@@ -0,0 +1,1230 @@
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' (KindedType ty1 _) ty2 = ty1 `unifyTypes` ty2
128+ unifyTypes' ty1 (KindedType ty2 _) = ty1 `unifyTypes` ty2
129+ unifyTypes' r1@RCons{} r2 = unifyRows r1 r2
130+ unifyTypes' r1 r2@RCons{} = unifyRows r1 r2
131+ unifyTypes' r1@REmpty r2 = unifyRows r1 r2
132+ unifyTypes' r1 r2@REmpty = unifyRows r1 r2
133+ unifyTypes' t@(ConstrainedType _ _) _ = throwError . strMsg $ "Attempted to unify a constrained type " ++ prettyPrintType t ++ " with another type."
134+ unifyTypes' t3 t4@(ConstrainedType _ _) = unifyTypes' t4 t3
135+ unifyTypes' t3 t4 = throwError . strMsg $ "Cannot unify " ++ prettyPrintType t3 ++ " with " ++ prettyPrintType t4 ++ "."
138+-- Unify two rows, updating the current substitution
140+-- Common labels are first identified, and unified. Remaining labels and types are unified with a
141+-- trailing row unification variable, if appropriate, otherwise leftover labels result in a unification
144+unifyRows :: Type -> Type -> UnifyT Type Check ()
147+ (s1, r1') = rowToList r1
148+ (s2, r2') = rowToList r2
149+ int = [ (t1, t2) | (name, t1) <- s1, (name', t2) <- s2, name == name' ]
150+ sd1 = [ (name, t1) | (name, t1) <- s1, name `notElem` map fst s2 ]
151+ sd2 = [ (name, t2) | (name, t2) <- s2, name `notElem` map fst s1 ]
153+ forM_ int (uncurry (=?=))
154+ unifyRows' sd1 r1' sd2 r2'
156+ unifyRows' :: [(String, Type)] -> Type -> [(String, Type)] -> Type -> UnifyT Type Check ()
157+ unifyRows' [] (TUnknown u) sd r = u =:= rowFromList (sd, r)
158+ unifyRows' sd r [] (TUnknown u) = u =:= rowFromList (sd, r)
159+ unifyRows' sd1 (TUnknown u1) sd2 (TUnknown u2) = do
160+ forM_ sd1 $ \(_, t) -> occursCheck u2 t
161+ forM_ sd2 $ \(_, t) -> occursCheck u1 t
163+ u1 =:= rowFromList (sd2, rest)
164+ u2 =:= rowFromList (sd1, rest)
165+ unifyRows' [] REmpty [] REmpty = return ()
166+ unifyRows' [] (TypeVar v1) [] (TypeVar v2) | v1 == v2 = return ()
167+ unifyRows' [] (Skolem _ s1 _) [] (Skolem _ s2 _) | s1 == s2 = return ()
168+ unifyRows' sd3 r3 sd4 r4 = throwError . strMsg $ "Cannot unify (" ++ prettyPrintRow (rowFromList (sd3, r3)) ++ ") with (" ++ prettyPrintRow (rowFromList (sd4, r4)) ++ ")"
171+-- Infer the types of multiple mutually-recursive values, and return elaborated values including
172+-- type class dictionaries and type annotations.
174+typesOf :: Maybe ModuleName -> ModuleName -> [(Ident, Expr)] -> Check [(Ident, (Expr, Type))]
175+typesOf mainModuleName moduleName vals = do
176+ tys <- fmap tidyUp . liftUnify $ do
177+ (untyped, typed, dict, untypedDict) <- typeDictionaryForBindingGroup moduleName vals
178+ ds1 <- parU typed $ \e -> do
179+ triple@(_, (_, ty)) <- checkTypedBindingGroupElement moduleName e dict
180+ checkMain (fst e) ty
182+ ds2 <- forM untyped $ \e -> do
183+ triple@(_, (_, ty)) <- typeForBindingGroupElement e dict untypedDict
184+ checkMain (fst e) ty
188+ forM tys $ \(ident, (val, ty)) -> do
189+ -- Replace type class dictionary placeholders with actual dictionaries
190+ val' <- replaceTypeClassDictionaries moduleName val
191+ -- Check skolem variables did not escape their scope
192+ skolemEscapeCheck val'
193+ -- Check rows do not contain duplicate labels
194+ checkDuplicateLabels val'
195+ -- Remove type synonyms placeholders, remove duplicate row fields, and replace
196+ -- top-level unification variables with named type variables.
197+ let val'' = overTypes (desaturateAllTypeSynonyms . setifyAll) val'
198+ ty' = varIfUnknown . desaturateAllTypeSynonyms . setifyAll $ ty
199+ return (ident, (val'', ty'))
201+ -- Apply the substitution that was returned from runUnify to both types and (type-annotated) values
202+ tidyUp (ts, sub) = map (\(i, (val, ty)) -> (i, (overTypes (sub $?) val, sub $? ty))) ts
203+ -- If --main is enabled, need to check that `main` has type Eff eff a for some eff, a
204+ checkMain nm ty = when (Just moduleName == mainModuleName && nm == Ident C.main) $ do
205+ [eff, a] <- replicateM 2 fresh
206+ ty =?= TypeApp (TypeApp (TypeConstructor (Qualified (Just (ModuleName [ProperName "Control", ProperName "Monad", ProperName "Eff"])) (ProperName "Eff"))) eff) a
208+type TypeData = M.Map (ModuleName, Ident) (Type, NameKind, NameVisibility)
210+type UntypedData = [(Ident, Type)]
212+typeDictionaryForBindingGroup :: ModuleName -> [(Ident, Expr)] -> UnifyT Type Check ([(Ident, Expr)], [(Ident, (Expr, Type, Bool))], TypeData, UntypedData)
213+typeDictionaryForBindingGroup moduleName vals = do
215+ -- Map each declaration to a name/value pair, with an optional type, if the declaration is typed
216+ es = map isTyped vals
217+ -- Filter the typed and untyped declarations
220+ -- Make a map of names to typed declarations
221+ typedDict = map (\(ident, (_, ty, _)) -> (ident, ty)) typed
223+ -- Create fresh unification variables for the types of untyped declarations
224+ untypedNames <- replicateM (length untyped) fresh
227+ -- Make a map of names to the unification variables of untyped declarations
228+ untypedDict = zip (map fst untyped) untypedNames
229+ -- Create the dictionary of all name/type pairs, which will be added to the environment during type checking
230+ dict = M.fromList (map (\(ident, ty) -> ((moduleName, ident), (ty, LocalVariable, Undefined))) $ typedDict ++ untypedDict)
231+ return (untyped, typed, dict, untypedDict)
233+checkTypedBindingGroupElement :: ModuleName -> (Ident, (Expr, Type, Bool)) -> TypeData -> UnifyT Type Check (Ident, (Expr, Type))
234+checkTypedBindingGroupElement moduleName (ident, (val', ty, checkType)) dict = do
236+ kind <- liftCheck $ kindOf moduleName ty
237+ guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
238+ -- Check the type with the new names in scope
239+ ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
240+ val'' <- if checkType
241+ then bindNames dict $ TypedValue True <$> check val' ty' <*> pure ty'
242+ else return (TypedValue False val' ty')
243+ return (ident, (val'', ty'))
245+typeForBindingGroupElement :: (Ident, Expr) -> TypeData -> UntypedData -> UnifyT Type Check (Ident, (Expr, Type))
246+typeForBindingGroupElement (ident, val) dict untypedDict = do
247+ -- Infer the type with the new names in scope
248+ TypedValue _ val' ty <- bindNames dict $ infer val
249+ ty =?= fromMaybe (error "name not found in dictionary") (lookup ident untypedDict)
250+ return (ident, (TypedValue True val' ty, ty))
253+-- Check if a value contains a type annotation
255+isTyped :: (Ident, Expr) -> (Either (Ident, Expr) (Ident, (Expr, Type, Bool)))
256+isTyped (name, TypedValue checkType value ty) = Right (name, (value, ty, checkType))
257+isTyped (name, value) = Left (name, value)
260+-- Map a function over type annotations appearing inside a value
262+overTypes :: (Type -> Type) -> Expr -> Expr
263+overTypes f = let (_, f', _) = everywhereOnValues id g id in f'
266+ g (TypedValue checkTy val t) = TypedValue checkTy val (f t)
267+ g (TypeClassDictionary b (nm, tys) sco) = TypeClassDictionary b (nm, map f tys) sco
271+-- Replace type class dictionary placeholders with inferred type class dictionaries
273+replaceTypeClassDictionaries :: ModuleName -> Expr -> Check Expr
274+replaceTypeClassDictionaries mn =
275+ let (_, f, _) = everywhereOnValuesTopDownM return go return
278+ go (TypeClassDictionary trySuperclasses constraint dicts) = do
280+ entails env mn dicts constraint trySuperclasses
281+ go other = return other
284+-- A simplified representation of expressions which are used to represent type
285+-- class dictionaries at runtime, which can be compared for equality
289+ -- A dictionary which is brought into scope by a local constraint
291+ = LocalDictionaryValue (Qualified Ident)
293+ -- A dictionary which is brought into scope by an instance declaration
295+ | GlobalDictionaryValue (Qualified Ident)
297+ -- A dictionary which depends on other dictionaries
299+ | DependentDictionaryValue (Qualified Ident) [DictionaryValue]
301+ -- A subclass dictionary
303+ | SubclassDictionaryValue DictionaryValue (Qualified ProperName) Integer
304+ deriving (Show, Ord, Eq)
307+-- Check that the current set of type class dictionaries entail the specified type class goal, and, if so,
308+-- return a type class dictionary reference.
310+entails :: Environment -> ModuleName -> [TypeClassDictionaryInScope] -> (Qualified ProperName, [Type]) -> Bool -> Check Expr
311+entails env moduleName context = solve (sortedNubBy canonicalizeDictionary (filter filterModule context))
313+ sortedNubBy :: (Ord k) => (v -> k) -> [v] -> [v]
314+ sortedNubBy f vs = M.elems (M.fromList (map (f &&& id) vs))
316+ -- Filter out type dictionaries which are in scope in the current module
317+ filterModule :: TypeClassDictionaryInScope -> Bool
318+ filterModule (TypeClassDictionaryInScope { tcdName = Qualified (Just mn) _ }) | mn == moduleName = True
319+ filterModule (TypeClassDictionaryInScope { tcdName = Qualified Nothing _ }) = True
320+ filterModule _ = False
322+ solve context' (className, tys) trySuperclasses =
323+ checkOverlaps $ go trySuperclasses className tys
325+ go trySuperclasses' className' tys' =
326+ -- Look for regular type instances
327+ [ mkDictionary (canonicalizeDictionary tcd) args
329+ -- Make sure the type class name matches the one we are trying to satisfy
330+ , className' == tcdClassName tcd
331+ -- Make sure the type unifies with the type in the type instance definition
332+ , subst <- maybeToList . (>>= verifySubstitution) . fmap concat $ zipWithM (typeHeadsAreEqual moduleName env) tys' (tcdInstanceTypes tcd)
333+ -- Solve any necessary subgoals
334+ , args <- solveSubgoals subst (tcdDependencies tcd) ] ++
336+ -- Look for implementations via superclasses
337+ [ SubclassDictionaryValue suDict superclass index
339+ , (subclassName, (args, _, implies)) <- M.toList (typeClasses env)
340+ -- Try each superclass
341+ , (index, (superclass, suTyArgs)) <- zip [0..] implies
342+ -- Make sure the type class name matches the superclass name
343+ , className' == superclass
344+ -- Make sure the types unify with the types in the superclass implication
345+ , subst <- maybeToList . (>>= verifySubstitution) . fmap concat $ zipWithM (typeHeadsAreEqual moduleName env) tys' suTyArgs
346+ -- Finally, satisfy the subclass constraint
347+ , args' <- maybeToList $ mapM (flip lookup subst) (map fst args)
348+ , suDict <- go True subclassName args' ]
350+ -- Create dictionaries for subgoals which still need to be solved by calling go recursively
351+ -- E.g. the goal (Show a, Show b) => Show (Either a b) can be satisfied if the current type
352+ -- unifies with Either a b, and we can satisfy the subgoals Show a and Show b recursively.
353+ solveSubgoals :: [(String, Type)] -> Maybe [(Qualified ProperName, [Type])] -> [Maybe [DictionaryValue]]
354+ solveSubgoals _ Nothing = return Nothing
355+ solveSubgoals subst (Just subgoals) = do
356+ dict <- mapM (uncurry (go True) . second (map (replaceAllTypeVars subst))) subgoals
358+ -- Make a dictionary from subgoal dictionaries by applying the correct function
359+ mkDictionary :: Qualified Ident -> Maybe [DictionaryValue] -> DictionaryValue
360+ mkDictionary fnName Nothing = LocalDictionaryValue fnName
361+ mkDictionary fnName (Just []) = GlobalDictionaryValue fnName
362+ mkDictionary fnName (Just dicts) = DependentDictionaryValue fnName dicts
363+ -- Turn a DictionaryValue into a Expr
364+ dictionaryValueToValue :: DictionaryValue -> Expr
365+ dictionaryValueToValue (LocalDictionaryValue fnName) = Var fnName
366+ dictionaryValueToValue (GlobalDictionaryValue fnName) = Var fnName
367+ dictionaryValueToValue (DependentDictionaryValue fnName dicts) = foldl App (Var fnName) (map dictionaryValueToValue dicts)
368+ dictionaryValueToValue (SubclassDictionaryValue dict superclassName index) =
369+ App (Accessor (C.__superclass_ ++ show superclassName ++ "_" ++ show index)
370+ (dictionaryValueToValue dict))
372+ -- Ensure that a substitution is valid
373+ verifySubstitution :: [(String, Type)] -> Maybe [(String, Type)]
374+ verifySubstitution subst = do
375+ let grps = groupBy ((==) `on` fst) subst
376+ guard (all (pairwise (unifiesWith env) . map snd) grps)
377+ return $ map head grps
379+ -- Check for overlapping instances
381+ checkOverlaps :: [DictionaryValue] -> Check Expr
382+ checkOverlaps dicts =
383+ case [ (d1, d2) | d1 <- dicts, d2 <- dicts, d1 `overlapping` d2 ] of
384+ (d1, d2) : _ -> throwError . strMsg $ unlines
385+ [ "Overlapping instances found for " ++ show className ++ " " ++ unwords (map prettyPrintType tys) ++ "."
387+ , prettyPrintDictionaryValue d1
389+ , prettyPrintDictionaryValue d2
391+ _ -> case chooseSimplestDictionaries dicts of
392+ [] -> throwError . strMsg $
393+ "No instance found for " ++ show className ++ " " ++ unwords (map prettyPrintTypeAtom tys)
394+ d : _ -> return $ dictionaryValueToValue d
395+ -- Choose the simplest DictionaryValues from a list of candidates
396+ -- The reason for this function is as follows:
397+ -- When considering overlapping instances, we don't want to consider the same dictionary
398+ -- to be an overlap of itself when obtained as a superclass of another class.
399+ -- Observing that we probably don't want to select a superclass instance when an instance
400+ -- is available directly, and that there is no way for a superclass instance to actually
401+ -- introduce an overlap that wouldn't have been there already, we simply remove dictionaries
402+ -- obtained as superclass instances if there are simpler instances available.
403+ chooseSimplestDictionaries :: [DictionaryValue] -> [DictionaryValue]
404+ chooseSimplestDictionaries ds = case filter isSimpleDictionaryValue ds of
407+ isSimpleDictionaryValue SubclassDictionaryValue{} = False
408+ isSimpleDictionaryValue (DependentDictionaryValue _ ds) = all isSimpleDictionaryValue ds
409+ isSimpleDictionaryValue _ = True
411+ -- Check if two dictionaries are overlapping
413+ -- Dictionaries which are subclass dictionaries cannot overlap, since otherwise the overlap would have
414+ -- been caught when constructing superclass dictionaries.
416+ overlapping :: DictionaryValue -> DictionaryValue -> Bool
417+ overlapping (LocalDictionaryValue nm1) (LocalDictionaryValue nm2) | nm1 == nm2 = False
418+ overlapping (GlobalDictionaryValue nm1) (GlobalDictionaryValue nm2) | nm1 == nm2 = False
419+ overlapping (DependentDictionaryValue nm1 ds1) (DependentDictionaryValue nm2 ds2)
420+ | nm1 == nm2 = any id $ zipWith overlapping ds1 ds2
421+ overlapping (SubclassDictionaryValue _ _ _) _ = False
422+ overlapping _ (SubclassDictionaryValue _ _ _) = False
423+ overlapping _ _ = True
425+ -- Render a DictionaryValue fit for human consumption in error messages
427+ prettyPrintDictionaryValue :: DictionaryValue -> String
428+ prettyPrintDictionaryValue = unlines . indented 0
430+ indented n (LocalDictionaryValue _) = [spaces n ++ "Dictionary in scope"]
431+ indented n (GlobalDictionaryValue nm) = [spaces n ++ show nm]
432+ indented n (DependentDictionaryValue nm args) = (spaces n ++ show nm ++ " via") : concatMap (indented (n + 2)) args
433+ indented n (SubclassDictionaryValue sup nm _) = (spaces n ++ show nm ++ " via superclass") : indented (n + 2) sup
435+ spaces n = replicate n ' ' ++ "- "
437+ valUndefined :: Expr
438+ valUndefined = Var (Qualified (Just (ModuleName [ProperName C.prim])) (Ident C.undefined))
441+-- Check all values in a list pairwise match a predicate
443+pairwise :: (a -> a -> Bool) -> [a] -> Bool
445+pairwise _ [_] = True
446+pairwise p (x : xs) = all (p x) xs && pairwise p xs
449+-- Check that two types unify
451+unifiesWith :: Environment -> Type -> Type -> Bool
452+unifiesWith _ (TUnknown u1) (TUnknown u2) | u1 == u2 = True
453+unifiesWith _ (Skolem _ s1 _) (Skolem _ s2 _) | s1 == s2 = True
454+unifiesWith _ (TypeVar v1) (TypeVar v2) | v1 == v2 = True
455+unifiesWith _ (TypeConstructor c1) (TypeConstructor c2) | c1 == c2 = True
456+unifiesWith e (TypeApp h1 t1) (TypeApp h2 t2) = unifiesWith e h1 h2 && unifiesWith e t1 t2
457+unifiesWith e (SaturatedTypeSynonym name args) t2 =
458+ case expandTypeSynonym' e name args of
460+ Right t1 -> unifiesWith e t1 t2
461+unifiesWith e t1 t2@(SaturatedTypeSynonym _ _) = unifiesWith e t2 t1
462+unifiesWith _ _ _ = False
465+-- Check whether the type heads of two types are equal (for the purposes of type class dictionary lookup),
466+-- and return a substitution from type variables to types which makes the type heads unify.
468+typeHeadsAreEqual :: ModuleName -> Environment -> Type -> Type -> Maybe [(String, Type)]
469+typeHeadsAreEqual _ _ (Skolem _ s1 _) (Skolem _ s2 _) | s1 == s2 = Just []
470+typeHeadsAreEqual _ _ t (TypeVar v) = Just [(v, t)]
471+typeHeadsAreEqual _ _ (TypeConstructor c1) (TypeConstructor c2) | c1 == c2 = Just []
472+typeHeadsAreEqual m e (TypeApp h1 t1) (TypeApp h2 t2) = (++) <$> typeHeadsAreEqual m e h1 h2 <*> typeHeadsAreEqual m e t1 t2
473+typeHeadsAreEqual m e (SaturatedTypeSynonym name args) t2 = case expandTypeSynonym' e name args of
475+ Right t1 -> typeHeadsAreEqual m e t1 t2
476+typeHeadsAreEqual _ _ _ _ = Nothing
479+-- Ensure skolem variables do not escape their scope
481+skolemEscapeCheck :: Expr -> Check ()
482+skolemEscapeCheck (TypedValue False _ _) = return ()
483+skolemEscapeCheck root@TypedValue{} =
484+ -- Every skolem variable is created when a ForAll type is skolemized.
485+ -- This determines the scope of that skolem variable, which is copied from the SkolemScope
486+ -- field of the ForAll constructor.
487+ -- We traverse the tree top-down, and collect any SkolemScopes introduced by ForAlls.
488+ -- If a Skolem is encountered whose SkolemScope is not in the current list, we have found
489+ -- an escaped skolem variable.
490+ let (_, f, _, _, _) = everythingWithContextOnValues [] [] (++) def go def def def
493+ ((binding, val) : _) -> throwError $ mkErrorStack ("Rigid/skolem type variable " ++ maybe "" (("bound by " ++) . prettyPrintValue) binding ++ " has escaped.") (Just (ExprError val))
497+ go :: [(SkolemScope, Expr)] -> Expr -> ([(SkolemScope, Expr)], [(Maybe Expr, Expr)])
498+ go scos val@(TypedValue _ _ (ForAll _ _ (Just sco))) = ((sco, val) : scos, [])
499+ go scos val@(TypedValue _ _ ty) = case collectSkolems ty \\ map fst scos of
500+ (sco : _) -> (scos, [(findBindingScope sco, val)])
503+ collectSkolems :: Type -> [SkolemScope]
504+ collectSkolems = nub . everythingOnTypes (++) collect
506+ collect (Skolem _ _ scope) = [scope]
508+ go scos _ = (scos, [])
509+ findBindingScope :: SkolemScope -> Maybe Expr
510+ findBindingScope sco =
511+ let (_, f, _, _, _) = everythingOnValues mappend (const mempty) go' (const mempty) (const mempty) (const mempty)
512+ in getFirst $ f root
514+ go' val@(TypedValue _ _ (ForAll _ _ (Just sco'))) | sco == sco' = First (Just val)
516+skolemEscapeCheck val = throwError $ mkErrorStack "Untyped value passed to skolemEscapeCheck" (Just (ExprError val))
519+-- Ensure rows do not contain duplicate labels
521+checkDuplicateLabels :: Expr -> Check ()
522+checkDuplicateLabels =
523+ let (_, f, _) = everywhereOnValuesM def go def
529+ go :: Expr -> Check Expr
530+ go e@(TypedValue _ _ ty) = checkDups ty >> return e
531+ go other = return other
533+ checkDups :: Type -> Check ()
534+ checkDups (TypeApp t1 t2) = checkDups t1 >> checkDups t2
535+ checkDups (SaturatedTypeSynonym _ ts) = mapM_ checkDups ts
536+ checkDups (ForAll _ t _) = checkDups t
537+ checkDups (ConstrainedType args t) = do
538+ mapM_ (checkDups) $ concatMap snd args
540+ checkDups r@(RCons _ _ _) =
541+ let (ls, _) = rowToList r in
542+ case firstDup . sort . map fst $ ls of
543+ Just l -> throwError . strMsg $ "Duplicate label " ++ show l ++ " in row"
544+ Nothing -> return ()
545+ checkDups _ = return ()
547+ firstDup :: (Eq a) => [a] -> Maybe a
548+ firstDup (x : xs@(x' : _))
550+ | otherwise = firstDup xs
551+ firstDup _ = Nothing
554+-- Ensure a row contains no duplicate labels
556+setify :: Type -> Type
557+setify = rowFromList . first (M.toList . M.fromList) . rowToList
560+-- \"Setify\" all rows occuring inside a value
562+setifyAll :: Type -> Type
563+setifyAll = everywhereOnTypes setify
566+-- Replace outermost unsolved unification variables with named type variables
568+varIfUnknown :: Type -> Type
570+ let unks = nub $ unknowns ty
571+ toName = (:) 't' . show
572+ ty' = everywhereOnTypes typeToVar ty
573+ typeToVar :: Type -> Type
574+ typeToVar (TUnknown u) = TypeVar (toName u)
576+ in mkForAll (sort . map toName $ unks) ty'
579+-- Remove any ForAlls and ConstrainedType constructors in a type by introducing new unknowns
580+-- or TypeClassDictionary values.
582+-- This is necessary during type checking to avoid unifying a polymorphic type with a
583+-- unification variable.
585+instantiatePolyTypeWithUnknowns :: Expr -> Type -> UnifyT Type Check (Expr, Type)
586+instantiatePolyTypeWithUnknowns val (ForAll ident ty _) = do
587+ ty' <- replaceVarWithUnknown ident ty
588+ instantiatePolyTypeWithUnknowns val ty'
589+instantiatePolyTypeWithUnknowns val (ConstrainedType constraints ty) = do
590+ dicts <- getTypeClassDictionaries
591+ (_, ty') <- instantiatePolyTypeWithUnknowns (error "Types under a constraint cannot themselves be constrained") ty
592+ return (foldl App val (map (flip (TypeClassDictionary True) dicts) constraints), ty')
593+instantiatePolyTypeWithUnknowns val ty = return (val, ty)
596+-- Replace a single type variable with a new unification variable
598+replaceVarWithUnknown :: String -> Type -> UnifyT Type Check Type
599+replaceVarWithUnknown ident ty = do
601+ return $ replaceTypeVars ident tu ty
604+-- Replace fully applied type synonyms with the @SaturatedTypeSynonym@ data constructor, which helps generate
605+-- better error messages during unification.
607+replaceAllTypeSynonyms' :: Environment -> Type -> Either String Type
608+replaceAllTypeSynonyms' env d =
610+ syns = map (\(name, (args, _)) -> (name, length args)) . M.toList $ typeSynonyms env
612+ saturateAllTypeSynonyms syns d
614+replaceAllTypeSynonyms :: (Error e, Functor m, Monad m, MonadState CheckState m, MonadError e m) => Type -> m Type
615+replaceAllTypeSynonyms d = do
617+ either (throwError . strMsg) return $ replaceAllTypeSynonyms' env d
620+-- \"Desaturate\" @SaturatedTypeSynonym@s
622+desaturateAllTypeSynonyms :: Type -> Type
623+desaturateAllTypeSynonyms = everywhereOnTypes replaceSaturatedTypeSynonym
625+ replaceSaturatedTypeSynonym (SaturatedTypeSynonym name args) = foldl TypeApp (TypeConstructor name) args
626+ replaceSaturatedTypeSynonym t = t
629+-- Replace a type synonym and its arguments with the aliased type
631+expandTypeSynonym' :: Environment -> Qualified ProperName -> [Type] -> Either String Type
632+expandTypeSynonym' env name args =
633+ case M.lookup name (typeSynonyms env) of
634+ Just (synArgs, body) -> do
635+ let repl = replaceAllTypeVars (zip (map fst synArgs) args) body
636+ replaceAllTypeSynonyms' env repl
637+ Nothing -> error "Type synonym was not defined"
639+expandTypeSynonym :: (Error e, Functor m, Monad m, MonadState CheckState m, MonadError e m) => Qualified ProperName -> [Type] -> m Type
640+expandTypeSynonym name args = do
642+ either (throwError . strMsg) return $ expandTypeSynonym' env name args
644+expandAllTypeSynonyms :: (Error e, Functor m, Applicative m, Monad m, MonadState CheckState m, MonadError e m) => Type -> m Type
645+expandAllTypeSynonyms = everywhereOnTypesTopDownM go
647+ go (SaturatedTypeSynonym name args) = expandTypeSynonym name args
648+ go other = return other
651+-- Ensure a set of property names and value does not contain duplicate labels
653+ensureNoDuplicateProperties :: (Error e, MonadError e m) => [(String, Expr)] -> m ()
654+ensureNoDuplicateProperties ps = guardWith (strMsg "Duplicate property names") $ length (nub . map fst $ ps) == length ps
657+-- Infer a type for a value, rethrowing any error to provide a more useful error message
659+infer :: Expr -> UnifyT Type Check Expr
660+infer val = rethrow (mkErrorStack "Error inferring type of value" (Just (ExprError val)) <>) $ infer' val
663+-- Infer a type for a value
665+infer' :: Expr -> UnifyT Type Check Expr
666+infer' v@(NumericLiteral _) = return $ TypedValue True v tyNumber
667+infer' v@(StringLiteral _) = return $ TypedValue True v tyString
668+infer' v@(BooleanLiteral _) = return $ TypedValue True v tyBoolean
669+infer' (ArrayLiteral vals) = do
670+ ts <- mapM infer vals
672+ forM_ ts $ \(TypedValue _ _ t) -> els =?= t
673+ return $ TypedValue True (ArrayLiteral ts) (TypeApp tyArray els)
674+infer' (ObjectLiteral ps) = do
675+ ensureNoDuplicateProperties ps
676+ ts <- mapM (infer . snd) ps
677+ let fields = zipWith (\name (TypedValue _ _ t) -> (name, t)) (map fst ps) ts
678+ ty = TypeApp tyObject $ rowFromList (fields, REmpty)
679+ return $ TypedValue True (ObjectLiteral (zip (map fst ps) ts)) ty
680+infer' (ObjectUpdate o ps) = do
681+ ensureNoDuplicateProperties ps
683+ newVals <- zipWith (\(name, _) t -> (name, t)) ps <$> mapM (infer . snd) ps
684+ let newTys = map (\(name, TypedValue _ _ ty) -> (name, ty)) newVals
685+ oldTys <- zip (map fst ps) <$> replicateM (length ps) fresh
686+ let oldTy = TypeApp tyObject $ rowFromList (oldTys, row)
687+ o' <- TypedValue True <$> check o oldTy <*> pure oldTy
688+ return $ TypedValue True (ObjectUpdate o' newVals) $ TypeApp tyObject $ rowFromList (newTys, row)
689+infer' (Accessor prop val) = do
690+ typed@(TypedValue _ _ objTy) <- infer val
691+ propTy <- inferProperty objTy prop
696+ _ <- subsumes Nothing objTy (TypeApp tyObject (RCons prop field rest))
697+ return $ TypedValue True (Accessor prop typed) field
698+ Just ty -> return $ TypedValue True (Accessor prop typed) ty
699+infer' (Abs (Left arg) ret) = do
701+ Just moduleName <- checkCurrentModule <$> get
702+ makeBindingGroupVisible $ bindLocalVariables moduleName [(arg, ty, Defined)] $ do
703+ body@(TypedValue _ _ bodyTy) <- infer' ret
704+ return $ TypedValue True (Abs (Left arg) body) $ function ty bodyTy
705+infer' (Abs (Right _) _) = error "Binder was not desugared"
706+infer' (App f arg) = do
707+ f'@(TypedValue _ _ ft) <- infer f
708+ (ret, app) <- checkFunctionApplication f' ft arg Nothing
709+ return $ TypedValue True app ret
710+infer' (Var var) = do
711+ Just moduleName <- checkCurrentModule <$> get
712+ checkVisibility moduleName var
713+ ty <- introduceSkolemScope <=< replaceAllTypeSynonyms <=< lookupVariable moduleName $ var
715+ ConstrainedType constraints ty' -> do
716+ dicts <- getTypeClassDictionaries
717+ return $ TypedValue True (foldl App (Var var) (map (flip (TypeClassDictionary True) dicts) constraints)) ty'
718+ _ -> return $ TypedValue True (Var var) ty
719+infer' v@(Constructor c) = do
721+ case M.lookup c (dataConstructors env) of
722+ Nothing -> throwError . strMsg $ "Constructor " ++ show c ++ " is undefined"
723+ Just (_, _, ty) -> do ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
724+ return $ TypedValue True v ty'
725+infer' (Case vals binders) = do
726+ ts <- mapM infer vals
728+ binders' <- checkBinders (map (\(TypedValue _ _ t) -> t) ts) ret binders
729+ return $ TypedValue True (Case ts binders') ret
730+infer' (IfThenElse cond th el) = do
731+ cond' <- check cond tyBoolean
732+ v2@(TypedValue _ _ t2) <- infer th
733+ v3@(TypedValue _ _ t3) <- infer el
734+ (v2', v3', t) <- meet v2 v3 t2 t3
735+ return $ TypedValue True (IfThenElse cond' v2' v3') t
736+infer' (Let ds val) = do
737+ (ds', val'@(TypedValue _ _ valTy)) <- inferLetBinding [] ds val infer
738+ return $ TypedValue True (Let ds' val') valTy
739+infer' (SuperClassDictionary className tys) = do
740+ dicts <- getTypeClassDictionaries
741+ return $ TypeClassDictionary False (className, tys) dicts
742+infer' (TypedValue checkType val ty) = do
743+ Just moduleName <- checkCurrentModule <$> get
744+ kind <- liftCheck $ kindOf moduleName ty
745+ guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
746+ ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
747+ val' <- if checkType then check val ty' else return val
748+ return $ TypedValue True val' ty'
749+infer' (PositionedValue pos val) = rethrowWithPosition pos $ infer' val
750+infer' _ = error "Invalid argument to infer"
752+inferLetBinding :: [Declaration] -> [Declaration] -> Expr -> (Expr -> UnifyT Type Check Expr) -> UnifyT Type Check ([Declaration], Expr)
753+inferLetBinding seen [] ret j = (,) seen <$> makeBindingGroupVisible (j ret)
754+inferLetBinding seen (ValueDeclaration ident nameKind [] Nothing tv@(TypedValue checkType val ty) : rest) ret j = do
755+ Just moduleName <- checkCurrentModule <$> get
756+ kind <- liftCheck $ kindOf moduleName ty
757+ guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
758+ let dict = M.singleton (moduleName, ident) (ty, nameKind, Undefined)
759+ ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
760+ TypedValue _ val' ty'' <- if checkType then bindNames dict (check val ty') else return tv
761+ bindNames (M.singleton (moduleName, ident) (ty'', nameKind, Defined)) $ inferLetBinding (seen ++ [ValueDeclaration ident nameKind [] Nothing (TypedValue checkType val' ty'')]) rest ret j
762+inferLetBinding seen (ValueDeclaration ident nameKind [] Nothing val : rest) ret j = do
764+ Just moduleName <- checkCurrentModule <$> get
765+ let dict = M.singleton (moduleName, ident) (valTy, nameKind, Undefined)
766+ TypedValue _ val' valTy' <- bindNames dict $ infer val
768+ bindNames (M.singleton (moduleName, ident) (valTy', nameKind, Defined)) $ inferLetBinding (seen ++ [ValueDeclaration ident nameKind [] Nothing val']) rest ret j
769+inferLetBinding seen (BindingGroupDeclaration ds : rest) ret j = do
770+ Just moduleName <- checkCurrentModule <$> get
771+ (untyped, typed, dict, untypedDict) <- typeDictionaryForBindingGroup moduleName (map (\(i, _, v) -> (i, v)) ds)
772+ ds1' <- parU typed $ \e -> checkTypedBindingGroupElement moduleName e dict
773+ ds2' <- forM untyped $ \e -> typeForBindingGroupElement e dict untypedDict
774+ let ds' = [(ident, LocalVariable, val') | (ident, (val', _)) <- ds1' ++ ds2']
775+ makeBindingGroupVisible $ bindNames dict $ inferLetBinding (seen ++ [BindingGroupDeclaration ds']) rest ret j
776+inferLetBinding seen (PositionedDeclaration pos d : ds) ret j = rethrowWithPosition pos $ do
777+ ((d' : ds'), val') <- inferLetBinding seen (d : ds) ret j
778+ return (PositionedDeclaration pos d' : ds', val')
779+inferLetBinding _ _ _ _ = error "Invalid argument to inferLetBinding"
782+-- Infer the type of a property inside a record with a given type
784+inferProperty :: Type -> String -> UnifyT Type Check (Maybe Type)
785+inferProperty (TypeApp obj row) prop | obj == tyObject = do
786+ let (props, _) = rowToList row
787+ return $ lookup prop props
788+inferProperty (SaturatedTypeSynonym name args) prop = do
789+ replaced <- introduceSkolemScope <=< expandTypeSynonym name $ args
790+ inferProperty replaced prop
791+inferProperty (ForAll ident ty _) prop = do
792+ replaced <- replaceVarWithUnknown ident ty
793+ inferProperty replaced prop
794+inferProperty _ _ = return Nothing
797+-- Infer the types of variables brought into scope by a binder
799+inferBinder :: Type -> Binder -> UnifyT Type Check (M.Map Ident Type)
800+inferBinder _ NullBinder = return M.empty
801+inferBinder val (StringBinder _) = val =?= tyString >> return M.empty
802+inferBinder val (NumberBinder _) = val =?= tyNumber >> return M.empty
803+inferBinder val (BooleanBinder _) = val =?= tyBoolean >> return M.empty
804+inferBinder val (VarBinder name) = return $ M.singleton name val
805+inferBinder val (ConstructorBinder ctor binders) = do
807+ case M.lookup ctor (dataConstructors env) of
808+ Just (_, _, ty) -> do
809+ (_, fn) <- instantiatePolyTypeWithUnknowns (error "Data constructor types cannot contain constraints") ty
810+ fn' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ fn
814+ _ <- subsumes Nothing val ty'
816+ go (binder : binders') (TypeApp (TypeApp t obj) ret) | t == tyFunction =
817+ M.union <$> inferBinder obj binder <*> go binders' ret
818+ go _ _ = throwError . strMsg $ "Wrong number of arguments to constructor " ++ show ctor
819+ _ -> throwError . strMsg $ "Constructor " ++ show ctor ++ " is not defined"
820+inferBinder val (ObjectBinder props) = do
823+ m1 <- inferRowProperties row rest props
824+ val =?= TypeApp tyObject row
827+ inferRowProperties :: Type -> Type -> [(String, Binder)] -> UnifyT Type Check (M.Map Ident Type)
828+ inferRowProperties nrow row [] = nrow =?= row >> return M.empty
829+ inferRowProperties nrow row ((name, binder):binders) = do
831+ m1 <- inferBinder propTy binder
832+ m2 <- inferRowProperties nrow (RCons name propTy row) binders
833+ return $ m1 `M.union` m2
834+inferBinder val (ArrayBinder binders) = do
836+ m1 <- M.unions <$> mapM (inferBinder el) binders
837+ val =?= TypeApp tyArray el
839+inferBinder val (ConsBinder headBinder tailBinder) = do
841+ m1 <- inferBinder el headBinder
842+ m2 <- inferBinder val tailBinder
843+ val =?= TypeApp tyArray el
844+ return $ m1 `M.union` m2
845+inferBinder val (NamedBinder name binder) = do
846+ m <- inferBinder val binder
847+ return $ M.insert name val m
848+inferBinder val (PositionedBinder pos binder) =
849+ rethrowWithPosition pos $ inferBinder val binder
852+-- Check the types of the return values in a set of binders in a case statement
854+checkBinders :: [Type] -> Type -> [CaseAlternative] -> UnifyT Type Check [CaseAlternative]
855+checkBinders _ _ [] = return []
856+checkBinders nvals ret (CaseAlternative binders grd val : bs) = do
857+ guardWith (strMsg "Overlapping binders in case statement") $
858+ let ns = concatMap binderNames binders in length (nub ns) == length ns
859+ Just moduleName <- checkCurrentModule <$> get
860+ m1 <- M.unions <$> zipWithM inferBinder nvals binders
861+ r <- bindLocalVariables moduleName [ (name, ty, Defined) | (name, ty) <- M.toList m1 ] $ do
862+ val' <- TypedValue True <$> check val ret <*> pure ret
864+ Nothing -> return $ CaseAlternative binders Nothing val'
866+ g' <- check g tyBoolean
867+ return $ CaseAlternative binders (Just g') val'
868+ rs <- checkBinders nvals ret bs
872+-- Generate a new skolem constant
874+newSkolemConstant :: UnifyT Type Check Int
875+newSkolemConstant = fresh'
878+-- Generate a new skolem scope
880+newSkolemScope :: UnifyT Type Check SkolemScope
881+newSkolemScope = SkolemScope <$> fresh'
884+-- Skolemize a type variable by replacing its instances with fresh skolem constants
886+skolemize :: String -> Int -> SkolemScope -> Type -> Type
887+skolemize ident sko scope = replaceTypeVars ident (Skolem ident sko scope)
890+-- This function has one purpose - to skolemize type variables appearing in a
891+-- SuperClassDictionary placeholder. These type variables are somewhat unique since they are the
892+-- only example of scoped type variables.
894+skolemizeTypesInValue :: String -> Int -> SkolemScope -> Expr -> Expr
895+skolemizeTypesInValue ident sko scope = let (_, f, _) = everywhereOnValues id go id in f
897+ go (SuperClassDictionary c ts) = SuperClassDictionary c (map (skolemize ident sko scope) ts)
901+-- Introduce skolem scope at every occurence of a ForAll
903+introduceSkolemScope :: Type -> UnifyT Type Check Type
904+introduceSkolemScope = everywhereOnTypesM go
906+ go (ForAll ident ty Nothing) = ForAll ident ty <$> (Just <$> newSkolemScope)
907+ go other = return other
910+-- Check the type of a value, rethrowing errors to provide a better error message
912+check :: Expr -> Type -> UnifyT Type Check Expr
913+check val ty = rethrow (mkErrorStack errorMessage (Just (ExprError val)) <>) $ check' val ty
916+ "Error checking type of term " ++
917+ prettyPrintValue val ++
922+-- Check the type of a value
924+check' :: Expr -> Type -> UnifyT Type Check Expr
925+check' val (ForAll ident ty _) = do
926+ scope <- newSkolemScope
927+ sko <- newSkolemConstant
928+ let sk = skolemize ident sko scope ty
929+ let skVal = skolemizeTypesInValue ident sko scope val
930+ val' <- check skVal sk
931+ return $ TypedValue True val' (ForAll ident ty (Just scope))
932+check' val t@(ConstrainedType constraints ty) = do
933+ dictNames <- forM constraints $ \(Qualified _ (ProperName className), _) -> do
934+ n <- liftCheck freshDictionaryName
935+ return $ Ident $ "__dict_" ++ className ++ "_" ++ show n
936+ val' <- makeBindingGroupVisible $ withTypeClassDictionaries (zipWith (\name (className, instanceTy) ->
937+ TypeClassDictionaryInScope name className instanceTy Nothing TCDRegular False) (map (Qualified Nothing) dictNames)
938+ constraints) $ check val ty
939+ return $ TypedValue True (foldr (Abs . Left) val' dictNames) t
940+check' val (SaturatedTypeSynonym name args) = do
941+ ty <- introduceSkolemScope <=< expandTypeSynonym name $ args
943+check' val u@(TUnknown _) = do
944+ val'@(TypedValue _ _ ty) <- infer val
945+ -- Don't unify an unknown with an inferred polytype
946+ (val'', ty') <- instantiatePolyTypeWithUnknowns val' ty
948+ return $ TypedValue True val'' ty'
949+check' v@(NumericLiteral _) t | t == tyNumber =
950+ return $ TypedValue True v t
951+check' v@(StringLiteral _) t | t == tyString =
952+ return $ TypedValue True v t
953+check' v@(BooleanLiteral _) t | t == tyBoolean =
954+ return $ TypedValue True v t
955+check' (ArrayLiteral vals) t@(TypeApp a ty) = do
957+ array <- ArrayLiteral <$> forM vals (`check` ty)
958+ return $ TypedValue True array t
959+check' (Abs (Left arg) ret) ty@(TypeApp (TypeApp t argTy) retTy) | t == tyFunction = do
960+ Just moduleName <- checkCurrentModule <$> get
961+ ret' <- makeBindingGroupVisible $ bindLocalVariables moduleName [(arg, argTy, Defined)] $ check ret retTy
962+ return $ TypedValue True (Abs (Left arg) ret') ty
963+check' (Abs (Right _) _) _ = error "Binder was not desugared"
964+check' (App f arg) ret = do
965+ f'@(TypedValue _ _ ft) <- infer f
966+ (_, app) <- checkFunctionApplication f' ft arg (Just ret)
967+ return $ TypedValue True app ret
968+check' v@(Var var) ty = do
969+ Just moduleName <- checkCurrentModule <$> get
970+ checkVisibility moduleName var
971+ repl <- introduceSkolemScope <=< replaceAllTypeSynonyms <=< lookupVariable moduleName $ var
972+ ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
973+ v' <- subsumes (Just v) repl ty'
975+ Nothing -> throwError . strMsg $ "Unable to check type subsumption"
976+ Just v'' -> return $ TypedValue True v'' ty'
977+check' (SuperClassDictionary className tys) _ = do
979+ -- Here, we replace a placeholder for a superclass dictionary with a regular
980+ -- TypeClassDictionary placeholder. The reason we do this is that it is necessary to have the
981+ -- correct super instance dictionaries in scope, and these are not available when the type class
982+ -- declaration gets desugared.
984+ -- Note also that the first argument to TypeClassDictionary is False, meaning we _do not_ want
985+ -- to consider superclass instances when searching for this dictionary - doing so might lead
986+ -- to traversing a cycle in the instance graph.
988+ dicts <- getTypeClassDictionaries
989+ return $ TypeClassDictionary False (className, tys) dicts
990+check' (TypedValue checkType val ty1) ty2 = do
991+ Just moduleName <- checkCurrentModule <$> get
992+ kind <- liftCheck $ kindOf moduleName ty1
993+ guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
994+ ty1' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty1
995+ ty2' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty2
996+ val' <- subsumes (Just val) ty1' ty2'
998+ Nothing -> throwError . strMsg $ "Unable to check type subsumption"
1000+ val''' <- if checkType then check val'' ty2' else return val''
1001+ return $ TypedValue checkType (TypedValue True val''' ty1') ty2'
1002+check' (Case vals binders) ret = do
1003+ vals' <- mapM infer vals
1004+ let ts = map (\(TypedValue _ _ t) -> t) vals'
1005+ binders' <- checkBinders ts ret binders
1006+ return $ TypedValue True (Case vals' binders') ret
1007+check' (IfThenElse cond th el) ty = do
1008+ cond' <- check cond tyBoolean
1011+ return $ TypedValue True (IfThenElse cond' th' el') ty
1012+check' (ObjectLiteral ps) t@(TypeApp obj row) | obj == tyObject = do
1013+ ensureNoDuplicateProperties ps
1014+ ps' <- checkProperties ps row False
1015+ return $ TypedValue True (ObjectLiteral ps') t
1016+check' (TypeClassDictionaryConstructorApp name ps) t = do
1018+ return $ TypedValue True (TypeClassDictionaryConstructorApp name ps') t
1019+check' (ObjectUpdate obj ps) t@(TypeApp o row) | o == tyObject = do
1020+ ensureNoDuplicateProperties ps
1021+ us <- zip (map fst ps) <$> replicateM (length ps) fresh
1022+ let (propsToCheck, rest) = rowToList row
1023+ propsToRemove = map fst ps
1024+ remainingProps = filter (\(p, _) -> p `notElem` propsToRemove) propsToCheck
1025+ obj' <- check obj (TypeApp tyObject (rowFromList (us ++ remainingProps, rest)))
1026+ ps' <- checkProperties ps row True
1027+ return $ TypedValue True (ObjectUpdate obj' ps') t
1028+check' (Accessor prop val) ty = do
1030+ val' <- check val (TypeApp tyObject (RCons prop ty rest))
1031+ return $ TypedValue True (Accessor prop val') ty
1032+check' (Constructor c) ty = do
1034+ case M.lookup c (dataConstructors env) of
1035+ Nothing -> throwError . strMsg $ "Constructor " ++ show c ++ " is undefined"
1036+ Just (_, _, ty1) -> do
1037+ repl <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty1
1038+ _ <- subsumes Nothing repl ty
1039+ return $ TypedValue True (Constructor c) ty
1040+check' (Let ds val) ty = do
1041+ (ds', val') <- inferLetBinding [] ds val (flip check ty)
1042+ return $ TypedValue True (Let ds' val') ty
1043+check' val ty | containsTypeSynonyms ty = do
1044+ ty' <- introduceSkolemScope <=< expandAllTypeSynonyms $ ty
1046+check' val kt@(KindedType ty kind) = do
1047+ guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
1048+ val' <- check' val ty
1049+ return $ TypedValue True val' kt
1050+check' (PositionedValue pos val) ty =
1051+ rethrowWithPosition pos $ check val ty
1052+check' val ty = throwError $ mkErrorStack ("Expr does not have type " ++ prettyPrintType ty) (Just (ExprError val))
1054+containsTypeSynonyms :: Type -> Bool
1055+containsTypeSynonyms = everythingOnTypes (||) go where
1056+ go (SaturatedTypeSynonym _ _) = True
1060+-- Check the type of a collection of named record fields
1062+-- The @lax@ parameter controls whether or not every record member has to be provided. For object updates, this is not the case.
1064+checkProperties :: [(String, Expr)] -> Type -> Bool -> UnifyT Type Check [(String, Expr)]
1065+checkProperties ps row lax = let (ts, r') = rowToList row in go ps ts r' where
1066+ go [] [] REmpty = return []
1067+ go [] [] u@(TUnknown _) = do u =?= REmpty
1069+ go [] [] (Skolem _ _ _) | lax = return []
1070+ go [] ((p, _): _) _ | lax = return []
1071+ | otherwise = throwError $ mkErrorStack ("Object does not have property " ++ p) (Just (ExprError (ObjectLiteral ps)))
1072+ go ((p,_):_) [] REmpty = throwError $ mkErrorStack ("Property " ++ p ++ " is not present in closed object type " ++ prettyPrintRow row) (Just (ExprError (ObjectLiteral ps)))
1073+ go ((p,v):ps') [] u@(TUnknown _) = do
1074+ v'@(TypedValue _ _ ty) <- infer v
1076+ u =?= RCons p ty rest
1077+ ps'' <- go ps' [] rest
1078+ return $ (p, v') : ps''
1079+ go ((p,v):ps') ts r =
1080+ case lookup p ts of
1082+ v'@(TypedValue _ _ ty) <- infer v
1084+ r =?= RCons p ty rest
1085+ ps'' <- go ps' ts rest
1086+ return $ (p, v') : ps''
1089+ ps'' <- go ps' (delete (p, ty) ts) r
1090+ return $ (p, v') : ps''
1091+ go _ _ _ = throwError $ mkErrorStack ("Object does not have type " ++ prettyPrintType (TypeApp tyObject row)) (Just (ExprError (ObjectLiteral ps)))
1094+-- Check the type of a function application, rethrowing errors to provide a better error message
1096+checkFunctionApplication :: Expr -> Type -> Expr -> Maybe Type -> UnifyT Type Check (Type, Expr)
1097+checkFunctionApplication fn fnTy arg ret = rethrow (mkErrorStack errorMessage (Just (ExprError fn)) <>) $ do
1098+ subst <- unifyCurrentSubstitution <$> UnifyT get
1099+ checkFunctionApplication' fn (subst $? fnTy) arg (($?) subst <$> ret)
1101+ errorMessage = "Error applying function of type "
1102+ ++ prettyPrintType fnTy
1103+ ++ " to argument " ++ prettyPrintValue arg
1106+-- Check the type of a function application
1108+checkFunctionApplication' :: Expr -> Type -> Expr -> Maybe Type -> UnifyT Type Check (Type, Expr)
1109+checkFunctionApplication' fn (TypeApp (TypeApp tyFunction' argTy) retTy) arg ret = do
1110+ tyFunction' =?= tyFunction
1111+ arg' <- check arg argTy
1113+ Nothing -> return (retTy, App fn arg')
1115+ Just app' <- subsumes (Just (App fn arg')) retTy ret'
1116+ return (retTy, app')
1117+checkFunctionApplication' fn (ForAll ident ty _) arg ret = do
1118+ replaced <- replaceVarWithUnknown ident ty
1119+ checkFunctionApplication fn replaced arg ret
1120+checkFunctionApplication' fn u@(TUnknown _) arg ret = do
1122+ TypedValue _ arg' t <- infer arg
1123+ (arg'', t') <- instantiatePolyTypeWithUnknowns arg' t
1124+ return $ TypedValue True arg'' t'
1125+ let ty = (\(TypedValue _ _ t) -> t) arg'
1126+ ret' <- maybe fresh return ret
1127+ u =?= function ty ret'
1128+ return (ret', App fn arg')
1129+checkFunctionApplication' fn (SaturatedTypeSynonym name tyArgs) arg ret = do
1130+ ty <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
1131+ checkFunctionApplication fn ty arg ret
1132+checkFunctionApplication' fn (KindedType ty _) arg ret = do
1133+ checkFunctionApplication fn ty arg ret
1134+checkFunctionApplication' fn (ConstrainedType constraints fnTy) arg ret = do
1135+ dicts <- getTypeClassDictionaries
1136+ checkFunctionApplication' (foldl App fn (map (flip (TypeClassDictionary True) dicts) constraints)) fnTy arg ret
1137+checkFunctionApplication' fn fnTy dict@(TypeClassDictionary _ _ _) _ =
1138+ return (fnTy, App fn dict)
1139+checkFunctionApplication' _ fnTy arg _ = throwError . strMsg $ "Cannot apply a function of type "
1140+ ++ prettyPrintType fnTy
1141+ ++ " to argument " ++ prettyPrintValue arg
1144+-- Check whether one type subsumes another, rethrowing errors to provide a better error message
1146+subsumes :: Maybe Expr -> Type -> Type -> UnifyT Type Check (Maybe Expr)
1147+subsumes val ty1 ty2 = rethrow (mkErrorStack errorMessage (ExprError <$> val) <>) $ subsumes' val ty1 ty2
1149+ errorMessage = "Error checking that type "
1150+ ++ prettyPrintType ty1
1151+ ++ " subsumes type "
1152+ ++ prettyPrintType ty2
1155+-- Check whether one type subsumes another
1157+subsumes' :: Maybe Expr -> Type -> Type -> UnifyT Type Check (Maybe Expr)
1158+subsumes' val (ForAll ident ty1 _) ty2 = do
1159+ replaced <- replaceVarWithUnknown ident ty1
1160+ subsumes val replaced ty2
1161+subsumes' val ty1 (ForAll ident ty2 sco) =
1164+ sko <- newSkolemConstant
1165+ let sk = skolemize ident sko sco' ty2
1166+ subsumes val ty1 sk
1167+ Nothing -> throwError . strMsg $ "Skolem variable scope is unspecified"
1168+subsumes' val (TypeApp (TypeApp f1 arg1) ret1) (TypeApp (TypeApp f2 arg2) ret2) | f1 == tyFunction && f2 == tyFunction = do
1169+ _ <- subsumes Nothing arg2 arg1
1170+ _ <- subsumes Nothing ret1 ret2
1172+subsumes' val (SaturatedTypeSynonym name tyArgs) ty2 = do
1173+ ty1 <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
1174+ subsumes val ty1 ty2
1175+subsumes' val ty1 (SaturatedTypeSynonym name tyArgs) = do
1176+ ty2 <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
1177+ subsumes val ty1 ty2
1178+subsumes' val (KindedType ty1 _) ty2 = do
1179+ subsumes val ty1 ty2
1180+subsumes' val ty1 (KindedType ty2 _) = do
1181+ subsumes val ty1 ty2
1182+subsumes' (Just val) (ConstrainedType constraints ty1) ty2 = do
1183+ dicts <- getTypeClassDictionaries
1184+ subsumes' (Just $ foldl App val (map (flip (TypeClassDictionary True) dicts) constraints)) ty1 ty2
1185+subsumes' val (TypeApp f1 r1) (TypeApp f2 r2) | f1 == tyObject && f2 == tyObject = do
1187+ (ts1, r1') = rowToList r1
1188+ (ts2, r2') = rowToList r2
1189+ ts1' = sortBy (comparing fst) ts1
1190+ ts2' = sortBy (comparing fst) ts2
1191+ go ts1' ts2' r1' r2'
1194+ go [] ts2 r1' r2' = r1' =?= rowFromList (ts2, r2')
1195+ go ts1 [] r1' r2' = r2' =?= rowFromList (ts1, r1')
1196+ go ((p1, ty1) : ts1) ((p2, ty2) : ts2) r1' r2'
1197+ | p1 == p2 = do _ <- subsumes Nothing ty1 ty2
1199+ | p1 < p2 = do rest <- fresh
1200+ r2' =?= RCons p1 ty1 rest
1201+ go ts1 ((p2, ty2) : ts2) r1' rest
1202+ | otherwise = do rest <- fresh
1203+ r1' =?= RCons p2 ty2 rest
1204+ go ((p1, ty1) : ts1) ts2 rest r2'
1205+subsumes' val ty1 ty2@(TypeApp obj _) | obj == tyObject = subsumes val ty2 ty1
1206+subsumes' val ty1 ty2 = do
1211+-- Compute the meet of two types, i.e. the most general type which both types subsume.
1212+-- TODO: handle constrained types
1214+meet :: Expr -> Expr -> Type -> Type -> UnifyT Type Check (Expr, Expr, Type)
1215+meet e1 e2 (ForAll ident t1 _) t2 = do
1216+ t1' <- replaceVarWithUnknown ident t1
1218+meet e1 e2 t1 (ForAll ident t2 _) = do
1219+ t2' <- replaceVarWithUnknown ident t2
1221+meet e1 e2 t1 t2 = do
1223+ return (e1, e2, t1)