@@ -0,0 +1,1181 @@
1+-----------------------------------------------------------------------------
3+-- Module : Language.PureScript.TypeChecker.Types
4+-- Copyright : (c) Phil Freeman 2013
7+-- Maintainer : Phil Freeman <paf31@cantab.net>
8+-- Stability : experimental
12+-- This module implements the type checker
14+-----------------------------------------------------------------------------
16+{-# OPTIONS_GHC -fno-warn-orphans #-}
17+{-# LANGUAGE FlexibleInstances #-}
18+{-# LANGUAGE FlexibleContexts #-}
19+{-# LANGUAGE MultiParamTypeClasses #-}
21+module Language.PureScript.TypeChecker.Types (
26+ The following functions represent the corresponding type checking judgements:
29+ Synthesize a type for a value
32+ Check a value has a given type
35+ Check an object with a given type contains specified properties
37+ checkFunctionApplication
38+ Check a function of a given type returns a value of another type when applied to its arguments
41+ Check a type subsumes another type
45+import Data.Maybe (maybeToList, fromMaybe)
46+import Data.Function (on)
47+import Data.Ord (comparing)
49+import Data.Either (lefts, rights)
51+import Language.PureScript.Declarations
52+import Language.PureScript.Types
53+import Language.PureScript.Kinds
54+import Language.PureScript.Names
55+import Language.PureScript.TypeClassDictionaries
56+import Language.PureScript.TypeChecker.Monad
57+import Language.PureScript.TypeChecker.Kinds
58+import Language.PureScript.TypeChecker.Synonyms
59+import Language.PureScript.Pretty
60+import Language.PureScript.Environment
61+import Language.PureScript.Errors
62+import qualified Language.PureScript.Constants as C
64+import Control.Monad.State
65+import Control.Monad.Error
66+import Control.Monad.Unify
68+import Control.Applicative
69+import Control.Arrow (Arrow(..))
71+import qualified Data.Map as M
72+import qualified Data.HashMap.Strict as H
74+instance Partial Type where
76+ isUnknown (TUnknown u) = Just u
77+ isUnknown _ = Nothing
78+ unknowns = everythingOnTypes (++) go
80+ go (TUnknown u) = [u]
82+ ($?) sub = everywhereOnTypes go
84+ go t@(TUnknown u) = case H.lookup u (runSubstitution sub) of
89+instance Unifiable Check Type where
93+-- Unify two types, updating the current substitution
95+unifyTypes :: Type -> Type -> UnifyT Type Check ()
96+unifyTypes t1 t2 = rethrow (mkErrorStack ("Error unifying type " ++ prettyPrintType t1 ++ " with type " ++ prettyPrintType t2) Nothing <>) $
99+ unifyTypes' (TUnknown u1) (TUnknown u2) | u1 == u2 = return ()
100+ unifyTypes' (TUnknown u) t = u =:= t
101+ unifyTypes' t (TUnknown u) = u =:= t
102+ unifyTypes' (SaturatedTypeSynonym name args) ty = do
103+ ty1 <- introduceSkolemScope <=< expandTypeSynonym name $ args
105+ unifyTypes' ty s@(SaturatedTypeSynonym _ _) = s `unifyTypes` ty
106+ unifyTypes' (ForAll ident1 ty1 sc1) (ForAll ident2 ty2 sc2) =
108+ (Just sc1', Just sc2') -> do
109+ sko <- newSkolemConstant
110+ let sk1 = skolemize ident1 sko sc1' ty1
111+ let sk2 = skolemize ident2 sko sc2' ty2
112+ sk1 `unifyTypes` sk2
113+ _ -> error "Skolemized type variable was not given a scope"
114+ unifyTypes' (ForAll ident ty1 (Just sc)) ty2 = do
115+ sko <- newSkolemConstant
116+ let sk = skolemize ident sko sc ty1
118+ unifyTypes' ForAll{} _ = throwError . strMsg $ "Skolem variable scope is unspecified"
119+ unifyTypes' ty f@ForAll{} = f `unifyTypes` ty
120+ unifyTypes' (TypeVar v1) (TypeVar v2) | v1 == v2 = return ()
121+ unifyTypes' (TypeConstructor c1) (TypeConstructor c2) =
122+ guardWith (strMsg ("Cannot unify " ++ show c1 ++ " with " ++ show c2 ++ ".")) (c1 == c2)
123+ unifyTypes' (TypeApp t3 t4) (TypeApp t5 t6) = do
126+ unifyTypes' (Skolem _ s1 _) (Skolem _ s2 _) | s1 == s2 = return ()
127+ unifyTypes' r1@RCons{} r2 = unifyRows r1 r2
128+ unifyTypes' r1 r2@RCons{} = unifyRows r1 r2
129+ unifyTypes' r1@REmpty r2 = unifyRows r1 r2
130+ unifyTypes' r1 r2@REmpty = unifyRows r1 r2
131+ unifyTypes' t@(ConstrainedType _ _) _ = throwError . strMsg $ "Attempted to unify a constrained type " ++ prettyPrintType t ++ " with another type."
132+ unifyTypes' t3 t4@(ConstrainedType _ _) = unifyTypes' t4 t3
133+ unifyTypes' t3 t4 = throwError . strMsg $ "Cannot unify " ++ prettyPrintType t3 ++ " with " ++ prettyPrintType t4 ++ "."
136+-- Unify two rows, updating the current substitution
138+-- Common labels are first identified, and unified. Remaining labels and types are unified with a
139+-- trailing row unification variable, if appropriate, otherwise leftover labels result in a unification
142+unifyRows :: Type -> Type -> UnifyT Type Check ()
145+ (s1, r1') = rowToList r1
146+ (s2, r2') = rowToList r2
147+ int = [ (t1, t2) | (name, t1) <- s1, (name', t2) <- s2, name == name' ]
148+ sd1 = [ (name, t1) | (name, t1) <- s1, name `notElem` map fst s2 ]
149+ sd2 = [ (name, t2) | (name, t2) <- s2, name `notElem` map fst s1 ]
151+ forM_ int (uncurry (=?=))
152+ unifyRows' sd1 r1' sd2 r2'
154+ unifyRows' :: [(String, Type)] -> Type -> [(String, Type)] -> Type -> UnifyT Type Check ()
155+ unifyRows' [] (TUnknown u) sd r = u =:= rowFromList (sd, r)
156+ unifyRows' sd r [] (TUnknown u) = u =:= rowFromList (sd, r)
157+ unifyRows' ((name, ty):row) r others u@(TUnknown un) = do
159+ forM_ row $ \(_, t) -> occursCheck un t
161+ u =?= RCons name ty u'
162+ unifyRows' row r others u'
163+ unifyRows' [] REmpty [] REmpty = return ()
164+ unifyRows' [] (TypeVar v1) [] (TypeVar v2) | v1 == v2 = return ()
165+ unifyRows' [] (Skolem _ s1 _) [] (Skolem _ s2 _) | s1 == s2 = return ()
166+ unifyRows' sd3 r3 sd4 r4 = throwError . strMsg $ "Cannot unify (" ++ prettyPrintRow (rowFromList (sd3, r3)) ++ ") with (" ++ prettyPrintRow (rowFromList (sd4, r4)) ++ ")"
169+-- Infer the types of multiple mutually-recursive values, and return elaborated values including
170+-- type class dictionaries and type annotations.
172+typesOf :: Maybe ModuleName -> ModuleName -> [(Ident, Expr)] -> Check [(Ident, (Expr, Type))]
173+typesOf mainModuleName moduleName vals = do
174+ tys <- fmap tidyUp . liftUnify $ do
175+ (untyped, typed, dict, untypedDict) <- typeDictionaryForBindingGroup moduleName vals
176+ ds1 <- parU typed $ \e -> do
177+ triple@(_, (_, ty)) <- checkTypedBindingGroupElement moduleName e dict
178+ checkMain (fst e) ty
180+ ds2 <- forM untyped $ \e -> do
181+ triple@(_, (_, ty)) <- typeForBindingGroupElement e dict untypedDict
182+ checkMain (fst e) ty
186+ forM tys $ \(ident, (val, ty)) -> do
187+ -- Replace type class dictionary placeholders with actual dictionaries
188+ val' <- replaceTypeClassDictionaries moduleName val
189+ -- Check skolem variables did not escape their scope
190+ skolemEscapeCheck val'
191+ -- Remove type synonyms placeholders, remove duplicate row fields, and replace
192+ -- top-level unification variables with named type variables.
193+ let val'' = overTypes (desaturateAllTypeSynonyms . setifyAll) val'
194+ ty' = varIfUnknown . desaturateAllTypeSynonyms . setifyAll $ ty
195+ return (ident, (val'', ty'))
197+ -- Apply the substitution that was returned from runUnify to both types and (type-annotated) values
198+ tidyUp (ts, sub) = map (\(i, (val, ty)) -> (i, (overTypes (sub $?) val, sub $? ty))) ts
199+ -- If --main is enabled, need to check that `main` has type Eff eff a for some eff, a
200+ checkMain nm ty = when (Just moduleName == mainModuleName && nm == Ident C.main) $ do
201+ [eff, a] <- replicateM 2 fresh
202+ ty =?= TypeApp (TypeApp (TypeConstructor (Qualified (Just (ModuleName [ProperName "Control", ProperName "Monad", ProperName "Eff"])) (ProperName "Eff"))) eff) a
204+type TypeData = M.Map (ModuleName, Ident) (Type, NameKind, NameVisibility)
206+type UntypedData = [(Ident, Type)]
208+typeDictionaryForBindingGroup :: ModuleName -> [(Ident, Expr)] -> UnifyT Type Check ([(Ident, Expr)], [(Ident, (Expr, Type, Bool))], TypeData, UntypedData)
209+typeDictionaryForBindingGroup moduleName vals = do
211+ -- Map each declaration to a name/value pair, with an optional type, if the declaration is typed
212+ es = map isTyped vals
213+ -- Filter the typed and untyped declarations
216+ -- Make a map of names to typed declarations
217+ typedDict = map (\(ident, (_, ty, _)) -> (ident, ty)) typed
219+ -- Create fresh unification variables for the types of untyped declarations
220+ untypedNames <- replicateM (length untyped) fresh
223+ -- Make a map of names to the unification variables of untyped declarations
224+ untypedDict = zip (map fst untyped) untypedNames
225+ -- Create the dictionary of all name/type pairs, which will be added to the environment during type checking
226+ dict = M.fromList (map (\(ident, ty) -> ((moduleName, ident), (ty, LocalVariable, Undefined))) $ typedDict ++ untypedDict)
227+ return (untyped, typed, dict, untypedDict)
229+checkTypedBindingGroupElement :: ModuleName -> (Ident, (Expr, Type, Bool)) -> TypeData -> UnifyT Type Check (Ident, (Expr, Type))
230+checkTypedBindingGroupElement moduleName (ident, (val', ty, checkType)) dict = do
232+ kind <- liftCheck $ kindOf moduleName ty
233+ guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
234+ -- Check the type with the new names in scope
235+ ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
236+ val'' <- if checkType
237+ then bindNames dict $ TypedValue True <$> check val' ty' <*> pure ty'
238+ else return (TypedValue False val' ty')
239+ return (ident, (val'', ty'))
241+typeForBindingGroupElement :: (Ident, Expr) -> TypeData -> UntypedData -> UnifyT Type Check (Ident, (Expr, Type))
242+typeForBindingGroupElement (ident, val) dict untypedDict = do
243+ -- Infer the type with the new names in scope
244+ TypedValue _ val' ty <- bindNames dict $ infer val
245+ ty =?= fromMaybe (error "name not found in dictionary") (lookup ident untypedDict)
246+ return (ident, (TypedValue True val' ty, ty))
249+-- Check if a value contains a type annotation
251+isTyped :: (Ident, Expr) -> (Either (Ident, Expr) (Ident, (Expr, Type, Bool)))
252+isTyped (name, TypedValue checkType value ty) = Right (name, (value, ty, checkType))
253+isTyped (name, value) = Left (name, value)
256+-- Map a function over type annotations appearing inside a value
258+overTypes :: (Type -> Type) -> Expr -> Expr
259+overTypes f = let (_, f', _) = everywhereOnValues id g id in f'
262+ g (TypedValue checkTy val t) = TypedValue checkTy val (f t)
263+ g (TypeClassDictionary b (nm, tys) sco) = TypeClassDictionary b (nm, map f tys) sco
267+-- Replace type class dictionary placeholders with inferred type class dictionaries
269+replaceTypeClassDictionaries :: ModuleName -> Expr -> Check Expr
270+replaceTypeClassDictionaries mn =
271+ let (_, f, _) = everywhereOnValuesTopDownM return go return
274+ go (TypeClassDictionary trySuperclasses constraint dicts) = do
276+ entails env mn dicts constraint trySuperclasses
277+ go other = return other
280+-- A simplified representation of expressions which are used to represent type
281+-- class dictionaries at runtime, which can be compared for equality
285+ -- A dictionary which is brought into scope by a local constraint
287+ = LocalDictionaryValue (Qualified Ident)
289+ -- A dictionary which is brought into scope by an instance declaration
291+ | GlobalDictionaryValue (Qualified Ident)
293+ -- A dictionary which depends on other dictionaries
295+ | DependentDictionaryValue (Qualified Ident) [DictionaryValue]
297+ -- A subclass dictionary
299+ | SubclassDictionaryValue DictionaryValue (Qualified ProperName) Integer
300+ deriving (Show, Ord, Eq)
303+-- Check that the current set of type class dictionaries entail the specified type class goal, and, if so,
304+-- return a type class dictionary reference.
306+entails :: Environment -> ModuleName -> [TypeClassDictionaryInScope] -> (Qualified ProperName, [Type]) -> Bool -> Check Expr
307+entails env moduleName context = solve (sortedNubBy canonicalizeDictionary (filter filterModule context))
309+ sortedNubBy :: (Ord k) => (v -> k) -> [v] -> [v]
310+ sortedNubBy f vs = M.elems (M.fromList (map (f &&& id) vs))
312+ -- Filter out type dictionaries which are in scope in the current module
313+ filterModule :: TypeClassDictionaryInScope -> Bool
314+ filterModule (TypeClassDictionaryInScope { tcdName = Qualified (Just mn) _ }) | mn == moduleName = True
315+ filterModule (TypeClassDictionaryInScope { tcdName = Qualified Nothing _ }) = True
316+ filterModule _ = False
318+ solve context' (className, tys) trySuperclasses =
319+ checkOverlaps $ go trySuperclasses className tys
321+ go trySuperclasses' className' tys' =
322+ -- Look for regular type instances
323+ [ mkDictionary (canonicalizeDictionary tcd) args
325+ -- Make sure the type class name matches the one we are trying to satisfy
326+ , className' == tcdClassName tcd
327+ -- Make sure the type unifies with the type in the type instance definition
328+ , subst <- maybeToList . (>>= verifySubstitution) . fmap concat $ zipWithM (typeHeadsAreEqual moduleName env) tys' (tcdInstanceTypes tcd)
329+ -- Solve any necessary subgoals
330+ , args <- solveSubgoals subst (tcdDependencies tcd) ] ++
332+ -- Look for implementations via superclasses
333+ [ SubclassDictionaryValue suDict superclass index
335+ , (subclassName, (args, _, implies)) <- M.toList (typeClasses env)
336+ -- Try each superclass
337+ , (index, (superclass, suTyArgs)) <- zip [0..] implies
338+ -- Make sure the type class name matches the superclass name
339+ , className' == superclass
340+ -- Make sure the types unify with the types in the superclass implication
341+ , subst <- maybeToList . (>>= verifySubstitution) . fmap concat $ zipWithM (typeHeadsAreEqual moduleName env) tys' suTyArgs
342+ -- Finally, satisfy the subclass constraint
343+ , args' <- maybeToList $ mapM (flip lookup subst) args
344+ , suDict <- go True subclassName args' ]
346+ -- Create dictionaries for subgoals which still need to be solved by calling go recursively
347+ -- E.g. the goal (Show a, Show b) => Show (Either a b) can be satisfied if the current type
348+ -- unifies with Either a b, and we can satisfy the subgoals Show a and Show b recursively.
349+ solveSubgoals :: [(String, Type)] -> Maybe [(Qualified ProperName, [Type])] -> [Maybe [DictionaryValue]]
350+ solveSubgoals _ Nothing = return Nothing
351+ solveSubgoals subst (Just subgoals) = do
352+ dict <- mapM (uncurry (go True) . second (map (replaceAllTypeVars subst))) subgoals
354+ -- Make a dictionary from subgoal dictionaries by applying the correct function
355+ mkDictionary :: Qualified Ident -> Maybe [DictionaryValue] -> DictionaryValue
356+ mkDictionary fnName Nothing = LocalDictionaryValue fnName
357+ mkDictionary fnName (Just []) = GlobalDictionaryValue fnName
358+ mkDictionary fnName (Just dicts) = DependentDictionaryValue fnName dicts
359+ -- Turn a DictionaryValue into a Expr
360+ dictionaryValueToValue :: DictionaryValue -> Expr
361+ dictionaryValueToValue (LocalDictionaryValue fnName) = Var fnName
362+ dictionaryValueToValue (GlobalDictionaryValue fnName) = App (Var fnName) valUndefined
363+ dictionaryValueToValue (DependentDictionaryValue fnName dicts) = foldl App (Var fnName) (map dictionaryValueToValue dicts)
364+ dictionaryValueToValue (SubclassDictionaryValue dict superclassName index) =
365+ App (Accessor (C.__superclass_ ++ show superclassName ++ "_" ++ show index)
366+ (dictionaryValueToValue dict))
368+ -- Ensure that a substitution is valid
369+ verifySubstitution :: [(String, Type)] -> Maybe [(String, Type)]
370+ verifySubstitution subst = do
371+ let grps = groupBy ((==) `on` fst) subst
372+ guard (all (pairwise (unifiesWith env) . map snd) grps)
373+ return $ map head grps
375+ -- Check for overlapping instances
377+ checkOverlaps :: [DictionaryValue] -> Check Expr
378+ checkOverlaps dicts =
379+ case [ (d1, d2) | d1 <- dicts, d2 <- dicts, d1 `overlapping` d2 ] of
380+ (d1, d2) : _ -> throwError . strMsg $ unlines
381+ [ "Overlapping instances found for " ++ show className ++ " " ++ unwords (map prettyPrintType tys) ++ "."
383+ , prettyPrintDictionaryValue d1
385+ , prettyPrintDictionaryValue d2
387+ _ -> case chooseSimplestDictionaries dicts of
388+ [] -> throwError . strMsg $
389+ "No instance found for " ++ show className ++ " " ++ unwords (map prettyPrintTypeAtom tys)
390+ d : _ -> return $ dictionaryValueToValue d
391+ -- Choose the simplest DictionaryValues from a list of candidates
392+ -- The reason for this function is as follows:
393+ -- When considering overlapping instances, we don't want to consider the same dictionary
394+ -- to be an overlap of itself when obtained as a superclass of another class.
395+ -- Observing that we probably don't want to select a superclass instance when an instance
396+ -- is available directly, and that there is no way for a superclass instance to actually
397+ -- introduce an overlap that wouldn't have been there already, we simply remove dictionaries
398+ -- obtained as superclass instances if there are simpler instances available.
399+ chooseSimplestDictionaries :: [DictionaryValue] -> [DictionaryValue]
400+ chooseSimplestDictionaries ds = case filter isSimpleDictionaryValue ds of
403+ isSimpleDictionaryValue SubclassDictionaryValue{} = False
404+ isSimpleDictionaryValue (DependentDictionaryValue _ ds) = all isSimpleDictionaryValue ds
405+ isSimpleDictionaryValue _ = True
407+ -- Check if two dictionaries are overlapping
409+ -- Dictionaries which are subclass dictionaries cannot overlap, since otherwise the overlap would have
410+ -- been caught when constructing superclass dictionaries.
412+ overlapping :: DictionaryValue -> DictionaryValue -> Bool
413+ overlapping (LocalDictionaryValue nm1) (LocalDictionaryValue nm2) | nm1 == nm2 = False
414+ overlapping (GlobalDictionaryValue nm1) (GlobalDictionaryValue nm2) | nm1 == nm2 = False
415+ overlapping (DependentDictionaryValue nm1 ds1) (DependentDictionaryValue nm2 ds2)
416+ | nm1 == nm2 = any id $ zipWith overlapping ds1 ds2
417+ overlapping (SubclassDictionaryValue _ _ _) _ = False
418+ overlapping _ (SubclassDictionaryValue _ _ _) = False
419+ overlapping _ _ = True
421+ -- Render a DictionaryValue fit for human consumption in error messages
423+ prettyPrintDictionaryValue :: DictionaryValue -> String
424+ prettyPrintDictionaryValue = unlines . indented 0
426+ indented n (LocalDictionaryValue _) = [spaces n ++ "Dictionary in scope"]
427+ indented n (GlobalDictionaryValue nm) = [spaces n ++ show nm]
428+ indented n (DependentDictionaryValue nm args) = (spaces n ++ show nm ++ " via") : concatMap (indented (n + 2)) args
429+ indented n (SubclassDictionaryValue sup nm _) = (spaces n ++ show nm ++ " via superclass") : indented (n + 2) sup
431+ spaces n = replicate n ' ' ++ "- "
433+ valUndefined :: Expr
434+ valUndefined = Var (Qualified (Just (ModuleName [ProperName C.prim])) (Ident C.undefined))
437+-- Check all values in a list pairwise match a predicate
439+pairwise :: (a -> a -> Bool) -> [a] -> Bool
441+pairwise _ [_] = True
442+pairwise p (x : xs) = all (p x) xs && pairwise p xs
445+-- Check that two types unify
447+unifiesWith :: Environment -> Type -> Type -> Bool
448+unifiesWith _ (TUnknown u1) (TUnknown u2) | u1 == u2 = True
449+unifiesWith _ (Skolem _ s1 _) (Skolem _ s2 _) | s1 == s2 = True
450+unifiesWith _ (TypeVar v1) (TypeVar v2) | v1 == v2 = True
451+unifiesWith _ (TypeConstructor c1) (TypeConstructor c2) | c1 == c2 = True
452+unifiesWith e (TypeApp h1 t1) (TypeApp h2 t2) = unifiesWith e h1 h2 && unifiesWith e t1 t2
453+unifiesWith e (SaturatedTypeSynonym name args) t2 =
454+ case expandTypeSynonym' e name args of
456+ Right t1 -> unifiesWith e t1 t2
457+unifiesWith e t1 t2@(SaturatedTypeSynonym _ _) = unifiesWith e t2 t1
458+unifiesWith _ _ _ = False
461+-- Check whether the type heads of two types are equal (for the purposes of type class dictionary lookup),
462+-- and return a substitution from type variables to types which makes the type heads unify.
464+typeHeadsAreEqual :: ModuleName -> Environment -> Type -> Type -> Maybe [(String, Type)]
465+typeHeadsAreEqual _ _ (Skolem _ s1 _) (Skolem _ s2 _) | s1 == s2 = Just []
466+typeHeadsAreEqual _ _ t (TypeVar v) = Just [(v, t)]
467+typeHeadsAreEqual _ _ (TypeConstructor c1) (TypeConstructor c2) | c1 == c2 = Just []
468+typeHeadsAreEqual m e (TypeApp h1 t1) (TypeApp h2 t2) = (++) <$> typeHeadsAreEqual m e h1 h2 <*> typeHeadsAreEqual m e t1 t2
469+typeHeadsAreEqual m e (SaturatedTypeSynonym name args) t2 = case expandTypeSynonym' e name args of
471+ Right t1 -> typeHeadsAreEqual m e t1 t2
472+typeHeadsAreEqual _ _ _ _ = Nothing
475+-- Ensure skolem variables do not escape their scope
477+skolemEscapeCheck :: Expr -> Check ()
478+skolemEscapeCheck (TypedValue False _ _) = return ()
479+skolemEscapeCheck root@TypedValue{} =
480+ -- Every skolem variable is created when a ForAll type is skolemized.
481+ -- This determines the scope of that skolem variable, which is copied from the SkolemScope
482+ -- field of the ForAll constructor.
483+ -- We traverse the tree top-down, and collect any SkolemScopes introduced by ForAlls.
484+ -- If a Skolem is encountered whose SkolemScope is not in the current list, we have found
485+ -- an escaped skolem variable.
486+ let (_, f, _, _, _) = everythingWithContextOnValues [] [] (++) def go def def def
489+ ((binding, val) : _) -> throwError $ mkErrorStack ("Rigid/skolem type variable " ++ maybe "" (("bound by " ++) . prettyPrintValue) binding ++ " has escaped.") (Just (ExprError val))
493+ go :: [(SkolemScope, Expr)] -> Expr -> ([(SkolemScope, Expr)], [(Maybe Expr, Expr)])
494+ go scos val@(TypedValue _ _ (ForAll _ _ (Just sco))) = ((sco, val) : scos, [])
495+ go scos val@(TypedValue _ _ ty) = case collectSkolems ty \\ map fst scos of
496+ (sco : _) -> (scos, [(findBindingScope sco, val)])
499+ collectSkolems :: Type -> [SkolemScope]
500+ collectSkolems = nub . everythingOnTypes (++) collect
502+ collect (Skolem _ _ scope) = [scope]
504+ go scos _ = (scos, [])
505+ findBindingScope :: SkolemScope -> Maybe Expr
506+ findBindingScope sco =
507+ let (_, f, _, _, _) = everythingOnValues mappend (const mempty) go' (const mempty) (const mempty) (const mempty)
508+ in getFirst $ f root
510+ go' val@(TypedValue _ _ (ForAll _ _ (Just sco'))) | sco == sco' = First (Just val)
512+skolemEscapeCheck val = throwError $ mkErrorStack "Untyped value passed to skolemEscapeCheck" (Just (ExprError val))
515+-- Ensure a row contains no duplicate labels
517+setify :: Type -> Type
518+setify = rowFromList . first (M.toList . M.fromList) . rowToList
521+-- \"Setify\" all rows occuring inside a value
523+setifyAll :: Type -> Type
524+setifyAll = everywhereOnTypes setify
527+-- Replace outermost unsolved unification variables with named type variables
529+varIfUnknown :: Type -> Type
531+ let unks = nub $ unknowns ty
532+ toName = (:) 't' . show
533+ ty' = everywhereOnTypes typeToVar ty
534+ typeToVar :: Type -> Type
535+ typeToVar (TUnknown u) = TypeVar (toName u)
537+ in mkForAll (sort . map toName $ unks) ty'
540+-- Remove any ForAlls and ConstrainedType constructors in a type by introducing new unknowns
541+-- or TypeClassDictionary values.
543+-- This is necessary during type checking to avoid unifying a polymorphic type with a
544+-- unification variable.
546+instantiatePolyTypeWithUnknowns :: Expr -> Type -> UnifyT Type Check (Expr, Type)
547+instantiatePolyTypeWithUnknowns val (ForAll ident ty _) = do
548+ ty' <- replaceVarWithUnknown ident ty
549+ instantiatePolyTypeWithUnknowns val ty'
550+instantiatePolyTypeWithUnknowns val (ConstrainedType constraints ty) = do
551+ dicts <- getTypeClassDictionaries
552+ (_, ty') <- instantiatePolyTypeWithUnknowns (error "Types under a constraint cannot themselves be constrained") ty
553+ return (foldl App val (map (flip (TypeClassDictionary True) dicts) constraints), ty')
554+instantiatePolyTypeWithUnknowns val ty = return (val, ty)
557+-- Replace a single type variable with a new unification variable
559+replaceVarWithUnknown :: String -> Type -> UnifyT Type Check Type
560+replaceVarWithUnknown ident ty = do
562+ return $ replaceTypeVars ident tu ty
565+-- Replace fully applied type synonyms with the @SaturatedTypeSynonym@ data constructor, which helps generate
566+-- better error messages during unification.
568+replaceAllTypeSynonyms' :: Environment -> Type -> Either String Type
569+replaceAllTypeSynonyms' env d =
571+ syns = map (\(name, (args, _)) -> (name, length args)) . M.toList $ typeSynonyms env
573+ saturateAllTypeSynonyms syns d
575+replaceAllTypeSynonyms :: (Error e, Functor m, Monad m, MonadState CheckState m, MonadError e m) => Type -> m Type
576+replaceAllTypeSynonyms d = do
578+ either (throwError . strMsg) return $ replaceAllTypeSynonyms' env d
581+-- \"Desaturate\" @SaturatedTypeSynonym@s
583+desaturateAllTypeSynonyms :: Type -> Type
584+desaturateAllTypeSynonyms = everywhereOnTypes replaceSaturatedTypeSynonym
586+ replaceSaturatedTypeSynonym (SaturatedTypeSynonym name args) = foldl TypeApp (TypeConstructor name) args
587+ replaceSaturatedTypeSynonym t = t
590+-- Replace a type synonym and its arguments with the aliased type
592+expandTypeSynonym' :: Environment -> Qualified ProperName -> [Type] -> Either String Type
593+expandTypeSynonym' env name args =
594+ case M.lookup name (typeSynonyms env) of
595+ Just (synArgs, body) -> do
596+ let repl = replaceAllTypeVars (zip synArgs args) body
597+ replaceAllTypeSynonyms' env repl
598+ Nothing -> error "Type synonym was not defined"
600+expandTypeSynonym :: (Error e, Functor m, Monad m, MonadState CheckState m, MonadError e m) => Qualified ProperName -> [Type] -> m Type
601+expandTypeSynonym name args = do
603+ either (throwError . strMsg) return $ expandTypeSynonym' env name args
605+expandAllTypeSynonyms :: (Error e, Functor m, Applicative m, Monad m, MonadState CheckState m, MonadError e m) => Type -> m Type
606+expandAllTypeSynonyms = everywhereOnTypesTopDownM go
608+ go (SaturatedTypeSynonym name args) = expandTypeSynonym name args
609+ go other = return other
612+-- Ensure a set of property names and value does not contain duplicate labels
614+ensureNoDuplicateProperties :: (Error e, MonadError e m) => [(String, Expr)] -> m ()
615+ensureNoDuplicateProperties ps = guardWith (strMsg "Duplicate property names") $ length (nub . map fst $ ps) == length ps
618+-- Infer a type for a value, rethrowing any error to provide a more useful error message
620+infer :: Expr -> UnifyT Type Check Expr
621+infer val = rethrow (mkErrorStack "Error inferring type of value" (Just (ExprError val)) <>) $ infer' val
624+-- Infer a type for a value
626+infer' :: Expr -> UnifyT Type Check Expr
627+infer' v@(NumericLiteral _) = return $ TypedValue True v tyNumber
628+infer' v@(StringLiteral _) = return $ TypedValue True v tyString
629+infer' v@(BooleanLiteral _) = return $ TypedValue True v tyBoolean
630+infer' (ArrayLiteral vals) = do
631+ ts <- mapM infer vals
633+ forM_ ts $ \(TypedValue _ _ t) -> els =?= t
634+ return $ TypedValue True (ArrayLiteral ts) (TypeApp tyArray els)
635+infer' (ObjectLiteral ps) = do
636+ ensureNoDuplicateProperties ps
637+ ts <- mapM (infer . snd) ps
638+ let fields = zipWith (\name (TypedValue _ _ t) -> (name, t)) (map fst ps) ts
639+ ty = TypeApp tyObject $ rowFromList (fields, REmpty)
640+ return $ TypedValue True (ObjectLiteral (zip (map fst ps) ts)) ty
641+infer' (ObjectUpdate o ps) = do
642+ ensureNoDuplicateProperties ps
644+ newVals <- zipWith (\(name, _) t -> (name, t)) ps <$> mapM (infer . snd) ps
645+ let newTys = map (\(name, TypedValue _ _ ty) -> (name, ty)) newVals
646+ oldTys <- zip (map fst ps) <$> replicateM (length ps) fresh
647+ let oldTy = TypeApp tyObject $ rowFromList (oldTys, row)
648+ o' <- TypedValue True <$> check o oldTy <*> pure oldTy
649+ return $ TypedValue True (ObjectUpdate o' newVals) $ TypeApp tyObject $ rowFromList (newTys, row)
650+infer' (Accessor prop val) = do
651+ typed@(TypedValue _ _ objTy) <- infer val
652+ propTy <- inferProperty objTy prop
657+ _ <- subsumes Nothing objTy (TypeApp tyObject (RCons prop field rest))
658+ return $ TypedValue True (Accessor prop typed) field
659+ Just ty -> return $ TypedValue True (Accessor prop typed) ty
660+infer' (Abs (Left arg) ret) = do
662+ Just moduleName <- checkCurrentModule <$> get
663+ makeBindingGroupVisible $ bindLocalVariables moduleName [(arg, ty, Defined)] $ do
664+ body@(TypedValue _ _ bodyTy) <- infer' ret
665+ return $ TypedValue True (Abs (Left arg) body) $ function ty bodyTy
666+infer' (Abs (Right _) _) = error "Binder was not desugared"
667+infer' (App f arg) = do
668+ f'@(TypedValue _ _ ft) <- infer f
669+ (ret, app) <- checkFunctionApplication f' ft arg Nothing
670+ return $ TypedValue True app ret
671+infer' (Var var) = do
672+ Just moduleName <- checkCurrentModule <$> get
673+ checkVisibility moduleName var
674+ ty <- introduceSkolemScope <=< replaceAllTypeSynonyms <=< lookupVariable moduleName $ var
676+ ConstrainedType constraints ty' -> do
677+ dicts <- getTypeClassDictionaries
678+ return $ TypedValue True (foldl App (Var var) (map (flip (TypeClassDictionary True) dicts) constraints)) ty'
679+ _ -> return $ TypedValue True (Var var) ty
680+infer' v@(Constructor c) = do
682+ case M.lookup c (dataConstructors env) of
683+ Nothing -> throwError . strMsg $ "Constructor " ++ show c ++ " is undefined"
684+ Just (_, _, ty) -> do ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
685+ return $ TypedValue True v ty'
686+infer' (Case vals binders) = do
687+ ts <- mapM infer vals
689+ binders' <- checkBinders (map (\(TypedValue _ _ t) -> t) ts) ret binders
690+ return $ TypedValue True (Case ts binders') ret
691+infer' (IfThenElse cond th el) = do
692+ cond' <- check cond tyBoolean
693+ v2@(TypedValue _ _ t2) <- infer th
694+ v3@(TypedValue _ _ t3) <- infer el
695+ (v2', v3', t) <- meet v2 v3 t2 t3
696+ return $ TypedValue True (IfThenElse cond' v2' v3') t
697+infer' (Let ds val) = do
698+ (ds', val'@(TypedValue _ _ valTy)) <- inferLetBinding [] ds val infer
699+ return $ TypedValue True (Let ds' val') valTy
700+infer' (SuperClassDictionary className tys) = do
701+ dicts <- getTypeClassDictionaries
702+ return $ TypeClassDictionary False (className, tys) dicts
703+infer' (TypedValue checkType val ty) = do
704+ Just moduleName <- checkCurrentModule <$> get
705+ kind <- liftCheck $ kindOf moduleName ty
706+ guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
707+ ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
708+ val' <- if checkType then check val ty' else return val
709+ return $ TypedValue True val' ty'
710+infer' (PositionedValue pos val) = rethrowWithPosition pos $ infer' val
711+infer' _ = error "Invalid argument to infer"
713+inferLetBinding :: [Declaration] -> [Declaration] -> Expr -> (Expr -> UnifyT Type Check Expr) -> UnifyT Type Check ([Declaration], Expr)
714+inferLetBinding seen [] ret j = (,) seen <$> makeBindingGroupVisible (j ret)
715+inferLetBinding seen (ValueDeclaration ident nameKind [] Nothing tv@(TypedValue checkType val ty) : rest) ret j = do
716+ Just moduleName <- checkCurrentModule <$> get
717+ kind <- liftCheck $ kindOf moduleName ty
718+ guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
719+ let dict = M.singleton (moduleName, ident) (ty, nameKind, Undefined)
720+ ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
721+ TypedValue _ val' ty'' <- if checkType then bindNames dict (check val ty') else return tv
722+ bindNames (M.singleton (moduleName, ident) (ty'', nameKind, Defined)) $ inferLetBinding (seen ++ [ValueDeclaration ident nameKind [] Nothing (TypedValue checkType val' ty'')]) rest ret j
723+inferLetBinding seen (ValueDeclaration ident nameKind [] Nothing val : rest) ret j = do
725+ Just moduleName <- checkCurrentModule <$> get
726+ let dict = M.singleton (moduleName, ident) (valTy, nameKind, Undefined)
727+ TypedValue _ val' valTy' <- bindNames dict $ infer val
729+ bindNames (M.singleton (moduleName, ident) (valTy', nameKind, Defined)) $ inferLetBinding (seen ++ [ValueDeclaration ident nameKind [] Nothing val']) rest ret j
730+inferLetBinding seen (BindingGroupDeclaration ds : rest) ret j = do
731+ Just moduleName <- checkCurrentModule <$> get
732+ (untyped, typed, dict, untypedDict) <- typeDictionaryForBindingGroup moduleName (map (\(i, _, v) -> (i, v)) ds)
733+ ds1' <- parU typed $ \e -> checkTypedBindingGroupElement moduleName e dict
734+ ds2' <- forM untyped $ \e -> typeForBindingGroupElement e dict untypedDict
735+ let ds' = [(ident, LocalVariable, val') | (ident, (val', _)) <- ds1' ++ ds2']
736+ makeBindingGroupVisible $ bindNames dict $ inferLetBinding (seen ++ [BindingGroupDeclaration ds']) rest ret j
737+inferLetBinding seen (PositionedDeclaration pos d : ds) ret j = rethrowWithPosition pos $ do
738+ ((d' : ds'), val') <- inferLetBinding seen (d : ds) ret j
739+ return (PositionedDeclaration pos d' : ds', val')
740+inferLetBinding _ _ _ _ = error "Invalid argument to inferLetBinding"
743+-- Infer the type of a property inside a record with a given type
745+inferProperty :: Type -> String -> UnifyT Type Check (Maybe Type)
746+inferProperty (TypeApp obj row) prop | obj == tyObject = do
747+ let (props, _) = rowToList row
748+ return $ lookup prop props
749+inferProperty (SaturatedTypeSynonym name args) prop = do
750+ replaced <- introduceSkolemScope <=< expandTypeSynonym name $ args
751+ inferProperty replaced prop
752+inferProperty (ForAll ident ty _) prop = do
753+ replaced <- replaceVarWithUnknown ident ty
754+ inferProperty replaced prop
755+inferProperty _ _ = return Nothing
758+-- Infer the types of variables brought into scope by a binder
760+inferBinder :: Type -> Binder -> UnifyT Type Check (M.Map Ident Type)
761+inferBinder _ NullBinder = return M.empty
762+inferBinder val (StringBinder _) = val =?= tyString >> return M.empty
763+inferBinder val (NumberBinder _) = val =?= tyNumber >> return M.empty
764+inferBinder val (BooleanBinder _) = val =?= tyBoolean >> return M.empty
765+inferBinder val (VarBinder name) = return $ M.singleton name val
766+inferBinder val (ConstructorBinder ctor binders) = do
768+ case M.lookup ctor (dataConstructors env) of
769+ Just (_, _, ty) -> do
770+ (_, fn) <- instantiatePolyTypeWithUnknowns (error "Data constructor types cannot contain constraints") ty
771+ fn' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ fn
775+ _ <- subsumes Nothing val ty'
777+ go (binder : binders') (TypeApp (TypeApp t obj) ret) | t == tyFunction =
778+ M.union <$> inferBinder obj binder <*> go binders' ret
779+ go _ _ = throwError . strMsg $ "Wrong number of arguments to constructor " ++ show ctor
780+ _ -> throwError . strMsg $ "Constructor " ++ show ctor ++ " is not defined"
781+inferBinder val (ObjectBinder props) = do
784+ m1 <- inferRowProperties row rest props
785+ val =?= TypeApp tyObject row
788+ inferRowProperties :: Type -> Type -> [(String, Binder)] -> UnifyT Type Check (M.Map Ident Type)
789+ inferRowProperties nrow row [] = nrow =?= row >> return M.empty
790+ inferRowProperties nrow row ((name, binder):binders) = do
792+ m1 <- inferBinder propTy binder
793+ m2 <- inferRowProperties nrow (RCons name propTy row) binders
794+ return $ m1 `M.union` m2
795+inferBinder val (ArrayBinder binders) = do
797+ m1 <- M.unions <$> mapM (inferBinder el) binders
798+ val =?= TypeApp tyArray el
800+inferBinder val (ConsBinder headBinder tailBinder) = do
802+ m1 <- inferBinder el headBinder
803+ m2 <- inferBinder val tailBinder
804+ val =?= TypeApp tyArray el
805+ return $ m1 `M.union` m2
806+inferBinder val (NamedBinder name binder) = do
807+ m <- inferBinder val binder
808+ return $ M.insert name val m
809+inferBinder val (PositionedBinder pos binder) =
810+ rethrowWithPosition pos $ inferBinder val binder
813+-- Check the types of the return values in a set of binders in a case statement
815+checkBinders :: [Type] -> Type -> [CaseAlternative] -> UnifyT Type Check [CaseAlternative]
816+checkBinders _ _ [] = return []
817+checkBinders nvals ret (CaseAlternative binders grd val : bs) = do
818+ guardWith (strMsg "Overlapping binders in case statement") $
819+ let ns = concatMap binderNames binders in length (nub ns) == length ns
820+ Just moduleName <- checkCurrentModule <$> get
821+ m1 <- M.unions <$> zipWithM inferBinder nvals binders
822+ r <- bindLocalVariables moduleName [ (name, ty, Defined) | (name, ty) <- M.toList m1 ] $ do
823+ val' <- TypedValue True <$> check val ret <*> pure ret
825+ Nothing -> return $ CaseAlternative binders Nothing val'
827+ g' <- check g tyBoolean
828+ return $ CaseAlternative binders (Just g') val'
829+ rs <- checkBinders nvals ret bs
833+-- Generate a new skolem constant
835+newSkolemConstant :: UnifyT Type Check Int
836+newSkolemConstant = fresh'
839+-- Generate a new skolem scope
841+newSkolemScope :: UnifyT Type Check SkolemScope
842+newSkolemScope = SkolemScope <$> fresh'
845+-- Skolemize a type variable by replacing its instances with fresh skolem constants
847+skolemize :: String -> Int -> SkolemScope -> Type -> Type
848+skolemize ident sko scope = replaceTypeVars ident (Skolem ident sko scope)
851+-- This function has one purpose - to skolemize type variables appearing in a
852+-- SuperClassDictionary placeholder. These type variables are somewhat unique since they are the
853+-- only example of scoped type variables.
855+skolemizeTypesInValue :: String -> Int -> SkolemScope -> Expr -> Expr
856+skolemizeTypesInValue ident sko scope = let (_, f, _) = everywhereOnValues id go id in f
858+ go (SuperClassDictionary c ts) = SuperClassDictionary c (map (skolemize ident sko scope) ts)
862+-- Introduce skolem scope at every occurence of a ForAll
864+introduceSkolemScope :: Type -> UnifyT Type Check Type
865+introduceSkolemScope = everywhereOnTypesM go
867+ go (ForAll ident ty Nothing) = ForAll ident ty <$> (Just <$> newSkolemScope)
868+ go other = return other
871+-- Check the type of a value, rethrowing errors to provide a better error message
873+check :: Expr -> Type -> UnifyT Type Check Expr
874+check val ty = rethrow (mkErrorStack errorMessage (Just (ExprError val)) <>) $ check' val ty
877+ "Error checking type of term " ++
878+ prettyPrintValue val ++
883+-- Check the type of a value
885+check' :: Expr -> Type -> UnifyT Type Check Expr
886+check' val (ForAll ident ty _) = do
887+ scope <- newSkolemScope
888+ sko <- newSkolemConstant
889+ let sk = skolemize ident sko scope ty
890+ let skVal = skolemizeTypesInValue ident sko scope val
891+ val' <- check skVal sk
892+ return $ TypedValue True val' (ForAll ident ty (Just scope))
893+check' val t@(ConstrainedType constraints ty) = do
894+ dictNames <- forM constraints $ \(Qualified _ (ProperName className), _) -> do
895+ n <- liftCheck freshDictionaryName
896+ return $ Ident $ "__dict_" ++ className ++ "_" ++ show n
897+ val' <- makeBindingGroupVisible $ withTypeClassDictionaries (zipWith (\name (className, instanceTy) ->
898+ TypeClassDictionaryInScope name className instanceTy Nothing TCDRegular False) (map (Qualified Nothing) dictNames)
899+ constraints) $ check val ty
900+ return $ TypedValue True (foldr (Abs . Left) val' dictNames) t
901+check' val (SaturatedTypeSynonym name args) = do
902+ ty <- introduceSkolemScope <=< expandTypeSynonym name $ args
904+check' val u@(TUnknown _) = do
905+ val'@(TypedValue _ _ ty) <- infer val
906+ -- Don't unify an unknown with an inferred polytype
907+ (val'', ty') <- instantiatePolyTypeWithUnknowns val' ty
909+ return $ TypedValue True val'' ty'
910+check' v@(NumericLiteral _) t | t == tyNumber =
911+ return $ TypedValue True v t
912+check' v@(StringLiteral _) t | t == tyString =
913+ return $ TypedValue True v t
914+check' v@(BooleanLiteral _) t | t == tyBoolean =
915+ return $ TypedValue True v t
916+check' (ArrayLiteral vals) t@(TypeApp a ty) = do
918+ array <- ArrayLiteral <$> forM vals (`check` ty)
919+ return $ TypedValue True array t
920+check' (Abs (Left arg) ret) ty@(TypeApp (TypeApp t argTy) retTy) | t == tyFunction = do
921+ Just moduleName <- checkCurrentModule <$> get
922+ ret' <- makeBindingGroupVisible $ bindLocalVariables moduleName [(arg, argTy, Defined)] $ check ret retTy
923+ return $ TypedValue True (Abs (Left arg) ret') ty
924+check' (Abs (Right _) _) _ = error "Binder was not desugared"
925+check' (App f arg) ret = do
926+ f'@(TypedValue _ _ ft) <- infer f
927+ (_, app) <- checkFunctionApplication f' ft arg (Just ret)
928+ return $ TypedValue True app ret
929+check' v@(Var var) ty = do
930+ Just moduleName <- checkCurrentModule <$> get
931+ checkVisibility moduleName var
932+ repl <- introduceSkolemScope <=< replaceAllTypeSynonyms <=< lookupVariable moduleName $ var
933+ ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
934+ v' <- subsumes (Just v) repl ty'
936+ Nothing -> throwError . strMsg $ "Unable to check type subsumption"
937+ Just v'' -> return $ TypedValue True v'' ty'
938+check' (SuperClassDictionary className tys) _ = do
940+ -- Here, we replace a placeholder for a superclass dictionary with a regular
941+ -- TypeClassDictionary placeholder. The reason we do this is that it is necessary to have the
942+ -- correct super instance dictionaries in scope, and these are not available when the type class
943+ -- declaration gets desugared.
945+ -- Note also that the first argument to TypeClassDictionary is False, meaning we _do not_ want
946+ -- to consider superclass instances when searching for this dictionary - doing so might lead
947+ -- to traversing a cycle in the instance graph.
949+ dicts <- getTypeClassDictionaries
950+ return $ TypeClassDictionary False (className, tys) dicts
951+check' (TypedValue checkType val ty1) ty2 = do
952+ Just moduleName <- checkCurrentModule <$> get
953+ kind <- liftCheck $ kindOf moduleName ty1
954+ guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
955+ ty1' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty1
956+ ty2' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty2
957+ val' <- subsumes (Just val) ty1' ty2'
959+ Nothing -> throwError . strMsg $ "Unable to check type subsumption"
961+ val''' <- if checkType then check val'' ty2' else return val''
962+ return $ TypedValue checkType (TypedValue True val''' ty1') ty2'
963+check' (Case vals binders) ret = do
964+ vals' <- mapM infer vals
965+ let ts = map (\(TypedValue _ _ t) -> t) vals'
966+ binders' <- checkBinders ts ret binders
967+ return $ TypedValue True (Case vals' binders') ret
968+check' (IfThenElse cond th el) ty = do
969+ cond' <- check cond tyBoolean
972+ return $ TypedValue True (IfThenElse cond' th' el') ty
973+check' (ObjectLiteral ps) t@(TypeApp obj row) | obj == tyObject = do
974+ ensureNoDuplicateProperties ps
975+ ps' <- checkProperties ps row False
976+ return $ TypedValue True (ObjectLiteral ps') t
977+check' (TypeClassDictionaryConstructorApp name ps) t = do
979+ return $ TypedValue True (TypeClassDictionaryConstructorApp name ps') t
980+check' (ObjectUpdate obj ps) t@(TypeApp o row) | o == tyObject = do
981+ ensureNoDuplicateProperties ps
982+ us <- zip (map fst ps) <$> replicateM (length ps) fresh
983+ let (propsToCheck, rest) = rowToList row
984+ propsToRemove = map fst ps
985+ remainingProps = filter (\(p, _) -> p `notElem` propsToRemove) propsToCheck
986+ obj' <- check obj (TypeApp tyObject (rowFromList (us ++ remainingProps, rest)))
987+ ps' <- checkProperties ps row True
988+ return $ TypedValue True (ObjectUpdate obj' ps') t
989+check' (Accessor prop val) ty = do
991+ val' <- check val (TypeApp tyObject (RCons prop ty rest))
992+ return $ TypedValue True (Accessor prop val') ty
993+check' (Constructor c) ty = do
995+ case M.lookup c (dataConstructors env) of
996+ Nothing -> throwError . strMsg $ "Constructor " ++ show c ++ " is undefined"
997+ Just (_, _, ty1) -> do
998+ repl <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty1
999+ _ <- subsumes Nothing repl ty
1000+ return $ TypedValue True (Constructor c) ty
1001+check' (Let ds val) ty = do
1002+ (ds', val') <- inferLetBinding [] ds val (flip check ty)
1003+ return $ TypedValue True (Let ds' val') ty
1004+check' val ty | containsTypeSynonyms ty = do
1005+ ty' <- introduceSkolemScope <=< expandAllTypeSynonyms $ ty
1007+check' (PositionedValue pos val) ty =
1008+ rethrowWithPosition pos $ check val ty
1009+check' val ty = throwError $ mkErrorStack ("Expr does not have type " ++ prettyPrintType ty) (Just (ExprError val))
1011+containsTypeSynonyms :: Type -> Bool
1012+containsTypeSynonyms = everythingOnTypes (||) go where
1013+ go (SaturatedTypeSynonym _ _) = True
1017+-- Check the type of a collection of named record fields
1019+-- The @lax@ parameter controls whether or not every record member has to be provided. For object updates, this is not the case.
1021+checkProperties :: [(String, Expr)] -> Type -> Bool -> UnifyT Type Check [(String, Expr)]
1022+checkProperties ps row lax = let (ts, r') = rowToList row in go ps ts r' where
1023+ go [] [] REmpty = return []
1024+ go [] [] u@(TUnknown _) = do u =?= REmpty
1026+ go [] [] (Skolem _ _ _) | lax = return []
1027+ go [] ((p, _): _) _ | lax = return []
1028+ | otherwise = throwError $ mkErrorStack ("Object does not have property " ++ p) (Just (ExprError (ObjectLiteral ps)))
1029+ go ((p,_):_) [] REmpty = throwError $ mkErrorStack ("Property " ++ p ++ " is not present in closed object type " ++ prettyPrintRow row) (Just (ExprError (ObjectLiteral ps)))
1030+ go ((p,v):ps') [] u@(TUnknown _) = do
1031+ v'@(TypedValue _ _ ty) <- infer v
1033+ u =?= RCons p ty rest
1034+ ps'' <- go ps' [] rest
1035+ return $ (p, v') : ps''
1036+ go ((p,v):ps') ts r =
1037+ case lookup p ts of
1039+ v'@(TypedValue _ _ ty) <- infer v
1041+ r =?= RCons p ty rest
1042+ ps'' <- go ps' ts rest
1043+ return $ (p, v') : ps''
1046+ ps'' <- go ps' (delete (p, ty) ts) r
1047+ return $ (p, v') : ps''
1048+ go _ _ _ = throwError $ mkErrorStack ("Object does not have type " ++ prettyPrintType (TypeApp tyObject row)) (Just (ExprError (ObjectLiteral ps)))
1051+-- Check the type of a function application, rethrowing errors to provide a better error message
1053+checkFunctionApplication :: Expr -> Type -> Expr -> Maybe Type -> UnifyT Type Check (Type, Expr)
1054+checkFunctionApplication fn fnTy arg ret = rethrow (mkErrorStack errorMessage (Just (ExprError fn)) <>) $ do
1055+ subst <- unifyCurrentSubstitution <$> UnifyT get
1056+ checkFunctionApplication' fn (subst $? fnTy) arg (($?) subst <$> ret)
1058+ errorMessage = "Error applying function of type "
1059+ ++ prettyPrintType fnTy
1060+ ++ " to argument " ++ prettyPrintValue arg
1063+-- Check the type of a function application
1065+checkFunctionApplication' :: Expr -> Type -> Expr -> Maybe Type -> UnifyT Type Check (Type, Expr)
1066+checkFunctionApplication' fn (TypeApp (TypeApp tyFunction' argTy) retTy) arg ret = do
1067+ tyFunction' =?= tyFunction
1068+ arg' <- check arg argTy
1070+ Nothing -> return (retTy, App fn arg')
1072+ Just app' <- subsumes (Just (App fn arg')) retTy ret'
1073+ return (retTy, app')
1074+checkFunctionApplication' fn (ForAll ident ty _) arg ret = do
1075+ replaced <- replaceVarWithUnknown ident ty
1076+ checkFunctionApplication fn replaced arg ret
1077+checkFunctionApplication' fn u@(TUnknown _) arg ret = do
1079+ TypedValue _ arg' t <- infer arg
1080+ (arg'', t') <- instantiatePolyTypeWithUnknowns arg' t
1081+ return $ TypedValue True arg'' t'
1082+ let ty = (\(TypedValue _ _ t) -> t) arg'
1083+ ret' <- maybe fresh return ret
1084+ u =?= function ty ret'
1085+ return (ret', App fn arg')
1086+checkFunctionApplication' fn (SaturatedTypeSynonym name tyArgs) arg ret = do
1087+ ty <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
1088+ checkFunctionApplication fn ty arg ret
1089+checkFunctionApplication' fn (ConstrainedType constraints fnTy) arg ret = do
1090+ dicts <- getTypeClassDictionaries
1091+ checkFunctionApplication' (foldl App fn (map (flip (TypeClassDictionary True) dicts) constraints)) fnTy arg ret
1092+checkFunctionApplication' fn fnTy dict@(TypeClassDictionary _ _ _) _ =
1093+ return (fnTy, App fn dict)
1094+checkFunctionApplication' _ fnTy arg _ = throwError . strMsg $ "Cannot apply a function of type "
1095+ ++ prettyPrintType fnTy
1096+ ++ " to argument " ++ prettyPrintValue arg
1099+-- Check whether one type subsumes another, rethrowing errors to provide a better error message
1101+subsumes :: Maybe Expr -> Type -> Type -> UnifyT Type Check (Maybe Expr)
1102+subsumes val ty1 ty2 = rethrow (mkErrorStack errorMessage (ExprError <$> val) <>) $ subsumes' val ty1 ty2
1104+ errorMessage = "Error checking that type "
1105+ ++ prettyPrintType ty1
1106+ ++ " subsumes type "
1107+ ++ prettyPrintType ty2
1110+-- Check whether one type subsumes another
1112+subsumes' :: Maybe Expr -> Type -> Type -> UnifyT Type Check (Maybe Expr)
1113+subsumes' val (ForAll ident ty1 _) ty2 = do
1114+ replaced <- replaceVarWithUnknown ident ty1
1115+ subsumes val replaced ty2
1116+subsumes' val ty1 (ForAll ident ty2 sco) =
1119+ sko <- newSkolemConstant
1120+ let sk = skolemize ident sko sco' ty2
1121+ subsumes val ty1 sk
1122+ Nothing -> throwError . strMsg $ "Skolem variable scope is unspecified"
1123+subsumes' val (TypeApp (TypeApp f1 arg1) ret1) (TypeApp (TypeApp f2 arg2) ret2) | f1 == tyFunction && f2 == tyFunction = do
1124+ _ <- subsumes Nothing arg2 arg1
1125+ _ <- subsumes Nothing ret1 ret2
1127+subsumes' val (SaturatedTypeSynonym name tyArgs) ty2 = do
1128+ ty1 <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
1129+ subsumes val ty1 ty2
1130+subsumes' val ty1 (SaturatedTypeSynonym name tyArgs) = do
1131+ ty2 <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
1132+ subsumes val ty1 ty2
1133+subsumes' (Just val) (ConstrainedType constraints ty1) ty2 = do
1134+ dicts <- getTypeClassDictionaries
1135+ subsumes' (Just $ foldl App val (map (flip (TypeClassDictionary True) dicts) constraints)) ty1 ty2
1136+subsumes' val (TypeApp f1 r1) (TypeApp f2 r2) | f1 == tyObject && f2 == tyObject = do
1138+ (ts1, r1') = rowToList r1
1139+ (ts2, r2') = rowToList r2
1140+ ts1' = sortBy (comparing fst) ts1
1141+ ts2' = sortBy (comparing fst) ts2
1142+ go ts1' ts2' r1' r2'
1145+ go [] ts2 r1' r2' = r1' =?= rowFromList (ts2, r2')
1146+ go ts1 [] r1' r2' = r2' =?= rowFromList (ts1, r1')
1147+ go ((p1, ty1) : ts1) ((p2, ty2) : ts2) r1' r2'
1148+ | p1 == p2 = do _ <- subsumes Nothing ty1 ty2
1150+ | p1 < p2 = do rest <- fresh
1151+ r2' =?= RCons p1 ty1 rest
1152+ go ts1 ((p2, ty2) : ts2) r1' rest
1153+ | otherwise = do rest <- fresh
1154+ r1' =?= RCons p2 ty2 rest
1155+ go ((p1, ty1) : ts1) ts2 rest r2'
1156+subsumes' val ty1 ty2@(TypeApp obj _) | obj == tyObject = subsumes val ty2 ty1
1157+subsumes' val ty1 ty2 = do
1162+-- Compute the meet of two types, i.e. the most general type which both types subsume.
1163+-- TODO: handle constrained types
1165+meet :: Expr -> Expr -> Type -> Type -> UnifyT Type Check (Expr, Expr, Type)
1166+meet e1 e2 (ForAll ident t1 _) t2 = do
1167+ t1' <- replaceVarWithUnknown ident t1
1169+meet e1 e2 t1 (ForAll ident t2 _) = do
1170+ t2' <- replaceVarWithUnknown ident t2
1172+meet e1 e2 t1 t2 = do
1174+ return (e1, e2, t1)