@@ -0,0 +1,1125 @@
1+-----------------------------------------------------------------------------
2+--
3+-- Module : Language.PureScript.TypeChecker.Types
4+-- Copyright : (c) Phil Freeman 2013
5+-- License : MIT
6+--
7+-- Maintainer : Phil Freeman <paf31@cantab.net>
8+-- Stability : experimental
9+-- Portability :
10+--
11+-- |
12+-- This module implements the type checker
13+--
14+-----------------------------------------------------------------------------
15+
16+{-# OPTIONS_GHC -fno-warn-orphans #-}
17+{-# LANGUAGE FlexibleInstances #-}
18+{-# LANGUAGE FlexibleContexts #-}
19+{-# LANGUAGE MultiParamTypeClasses #-}
20+
21+module Language.PureScript.TypeChecker.Types (
22+ typesOf
23+) where
24+
25+{-
26+ The following functions represent the corresponding type checking judgements:
27+
28+ infer
29+ Synthesize a type for a value
30+
31+ check
32+ Check a value has a given type
33+
34+ checkProperties
35+ Check an object with a given type contains specified properties
36+
37+ checkFunctionApplication
38+ Check a function of a given type returns a value of another type when applied to its arguments
39+
40+ subsumes
41+ Check a type subsumes another type
42+-}
43+
44+import Data.List
45+import Data.Maybe (maybeToList, isNothing, isJust, fromMaybe)
46+import Data.Function (on)
47+import Data.Ord (comparing)
48+import Data.Monoid
49+
50+import Language.PureScript.Declarations
51+import Language.PureScript.Types
52+import Language.PureScript.Kinds
53+import Language.PureScript.Names
54+import Language.PureScript.TypeClassDictionaries
55+import Language.PureScript.TypeChecker.Monad
56+import Language.PureScript.TypeChecker.Kinds
57+import Language.PureScript.TypeChecker.Synonyms
58+import Language.PureScript.Pretty
59+import Language.PureScript.Environment
60+import Language.PureScript.Errors
61+import qualified Language.PureScript.Constants as C
62+
63+import Control.Monad.State
64+import Control.Monad.Error
65+import Control.Monad.Unify
66+
67+import Control.Applicative
68+import Control.Arrow (Arrow(..))
69+
70+import qualified Data.Map as M
71+import qualified Data.HashMap.Strict as H
72+
73+instance Partial Type where
74+ unknown = TUnknown
75+ isUnknown (TUnknown u) = Just u
76+ isUnknown _ = Nothing
77+ unknowns = everythingOnTypes (++) go
78+ where
79+ go (TUnknown u) = [u]
80+ go _ = []
81+ ($?) sub = everywhereOnTypes go
82+ where
83+ go t@(TUnknown u) = case H.lookup u (runSubstitution sub) of
84+ Nothing -> t
85+ Just t' -> t'
86+ go other = other
87+
88+instance Unifiable Check Type where
89+ (=?=) = unifyTypes
90+
91+-- |
92+-- Unify two types, updating the current substitution
93+--
94+unifyTypes :: Type -> Type -> UnifyT Type Check ()
95+unifyTypes t1 t2 = rethrow (mkErrorStack ("Error unifying type " ++ prettyPrintType t1 ++ " with type " ++ prettyPrintType t2) Nothing <>) $
96+ unifyTypes' t1 t2
97+ where
98+ unifyTypes' (TUnknown u1) (TUnknown u2) | u1 == u2 = return ()
99+ unifyTypes' (TUnknown u) t = u =:= t
100+ unifyTypes' t (TUnknown u) = u =:= t
101+ unifyTypes' (SaturatedTypeSynonym name args) ty = do
102+ ty1 <- introduceSkolemScope <=< expandTypeSynonym name $ args
103+ ty1 `unifyTypes` ty
104+ unifyTypes' ty s@(SaturatedTypeSynonym _ _) = s `unifyTypes` ty
105+ unifyTypes' (ForAll ident1 ty1 sc1) (ForAll ident2 ty2 sc2) =
106+ case (sc1, sc2) of
107+ (Just sc1', Just sc2') -> do
108+ sko <- newSkolemConstant
109+ let sk1 = skolemize ident1 sko sc1' ty1
110+ let sk2 = skolemize ident2 sko sc2' ty2
111+ sk1 `unifyTypes` sk2
112+ _ -> error "Skolemized type variable was not given a scope"
113+ unifyTypes' (ForAll ident ty1 (Just sc)) ty2 = do
114+ sko <- newSkolemConstant
115+ let sk = skolemize ident sko sc ty1
116+ sk `unifyTypes` ty2
117+ unifyTypes' ForAll{} _ = throwError . strMsg $ "Skolem variable scope is unspecified"
118+ unifyTypes' ty f@ForAll{} = f `unifyTypes` ty
119+ unifyTypes' (TypeVar v1) (TypeVar v2) | v1 == v2 = return ()
120+ unifyTypes' (TypeConstructor c1) (TypeConstructor c2) =
121+ guardWith (strMsg ("Cannot unify " ++ show c1 ++ " with " ++ show c2 ++ ".")) (c1 == c2)
122+ unifyTypes' (TypeApp t3 t4) (TypeApp t5 t6) = do
123+ t3 `unifyTypes` t5
124+ t4 `unifyTypes` t6
125+ unifyTypes' (Skolem _ s1 _) (Skolem _ s2 _) | s1 == s2 = return ()
126+ unifyTypes' r1@RCons{} r2 = unifyRows r1 r2
127+ unifyTypes' r1 r2@RCons{} = unifyRows r1 r2
128+ unifyTypes' r1@REmpty r2 = unifyRows r1 r2
129+ unifyTypes' r1 r2@REmpty = unifyRows r1 r2
130+ unifyTypes' t@(ConstrainedType _ _) _ = throwError . strMsg $ "Attempted to unify a constrained type " ++ prettyPrintType t ++ " with another type."
131+ unifyTypes' t3 t4@(ConstrainedType _ _) = unifyTypes' t4 t3
132+ unifyTypes' t3 t4 = throwError . strMsg $ "Cannot unify " ++ prettyPrintType t3 ++ " with " ++ prettyPrintType t4 ++ "."
133+
134+-- |
135+-- Unify two rows, updating the current substitution
136+--
137+-- Common labels are first identified, and unified. Remaining labels and types are unified with a
138+-- trailing row unification variable, if appropriate, otherwise leftover labels result in a unification
139+-- error.
140+--
141+unifyRows :: Type -> Type -> UnifyT Type Check ()
142+unifyRows r1 r2 =
143+ let
144+ (s1, r1') = rowToList r1
145+ (s2, r2') = rowToList r2
146+ int = [ (t1, t2) | (name, t1) <- s1, (name', t2) <- s2, name == name' ]
147+ sd1 = [ (name, t1) | (name, t1) <- s1, name `notElem` map fst s2 ]
148+ sd2 = [ (name, t2) | (name, t2) <- s2, name `notElem` map fst s1 ]
149+ in do
150+ forM_ int (uncurry (=?=))
151+ unifyRows' sd1 r1' sd2 r2'
152+ where
153+ unifyRows' :: [(String, Type)] -> Type -> [(String, Type)] -> Type -> UnifyT Type Check ()
154+ unifyRows' [] (TUnknown u) sd r = u =:= rowFromList (sd, r)
155+ unifyRows' sd r [] (TUnknown u) = u =:= rowFromList (sd, r)
156+ unifyRows' ((name, ty):row) r others u@(TUnknown un) = do
157+ occursCheck un ty
158+ forM_ row $ \(_, t) -> occursCheck un t
159+ u' <- fresh
160+ u =?= RCons name ty u'
161+ unifyRows' row r others u'
162+ unifyRows' [] REmpty [] REmpty = return ()
163+ unifyRows' [] (TypeVar v1) [] (TypeVar v2) | v1 == v2 = return ()
164+ unifyRows' [] (Skolem _ s1 _) [] (Skolem _ s2 _) | s1 == s2 = return ()
165+ unifyRows' sd3 r3 sd4 r4 = throwError . strMsg $ "Cannot unify (" ++ prettyPrintRow (rowFromList (sd3, r3)) ++ ") with (" ++ prettyPrintRow (rowFromList (sd4, r4)) ++ ")"
166+
167+-- |
168+-- Infer the types of multiple mutually-recursive values, and return elaborated values including
169+-- type class dictionaries and type annotations.
170+--
171+typesOf :: Maybe ModuleName -> ModuleName -> [(Ident, Expr)] -> Check [(Ident, (Expr, Type))]
172+typesOf mainModuleName moduleName vals = do
173+ tys <- fmap tidyUp . liftUnify $ do
174+ (es, dict, untypedDict) <- typeDictionaryForBindingGroup moduleName vals
175+ forM es $ \e -> do
176+ triple@(_, (_, ty)) <- typeForBindingGroupElement moduleName e dict untypedDict
177+ -- If --main is enabled, need to check that `main` has type Eff eff a for some eff, a
178+ when (Just moduleName == mainModuleName && fst e == Ident C.main) $ do
179+ [eff, a] <- replicateM 2 fresh
180+ ty =?= TypeApp (TypeApp (TypeConstructor (Qualified (Just (ModuleName [ProperName "Control", ProperName "Monad", ProperName "Eff"])) (ProperName "Eff"))) eff) a
181+ return triple
182+
183+ forM tys $ \(ident, (val, ty)) -> do
184+ -- Replace type class dictionary placeholders with actual dictionaries
185+ val' <- replaceTypeClassDictionaries moduleName val
186+ -- Check skolem variables did not escape their scope
187+ skolemEscapeCheck val'
188+ -- Remove type synonyms placeholders, remove duplicate row fields, and replace
189+ -- top-level unification variables with named type variables.
190+ let val'' = overTypes (desaturateAllTypeSynonyms . setifyAll) val'
191+ ty' = varIfUnknown . desaturateAllTypeSynonyms . setifyAll $ ty
192+ return (ident, (val'', ty'))
193+ where
194+ -- Apply the substitution that was returned from runUnify to both types and (type-annotated) values
195+ tidyUp (ts, sub) = map (\(i, (val, ty)) -> (i, (overTypes (sub $?) val, sub $? ty))) ts
196+
197+typeDictionaryForBindingGroup :: ModuleName -> [(Ident, Expr)] -> UnifyT Type Check ([(Ident, (Expr, Maybe (Type, Bool)))], M.Map (ModuleName, Ident) (Type, NameKind, NameVisibility), [(Ident, Type)])
198+typeDictionaryForBindingGroup moduleName vals = do
199+ let
200+ -- Map each declaration to a name/value pair, with an optional type, if the declaration is typed
201+ es = map isTyped vals
202+ -- Filter the typed and untyped declarations
203+ typed = filter (isJust . snd . snd) es
204+ untyped = filter (isNothing . snd . snd) es
205+ -- Make a map of names to typed declarations
206+ typedDict = map (\(ident, (_, Just (ty, _))) -> (ident, ty)) typed
207+
208+ -- Create fresh unification variables for the types of untyped declarations
209+ untypedNames <- replicateM (length untyped) fresh
210+
211+ let
212+ -- Make a map of names to the unification variables of untyped declarations
213+ untypedDict = zip (map fst untyped) untypedNames
214+ -- Create the dictionary of all name/type pairs, which will be added to the environment during type checking
215+ dict = M.fromList (map (\(ident, ty) -> ((moduleName, ident), (ty, LocalVariable, Undefined))) $ typedDict ++ untypedDict)
216+ return (es, dict, untypedDict)
217+
218+typeForBindingGroupElement :: ModuleName -> (Ident, (Expr, Maybe (Type, Bool))) -> M.Map (ModuleName, Ident) (Type, NameKind, NameVisibility) -> [(Ident, Type)] -> UnifyT Type Check (Ident, (Expr, Type))
219+typeForBindingGroupElement moduleName el dict untypedDict =
220+ -- If the declaration is a function, it has access to other values in the binding group.
221+ -- If not, the generated code might fail at runtime since those values might be undefined.
222+ case el of
223+ -- Typed declarations
224+ (ident, (val', Just (ty, checkType))) -> do
225+ -- Kind check
226+ kind <- liftCheck $ kindOf moduleName ty
227+ guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
228+ -- Check the type with the new names in scope
229+ ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
230+ val'' <- if checkType
231+ then bindNames dict $ TypedValue True <$> check val' ty' <*> pure ty'
232+ else return (TypedValue False val' ty')
233+ return (ident, (val'', ty'))
234+ -- Untyped declarations
235+ (ident, (val', Nothing)) -> do
236+ -- Infer the type with the new names in scope
237+ TypedValue _ val'' ty <- bindNames dict $ infer val'
238+ ty =?= fromMaybe (error "name not found in dictionary") (lookup ident untypedDict)
239+ return (ident, (TypedValue True val'' ty, ty))
240+
241+-- |
242+-- Check if a value contains a type annotation
243+--
244+isTyped :: (Ident, Expr) -> (Ident, (Expr, Maybe (Type, Bool)))
245+isTyped (name, TypedValue checkType value ty) = (name, (value, Just (ty, checkType)))
246+isTyped (name, value) = (name, (value, Nothing))
247+
248+-- |
249+-- Map a function over type annotations appearing inside a value
250+--
251+overTypes :: (Type -> Type) -> Expr -> Expr
252+overTypes f = let (_, f', _) = everywhereOnValues id g id in f'
253+ where
254+ g :: Expr -> Expr
255+ g (TypedValue checkTy val t) = TypedValue checkTy val (f t)
256+ g (TypeClassDictionary b (nm, tys) sco) = TypeClassDictionary b (nm, map f tys) sco
257+ g other = other
258+
259+-- |
260+-- Replace type class dictionary placeholders with inferred type class dictionaries
261+--
262+replaceTypeClassDictionaries :: ModuleName -> Expr -> Check Expr
263+replaceTypeClassDictionaries mn =
264+ let (_, f, _) = everywhereOnValuesTopDownM return go return
265+ in f
266+ where
267+ go (TypeClassDictionary trySuperclasses constraint dicts) = do
268+ env <- getEnv
269+ entails env mn dicts constraint trySuperclasses
270+ go other = return other
271+
272+-- |
273+-- A simplified representation of expressions which are used to represent type
274+-- class dictionaries at runtime, which can be compared for equality
275+--
276+data DictionaryValue
277+ -- |
278+ -- A dictionary which is brought into scope by a local constraint
279+ --
280+ = LocalDictionaryValue (Qualified Ident)
281+ -- |
282+ -- A dictionary which is brought into scope by an instance declaration
283+ --
284+ | GlobalDictionaryValue (Qualified Ident)
285+ -- |
286+ -- A dictionary which depends on other dictionaries
287+ --
288+ | DependentDictionaryValue (Qualified Ident) [DictionaryValue]
289+ -- |
290+ -- A subclass dictionary
291+ --
292+ | SubclassDictionaryValue DictionaryValue (Qualified ProperName) Integer
293+ deriving (Show, Ord, Eq)
294+
295+-- |
296+-- Check that the current set of type class dictionaries entail the specified type class goal, and, if so,
297+-- return a type class dictionary reference.
298+--
299+entails :: Environment -> ModuleName -> [TypeClassDictionaryInScope] -> (Qualified ProperName, [Type]) -> Bool -> Check Expr
300+entails env moduleName context = solve (sortedNubBy canonicalizeDictionary (filter filterModule context))
301+ where
302+ sortedNubBy :: (Ord k) => (v -> k) -> [v] -> [v]
303+ sortedNubBy f vs = M.elems (M.fromList (map (f &&& id) vs))
304+
305+ -- Filter out type dictionaries which are in scope in the current module
306+ filterModule :: TypeClassDictionaryInScope -> Bool
307+ filterModule (TypeClassDictionaryInScope { tcdName = Qualified (Just mn) _ }) | mn == moduleName = True
308+ filterModule (TypeClassDictionaryInScope { tcdName = Qualified Nothing _ }) = True
309+ filterModule _ = False
310+
311+ solve context' (className, tys) trySuperclasses =
312+ let
313+ dicts = go trySuperclasses className tys
314+ in case sortedNubBy dictTrace (chooseSimplestDictionaries dicts) of
315+ [] -> throwError . strMsg $ "No instance found for " ++ show className ++ " " ++ unwords (map prettyPrintTypeAtom tys)
316+ [_] -> return $ dictionaryValueToValue $ head dicts
317+ _ -> throwError . strMsg $ "Overlapping instances found for " ++ show className ++ " " ++ unwords (map prettyPrintTypeAtom tys)
318+ where
319+ go trySuperclasses' className' tys' =
320+ -- Look for regular type instances
321+ [ mkDictionary (canonicalizeDictionary tcd) args
322+ | tcd <- context'
323+ -- Make sure the type class name matches the one we are trying to satisfy
324+ , className' == tcdClassName tcd
325+ -- Make sure the type unifies with the type in the type instance definition
326+ , subst <- maybeToList . (>>= verifySubstitution) . fmap concat $ zipWithM (typeHeadsAreEqual moduleName env) tys' (tcdInstanceTypes tcd)
327+ -- Solve any necessary subgoals
328+ , args <- solveSubgoals subst (tcdDependencies tcd) ] ++
329+
330+ -- Look for implementations via superclasses
331+ [ SubclassDictionaryValue suDict superclass index
332+ | trySuperclasses'
333+ , (subclassName, (args, _, implies)) <- M.toList (typeClasses env)
334+ -- Try each superclass
335+ , (index, (superclass, suTyArgs)) <- zip [0..] implies
336+ -- Make sure the type class name matches the superclass name
337+ , className' == superclass
338+ -- Make sure the types unify with the types in the superclass implication
339+ , subst <- maybeToList . (>>= verifySubstitution) . fmap concat $ zipWithM (typeHeadsAreEqual moduleName env) tys' suTyArgs
340+ -- Finally, satisfy the subclass constraint
341+ , args' <- maybeToList $ mapM (flip lookup subst) args
342+ , suDict <- go True subclassName args' ]
343+
344+ -- Create dictionaries for subgoals which still need to be solved by calling go recursively
345+ -- E.g. the goal (Show a, Show b) => Show (Either a b) can be satisfied if the current type
346+ -- unifies with Either a b, and we can satisfy the subgoals Show a and Show b recursively.
347+ solveSubgoals :: [(String, Type)] -> Maybe [(Qualified ProperName, [Type])] -> [Maybe [DictionaryValue]]
348+ solveSubgoals _ Nothing = return Nothing
349+ solveSubgoals subst (Just subgoals) = do
350+ dict <- mapM (uncurry (go True) . second (map (replaceAllTypeVars subst))) subgoals
351+ return $ Just dict
352+ -- Make a dictionary from subgoal dictionaries by applying the correct function
353+ mkDictionary :: Qualified Ident -> Maybe [DictionaryValue] -> DictionaryValue
354+ mkDictionary fnName Nothing = LocalDictionaryValue fnName
355+ mkDictionary fnName (Just []) = GlobalDictionaryValue fnName
356+ mkDictionary fnName (Just dicts) = DependentDictionaryValue fnName dicts
357+ -- Turn a DictionaryValue into a Expr
358+ dictionaryValueToValue :: DictionaryValue -> Expr
359+ dictionaryValueToValue (LocalDictionaryValue fnName) = Var fnName
360+ dictionaryValueToValue (GlobalDictionaryValue fnName) = App (Var fnName) valUnit
361+ dictionaryValueToValue (DependentDictionaryValue fnName dicts) = foldl App (Var fnName) (map dictionaryValueToValue dicts)
362+ dictionaryValueToValue (SubclassDictionaryValue dict superclassName index) =
363+ App (Accessor (C.__superclass_ ++ show superclassName ++ "_" ++ show index)
364+ (dictionaryValueToValue dict))
365+ valUnit
366+ -- Ensure that a substitution is valid
367+ verifySubstitution :: [(String, Type)] -> Maybe [(String, Type)]
368+ verifySubstitution subst = do
369+ let grps = groupBy ((==) `on` fst) subst
370+ guard (all (pairwise (unifiesWith env) . map snd) grps)
371+ return $ map head grps
372+ -- Choose the simplest DictionaryValues from a list of candidates
373+ -- The reason for this function is as follows:
374+ -- When considering overlapping instances, we don't want to consider the same dictionary
375+ -- to be an overlap of itself when obtained as a superclass of another class.
376+ -- Observing that we probably don't want to select a superclass instance when an instance
377+ -- is available directly, and that there is no way for a superclass instance to actually
378+ -- introduce an overlap that wouldn't have been there already, we simply remove dictionaries
379+ -- obtained as superclass instances if there are simpler instances available.
380+ chooseSimplestDictionaries :: [DictionaryValue] -> [DictionaryValue]
381+ chooseSimplestDictionaries ds = case filter isSimpleDictionaryValue ds of
382+ [] -> ds
383+ simple -> simple
384+ isSimpleDictionaryValue SubclassDictionaryValue{} = False
385+ isSimpleDictionaryValue (DependentDictionaryValue _ ds) = all isSimpleDictionaryValue ds
386+ isSimpleDictionaryValue _ = True
387+ -- |
388+ -- Get the "trace" of a DictionaryValue - that is, remove all SubclassDictionaryValue
389+ -- data constructors
390+ --
391+ dictTrace :: DictionaryValue -> DictionaryValue
392+ dictTrace (DependentDictionaryValue fnName dicts) = DependentDictionaryValue fnName $ map dictTrace dicts
393+ dictTrace (SubclassDictionaryValue dict _ _) = dictTrace dict
394+ dictTrace other = other
395+
396+ valUnit :: Expr
397+ valUnit = Var (Qualified (Just (ModuleName [ProperName C.prelude])) (Ident C.unit))
398+
399+-- |
400+-- Check all values in a list pairwise match a predicate
401+--
402+pairwise :: (a -> a -> Bool) -> [a] -> Bool
403+pairwise _ [] = True
404+pairwise _ [_] = True
405+pairwise p (x : xs) = all (p x) xs && pairwise p xs
406+
407+-- |
408+-- Check that two types unify
409+--
410+unifiesWith :: Environment -> Type -> Type -> Bool
411+unifiesWith _ (TUnknown u1) (TUnknown u2) | u1 == u2 = True
412+unifiesWith _ (Skolem _ s1 _) (Skolem _ s2 _) | s1 == s2 = True
413+unifiesWith _ (TypeVar v1) (TypeVar v2) | v1 == v2 = True
414+unifiesWith _ (TypeConstructor c1) (TypeConstructor c2) | c1 == c2 = True
415+unifiesWith e (TypeApp h1 t1) (TypeApp h2 t2) = unifiesWith e h1 h2 && unifiesWith e t1 t2
416+unifiesWith e (SaturatedTypeSynonym name args) t2 =
417+ case expandTypeSynonym' e name args of
418+ Left _ -> False
419+ Right t1 -> unifiesWith e t1 t2
420+unifiesWith e t1 t2@(SaturatedTypeSynonym _ _) = unifiesWith e t2 t1
421+unifiesWith _ _ _ = False
422+
423+-- |
424+-- Check whether the type heads of two types are equal (for the purposes of type class dictionary lookup),
425+-- and return a substitution from type variables to types which makes the type heads unify.
426+--
427+typeHeadsAreEqual :: ModuleName -> Environment -> Type -> Type -> Maybe [(String, Type)]
428+typeHeadsAreEqual _ _ (Skolem _ s1 _) (Skolem _ s2 _) | s1 == s2 = Just []
429+typeHeadsAreEqual _ _ t (TypeVar v) = Just [(v, t)]
430+typeHeadsAreEqual _ _ (TypeConstructor c1) (TypeConstructor c2) | c1 == c2 = Just []
431+typeHeadsAreEqual m e (TypeApp h1 t1) (TypeApp h2 t2) = (++) <$> typeHeadsAreEqual m e h1 h2 <*> typeHeadsAreEqual m e t1 t2
432+typeHeadsAreEqual m e (SaturatedTypeSynonym name args) t2 = case expandTypeSynonym' e name args of
433+ Left _ -> Nothing
434+ Right t1 -> typeHeadsAreEqual m e t1 t2
435+typeHeadsAreEqual _ _ _ _ = Nothing
436+
437+-- |
438+-- Ensure skolem variables do not escape their scope
439+--
440+skolemEscapeCheck :: Expr -> Check ()
441+skolemEscapeCheck (TypedValue False _ _) = return ()
442+skolemEscapeCheck root@TypedValue{} =
443+ -- Every skolem variable is created when a ForAll type is skolemized.
444+ -- This determines the scope of that skolem variable, which is copied from the SkolemScope
445+ -- field of the ForAll constructor.
446+ -- We traverse the tree top-down, and collect any SkolemScopes introduced by ForAlls.
447+ -- If a Skolem is encountered whose SkolemScope is not in the current list, we have found
448+ -- an escaped skolem variable.
449+ let (_, f, _, _, _) = everythingWithContextOnValues [] [] (++) def go def def def
450+ in case f root of
451+ [] -> return ()
452+ ((binding, val) : _) -> throwError $ mkErrorStack ("Rigid/skolem type variable " ++ maybe "" (("bound by " ++) . prettyPrintValue) binding ++ " has escaped.") (Just (ExprError val))
453+ where
454+ def s _ = (s, [])
455+
456+ go :: [(SkolemScope, Expr)] -> Expr -> ([(SkolemScope, Expr)], [(Maybe Expr, Expr)])
457+ go scos val@(TypedValue _ _ (ForAll _ _ (Just sco))) = ((sco, val) : scos, [])
458+ go scos val@(TypedValue _ _ ty) = case collectSkolems ty \\ map fst scos of
459+ (sco : _) -> (scos, [(findBindingScope sco, val)])
460+ _ -> (scos, [])
461+ where
462+ collectSkolems :: Type -> [SkolemScope]
463+ collectSkolems = nub . everythingOnTypes (++) collect
464+ where
465+ collect (Skolem _ _ scope) = [scope]
466+ collect _ = []
467+ go scos _ = (scos, [])
468+ findBindingScope :: SkolemScope -> Maybe Expr
469+ findBindingScope sco =
470+ let (_, f, _, _, _) = everythingOnValues mappend (const mempty) go' (const mempty) (const mempty) (const mempty)
471+ in getFirst $ f root
472+ where
473+ go' val@(TypedValue _ _ (ForAll _ _ (Just sco'))) | sco == sco' = First (Just val)
474+ go' _ = mempty
475+skolemEscapeCheck val = throwError $ mkErrorStack "Untyped value passed to skolemEscapeCheck" (Just (ExprError val))
476+
477+-- |
478+-- Ensure a row contains no duplicate labels
479+--
480+setify :: Type -> Type
481+setify = rowFromList . first (M.toList . M.fromList) . rowToList
482+
483+-- |
484+-- \"Setify\" all rows occuring inside a value
485+--
486+setifyAll :: Type -> Type
487+setifyAll = everywhereOnTypes setify
488+
489+-- |
490+-- Replace outermost unsolved unification variables with named type variables
491+--
492+varIfUnknown :: Type -> Type
493+varIfUnknown ty =
494+ let unks = nub $ unknowns ty
495+ toName = (:) 't' . show
496+ ty' = everywhereOnTypes typeToVar ty
497+ typeToVar :: Type -> Type
498+ typeToVar (TUnknown u) = TypeVar (toName u)
499+ typeToVar t = t
500+ in mkForAll (sort . map toName $ unks) ty'
501+
502+-- |
503+-- Remove any ForAlls and ConstrainedType constructors in a type by introducing new unknowns
504+-- or TypeClassDictionary values.
505+--
506+-- This is necessary during type checking to avoid unifying a polymorphic type with a
507+-- unification variable.
508+--
509+instantiatePolyTypeWithUnknowns :: Expr -> Type -> UnifyT Type Check (Expr, Type)
510+instantiatePolyTypeWithUnknowns val (ForAll ident ty _) = do
511+ ty' <- replaceVarWithUnknown ident ty
512+ instantiatePolyTypeWithUnknowns val ty'
513+instantiatePolyTypeWithUnknowns val (ConstrainedType constraints ty) = do
514+ dicts <- getTypeClassDictionaries
515+ (_, ty') <- instantiatePolyTypeWithUnknowns (error "Types under a constraint cannot themselves be constrained") ty
516+ return (foldl App val (map (flip (TypeClassDictionary True) dicts) constraints), ty')
517+instantiatePolyTypeWithUnknowns val ty = return (val, ty)
518+
519+-- |
520+-- Replace a single type variable with a new unification variable
521+--
522+replaceVarWithUnknown :: String -> Type -> UnifyT Type Check Type
523+replaceVarWithUnknown ident ty = do
524+ tu <- fresh
525+ return $ replaceTypeVars ident tu ty
526+
527+-- |
528+-- Replace fully applied type synonyms with the @SaturatedTypeSynonym@ data constructor, which helps generate
529+-- better error messages during unification.
530+--
531+replaceAllTypeSynonyms' :: Environment -> Type -> Either String Type
532+replaceAllTypeSynonyms' env d =
533+ let
534+ syns = map (\(name, (args, _)) -> (name, length args)) . M.toList $ typeSynonyms env
535+ in
536+ saturateAllTypeSynonyms syns d
537+
538+replaceAllTypeSynonyms :: (Error e, Functor m, Monad m, MonadState CheckState m, MonadError e m) => Type -> m Type
539+replaceAllTypeSynonyms d = do
540+ env <- getEnv
541+ either (throwError . strMsg) return $ replaceAllTypeSynonyms' env d
542+
543+-- |
544+-- \"Desaturate\" @SaturatedTypeSynonym@s
545+--
546+desaturateAllTypeSynonyms :: Type -> Type
547+desaturateAllTypeSynonyms = everywhereOnTypes replaceSaturatedTypeSynonym
548+ where
549+ replaceSaturatedTypeSynonym (SaturatedTypeSynonym name args) = foldl TypeApp (TypeConstructor name) args
550+ replaceSaturatedTypeSynonym t = t
551+
552+-- |
553+-- Replace a type synonym and its arguments with the aliased type
554+--
555+expandTypeSynonym' :: Environment -> Qualified ProperName -> [Type] -> Either String Type
556+expandTypeSynonym' env name args =
557+ case M.lookup name (typeSynonyms env) of
558+ Just (synArgs, body) -> do
559+ let repl = replaceAllTypeVars (zip synArgs args) body
560+ replaceAllTypeSynonyms' env repl
561+ Nothing -> error "Type synonym was not defined"
562+
563+expandTypeSynonym :: (Error e, Functor m, Monad m, MonadState CheckState m, MonadError e m) => Qualified ProperName -> [Type] -> m Type
564+expandTypeSynonym name args = do
565+ env <- getEnv
566+ either (throwError . strMsg) return $ expandTypeSynonym' env name args
567+
568+expandAllTypeSynonyms :: (Error e, Functor m, Applicative m, Monad m, MonadState CheckState m, MonadError e m) => Type -> m Type
569+expandAllTypeSynonyms = everywhereOnTypesTopDownM go
570+ where
571+ go (SaturatedTypeSynonym name args) = expandTypeSynonym name args
572+ go other = return other
573+
574+-- |
575+-- Ensure a set of property names and value does not contain duplicate labels
576+--
577+ensureNoDuplicateProperties :: (Error e, MonadError e m) => [(String, Expr)] -> m ()
578+ensureNoDuplicateProperties ps = guardWith (strMsg "Duplicate property names") $ length (nub . map fst $ ps) == length ps
579+
580+-- |
581+-- Infer a type for a value, rethrowing any error to provide a more useful error message
582+--
583+infer :: Expr -> UnifyT Type Check Expr
584+infer val = rethrow (mkErrorStack "Error inferring type of value" (Just (ExprError val)) <>) $ infer' val
585+
586+-- |
587+-- Infer a type for a value
588+--
589+infer' :: Expr -> UnifyT Type Check Expr
590+infer' v@(NumericLiteral _) = return $ TypedValue True v tyNumber
591+infer' v@(StringLiteral _) = return $ TypedValue True v tyString
592+infer' v@(BooleanLiteral _) = return $ TypedValue True v tyBoolean
593+infer' (ArrayLiteral vals) = do
594+ ts <- mapM infer vals
595+ els <- fresh
596+ forM_ ts $ \(TypedValue _ _ t) -> els =?= t
597+ return $ TypedValue True (ArrayLiteral ts) (TypeApp tyArray els)
598+infer' (ObjectLiteral ps) = do
599+ ensureNoDuplicateProperties ps
600+ ts <- mapM (infer . snd) ps
601+ let fields = zipWith (\name (TypedValue _ _ t) -> (name, t)) (map fst ps) ts
602+ ty = TypeApp tyObject $ rowFromList (fields, REmpty)
603+ return $ TypedValue True (ObjectLiteral (zip (map fst ps) ts)) ty
604+infer' (ObjectUpdate o ps) = do
605+ ensureNoDuplicateProperties ps
606+ row <- fresh
607+ newVals <- zipWith (\(name, _) t -> (name, t)) ps <$> mapM (infer . snd) ps
608+ let newTys = map (\(name, TypedValue _ _ ty) -> (name, ty)) newVals
609+ oldTys <- zip (map fst ps) <$> replicateM (length ps) fresh
610+ let oldTy = TypeApp tyObject $ rowFromList (oldTys, row)
611+ o' <- TypedValue True <$> check o oldTy <*> pure oldTy
612+ return $ TypedValue True (ObjectUpdate o' newVals) $ TypeApp tyObject $ rowFromList (newTys, row)
613+infer' (Accessor prop val) = do
614+ typed@(TypedValue _ _ objTy) <- infer val
615+ propTy <- inferProperty objTy prop
616+ case propTy of
617+ Nothing -> do
618+ field <- fresh
619+ rest <- fresh
620+ _ <- subsumes Nothing objTy (TypeApp tyObject (RCons prop field rest))
621+ return $ TypedValue True (Accessor prop typed) field
622+ Just ty -> return $ TypedValue True (Accessor prop typed) ty
623+infer' (Abs (Left arg) ret) = do
624+ ty <- fresh
625+ Just moduleName <- checkCurrentModule <$> get
626+ makeBindingGroupVisible $ bindLocalVariables moduleName [(arg, ty, Defined)] $ do
627+ body@(TypedValue _ _ bodyTy) <- infer' ret
628+ return $ TypedValue True (Abs (Left arg) body) $ function ty bodyTy
629+infer' (Abs (Right _) _) = error "Binder was not desugared"
630+infer' (App f arg) = do
631+ f'@(TypedValue _ _ ft) <- infer f
632+ (ret, app) <- checkFunctionApplication f' ft arg Nothing
633+ return $ TypedValue True app ret
634+infer' (Var var) = do
635+ Just moduleName <- checkCurrentModule <$> get
636+ checkVisibility moduleName var
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] -> Expr -> (Expr -> UnifyT Type Check Expr) -> UnifyT Type Check ([Declaration], Expr)
677+inferLetBinding seen [] ret j = (,) seen <$> makeBindingGroupVisible (j ret)
678+inferLetBinding seen (ValueDeclaration ident nameKind [] Nothing tv@(TypedValue checkType val ty) : rest) ret j = do
679+ Just moduleName <- checkCurrentModule <$> get
680+ kind <- liftCheck $ kindOf moduleName ty
681+ guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
682+ let dict = M.singleton (moduleName, ident) (ty, nameKind, Undefined)
683+ ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
684+ TypedValue _ val' ty'' <- if checkType then bindNames dict (check val ty') else return tv
685+ bindNames (M.singleton (moduleName, ident) (ty'', nameKind, Defined)) $ inferLetBinding (seen ++ [ValueDeclaration ident nameKind [] Nothing (TypedValue checkType val' ty'')]) rest ret j
686+inferLetBinding seen (ValueDeclaration ident nameKind [] Nothing val : rest) ret j = do
687+ valTy <- fresh
688+ Just moduleName <- checkCurrentModule <$> get
689+ let dict = M.singleton (moduleName, ident) (valTy, nameKind, Undefined)
690+ TypedValue _ val' valTy' <- bindNames dict $ infer val
691+ valTy =?= valTy'
692+ bindNames (M.singleton (moduleName, ident) (valTy', nameKind, Defined)) $ inferLetBinding (seen ++ [ValueDeclaration ident nameKind [] Nothing val']) rest ret j
693+inferLetBinding seen (BindingGroupDeclaration ds : rest) ret j = do
694+ Just moduleName <- checkCurrentModule <$> get
695+ (es, dict, untypedDict) <- typeDictionaryForBindingGroup moduleName (map (\(i, _, v) -> (i, v)) ds)
696+ ds' <- forM es $ \e -> do
697+ (ident, (val', _)) <- typeForBindingGroupElement moduleName e dict untypedDict
698+ return $ (ident, LocalVariable, val')
699+ makeBindingGroupVisible $ bindNames dict $ inferLetBinding (seen ++ [BindingGroupDeclaration ds']) rest ret j
700+inferLetBinding seen (PositionedDeclaration pos d : ds) ret j = rethrowWithPosition pos $ do
701+ ((d' : ds'), val') <- inferLetBinding seen (d : ds) ret j
702+ return (PositionedDeclaration pos d' : ds', val')
703+inferLetBinding _ _ _ _ = error "Invalid argument to inferLetBinding"
704+
705+-- |
706+-- Infer the type of a property inside a record with a given type
707+--
708+inferProperty :: Type -> String -> UnifyT Type Check (Maybe Type)
709+inferProperty (TypeApp obj row) prop | obj == tyObject = do
710+ let (props, _) = rowToList row
711+ return $ lookup prop props
712+inferProperty (SaturatedTypeSynonym name args) prop = do
713+ replaced <- introduceSkolemScope <=< expandTypeSynonym name $ args
714+ inferProperty replaced prop
715+inferProperty (ForAll ident ty _) prop = do
716+ replaced <- replaceVarWithUnknown ident ty
717+ inferProperty replaced prop
718+inferProperty _ _ = return Nothing
719+
720+-- |
721+-- Infer the types of variables brought into scope by a binder
722+--
723+inferBinder :: Type -> Binder -> UnifyT Type Check (M.Map Ident Type)
724+inferBinder _ NullBinder = return M.empty
725+inferBinder val (StringBinder _) = val =?= tyString >> return M.empty
726+inferBinder val (NumberBinder _) = val =?= tyNumber >> return M.empty
727+inferBinder val (BooleanBinder _) = val =?= tyBoolean >> return M.empty
728+inferBinder val (VarBinder name) = return $ M.singleton name val
729+inferBinder val (ConstructorBinder ctor binders) = do
730+ env <- getEnv
731+ case M.lookup ctor (dataConstructors env) of
732+ Just (_, _, ty) -> do
733+ (_, fn) <- instantiatePolyTypeWithUnknowns (error "Data constructor types cannot contain constraints") ty
734+ fn' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ fn
735+ go binders fn'
736+ where
737+ go [] ty' = do
738+ _ <- subsumes Nothing val ty'
739+ return M.empty
740+ go (binder : binders') (TypeApp (TypeApp t obj) ret) | t == tyFunction =
741+ M.union <$> inferBinder obj binder <*> go binders' ret
742+ go _ _ = throwError . strMsg $ "Wrong number of arguments to constructor " ++ show ctor
743+ _ -> throwError . strMsg $ "Constructor " ++ show ctor ++ " is not defined"
744+inferBinder val (ObjectBinder props) = do
745+ row <- fresh
746+ rest <- fresh
747+ m1 <- inferRowProperties row rest props
748+ val =?= TypeApp tyObject row
749+ return m1
750+ where
751+ inferRowProperties :: Type -> Type -> [(String, Binder)] -> UnifyT Type Check (M.Map Ident Type)
752+ inferRowProperties nrow row [] = nrow =?= row >> return M.empty
753+ inferRowProperties nrow row ((name, binder):binders) = do
754+ propTy <- fresh
755+ m1 <- inferBinder propTy binder
756+ m2 <- inferRowProperties nrow (RCons name propTy row) binders
757+ return $ m1 `M.union` m2
758+inferBinder val (ArrayBinder binders) = do
759+ el <- fresh
760+ m1 <- M.unions <$> mapM (inferBinder el) binders
761+ val =?= TypeApp tyArray el
762+ return m1
763+inferBinder val (ConsBinder headBinder tailBinder) = do
764+ el <- fresh
765+ m1 <- inferBinder el headBinder
766+ m2 <- inferBinder val tailBinder
767+ val =?= TypeApp tyArray el
768+ return $ m1 `M.union` m2
769+inferBinder val (NamedBinder name binder) = do
770+ m <- inferBinder val binder
771+ return $ M.insert name val m
772+inferBinder val (PositionedBinder pos binder) =
773+ rethrowWithPosition pos $ inferBinder val binder
774+
775+-- |
776+-- Check the types of the return values in a set of binders in a case statement
777+--
778+checkBinders :: [Type] -> Type -> [CaseAlternative] -> UnifyT Type Check [CaseAlternative]
779+checkBinders _ _ [] = return []
780+checkBinders nvals ret (CaseAlternative binders grd val : bs) = do
781+ Just moduleName <- checkCurrentModule <$> get
782+ m1 <- M.unions <$> zipWithM inferBinder nvals binders
783+ r <- bindLocalVariables moduleName [ (name, ty, Defined) | (name, ty) <- M.toList m1 ] $ do
784+ val' <- TypedValue True <$> check val ret <*> pure ret
785+ case grd of
786+ Nothing -> return $ CaseAlternative binders Nothing val'
787+ Just g -> do
788+ g' <- check g tyBoolean
789+ return $ CaseAlternative binders (Just g') val'
790+ rs <- checkBinders nvals ret bs
791+ return $ r : rs
792+
793+-- |
794+-- Generate a new skolem constant
795+--
796+newSkolemConstant :: UnifyT Type Check Int
797+newSkolemConstant = fresh'
798+
799+-- |
800+-- Generate a new skolem scope
801+--
802+newSkolemScope :: UnifyT Type Check SkolemScope
803+newSkolemScope = SkolemScope <$> fresh'
804+
805+-- |
806+-- Skolemize a type variable by replacing its instances with fresh skolem constants
807+--
808+skolemize :: String -> Int -> SkolemScope -> Type -> Type
809+skolemize ident sko scope = replaceTypeVars ident (Skolem ident sko scope)
810+
811+-- |
812+-- This function has one purpose - to skolemize type variables appearing in a
813+-- SuperClassDictionary placeholder. These type variables are somewhat unique since they are the
814+-- only example of scoped type variables.
815+--
816+skolemizeTypesInValue :: String -> Int -> SkolemScope -> Expr -> Expr
817+skolemizeTypesInValue ident sko scope = let (_, f, _) = everywhereOnValues id go id in f
818+ where
819+ go (SuperClassDictionary c ts) = SuperClassDictionary c (map (skolemize ident sko scope) ts)
820+ go other = other
821+
822+-- |
823+-- Introduce skolem scope at every occurence of a ForAll
824+--
825+introduceSkolemScope :: Type -> UnifyT Type Check Type
826+introduceSkolemScope = everywhereOnTypesM go
827+ where
828+ go (ForAll ident ty Nothing) = ForAll ident ty <$> (Just <$> newSkolemScope)
829+ go other = return other
830+
831+-- |
832+-- Check the type of a value, rethrowing errors to provide a better error message
833+--
834+check :: Expr -> Type -> UnifyT Type Check Expr
835+check val ty = rethrow (mkErrorStack errorMessage (Just (ExprError val)) <>) $ check' val ty
836+ where
837+ errorMessage =
838+ "Error checking type of term " ++
839+ prettyPrintValue val ++
840+ " against type " ++
841+ prettyPrintType ty
842+
843+-- |
844+-- Check the type of a value
845+--
846+check' :: Expr -> Type -> UnifyT Type Check Expr
847+check' val (ForAll ident ty _) = do
848+ scope <- newSkolemScope
849+ sko <- newSkolemConstant
850+ let sk = skolemize ident sko scope ty
851+ let skVal = skolemizeTypesInValue ident sko scope val
852+ val' <- check skVal sk
853+ return $ TypedValue True val' (ForAll ident ty (Just scope))
854+check' val t@(ConstrainedType constraints ty) = do
855+ dictNames <- forM constraints $ \(Qualified _ (ProperName className), _) -> do
856+ n <- liftCheck freshDictionaryName
857+ return $ Ident $ "__dict_" ++ className ++ "_" ++ show n
858+ val' <- makeBindingGroupVisible $ withTypeClassDictionaries (zipWith (\name (className, instanceTy) ->
859+ TypeClassDictionaryInScope name className instanceTy Nothing TCDRegular) (map (Qualified Nothing) dictNames)
860+ constraints) $ check val ty
861+ return $ TypedValue True (foldr (Abs . Left) val' dictNames) t
862+check' val (SaturatedTypeSynonym name args) = do
863+ ty <- introduceSkolemScope <=< expandTypeSynonym name $ args
864+ check val ty
865+check' val u@(TUnknown _) = do
866+ val'@(TypedValue _ _ ty) <- infer val
867+ -- Don't unify an unknown with an inferred polytype
868+ (val'', ty') <- instantiatePolyTypeWithUnknowns val' ty
869+ ty' =?= u
870+ return $ TypedValue True val'' ty'
871+check' v@(NumericLiteral _) t | t == tyNumber =
872+ return $ TypedValue True v t
873+check' v@(StringLiteral _) t | t == tyString =
874+ return $ TypedValue True v t
875+check' v@(BooleanLiteral _) t | t == tyBoolean =
876+ return $ TypedValue True v t
877+check' (ArrayLiteral vals) t@(TypeApp a ty) = do
878+ a =?= tyArray
879+ array <- ArrayLiteral <$> forM vals (`check` ty)
880+ return $ TypedValue True array t
881+check' (Abs (Left arg) ret) ty@(TypeApp (TypeApp t argTy) retTy) | t == tyFunction = do
882+ Just moduleName <- checkCurrentModule <$> get
883+ ret' <- makeBindingGroupVisible $ bindLocalVariables moduleName [(arg, argTy, Defined)] $ check ret retTy
884+ return $ TypedValue True (Abs (Left arg) ret') ty
885+check' (Abs (Right _) _) _ = error "Binder was not desugared"
886+check' (App f arg) ret = do
887+ f'@(TypedValue _ _ ft) <- infer f
888+ (_, app) <- checkFunctionApplication f' ft arg (Just ret)
889+ return $ TypedValue True app ret
890+check' v@(Var var) ty = do
891+ Just moduleName <- checkCurrentModule <$> get
892+ checkVisibility moduleName var
893+ repl <- introduceSkolemScope <=< replaceAllTypeSynonyms <=< lookupVariable moduleName $ var
894+ ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
895+ v' <- subsumes (Just v) repl ty'
896+ case v' of
897+ Nothing -> throwError . strMsg $ "Unable to check type subsumption"
898+ Just v'' -> return $ TypedValue True v'' ty'
899+check' (SuperClassDictionary className tys) _ = do
900+ {-
901+ -- Here, we replace a placeholder for a superclass dictionary with a regular
902+ -- TypeClassDictionary placeholder. The reason we do this is that it is necessary to have the
903+ -- correct super instance dictionaries in scope, and these are not available when the type class
904+ -- declaration gets desugared.
905+ --
906+ -- Note also that the first argument to TypeClassDictionary is False, meaning we _do not_ want
907+ -- to consider superclass instances when searching for this dictionary - doing so might lead
908+ -- to traversing a cycle in the instance graph.
909+ -}
910+ dicts <- getTypeClassDictionaries
911+ return $ TypeClassDictionary False (className, tys) dicts
912+check' (TypedValue checkType val ty1) ty2 = do
913+ Just moduleName <- checkCurrentModule <$> get
914+ kind <- liftCheck $ kindOf moduleName ty1
915+ guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
916+ ty1' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty1
917+ ty2' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty2
918+ val' <- subsumes (Just val) ty1' ty2'
919+ case val' of
920+ Nothing -> throwError . strMsg $ "Unable to check type subsumption"
921+ Just val'' -> do
922+ val''' <- if checkType then check val'' ty2' else return val''
923+ return $ TypedValue checkType (TypedValue True val''' ty1') ty2'
924+check' (Case vals binders) ret = do
925+ vals' <- mapM infer vals
926+ let ts = map (\(TypedValue _ _ t) -> t) vals'
927+ binders' <- checkBinders ts ret binders
928+ return $ TypedValue True (Case vals' binders') ret
929+check' (IfThenElse cond th el) ty = do
930+ cond' <- check cond tyBoolean
931+ th' <- check th ty
932+ el' <- check el ty
933+ return $ TypedValue True (IfThenElse cond' th' el') ty
934+check' (ObjectLiteral ps) t@(TypeApp obj row) | obj == tyObject = do
935+ ensureNoDuplicateProperties ps
936+ ps' <- checkProperties ps row False
937+ return $ TypedValue True (ObjectLiteral ps') t
938+check' (TypeClassDictionaryConstructorApp name ps) t = do
939+ ps' <- check' ps t
940+ return $ TypedValue True (TypeClassDictionaryConstructorApp name ps') t
941+check' (ObjectUpdate obj ps) t@(TypeApp o row) | o == tyObject = do
942+ ensureNoDuplicateProperties ps
943+ us <- zip (map fst ps) <$> replicateM (length ps) fresh
944+ let (propsToCheck, rest) = rowToList row
945+ propsToRemove = map fst ps
946+ remainingProps = filter (\(p, _) -> p `notElem` propsToRemove) propsToCheck
947+ obj' <- check obj (TypeApp tyObject (rowFromList (us ++ remainingProps, rest)))
948+ ps' <- checkProperties ps row True
949+ return $ TypedValue True (ObjectUpdate obj' ps') t
950+check' (Accessor prop val) ty = do
951+ rest <- fresh
952+ val' <- check val (TypeApp tyObject (RCons prop ty rest))
953+ return $ TypedValue True (Accessor prop val') ty
954+check' (Constructor c) ty = do
955+ env <- getEnv
956+ case M.lookup c (dataConstructors env) of
957+ Nothing -> throwError . strMsg $ "Constructor " ++ show c ++ " is undefined"
958+ Just (_, _, ty1) -> do
959+ repl <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty1
960+ _ <- subsumes Nothing repl ty
961+ return $ TypedValue True (Constructor c) ty
962+check' (Let ds val) ty = do
963+ (ds', val') <- inferLetBinding [] ds val (flip check ty)
964+ return $ TypedValue True (Let ds' val') ty
965+check' val ty | containsTypeSynonyms ty = do
966+ ty' <- introduceSkolemScope <=< expandAllTypeSynonyms $ ty
967+ check val ty'
968+check' (PositionedValue pos val) ty =
969+ rethrowWithPosition pos $ check val ty
970+check' val ty = throwError $ mkErrorStack ("Expr does not have type " ++ prettyPrintType ty) (Just (ExprError val))
971+
972+containsTypeSynonyms :: Type -> Bool
973+containsTypeSynonyms = everythingOnTypes (||) go where
974+ go (SaturatedTypeSynonym _ _) = True
975+ go _ = False
976+
977+-- |
978+-- Check the type of a collection of named record fields
979+--
980+-- The @lax@ parameter controls whether or not every record member has to be provided. For object updates, this is not the case.
981+--
982+checkProperties :: [(String, Expr)] -> Type -> Bool -> UnifyT Type Check [(String, Expr)]
983+checkProperties ps row lax = let (ts, r') = rowToList row in go ps ts r' where
984+ go [] [] REmpty = return []
985+ go [] [] u@(TUnknown _) = do u =?= REmpty
986+ return []
987+ go [] [] (Skolem _ _ _) | lax = return []
988+ go [] ((p, _): _) _ | lax = return []
989+ | otherwise = throwError $ mkErrorStack ("Object does not have property " ++ p) (Just (ExprError (ObjectLiteral ps)))
990+ go ((p,_):_) [] REmpty = throwError $ mkErrorStack ("Property " ++ p ++ " is not present in closed object type " ++ prettyPrintRow row) (Just (ExprError (ObjectLiteral ps)))
991+ go ((p,v):ps') [] u@(TUnknown _) = do
992+ v'@(TypedValue _ _ ty) <- infer v
993+ rest <- fresh
994+ u =?= RCons p ty rest
995+ ps'' <- go ps' [] rest
996+ return $ (p, v') : ps''
997+ go ((p,v):ps') ts r =
998+ case lookup p ts of
999+ Nothing -> do
1000+ v'@(TypedValue _ _ ty) <- infer v
1001+ rest <- fresh
1002+ r =?= RCons p ty rest
1003+ ps'' <- go ps' ts rest
1004+ return $ (p, v') : ps''
1005+ Just ty -> do
1006+ v' <- check v ty
1007+ ps'' <- go ps' (delete (p, ty) ts) r
1008+ return $ (p, v') : ps''
1009+ go _ _ _ = throwError $ mkErrorStack ("Object does not have type " ++ prettyPrintType (TypeApp tyObject row)) (Just (ExprError (ObjectLiteral ps)))
1010+
1011+-- |
1012+-- Check the type of a function application, rethrowing errors to provide a better error message
1013+--
1014+checkFunctionApplication :: Expr -> Type -> Expr -> Maybe Type -> UnifyT Type Check (Type, Expr)
1015+checkFunctionApplication fn fnTy arg ret = rethrow (mkErrorStack errorMessage (Just (ExprError fn)) <>) $ do
1016+ subst <- unifyCurrentSubstitution <$> UnifyT get
1017+ checkFunctionApplication' fn (subst $? fnTy) arg (($?) subst <$> ret)
1018+ where
1019+ errorMessage = "Error applying function of type "
1020+ ++ prettyPrintType fnTy
1021+ ++ " to argument " ++ prettyPrintValue arg
1022+
1023+-- |
1024+-- Check the type of a function application
1025+--
1026+checkFunctionApplication' :: Expr -> Type -> Expr -> Maybe Type -> UnifyT Type Check (Type, Expr)
1027+checkFunctionApplication' fn (TypeApp (TypeApp tyFunction' argTy) retTy) arg ret = do
1028+ tyFunction' =?= tyFunction
1029+ arg' <- check arg argTy
1030+ case ret of
1031+ Nothing -> return (retTy, App fn arg')
1032+ Just ret' -> do
1033+ Just app' <- subsumes (Just (App fn arg')) retTy ret'
1034+ return (retTy, app')
1035+checkFunctionApplication' fn (ForAll ident ty _) arg ret = do
1036+ replaced <- replaceVarWithUnknown ident ty
1037+ checkFunctionApplication fn replaced arg ret
1038+checkFunctionApplication' fn u@(TUnknown _) arg ret = do
1039+ arg' <- do
1040+ TypedValue _ arg' t <- infer arg
1041+ (arg'', t') <- instantiatePolyTypeWithUnknowns arg' t
1042+ return $ TypedValue True arg'' t'
1043+ let ty = (\(TypedValue _ _ t) -> t) arg'
1044+ ret' <- maybe fresh return ret
1045+ u =?= function ty ret'
1046+ return (ret', App fn arg')
1047+checkFunctionApplication' fn (SaturatedTypeSynonym name tyArgs) arg ret = do
1048+ ty <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
1049+ checkFunctionApplication fn ty arg ret
1050+checkFunctionApplication' fn (ConstrainedType constraints fnTy) arg ret = do
1051+ dicts <- getTypeClassDictionaries
1052+ checkFunctionApplication' (foldl App fn (map (flip (TypeClassDictionary True) dicts) constraints)) fnTy arg ret
1053+checkFunctionApplication' fn fnTy dict@(TypeClassDictionary _ _ _) _ =
1054+ return (fnTy, App fn dict)
1055+checkFunctionApplication' _ fnTy arg _ = throwError . strMsg $ "Cannot apply a function of type "
1056+ ++ prettyPrintType fnTy
1057+ ++ " to argument " ++ prettyPrintValue arg
1058+
1059+-- |
1060+-- Check whether one type subsumes another, rethrowing errors to provide a better error message
1061+--
1062+subsumes :: Maybe Expr -> Type -> Type -> UnifyT Type Check (Maybe Expr)
1063+subsumes val ty1 ty2 = rethrow (mkErrorStack errorMessage (ExprError <$> val) <>) $ subsumes' val ty1 ty2
1064+ where
1065+ errorMessage = "Error checking that type "
1066+ ++ prettyPrintType ty1
1067+ ++ " subsumes type "
1068+ ++ prettyPrintType ty2
1069+
1070+-- |
1071+-- Check whether one type subsumes another
1072+--
1073+subsumes' :: Maybe Expr -> Type -> Type -> UnifyT Type Check (Maybe Expr)
1074+subsumes' val (ForAll ident ty1 _) ty2 = do
1075+ replaced <- replaceVarWithUnknown ident ty1
1076+ subsumes val replaced ty2
1077+subsumes' val ty1 (ForAll ident ty2 sco) =
1078+ case sco of
1079+ Just sco' -> do
1080+ sko <- newSkolemConstant
1081+ let sk = skolemize ident sko sco' ty2
1082+ subsumes val ty1 sk
1083+ Nothing -> throwError . strMsg $ "Skolem variable scope is unspecified"
1084+subsumes' val (TypeApp (TypeApp f1 arg1) ret1) (TypeApp (TypeApp f2 arg2) ret2) | f1 == tyFunction && f2 == tyFunction = do
1085+ _ <- subsumes Nothing arg2 arg1
1086+ _ <- subsumes Nothing ret1 ret2
1087+ return val
1088+subsumes' val (SaturatedTypeSynonym name tyArgs) ty2 = do
1089+ ty1 <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
1090+ subsumes val ty1 ty2
1091+subsumes' val ty1 (SaturatedTypeSynonym name tyArgs) = do
1092+ ty2 <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
1093+ subsumes val ty1 ty2
1094+subsumes' (Just val) (ConstrainedType constraints ty1) ty2 = do
1095+ dicts <- getTypeClassDictionaries
1096+ subsumes' (Just $ foldl App val (map (flip (TypeClassDictionary True) dicts) constraints)) ty1 ty2
1097+subsumes' val (TypeApp f1 r1) (TypeApp f2 r2) | f1 == tyObject && f2 == tyObject = do
1098+ let
1099+ (ts1, r1') = rowToList r1
1100+ (ts2, r2') = rowToList r2
1101+ ts1' = sortBy (comparing fst) ts1
1102+ ts2' = sortBy (comparing fst) ts2
1103+ go ts1' ts2' r1' r2'
1104+ return val
1105+ where
1106+ go [] ts2 r1' r2' = r1' =?= rowFromList (ts2, r2')
1107+ go ts1 [] r1' r2' = r2' =?= rowFromList (ts1, r1')
1108+ go ((p1, ty1) : ts1) ((p2, ty2) : ts2) r1' r2'
1109+ | p1 == p2 = do _ <- subsumes Nothing ty1 ty2
1110+ go ts1 ts2 r1' r2'
1111+ | p1 < p2 = do rest <- fresh
1112+ r2' =?= RCons p1 ty1 rest
1113+ go ts1 ((p2, ty2) : ts2) r1' rest
1114+ | otherwise = do rest <- fresh
1115+ r1' =?= RCons p2 ty2 rest
1116+ go ((p1, ty1) : ts1) ts2 rest r2'
1117+subsumes' val ty1 ty2@(TypeApp obj _) | obj == tyObject = subsumes val ty2 ty1
1118+subsumes' val ty1 ty2 = do
1119+ ty1 =?= ty2
1120+ return val
1121+
1122+
1123+
1124+
1125+