@@ -0,0 +1,1046 @@
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, everything, mkT,
49+ 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 f)
257+
258+-- |
259+-- Replace type class dictionary placeholders with inferred type class dictionaries
260+--
261+replaceTypeClassDictionaries :: ModuleName -> Value -> Check Value
262+replaceTypeClassDictionaries mn = everywhereM' (mkM go)
263+ where
264+ go (TypeClassDictionary constraint dicts) = do
265+ env <- getEnv
266+ let dicts' = fromMaybe (typeClassDictionaries env) dicts
267+ entails env mn dicts' constraint
268+ go other = return other
269+
270+-- |
271+-- A simplified representation of expressions which are used to represent type
272+-- class dictionaries at runtime, which can be compared for equality
273+--
274+data DictionaryValue
275+ -- |
276+ -- A dictionary which is brought into scope by a local constraint
277+ --
278+ = LocalDictionaryValue (Qualified Ident)
279+ -- |
280+ -- A dictionary which is brought into scope by an instance declaration
281+ --
282+ | GlobalDictionaryValue (Qualified Ident)
283+ -- |
284+ -- A dictionary which depends on other dictionaries
285+ --
286+ | DependentDictionaryValue (Qualified Ident) [DictionaryValue]
287+ -- |
288+ -- A subclass dictionary
289+ --
290+ | SubclassDictionaryValue DictionaryValue Integer
291+ deriving (Show, Ord, Eq)
292+
293+-- |
294+-- Check that the current set of type class dictionaries entail the specified type class goal, and, if so,
295+-- return a type class dictionary reference.
296+--
297+entails :: Environment -> ModuleName -> [TypeClassDictionaryInScope] -> (Qualified ProperName, [Type]) -> Check Value
298+entails env moduleName context = solve (sortedNubBy canonicalizeDictionary (filter filterModule context))
299+ where
300+ sortedNubBy :: (Ord k) => (v -> k) -> [v] -> [v]
301+ sortedNubBy f vs = M.elems (M.fromList (map (f &&& id) vs))
302+
303+ -- Filter out type dictionaries which are in scope in the current module
304+ filterModule :: TypeClassDictionaryInScope -> Bool
305+ filterModule (TypeClassDictionaryInScope { tcdName = Qualified (Just mn) _ }) | mn == moduleName = True
306+ filterModule (TypeClassDictionaryInScope { tcdName = Qualified Nothing _ }) = True
307+ filterModule _ = False
308+
309+ solve context' goal@(className, tys) =
310+ case go goal of
311+ [] -> throwError . strMsg $ "No instance found for " ++ show className ++ " " ++ unwords (map prettyPrintTypeAtom tys)
312+ (dict : _) -> return (dictionaryValueToValue dict)
313+ --_ -> throwError . strMsg $ "Overlapping instances found for " ++ show className ++ " " ++ unwords (map prettyPrintTypeAtom tys)
314+ where
315+ go (className', tys') =
316+ [ mkDictionary (canonicalizeDictionary tcd) args
317+ | tcd <- context'
318+ -- Make sure the type class name matches the one we are trying to satisfy
319+ , className' == tcdClassName tcd
320+ -- Make sure the type unifies with the type in the type instance definition
321+ , subst <- maybeToList . (>>= verifySubstitution) . fmap concat $ zipWithM (typeHeadsAreEqual moduleName env) tys' (tcdInstanceTypes tcd)
322+ -- Solve any necessary subgoals
323+ , args <- solveSubgoals subst (tcdDependencies tcd) ] ++
324+
325+ -- Look for implementations via superclasses
326+ [ SubclassDictionaryValue suDict index
327+ | tcd <- context'
328+ , let (_, _, implies) = fromMaybe (error "Type class was not defined") $ M.lookup (tcdClassName tcd) (typeClasses env)
329+ -- Try each superclass
330+ , (index, (superclass, suTyArgs)) <- zip [0..] implies
331+ -- Make sure the types unify with the types in the superclass implication
332+ , subst <- maybeToList . (>>= verifySubstitution) . fmap concat $ zipWithM (typeHeadsAreEqual moduleName env) tys' suTyArgs
333+ -- Make sure the type class name matches the superclass name
334+ , className' == superclass
335+ -- Finally, satisfy the subclass constraint
336+ , suDict <- go (tcdClassName tcd, map (applySubst subst) tys') ]
337+
338+ -- Create dictionaries for subgoals which still need to be solved by calling go recursively
339+ -- E.g. the goal (Show a, Show b) => Show (Either a b) can be satisfied if the current type
340+ -- unifies with Either a b, and we can satisfy the subgoals Show a and Show b recursively.
341+ solveSubgoals :: [(String, Type)] -> Maybe [(Qualified ProperName, [Type])] -> [Maybe [DictionaryValue]]
342+ solveSubgoals _ Nothing = return Nothing
343+ solveSubgoals subst (Just subgoals) = do
344+ dict <- mapM (go . second (map (replaceAllTypeVars subst))) subgoals
345+ return $ Just dict
346+ -- Make a dictionary from subgoal dictionaries by applying the correct function
347+ mkDictionary :: Qualified Ident -> Maybe [DictionaryValue] -> DictionaryValue
348+ mkDictionary fnName Nothing = LocalDictionaryValue fnName
349+ mkDictionary fnName (Just []) = GlobalDictionaryValue fnName
350+ mkDictionary fnName (Just dicts) = DependentDictionaryValue fnName dicts
351+ -- Turn a DictionaryValue into a Value
352+ dictionaryValueToValue :: DictionaryValue -> Value
353+ dictionaryValueToValue (LocalDictionaryValue fnName) = Var fnName
354+ dictionaryValueToValue (GlobalDictionaryValue fnName) = App (Var fnName) (ObjectLiteral [])
355+ dictionaryValueToValue (DependentDictionaryValue fnName dicts) = foldl App (Var fnName) (map dictionaryValueToValue dicts)
356+ dictionaryValueToValue (SubclassDictionaryValue dict index) =
357+ App (App (Var (Qualified (Just (ModuleName [ProperName C.prelude])) (Ident (C.!!))))
358+ (Accessor "__superclasses" (dictionaryValueToValue dict)))
359+ (NumericLiteral (Left index))
360+ -- Ensure that a substitution is valid
361+ verifySubstitution :: [(String, Type)] -> Maybe [(String, Type)]
362+ verifySubstitution subst = do
363+ let grps = groupBy ((==) `on` fst) subst
364+ guard (all (pairwise (unifiesWith env) . map snd) grps)
365+ return $ map head grps
366+ -- Apply a substitution to a type
367+ applySubst :: [(String, Type)] -> Type -> Type
368+ applySubst subst = everywhere (mkT replace)
369+ where
370+ replace t@(TypeVar v) = fromMaybe t $ lookup v subst
371+ replace other = other
372+
373+-- |
374+-- Check all values in a list pairwise match a predicate
375+--
376+pairwise :: (a -> a -> Bool) -> [a] -> Bool
377+pairwise _ [] = True
378+pairwise _ [_] = True
379+pairwise p (x : xs) = all (p x) xs && pairwise p xs
380+
381+-- |
382+-- Check that two types unify
383+--
384+unifiesWith :: Environment -> Type -> Type -> Bool
385+unifiesWith _ (TUnknown _) _ = True
386+unifiesWith _ _ (TUnknown _) = True
387+unifiesWith _ (Skolem s1 _) (Skolem s2 _) | s1 == s2 = True
388+unifiesWith _ (TypeVar v1) (TypeVar v2) | v1 == v2 = True
389+unifiesWith _ (TypeConstructor c1) (TypeConstructor c2) | c1 == c2 = True
390+unifiesWith e (TypeApp h1 t1) (TypeApp h2 t2) = unifiesWith e h1 h2 && unifiesWith e t1 t2
391+unifiesWith e (SaturatedTypeSynonym name args) t2 =
392+ case expandTypeSynonym' e name args of
393+ Left _ -> False
394+ Right t1 -> unifiesWith e t1 t2
395+unifiesWith e t1 t2@(SaturatedTypeSynonym _ _) = unifiesWith e t2 t1
396+unifiesWith _ _ _ = False
397+
398+-- |
399+-- Check whether the type heads of two types are equal (for the purposes of type class dictionary lookup),
400+-- and return a substitution from type variables to types which makes the type heads unify.
401+--
402+typeHeadsAreEqual :: ModuleName -> Environment -> Type -> Type -> Maybe [(String, Type)]
403+typeHeadsAreEqual _ _ (Skolem s1 _) (Skolem s2 _) | s1 == s2 = Just []
404+typeHeadsAreEqual _ _ t (TypeVar v) = Just [(v, t)]
405+typeHeadsAreEqual _ _ (TypeConstructor c1) (TypeConstructor c2) | c1 == c2 = Just []
406+typeHeadsAreEqual m e (TypeApp h1 t1) (TypeApp h2 t2) = (++) <$> typeHeadsAreEqual m e h1 h2 <*> typeHeadsAreEqual m e t1 t2
407+typeHeadsAreEqual m e (SaturatedTypeSynonym name args) t2 = case expandTypeSynonym' e name args of
408+ Left _ -> Nothing
409+ Right t1 -> typeHeadsAreEqual m e t1 t2
410+typeHeadsAreEqual _ _ _ _ = Nothing
411+
412+-- |
413+-- Ensure skolem variables do not escape their scope
414+--
415+skolemEscapeCheck :: Value -> Check ()
416+skolemEscapeCheck (TypedValue False _ _) = return ()
417+skolemEscapeCheck root@TypedValue{} =
418+ -- Every skolem variable is created when a ForAll type is skolemized.
419+ -- This determines the scope of that skolem variable, which is copied from the SkolemScope
420+ -- field of the ForAll constructor.
421+ -- We traverse the tree top-down, and collect any SkolemScopes introduced by ForAlls.
422+ -- If a Skolem is encountered whose SkolemScope is not in the current list, we have found
423+ -- an escaped skolem variable.
424+ case everythingWithContext [] (++) (mkQ ((,) []) go) root of
425+ [] -> return ()
426+ ((binding, val) : _) -> throwError $ mkErrorStack ("Rigid/skolem type variable " ++ maybe "" (("bound by " ++) . prettyPrintValue) binding ++ " has escaped.") (Just (ValueError val))
427+ where
428+ go :: Value -> [(SkolemScope, Value)] -> ([(Maybe Value, Value)], [(SkolemScope, Value)])
429+ go val@(TypedValue _ _ (ForAll _ _ (Just sco))) scos = ([], (sco, val) : scos)
430+ go val@(TypedValue _ _ ty) scos = case collectSkolems ty \\ map fst scos of
431+ (sco : _) -> ([(findBindingScope sco, val)], scos)
432+ _ -> ([], scos)
433+ where
434+ collectSkolems :: Type -> [SkolemScope]
435+ collectSkolems = nub . everything (++) (mkQ [] collect)
436+ where
437+ collect (Skolem _ scope) = [scope]
438+ collect _ = []
439+ go _ scos = ([], scos)
440+ findBindingScope :: SkolemScope -> Maybe Value
441+ findBindingScope sco = something (mkQ Nothing go') root
442+ where
443+ go' val@(TypedValue _ _ (ForAll _ _ (Just sco'))) | sco == sco' = Just val
444+ go' _ = Nothing
445+skolemEscapeCheck val = throwError $ mkErrorStack "Untyped value passed to skolemEscapeCheck" (Just (ValueError val))
446+
447+-- |
448+-- Ensure a row contains no duplicate labels
449+--
450+setify :: Type -> Type
451+setify = rowFromList . first (M.toList . M.fromList) . rowToList
452+
453+-- |
454+-- \"Setify\" all rows occuring inside a value
455+--
456+setifyAll :: (D.Data d) => d -> d
457+setifyAll = everywhere (mkT setify)
458+
459+-- |
460+-- Replace outermost unsolved unification variables with named type variables
461+--
462+varIfUnknown :: Type -> Type
463+varIfUnknown ty =
464+ let unks = nub $ unknowns ty
465+ toName = (:) 't' . show
466+ ty' = everywhere (mkT typeToVar) ty
467+ typeToVar :: Type -> Type
468+ typeToVar (TUnknown (Unknown u)) = TypeVar (toName u)
469+ typeToVar t = t
470+ in mkForAll (sort . map (toName . runUnknown) $ unks) ty'
471+
472+-- |
473+-- Remove any ForAlls and ConstrainedType constructors in a type by introducing new unknowns
474+-- or TypeClassDictionary values.
475+--
476+-- This is necessary during type checking to avoid unifying a polymorphic type with a
477+-- unification variable.
478+--
479+instantiatePolyTypeWithUnknowns :: Value -> Type -> UnifyT Type Check (Value, Type)
480+instantiatePolyTypeWithUnknowns val (ForAll ident ty _) = do
481+ ty' <- replaceVarWithUnknown ident ty
482+ instantiatePolyTypeWithUnknowns val ty'
483+instantiatePolyTypeWithUnknowns val (ConstrainedType constraints ty) = do
484+ dicts <- getTypeClassDictionaries
485+ (_, ty') <- instantiatePolyTypeWithUnknowns (error "Types under a constraint cannot themselves be constrained") ty
486+ return (foldl App val (map (flip TypeClassDictionary (Just dicts)) constraints), ty')
487+instantiatePolyTypeWithUnknowns val ty = return (val, ty)
488+
489+-- |
490+-- Replace a single type variable with a new unification variable
491+--
492+replaceVarWithUnknown :: String -> Type -> UnifyT Type Check Type
493+replaceVarWithUnknown ident ty = do
494+ tu <- fresh
495+ return $ replaceTypeVars ident tu ty
496+
497+-- |
498+-- Replace fully applied type synonyms with the @SaturatedTypeSynonym@ data constructor, which helps generate
499+-- better error messages during unification.
500+--
501+replaceAllTypeSynonyms' :: (D.Data d) => Environment -> d -> Either String d
502+replaceAllTypeSynonyms' env d =
503+ let
504+ syns = map (\(name, (args, _)) -> (name, length args)) . M.toList $ typeSynonyms env
505+ in
506+ saturateAllTypeSynonyms syns d
507+
508+replaceAllTypeSynonyms :: (Error e, Functor m, Monad m, MonadState CheckState m, MonadError e m) => (D.Data d) => d -> m d
509+replaceAllTypeSynonyms d = do
510+ env <- getEnv
511+ either (throwError . strMsg) return $ replaceAllTypeSynonyms' env d
512+
513+-- |
514+-- \"Desaturate\" @SaturatedTypeSynonym@s
515+--
516+desaturateAllTypeSynonyms :: (D.Data d) => d -> d
517+desaturateAllTypeSynonyms = everywhere (mkT replaceSaturatedTypeSynonym)
518+ where
519+ replaceSaturatedTypeSynonym (SaturatedTypeSynonym name args) = foldl TypeApp (TypeConstructor name) args
520+ replaceSaturatedTypeSynonym t = t
521+
522+-- |
523+-- Replace a type synonym and its arguments with the aliased type
524+--
525+expandTypeSynonym' :: Environment -> Qualified ProperName -> [Type] -> Either String Type
526+expandTypeSynonym' env name args =
527+ case M.lookup name (typeSynonyms env) of
528+ Just (synArgs, body) -> do
529+ let repl = replaceAllTypeVars (zip synArgs args) body
530+ replaceAllTypeSynonyms' env repl
531+ Nothing -> error "Type synonym was not defined"
532+
533+expandTypeSynonym :: (Error e, Functor m, Monad m, MonadState CheckState m, MonadError e m) => Qualified ProperName -> [Type] -> m Type
534+expandTypeSynonym name args = do
535+ env <- getEnv
536+ either (throwError . strMsg) return $ expandTypeSynonym' env name args
537+
538+expandAllTypeSynonyms :: (Error e, Functor m, Monad m, MonadState CheckState m, MonadError e m) => Type -> m Type
539+expandAllTypeSynonyms = everywhereM' (mkM go)
540+ where
541+ go (SaturatedTypeSynonym name args) = expandTypeSynonym name args
542+ go other = return other
543+
544+-- |
545+-- Ensure a set of property names and value does not contain duplicate labels
546+--
547+ensureNoDuplicateProperties :: (Error e, MonadError e m) => [(String, Value)] -> m ()
548+ensureNoDuplicateProperties ps = guardWith (strMsg "Duplicate property names") $ length (nub . map fst $ ps) == length ps
549+
550+-- |
551+-- Infer a type for a value, rethrowing any error to provide a more useful error message
552+--
553+infer :: Value -> UnifyT Type Check Value
554+infer val = rethrow (mkErrorStack "Error inferring type of value" (Just (ValueError val)) <>) $ infer' val
555+
556+-- |
557+-- Infer a type for a value
558+--
559+infer' :: Value -> UnifyT Type Check Value
560+infer' v@(NumericLiteral _) = return $ TypedValue True v tyNumber
561+infer' v@(StringLiteral _) = return $ TypedValue True v tyString
562+infer' v@(BooleanLiteral _) = return $ TypedValue True v tyBoolean
563+infer' (ArrayLiteral vals) = do
564+ ts <- mapM infer vals
565+ els <- fresh
566+ forM_ ts $ \(TypedValue _ _ t) -> els =?= TypeApp tyArray t
567+ return $ TypedValue True (ArrayLiteral ts) els
568+infer' (ObjectLiteral ps) = do
569+ ensureNoDuplicateProperties ps
570+ ts <- mapM (infer . snd) ps
571+ let fields = zipWith (\name (TypedValue _ _ t) -> (name, t)) (map fst ps) ts
572+ ty = TypeApp tyObject $ rowFromList (fields, REmpty)
573+ return $ TypedValue True (ObjectLiteral (zip (map fst ps) ts)) ty
574+infer' (ObjectUpdate o ps) = do
575+ ensureNoDuplicateProperties ps
576+ row <- fresh
577+ newVals <- zipWith (\(name, _) t -> (name, t)) ps <$> mapM (infer . snd) ps
578+ let newTys = map (\(name, TypedValue _ _ ty) -> (name, ty)) newVals
579+ oldTys <- zip (map fst ps) <$> replicateM (length ps) fresh
580+ let oldTy = TypeApp tyObject $ rowFromList (oldTys, row)
581+ o' <- TypedValue True <$> check o oldTy <*> pure oldTy
582+ return $ TypedValue True (ObjectUpdate o' newVals) $ TypeApp tyObject $ rowFromList (newTys, row)
583+infer' (Accessor prop val) = do
584+ typed@(TypedValue _ _ objTy) <- infer val
585+ propTy <- inferProperty objTy prop
586+ case propTy of
587+ Nothing -> do
588+ field <- fresh
589+ rest <- fresh
590+ _ <- subsumes Nothing objTy (TypeApp tyObject (RCons prop field rest))
591+ return $ TypedValue True (Accessor prop typed) field
592+ Just ty -> return $ TypedValue True (Accessor prop typed) ty
593+infer' (Abs (Left arg) ret) = do
594+ ty <- fresh
595+ Just moduleName <- checkCurrentModule <$> get
596+ bindLocalVariables moduleName [(arg, ty)] $ do
597+ body@(TypedValue _ _ bodyTy) <- infer' ret
598+ return $ TypedValue True (Abs (Left arg) body) $ function ty bodyTy
599+infer' (Abs (Right _) _) = error "Binder was not desugared"
600+infer' (App f arg) = do
601+ f'@(TypedValue _ _ ft) <- infer f
602+ (ret, app) <- checkFunctionApplication f' ft arg Nothing
603+ return $ TypedValue True app ret
604+infer' (Var var) = do
605+ Just moduleName <- checkCurrentModule <$> get
606+ ty <- introduceSkolemScope <=< replaceAllTypeSynonyms <=< lookupVariable moduleName $ var
607+ case ty of
608+ ConstrainedType constraints ty' -> do
609+ dicts <- getTypeClassDictionaries
610+ return $ TypedValue True (foldl App (Var var) (map (flip TypeClassDictionary (Just dicts)) constraints)) ty'
611+ _ -> return $ TypedValue True (Var var) ty
612+infer' v@(Constructor c) = do
613+ env <- getEnv
614+ case M.lookup c (dataConstructors env) of
615+ Nothing -> throwError . strMsg $ "Constructor " ++ show c ++ " is undefined"
616+ Just (_, ty) -> do ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
617+ return $ TypedValue True v ty'
618+infer' (Case vals binders) = do
619+ ts <- mapM infer vals
620+ ret <- fresh
621+ binders' <- checkBinders (map (\(TypedValue _ _ t) -> t) ts) ret binders
622+ return $ TypedValue True (Case ts binders') ret
623+infer' (IfThenElse cond th el) = do
624+ cond' <- check cond tyBoolean
625+ v2@(TypedValue _ _ t2) <- infer th
626+ v3@(TypedValue _ _ t3) <- infer el
627+ t2 =?= t3
628+ return $ TypedValue True (IfThenElse cond' v2 v3) t2
629+infer' (Let ds val) = do
630+ (ds', val'@(TypedValue _ _ valTy)) <- inferLetBinding [] ds val infer
631+ return $ TypedValue True (Let ds' val') valTy
632+infer' (TypedValue checkType val ty) = do
633+ Just moduleName <- checkCurrentModule <$> get
634+ kind <- liftCheck $ kindOf moduleName ty
635+ guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
636+ ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
637+ val' <- if checkType then check val ty' else return val
638+ return $ TypedValue True val' ty'
639+infer' (PositionedValue pos val) = rethrowWithPosition pos $ infer' val
640+infer' _ = error "Invalid argument to infer"
641+
642+inferLetBinding :: [Declaration] -> [Declaration] -> Value -> (Value -> UnifyT Type Check Value) -> UnifyT Type Check ([Declaration], Value)
643+inferLetBinding seen [] ret j = (,) seen <$> j ret
644+inferLetBinding seen (ValueDeclaration ident nameKind [] Nothing val : rest) ret j = do
645+ valTy <- fresh
646+ Just moduleName <- checkCurrentModule <$> get
647+ let dict = if isFunction val then M.singleton (moduleName, ident) (valTy, nameKind) else M.empty
648+ TypedValue _ val' valTy' <- bindNames dict $ infer val
649+ valTy =?= valTy'
650+ bindNames (M.singleton (moduleName, ident) (valTy', nameKind)) $ inferLetBinding (seen ++ [ValueDeclaration ident nameKind [] Nothing val']) rest ret j
651+inferLetBinding seen (BindingGroupDeclaration ds : rest) ret j = do
652+ Just moduleName <- checkCurrentModule <$> get
653+ (es, dict, untypedDict) <- typeDictionaryForBindingGroup moduleName (map (\(i, _, v) -> (i, v)) ds)
654+ ds' <- forM es $ \e -> do
655+ (ident, (val', _)) <- typeForBindingGroupElement moduleName e dict untypedDict
656+ return $ (ident, LocalVariable, val')
657+ bindNames dict $ inferLetBinding (seen ++ [BindingGroupDeclaration ds']) rest ret j
658+inferLetBinding seen (PositionedDeclaration pos d : ds) ret j = do
659+ ((d' : ds'), val') <- inferLetBinding seen (d : ds) ret j
660+ return (PositionedDeclaration pos d' : ds', val')
661+inferLetBinding _ _ _ _ = error "Invalid argument to inferLetBinding"
662+
663+-- |
664+-- Infer the type of a property inside a record with a given type
665+--
666+inferProperty :: Type -> String -> UnifyT Type Check (Maybe Type)
667+inferProperty (TypeApp obj row) prop | obj == tyObject = do
668+ let (props, _) = rowToList row
669+ return $ lookup prop props
670+inferProperty (SaturatedTypeSynonym name args) prop = do
671+ replaced <- introduceSkolemScope <=< expandTypeSynonym name $ args
672+ inferProperty replaced prop
673+inferProperty (ForAll ident ty _) prop = do
674+ replaced <- replaceVarWithUnknown ident ty
675+ inferProperty replaced prop
676+inferProperty _ _ = return Nothing
677+
678+-- |
679+-- Infer the types of variables brought into scope by a binder
680+--
681+inferBinder :: Type -> Binder -> UnifyT Type Check (M.Map Ident Type)
682+inferBinder _ NullBinder = return M.empty
683+inferBinder val (StringBinder _) = val =?= tyString >> return M.empty
684+inferBinder val (NumberBinder _) = val =?= tyNumber >> return M.empty
685+inferBinder val (BooleanBinder _) = val =?= tyBoolean >> return M.empty
686+inferBinder val (VarBinder name) = return $ M.singleton name val
687+inferBinder val (ConstructorBinder ctor binders) = do
688+ env <- getEnv
689+ case M.lookup ctor (dataConstructors env) of
690+ Just (_, ty) -> do
691+ (_, fn) <- instantiatePolyTypeWithUnknowns (error "Data constructor types cannot contain constraints") ty
692+ fn' <- replaceAllTypeSynonyms fn
693+ go binders fn'
694+ where
695+ go [] ty' = do
696+ _ <- subsumes Nothing val ty'
697+ return M.empty
698+ go (binder : binders') (TypeApp (TypeApp t obj) ret) | t == tyFunction =
699+ M.union <$> inferBinder obj binder <*> go binders' ret
700+ go _ _ = throwError . strMsg $ "Wrong number of arguments to constructor " ++ show ctor
701+ _ -> throwError . strMsg $ "Constructor " ++ show ctor ++ " is not defined"
702+inferBinder val (ObjectBinder props) = do
703+ row <- fresh
704+ rest <- fresh
705+ m1 <- inferRowProperties row rest props
706+ val =?= TypeApp tyObject row
707+ return m1
708+ where
709+ inferRowProperties :: Type -> Type -> [(String, Binder)] -> UnifyT Type Check (M.Map Ident Type)
710+ inferRowProperties nrow row [] = nrow =?= row >> return M.empty
711+ inferRowProperties nrow row ((name, binder):binders) = do
712+ propTy <- fresh
713+ m1 <- inferBinder propTy binder
714+ m2 <- inferRowProperties nrow (RCons name propTy row) binders
715+ return $ m1 `M.union` m2
716+inferBinder val (ArrayBinder binders) = do
717+ el <- fresh
718+ m1 <- M.unions <$> mapM (inferBinder el) binders
719+ val =?= TypeApp tyArray el
720+ return m1
721+inferBinder val (ConsBinder headBinder tailBinder) = do
722+ el <- fresh
723+ m1 <- inferBinder el headBinder
724+ m2 <- inferBinder val tailBinder
725+ val =?= TypeApp tyArray el
726+ return $ m1 `M.union` m2
727+inferBinder val (NamedBinder name binder) = do
728+ m <- inferBinder val binder
729+ return $ M.insert name val m
730+inferBinder val (PositionedBinder pos binder) =
731+ rethrowWithPosition pos $ inferBinder val binder
732+
733+-- |
734+-- Check the types of the return values in a set of binders in a case statement
735+--
736+checkBinders :: [Type] -> Type -> [CaseAlternative] -> UnifyT Type Check [CaseAlternative]
737+checkBinders _ _ [] = return []
738+checkBinders nvals ret (CaseAlternative binders grd val : bs) = do
739+ Just moduleName <- checkCurrentModule <$> get
740+ m1 <- M.unions <$> zipWithM inferBinder nvals binders
741+ r <- bindLocalVariables moduleName (M.toList m1) $ do
742+ val' <- TypedValue True <$> check val ret <*> pure ret
743+ case grd of
744+ Nothing -> return $ CaseAlternative binders Nothing val'
745+ Just g -> do
746+ g' <- check g tyBoolean
747+ return $ CaseAlternative binders (Just g') val'
748+ rs <- checkBinders nvals ret bs
749+ return $ r : rs
750+
751+-- |
752+-- Generate a new skolem constant
753+--
754+newSkolemConstant :: UnifyT Type Check Int
755+newSkolemConstant = runUnknown <$> fresh'
756+
757+-- |
758+-- Generate a new skolem scope
759+--
760+newSkolemScope :: UnifyT Type Check SkolemScope
761+newSkolemScope = SkolemScope . runUnknown <$> fresh'
762+
763+-- |
764+-- Skolemize a type variable by replacing its instances with fresh skolem constants
765+--
766+skolemize :: String -> Int -> SkolemScope -> Type -> Type
767+skolemize ident sko scope = replaceTypeVars ident (Skolem sko scope)
768+
769+-- |
770+-- Introduce skolem scope at every occurence of a ForAll
771+--
772+introduceSkolemScope :: Type -> UnifyT Type Check Type
773+introduceSkolemScope = everywhereM (mkM go)
774+ where
775+ go (ForAll ident ty Nothing) = ForAll ident ty <$> (Just <$> newSkolemScope)
776+ go other = return other
777+
778+-- |
779+-- Check the type of a value, rethrowing errors to provide a better error message
780+--
781+check :: Value -> Type -> UnifyT Type Check Value
782+check val ty = rethrow (mkErrorStack errorMessage (Just (ValueError val)) <>) $ check' val ty
783+ where
784+ errorMessage =
785+ "Error checking type of term " ++
786+ prettyPrintValue val ++
787+ " against type " ++
788+ prettyPrintType ty
789+
790+-- |
791+-- Check the type of a value
792+--
793+check' :: Value -> Type -> UnifyT Type Check Value
794+check' val (ForAll ident ty _) = do
795+ scope <- newSkolemScope
796+ sko <- newSkolemConstant
797+ let sk = skolemize ident sko scope ty
798+ val' <- check val sk
799+ return $ TypedValue True val' (ForAll ident ty (Just scope))
800+check' val t@(ConstrainedType constraints ty) = do
801+ dictNames <- forM constraints $ \(Qualified _ (ProperName className), _) -> do
802+ n <- liftCheck freshDictionaryName
803+ return $ Ident $ "__dict_" ++ className ++ "_" ++ show n
804+ val' <- withTypeClassDictionaries (zipWith (\name (className, instanceTy) ->
805+ TypeClassDictionaryInScope name className instanceTy Nothing TCDRegular) (map (Qualified Nothing) dictNames)
806+ constraints) $ check val ty
807+ return $ TypedValue True (foldr (Abs . Left) val' dictNames) t
808+check' val (SaturatedTypeSynonym name args) = do
809+ ty <- introduceSkolemScope <=< expandTypeSynonym name $ args
810+ check val ty
811+check' val u@(TUnknown _) = do
812+ val'@(TypedValue _ _ ty) <- infer val
813+ -- Don't unify an unknown with an inferred polytype
814+ (val'', ty') <- instantiatePolyTypeWithUnknowns val' ty
815+ ty' =?= u
816+ return $ TypedValue True val'' ty'
817+check' v@(NumericLiteral _) t | t == tyNumber =
818+ return $ TypedValue True v t
819+check' v@(StringLiteral _) t | t == tyString =
820+ return $ TypedValue True v t
821+check' v@(BooleanLiteral _) t | t == tyBoolean =
822+ return $ TypedValue True v t
823+check' (ArrayLiteral vals) t@(TypeApp a ty) = do
824+ a =?= tyArray
825+ array <- ArrayLiteral <$> forM vals (`check` ty)
826+ return $ TypedValue True array t
827+check' (Abs (Left arg) ret) ty@(TypeApp (TypeApp t argTy) retTy) | t == tyFunction = do
828+ Just moduleName <- checkCurrentModule <$> get
829+ ret' <- bindLocalVariables moduleName [(arg, argTy)] $ check ret retTy
830+ return $ TypedValue True (Abs (Left arg) ret') ty
831+check' (Abs (Right _) _) _ = error "Binder was not desugared"
832+check' (App f arg) ret = do
833+ f'@(TypedValue _ _ ft) <- infer f
834+ (_, app) <- checkFunctionApplication f' ft arg (Just ret)
835+ return $ TypedValue True app ret
836+check' v@(Var var) ty = do
837+ Just moduleName <- checkCurrentModule <$> get
838+ repl <- introduceSkolemScope <=< replaceAllTypeSynonyms <=< lookupVariable moduleName $ var
839+ ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
840+ v' <- subsumes (Just v) repl ty'
841+ case v' of
842+ Nothing -> throwError . strMsg $ "Unable to check type subsumption"
843+ Just v'' -> return $ TypedValue True v'' ty'
844+check' (TypedValue checkType val ty1) ty2 = do
845+ Just moduleName <- checkCurrentModule <$> get
846+ kind <- liftCheck $ kindOf moduleName ty1
847+ guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
848+ ty1' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty1
849+ val' <- subsumes (Just val) ty1' ty2
850+ case val' of
851+ Nothing -> throwError . strMsg $ "Unable to check type subsumption"
852+ Just val'' -> do
853+ val''' <- if checkType then check val'' ty1' else return val''
854+ return $ TypedValue checkType (TypedValue True val''' ty1) ty2
855+check' (Case vals binders) ret = do
856+ vals' <- mapM infer vals
857+ let ts = map (\(TypedValue _ _ t) -> t) vals'
858+ binders' <- checkBinders ts ret binders
859+ return $ TypedValue True (Case vals' binders') ret
860+check' (IfThenElse cond th el) ty = do
861+ cond' <- check cond tyBoolean
862+ th' <- check th ty
863+ el' <- check el ty
864+ return $ TypedValue True (IfThenElse cond' th' el') ty
865+check' (ObjectLiteral ps) t@(TypeApp obj row) | obj == tyObject = do
866+ ensureNoDuplicateProperties ps
867+ ps' <- checkProperties ps row False
868+ return $ TypedValue True (ObjectLiteral ps') t
869+check' (ObjectUpdate obj ps) t@(TypeApp o row) | o == tyObject = do
870+ ensureNoDuplicateProperties ps
871+ us <- zip (map fst ps) <$> replicateM (length ps) fresh
872+ let (propsToCheck, rest) = rowToList row
873+ propsToRemove = map fst ps
874+ remainingProps = filter (\(p, _) -> p `notElem` propsToRemove) propsToCheck
875+ obj' <- check obj (TypeApp tyObject (rowFromList (us ++ remainingProps, rest)))
876+ ps' <- checkProperties ps row True
877+ return $ TypedValue True (ObjectUpdate obj' ps') t
878+check' (Accessor prop val) ty = do
879+ rest <- fresh
880+ val' <- check val (TypeApp tyObject (RCons prop ty rest))
881+ return $ TypedValue True (Accessor prop val') ty
882+check' (Constructor c) ty = do
883+ env <- getEnv
884+ case M.lookup c (dataConstructors env) of
885+ Nothing -> throwError . strMsg $ "Constructor " ++ show c ++ " is undefined"
886+ Just (_, ty1) -> do
887+ repl <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty1
888+ _ <- subsumes Nothing repl ty
889+ return $ TypedValue True (Constructor c) ty
890+check' (Let ds val) ty = do
891+ (ds', val') <- inferLetBinding [] ds val (flip check ty)
892+ return $ TypedValue True (Let ds' val') ty
893+check' val ty | containsTypeSynonyms ty = do
894+ ty' <- introduceSkolemScope <=< expandAllTypeSynonyms $ ty
895+ check val ty'
896+check' (PositionedValue pos val) ty =
897+ rethrowWithPosition pos $ check val ty
898+check' val ty = throwError $ mkErrorStack ("Value does not have type " ++ prettyPrintType ty) (Just (ValueError val))
899+
900+containsTypeSynonyms :: Type -> Bool
901+containsTypeSynonyms = everything (||) (mkQ False go) where
902+ go (SaturatedTypeSynonym _ _) = True
903+ go _ = False
904+
905+-- |
906+-- Check the type of a collection of named record fields
907+--
908+-- The @lax@ parameter controls whether or not every record member has to be provided. For object updates, this is not the case.
909+--
910+checkProperties :: [(String, Value)] -> Type -> Bool -> UnifyT Type Check [(String, Value)]
911+checkProperties ps row lax = let (ts, r') = rowToList row in go ps ts r' where
912+ go [] [] REmpty = return []
913+ go [] [] u@(TUnknown _) = do u =?= REmpty
914+ return []
915+ go [] [] (Skolem _ _) | lax = return []
916+ go [] ((p, _): _) _ | lax = return []
917+ | otherwise = throwError $ mkErrorStack ("Object does not have property " ++ p) (Just (ValueError (ObjectLiteral ps)))
918+ go ((p,_):_) [] REmpty = throwError $ mkErrorStack ("Property " ++ p ++ " is not present in closed object type " ++ prettyPrintRow row) (Just (ValueError (ObjectLiteral ps)))
919+ go ((p,v):ps') [] u@(TUnknown _) = do
920+ v'@(TypedValue _ _ ty) <- infer v
921+ rest <- fresh
922+ u =?= RCons p ty rest
923+ ps'' <- go ps' [] rest
924+ return $ (p, v') : ps''
925+ go ((p,v):ps') ts r =
926+ case lookup p ts of
927+ Nothing -> do
928+ v'@(TypedValue _ _ ty) <- infer v
929+ rest <- fresh
930+ r =?= RCons p ty rest
931+ ps'' <- go ps' ts rest
932+ return $ (p, v') : ps''
933+ Just ty -> do
934+ v' <- check v ty
935+ ps'' <- go ps' (delete (p, ty) ts) r
936+ return $ (p, v') : ps''
937+ go _ _ _ = throwError $ mkErrorStack ("Object does not have type " ++ prettyPrintType (TypeApp tyObject row)) (Just (ValueError (ObjectLiteral ps)))
938+
939+-- |
940+-- Check the type of a function application, rethrowing errors to provide a better error message
941+--
942+checkFunctionApplication :: Value -> Type -> Value -> Maybe Type -> UnifyT Type Check (Type, Value)
943+checkFunctionApplication fn fnTy arg ret = rethrow (mkErrorStack errorMessage (Just (ValueError fn)) <>) $ checkFunctionApplication' fn fnTy arg ret
944+ where
945+ errorMessage = "Error applying function of type "
946+ ++ prettyPrintType fnTy
947+ ++ " to argument " ++ prettyPrintValue arg
948+
949+-- |
950+-- Check the type of a function application
951+--
952+checkFunctionApplication' :: Value -> Type -> Value -> Maybe Type -> UnifyT Type Check (Type, Value)
953+checkFunctionApplication' fn (TypeApp (TypeApp tyFunction' argTy) retTy) arg ret = do
954+ tyFunction' =?= tyFunction
955+ _ <- maybe (return Nothing) (subsumes Nothing retTy) ret
956+ subst <- unifyCurrentSubstitution <$> UnifyT get
957+ arg' <- check arg (subst $? argTy)
958+ return (retTy, App fn arg')
959+checkFunctionApplication' fn (ForAll ident ty _) arg ret = do
960+ replaced <- replaceVarWithUnknown ident ty
961+ checkFunctionApplication fn replaced arg ret
962+checkFunctionApplication' fn u@(TUnknown _) arg ret = do
963+ arg' <- do
964+ TypedValue _ arg' t <- infer arg
965+ (arg'', t') <- instantiatePolyTypeWithUnknowns arg' t
966+ return $ TypedValue True arg'' t'
967+ let ty = (\(TypedValue _ _ t) -> t) arg'
968+ ret' <- maybe fresh return ret
969+ u =?= function ty ret'
970+ return (ret', App fn arg')
971+checkFunctionApplication' fn (SaturatedTypeSynonym name tyArgs) arg ret = do
972+ ty <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
973+ checkFunctionApplication fn ty arg ret
974+checkFunctionApplication' fn (ConstrainedType constraints fnTy) arg ret = do
975+ dicts <- getTypeClassDictionaries
976+ checkFunctionApplication' (foldl App fn (map (flip TypeClassDictionary (Just dicts)) constraints)) fnTy arg ret
977+checkFunctionApplication' _ fnTy arg _ = throwError . strMsg $ "Cannot apply a function of type "
978+ ++ prettyPrintType fnTy
979+ ++ " to argument " ++ prettyPrintValue arg
980+
981+-- |
982+-- Check whether one type subsumes another, rethrowing errors to provide a better error message
983+--
984+subsumes :: Maybe Value -> Type -> Type -> UnifyT Type Check (Maybe Value)
985+subsumes val ty1 ty2 = rethrow (mkErrorStack errorMessage (ValueError <$> val) <>) $ subsumes' val ty1 ty2
986+ where
987+ errorMessage = "Error checking that type "
988+ ++ prettyPrintType ty1
989+ ++ " subsumes type "
990+ ++ prettyPrintType ty2
991+
992+-- |
993+-- Check whether one type subsumes another
994+--
995+subsumes' :: Maybe Value -> Type -> Type -> UnifyT Type Check (Maybe Value)
996+subsumes' val (ForAll ident ty1 _) ty2 = do
997+ replaced <- replaceVarWithUnknown ident ty1
998+ subsumes val replaced ty2
999+subsumes' val ty1 (ForAll ident ty2 sco) =
1000+ case sco of
1001+ Just sco' -> do
1002+ sko <- newSkolemConstant
1003+ let sk = skolemize ident sko sco' ty2
1004+ subsumes val ty1 sk
1005+ Nothing -> throwError . strMsg $ "Skolem variable scope is unspecified"
1006+subsumes' val (TypeApp (TypeApp f1 arg1) ret1) (TypeApp (TypeApp f2 arg2) ret2) | f1 == tyFunction && f2 == tyFunction = do
1007+ _ <- subsumes Nothing arg2 arg1
1008+ _ <- subsumes Nothing ret1 ret2
1009+ return val
1010+subsumes' val (SaturatedTypeSynonym name tyArgs) ty2 = do
1011+ ty1 <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
1012+ subsumes val ty1 ty2
1013+subsumes' val ty1 (SaturatedTypeSynonym name tyArgs) = do
1014+ ty2 <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
1015+ subsumes val ty1 ty2
1016+subsumes' (Just val) (ConstrainedType constraints ty1) ty2 = do
1017+ dicts <- getTypeClassDictionaries
1018+ _ <- subsumes' Nothing ty1 ty2
1019+ return . Just $ foldl App val (map (flip TypeClassDictionary (Just dicts)) constraints)
1020+subsumes' val (TypeApp f1 r1) (TypeApp f2 r2) | f1 == tyObject && f2 == tyObject = do
1021+ let
1022+ (ts1, r1') = rowToList r1
1023+ (ts2, r2') = rowToList r2
1024+ ts1' = sortBy (comparing fst) ts1
1025+ ts2' = sortBy (comparing fst) ts2
1026+ go ts1' ts2' r1' r2'
1027+ return val
1028+ where
1029+ go [] ts2 r1' r2' = r1' =?= rowFromList (ts2, r2')
1030+ go ts1 [] r1' r2' = r2' =?= rowFromList (ts1, r1')
1031+ go ((p1, ty1) : ts1) ((p2, ty2) : ts2) r1' r2'
1032+ | p1 == p2 = do _ <- subsumes Nothing ty1 ty2
1033+ go ts1 ts2 r1' r2'
1034+ | p1 < p2 = do rest <- fresh
1035+ r2' =?= RCons p1 ty1 rest
1036+ go ts1 ((p2, ty2) : ts2) r1' rest
1037+ | otherwise = do rest <- fresh
1038+ r1' =?= RCons p2 ty2 rest
1039+ go ((p1, ty1) : ts1) ts2 rest r2'
1040+subsumes' val ty1 ty2@(TypeApp obj _) | obj == tyObject = subsumes val ty2 ty1
1041+subsumes' val ty1 ty2 = do
1042+ ty1 =?= ty2
1043+ return val
1044+
1045+
1046+