@@ -0,0 +1,1121 @@
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.Function (on)
47+import Data.Ord (comparing)
48+import Data.Monoid
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 qualified Data.HashMap.Strict as H
72+
73+instance Partial Type where
74+ unknown = TUnknown
75+ isUnknown (TUnknown u) = Just u
76+ isUnknown _ = Nothing
77+ unknowns = everythingOnTypes (++) go
78+ where
79+ go (TUnknown u) = [u]
80+ go _ = []
81+ ($?) sub = everywhereOnTypes go
82+ where
83+ go t@(TUnknown u) = case H.lookup u (runSubstitution sub) of
84+ Nothing -> t
85+ Just t' -> t'
86+ go other = other
87+
88+instance Unifiable Check Type where
89+ (=?=) = unifyTypes
90+
91+-- |
92+-- Unify two types, updating the current substitution
93+--
94+unifyTypes :: Type -> Type -> UnifyT Type Check ()
95+unifyTypes t1 t2 = rethrow (mkErrorStack ("Error unifying type " ++ prettyPrintType t1 ++ " with type " ++ prettyPrintType t2) Nothing <>) $
96+ unifyTypes' t1 t2
97+ where
98+ unifyTypes' (TUnknown u1) (TUnknown u2) | u1 == u2 = return ()
99+ unifyTypes' (TUnknown u) t = u =:= t
100+ unifyTypes' t (TUnknown u) = u =:= t
101+ unifyTypes' (SaturatedTypeSynonym name args) ty = do
102+ ty1 <- introduceSkolemScope <=< expandTypeSynonym name $ args
103+ ty1 `unifyTypes` ty
104+ unifyTypes' ty s@(SaturatedTypeSynonym _ _) = s `unifyTypes` ty
105+ unifyTypes' (ForAll ident1 ty1 sc1) (ForAll ident2 ty2 sc2) =
106+ case (sc1, sc2) of
107+ (Just sc1', Just sc2') -> do
108+ sko <- newSkolemConstant
109+ let sk1 = skolemize ident1 sko sc1' ty1
110+ let sk2 = skolemize ident2 sko sc2' ty2
111+ sk1 `unifyTypes` sk2
112+ _ -> error "Skolemized type variable was not given a scope"
113+ unifyTypes' (ForAll ident ty1 (Just sc)) ty2 = do
114+ sko <- newSkolemConstant
115+ let sk = skolemize ident sko sc ty1
116+ sk `unifyTypes` ty2
117+ unifyTypes' ForAll{} _ = throwError . strMsg $ "Skolem variable scope is unspecified"
118+ unifyTypes' ty f@ForAll{} = f `unifyTypes` ty
119+ unifyTypes' (TypeVar v1) (TypeVar v2) | v1 == v2 = return ()
120+ unifyTypes' (TypeConstructor c1) (TypeConstructor c2) =
121+ guardWith (strMsg ("Cannot unify " ++ show c1 ++ " with " ++ show c2 ++ ".")) (c1 == c2)
122+ unifyTypes' (TypeApp t3 t4) (TypeApp t5 t6) = do
123+ t3 `unifyTypes` t5
124+ t4 `unifyTypes` t6
125+ unifyTypes' (Skolem _ s1 _) (Skolem _ s2 _) | s1 == s2 = return ()
126+ unifyTypes' r1@RCons{} r2 = unifyRows r1 r2
127+ unifyTypes' r1 r2@RCons{} = unifyRows r1 r2
128+ unifyTypes' r1@REmpty r2 = unifyRows r1 r2
129+ unifyTypes' r1 r2@REmpty = unifyRows r1 r2
130+ unifyTypes' t@(ConstrainedType _ _) _ = throwError . strMsg $ "Attempted to unify a constrained type " ++ prettyPrintType t ++ " with another type."
131+ unifyTypes' t3 t4@(ConstrainedType _ _) = unifyTypes' t4 t3
132+ unifyTypes' t3 t4 = throwError . strMsg $ "Cannot unify " ++ prettyPrintType t3 ++ " with " ++ prettyPrintType t4 ++ "."
133+
134+-- |
135+-- Unify two rows, updating the current substitution
136+--
137+-- Common labels are first identified, and unified. Remaining labels and types are unified with a
138+-- trailing row unification variable, if appropriate, otherwise leftover labels result in a unification
139+-- error.
140+--
141+unifyRows :: Type -> Type -> UnifyT Type Check ()
142+unifyRows r1 r2 =
143+ let
144+ (s1, r1') = rowToList r1
145+ (s2, r2') = rowToList r2
146+ int = [ (t1, t2) | (name, t1) <- s1, (name', t2) <- s2, name == name' ]
147+ sd1 = [ (name, t1) | (name, t1) <- s1, name `notElem` map fst s2 ]
148+ sd2 = [ (name, t2) | (name, t2) <- s2, name `notElem` map fst s1 ]
149+ in do
150+ forM_ int (uncurry (=?=))
151+ unifyRows' sd1 r1' sd2 r2'
152+ where
153+ unifyRows' :: [(String, Type)] -> Type -> [(String, Type)] -> Type -> UnifyT Type Check ()
154+ unifyRows' [] (TUnknown u) sd r = u =:= rowFromList (sd, r)
155+ unifyRows' sd r [] (TUnknown u) = u =:= rowFromList (sd, r)
156+ unifyRows' ((name, ty):row) r others u@(TUnknown un) = do
157+ occursCheck un ty
158+ forM_ row $ \(_, t) -> occursCheck un t
159+ u' <- fresh
160+ u =?= RCons name ty u'
161+ unifyRows' row r others u'
162+ unifyRows' [] REmpty [] REmpty = return ()
163+ unifyRows' [] (TypeVar v1) [] (TypeVar v2) | v1 == v2 = return ()
164+ unifyRows' [] (Skolem _ s1 _) [] (Skolem _ s2 _) | s1 == s2 = return ()
165+ unifyRows' sd3 r3 sd4 r4 = throwError . strMsg $ "Cannot unify (" ++ prettyPrintRow (rowFromList (sd3, r3)) ++ ") with (" ++ prettyPrintRow (rowFromList (sd4, r4)) ++ ")"
166+
167+-- |
168+-- Infer the types of multiple mutually-recursive values, and return elaborated values including
169+-- type class dictionaries and type annotations.
170+--
171+typesOf :: Maybe ModuleName -> ModuleName -> [(Ident, Value)] -> Check [(Ident, (Value, Type))]
172+typesOf mainModuleName moduleName vals = do
173+ tys <- fmap tidyUp . liftUnify $ do
174+ (es, dict, untypedDict) <- typeDictionaryForBindingGroup moduleName vals
175+ forM es $ \e -> do
176+ triple@(_, (_, ty)) <- typeForBindingGroupElement moduleName e dict untypedDict
177+ -- If --main is enabled, need to check that `main` has type Eff eff a for some eff, a
178+ when (Just moduleName == mainModuleName && fst e == Ident C.main) $ do
179+ [eff, a] <- replicateM 2 fresh
180+ ty =?= TypeApp (TypeApp (TypeConstructor (Qualified (Just (ModuleName [ProperName "Control", ProperName "Monad", ProperName "Eff"])) (ProperName "Eff"))) eff) a
181+ return triple
182+
183+ forM tys $ \(ident, (val, ty)) -> do
184+ -- Replace type class dictionary placeholders with actual dictionaries
185+ val' <- replaceTypeClassDictionaries moduleName val
186+ -- Check skolem variables did not escape their scope
187+ skolemEscapeCheck val'
188+ -- Remove type synonyms placeholders, remove duplicate row fields, and replace
189+ -- top-level unification variables with named type variables.
190+ let val'' = overTypes (desaturateAllTypeSynonyms . setifyAll) val'
191+ ty' = varIfUnknown . desaturateAllTypeSynonyms . setifyAll $ ty
192+ return (ident, (val'', ty'))
193+ where
194+ -- Apply the substitution that was returned from runUnify to both types and (type-annotated) values
195+ tidyUp (ts, sub) = map (\(i, (val, ty)) -> (i, (overTypes (sub $?) val, sub $? ty))) ts
196+
197+typeDictionaryForBindingGroup :: ModuleName -> [(Ident, Value)] -> UnifyT Type Check ([(Ident, (Value, Maybe (Type, Bool)))], M.Map (ModuleName, Ident) (Type, NameKind), [(Ident, Type)])
198+typeDictionaryForBindingGroup moduleName vals = do
199+ let
200+ -- Map each declaration to a name/value pair, with an optional type, if the declaration is typed
201+ es = map isTyped vals
202+ -- Filter the typed and untyped declarations
203+ typed = filter (isJust . snd . snd) es
204+ untyped = filter (isNothing . snd . snd) es
205+ -- Make a map of names to typed declarations
206+ typedDict = map (\(ident, (_, Just (ty, _))) -> (ident, ty)) typed
207+
208+ -- Create fresh unification variables for the types of untyped declarations
209+ untypedNames <- replicateM (length untyped) fresh
210+
211+ let
212+ -- Make a map of names to the unification variables of untyped declarations
213+ untypedDict = zip (map fst untyped) untypedNames
214+ -- Create the dictionary of all name/type pairs, which will be added to the environment during type checking
215+ dict = M.fromList (map (\(ident, ty) -> ((moduleName, ident), (ty, LocalVariable))) $ typedDict ++ untypedDict)
216+ return (es, dict, untypedDict)
217+
218+typeForBindingGroupElement :: ModuleName -> (Ident, (Value, Maybe (Type, Bool))) -> M.Map (ModuleName, Ident) (Type, NameKind) -> [(Ident, Type)] -> UnifyT Type Check (Ident, (Value, Type))
219+typeForBindingGroupElement moduleName e@(_, (val, _)) dict untypedDict = do
220+ -- If the declaration is a function, it has access to other values in the binding group.
221+ -- If not, the generated code might fail at runtime since those values might be undefined.
222+ let dict' = if isFunction val then dict else M.empty
223+ case e of
224+ -- Typed declarations
225+ (ident, (val', Just (ty, checkType))) -> do
226+ -- Kind check
227+ kind <- liftCheck $ kindOf moduleName ty
228+ guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
229+ -- Check the type with the new names in scope
230+ ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
231+ val'' <- bindNames dict' $ if checkType
232+ then TypedValue True <$> check val' ty' <*> pure ty'
233+ else return (TypedValue False val' ty')
234+ return (ident, (val'', ty'))
235+ -- Untyped declarations
236+ (ident, (val', Nothing)) -> do
237+ -- Infer the type with the new names in scope
238+ TypedValue _ val'' ty <- bindNames dict' $ infer val'
239+ ty =?= fromMaybe (error "name not found in dictionary") (lookup ident untypedDict)
240+ return (ident, (TypedValue True val'' ty, ty))
241+
242+-- |
243+-- Check if a value introduces a function
244+--
245+isFunction :: Value -> Bool
246+isFunction (Abs _ _) = True
247+isFunction (TypedValue _ val _) = isFunction val
248+isFunction (PositionedValue _ val) = isFunction val
249+isFunction _ = False
250+
251+-- |
252+-- Check if a value contains a type annotation
253+--
254+isTyped :: (Ident, Value) -> (Ident, (Value, Maybe (Type, Bool)))
255+isTyped (name, TypedValue checkType value ty) = (name, (value, Just (ty, checkType)))
256+isTyped (name, value) = (name, (value, Nothing))
257+
258+-- |
259+-- Map a function over type annotations appearing inside a value
260+--
261+overTypes :: (Type -> Type) -> Value -> Value
262+overTypes f = let (_, f', _) = everywhereOnValues id g id in f'
263+ where
264+ g :: Value -> Value
265+ g (TypedValue checkTy val t) = TypedValue checkTy val (f t)
266+ g (TypeClassDictionary b (nm, tys) sco) = TypeClassDictionary b (nm, map f tys) sco
267+ g other = other
268+
269+-- |
270+-- Replace type class dictionary placeholders with inferred type class dictionaries
271+--
272+replaceTypeClassDictionaries :: ModuleName -> Value -> Check Value
273+replaceTypeClassDictionaries mn =
274+ let (_, f, _) = everywhereOnValuesTopDownM return go return
275+ in f
276+ where
277+ go (TypeClassDictionary trySuperclasses constraint dicts) = do
278+ env <- getEnv
279+ entails env mn dicts constraint trySuperclasses
280+ go other = return other
281+
282+-- |
283+-- A simplified representation of expressions which are used to represent type
284+-- class dictionaries at runtime, which can be compared for equality
285+--
286+data DictionaryValue
287+ -- |
288+ -- A dictionary which is brought into scope by a local constraint
289+ --
290+ = LocalDictionaryValue (Qualified Ident)
291+ -- |
292+ -- A dictionary which is brought into scope by an instance declaration
293+ --
294+ | GlobalDictionaryValue (Qualified Ident)
295+ -- |
296+ -- A dictionary which depends on other dictionaries
297+ --
298+ | DependentDictionaryValue (Qualified Ident) [DictionaryValue]
299+ -- |
300+ -- A subclass dictionary
301+ --
302+ | SubclassDictionaryValue DictionaryValue (Qualified ProperName) Integer
303+ deriving (Show, Ord, Eq)
304+
305+-- |
306+-- Check that the current set of type class dictionaries entail the specified type class goal, and, if so,
307+-- return a type class dictionary reference.
308+--
309+entails :: Environment -> ModuleName -> [TypeClassDictionaryInScope] -> (Qualified ProperName, [Type]) -> Bool -> Check Value
310+entails env moduleName context = solve (sortedNubBy canonicalizeDictionary (filter filterModule context))
311+ where
312+ sortedNubBy :: (Ord k) => (v -> k) -> [v] -> [v]
313+ sortedNubBy f vs = M.elems (M.fromList (map (f &&& id) vs))
314+
315+ -- Filter out type dictionaries which are in scope in the current module
316+ filterModule :: TypeClassDictionaryInScope -> Bool
317+ filterModule (TypeClassDictionaryInScope { tcdName = Qualified (Just mn) _ }) | mn == moduleName = True
318+ filterModule (TypeClassDictionaryInScope { tcdName = Qualified Nothing _ }) = True
319+ filterModule _ = False
320+
321+ solve context' (className, tys) trySuperclasses =
322+ let
323+ dicts = go trySuperclasses className tys
324+ in case sortedNubBy dictTrace (chooseSimplestDictionaries dicts) of
325+ [] -> throwError . strMsg $ "No instance found for " ++ show className ++ " " ++ unwords (map prettyPrintTypeAtom tys)
326+ [_] -> return $ dictionaryValueToValue $ head dicts
327+ _ -> throwError . strMsg $ "Overlapping instances found for " ++ show className ++ " " ++ unwords (map prettyPrintTypeAtom tys)
328+ where
329+ go trySuperclasses' className' tys' =
330+ -- Look for regular type instances
331+ [ mkDictionary (canonicalizeDictionary tcd) args
332+ | tcd <- context'
333+ -- Make sure the type class name matches the one we are trying to satisfy
334+ , className' == tcdClassName tcd
335+ -- Make sure the type unifies with the type in the type instance definition
336+ , subst <- maybeToList . (>>= verifySubstitution) . fmap concat $ zipWithM (typeHeadsAreEqual moduleName env) tys' (tcdInstanceTypes tcd)
337+ -- Solve any necessary subgoals
338+ , args <- solveSubgoals subst (tcdDependencies tcd) ] ++
339+
340+ -- Look for implementations via superclasses
341+ [ SubclassDictionaryValue suDict superclass index
342+ | trySuperclasses'
343+ , (subclassName, (args, _, implies)) <- M.toList (typeClasses env)
344+ -- Try each superclass
345+ , (index, (superclass, suTyArgs)) <- zip [0..] implies
346+ -- Make sure the type class name matches the superclass name
347+ , className' == superclass
348+ -- Make sure the types unify with the types in the superclass implication
349+ , subst <- maybeToList . (>>= verifySubstitution) . fmap concat $ zipWithM (typeHeadsAreEqual moduleName env) tys' suTyArgs
350+ -- Finally, satisfy the subclass constraint
351+ , args' <- maybeToList $ mapM (flip lookup subst) args
352+ , suDict <- go True subclassName args' ]
353+
354+ -- Create dictionaries for subgoals which still need to be solved by calling go recursively
355+ -- E.g. the goal (Show a, Show b) => Show (Either a b) can be satisfied if the current type
356+ -- unifies with Either a b, and we can satisfy the subgoals Show a and Show b recursively.
357+ solveSubgoals :: [(String, Type)] -> Maybe [(Qualified ProperName, [Type])] -> [Maybe [DictionaryValue]]
358+ solveSubgoals _ Nothing = return Nothing
359+ solveSubgoals subst (Just subgoals) = do
360+ dict <- mapM (uncurry (go True) . second (map (replaceAllTypeVars subst))) subgoals
361+ return $ Just dict
362+ -- Make a dictionary from subgoal dictionaries by applying the correct function
363+ mkDictionary :: Qualified Ident -> Maybe [DictionaryValue] -> DictionaryValue
364+ mkDictionary fnName Nothing = LocalDictionaryValue fnName
365+ mkDictionary fnName (Just []) = GlobalDictionaryValue fnName
366+ mkDictionary fnName (Just dicts) = DependentDictionaryValue fnName dicts
367+ -- Turn a DictionaryValue into a Value
368+ dictionaryValueToValue :: DictionaryValue -> Value
369+ dictionaryValueToValue (LocalDictionaryValue fnName) = Var fnName
370+ dictionaryValueToValue (GlobalDictionaryValue fnName) = App (Var fnName) (ObjectLiteral [])
371+ dictionaryValueToValue (DependentDictionaryValue fnName dicts) = foldl App (Var fnName) (map dictionaryValueToValue dicts)
372+ dictionaryValueToValue (SubclassDictionaryValue dict superclassName index) =
373+ App (Accessor (show superclassName ++ "_" ++ show index)
374+ (Accessor C.__superclasses (dictionaryValueToValue dict)))
375+ (ObjectLiteral [])
376+ -- Ensure that a substitution is valid
377+ verifySubstitution :: [(String, Type)] -> Maybe [(String, Type)]
378+ verifySubstitution subst = do
379+ let grps = groupBy ((==) `on` fst) subst
380+ guard (all (pairwise (unifiesWith env) . map snd) grps)
381+ return $ map head grps
382+ -- Choose the simplest DictionaryValues from a list of candidates
383+ -- The reason for this function is as follows:
384+ -- When considering overlapping instances, we don't want to consider the same dictionary
385+ -- to be an overlap of itself when obtained as a superclass of another class.
386+ -- Observing that we probably don't want to select a superclass instance when an instance
387+ -- is available directly, and that there is no way for a superclass instance to actually
388+ -- introduce an overlap that wouldn't have been there already, we simply remove dictionaries
389+ -- obtained as superclass instances if there are simpler instances available.
390+ chooseSimplestDictionaries :: [DictionaryValue] -> [DictionaryValue]
391+ chooseSimplestDictionaries ds = case filter isSimpleDictionaryValue ds of
392+ [] -> ds
393+ simple -> simple
394+ isSimpleDictionaryValue SubclassDictionaryValue{} = False
395+ isSimpleDictionaryValue (DependentDictionaryValue _ ds) = all isSimpleDictionaryValue ds
396+ isSimpleDictionaryValue _ = True
397+ -- |
398+ -- Get the "trace" of a DictionaryValue - that is, remove all SubclassDictionaryValue
399+ -- data constructors
400+ --
401+ dictTrace :: DictionaryValue -> DictionaryValue
402+ dictTrace (DependentDictionaryValue fnName dicts) = DependentDictionaryValue fnName $ map dictTrace dicts
403+ dictTrace (SubclassDictionaryValue dict _ _) = dictTrace dict
404+ dictTrace other = other
405+
406+-- |
407+-- Check all values in a list pairwise match a predicate
408+--
409+pairwise :: (a -> a -> Bool) -> [a] -> Bool
410+pairwise _ [] = True
411+pairwise _ [_] = True
412+pairwise p (x : xs) = all (p x) xs && pairwise p xs
413+
414+-- |
415+-- Check that two types unify
416+--
417+unifiesWith :: Environment -> Type -> Type -> Bool
418+unifiesWith _ (TUnknown u1) (TUnknown u2) | u1 == u2 = True
419+unifiesWith _ (Skolem _ s1 _) (Skolem _ s2 _) | s1 == s2 = True
420+unifiesWith _ (TypeVar v1) (TypeVar v2) | v1 == v2 = True
421+unifiesWith _ (TypeConstructor c1) (TypeConstructor c2) | c1 == c2 = True
422+unifiesWith e (TypeApp h1 t1) (TypeApp h2 t2) = unifiesWith e h1 h2 && unifiesWith e t1 t2
423+unifiesWith e (SaturatedTypeSynonym name args) t2 =
424+ case expandTypeSynonym' e name args of
425+ Left _ -> False
426+ Right t1 -> unifiesWith e t1 t2
427+unifiesWith e t1 t2@(SaturatedTypeSynonym _ _) = unifiesWith e t2 t1
428+unifiesWith _ _ _ = False
429+
430+-- |
431+-- Check whether the type heads of two types are equal (for the purposes of type class dictionary lookup),
432+-- and return a substitution from type variables to types which makes the type heads unify.
433+--
434+typeHeadsAreEqual :: ModuleName -> Environment -> Type -> Type -> Maybe [(String, Type)]
435+typeHeadsAreEqual _ _ (Skolem _ s1 _) (Skolem _ s2 _) | s1 == s2 = Just []
436+typeHeadsAreEqual _ _ t (TypeVar v) = Just [(v, t)]
437+typeHeadsAreEqual _ _ (TypeConstructor c1) (TypeConstructor c2) | c1 == c2 = Just []
438+typeHeadsAreEqual m e (TypeApp h1 t1) (TypeApp h2 t2) = (++) <$> typeHeadsAreEqual m e h1 h2 <*> typeHeadsAreEqual m e t1 t2
439+typeHeadsAreEqual m e (SaturatedTypeSynonym name args) t2 = case expandTypeSynonym' e name args of
440+ Left _ -> Nothing
441+ Right t1 -> typeHeadsAreEqual m e t1 t2
442+typeHeadsAreEqual _ _ _ _ = Nothing
443+
444+-- |
445+-- Ensure skolem variables do not escape their scope
446+--
447+skolemEscapeCheck :: Value -> Check ()
448+skolemEscapeCheck (TypedValue False _ _) = return ()
449+skolemEscapeCheck root@TypedValue{} =
450+ -- Every skolem variable is created when a ForAll type is skolemized.
451+ -- This determines the scope of that skolem variable, which is copied from the SkolemScope
452+ -- field of the ForAll constructor.
453+ -- We traverse the tree top-down, and collect any SkolemScopes introduced by ForAlls.
454+ -- If a Skolem is encountered whose SkolemScope is not in the current list, we have found
455+ -- an escaped skolem variable.
456+ let (_, f, _, _, _) = everythingWithContextOnValues [] [] (++) def go def def def
457+ in case f root of
458+ [] -> return ()
459+ ((binding, val) : _) -> throwError $ mkErrorStack ("Rigid/skolem type variable " ++ maybe "" (("bound by " ++) . prettyPrintValue) binding ++ " has escaped.") (Just (ValueError val))
460+ where
461+ def s _ = (s, [])
462+
463+ go :: [(SkolemScope, Value)] -> Value -> ([(SkolemScope, Value)], [(Maybe Value, Value)])
464+ go scos val@(TypedValue _ _ (ForAll _ _ (Just sco))) = ((sco, val) : scos, [])
465+ go scos val@(TypedValue _ _ ty) = case collectSkolems ty \\ map fst scos of
466+ (sco : _) -> (scos, [(findBindingScope sco, val)])
467+ _ -> (scos, [])
468+ where
469+ collectSkolems :: Type -> [SkolemScope]
470+ collectSkolems = nub . everythingOnTypes (++) collect
471+ where
472+ collect (Skolem _ _ scope) = [scope]
473+ collect _ = []
474+ go scos _ = (scos, [])
475+ findBindingScope :: SkolemScope -> Maybe Value
476+ findBindingScope sco =
477+ let (_, f, _, _, _) = everythingOnValues mappend (const mempty) go' (const mempty) (const mempty) (const mempty)
478+ in getFirst $ f root
479+ where
480+ go' val@(TypedValue _ _ (ForAll _ _ (Just sco'))) | sco == sco' = First (Just val)
481+ go' _ = mempty
482+skolemEscapeCheck val = throwError $ mkErrorStack "Untyped value passed to skolemEscapeCheck" (Just (ValueError val))
483+
484+-- |
485+-- Ensure a row contains no duplicate labels
486+--
487+setify :: Type -> Type
488+setify = rowFromList . first (M.toList . M.fromList) . rowToList
489+
490+-- |
491+-- \"Setify\" all rows occuring inside a value
492+--
493+setifyAll :: Type -> Type
494+setifyAll = everywhereOnTypes setify
495+
496+-- |
497+-- Replace outermost unsolved unification variables with named type variables
498+--
499+varIfUnknown :: Type -> Type
500+varIfUnknown ty =
501+ let unks = nub $ unknowns ty
502+ toName = (:) 't' . show
503+ ty' = everywhereOnTypes typeToVar ty
504+ typeToVar :: Type -> Type
505+ typeToVar (TUnknown u) = TypeVar (toName u)
506+ typeToVar t = t
507+ in mkForAll (sort . map toName $ unks) ty'
508+
509+-- |
510+-- Remove any ForAlls and ConstrainedType constructors in a type by introducing new unknowns
511+-- or TypeClassDictionary values.
512+--
513+-- This is necessary during type checking to avoid unifying a polymorphic type with a
514+-- unification variable.
515+--
516+instantiatePolyTypeWithUnknowns :: Value -> Type -> UnifyT Type Check (Value, Type)
517+instantiatePolyTypeWithUnknowns val (ForAll ident ty _) = do
518+ ty' <- replaceVarWithUnknown ident ty
519+ instantiatePolyTypeWithUnknowns val ty'
520+instantiatePolyTypeWithUnknowns val (ConstrainedType constraints ty) = do
521+ dicts <- getTypeClassDictionaries
522+ (_, ty') <- instantiatePolyTypeWithUnknowns (error "Types under a constraint cannot themselves be constrained") ty
523+ return (foldl App val (map (flip (TypeClassDictionary True) dicts) constraints), ty')
524+instantiatePolyTypeWithUnknowns val ty = return (val, ty)
525+
526+-- |
527+-- Replace a single type variable with a new unification variable
528+--
529+replaceVarWithUnknown :: String -> Type -> UnifyT Type Check Type
530+replaceVarWithUnknown ident ty = do
531+ tu <- fresh
532+ return $ replaceTypeVars ident tu ty
533+
534+-- |
535+-- Replace fully applied type synonyms with the @SaturatedTypeSynonym@ data constructor, which helps generate
536+-- better error messages during unification.
537+--
538+replaceAllTypeSynonyms' :: Environment -> Type -> Either String Type
539+replaceAllTypeSynonyms' env d =
540+ let
541+ syns = map (\(name, (args, _)) -> (name, length args)) . M.toList $ typeSynonyms env
542+ in
543+ saturateAllTypeSynonyms syns d
544+
545+replaceAllTypeSynonyms :: (Error e, Functor m, Monad m, MonadState CheckState m, MonadError e m) => Type -> m Type
546+replaceAllTypeSynonyms d = do
547+ env <- getEnv
548+ either (throwError . strMsg) return $ replaceAllTypeSynonyms' env d
549+
550+-- |
551+-- \"Desaturate\" @SaturatedTypeSynonym@s
552+--
553+desaturateAllTypeSynonyms :: Type -> Type
554+desaturateAllTypeSynonyms = everywhereOnTypes replaceSaturatedTypeSynonym
555+ where
556+ replaceSaturatedTypeSynonym (SaturatedTypeSynonym name args) = foldl TypeApp (TypeConstructor name) args
557+ replaceSaturatedTypeSynonym t = t
558+
559+-- |
560+-- Replace a type synonym and its arguments with the aliased type
561+--
562+expandTypeSynonym' :: Environment -> Qualified ProperName -> [Type] -> Either String Type
563+expandTypeSynonym' env name args =
564+ case M.lookup name (typeSynonyms env) of
565+ Just (synArgs, body) -> do
566+ let repl = replaceAllTypeVars (zip synArgs args) body
567+ replaceAllTypeSynonyms' env repl
568+ Nothing -> error "Type synonym was not defined"
569+
570+expandTypeSynonym :: (Error e, Functor m, Monad m, MonadState CheckState m, MonadError e m) => Qualified ProperName -> [Type] -> m Type
571+expandTypeSynonym name args = do
572+ env <- getEnv
573+ either (throwError . strMsg) return $ expandTypeSynonym' env name args
574+
575+expandAllTypeSynonyms :: (Error e, Functor m, Applicative m, Monad m, MonadState CheckState m, MonadError e m) => Type -> m Type
576+expandAllTypeSynonyms = everywhereOnTypesTopDownM go
577+ where
578+ go (SaturatedTypeSynonym name args) = expandTypeSynonym name args
579+ go other = return other
580+
581+-- |
582+-- Ensure a set of property names and value does not contain duplicate labels
583+--
584+ensureNoDuplicateProperties :: (Error e, MonadError e m) => [(String, Value)] -> m ()
585+ensureNoDuplicateProperties ps = guardWith (strMsg "Duplicate property names") $ length (nub . map fst $ ps) == length ps
586+
587+-- |
588+-- Infer a type for a value, rethrowing any error to provide a more useful error message
589+--
590+infer :: Value -> UnifyT Type Check Value
591+infer val = rethrow (mkErrorStack "Error inferring type of value" (Just (ValueError val)) <>) $ infer' val
592+
593+-- |
594+-- Infer a type for a value
595+--
596+infer' :: Value -> UnifyT Type Check Value
597+infer' v@(NumericLiteral _) = return $ TypedValue True v tyNumber
598+infer' v@(StringLiteral _) = return $ TypedValue True v tyString
599+infer' v@(BooleanLiteral _) = return $ TypedValue True v tyBoolean
600+infer' (ArrayLiteral vals) = do
601+ ts <- mapM infer vals
602+ els <- fresh
603+ forM_ ts $ \(TypedValue _ _ t) -> els =?= t
604+ return $ TypedValue True (ArrayLiteral ts) (TypeApp tyArray els)
605+infer' (ObjectLiteral ps) = do
606+ ensureNoDuplicateProperties ps
607+ ts <- mapM (infer . snd) ps
608+ let fields = zipWith (\name (TypedValue _ _ t) -> (name, t)) (map fst ps) ts
609+ ty = TypeApp tyObject $ rowFromList (fields, REmpty)
610+ return $ TypedValue True (ObjectLiteral (zip (map fst ps) ts)) ty
611+infer' (ObjectUpdate o ps) = do
612+ ensureNoDuplicateProperties ps
613+ row <- fresh
614+ newVals <- zipWith (\(name, _) t -> (name, t)) ps <$> mapM (infer . snd) ps
615+ let newTys = map (\(name, TypedValue _ _ ty) -> (name, ty)) newVals
616+ oldTys <- zip (map fst ps) <$> replicateM (length ps) fresh
617+ let oldTy = TypeApp tyObject $ rowFromList (oldTys, row)
618+ o' <- TypedValue True <$> check o oldTy <*> pure oldTy
619+ return $ TypedValue True (ObjectUpdate o' newVals) $ TypeApp tyObject $ rowFromList (newTys, row)
620+infer' (Accessor prop val) = do
621+ typed@(TypedValue _ _ objTy) <- infer val
622+ propTy <- inferProperty objTy prop
623+ case propTy of
624+ Nothing -> do
625+ field <- fresh
626+ rest <- fresh
627+ _ <- subsumes Nothing objTy (TypeApp tyObject (RCons prop field rest))
628+ return $ TypedValue True (Accessor prop typed) field
629+ Just ty -> return $ TypedValue True (Accessor prop typed) ty
630+infer' (Abs (Left arg) ret) = do
631+ ty <- fresh
632+ Just moduleName <- checkCurrentModule <$> get
633+ bindLocalVariables moduleName [(arg, ty)] $ do
634+ body@(TypedValue _ _ bodyTy) <- infer' ret
635+ return $ TypedValue True (Abs (Left arg) body) $ function ty bodyTy
636+infer' (Abs (Right _) _) = error "Binder was not desugared"
637+infer' (App f arg) = do
638+ f'@(TypedValue _ _ ft) <- infer f
639+ (ret, app) <- checkFunctionApplication f' ft arg Nothing
640+ return $ TypedValue True app ret
641+infer' (Var var) = do
642+ Just moduleName <- checkCurrentModule <$> get
643+ ty <- introduceSkolemScope <=< replaceAllTypeSynonyms <=< lookupVariable moduleName $ var
644+ case ty of
645+ ConstrainedType constraints ty' -> do
646+ dicts <- getTypeClassDictionaries
647+ return $ TypedValue True (foldl App (Var var) (map (flip (TypeClassDictionary True) dicts) constraints)) ty'
648+ _ -> return $ TypedValue True (Var var) ty
649+infer' v@(Constructor c) = do
650+ env <- getEnv
651+ case M.lookup c (dataConstructors env) of
652+ Nothing -> throwError . strMsg $ "Constructor " ++ show c ++ " is undefined"
653+ Just (_, ty) -> do ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
654+ return $ TypedValue True v ty'
655+infer' (Case vals binders) = do
656+ ts <- mapM infer vals
657+ ret <- fresh
658+ binders' <- checkBinders (map (\(TypedValue _ _ t) -> t) ts) ret binders
659+ return $ TypedValue True (Case ts binders') ret
660+infer' (IfThenElse cond th el) = do
661+ cond' <- check cond tyBoolean
662+ v2@(TypedValue _ _ t2) <- infer th
663+ v3@(TypedValue _ _ t3) <- infer el
664+ t2 =?= t3
665+ return $ TypedValue True (IfThenElse cond' v2 v3) t2
666+infer' (Let ds val) = do
667+ (ds', val'@(TypedValue _ _ valTy)) <- inferLetBinding [] ds val infer
668+ return $ TypedValue True (Let ds' val') valTy
669+infer' (SuperClassDictionary className tys) = do
670+ dicts <- getTypeClassDictionaries
671+ return $ TypeClassDictionary False (className, tys) dicts
672+infer' (TypedValue checkType val ty) = do
673+ Just moduleName <- checkCurrentModule <$> get
674+ kind <- liftCheck $ kindOf moduleName ty
675+ guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
676+ ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
677+ val' <- if checkType then check val ty' else return val
678+ return $ TypedValue True val' ty'
679+infer' (PositionedValue pos val) = rethrowWithPosition pos $ infer' val
680+infer' _ = error "Invalid argument to infer"
681+
682+inferLetBinding :: [Declaration] -> [Declaration] -> Value -> (Value -> UnifyT Type Check Value) -> UnifyT Type Check ([Declaration], Value)
683+inferLetBinding seen [] ret j = (,) seen <$> j ret
684+inferLetBinding seen (ValueDeclaration ident nameKind [] Nothing tv@(TypedValue checkType val ty) : rest) ret j = do
685+ Just moduleName <- checkCurrentModule <$> get
686+ kind <- liftCheck $ kindOf moduleName ty
687+ guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
688+ let dict = if isFunction val then M.singleton (moduleName, ident) (ty, nameKind) else M.empty
689+ ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
690+ TypedValue _ val' ty'' <- if checkType then bindNames dict (check val ty') else return tv
691+ bindNames (M.singleton (moduleName, ident) (ty'', nameKind)) $ inferLetBinding (seen ++ [ValueDeclaration ident nameKind [] Nothing (TypedValue checkType val' ty'')]) rest ret j
692+inferLetBinding seen (ValueDeclaration ident nameKind [] Nothing val : rest) ret j = do
693+ valTy <- fresh
694+ Just moduleName <- checkCurrentModule <$> get
695+ let dict = if isFunction val then M.singleton (moduleName, ident) (valTy, nameKind) else M.empty
696+ TypedValue _ val' valTy' <- bindNames dict $ infer val
697+ valTy =?= valTy'
698+ bindNames (M.singleton (moduleName, ident) (valTy', nameKind)) $ inferLetBinding (seen ++ [ValueDeclaration ident nameKind [] Nothing val']) rest ret j
699+inferLetBinding seen (BindingGroupDeclaration ds : rest) ret j = do
700+ Just moduleName <- checkCurrentModule <$> get
701+ (es, dict, untypedDict) <- typeDictionaryForBindingGroup moduleName (map (\(i, _, v) -> (i, v)) ds)
702+ ds' <- forM es $ \e -> do
703+ (ident, (val', _)) <- typeForBindingGroupElement moduleName e dict untypedDict
704+ return $ (ident, LocalVariable, val')
705+ bindNames dict $ inferLetBinding (seen ++ [BindingGroupDeclaration ds']) rest ret j
706+inferLetBinding seen (PositionedDeclaration pos d : ds) ret j = rethrowWithPosition pos $ do
707+ ((d' : ds'), val') <- inferLetBinding seen (d : ds) ret j
708+ return (PositionedDeclaration pos d' : ds', val')
709+inferLetBinding _ _ _ _ = error "Invalid argument to inferLetBinding"
710+
711+-- |
712+-- Infer the type of a property inside a record with a given type
713+--
714+inferProperty :: Type -> String -> UnifyT Type Check (Maybe Type)
715+inferProperty (TypeApp obj row) prop | obj == tyObject = do
716+ let (props, _) = rowToList row
717+ return $ lookup prop props
718+inferProperty (SaturatedTypeSynonym name args) prop = do
719+ replaced <- introduceSkolemScope <=< expandTypeSynonym name $ args
720+ inferProperty replaced prop
721+inferProperty (ForAll ident ty _) prop = do
722+ replaced <- replaceVarWithUnknown ident ty
723+ inferProperty replaced prop
724+inferProperty _ _ = return Nothing
725+
726+-- |
727+-- Infer the types of variables brought into scope by a binder
728+--
729+inferBinder :: Type -> Binder -> UnifyT Type Check (M.Map Ident Type)
730+inferBinder _ NullBinder = return M.empty
731+inferBinder val (StringBinder _) = val =?= tyString >> return M.empty
732+inferBinder val (NumberBinder _) = val =?= tyNumber >> return M.empty
733+inferBinder val (BooleanBinder _) = val =?= tyBoolean >> return M.empty
734+inferBinder val (VarBinder name) = return $ M.singleton name val
735+inferBinder val (ConstructorBinder ctor binders) = do
736+ env <- getEnv
737+ case M.lookup ctor (dataConstructors env) of
738+ Just (_, ty) -> do
739+ (_, fn) <- instantiatePolyTypeWithUnknowns (error "Data constructor types cannot contain constraints") ty
740+ fn' <- replaceAllTypeSynonyms fn
741+ go binders fn'
742+ where
743+ go [] ty' = do
744+ _ <- subsumes Nothing val ty'
745+ return M.empty
746+ go (binder : binders') (TypeApp (TypeApp t obj) ret) | t == tyFunction =
747+ M.union <$> inferBinder obj binder <*> go binders' ret
748+ go _ _ = throwError . strMsg $ "Wrong number of arguments to constructor " ++ show ctor
749+ _ -> throwError . strMsg $ "Constructor " ++ show ctor ++ " is not defined"
750+inferBinder val (ObjectBinder props) = do
751+ row <- fresh
752+ rest <- fresh
753+ m1 <- inferRowProperties row rest props
754+ val =?= TypeApp tyObject row
755+ return m1
756+ where
757+ inferRowProperties :: Type -> Type -> [(String, Binder)] -> UnifyT Type Check (M.Map Ident Type)
758+ inferRowProperties nrow row [] = nrow =?= row >> return M.empty
759+ inferRowProperties nrow row ((name, binder):binders) = do
760+ propTy <- fresh
761+ m1 <- inferBinder propTy binder
762+ m2 <- inferRowProperties nrow (RCons name propTy row) binders
763+ return $ m1 `M.union` m2
764+inferBinder val (ArrayBinder binders) = do
765+ el <- fresh
766+ m1 <- M.unions <$> mapM (inferBinder el) binders
767+ val =?= TypeApp tyArray el
768+ return m1
769+inferBinder val (ConsBinder headBinder tailBinder) = do
770+ el <- fresh
771+ m1 <- inferBinder el headBinder
772+ m2 <- inferBinder val tailBinder
773+ val =?= TypeApp tyArray el
774+ return $ m1 `M.union` m2
775+inferBinder val (NamedBinder name binder) = do
776+ m <- inferBinder val binder
777+ return $ M.insert name val m
778+inferBinder val (PositionedBinder pos binder) =
779+ rethrowWithPosition pos $ inferBinder val binder
780+
781+-- |
782+-- Check the types of the return values in a set of binders in a case statement
783+--
784+checkBinders :: [Type] -> Type -> [CaseAlternative] -> UnifyT Type Check [CaseAlternative]
785+checkBinders _ _ [] = return []
786+checkBinders nvals ret (CaseAlternative binders grd val : bs) = do
787+ Just moduleName <- checkCurrentModule <$> get
788+ m1 <- M.unions <$> zipWithM inferBinder nvals binders
789+ r <- bindLocalVariables moduleName (M.toList m1) $ do
790+ val' <- TypedValue True <$> check val ret <*> pure ret
791+ case grd of
792+ Nothing -> return $ CaseAlternative binders Nothing val'
793+ Just g -> do
794+ g' <- check g tyBoolean
795+ return $ CaseAlternative binders (Just g') val'
796+ rs <- checkBinders nvals ret bs
797+ return $ r : rs
798+
799+-- |
800+-- Generate a new skolem constant
801+--
802+newSkolemConstant :: UnifyT Type Check Int
803+newSkolemConstant = fresh'
804+
805+-- |
806+-- Generate a new skolem scope
807+--
808+newSkolemScope :: UnifyT Type Check SkolemScope
809+newSkolemScope = SkolemScope <$> fresh'
810+
811+-- |
812+-- Skolemize a type variable by replacing its instances with fresh skolem constants
813+--
814+skolemize :: String -> Int -> SkolemScope -> Type -> Type
815+skolemize ident sko scope = replaceTypeVars ident (Skolem ident sko scope)
816+
817+-- |
818+-- This function has one purpose - to skolemize type variables appearing in a
819+-- SuperClassDictionary placeholder. These type variables are somewhat unique since they are the
820+-- only example of scoped type variables.
821+--
822+skolemizeTypesInValue :: String -> Int -> SkolemScope -> Value -> Value
823+skolemizeTypesInValue ident sko scope = let (_, f, _) = everywhereOnValues id go id in f
824+ where
825+ go (SuperClassDictionary c ts) = SuperClassDictionary c (map (skolemize ident sko scope) ts)
826+ go other = other
827+
828+-- |
829+-- Introduce skolem scope at every occurence of a ForAll
830+--
831+introduceSkolemScope :: Type -> UnifyT Type Check Type
832+introduceSkolemScope = everywhereOnTypesM go
833+ where
834+ go (ForAll ident ty Nothing) = ForAll ident ty <$> (Just <$> newSkolemScope)
835+ go other = return other
836+
837+-- |
838+-- Check the type of a value, rethrowing errors to provide a better error message
839+--
840+check :: Value -> Type -> UnifyT Type Check Value
841+check val ty = rethrow (mkErrorStack errorMessage (Just (ValueError val)) <>) $ check' val ty
842+ where
843+ errorMessage =
844+ "Error checking type of term " ++
845+ prettyPrintValue val ++
846+ " against type " ++
847+ prettyPrintType ty
848+
849+-- |
850+-- Check the type of a value
851+--
852+check' :: Value -> Type -> UnifyT Type Check Value
853+check' val (ForAll ident ty _) = do
854+ scope <- newSkolemScope
855+ sko <- newSkolemConstant
856+ let sk = skolemize ident sko scope ty
857+ let skVal = skolemizeTypesInValue ident sko scope val
858+ val' <- check skVal sk
859+ return $ TypedValue True val' (ForAll ident ty (Just scope))
860+check' val t@(ConstrainedType constraints ty) = do
861+ dictNames <- forM constraints $ \(Qualified _ (ProperName className), _) -> do
862+ n <- liftCheck freshDictionaryName
863+ return $ Ident $ "__dict_" ++ className ++ "_" ++ show n
864+ val' <- withTypeClassDictionaries (zipWith (\name (className, instanceTy) ->
865+ TypeClassDictionaryInScope name className instanceTy Nothing TCDRegular) (map (Qualified Nothing) dictNames)
866+ constraints) $ check val ty
867+ return $ TypedValue True (foldr (Abs . Left) val' dictNames) t
868+check' val (SaturatedTypeSynonym name args) = do
869+ ty <- introduceSkolemScope <=< expandTypeSynonym name $ args
870+ check val ty
871+check' val u@(TUnknown _) = do
872+ val'@(TypedValue _ _ ty) <- infer val
873+ -- Don't unify an unknown with an inferred polytype
874+ (val'', ty') <- instantiatePolyTypeWithUnknowns val' ty
875+ ty' =?= u
876+ return $ TypedValue True val'' ty'
877+check' v@(NumericLiteral _) t | t == tyNumber =
878+ return $ TypedValue True v t
879+check' v@(StringLiteral _) t | t == tyString =
880+ return $ TypedValue True v t
881+check' v@(BooleanLiteral _) t | t == tyBoolean =
882+ return $ TypedValue True v t
883+check' (ArrayLiteral vals) t@(TypeApp a ty) = do
884+ a =?= tyArray
885+ array <- ArrayLiteral <$> forM vals (`check` ty)
886+ return $ TypedValue True array t
887+check' (Abs (Left arg) ret) ty@(TypeApp (TypeApp t argTy) retTy) | t == tyFunction = do
888+ Just moduleName <- checkCurrentModule <$> get
889+ ret' <- bindLocalVariables moduleName [(arg, argTy)] $ check ret retTy
890+ return $ TypedValue True (Abs (Left arg) ret') ty
891+check' (Abs (Right _) _) _ = error "Binder was not desugared"
892+check' (App f arg) ret = do
893+ f'@(TypedValue _ _ ft) <- infer f
894+ (_, app) <- checkFunctionApplication f' ft arg (Just ret)
895+ return $ TypedValue True app ret
896+check' v@(Var var) ty = do
897+ Just moduleName <- checkCurrentModule <$> get
898+ repl <- introduceSkolemScope <=< replaceAllTypeSynonyms <=< lookupVariable moduleName $ var
899+ ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
900+ v' <- subsumes (Just v) repl ty'
901+ case v' of
902+ Nothing -> throwError . strMsg $ "Unable to check type subsumption"
903+ Just v'' -> return $ TypedValue True v'' ty'
904+check' (SuperClassDictionary className tys) _ = do
905+ {-
906+ -- Here, we replace a placeholder for a superclass dictionary with a regular
907+ -- TypeClassDictionary placeholder. The reason we do this is that it is necessary to have the
908+ -- correct super instance dictionaries in scope, and these are not available when the type class
909+ -- declaration gets desugared.
910+ --
911+ -- Note also that the first argument to TypeClassDictionary is False, meaning we _do not_ want
912+ -- to consider superclass instances when searching for this dictionary - doing so might lead
913+ -- to traversing a cycle in the instance graph.
914+ -}
915+ dicts <- getTypeClassDictionaries
916+ return $ TypeClassDictionary False (className, tys) dicts
917+check' (TypedValue checkType val ty1) ty2 = do
918+ Just moduleName <- checkCurrentModule <$> get
919+ kind <- liftCheck $ kindOf moduleName ty1
920+ guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
921+ ty1' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty1
922+ val' <- subsumes (Just val) ty1' ty2
923+ case val' of
924+ Nothing -> throwError . strMsg $ "Unable to check type subsumption"
925+ Just val'' -> do
926+ val''' <- if checkType then check val'' ty1' else return val''
927+ return $ TypedValue checkType (TypedValue True val''' ty1) ty2
928+check' (Case vals binders) ret = do
929+ vals' <- mapM infer vals
930+ let ts = map (\(TypedValue _ _ t) -> t) vals'
931+ binders' <- checkBinders ts ret binders
932+ return $ TypedValue True (Case vals' binders') ret
933+check' (IfThenElse cond th el) ty = do
934+ cond' <- check cond tyBoolean
935+ th' <- check th ty
936+ el' <- check el ty
937+ return $ TypedValue True (IfThenElse cond' th' el') ty
938+check' (ObjectLiteral ps) t@(TypeApp obj row) | obj == tyObject = do
939+ ensureNoDuplicateProperties ps
940+ ps' <- checkProperties ps row False
941+ return $ TypedValue True (ObjectLiteral ps') t
942+check' (ObjectUpdate obj ps) t@(TypeApp o row) | o == tyObject = do
943+ ensureNoDuplicateProperties ps
944+ us <- zip (map fst ps) <$> replicateM (length ps) fresh
945+ let (propsToCheck, rest) = rowToList row
946+ propsToRemove = map fst ps
947+ remainingProps = filter (\(p, _) -> p `notElem` propsToRemove) propsToCheck
948+ obj' <- check obj (TypeApp tyObject (rowFromList (us ++ remainingProps, rest)))
949+ ps' <- checkProperties ps row True
950+ return $ TypedValue True (ObjectUpdate obj' ps') t
951+check' (Accessor prop val) ty = do
952+ rest <- fresh
953+ val' <- check val (TypeApp tyObject (RCons prop ty rest))
954+ return $ TypedValue True (Accessor prop val') ty
955+check' (Constructor c) ty = do
956+ env <- getEnv
957+ case M.lookup c (dataConstructors env) of
958+ Nothing -> throwError . strMsg $ "Constructor " ++ show c ++ " is undefined"
959+ Just (_, ty1) -> do
960+ repl <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty1
961+ _ <- subsumes Nothing repl ty
962+ return $ TypedValue True (Constructor c) ty
963+check' (Let ds val) ty = do
964+ (ds', val') <- inferLetBinding [] ds val (flip check ty)
965+ return $ TypedValue True (Let ds' val') ty
966+check' val ty | containsTypeSynonyms ty = do
967+ ty' <- introduceSkolemScope <=< expandAllTypeSynonyms $ ty
968+ check val ty'
969+check' (PositionedValue pos val) ty =
970+ rethrowWithPosition pos $ check val ty
971+check' val ty = throwError $ mkErrorStack ("Value does not have type " ++ prettyPrintType ty) (Just (ValueError val))
972+
973+containsTypeSynonyms :: Type -> Bool
974+containsTypeSynonyms = everythingOnTypes (||) go where
975+ go (SaturatedTypeSynonym _ _) = True
976+ go _ = False
977+
978+-- |
979+-- Check the type of a collection of named record fields
980+--
981+-- The @lax@ parameter controls whether or not every record member has to be provided. For object updates, this is not the case.
982+--
983+checkProperties :: [(String, Value)] -> Type -> Bool -> UnifyT Type Check [(String, Value)]
984+checkProperties ps row lax = let (ts, r') = rowToList row in go ps ts r' where
985+ go [] [] REmpty = return []
986+ go [] [] u@(TUnknown _) = do u =?= REmpty
987+ return []
988+ go [] [] (Skolem _ _ _) | lax = return []
989+ go [] ((p, _): _) _ | lax = return []
990+ | otherwise = throwError $ mkErrorStack ("Object does not have property " ++ p) (Just (ValueError (ObjectLiteral ps)))
991+ go ((p,_):_) [] REmpty = throwError $ mkErrorStack ("Property " ++ p ++ " is not present in closed object type " ++ prettyPrintRow row) (Just (ValueError (ObjectLiteral ps)))
992+ go ((p,v):ps') [] u@(TUnknown _) = do
993+ v'@(TypedValue _ _ ty) <- infer v
994+ rest <- fresh
995+ u =?= RCons p ty rest
996+ ps'' <- go ps' [] rest
997+ return $ (p, v') : ps''
998+ go ((p,v):ps') ts r =
999+ case lookup p ts of
1000+ Nothing -> do
1001+ v'@(TypedValue _ _ ty) <- infer v
1002+ rest <- fresh
1003+ r =?= RCons p ty rest
1004+ ps'' <- go ps' ts rest
1005+ return $ (p, v') : ps''
1006+ Just ty -> do
1007+ v' <- check v ty
1008+ ps'' <- go ps' (delete (p, ty) ts) r
1009+ return $ (p, v') : ps''
1010+ go _ _ _ = throwError $ mkErrorStack ("Object does not have type " ++ prettyPrintType (TypeApp tyObject row)) (Just (ValueError (ObjectLiteral ps)))
1011+
1012+-- |
1013+-- Check the type of a function application, rethrowing errors to provide a better error message
1014+--
1015+checkFunctionApplication :: Value -> Type -> Value -> Maybe Type -> UnifyT Type Check (Type, Value)
1016+checkFunctionApplication fn fnTy arg ret = rethrow (mkErrorStack errorMessage (Just (ValueError fn)) <>) $ checkFunctionApplication' fn fnTy arg ret
1017+ where
1018+ errorMessage = "Error applying function of type "
1019+ ++ prettyPrintType fnTy
1020+ ++ " to argument " ++ prettyPrintValue arg
1021+
1022+-- |
1023+-- Check the type of a function application
1024+--
1025+checkFunctionApplication' :: Value -> Type -> Value -> Maybe Type -> UnifyT Type Check (Type, Value)
1026+checkFunctionApplication' fn (TypeApp (TypeApp tyFunction' argTy) retTy) arg ret = do
1027+ tyFunction' =?= tyFunction
1028+ _ <- maybe (return Nothing) (subsumes Nothing retTy) ret
1029+ subst <- unifyCurrentSubstitution <$> UnifyT get
1030+ arg' <- check arg (subst $? argTy)
1031+ return (retTy, App fn arg')
1032+checkFunctionApplication' fn (ForAll ident ty _) arg ret = do
1033+ replaced <- replaceVarWithUnknown ident ty
1034+ checkFunctionApplication fn replaced arg ret
1035+checkFunctionApplication' fn u@(TUnknown _) arg ret = do
1036+ arg' <- do
1037+ TypedValue _ arg' t <- infer arg
1038+ (arg'', t') <- instantiatePolyTypeWithUnknowns arg' t
1039+ return $ TypedValue True arg'' t'
1040+ let ty = (\(TypedValue _ _ t) -> t) arg'
1041+ ret' <- maybe fresh return ret
1042+ u =?= function ty ret'
1043+ return (ret', App fn arg')
1044+checkFunctionApplication' fn (SaturatedTypeSynonym name tyArgs) arg ret = do
1045+ ty <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
1046+ checkFunctionApplication fn ty arg ret
1047+checkFunctionApplication' fn (ConstrainedType constraints fnTy) arg ret = do
1048+ dicts <- getTypeClassDictionaries
1049+ checkFunctionApplication' (foldl App fn (map (flip (TypeClassDictionary True) dicts) constraints)) fnTy arg ret
1050+checkFunctionApplication' _ fnTy arg _ = throwError . strMsg $ "Cannot apply a function of type "
1051+ ++ prettyPrintType fnTy
1052+ ++ " to argument " ++ prettyPrintValue arg
1053+
1054+-- |
1055+-- Check whether one type subsumes another, rethrowing errors to provide a better error message
1056+--
1057+subsumes :: Maybe Value -> Type -> Type -> UnifyT Type Check (Maybe Value)
1058+subsumes val ty1 ty2 = rethrow (mkErrorStack errorMessage (ValueError <$> val) <>) $ subsumes' val ty1 ty2
1059+ where
1060+ errorMessage = "Error checking that type "
1061+ ++ prettyPrintType ty1
1062+ ++ " subsumes type "
1063+ ++ prettyPrintType ty2
1064+
1065+-- |
1066+-- Check whether one type subsumes another
1067+--
1068+subsumes' :: Maybe Value -> Type -> Type -> UnifyT Type Check (Maybe Value)
1069+subsumes' val (ForAll ident ty1 _) ty2 = do
1070+ replaced <- replaceVarWithUnknown ident ty1
1071+ subsumes val replaced ty2
1072+subsumes' val ty1 (ForAll ident ty2 sco) =
1073+ case sco of
1074+ Just sco' -> do
1075+ sko <- newSkolemConstant
1076+ let sk = skolemize ident sko sco' ty2
1077+ subsumes val ty1 sk
1078+ Nothing -> throwError . strMsg $ "Skolem variable scope is unspecified"
1079+subsumes' val (TypeApp (TypeApp f1 arg1) ret1) (TypeApp (TypeApp f2 arg2) ret2) | f1 == tyFunction && f2 == tyFunction = do
1080+ _ <- subsumes Nothing arg2 arg1
1081+ _ <- subsumes Nothing ret1 ret2
1082+ return val
1083+subsumes' val (SaturatedTypeSynonym name tyArgs) ty2 = do
1084+ ty1 <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
1085+ subsumes val ty1 ty2
1086+subsumes' val ty1 (SaturatedTypeSynonym name tyArgs) = do
1087+ ty2 <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
1088+ subsumes val ty1 ty2
1089+subsumes' (Just val) (ConstrainedType constraints ty1) ty2 = do
1090+ dicts <- getTypeClassDictionaries
1091+ _ <- subsumes' Nothing ty1 ty2
1092+ return . Just $ foldl App val (map (flip (TypeClassDictionary True) dicts) constraints)
1093+subsumes' val (TypeApp f1 r1) (TypeApp f2 r2) | f1 == tyObject && f2 == tyObject = do
1094+ let
1095+ (ts1, r1') = rowToList r1
1096+ (ts2, r2') = rowToList r2
1097+ ts1' = sortBy (comparing fst) ts1
1098+ ts2' = sortBy (comparing fst) ts2
1099+ go ts1' ts2' r1' r2'
1100+ return val
1101+ where
1102+ go [] ts2 r1' r2' = r1' =?= rowFromList (ts2, r2')
1103+ go ts1 [] r1' r2' = r2' =?= rowFromList (ts1, r1')
1104+ go ((p1, ty1) : ts1) ((p2, ty2) : ts2) r1' r2'
1105+ | p1 == p2 = do _ <- subsumes Nothing ty1 ty2
1106+ go ts1 ts2 r1' r2'
1107+ | p1 < p2 = do rest <- fresh
1108+ r2' =?= RCons p1 ty1 rest
1109+ go ts1 ((p2, ty2) : ts2) r1' rest
1110+ | otherwise = do rest <- fresh
1111+ r1' =?= RCons p2 ty2 rest
1112+ go ((p1, ty1) : ts1) ts2 rest r2'
1113+subsumes' val ty1 ty2@(TypeApp obj _) | obj == tyObject = subsumes val ty2 ty1
1114+subsumes' val ty1 ty2 = do
1115+ ty1 =?= ty2
1116+ return val
1117+
1118+
1119+
1120+
1121+