@@ -0,0 +1,1111 @@
1+-----------------------------------------------------------------------------
2+--
3+-- Module : Language.PureScript.TypeChecker.Types
4+-- Copyright : (c) Phil Freeman 2013
5+-- License : MIT
6+--
7+-- Maintainer : Phil Freeman <paf31@cantab.net>
8+-- Stability : experimental
9+-- Portability :
10+--
11+-- |
12+-- This module implements the type checker
13+--
14+-----------------------------------------------------------------------------
15+
16+{-# OPTIONS_GHC -fno-warn-orphans #-}
17+{-# LANGUAGE FlexibleInstances #-}
18+{-# LANGUAGE FlexibleContexts #-}
19+{-# LANGUAGE MultiParamTypeClasses #-}
20+
21+module Language.PureScript.TypeChecker.Types (
22+ typesOf
23+) where
24+
25+{-
26+ The following functions represent the corresponding type checking judgements:
27+
28+ infer
29+ Synthesize a type for a value
30+
31+ check
32+ Check a value has a given type
33+
34+ checkProperties
35+ Check an object with a given type contains specified properties
36+
37+ checkFunctionApplication
38+ Check a function of a given type returns a value of another type when applied to its arguments
39+
40+ subsumes
41+ Check a type subsumes another type
42+-}
43+
44+import Data.List
45+import Data.Maybe (maybeToList, isNothing, isJust, fromMaybe)
46+import Data.Generics
47+ (everythingWithContext, mkM, mkT, something, everywhere, mkQ)
48+import Data.Generics.Extras
49+
50+import Language.PureScript.Declarations
51+import Language.PureScript.Types
52+import Language.PureScript.Kinds
53+import Language.PureScript.Names
54+import Language.PureScript.TypeClassDictionaries
55+import Language.PureScript.TypeChecker.Monad
56+import Language.PureScript.TypeChecker.Kinds
57+import Language.PureScript.TypeChecker.Synonyms
58+import Language.PureScript.Pretty
59+import Language.PureScript.Environment
60+import Language.PureScript.Errors
61+import qualified Language.PureScript.Constants as C
62+
63+import Control.Monad.State
64+import Control.Monad.Error
65+import Control.Monad.Unify
66+
67+import Control.Applicative
68+import Control.Arrow (Arrow(..))
69+
70+import qualified Data.Map as M
71+import Data.Function (on)
72+import Data.Ord (comparing)
73+import Data.Monoid ((<>))
74+
75+instance Partial Type where
76+ unknown = TUnknown
77+ isUnknown (TUnknown u) = Just u
78+ isUnknown _ = Nothing
79+
80+instance Unifiable Check Type where
81+ (=?=) = unifyTypes
82+
83+-- |
84+-- Unify two types, updating the current substitution
85+--
86+unifyTypes :: Type -> Type -> UnifyT Type Check ()
87+unifyTypes t1 t2 = rethrow (mkErrorStack ("Error unifying type " ++ prettyPrintType t1 ++ " with type " ++ prettyPrintType t2) Nothing <>) $
88+ unifyTypes' t1 t2
89+ where
90+ unifyTypes' (TUnknown u1) (TUnknown u2) | u1 == u2 = return ()
91+ unifyTypes' (TUnknown u) t = u =:= t
92+ unifyTypes' t (TUnknown u) = u =:= t
93+ unifyTypes' (SaturatedTypeSynonym name args) ty = do
94+ ty1 <- introduceSkolemScope <=< expandTypeSynonym name $ args
95+ ty1 `unifyTypes` ty
96+ unifyTypes' ty s@(SaturatedTypeSynonym _ _) = s `unifyTypes` ty
97+ unifyTypes' (ForAll ident1 ty1 sc1) (ForAll ident2 ty2 sc2) =
98+ case (sc1, sc2) of
99+ (Just sc1', Just sc2') -> do
100+ sko <- newSkolemConstant
101+ let sk1 = skolemize ident1 sko sc1' ty1
102+ let sk2 = skolemize ident2 sko sc2' ty2
103+ sk1 `unifyTypes` sk2
104+ _ -> error "Skolemized type variable was not given a scope"
105+ unifyTypes' (ForAll ident ty1 (Just sc)) ty2 = do
106+ sko <- newSkolemConstant
107+ let sk = skolemize ident sko sc ty1
108+ sk `unifyTypes` ty2
109+ unifyTypes' ForAll{} _ = throwError . strMsg $ "Skolem variable scope is unspecified"
110+ unifyTypes' ty f@ForAll{} = f `unifyTypes` ty
111+ unifyTypes' (TypeVar v1) (TypeVar v2) | v1 == v2 = return ()
112+ unifyTypes' (TypeConstructor c1) (TypeConstructor c2) =
113+ guardWith (strMsg ("Cannot unify " ++ show c1 ++ " with " ++ show c2 ++ ".")) (c1 == c2)
114+ unifyTypes' (TypeApp t3 t4) (TypeApp t5 t6) = do
115+ t3 `unifyTypes` t5
116+ t4 `unifyTypes` t6
117+ unifyTypes' (Skolem _ s1 _) (Skolem _ s2 _) | s1 == s2 = return ()
118+ unifyTypes' r1@RCons{} r2 = unifyRows r1 r2
119+ unifyTypes' r1 r2@RCons{} = unifyRows r1 r2
120+ unifyTypes' r1@REmpty r2 = unifyRows r1 r2
121+ unifyTypes' r1 r2@REmpty = unifyRows r1 r2
122+ unifyTypes' t@(ConstrainedType _ _) _ = throwError . strMsg $ "Attempted to unify a constrained type " ++ prettyPrintType t ++ " with another type."
123+ unifyTypes' t3 t4@(ConstrainedType _ _) = unifyTypes' t4 t3
124+ unifyTypes' t3 t4 = throwError . strMsg $ "Cannot unify " ++ prettyPrintType t3 ++ " with " ++ prettyPrintType t4 ++ "."
125+
126+-- |
127+-- Unify two rows, updating the current substitution
128+--
129+-- Common labels are first identified, and unified. Remaining labels and types are unified with a
130+-- trailing row unification variable, if appropriate, otherwise leftover labels result in a unification
131+-- error.
132+--
133+unifyRows :: Type -> Type -> UnifyT Type Check ()
134+unifyRows r1 r2 =
135+ let
136+ (s1, r1') = rowToList r1
137+ (s2, r2') = rowToList r2
138+ int = [ (t1, t2) | (name, t1) <- s1, (name', t2) <- s2, name == name' ]
139+ sd1 = [ (name, t1) | (name, t1) <- s1, name `notElem` map fst s2 ]
140+ sd2 = [ (name, t2) | (name, t2) <- s2, name `notElem` map fst s1 ]
141+ in do
142+ forM_ int (uncurry (=?=))
143+ unifyRows' sd1 r1' sd2 r2'
144+ where
145+ unifyRows' :: [(String, Type)] -> Type -> [(String, Type)] -> Type -> UnifyT Type Check ()
146+ unifyRows' [] (TUnknown u) sd r = u =:= rowFromList (sd, r)
147+ unifyRows' sd r [] (TUnknown u) = u =:= rowFromList (sd, r)
148+ unifyRows' ((name, ty):row) r others u@(TUnknown un) = do
149+ occursCheck un ty
150+ forM_ row $ \(_, t) -> occursCheck un t
151+ u' <- fresh
152+ u =?= RCons name ty u'
153+ unifyRows' row r others u'
154+ unifyRows' [] REmpty [] REmpty = return ()
155+ unifyRows' [] (TypeVar v1) [] (TypeVar v2) | v1 == v2 = return ()
156+ unifyRows' [] (Skolem _ s1 _) [] (Skolem _ s2 _) | s1 == s2 = return ()
157+ unifyRows' sd3 r3 sd4 r4 = throwError . strMsg $ "Cannot unify (" ++ prettyPrintRow (rowFromList (sd3, r3)) ++ ") with (" ++ prettyPrintRow (rowFromList (sd4, r4)) ++ ")"
158+
159+-- |
160+-- Infer the types of multiple mutually-recursive values, and return elaborated values including
161+-- type class dictionaries and type annotations.
162+--
163+typesOf :: Maybe ModuleName -> ModuleName -> [(Ident, Value)] -> Check [(Ident, (Value, Type))]
164+typesOf mainModuleName moduleName vals = do
165+ tys <- fmap tidyUp . liftUnify $ do
166+ (es, dict, untypedDict) <- typeDictionaryForBindingGroup moduleName vals
167+ forM es $ \e -> do
168+ triple@(_, (_, ty)) <- typeForBindingGroupElement moduleName e dict untypedDict
169+ -- If --main is enabled, need to check that `main` has type Eff eff a for some eff, a
170+ when (Just moduleName == mainModuleName && fst e == Ident C.main) $ do
171+ [eff, a] <- replicateM 2 fresh
172+ ty =?= TypeApp (TypeApp (TypeConstructor (Qualified (Just (ModuleName [ProperName "Control", ProperName "Monad", ProperName "Eff"])) (ProperName "Eff"))) eff) a
173+ return triple
174+
175+ forM tys $ \(ident, (val, ty)) -> do
176+ -- Replace type class dictionary placeholders with actual dictionaries
177+ val' <- replaceTypeClassDictionaries moduleName val
178+ -- Check skolem variables did not escape their scope
179+ skolemEscapeCheck val'
180+ -- Remove type synonyms placeholders, remove duplicate row fields, and replace
181+ -- top-level unification variables with named type variables.
182+ let val'' = overTypes (desaturateAllTypeSynonyms . setifyAll) val'
183+ ty' = varIfUnknown . desaturateAllTypeSynonyms . setifyAll $ ty
184+ return (ident, (val'', ty'))
185+ where
186+ -- Apply the substitution that was returned from runUnify to both types and (type-annotated) values
187+ tidyUp (ts, sub) = map (\(i, (val, ty)) -> (i, (overTypes (sub $?) val, sub $? ty))) ts
188+
189+typeDictionaryForBindingGroup :: ModuleName -> [(Ident, Value)] -> UnifyT Type Check ([(Ident, (Value, Maybe (Type, Bool)))], M.Map (ModuleName, Ident) (Type, NameKind), [(Ident, Type)])
190+typeDictionaryForBindingGroup moduleName vals = do
191+ let
192+ -- Map each declaration to a name/value pair, with an optional type, if the declaration is typed
193+ es = map isTyped vals
194+ -- Filter the typed and untyped declarations
195+ typed = filter (isJust . snd . snd) es
196+ untyped = filter (isNothing . snd . snd) es
197+ -- Make a map of names to typed declarations
198+ typedDict = map (\(ident, (_, Just (ty, _))) -> (ident, ty)) typed
199+
200+ -- Create fresh unification variables for the types of untyped declarations
201+ untypedNames <- replicateM (length untyped) fresh
202+
203+ let
204+ -- Make a map of names to the unification variables of untyped declarations
205+ untypedDict = zip (map fst untyped) untypedNames
206+ -- Create the dictionary of all name/type pairs, which will be added to the environment during type checking
207+ dict = M.fromList (map (\(ident, ty) -> ((moduleName, ident), (ty, LocalVariable))) $ typedDict ++ untypedDict)
208+ return (es, dict, untypedDict)
209+
210+typeForBindingGroupElement :: ModuleName -> (Ident, (Value, Maybe (Type, Bool))) -> M.Map (ModuleName, Ident) (Type, NameKind) -> [(Ident, Type)] -> UnifyT Type Check (Ident, (Value, Type))
211+typeForBindingGroupElement moduleName e@(_, (val, _)) dict untypedDict = do
212+ -- If the declaration is a function, it has access to other values in the binding group.
213+ -- If not, the generated code might fail at runtime since those values might be undefined.
214+ let dict' = if isFunction val then dict else M.empty
215+ case e of
216+ -- Typed declarations
217+ (ident, (val', Just (ty, checkType))) -> do
218+ -- Kind check
219+ kind <- liftCheck $ kindOf moduleName ty
220+ guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
221+ -- Check the type with the new names in scope
222+ ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
223+ val'' <- bindNames dict' $ if checkType
224+ then TypedValue True <$> check val' ty' <*> pure ty'
225+ else return (TypedValue False val' ty')
226+ return (ident, (val'', ty'))
227+ -- Untyped declarations
228+ (ident, (val', Nothing)) -> do
229+ -- Infer the type with the new names in scope
230+ TypedValue _ val'' ty <- bindNames dict' $ infer val'
231+ ty =?= fromMaybe (error "name not found in dictionary") (lookup ident untypedDict)
232+ return (ident, (TypedValue True val'' ty, ty))
233+
234+-- |
235+-- Check if a value introduces a function
236+--
237+isFunction :: Value -> Bool
238+isFunction (Abs _ _) = True
239+isFunction (TypedValue _ val _) = isFunction val
240+isFunction (PositionedValue _ val) = isFunction val
241+isFunction _ = False
242+
243+-- |
244+-- Check if a value contains a type annotation
245+--
246+isTyped :: (Ident, Value) -> (Ident, (Value, Maybe (Type, Bool)))
247+isTyped (name, TypedValue checkType value ty) = (name, (value, Just (ty, checkType)))
248+isTyped (name, value) = (name, (value, Nothing))
249+
250+-- |
251+-- Map a function over type annotations appearing inside a value
252+--
253+overTypes :: (Type -> Type) -> Value -> Value
254+overTypes f = everywhere (mkT g)
255+ where
256+ g :: Value -> Value
257+ g (TypedValue checkTy val t) = TypedValue checkTy val (f t)
258+ g (TypeClassDictionary b (nm, tys) sco) = TypeClassDictionary b (nm, map f tys) sco
259+ g other = other
260+
261+-- |
262+-- Replace type class dictionary placeholders with inferred type class dictionaries
263+--
264+replaceTypeClassDictionaries :: ModuleName -> Value -> Check Value
265+replaceTypeClassDictionaries mn = everywhereM' (mkM go)
266+ where
267+ go (TypeClassDictionary trySuperclasses constraint dicts) = do
268+ env <- getEnv
269+ entails env mn dicts constraint trySuperclasses
270+ go other = return other
271+
272+-- |
273+-- A simplified representation of expressions which are used to represent type
274+-- class dictionaries at runtime, which can be compared for equality
275+--
276+data DictionaryValue
277+ -- |
278+ -- A dictionary which is brought into scope by a local constraint
279+ --
280+ = LocalDictionaryValue (Qualified Ident)
281+ -- |
282+ -- A dictionary which is brought into scope by an instance declaration
283+ --
284+ | GlobalDictionaryValue (Qualified Ident)
285+ -- |
286+ -- A dictionary which depends on other dictionaries
287+ --
288+ | DependentDictionaryValue (Qualified Ident) [DictionaryValue]
289+ -- |
290+ -- A subclass dictionary
291+ --
292+ | SubclassDictionaryValue DictionaryValue (Qualified ProperName) Integer
293+ deriving (Show, Ord, Eq)
294+
295+-- |
296+-- Check that the current set of type class dictionaries entail the specified type class goal, and, if so,
297+-- return a type class dictionary reference.
298+--
299+entails :: Environment -> ModuleName -> [TypeClassDictionaryInScope] -> (Qualified ProperName, [Type]) -> Bool -> Check Value
300+entails env moduleName context = solve (sortedNubBy canonicalizeDictionary (filter filterModule context))
301+ where
302+ sortedNubBy :: (Ord k) => (v -> k) -> [v] -> [v]
303+ sortedNubBy f vs = M.elems (M.fromList (map (f &&& id) vs))
304+
305+ -- Filter out type dictionaries which are in scope in the current module
306+ filterModule :: TypeClassDictionaryInScope -> Bool
307+ filterModule (TypeClassDictionaryInScope { tcdName = Qualified (Just mn) _ }) | mn == moduleName = True
308+ filterModule (TypeClassDictionaryInScope { tcdName = Qualified Nothing _ }) = True
309+ filterModule _ = False
310+
311+ solve context' (className, tys) trySuperclasses =
312+ let
313+ dicts = go trySuperclasses className tys
314+ in case sortedNubBy dictTrace (chooseSimplestDictionaries dicts) of
315+ [] -> throwError . strMsg $ "No instance found for " ++ show className ++ " " ++ unwords (map prettyPrintTypeAtom tys)
316+ [_] -> return $ dictionaryValueToValue $ head dicts
317+ _ -> throwError . strMsg $ "Overlapping instances found for " ++ show className ++ " " ++ unwords (map prettyPrintTypeAtom tys)
318+ where
319+ go trySuperclasses' className' tys' =
320+ -- Look for regular type instances
321+ [ mkDictionary (canonicalizeDictionary tcd) args
322+ | tcd <- context'
323+ -- Make sure the type class name matches the one we are trying to satisfy
324+ , className' == tcdClassName tcd
325+ -- Make sure the type unifies with the type in the type instance definition
326+ , subst <- maybeToList . (>>= verifySubstitution) . fmap concat $ zipWithM (typeHeadsAreEqual moduleName env) tys' (tcdInstanceTypes tcd)
327+ -- Solve any necessary subgoals
328+ , args <- solveSubgoals subst (tcdDependencies tcd) ] ++
329+
330+ -- Look for implementations via superclasses
331+ [ SubclassDictionaryValue suDict superclass index
332+ | trySuperclasses'
333+ , (subclassName, (args, _, implies)) <- M.toList (typeClasses env)
334+ -- Try each superclass
335+ , (index, (superclass, suTyArgs)) <- zip [0..] implies
336+ -- Make sure the type class name matches the superclass name
337+ , className' == superclass
338+ -- Make sure the types unify with the types in the superclass implication
339+ , subst <- maybeToList . (>>= verifySubstitution) . fmap concat $ zipWithM (typeHeadsAreEqual moduleName env) tys' suTyArgs
340+ -- Finally, satisfy the subclass constraint
341+ , args' <- maybeToList $ mapM (applySubst subst . TypeVar) args
342+ , suDict <- go True subclassName args' ]
343+
344+ -- Create dictionaries for subgoals which still need to be solved by calling go recursively
345+ -- E.g. the goal (Show a, Show b) => Show (Either a b) can be satisfied if the current type
346+ -- unifies with Either a b, and we can satisfy the subgoals Show a and Show b recursively.
347+ solveSubgoals :: [(String, Type)] -> Maybe [(Qualified ProperName, [Type])] -> [Maybe [DictionaryValue]]
348+ solveSubgoals _ Nothing = return Nothing
349+ solveSubgoals subst (Just subgoals) = do
350+ dict <- mapM (uncurry (go True) . second (map (replaceAllTypeVars subst))) subgoals
351+ return $ Just dict
352+ -- Make a dictionary from subgoal dictionaries by applying the correct function
353+ mkDictionary :: Qualified Ident -> Maybe [DictionaryValue] -> DictionaryValue
354+ mkDictionary fnName Nothing = LocalDictionaryValue fnName
355+ mkDictionary fnName (Just []) = GlobalDictionaryValue fnName
356+ mkDictionary fnName (Just dicts) = DependentDictionaryValue fnName dicts
357+ -- Turn a DictionaryValue into a Value
358+ dictionaryValueToValue :: DictionaryValue -> Value
359+ dictionaryValueToValue (LocalDictionaryValue fnName) = Var fnName
360+ dictionaryValueToValue (GlobalDictionaryValue fnName) = App (Var fnName) (ObjectLiteral [])
361+ dictionaryValueToValue (DependentDictionaryValue fnName dicts) = foldl App (Var fnName) (map dictionaryValueToValue dicts)
362+ dictionaryValueToValue (SubclassDictionaryValue dict superclassName index) =
363+ App (Accessor (show superclassName ++ "_" ++ show index)
364+ (Accessor C.__superclasses (dictionaryValueToValue dict)))
365+ (ObjectLiteral [])
366+ -- Ensure that a substitution is valid
367+ verifySubstitution :: [(String, Type)] -> Maybe [(String, Type)]
368+ verifySubstitution subst = do
369+ let grps = groupBy ((==) `on` fst) subst
370+ guard (all (pairwise (unifiesWith env) . map snd) grps)
371+ return $ map head grps
372+ -- Apply a substitution to a type
373+ applySubst :: [(String, Type)] -> Type -> Maybe Type
374+ applySubst subst = everywhereOnTypesM replace
375+ where
376+ replace (TypeVar v) = lookup v subst
377+ replace other = Just other
378+ -- Choose the simplest DictionaryValues from a list of candidates
379+ -- The reason for this function is as follows:
380+ -- When considering overlapping instances, we don't want to consider the same dictionary
381+ -- to be an overlap of itself when obtained as a superclass of another class.
382+ -- Observing that we probably don't want to select a superclass instance when an instance
383+ -- is available directly, and that there is no way for a superclass instance to actually
384+ -- introduce an overlap that wouldn't have been there already, we simply remove dictionaries
385+ -- obtained as superclass instances if there are simpler instances available.
386+ chooseSimplestDictionaries :: [DictionaryValue] -> [DictionaryValue]
387+ chooseSimplestDictionaries ds = case filter isSimpleDictionaryValue ds of
388+ [] -> ds
389+ simple -> simple
390+ isSimpleDictionaryValue SubclassDictionaryValue{} = False
391+ isSimpleDictionaryValue (DependentDictionaryValue _ ds) = all isSimpleDictionaryValue ds
392+ isSimpleDictionaryValue _ = True
393+ -- |
394+ -- Get the "trace" of a DictionaryValue - that is, remove all SubclassDictionaryValue
395+ -- data constructors
396+ --
397+ dictTrace :: DictionaryValue -> DictionaryValue
398+ dictTrace (DependentDictionaryValue fnName dicts) = DependentDictionaryValue fnName $ map dictTrace dicts
399+ dictTrace (SubclassDictionaryValue dict _ _) = dictTrace dict
400+ dictTrace other = other
401+
402+-- |
403+-- Check all values in a list pairwise match a predicate
404+--
405+pairwise :: (a -> a -> Bool) -> [a] -> Bool
406+pairwise _ [] = True
407+pairwise _ [_] = True
408+pairwise p (x : xs) = all (p x) xs && pairwise p xs
409+
410+-- |
411+-- Check that two types unify
412+--
413+unifiesWith :: Environment -> Type -> Type -> Bool
414+unifiesWith _ (TUnknown _) _ = True
415+unifiesWith _ _ (TUnknown _) = True
416+unifiesWith _ (Skolem _ s1 _) (Skolem _ s2 _) | s1 == s2 = True
417+unifiesWith _ (TypeVar v1) (TypeVar v2) | v1 == v2 = True
418+unifiesWith _ (TypeConstructor c1) (TypeConstructor c2) | c1 == c2 = True
419+unifiesWith e (TypeApp h1 t1) (TypeApp h2 t2) = unifiesWith e h1 h2 && unifiesWith e t1 t2
420+unifiesWith e (SaturatedTypeSynonym name args) t2 =
421+ case expandTypeSynonym' e name args of
422+ Left _ -> False
423+ Right t1 -> unifiesWith e t1 t2
424+unifiesWith e t1 t2@(SaturatedTypeSynonym _ _) = unifiesWith e t2 t1
425+unifiesWith _ _ _ = False
426+
427+-- |
428+-- Check whether the type heads of two types are equal (for the purposes of type class dictionary lookup),
429+-- and return a substitution from type variables to types which makes the type heads unify.
430+--
431+typeHeadsAreEqual :: ModuleName -> Environment -> Type -> Type -> Maybe [(String, Type)]
432+typeHeadsAreEqual _ _ (Skolem _ s1 _) (Skolem _ s2 _) | s1 == s2 = Just []
433+typeHeadsAreEqual _ _ t (TypeVar v) = Just [(v, t)]
434+typeHeadsAreEqual _ _ (TypeConstructor c1) (TypeConstructor c2) | c1 == c2 = Just []
435+typeHeadsAreEqual m e (TypeApp h1 t1) (TypeApp h2 t2) = (++) <$> typeHeadsAreEqual m e h1 h2 <*> typeHeadsAreEqual m e t1 t2
436+typeHeadsAreEqual m e (SaturatedTypeSynonym name args) t2 = case expandTypeSynonym' e name args of
437+ Left _ -> Nothing
438+ Right t1 -> typeHeadsAreEqual m e t1 t2
439+typeHeadsAreEqual _ _ _ _ = Nothing
440+
441+-- |
442+-- Ensure skolem variables do not escape their scope
443+--
444+skolemEscapeCheck :: Value -> Check ()
445+skolemEscapeCheck (TypedValue False _ _) = return ()
446+skolemEscapeCheck root@TypedValue{} =
447+ -- Every skolem variable is created when a ForAll type is skolemized.
448+ -- This determines the scope of that skolem variable, which is copied from the SkolemScope
449+ -- field of the ForAll constructor.
450+ -- We traverse the tree top-down, and collect any SkolemScopes introduced by ForAlls.
451+ -- If a Skolem is encountered whose SkolemScope is not in the current list, we have found
452+ -- an escaped skolem variable.
453+ case everythingWithContext [] (++) (mkQ ((,) []) go) root of
454+ [] -> return ()
455+ ((binding, val) : _) -> throwError $ mkErrorStack ("Rigid/skolem type variable " ++ maybe "" (("bound by " ++) . prettyPrintValue) binding ++ " has escaped.") (Just (ValueError val))
456+ where
457+ go :: Value -> [(SkolemScope, Value)] -> ([(Maybe Value, Value)], [(SkolemScope, Value)])
458+ go val@(TypedValue _ _ (ForAll _ _ (Just sco))) scos = ([], (sco, val) : scos)
459+ go val@(TypedValue _ _ ty) scos = case collectSkolems ty \\ map fst scos of
460+ (sco : _) -> ([(findBindingScope sco, val)], scos)
461+ _ -> ([], scos)
462+ where
463+ collectSkolems :: Type -> [SkolemScope]
464+ collectSkolems = nub . everythingOnTypes (++) collect
465+ where
466+ collect (Skolem _ _ scope) = [scope]
467+ collect _ = []
468+ go _ scos = ([], scos)
469+ findBindingScope :: SkolemScope -> Maybe Value
470+ findBindingScope sco = something (mkQ Nothing go') root
471+ where
472+ go' val@(TypedValue _ _ (ForAll _ _ (Just sco'))) | sco == sco' = Just val
473+ go' _ = Nothing
474+skolemEscapeCheck val = throwError $ mkErrorStack "Untyped value passed to skolemEscapeCheck" (Just (ValueError val))
475+
476+-- |
477+-- Ensure a row contains no duplicate labels
478+--
479+setify :: Type -> Type
480+setify = rowFromList . first (M.toList . M.fromList) . rowToList
481+
482+-- |
483+-- \"Setify\" all rows occuring inside a value
484+--
485+setifyAll :: Type -> Type
486+setifyAll = everywhereOnTypes setify
487+
488+-- |
489+-- Replace outermost unsolved unification variables with named type variables
490+--
491+varIfUnknown :: Type -> Type
492+varIfUnknown ty =
493+ let unks = nub $ unknowns ty
494+ toName = (:) 't' . show
495+ ty' = everywhereOnTypes typeToVar ty
496+ typeToVar :: Type -> Type
497+ typeToVar (TUnknown (Unknown u)) = TypeVar (toName u)
498+ typeToVar t = t
499+ in mkForAll (sort . map (toName . runUnknown) $ unks) ty'
500+
501+-- |
502+-- Remove any ForAlls and ConstrainedType constructors in a type by introducing new unknowns
503+-- or TypeClassDictionary values.
504+--
505+-- This is necessary during type checking to avoid unifying a polymorphic type with a
506+-- unification variable.
507+--
508+instantiatePolyTypeWithUnknowns :: Value -> Type -> UnifyT Type Check (Value, Type)
509+instantiatePolyTypeWithUnknowns val (ForAll ident ty _) = do
510+ ty' <- replaceVarWithUnknown ident ty
511+ instantiatePolyTypeWithUnknowns val ty'
512+instantiatePolyTypeWithUnknowns val (ConstrainedType constraints ty) = do
513+ dicts <- getTypeClassDictionaries
514+ (_, ty') <- instantiatePolyTypeWithUnknowns (error "Types under a constraint cannot themselves be constrained") ty
515+ return (foldl App val (map (flip (TypeClassDictionary True) dicts) constraints), ty')
516+instantiatePolyTypeWithUnknowns val ty = return (val, ty)
517+
518+-- |
519+-- Replace a single type variable with a new unification variable
520+--
521+replaceVarWithUnknown :: String -> Type -> UnifyT Type Check Type
522+replaceVarWithUnknown ident ty = do
523+ tu <- fresh
524+ return $ replaceTypeVars ident tu ty
525+
526+-- |
527+-- Replace fully applied type synonyms with the @SaturatedTypeSynonym@ data constructor, which helps generate
528+-- better error messages during unification.
529+--
530+replaceAllTypeSynonyms' :: Environment -> Type -> Either String Type
531+replaceAllTypeSynonyms' env d =
532+ let
533+ syns = map (\(name, (args, _)) -> (name, length args)) . M.toList $ typeSynonyms env
534+ in
535+ saturateAllTypeSynonyms syns d
536+
537+replaceAllTypeSynonyms :: (Error e, Functor m, Monad m, MonadState CheckState m, MonadError e m) => Type -> m Type
538+replaceAllTypeSynonyms d = do
539+ env <- getEnv
540+ either (throwError . strMsg) return $ replaceAllTypeSynonyms' env d
541+
542+-- |
543+-- \"Desaturate\" @SaturatedTypeSynonym@s
544+--
545+desaturateAllTypeSynonyms :: Type -> Type
546+desaturateAllTypeSynonyms = everywhereOnTypes replaceSaturatedTypeSynonym
547+ where
548+ replaceSaturatedTypeSynonym (SaturatedTypeSynonym name args) = foldl TypeApp (TypeConstructor name) args
549+ replaceSaturatedTypeSynonym t = t
550+
551+-- |
552+-- Replace a type synonym and its arguments with the aliased type
553+--
554+expandTypeSynonym' :: Environment -> Qualified ProperName -> [Type] -> Either String Type
555+expandTypeSynonym' env name args =
556+ case M.lookup name (typeSynonyms env) of
557+ Just (synArgs, body) -> do
558+ let repl = replaceAllTypeVars (zip synArgs args) body
559+ replaceAllTypeSynonyms' env repl
560+ Nothing -> error "Type synonym was not defined"
561+
562+expandTypeSynonym :: (Error e, Functor m, Monad m, MonadState CheckState m, MonadError e m) => Qualified ProperName -> [Type] -> m Type
563+expandTypeSynonym name args = do
564+ env <- getEnv
565+ either (throwError . strMsg) return $ expandTypeSynonym' env name args
566+
567+expandAllTypeSynonyms :: (Error e, Functor m, Applicative m, Monad m, MonadState CheckState m, MonadError e m) => Type -> m Type
568+expandAllTypeSynonyms = everywhereOnTypesTopDownM go
569+ where
570+ go (SaturatedTypeSynonym name args) = expandTypeSynonym name args
571+ go other = return other
572+
573+-- |
574+-- Ensure a set of property names and value does not contain duplicate labels
575+--
576+ensureNoDuplicateProperties :: (Error e, MonadError e m) => [(String, Value)] -> m ()
577+ensureNoDuplicateProperties ps = guardWith (strMsg "Duplicate property names") $ length (nub . map fst $ ps) == length ps
578+
579+-- |
580+-- Infer a type for a value, rethrowing any error to provide a more useful error message
581+--
582+infer :: Value -> UnifyT Type Check Value
583+infer val = rethrow (mkErrorStack "Error inferring type of value" (Just (ValueError val)) <>) $ infer' val
584+
585+-- |
586+-- Infer a type for a value
587+--
588+infer' :: Value -> UnifyT Type Check Value
589+infer' v@(NumericLiteral _) = return $ TypedValue True v tyNumber
590+infer' v@(StringLiteral _) = return $ TypedValue True v tyString
591+infer' v@(BooleanLiteral _) = return $ TypedValue True v tyBoolean
592+infer' (ArrayLiteral vals) = do
593+ ts <- mapM infer vals
594+ els <- fresh
595+ forM_ ts $ \(TypedValue _ _ t) -> els =?= TypeApp tyArray t
596+ return $ TypedValue True (ArrayLiteral ts) els
597+infer' (ObjectLiteral ps) = do
598+ ensureNoDuplicateProperties ps
599+ ts <- mapM (infer . snd) ps
600+ let fields = zipWith (\name (TypedValue _ _ t) -> (name, t)) (map fst ps) ts
601+ ty = TypeApp tyObject $ rowFromList (fields, REmpty)
602+ return $ TypedValue True (ObjectLiteral (zip (map fst ps) ts)) ty
603+infer' (ObjectUpdate o ps) = do
604+ ensureNoDuplicateProperties ps
605+ row <- fresh
606+ newVals <- zipWith (\(name, _) t -> (name, t)) ps <$> mapM (infer . snd) ps
607+ let newTys = map (\(name, TypedValue _ _ ty) -> (name, ty)) newVals
608+ oldTys <- zip (map fst ps) <$> replicateM (length ps) fresh
609+ let oldTy = TypeApp tyObject $ rowFromList (oldTys, row)
610+ o' <- TypedValue True <$> check o oldTy <*> pure oldTy
611+ return $ TypedValue True (ObjectUpdate o' newVals) $ TypeApp tyObject $ rowFromList (newTys, row)
612+infer' (Accessor prop val) = do
613+ typed@(TypedValue _ _ objTy) <- infer val
614+ propTy <- inferProperty objTy prop
615+ case propTy of
616+ Nothing -> do
617+ field <- fresh
618+ rest <- fresh
619+ _ <- subsumes Nothing objTy (TypeApp tyObject (RCons prop field rest))
620+ return $ TypedValue True (Accessor prop typed) field
621+ Just ty -> return $ TypedValue True (Accessor prop typed) ty
622+infer' (Abs (Left arg) ret) = do
623+ ty <- fresh
624+ Just moduleName <- checkCurrentModule <$> get
625+ bindLocalVariables moduleName [(arg, ty)] $ do
626+ body@(TypedValue _ _ bodyTy) <- infer' ret
627+ return $ TypedValue True (Abs (Left arg) body) $ function ty bodyTy
628+infer' (Abs (Right _) _) = error "Binder was not desugared"
629+infer' (App f arg) = do
630+ f'@(TypedValue _ _ ft) <- infer f
631+ (ret, app) <- checkFunctionApplication f' ft arg Nothing
632+ return $ TypedValue True app ret
633+infer' (Var var) = do
634+ Just moduleName <- checkCurrentModule <$> get
635+ ty <- introduceSkolemScope <=< replaceAllTypeSynonyms <=< lookupVariable moduleName $ var
636+ case ty of
637+ ConstrainedType constraints ty' -> do
638+ dicts <- getTypeClassDictionaries
639+ return $ TypedValue True (foldl App (Var var) (map (flip (TypeClassDictionary True) dicts) constraints)) ty'
640+ _ -> return $ TypedValue True (Var var) ty
641+infer' v@(Constructor c) = do
642+ env <- getEnv
643+ case M.lookup c (dataConstructors env) of
644+ Nothing -> throwError . strMsg $ "Constructor " ++ show c ++ " is undefined"
645+ Just (_, ty) -> do ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
646+ return $ TypedValue True v ty'
647+infer' (Case vals binders) = do
648+ ts <- mapM infer vals
649+ ret <- fresh
650+ binders' <- checkBinders (map (\(TypedValue _ _ t) -> t) ts) ret binders
651+ return $ TypedValue True (Case ts binders') ret
652+infer' (IfThenElse cond th el) = do
653+ cond' <- check cond tyBoolean
654+ v2@(TypedValue _ _ t2) <- infer th
655+ v3@(TypedValue _ _ t3) <- infer el
656+ t2 =?= t3
657+ return $ TypedValue True (IfThenElse cond' v2 v3) t2
658+infer' (Let ds val) = do
659+ (ds', val'@(TypedValue _ _ valTy)) <- inferLetBinding [] ds val infer
660+ return $ TypedValue True (Let ds' val') valTy
661+infer' (SuperClassDictionary className tys) = do
662+ dicts <- getTypeClassDictionaries
663+ return $ TypeClassDictionary False (className, tys) dicts
664+infer' (TypedValue checkType val ty) = do
665+ Just moduleName <- checkCurrentModule <$> get
666+ kind <- liftCheck $ kindOf moduleName ty
667+ guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
668+ ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
669+ val' <- if checkType then check val ty' else return val
670+ return $ TypedValue True val' ty'
671+infer' (PositionedValue pos val) = rethrowWithPosition pos $ infer' val
672+infer' _ = error "Invalid argument to infer"
673+
674+inferLetBinding :: [Declaration] -> [Declaration] -> Value -> (Value -> UnifyT Type Check Value) -> UnifyT Type Check ([Declaration], Value)
675+inferLetBinding seen [] ret j = (,) seen <$> j ret
676+inferLetBinding seen (ValueDeclaration ident nameKind [] Nothing tv@(TypedValue checkType val ty) : rest) ret j = do
677+ Just moduleName <- checkCurrentModule <$> get
678+ kind <- liftCheck $ kindOf moduleName ty
679+ guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
680+ let dict = if isFunction val then M.singleton (moduleName, ident) (ty, nameKind) else M.empty
681+ TypedValue _ val' ty' <- if checkType then bindNames dict (check val ty) else return tv
682+ bindNames (M.singleton (moduleName, ident) (ty', nameKind)) $ inferLetBinding (seen ++ [ValueDeclaration ident nameKind [] Nothing (TypedValue checkType val' ty')]) rest ret j
683+inferLetBinding seen (ValueDeclaration ident nameKind [] Nothing val : rest) ret j = do
684+ valTy <- fresh
685+ Just moduleName <- checkCurrentModule <$> get
686+ let dict = if isFunction val then M.singleton (moduleName, ident) (valTy, nameKind) else M.empty
687+ TypedValue _ val' valTy' <- bindNames dict $ infer val
688+ valTy =?= valTy'
689+ bindNames (M.singleton (moduleName, ident) (valTy', nameKind)) $ inferLetBinding (seen ++ [ValueDeclaration ident nameKind [] Nothing val']) rest ret j
690+inferLetBinding seen (BindingGroupDeclaration ds : rest) ret j = do
691+ Just moduleName <- checkCurrentModule <$> get
692+ (es, dict, untypedDict) <- typeDictionaryForBindingGroup moduleName (map (\(i, _, v) -> (i, v)) ds)
693+ ds' <- forM es $ \e -> do
694+ (ident, (val', _)) <- typeForBindingGroupElement moduleName e dict untypedDict
695+ return $ (ident, LocalVariable, val')
696+ bindNames dict $ inferLetBinding (seen ++ [BindingGroupDeclaration ds']) rest ret j
697+inferLetBinding seen (PositionedDeclaration pos d : ds) ret j = rethrowWithPosition pos $ do
698+ ((d' : ds'), val') <- inferLetBinding seen (d : ds) ret j
699+ return (PositionedDeclaration pos d' : ds', val')
700+inferLetBinding _ _ _ _ = error "Invalid argument to inferLetBinding"
701+
702+-- |
703+-- Infer the type of a property inside a record with a given type
704+--
705+inferProperty :: Type -> String -> UnifyT Type Check (Maybe Type)
706+inferProperty (TypeApp obj row) prop | obj == tyObject = do
707+ let (props, _) = rowToList row
708+ return $ lookup prop props
709+inferProperty (SaturatedTypeSynonym name args) prop = do
710+ replaced <- introduceSkolemScope <=< expandTypeSynonym name $ args
711+ inferProperty replaced prop
712+inferProperty (ForAll ident ty _) prop = do
713+ replaced <- replaceVarWithUnknown ident ty
714+ inferProperty replaced prop
715+inferProperty _ _ = return Nothing
716+
717+-- |
718+-- Infer the types of variables brought into scope by a binder
719+--
720+inferBinder :: Type -> Binder -> UnifyT Type Check (M.Map Ident Type)
721+inferBinder _ NullBinder = return M.empty
722+inferBinder val (StringBinder _) = val =?= tyString >> return M.empty
723+inferBinder val (NumberBinder _) = val =?= tyNumber >> return M.empty
724+inferBinder val (BooleanBinder _) = val =?= tyBoolean >> return M.empty
725+inferBinder val (VarBinder name) = return $ M.singleton name val
726+inferBinder val (ConstructorBinder ctor binders) = do
727+ env <- getEnv
728+ case M.lookup ctor (dataConstructors env) of
729+ Just (_, ty) -> do
730+ (_, fn) <- instantiatePolyTypeWithUnknowns (error "Data constructor types cannot contain constraints") ty
731+ fn' <- replaceAllTypeSynonyms fn
732+ go binders fn'
733+ where
734+ go [] ty' = do
735+ _ <- subsumes Nothing val ty'
736+ return M.empty
737+ go (binder : binders') (TypeApp (TypeApp t obj) ret) | t == tyFunction =
738+ M.union <$> inferBinder obj binder <*> go binders' ret
739+ go _ _ = throwError . strMsg $ "Wrong number of arguments to constructor " ++ show ctor
740+ _ -> throwError . strMsg $ "Constructor " ++ show ctor ++ " is not defined"
741+inferBinder val (ObjectBinder props) = do
742+ row <- fresh
743+ rest <- fresh
744+ m1 <- inferRowProperties row rest props
745+ val =?= TypeApp tyObject row
746+ return m1
747+ where
748+ inferRowProperties :: Type -> Type -> [(String, Binder)] -> UnifyT Type Check (M.Map Ident Type)
749+ inferRowProperties nrow row [] = nrow =?= row >> return M.empty
750+ inferRowProperties nrow row ((name, binder):binders) = do
751+ propTy <- fresh
752+ m1 <- inferBinder propTy binder
753+ m2 <- inferRowProperties nrow (RCons name propTy row) binders
754+ return $ m1 `M.union` m2
755+inferBinder val (ArrayBinder binders) = do
756+ el <- fresh
757+ m1 <- M.unions <$> mapM (inferBinder el) binders
758+ val =?= TypeApp tyArray el
759+ return m1
760+inferBinder val (ConsBinder headBinder tailBinder) = do
761+ el <- fresh
762+ m1 <- inferBinder el headBinder
763+ m2 <- inferBinder val tailBinder
764+ val =?= TypeApp tyArray el
765+ return $ m1 `M.union` m2
766+inferBinder val (NamedBinder name binder) = do
767+ m <- inferBinder val binder
768+ return $ M.insert name val m
769+inferBinder val (PositionedBinder pos binder) =
770+ rethrowWithPosition pos $ inferBinder val binder
771+
772+-- |
773+-- Check the types of the return values in a set of binders in a case statement
774+--
775+checkBinders :: [Type] -> Type -> [CaseAlternative] -> UnifyT Type Check [CaseAlternative]
776+checkBinders _ _ [] = return []
777+checkBinders nvals ret (CaseAlternative binders grd val : bs) = do
778+ Just moduleName <- checkCurrentModule <$> get
779+ m1 <- M.unions <$> zipWithM inferBinder nvals binders
780+ r <- bindLocalVariables moduleName (M.toList m1) $ do
781+ val' <- TypedValue True <$> check val ret <*> pure ret
782+ case grd of
783+ Nothing -> return $ CaseAlternative binders Nothing val'
784+ Just g -> do
785+ g' <- check g tyBoolean
786+ return $ CaseAlternative binders (Just g') val'
787+ rs <- checkBinders nvals ret bs
788+ return $ r : rs
789+
790+-- |
791+-- Generate a new skolem constant
792+--
793+newSkolemConstant :: UnifyT Type Check Int
794+newSkolemConstant = runUnknown <$> fresh'
795+
796+-- |
797+-- Generate a new skolem scope
798+--
799+newSkolemScope :: UnifyT Type Check SkolemScope
800+newSkolemScope = SkolemScope . runUnknown <$> fresh'
801+
802+-- |
803+-- Skolemize a type variable by replacing its instances with fresh skolem constants
804+--
805+skolemize :: String -> Int -> SkolemScope -> Type -> Type
806+skolemize ident sko scope = replaceTypeVars ident (Skolem ident sko scope)
807+
808+-- |
809+-- This function has one purpose - to skolemize type variables appearing in a
810+-- SuperClassDictionary placeholder. These type variables are somewhat unique since they are the
811+-- only example of scoped type variables.
812+--
813+skolemizeTypesInValue :: String -> Int -> SkolemScope -> Value -> Value
814+skolemizeTypesInValue ident sko scope = everywhere (mkT go)
815+ where
816+ go (SuperClassDictionary c ts) = SuperClassDictionary c (map (skolemize ident sko scope) ts)
817+ go other = other
818+
819+-- |
820+-- Introduce skolem scope at every occurence of a ForAll
821+--
822+introduceSkolemScope :: Type -> UnifyT Type Check Type
823+introduceSkolemScope = everywhereOnTypesM go
824+ where
825+ go (ForAll ident ty Nothing) = ForAll ident ty <$> (Just <$> newSkolemScope)
826+ go other = return other
827+
828+-- |
829+-- Check the type of a value, rethrowing errors to provide a better error message
830+--
831+check :: Value -> Type -> UnifyT Type Check Value
832+check val ty = rethrow (mkErrorStack errorMessage (Just (ValueError val)) <>) $ check' val ty
833+ where
834+ errorMessage =
835+ "Error checking type of term " ++
836+ prettyPrintValue val ++
837+ " against type " ++
838+ prettyPrintType ty
839+
840+-- |
841+-- Check the type of a value
842+--
843+check' :: Value -> Type -> UnifyT Type Check Value
844+check' val (ForAll ident ty _) = do
845+ scope <- newSkolemScope
846+ sko <- newSkolemConstant
847+ let sk = skolemize ident sko scope ty
848+ let skVal = skolemizeTypesInValue ident sko scope val
849+ val' <- check skVal sk
850+ return $ TypedValue True val' (ForAll ident ty (Just scope))
851+check' val t@(ConstrainedType constraints ty) = do
852+ dictNames <- forM constraints $ \(Qualified _ (ProperName className), _) -> do
853+ n <- liftCheck freshDictionaryName
854+ return $ Ident $ "__dict_" ++ className ++ "_" ++ show n
855+ val' <- withTypeClassDictionaries (zipWith (\name (className, instanceTy) ->
856+ TypeClassDictionaryInScope name className instanceTy Nothing TCDRegular) (map (Qualified Nothing) dictNames)
857+ constraints) $ check val ty
858+ return $ TypedValue True (foldr (Abs . Left) val' dictNames) t
859+check' val (SaturatedTypeSynonym name args) = do
860+ ty <- introduceSkolemScope <=< expandTypeSynonym name $ args
861+ check val ty
862+check' val u@(TUnknown _) = do
863+ val'@(TypedValue _ _ ty) <- infer val
864+ -- Don't unify an unknown with an inferred polytype
865+ (val'', ty') <- instantiatePolyTypeWithUnknowns val' ty
866+ ty' =?= u
867+ return $ TypedValue True val'' ty'
868+check' v@(NumericLiteral _) t | t == tyNumber =
869+ return $ TypedValue True v t
870+check' v@(StringLiteral _) t | t == tyString =
871+ return $ TypedValue True v t
872+check' v@(BooleanLiteral _) t | t == tyBoolean =
873+ return $ TypedValue True v t
874+check' (ArrayLiteral vals) t@(TypeApp a ty) = do
875+ a =?= tyArray
876+ array <- ArrayLiteral <$> forM vals (`check` ty)
877+ return $ TypedValue True array t
878+check' (Abs (Left arg) ret) ty@(TypeApp (TypeApp t argTy) retTy) | t == tyFunction = do
879+ Just moduleName <- checkCurrentModule <$> get
880+ ret' <- bindLocalVariables moduleName [(arg, argTy)] $ check ret retTy
881+ return $ TypedValue True (Abs (Left arg) ret') ty
882+check' (Abs (Right _) _) _ = error "Binder was not desugared"
883+check' (App f arg) ret = do
884+ f'@(TypedValue _ _ ft) <- infer f
885+ (_, app) <- checkFunctionApplication f' ft arg (Just ret)
886+ return $ TypedValue True app ret
887+check' v@(Var var) ty = do
888+ Just moduleName <- checkCurrentModule <$> get
889+ repl <- introduceSkolemScope <=< replaceAllTypeSynonyms <=< lookupVariable moduleName $ var
890+ ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
891+ v' <- subsumes (Just v) repl ty'
892+ case v' of
893+ Nothing -> throwError . strMsg $ "Unable to check type subsumption"
894+ Just v'' -> return $ TypedValue True v'' ty'
895+check' (SuperClassDictionary className tys) _ = do
896+ {-
897+ -- Here, we replace a placeholder for a superclass dictionary with a regular
898+ -- TypeClassDictionary placeholder. The reason we do this is that it is necessary to have the
899+ -- correct super instance dictionaries in scope, and these are not available when the type class
900+ -- declaration gets desugared.
901+ --
902+ -- Note also that the first argument to TypeClassDictionary is False, meaning we _do not_ want
903+ -- to consider superclass instances when searching for this dictionary - doing so might lead
904+ -- to traversing a cycle in the instance graph.
905+ -}
906+ dicts <- getTypeClassDictionaries
907+ return $ TypeClassDictionary False (className, tys) dicts
908+check' (TypedValue checkType val ty1) ty2 = do
909+ Just moduleName <- checkCurrentModule <$> get
910+ kind <- liftCheck $ kindOf moduleName ty1
911+ guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
912+ ty1' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty1
913+ val' <- subsumes (Just val) ty1' ty2
914+ case val' of
915+ Nothing -> throwError . strMsg $ "Unable to check type subsumption"
916+ Just val'' -> do
917+ val''' <- if checkType then check val'' ty1' else return val''
918+ return $ TypedValue checkType (TypedValue True val''' ty1) ty2
919+check' (Case vals binders) ret = do
920+ vals' <- mapM infer vals
921+ let ts = map (\(TypedValue _ _ t) -> t) vals'
922+ binders' <- checkBinders ts ret binders
923+ return $ TypedValue True (Case vals' binders') ret
924+check' (IfThenElse cond th el) ty = do
925+ cond' <- check cond tyBoolean
926+ th' <- check th ty
927+ el' <- check el ty
928+ return $ TypedValue True (IfThenElse cond' th' el') ty
929+check' (ObjectLiteral ps) t@(TypeApp obj row) | obj == tyObject = do
930+ ensureNoDuplicateProperties ps
931+ ps' <- checkProperties ps row False
932+ return $ TypedValue True (ObjectLiteral ps') t
933+check' (ObjectUpdate obj ps) t@(TypeApp o row) | o == tyObject = do
934+ ensureNoDuplicateProperties ps
935+ us <- zip (map fst ps) <$> replicateM (length ps) fresh
936+ let (propsToCheck, rest) = rowToList row
937+ propsToRemove = map fst ps
938+ remainingProps = filter (\(p, _) -> p `notElem` propsToRemove) propsToCheck
939+ obj' <- check obj (TypeApp tyObject (rowFromList (us ++ remainingProps, rest)))
940+ ps' <- checkProperties ps row True
941+ return $ TypedValue True (ObjectUpdate obj' ps') t
942+check' (Accessor prop val) ty = do
943+ rest <- fresh
944+ val' <- check val (TypeApp tyObject (RCons prop ty rest))
945+ return $ TypedValue True (Accessor prop val') ty
946+check' (Constructor c) ty = do
947+ env <- getEnv
948+ case M.lookup c (dataConstructors env) of
949+ Nothing -> throwError . strMsg $ "Constructor " ++ show c ++ " is undefined"
950+ Just (_, ty1) -> do
951+ repl <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty1
952+ _ <- subsumes Nothing repl ty
953+ return $ TypedValue True (Constructor c) ty
954+check' (Let ds val) ty = do
955+ (ds', val') <- inferLetBinding [] ds val (flip check ty)
956+ return $ TypedValue True (Let ds' val') ty
957+check' val ty | containsTypeSynonyms ty = do
958+ ty' <- introduceSkolemScope <=< expandAllTypeSynonyms $ ty
959+ check val ty'
960+check' (PositionedValue pos val) ty =
961+ rethrowWithPosition pos $ check val ty
962+check' val ty = throwError $ mkErrorStack ("Value does not have type " ++ prettyPrintType ty) (Just (ValueError val))
963+
964+containsTypeSynonyms :: Type -> Bool
965+containsTypeSynonyms = everythingOnTypes (||) go where
966+ go (SaturatedTypeSynonym _ _) = True
967+ go _ = False
968+
969+-- |
970+-- Check the type of a collection of named record fields
971+--
972+-- The @lax@ parameter controls whether or not every record member has to be provided. For object updates, this is not the case.
973+--
974+checkProperties :: [(String, Value)] -> Type -> Bool -> UnifyT Type Check [(String, Value)]
975+checkProperties ps row lax = let (ts, r') = rowToList row in go ps ts r' where
976+ go [] [] REmpty = return []
977+ go [] [] u@(TUnknown _) = do u =?= REmpty
978+ return []
979+ go [] [] (Skolem _ _ _) | lax = return []
980+ go [] ((p, _): _) _ | lax = return []
981+ | otherwise = throwError $ mkErrorStack ("Object does not have property " ++ p) (Just (ValueError (ObjectLiteral ps)))
982+ go ((p,_):_) [] REmpty = throwError $ mkErrorStack ("Property " ++ p ++ " is not present in closed object type " ++ prettyPrintRow row) (Just (ValueError (ObjectLiteral ps)))
983+ go ((p,v):ps') [] u@(TUnknown _) = do
984+ v'@(TypedValue _ _ ty) <- infer v
985+ rest <- fresh
986+ u =?= RCons p ty rest
987+ ps'' <- go ps' [] rest
988+ return $ (p, v') : ps''
989+ go ((p,v):ps') ts r =
990+ case lookup p ts of
991+ Nothing -> do
992+ v'@(TypedValue _ _ ty) <- infer v
993+ rest <- fresh
994+ r =?= RCons p ty rest
995+ ps'' <- go ps' ts rest
996+ return $ (p, v') : ps''
997+ Just ty -> do
998+ v' <- check v ty
999+ ps'' <- go ps' (delete (p, ty) ts) r
1000+ return $ (p, v') : ps''
1001+ go _ _ _ = throwError $ mkErrorStack ("Object does not have type " ++ prettyPrintType (TypeApp tyObject row)) (Just (ValueError (ObjectLiteral ps)))
1002+
1003+-- |
1004+-- Check the type of a function application, rethrowing errors to provide a better error message
1005+--
1006+checkFunctionApplication :: Value -> Type -> Value -> Maybe Type -> UnifyT Type Check (Type, Value)
1007+checkFunctionApplication fn fnTy arg ret = rethrow (mkErrorStack errorMessage (Just (ValueError fn)) <>) $ checkFunctionApplication' fn fnTy arg ret
1008+ where
1009+ errorMessage = "Error applying function of type "
1010+ ++ prettyPrintType fnTy
1011+ ++ " to argument " ++ prettyPrintValue arg
1012+
1013+-- |
1014+-- Check the type of a function application
1015+--
1016+checkFunctionApplication' :: Value -> Type -> Value -> Maybe Type -> UnifyT Type Check (Type, Value)
1017+checkFunctionApplication' fn (TypeApp (TypeApp tyFunction' argTy) retTy) arg ret = do
1018+ tyFunction' =?= tyFunction
1019+ _ <- maybe (return Nothing) (subsumes Nothing retTy) ret
1020+ subst <- unifyCurrentSubstitution <$> UnifyT get
1021+ arg' <- check arg (subst $? argTy)
1022+ return (retTy, App fn arg')
1023+checkFunctionApplication' fn (ForAll ident ty _) arg ret = do
1024+ replaced <- replaceVarWithUnknown ident ty
1025+ checkFunctionApplication fn replaced arg ret
1026+checkFunctionApplication' fn u@(TUnknown _) arg ret = do
1027+ arg' <- do
1028+ TypedValue _ arg' t <- infer arg
1029+ (arg'', t') <- instantiatePolyTypeWithUnknowns arg' t
1030+ return $ TypedValue True arg'' t'
1031+ let ty = (\(TypedValue _ _ t) -> t) arg'
1032+ ret' <- maybe fresh return ret
1033+ u =?= function ty ret'
1034+ return (ret', App fn arg')
1035+checkFunctionApplication' fn (SaturatedTypeSynonym name tyArgs) arg ret = do
1036+ ty <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
1037+ checkFunctionApplication fn ty arg ret
1038+checkFunctionApplication' fn (ConstrainedType constraints fnTy) arg ret = do
1039+ dicts <- getTypeClassDictionaries
1040+ checkFunctionApplication' (foldl App fn (map (flip (TypeClassDictionary True) dicts) constraints)) fnTy arg ret
1041+checkFunctionApplication' _ fnTy arg _ = throwError . strMsg $ "Cannot apply a function of type "
1042+ ++ prettyPrintType fnTy
1043+ ++ " to argument " ++ prettyPrintValue arg
1044+
1045+-- |
1046+-- Check whether one type subsumes another, rethrowing errors to provide a better error message
1047+--
1048+subsumes :: Maybe Value -> Type -> Type -> UnifyT Type Check (Maybe Value)
1049+subsumes val ty1 ty2 = rethrow (mkErrorStack errorMessage (ValueError <$> val) <>) $ subsumes' val ty1 ty2
1050+ where
1051+ errorMessage = "Error checking that type "
1052+ ++ prettyPrintType ty1
1053+ ++ " subsumes type "
1054+ ++ prettyPrintType ty2
1055+
1056+-- |
1057+-- Check whether one type subsumes another
1058+--
1059+subsumes' :: Maybe Value -> Type -> Type -> UnifyT Type Check (Maybe Value)
1060+subsumes' val (ForAll ident ty1 _) ty2 = do
1061+ replaced <- replaceVarWithUnknown ident ty1
1062+ subsumes val replaced ty2
1063+subsumes' val ty1 (ForAll ident ty2 sco) =
1064+ case sco of
1065+ Just sco' -> do
1066+ sko <- newSkolemConstant
1067+ let sk = skolemize ident sko sco' ty2
1068+ subsumes val ty1 sk
1069+ Nothing -> throwError . strMsg $ "Skolem variable scope is unspecified"
1070+subsumes' val (TypeApp (TypeApp f1 arg1) ret1) (TypeApp (TypeApp f2 arg2) ret2) | f1 == tyFunction && f2 == tyFunction = do
1071+ _ <- subsumes Nothing arg2 arg1
1072+ _ <- subsumes Nothing ret1 ret2
1073+ return val
1074+subsumes' val (SaturatedTypeSynonym name tyArgs) ty2 = do
1075+ ty1 <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
1076+ subsumes val ty1 ty2
1077+subsumes' val ty1 (SaturatedTypeSynonym name tyArgs) = do
1078+ ty2 <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
1079+ subsumes val ty1 ty2
1080+subsumes' (Just val) (ConstrainedType constraints ty1) ty2 = do
1081+ dicts <- getTypeClassDictionaries
1082+ _ <- subsumes' Nothing ty1 ty2
1083+ return . Just $ foldl App val (map (flip (TypeClassDictionary True) dicts) constraints)
1084+subsumes' val (TypeApp f1 r1) (TypeApp f2 r2) | f1 == tyObject && f2 == tyObject = do
1085+ let
1086+ (ts1, r1') = rowToList r1
1087+ (ts2, r2') = rowToList r2
1088+ ts1' = sortBy (comparing fst) ts1
1089+ ts2' = sortBy (comparing fst) ts2
1090+ go ts1' ts2' r1' r2'
1091+ return val
1092+ where
1093+ go [] ts2 r1' r2' = r1' =?= rowFromList (ts2, r2')
1094+ go ts1 [] r1' r2' = r2' =?= rowFromList (ts1, r1')
1095+ go ((p1, ty1) : ts1) ((p2, ty2) : ts2) r1' r2'
1096+ | p1 == p2 = do _ <- subsumes Nothing ty1 ty2
1097+ go ts1 ts2 r1' r2'
1098+ | p1 < p2 = do rest <- fresh
1099+ r2' =?= RCons p1 ty1 rest
1100+ go ts1 ((p2, ty2) : ts2) r1' rest
1101+ | otherwise = do rest <- fresh
1102+ r1' =?= RCons p2 ty2 rest
1103+ go ((p1, ty1) : ts1) ts2 rest r2'
1104+subsumes' val ty1 ty2@(TypeApp obj _) | obj == tyObject = subsumes val ty2 ty1
1105+subsumes' val ty1 ty2 = do
1106+ ty1 =?= ty2
1107+ return val
1108+
1109+
1110+
1111+