified ProperName -> Qualified ProperName -> Bool
153+typeConstructorsAreEqual env moduleName = (==) `on` canonicalizeType moduleName env
154+
155+-- |
156+-- Infer the types of multiple mutually-recursive values, and return elaborated values including
157+-- type class dictionaries and type annotations.
158+--
159+typesOf :: ModuleName -> [(Ident, Value)] -> Check [(Ident, (Value, Type))]
160+typesOf moduleName vals = do
161+ tys <- fmap tidyUp . liftUnify $ do
162+ let es = map isTyped vals
163+ typed = filter (isJust . snd . snd) es
164+ untyped = filter (isNothing . snd . snd) es
165+ typedDict = map (\(ident, (_, Just ty)) -> (ident, ty)) typed
166+ untypedNames <- replicateM (length untyped) fresh
167+ let untypedDict = zip (map fst untyped) untypedNames
168+ dict = M.fromList (map (\(ident, ty) -> ((moduleName, ident), (ty, LocalVariable))) $ (map (id *** fst) typedDict) ++ untypedDict)
169+ forM es $ \e -> do
170+ triple@(_, (val, ty)) <- case e of
171+ (ident, (val, Just (ty, checkType))) -> do
172+ kind <- liftCheck $ kindOf moduleName ty
173+ guardWith ("Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
174+ ty' <- replaceAllTypeSynonyms ty
175+ val' <- bindNames dict $ if checkType then check val ty' else return val
176+ return (ident, (val', ty'))
177+ (ident, (val, Nothing)) -> do
178+ TypedValue _ val' ty <- bindNames dict $ infer val
179+ ty =?= fromMaybe (error "name not found in dictionary") (lookup ident untypedDict)
180+ return (ident, (val', ty))
181+ when (moduleName == ModuleName (ProperName "Main") && fst e == Ident "main") $ do
182+ [eff, a] <- replicateM 2 fresh
183+ ty =?= TypeApp (TypeApp (TypeConstructor (Qualified (Just (ModuleName (ProperName "Eff"))) (ProperName "Eff"))) eff) a
184+ escapeCheck val ty
185+ return triple
186+ forM_ tys $ skolemEscapeCheck . snd . snd
187+ forM tys $ \(ident, (val, ty)) -> do
188+ val' <- replaceTypeClassDictionaries moduleName val
189+ return (ident, (overTypes (desaturateAllTypeSynonyms . setifyAll) $ val'
190+ , varIfUnknown . desaturateAllTypeSynonyms . setifyAll $ ty))
191+ where
192+ tidyUp (ts, sub) = map (\(i, (val, ty)) -> (i, (overTypes (sub $?) val, sub $? ty))) ts
193+
194+-- |
195+-- Check if a value contains a type annotation
196+--
197+isTyped :: (Ident, Value) -> (Ident, (Value, Maybe (Type, Bool)))
198+isTyped (name, TypedValue checkType value ty) = (name, (value, Just (ty, checkType)))
199+isTyped (name, value) = (name, (value, Nothing))
200+
201+-- |
202+-- Map a function over type annotations appearing inside a value
203+--
204+overTypes :: (Type -> Type) -> Value -> Value
205+overTypes f = everywhere (mkT f)
206+
207+-- |
208+-- Replace type class dictionary placeholders with inferred type class dictionaries
209+--
210+replaceTypeClassDictionaries :: ModuleName -> Value -> Check Value
211+replaceTypeClassDictionaries mn = everywhereM (mkM go)
212+ where
213+ go (TypeClassDictionary constraint dicts) = entails mn dicts constraint
214+ go other = return other
215+
216+-- |
217+-- Check that the current set of type class dictionaries entail the specified type class goal, and, if so,
218+-- return a type class dictionary reference.
219+--
220+entails :: ModuleName -> [TypeClassDictionaryInScope] -> (Qualified ProperName, Type) -> Check Value
221+entails moduleName context goal@(className, ty) = do
222+ env <- getEnv
223+ case go env goal of
224+ [] -> throwError $ "No " ++ show className ++ " instance found for " ++ prettyPrintType ty
225+ (dict : _) -> return dict
226+ where
227+ go env (className', ty') =
228+ [ mkDictionary (canonicalizeDictionary tcd) args
229+ | tcd <- context
230+ , filterModule tcd
231+ , typeConstructorsAreEqual env moduleName className' (tcdClassName tcd)
232+ , subst <- maybeToList $ typeHeadsAreEqual moduleName env ty' (tcdInstanceType tcd)
233+ , args <- solveSubgoals env subst (tcdDependencies tcd) ]
234+ solveSubgoals :: Environment -> [(String, Type)] -> Maybe [(Qualified ProperName, Type)] -> [Maybe [Value]]
235+ solveSubgoals _ _ Nothing = return Nothing
236+ solveSubgoals env subst (Just subgoals) = do
237+ dict <- mapM (go env) (replaceAllTypeVars subst subgoals)
238+ return $ Just dict
239+ mkDictionary :: Qualified Ident -> Maybe [Value] -> Value
240+ mkDictionary fnName Nothing = Var fnName
241+ mkDictionary fnName (Just dicts) = foldr (flip App) (Var fnName) dicts
242+ filterModule :: TypeClassDictionaryInScope -> Bool
243+ filterModule (TypeClassDictionaryInScope { tcdName = Qualified (Just mn) _ }) | mn == moduleName = True
244+ filterModule (TypeClassDictionaryInScope { tcdName = Qualified Nothing _ }) = True
245+ filterModule _ = False
246+ canonicalizeDictionary :: TypeClassDictionaryInScope -> Qualified Ident
247+ canonicalizeDictionary (TypeClassDictionaryInScope { tcdType = TCDRegular, tcdName = nm }) = nm
248+ canonicalizeDictionary (TypeClassDictionaryInScope { tcdType = TCDAlias nm }) = nm
249+
250+-- |
251+-- Check whether the type heads of two types are equal (for the purposes of type class dictionary lookup),
252+-- and return a substitution from type variables to types which makes the type heads unify.
253+--
254+typeHeadsAreEqual :: ModuleName -> Environment -> Type -> Type -> Maybe [(String, Type)]
255+typeHeadsAreEqual _ _ (Skolem s1) (Skolem s2) | s1 == s2 = Just []
256+typeHeadsAreEqual m e (TypeConstructor c1) (TypeConstructor c2) | typeConstructorsAreEqual e m c1 c2 = Just []
257+typeHeadsAreEqual m e (TypeApp h1 (TypeVar v)) (TypeApp h2 arg) = (:) (v, arg) <$> typeHeadsAreEqual m e h1 h2
258+typeHeadsAreEqual m e t1@(TypeApp _ _) t2@(TypeApp _ (TypeVar _)) = typeHeadsAreEqual m e t2 t1
259+typeHeadsAreEqual _ _ _ _ = Nothing
260+
261+-- |
262+-- Ensure unsolved unification variables do not escape
263+--
264+escapeCheck :: Value -> Type -> UnifyT Type Check ()
265+escapeCheck value ty = do
266+ subst <- unifyCurrentSubstitution <$> UnifyT get
267+ let visibleUnknowns = nub $ unknowns $ subst $? ty
268+ let allUnknowns = findAllTypes value
269+ forM_ allUnknowns $ \t -> do
270+ let unsolvedUnknowns = nub . unknowns $ subst $? t
271+ guardWith ("Escape check fails" ++ show (subst $? ty, subst $? t)) $ null $ unsolvedUnknowns \\ visibleUnknowns
272+
273+-- |
274+-- Find all type annotations occuring inside a value
275+--
276+findAllTypes :: Value -> [Type]
277+findAllTypes = everything (++) (mkQ [] go)
278+ where
279+ go (TypedValue _ _ ty) = [ty]
280+ go _ = []
281+
282+-- |
283+-- Ensure skolem variables do not escape their scope
284+--
285+skolemEscapeCheck :: Type -> Check ()
286+skolemEscapeCheck ty =
287+ case something (mkQ Nothing findSkolems) ty of
288+ Nothing -> return ()
289+ Just _ -> throwError $ "Skolem variables cannot escape. Consider adding a type signature."
290+ where
291+ findSkolems (Skolem _) = return ()
292+ findSkolems _ = mzero
293+
294+-- |
295+-- Ensure a row contains no duplicate labels
296+--
297+setify :: Type -> Type
298+setify = rowFromList . first (M.toList . M.fromList) . rowToList
299+
300+-- |
301+-- \"Setify\" all rows occuring inside a value
302+--
303+setifyAll :: (D.Data d) => d -> d
304+setifyAll = everywhere (mkT setify)
305+
306+-- |
307+-- Replace outermost unsolved unification variables with named type variables
308+--
309+varIfUnknown :: Type -> Type
310+varIfUnknown ty =
311+ let unks = nub $ unknowns ty
312+ toName = (:) 't' . show
313+ ty' = everywhere (mkT typeToVar) $ ty
314+ typeToVar :: Type -> Type
315+ typeToVar (TUnknown (Unknown u)) = TypeVar (toName u)
316+ typeToVar t = t
317+ in mkForAll (sort . map (toName . runUnknown) $ unks) ty'
318+
319+-- |
320+-- Replace named type variables with types
321+--
322+replaceAllTypeVars :: (D.Data d) => [(String, Type)] -> d -> d
323+replaceAllTypeVars = foldl' (\f (name, ty) -> replaceTypeVars name ty . f) id
324+
325+-- |
326+-- Replace named type variables with new unification variables
327+--
328+replaceAllVarsWithUnknowns :: Type -> UnifyT Type Check Type
329+replaceAllVarsWithUnknowns (ForAll ident ty) = replaceVarWithUnknown ident ty >>= replaceAllVarsWithUnknowns
330+replaceAllVarsWithUnknowns ty = return ty
331+
332+-- |
333+-- Replace a single type variable with a new unification variable
334+--
335+replaceVarWithUnknown :: String -> Type -> UnifyT Type Check Type
336+replaceVarWithUnknown ident ty = do
337+ tu <- fresh
338+ return $ replaceTypeVars ident tu $ ty
339+
340+-- |
341+-- Replace fully applied type synonyms with the @SaturatedTypeSynonym@ data constructor, which helps generate
342+-- better error messages during unification.
343+--
344+replaceAllTypeSynonyms :: (Functor m, MonadState CheckState m, MonadError String m) => (D.Data d) => d -> m d
345+replaceAllTypeSynonyms d = do
346+ env <- getEnv
347+ Just moduleName <- checkCurrentModule <$> get
348+ let syns = map (\((path, name), (args, _)) -> ((path, name), length args)) . M.toList $ typeSynonyms env
349+ either throwError return $ saturateAllTypeSynonyms env moduleName syns d
350+
351+-- |
352+-- \"Desaturate\" @SaturatedTypeSynonym@s
353+--
354+desaturateAllTypeSynonyms :: (D.Data d) => d -> d
355+desaturateAllTypeSynonyms = everywhere (mkT replaceSaturatedTypeSynonym)
356+ where
357+ replaceSaturatedTypeSynonym (SaturatedTypeSynonym name args) = foldl TypeApp (TypeConstructor name) args
358+ replaceSaturatedTypeSynonym t = t
359+
360+-- |
361+-- Replace a type synonym and its arguments with the aliased type
362+--
363+expandTypeSynonym :: Qualified ProperName -> [Type] -> UnifyT Type Check Type
364+expandTypeSynonym name args = do
365+ env <- getEnv
366+ Just moduleName <- checkCurrentModule <$> get
367+ case M.lookup (canonicalizeType moduleName env name) (typeSynonyms env) of
368+ Just (synArgs, body) -> return $ replaceAllTypeVars (zip synArgs args) body
369+ Nothing -> error "Type synonym was not defined"
370+
371+-- |
372+-- Ensure a set of property names and value does not contain duplicate labels
373+--
374+ensureNoDuplicateProperties :: (MonadError String m) => [(String, Value)] -> m ()
375+ensureNoDuplicateProperties ps = guardWith "Duplicate property names" $ length (nub . map fst $ ps) == length ps
376+
377+-- |
378+-- Infer a type for a value, rethrowing any error to provide a more useful error message
379+--
380+infer :: Value -> UnifyT Type Check Value
381+infer val = rethrow (\e -> "Error inferring type of term " ++ prettyPrintValue val ++ ":\n" ++ e) $ infer' val
382+
383+-- |
384+-- Infer a type for a value
385+--
386+infer' :: Value -> UnifyT Type Check Value
387+infer' v@(NumericLiteral _) = return $ TypedValue True v tyNumber
388+infer' v@(StringLiteral _) = return $ TypedValue True v tyString
389+infer' v@(BooleanLiteral _) = return $ TypedValue True v tyBoolean
390+infer' (ArrayLiteral vals) = do
391+ ts <- mapM infer vals
392+ els <- fresh
393+ forM_ ts $ \(TypedValue _ _ t) -> els =?= TypeApp tyArray t
394+ return $ TypedValue True (ArrayLiteral ts) els
395+infer' (ObjectLiteral ps) = do
396+ ensureNoDuplicateProperties ps
397+ ts <- mapM (infer . snd) ps
398+ let fields = zipWith (\name (TypedValue _ _ t) -> (name, t)) (map fst ps) ts
399+ ty = Object $ rowFromList (fields, REmpty)
400+ return $ TypedValue True (ObjectLiteral (zip (map fst ps) ts)) ty
401+infer' (ObjectUpdate o ps) = do
402+ ensureNoDuplicateProperties ps
403+ row <- fresh
404+ newVals <- zipWith (\(name, _) t -> (name, t)) ps <$> mapM (infer . snd) ps
405+ let newTys = map (\(name, TypedValue _ _ ty) -> (name, ty)) newVals
406+ oldTys <- zip (map fst ps) <$> replicateM (length ps) fresh
407+ o' <- check o $ Object $ rowFromList (oldTys, row)
408+ return $ TypedValue True (ObjectUpdate o' newVals) $ Object $ rowFromList (newTys, row)
409+infer' (Accessor prop val) = do
410+ typed@(TypedValue _ _ objTy) <- infer val
411+ propTy <- inferProperty objTy prop
412+ case propTy of
413+ Nothing -> do
414+ field <- fresh
415+ rest <- fresh
416+ _ <- subsumes Nothing objTy (Object (RCons prop field rest))
417+ return $ TypedValue True (Accessor prop typed) field
418+ Just ty -> return $ TypedValue True (Accessor prop typed) ty
419+infer' (Abs arg ret) = do
420+ ty <- fresh
421+ Just moduleName <- checkCurrentModule <$> get
422+ bindLocalVariables moduleName [(arg, ty)] $ do
423+ body@(TypedValue _ _ bodyTy) <- infer' ret
424+ return $ TypedValue True (Abs arg body) $ function ty bodyTy
425+infer' (App f arg) = do
426+ f'@(TypedValue _ _ ft) <- infer f
427+ ret <- fresh
428+ app <- checkFunctionApplication f' ft arg ret
429+ return $ TypedValue True app ret
430+infer' (Var var) = do
431+ Just moduleName <- checkCurrentModule <$> get
432+ ty <- lookupVariable moduleName var
433+ ty' <- replaceAllTypeSynonyms ty
434+ case ty' of
435+ ConstrainedType constraints _ -> do
436+ env <- getEnv
437+ dicts <- getTypeClassDictionaries
438+ return $ TypedValue True (foldl App (Var var) (map (flip TypeClassDictionary dicts) (qualifyAllUnqualifiedNames moduleName env constraints))) ty'
439+ _ -> return $ TypedValue True (Var var) ty'
440+infer' (Block ss) = do
441+ ret <- fresh
442+ (allCodePathsReturn, _, ss') <- checkBlock M.empty ret ss
443+ guardWith "Block is missing a return statement" allCodePathsReturn
444+ return $ TypedValue True (Block ss') ret
445+infer' v@(Constructor c) = do
446+ env <- getEnv
447+ Just moduleName <- checkCurrentModule <$> get
448+ case M.lookup (qualify moduleName c) (dataConstructors env) of
449+ Nothing -> throwError $ "Constructor " ++ show c ++ " is undefined"
450+ Just (ty, _) -> do ty' <- replaceAllTypeSynonyms ty
451+ return $ TypedValue True v ty'
452+infer' (Case vals binders) = do
453+ ts <- mapM infer vals
454+ ret <- fresh
455+ binders' <- checkBinders (map (\(TypedValue _ _ t) -> t) ts) ret binders
456+ return $ TypedValue True (Case ts binders') ret
457+infer' (IfThenElse cond th el) = do
458+ cond' <- check cond tyBoolean
459+ v2@(TypedValue _ _ t2) <- infer th
460+ v3@(TypedValue _ _ t3) <- infer el
461+ t2 =?= t3
462+ return $ TypedValue True (IfThenElse cond' v2 v3) t2
463+infer' (TypedValue checkType val ty) = do
464+ Just moduleName <- checkCurrentModule <$> get
465+ kind <- liftCheck $ kindOf moduleName ty
466+ guardWith ("Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
467+ ty' <- replaceAllTypeSynonyms ty
468+ val' <- if checkType then check val ty' else return val
469+ return $ TypedValue True val' ty
470+infer' _ = error "Invalid argument to infer"
471+
472+-- |
473+-- Infer the type of a property inside a record with a given type
474+--
475+inferProperty :: Type -> String -> UnifyT Type Check (Maybe Type)
476+inferProperty (Object row) prop = do
477+ let (props, _) = rowToList row
478+ return $ lookup prop props
479+inferProperty (SaturatedTypeSynonym name args) prop = do
480+ replaced <- expandTypeSynonym name args
481+ inferProperty replaced prop
482+inferProperty (ForAll ident ty) prop = do
483+ replaced <- replaceVarWithUnknown ident ty
484+ inferProperty replaced prop
485+inferProperty _ _ = return Nothing
486+
487+-- |
488+-- Infer the types of variables brought into scope by a binder
489+--
490+inferBinder :: Type -> Binder -> UnifyT Type Check (M.Map Ident Type)
491+inferBinder _ NullBinder = return M.empty
492+inferBinder val (StringBinder _) = val =?= tyString >> return M.empty
493+inferBinder val (NumberBinder _) = val =?= tyNumber >> return M.empty
494+inferBinder val (BooleanBinder _) = val =?= tyBoolean >> return M.empty
495+inferBinder val (VarBinder name) = return $ M.singleton name val
496+inferBinder val (NullaryBinder ctor) = do
497+ env <- getEnv
498+ Just moduleName <- checkCurrentModule <$> get
499+ case M.lookup (qualify moduleName ctor) (dataConstructors env) of
500+ Just (ty, _) -> do
501+ _ <- subsumes Nothing ty val
502+ return M.empty
503+ _ -> throwError $ "Constructor " ++ show ctor ++ " is not defined"
504+inferBinder val (UnaryBinder ctor binder) = do
505+ env <- getEnv
506+ Just moduleName <- checkCurrentModule <$> get
507+ case M.lookup (qualify moduleName ctor) (dataConstructors env) of
508+ Just (ty, _) -> do
509+ fn <- replaceAllVarsWithUnknowns ty
510+ case fn of
511+ TypeApp (TypeApp t obj) ret | t == tyFunction -> do
512+ _ <- subsumes Nothing val ret
513+ inferBinder obj binder
514+ _ -> throwError $ "Constructor " ++ show ctor ++ " is not a unary constructor"
515+ _ -> throwError $ "Constructor " ++ show ctor ++ " is not defined"
516+inferBinder val (ObjectBinder props) = do
517+ row <- fresh
518+ rest <- fresh
519+ m1 <- inferRowProperties row rest props
520+ val =?= Object row
521+ return m1
522+ where
523+ inferRowProperties :: Type -> Type -> [(String, Binder)] -> UnifyT Type Check (M.Map Ident Type)
524+ inferRowProperties nrow row [] = nrow =?= row >> return M.empty
525+ inferRowProperties nrow row ((name, binder):binders) = do
526+ propTy <- fresh
527+ m1 <- inferBinder propTy binder
528+ m2 <- inferRowProperties nrow (RCons name propTy row) binders
529+ return $ m1 `M.union` m2
530+inferBinder val (ArrayBinder binders) = do
531+ el <- fresh
532+ m1 <- M.unions <$> mapM (inferBinder el) binders
533+ val =?= TypeApp tyArray el
534+ return m1
535+inferBinder val (ConsBinder headBinder tailBinder) = do
536+ el <- fresh
537+ m1 <- inferBinder el headBinder
538+ m2 <- inferBinder val tailBinder
539+ val =?= TypeApp tyArray el
540+ return $ m1 `M.union` m2
541+inferBinder val (NamedBinder name binder) = do
542+ m <- inferBinder val binder
543+ return $ M.insert name val m
544+
545+-- |
546+-- Check the types of the return values in a set of binders in a case statement
547+--
548+checkBinders :: [Type] -> Type -> [([Binder], Maybe Guard, Value)] -> UnifyT Type Check [([Binder], Maybe Guard, Value)]
549+checkBinders _ _ [] = return []
550+checkBinders nvals ret ((binders, grd, val):bs) = do
551+ Just moduleName <- checkCurrentModule <$> get
552+ m1 <- M.unions <$> zipWithM inferBinder nvals binders
553+ r <- bindLocalVariables moduleName (M.toList m1) $ do
554+ val' <- check val ret
555+ case grd of
556+ Nothing -> return (binders, Nothing, val')
557+ Just g -> do
558+ g' <- check g tyBoolean
559+ return (binders, Just g', val')
560+ rs <- checkBinders nvals ret bs
561+ return $ r : rs
562+
563+-- |
564+-- Check that a local variable name is not already used
565+--
566+assignVariable :: Ident -> UnifyT Type Check ()
567+assignVariable name = do
568+ env <- checkEnv <$> get
569+ Just moduleName <- checkCurrentModule <$> get
570+ case M.lookup (moduleName, name) (names env) of
571+ Just _ -> UnifyT . lift . throwError $ "Variable with name " ++ show name ++ " already exists."
572+ _ -> return ()
573+
574+-- |
575+-- Check the type of the return values of a statement, returning whether or not the statement returns on
576+-- all code paths
577+--
578+checkStatement :: M.Map Ident Type -> Type -> Statement -> UnifyT Type Check (Bool, M.Map Ident Type, Statement)
579+checkStatement mass _ (VariableIntroduction name val) = do
580+ assignVariable name
581+ val'@(TypedValue _ _ t) <- infer val
582+ return (False, M.insert name t mass, VariableIntroduction name val')
583+checkStatement mass _ (Assignment ident val) = do
584+ val'@(TypedValue _ _ t) <- infer val
585+ case M.lookup ident mass of
586+ Nothing -> throwError $ "No local variable with name " ++ show ident
587+ Just ty -> do t =?= ty
588+ return (False, mass, Assignment ident val')
589+checkStatement mass ret (While val inner) = do
590+ val' <- check val tyBoolean
591+ (allCodePathsReturn, _, inner') <- checkBlock mass ret inner
592+ return (allCodePathsReturn, mass, While val' inner')
593+checkStatement mass ret (If ifst) = do
594+ (allCodePathsReturn, ifst') <- checkIfStatement mass ret ifst
595+ return (allCodePathsReturn, mass, If ifst')
596+checkStatement mass ret (For ident start end inner) = do
597+ Just moduleName <- checkCurrentModule <$> get
598+ assignVariable ident
599+ start' <- check start tyNumber
600+ end' <- check end tyNumber
601+ (allCodePathsReturn, _, inner') <- bindLocalVariables moduleName [(ident, tyNumber)] $ checkBlock mass ret inner
602+ return (allCodePathsReturn, mass, For ident start' end' inner')
603+checkStatement mass ret (Return val) = do
604+ val' <- check val ret
605+ return (True, mass, Return val')
606+
607+-- |
608+-- Check the type of an if-then-else statement
609+--
610+checkIfStatement :: M.Map Ident Type -> Type -> IfStatement -> UnifyT Type Check (Bool, IfStatement)
611+checkIfStatement mass ret (IfStatement val thens Nothing) = do
612+ val' <- check val tyBoolean
613+ (_, _, thens') <- checkBlock mass ret thens
614+ return (False, IfStatement val' thens' Nothing)
615+checkIfStatement mass ret (IfStatement val thens (Just elses)) = do
616+ val' <- check val tyBoolean
617+ (allCodePathsReturn1, _, thens') <- checkBlock mass ret thens
618+ (allCodePathsReturn2, elses') <- checkElseStatement mass ret elses
619+ return (allCodePathsReturn1 && allCodePathsReturn2, IfStatement val' thens' (Just elses'))
620+
621+-- |
622+-- Check the type of an else statement
623+--
624+checkElseStatement :: M.Map Ident Type -> Type -> ElseStatement -> UnifyT Type Check (Bool, ElseStatement)
625+checkElseStatement mass ret (Else elses) = do
626+ (allCodePathsReturn, _, elses') <- checkBlock mass ret elses
627+ return (allCodePathsReturn, Else elses')
628+checkElseStatement mass ret (ElseIf ifst) = (id *** ElseIf) <$> checkIfStatement mass ret ifst
629+
630+-- |
631+-- Check the type of the return value of a block of statements
632+--
633+checkBlock :: M.Map Ident Type -> Type -> [Statement] -> UnifyT Type Check (Bool, M.Map Ident Type, [Statement])
634+checkBlock mass _ [] = return (False, mass, [])
635+checkBlock mass ret (s:ss) = do
636+ Just moduleName <- checkCurrentModule <$> get
637+ (b1, mass1, s') <- checkStatement mass ret s
638+ bindLocalVariables moduleName (M.toList mass1) $ case (b1, ss) of
639+ (True, []) -> return (True, mass1, [s'])
640+ (True, _) -> throwError "Unreachable code"
641+ (False, ss') -> do
642+ (b, m, ss'') <- checkBlock mass1 ret ss'
643+ return (b, m, s':ss'')
644+
645+-- |
646+-- Skolemize a type variable by replacing its instances with fresh skolem constants
647+--
648+skolemize :: String -> Type -> UnifyT Type Check Type
649+skolemize ident ty = do
650+ tsk <- Skolem . runUnknown <$> fresh'
651+ return $ replaceTypeVars ident tsk ty
652+
653+-- |
654+-- Check the type of a value, rethrowing errors to provide a better error message
655+--
656+check :: Value -> Type -> UnifyT Type Check Value
657+check val ty = rethrow errorMessage $ check' val ty
658+ where
659+ errorMessage msg =
660+ "Error checking type of term " ++
661+ prettyPrintValue val ++
662+ " against type " ++
663+ prettyPrintType ty ++
664+ ":\n" ++
665+ msg
666+
667+-- |
668+-- Check the type of a value
669+--
670+check' :: Value -> Type -> UnifyT Type Check Value
671+check' val (ForAll idents ty) = do
672+ sk <- skolemize idents ty
673+ check val sk
674+check' val (ConstrainedType constraints ty) = do
675+ env <- getEnv
676+ Just moduleName <- checkCurrentModule <$> get
677+ dictNames <- flip mapM constraints $ \(Qualified _ (ProperName className), _) -> do
678+ n <- liftCheck freshDictionaryName
679+ return $ Ident $ "__dict_" ++ className ++ "_" ++ show n
680+ val' <- withTypeClassDictionaries (zipWith (\name (className, instanceTy) ->
681+ TypeClassDictionaryInScope name className instanceTy Nothing TCDRegular) (map (Qualified Nothing) dictNames)
682+ (qualifyAllUnqualifiedNames moduleName env constraints)) $
683+ check val ty
684+ return $ foldr Abs val' dictNames
685+check' val u@(TUnknown _) = do
686+ val'@(TypedValue _ _ ty) <- infer val
687+ -- Don't unify an unknown with an inferred polytype
688+ ty' <- replaceAllVarsWithUnknowns ty
689+ ty' =?= u
690+ return val'
691+check' v@(NumericLiteral _) t | t == tyNumber = return v
692+check' v@(StringLiteral _) t | t == tyString = return v
693+check' v@(BooleanLiteral _) t | t == tyBoolean = return v
694+check' (ArrayLiteral vals) (TypeApp a ty) | a == tyArray = ArrayLiteral <$> forM vals (\val -> check val ty)
695+check' (Abs arg ret) (TypeApp (TypeApp t argTy) retTy) | t == tyFunction = do
696+ Just moduleName <- checkCurrentModule <$> get
697+ ret' <- bindLocalVariables moduleName [(arg, argTy)] $ check ret retTy
698+ return $ Abs arg ret'
699+check' (App f arg) ret = do
700+ f'@(TypedValue _ _ ft) <- infer f
701+ app <- checkFunctionApplication f' ft arg ret
702+ return $ app
703+check' v@(Var var) ty = do
704+ Just moduleName <- checkCurrentModule <$> get
705+ ty1 <- lookupVariable moduleName var
706+ repl <- replaceAllTypeSynonyms ty1
707+ ty' <- replaceAllTypeSynonyms ty
708+ v' <- subsumes (Just v) repl ty'
709+ case v' of
710+ Nothing -> throwError "Unable to check type subsumption"
711+ Just v'' -> return v''
712+check' (TypedValue checkType val ty1) ty2 = do
713+ Just moduleName <- checkCurrentModule <$> get
714+ kind <- liftCheck $ kindOf moduleName ty1
715+ guardWith ("Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
716+ val' <- subsumes (Just val) ty1 ty2
717+ case val' of
718+ Nothing -> throwError "Unable to check type subsumption"
719+ Just val'' -> do
720+ val''' <- if checkType then check val'' ty1 else return val''
721+ return $ TypedValue True val''' ty1
722+check' (Case vals binders) ret = do
723+ vals' <- mapM infer vals
724+ let ts = map (\(TypedValue _ _ t) -> t) vals'
725+ binders' <- checkBinders ts ret binders
726+ return $ Case vals' binders'
727+check' (IfThenElse cond th el) ty = do
728+ cond' <- check cond tyBoolean
729+ th' <- check th ty
730+ el' <- check el ty
731+ return $ IfThenElse cond' th' el'
732+check' (ObjectLiteral ps) (Object row) = do
733+ ensureNoDuplicateProperties ps
734+ ps' <- checkProperties ps row False
735+ return $ ObjectLiteral ps'
736+check' (ObjectUpdate obj ps) (Object row) = do
737+ ensureNoDuplicateProperties ps
738+ us <- zip (map fst ps) <$> replicateM (length ps) fresh
739+ let (propsToCheck, rest) = rowToList row
740+ propsToRemove = map fst ps
741+ remainingProps = filter (\(p, _) -> p `notElem` propsToRemove) propsToCheck
742+ obj' <- check obj (Object (rowFromList (us ++ remainingProps, rest)))
743+ ps' <- checkProperties ps row True
744+ return $ ObjectUpdate obj' ps'
745+check' (Accessor prop val) ty = do
746+ rest <- fresh
747+ val' <- check val (Object (RCons prop ty rest))
748+ return $ Accessor prop val'
749+check' (Block ss) ret = do
750+ (allCodePathsReturn, _, ss') <- checkBlock M.empty ret ss
751+ guardWith "Block is missing a return statement" allCodePathsReturn
752+ return $ Block ss'
753+check' (Constructor c) ty = do
754+ env <- getEnv
755+ Just moduleName <- checkCurrentModule <$> get
756+ case M.lookup (qualify moduleName c) (dataConstructors env) of
757+ Nothing -> throwError $ "Constructor " ++ show c ++ " is undefined"
758+ Just (ty1, _) -> do
759+ repl <- replaceAllTypeSynonyms ty1
760+ _ <- subsumes Nothing repl ty
761+ return $ Constructor c
762+check' val (SaturatedTypeSynonym name args) = do
763+ ty <- expandTypeSynonym name args
764+ check val ty
765+check' val ty = throwError $ prettyPrintValue val ++ " does not have type " ++ prettyPrintType ty
766+
767+-- |
768+-- Check the type of a collection of named record fields
769+--
770+-- The @lax@ parameter controls whether or not every record member has to be provided. For object updates, this is not the case.
771+--
772+checkProperties :: [(String, Value)] -> Type -> Bool -> UnifyT Type Check [(String, Value)]
773+checkProperties ps row lax = let (ts, r') = rowToList row in go ps ts r' where
774+ go [] [] REmpty = return []
775+ go [] [] u@(TUnknown _) = do u =?= REmpty
776+ return []
777+ go [] [] (Skolem _) | lax = return []
778+ go [] ((p, _): _) _ | lax = return []
779+ | otherwise = throwError $ prettyPrintValue (ObjectLiteral ps) ++ " does not have property " ++ p
780+ go ((p,_):_) [] REmpty = throwError $ "Property " ++ p ++ " is not present in closed object type " ++ prettyPrintRow row
781+ go ((p,v):ps') [] u@(TUnknown _) = do
782+ v'@(TypedValue _ _ ty) <- infer v
783+ rest <- fresh
784+ u =?= RCons p ty rest
785+ ps'' <- go ps' [] rest
786+ return $ (p, v') : ps''
787+ go ((p,v):ps') ts r =
788+ case lookup p ts of
789+ Nothing -> do
790+ v'@(TypedValue _ _ ty) <- infer v
791+ rest <- fresh
792+ r =?= RCons p ty rest
793+ ps'' <- go ps' ts rest
794+ return $ (p, v') : ps''
795+ Just ty -> do
796+ v' <- check v ty
797+ ps'' <- go ps' (delete (p, ty) ts) r
798+ return $ (p, v') : ps''
799+ go _ _ _ = throwError $ prettyPrintValue (ObjectLiteral ps) ++ " does not have type " ++ prettyPrintType (Object row)
800+
801+-- |
802+-- Check the type of a function application, rethrowing errors to provide a better error message
803+--
804+checkFunctionApplication :: Value -> Type -> Value -> Type -> UnifyT Type Check Value
805+checkFunctionApplication fn fnTy arg ret = rethrow errorMessage $ checkFunctionApplication' fn fnTy arg ret
806+ where
807+ errorMessage msg = "Error applying function of type "
808+ ++ prettyPrintType fnTy
809+ ++ " to argument " ++ prettyPrintValue arg
810+ ++ ":\n" ++ msg
811+
812+-- |
813+-- Check the type of a function application
814+--
815+checkFunctionApplication' :: Value -> Type -> Value -> Type -> UnifyT Type Check Value
816+checkFunctionApplication' fn (TypeApp (TypeApp tyFunction' argTy) retTy) arg ret = do
817+ tyFunction' =?= tyFunction
818+ arg' <- check arg argTy
819+ _ <- subsumes Nothing retTy ret
820+ return $ App fn arg'
821+checkFunctionApplication' fn (ForAll ident ty) arg ret = do
822+ replaced <- replaceVarWithUnknown ident ty
823+ checkFunctionApplication fn replaced arg ret
824+checkFunctionApplication' fn u@(TUnknown _) arg ret = do
825+ arg' <- do
826+ TypedValue _ v t <- infer arg
827+ TypedValue True v <$> replaceAllVarsWithUnknowns t
828+ let ty = (\(TypedValue _ _ t) -> t) arg'
829+ u =?= function ty ret
830+ return $ App fn arg'
831+checkFunctionApplication' fn (SaturatedTypeSynonym name tyArgs) arg ret = do
832+ ty <- expandTypeSynonym name tyArgs
833+ checkFunctionApplication fn ty arg ret
834+checkFunctionApplication' fn (ConstrainedType constraints fnTy) arg ret = do
835+ env <- getEnv
836+ dicts <- getTypeClassDictionaries
837+ Just moduleName <- checkCurrentModule <$> get
838+ checkFunctionApplication' (foldl App fn (map (flip TypeClassDictionary dicts) (qualifyAllUnqualifiedNames moduleName env constraints))) fnTy arg ret
839+checkFunctionApplication' _ fnTy arg ret = throwError $ "Applying a function of type "
840+ ++ prettyPrintType fnTy
841+ ++ " to argument(s) " ++ prettyPrintValue arg
842+ ++ " does not yield a value of type " ++ prettyPrintType ret ++ "."
843+
844+-- |
845+-- Check whether one type subsumes another, rethrowing errors to provide a better error message
846+--
847+subsumes :: Maybe Value -> Type -> Type -> UnifyT Type Check (Maybe Value)
848+subsumes val ty1 ty2 = rethrow errorMessage $ subsumes' val ty1 ty2
849+ where
850+ errorMessage msg = "Error checking that type "
851+ ++ prettyPrintType ty1
852+ ++ " subsumes type "
853+ ++ prettyPrintType ty2
854+ ++ ":\n" ++ msg
855+
856+-- |
857+-- Check whether one type subsumes another
858+--
859+subsumes' :: Maybe Value -> Type -> Type -> UnifyT Type Check (Maybe Value)
860+subsumes' val (ForAll ident ty1) ty2 = do
861+ replaced <- replaceVarWithUnknown ident ty1
862+ subsumes val replaced ty2
863+subsumes' val (TypeApp (TypeApp f1 arg1) ret1) (TypeApp (TypeApp f2 arg2) ret2) | f1 == tyFunction && f2 == tyFunction = do
864+ subsumes Nothing arg2 arg1
865+ subsumes Nothing ret1 ret2
866+ return val
867+subsumes' val (SaturatedTypeSynonym name tyArgs) ty2 = do
868+ ty1 <- expandTypeSynonym name tyArgs
869+ subsumes val ty1 ty2
870+subsumes' val ty1 (SaturatedTypeSynonym name tyArgs) = do
871+ ty2 <- expandTypeSynonym name tyArgs
872+ subsumes val ty1 ty2
873+subsumes' (Just val) (ConstrainedType constraints ty1) ty2 = do
874+ env <- getEnv
875+ dicts <- getTypeClassDictionaries
876+ Just moduleName <- checkCurrentModule <$> get
877+ _ <- subsumes' Nothing ty1 ty2
878+ return . Just $ foldl App val (map (flip TypeClassDictionary dicts) (qualifyAllUnqualifiedNames moduleName env constraints))
879+subsumes' val ty1 ty2 = do
880+ ty1 =?= ty2
881+ return val
882+