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