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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, fromMaybe)
46+import Data.Function (on)
47+import Data.Ord (comparing)
48+import Data.Monoid
49+import Data.Either (lefts, rights)
50+
51+import Language.PureScript.Declarations
52+import Language.PureScript.Types
53+import Language.PureScript.Kinds
54+import Language.PureScript.Names
55+import Language.PureScript.TypeClassDictionaries
56+import Language.PureScript.TypeChecker.Monad
57+import Language.PureScript.TypeChecker.Kinds
58+import Language.PureScript.TypeChecker.Synonyms
59+import Language.PureScript.Pretty
60+import Language.PureScript.Environment
61+import Language.PureScript.Errors
62+import qualified Language.PureScript.Constants as C
63+
64+import Control.Monad.State
65+import Control.Monad.Error
66+import Control.Monad.Unify
67+
68+import Control.Applicative
69+import Control.Arrow (Arrow(..))
70+
71+import qualified Data.Map as M
72+import qualified Data.HashMap.Strict as H
73+
74+instance Partial Type where
75+ unknown = TUnknown
76+ isUnknown (TUnknown u) = Just u
77+ isUnknown _ = Nothing
78+ unknowns = everythingOnTypes (++) go
79+ where
80+ go (TUnknown u) = [u]
81+ go _ = []
82+ ($?) sub = everywhereOnTypes go
83+ where
84+ go t@(TUnknown u) = case H.lookup u (runSubstitution sub) of
85+ Nothing -> t
86+ Just t' -> t'
87+ go other = other
88+
89+instance Unifiable Check Type where
90+ (=?=) = unifyTypes
91+
92+-- |
93+-- Unify two types, updating the current substitution
94+--
95+unifyTypes :: Type -> Type -> UnifyT Type Check ()
96+unifyTypes t1 t2 = rethrow (mkErrorStack ("Error unifying type " ++ prettyPrintType t1 ++ " with type " ++ prettyPrintType t2) Nothing <>) $
97+ unifyTypes' t1 t2
98+ where
99+ unifyTypes' (TUnknown u1) (TUnknown u2) | u1 == u2 = return ()
100+ unifyTypes' (TUnknown u) t = u =:= t
101+ unifyTypes' t (TUnknown u) = u =:= t
102+ unifyTypes' (SaturatedTypeSynonym name args) ty = do
103+ ty1 <- introduceSkolemScope <=< expandTypeSynonym name $ args
104+ ty1 `unifyTypes` ty
105+ unifyTypes' ty s@(SaturatedTypeSynonym _ _) = s `unifyTypes` ty
106+ unifyTypes' (ForAll ident1 ty1 sc1) (ForAll ident2 ty2 sc2) =
107+ case (sc1, sc2) of
108+ (Just sc1', Just sc2') -> do
109+ sko <- newSkolemConstant
110+ let sk1 = skolemize ident1 sko sc1' ty1
111+ let sk2 = skolemize ident2 sko sc2' ty2
112+ sk1 `unifyTypes` sk2
113+ _ -> error "Skolemized type variable was not given a scope"
114+ unifyTypes' (ForAll ident ty1 (Just sc)) ty2 = do
115+ sko <- newSkolemConstant
116+ let sk = skolemize ident sko sc ty1
117+ sk `unifyTypes` ty2
118+ unifyTypes' ForAll{} _ = throwError . strMsg $ "Skolem variable scope is unspecified"
119+ unifyTypes' ty f@ForAll{} = f `unifyTypes` ty
120+ unifyTypes' (TypeVar v1) (TypeVar v2) | v1 == v2 = return ()
121+ unifyTypes' (TypeConstructor c1) (TypeConstructor c2) =
122+ guardWith (strMsg ("Cannot unify " ++ show c1 ++ " with " ++ show c2 ++ ".")) (c1 == c2)
123+ unifyTypes' (TypeApp t3 t4) (TypeApp t5 t6) = do
124+ t3 `unifyTypes` t5
125+ t4 `unifyTypes` t6
126+ unifyTypes' (Skolem _ s1 _) (Skolem _ s2 _) | s1 == s2 = return ()
127+ unifyTypes' r1@RCons{} r2 = unifyRows r1 r2
128+ unifyTypes' r1 r2@RCons{} = unifyRows r1 r2
129+ unifyTypes' r1@REmpty r2 = unifyRows r1 r2
130+ unifyTypes' r1 r2@REmpty = unifyRows r1 r2
131+ unifyTypes' t@(ConstrainedType _ _) _ = throwError . strMsg $ "Attempted to unify a constrained type " ++ prettyPrintType t ++ " with another type."
132+ unifyTypes' t3 t4@(ConstrainedType _ _) = unifyTypes' t4 t3
133+ unifyTypes' t3 t4 = throwError . strMsg $ "Cannot unify " ++ prettyPrintType t3 ++ " with " ++ prettyPrintType t4 ++ "."
134+
135+-- |
136+-- Unify two rows, updating the current substitution
137+--
138+-- Common labels are first identified, and unified. Remaining labels and types are unified with a
139+-- trailing row unification variable, if appropriate, otherwise leftover labels result in a unification
140+-- error.
141+--
142+unifyRows :: Type -> Type -> UnifyT Type Check ()
143+unifyRows r1 r2 =
144+ let
145+ (s1, r1') = rowToList r1
146+ (s2, r2') = rowToList r2
147+ int = [ (t1, t2) | (name, t1) <- s1, (name', t2) <- s2, name == name' ]
148+ sd1 = [ (name, t1) | (name, t1) <- s1, name `notElem` map fst s2 ]
149+ sd2 = [ (name, t2) | (name, t2) <- s2, name `notElem` map fst s1 ]
150+ in do
151+ forM_ int (uncurry (=?=))
152+ unifyRows' sd1 r1' sd2 r2'
153+ where
154+ unifyRows' :: [(String, Type)] -> Type -> [(String, Type)] -> Type -> UnifyT Type Check ()
155+ unifyRows' [] (TUnknown u) sd r = u =:= rowFromList (sd, r)
156+ unifyRows' sd r [] (TUnknown u) = u =:= rowFromList (sd, r)
157+ unifyRows' ((name, ty):row) r others u@(TUnknown un) = do
158+ occursCheck un ty
159+ forM_ row $ \(_, t) -> occursCheck un t
160+ u' <- fresh
161+ u =?= RCons name ty u'
162+ unifyRows' row r others u'
163+ unifyRows' [] REmpty [] REmpty = return ()
164+ unifyRows' [] (TypeVar v1) [] (TypeVar v2) | v1 == v2 = return ()
165+ unifyRows' [] (Skolem _ s1 _) [] (Skolem _ s2 _) | s1 == s2 = return ()
166+ unifyRows' sd3 r3 sd4 r4 = throwError . strMsg $ "Cannot unify (" ++ prettyPrintRow (rowFromList (sd3, r3)) ++ ") with (" ++ prettyPrintRow (rowFromList (sd4, r4)) ++ ")"
167+
168+-- |
169+-- Infer the types of multiple mutually-recursive values, and return elaborated values including
170+-- type class dictionaries and type annotations.
171+--
172+typesOf :: Maybe ModuleName -> ModuleName -> [(Ident, Expr)] -> Check [(Ident, (Expr, Type))]
173+typesOf mainModuleName moduleName vals = do
174+ tys <- fmap tidyUp . liftUnify $ do
175+ (untyped, typed, dict, untypedDict) <- typeDictionaryForBindingGroup moduleName vals
176+ ds1 <- parU typed $ \e -> do
177+ triple@(_, (_, ty)) <- checkTypedBindingGroupElement moduleName e dict
178+ checkMain (fst e) ty
179+ return triple
180+ ds2 <- forM untyped $ \e -> do
181+ triple@(_, (_, ty)) <- typeForBindingGroupElement e dict untypedDict
182+ checkMain (fst e) ty
183+ return triple
184+ return $ ds1 ++ ds2
185+
186+ forM tys $ \(ident, (val, ty)) -> do
187+ -- Replace type class dictionary placeholders with actual dictionaries
188+ val' <- replaceTypeClassDictionaries moduleName val
189+ -- Check skolem variables did not escape their scope
190+ skolemEscapeCheck val'
191+ -- Remove type synonyms placeholders, remove duplicate row fields, and replace
192+ -- top-level unification variables with named type variables.
193+ let val'' = overTypes (desaturateAllTypeSynonyms . setifyAll) val'
194+ ty' = varIfUnknown . desaturateAllTypeSynonyms . setifyAll $ ty
195+ return (ident, (val'', ty'))
196+ where
197+ -- Apply the substitution that was returned from runUnify to both types and (type-annotated) values
198+ tidyUp (ts, sub) = map (\(i, (val, ty)) -> (i, (overTypes (sub $?) val, sub $? ty))) ts
199+ -- If --main is enabled, need to check that `main` has type Eff eff a for some eff, a
200+ checkMain nm ty = when (Just moduleName == mainModuleName && nm == Ident C.main) $ do
201+ [eff, a] <- replicateM 2 fresh
202+ ty =?= TypeApp (TypeApp (TypeConstructor (Qualified (Just (ModuleName [ProperName "Control", ProperName "Monad", ProperName "Eff"])) (ProperName "Eff"))) eff) a
203+
204+type TypeData = M.Map (ModuleName, Ident) (Type, NameKind, NameVisibility)
205+
206+type UntypedData = [(Ident, Type)]
207+
208+typeDictionaryForBindingGroup :: ModuleName -> [(Ident, Expr)] -> UnifyT Type Check ([(Ident, Expr)], [(Ident, (Expr, Type, Bool))], TypeData, UntypedData)
209+typeDictionaryForBindingGroup moduleName vals = do
210+ let
211+ -- Map each declaration to a name/value pair, with an optional type, if the declaration is typed
212+ es = map isTyped vals
213+ -- Filter the typed and untyped declarations
214+ untyped = lefts es
215+ typed = rights es
216+ -- Make a map of names to typed declarations
217+ typedDict = map (\(ident, (_, ty, _)) -> (ident, ty)) typed
218+
219+ -- Create fresh unification variables for the types of untyped declarations
220+ untypedNames <- replicateM (length untyped) fresh
221+
222+ let
223+ -- Make a map of names to the unification variables of untyped declarations
224+ untypedDict = zip (map fst untyped) untypedNames
225+ -- Create the dictionary of all name/type pairs, which will be added to the environment during type checking
226+ dict = M.fromList (map (\(ident, ty) -> ((moduleName, ident), (ty, LocalVariable, Undefined))) $ typedDict ++ untypedDict)
227+ return (untyped, typed, dict, untypedDict)
228+
229+checkTypedBindingGroupElement :: ModuleName -> (Ident, (Expr, Type, Bool)) -> TypeData -> UnifyT Type Check (Ident, (Expr, Type))
230+checkTypedBindingGroupElement moduleName (ident, (val', ty, checkType)) dict = do
231+ -- Kind check
232+ kind <- liftCheck $ kindOf moduleName ty
233+ guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
234+ -- Check the type with the new names in scope
235+ ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
236+ val'' <- if checkType
237+ then bindNames dict $ TypedValue True <$> check val' ty' <*> pure ty'
238+ else return (TypedValue False val' ty')
239+ return (ident, (val'', ty'))
240+
241+typeForBindingGroupElement :: (Ident, Expr) -> TypeData -> UntypedData -> UnifyT Type Check (Ident, (Expr, Type))
242+typeForBindingGroupElement (ident, val) dict untypedDict = do
243+ -- Infer the type with the new names in scope
244+ TypedValue _ val' ty <- bindNames dict $ infer val
245+ ty =?= fromMaybe (error "name not found in dictionary") (lookup ident untypedDict)
246+ return (ident, (TypedValue True val' ty, ty))
247+
248+-- |
249+-- Check if a value contains a type annotation
250+--
251+isTyped :: (Ident, Expr) -> (Either (Ident, Expr) (Ident, (Expr, Type, Bool)))
252+isTyped (name, TypedValue checkType value ty) = Right (name, (value, ty, checkType))
253+isTyped (name, value) = Left (name, value)
254+
255+-- |
256+-- Map a function over type annotations appearing inside a value
257+--
258+overTypes :: (Type -> Type) -> Expr -> Expr
259+overTypes f = let (_, f', _) = everywhereOnValues id g id in f'
260+ where
261+ g :: Expr -> Expr
262+ g (TypedValue checkTy val t) = TypedValue checkTy val (f t)
263+ g (TypeClassDictionary b (nm, tys) sco) = TypeClassDictionary b (nm, map f tys) sco
264+ g other = other
265+
266+-- |
267+-- Replace type class dictionary placeholders with inferred type class dictionaries
268+--
269+replaceTypeClassDictionaries :: ModuleName -> Expr -> Check Expr
270+replaceTypeClassDictionaries mn =
271+ let (_, f, _) = everywhereOnValuesTopDownM return go return
272+ in f
273+ where
274+ go (TypeClassDictionary trySuperclasses constraint dicts) = do
275+ env <- getEnv
276+ entails env mn dicts constraint trySuperclasses
277+ go other = return other
278+
279+-- |
280+-- A simplified representation of expressions which are used to represent type
281+-- class dictionaries at runtime, which can be compared for equality
282+--
283+data DictionaryValue
284+ -- |
285+ -- A dictionary which is brought into scope by a local constraint
286+ --
287+ = LocalDictionaryValue (Qualified Ident)
288+ -- |
289+ -- A dictionary which is brought into scope by an instance declaration
290+ --
291+ | GlobalDictionaryValue (Qualified Ident)
292+ -- |
293+ -- A dictionary which depends on other dictionaries
294+ --
295+ | DependentDictionaryValue (Qualified Ident) [DictionaryValue]
296+ -- |
297+ -- A subclass dictionary
298+ --
299+ | SubclassDictionaryValue DictionaryValue (Qualified ProperName) Integer
300+ deriving (Show, Ord, Eq)
301+
302+-- |
303+-- Check that the current set of type class dictionaries entail the specified type class goal, and, if so,
304+-- return a type class dictionary reference.
305+--
306+entails :: Environment -> ModuleName -> [TypeClassDictionaryInScope] -> (Qualified ProperName, [Type]) -> Bool -> Check Expr
307+entails env moduleName context = solve (sortedNubBy canonicalizeDictionary (filter filterModule context))
308+ where
309+ sortedNubBy :: (Ord k) => (v -> k) -> [v] -> [v]
310+ sortedNubBy f vs = M.elems (M.fromList (map (f &&& id) vs))
311+
312+ -- Filter out type dictionaries which are in scope in the current module
313+ filterModule :: TypeClassDictionaryInScope -> Bool
314+ filterModule (TypeClassDictionaryInScope { tcdName = Qualified (Just mn) _ }) | mn == moduleName = True
315+ filterModule (TypeClassDictionaryInScope { tcdName = Qualified Nothing _ }) = True
316+ filterModule _ = False
317+
318+ solve context' (className, tys) trySuperclasses =
319+ checkOverlaps $ go trySuperclasses className tys
320+ where
321+ go trySuperclasses' className' tys' =
322+ -- Look for regular type instances
323+ [ mkDictionary (canonicalizeDictionary tcd) args
324+ | tcd <- context'
325+ -- Make sure the type class name matches the one we are trying to satisfy
326+ , className' == tcdClassName tcd
327+ -- Make sure the type unifies with the type in the type instance definition
328+ , subst <- maybeToList . (>>= verifySubstitution) . fmap concat $ zipWithM (typeHeadsAreEqual moduleName env) tys' (tcdInstanceTypes tcd)
329+ -- Solve any necessary subgoals
330+ , args <- solveSubgoals subst (tcdDependencies tcd) ] ++
331+
332+ -- Look for implementations via superclasses
333+ [ SubclassDictionaryValue suDict superclass index
334+ | trySuperclasses'
335+ , (subclassName, (args, _, implies)) <- M.toList (typeClasses env)
336+ -- Try each superclass
337+ , (index, (superclass, suTyArgs)) <- zip [0..] implies
338+ -- Make sure the type class name matches the superclass name
339+ , className' == superclass
340+ -- Make sure the types unify with the types in the superclass implication
341+ , subst <- maybeToList . (>>= verifySubstitution) . fmap concat $ zipWithM (typeHeadsAreEqual moduleName env) tys' suTyArgs
342+ -- Finally, satisfy the subclass constraint
343+ , args' <- maybeToList $ mapM (flip lookup subst) args
344+ , suDict <- go True subclassName args' ]
345+
346+ -- Create dictionaries for subgoals which still need to be solved by calling go recursively
347+ -- E.g. the goal (Show a, Show b) => Show (Either a b) can be satisfied if the current type
348+ -- unifies with Either a b, and we can satisfy the subgoals Show a and Show b recursively.
349+ solveSubgoals :: [(String, Type)] -> Maybe [(Qualified ProperName, [Type])] -> [Maybe [DictionaryValue]]
350+ solveSubgoals _ Nothing = return Nothing
351+ solveSubgoals subst (Just subgoals) = do
352+ dict <- mapM (uncurry (go True) . second (map (replaceAllTypeVars subst))) subgoals
353+ return $ Just dict
354+ -- Make a dictionary from subgoal dictionaries by applying the correct function
355+ mkDictionary :: Qualified Ident -> Maybe [DictionaryValue] -> DictionaryValue
356+ mkDictionary fnName Nothing = LocalDictionaryValue fnName
357+ mkDictionary fnName (Just []) = GlobalDictionaryValue fnName
358+ mkDictionary fnName (Just dicts) = DependentDictionaryValue fnName dicts
359+ -- Turn a DictionaryValue into a Expr
360+ dictionaryValueToValue :: DictionaryValue -> Expr
361+ dictionaryValueToValue (LocalDictionaryValue fnName) = Var fnName
362+ dictionaryValueToValue (GlobalDictionaryValue fnName) = App (Var fnName) valUndefined
363+ dictionaryValueToValue (DependentDictionaryValue fnName dicts) = foldl App (Var fnName) (map dictionaryValueToValue dicts)
364+ dictionaryValueToValue (SubclassDictionaryValue dict superclassName index) =
365+ App (Accessor (C.__superclass_ ++ show superclassName ++ "_" ++ show index)
366+ (dictionaryValueToValue dict))
367+ valUndefined
368+ -- Ensure that a substitution is valid
369+ verifySubstitution :: [(String, Type)] -> Maybe [(String, Type)]
370+ verifySubstitution subst = do
371+ let grps = groupBy ((==) `on` fst) subst
372+ guard (all (pairwise (unifiesWith env) . map snd) grps)
373+ return $ map head grps
374+ -- |
375+ -- Check for overlapping instances
376+ --
377+ checkOverlaps :: [DictionaryValue] -> Check Expr
378+ checkOverlaps dicts =
379+ case sortedNubBy dictTrace (chooseSimplestDictionaries dicts) of
380+ [] -> throwError . strMsg $ "No instance found for " ++ show className ++ " " ++ unwords (map prettyPrintTypeAtom tys)
381+ [_] -> return $ dictionaryValueToValue $ head dicts
382+ (d1 : d2 : _) -> throwError . strMsg $ unlines
383+ [ "Overlapping instances found for " ++ show className ++ " " ++ unwords (map prettyPrintType tys) ++ "."
384+ , "For example:"
385+ , prettyPrintDictionaryValue d1
386+ , "and:"
387+ , prettyPrintDictionaryValue d2
388+ ]
389+ -- Choose the simplest DictionaryValues from a list of candidates
390+ -- The reason for this function is as follows:
391+ -- When considering overlapping instances, we don't want to consider the same dictionary
392+ -- to be an overlap of itself when obtained as a superclass of another class.
393+ -- Observing that we probably don't want to select a superclass instance when an instance
394+ -- is available directly, and that there is no way for a superclass instance to actually
395+ -- introduce an overlap that wouldn't have been there already, we simply remove dictionaries
396+ -- obtained as superclass instances if there are simpler instances available.
397+ chooseSimplestDictionaries :: [DictionaryValue] -> [DictionaryValue]
398+ chooseSimplestDictionaries ds = case filter isSimpleDictionaryValue ds of
399+ [] -> ds
400+ simple -> simple
401+ isSimpleDictionaryValue SubclassDictionaryValue{} = False
402+ isSimpleDictionaryValue (DependentDictionaryValue _ ds) = all isSimpleDictionaryValue ds
403+ isSimpleDictionaryValue _ = True
404+ -- |
405+ -- Get the "trace" of a DictionaryValue - that is, remove all SubclassDictionaryValue
406+ -- data constructors
407+ --
408+ dictTrace :: DictionaryValue -> DictionaryValue
409+ dictTrace (DependentDictionaryValue fnName dicts) = DependentDictionaryValue fnName $ map dictTrace dicts
410+ dictTrace (SubclassDictionaryValue dict _ _) = dictTrace dict
411+ dictTrace other = other
412+ -- |
413+ -- Render a DictionaryValue fit for human consumption in error messages
414+ --
415+ prettyPrintDictionaryValue :: DictionaryValue -> String
416+ prettyPrintDictionaryValue = unlines . indented 0
417+ where
418+ indented n (LocalDictionaryValue _) = [spaces n ++ "Dictionary in scope"]
419+ indented n (GlobalDictionaryValue nm) = [spaces n ++ show nm]
420+ indented n (DependentDictionaryValue nm args) = (spaces n ++ show nm ++ " via") : concatMap (indented (n + 2)) args
421+ indented n (SubclassDictionaryValue sup nm _) = (spaces n ++ show nm ++ " via superclass") : indented (n + 2) sup
422+
423+ spaces n = replicate n ' ' ++ "- "
424+
425+ valUndefined :: Expr
426+ valUndefined = Var (Qualified (Just (ModuleName [ProperName C.prim])) (Ident C.undefined))
427+
428+-- |
429+-- Check all values in a list pairwise match a predicate
430+--
431+pairwise :: (a -> a -> Bool) -> [a] -> Bool
432+pairwise _ [] = True
433+pairwise _ [_] = True
434+pairwise p (x : xs) = all (p x) xs && pairwise p xs
435+
436+-- |
437+-- Check that two types unify
438+--
439+unifiesWith :: Environment -> Type -> Type -> Bool
440+unifiesWith _ (TUnknown u1) (TUnknown u2) | u1 == u2 = True
441+unifiesWith _ (Skolem _ s1 _) (Skolem _ s2 _) | s1 == s2 = True
442+unifiesWith _ (TypeVar v1) (TypeVar v2) | v1 == v2 = True
443+unifiesWith _ (TypeConstructor c1) (TypeConstructor c2) | c1 == c2 = True
444+unifiesWith e (TypeApp h1 t1) (TypeApp h2 t2) = unifiesWith e h1 h2 && unifiesWith e t1 t2
445+unifiesWith e (SaturatedTypeSynonym name args) t2 =
446+ case expandTypeSynonym' e name args of
447+ Left _ -> False
448+ Right t1 -> unifiesWith e t1 t2
449+unifiesWith e t1 t2@(SaturatedTypeSynonym _ _) = unifiesWith e t2 t1
450+unifiesWith _ _ _ = False
451+
452+-- |
453+-- Check whether the type heads of two types are equal (for the purposes of type class dictionary lookup),
454+-- and return a substitution from type variables to types which makes the type heads unify.
455+--
456+typeHeadsAreEqual :: ModuleName -> Environment -> Type -> Type -> Maybe [(String, Type)]
457+typeHeadsAreEqual _ _ (Skolem _ s1 _) (Skolem _ s2 _) | s1 == s2 = Just []
458+typeHeadsAreEqual _ _ t (TypeVar v) = Just [(v, t)]
459+typeHeadsAreEqual _ _ (TypeConstructor c1) (TypeConstructor c2) | c1 == c2 = Just []
460+typeHeadsAreEqual m e (TypeApp h1 t1) (TypeApp h2 t2) = (++) <$> typeHeadsAreEqual m e h1 h2 <*> typeHeadsAreEqual m e t1 t2
461+typeHeadsAreEqual m e (SaturatedTypeSynonym name args) t2 = case expandTypeSynonym' e name args of
462+ Left _ -> Nothing
463+ Right t1 -> typeHeadsAreEqual m e t1 t2
464+typeHeadsAreEqual _ _ _ _ = Nothing
465+
466+-- |
467+-- Ensure skolem variables do not escape their scope
468+--
469+skolemEscapeCheck :: Expr -> Check ()
470+skolemEscapeCheck (TypedValue False _ _) = return ()
471+skolemEscapeCheck root@TypedValue{} =
472+ -- Every skolem variable is created when a ForAll type is skolemized.
473+ -- This determines the scope of that skolem variable, which is copied from the SkolemScope
474+ -- field of the ForAll constructor.
475+ -- We traverse the tree top-down, and collect any SkolemScopes introduced by ForAlls.
476+ -- If a Skolem is encountered whose SkolemScope is not in the current list, we have found
477+ -- an escaped skolem variable.
478+ let (_, f, _, _, _) = everythingWithContextOnValues [] [] (++) def go def def def
479+ in case f root of
480+ [] -> return ()
481+ ((binding, val) : _) -> throwError $ mkErrorStack ("Rigid/skolem type variable " ++ maybe "" (("bound by " ++) . prettyPrintValue) binding ++ " has escaped.") (Just (ExprError val))
482+ where
483+ def s _ = (s, [])
484+
485+ go :: [(SkolemScope, Expr)] -> Expr -> ([(SkolemScope, Expr)], [(Maybe Expr, Expr)])
486+ go scos val@(TypedValue _ _ (ForAll _ _ (Just sco))) = ((sco, val) : scos, [])
487+ go scos val@(TypedValue _ _ ty) = case collectSkolems ty \\ map fst scos of
488+ (sco : _) -> (scos, [(findBindingScope sco, val)])
489+ _ -> (scos, [])
490+ where
491+ collectSkolems :: Type -> [SkolemScope]
492+ collectSkolems = nub . everythingOnTypes (++) collect
493+ where
494+ collect (Skolem _ _ scope) = [scope]
495+ collect _ = []
496+ go scos _ = (scos, [])
497+ findBindingScope :: SkolemScope -> Maybe Expr
498+ findBindingScope sco =
499+ let (_, f, _, _, _) = everythingOnValues mappend (const mempty) go' (const mempty) (const mempty) (const mempty)
500+ in getFirst $ f root
501+ where
502+ go' val@(TypedValue _ _ (ForAll _ _ (Just sco'))) | sco == sco' = First (Just val)
503+ go' _ = mempty
504+skolemEscapeCheck val = throwError $ mkErrorStack "Untyped value passed to skolemEscapeCheck" (Just (ExprError val))
505+
506+-- |
507+-- Ensure a row contains no duplicate labels
508+--
509+setify :: Type -> Type
510+setify = rowFromList . first (M.toList . M.fromList) . rowToList
511+
512+-- |
513+-- \"Setify\" all rows occuring inside a value
514+--
515+setifyAll :: Type -> Type
516+setifyAll = everywhereOnTypes setify
517+
518+-- |
519+-- Replace outermost unsolved unification variables with named type variables
520+--
521+varIfUnknown :: Type -> Type
522+varIfUnknown ty =
523+ let unks = nub $ unknowns ty
524+ toName = (:) 't' . show
525+ ty' = everywhereOnTypes typeToVar ty
526+ typeToVar :: Type -> Type
527+ typeToVar (TUnknown u) = TypeVar (toName u)
528+ typeToVar t = t
529+ in mkForAll (sort . map toName $ unks) ty'
530+
531+-- |
532+-- Remove any ForAlls and ConstrainedType constructors in a type by introducing new unknowns
533+-- or TypeClassDictionary values.
534+--
535+-- This is necessary during type checking to avoid unifying a polymorphic type with a
536+-- unification variable.
537+--
538+instantiatePolyTypeWithUnknowns :: Expr -> Type -> UnifyT Type Check (Expr, Type)
539+instantiatePolyTypeWithUnknowns val (ForAll ident ty _) = do
540+ ty' <- replaceVarWithUnknown ident ty
541+ instantiatePolyTypeWithUnknowns val ty'
542+instantiatePolyTypeWithUnknowns val (ConstrainedType constraints ty) = do
543+ dicts <- getTypeClassDictionaries
544+ (_, ty') <- instantiatePolyTypeWithUnknowns (error "Types under a constraint cannot themselves be constrained") ty
545+ return (foldl App val (map (flip (TypeClassDictionary True) dicts) constraints), ty')
546+instantiatePolyTypeWithUnknowns val ty = return (val, ty)
547+
548+-- |
549+-- Replace a single type variable with a new unification variable
550+--
551+replaceVarWithUnknown :: String -> Type -> UnifyT Type Check Type
552+replaceVarWithUnknown ident ty = do
553+ tu <- fresh
554+ return $ replaceTypeVars ident tu ty
555+
556+-- |
557+-- Replace fully applied type synonyms with the @SaturatedTypeSynonym@ data constructor, which helps generate
558+-- better error messages during unification.
559+--
560+replaceAllTypeSynonyms' :: Environment -> Type -> Either String Type
561+replaceAllTypeSynonyms' env d =
562+ let
563+ syns = map (\(name, (args, _)) -> (name, length args)) . M.toList $ typeSynonyms env
564+ in
565+ saturateAllTypeSynonyms syns d
566+
567+replaceAllTypeSynonyms :: (Error e, Functor m, Monad m, MonadState CheckState m, MonadError e m) => Type -> m Type
568+replaceAllTypeSynonyms d = do
569+ env <- getEnv
570+ either (throwError . strMsg) return $ replaceAllTypeSynonyms' env d
571+
572+-- |
573+-- \"Desaturate\" @SaturatedTypeSynonym@s
574+--
575+desaturateAllTypeSynonyms :: Type -> Type
576+desaturateAllTypeSynonyms = everywhereOnTypes replaceSaturatedTypeSynonym
577+ where
578+ replaceSaturatedTypeSynonym (SaturatedTypeSynonym name args) = foldl TypeApp (TypeConstructor name) args
579+ replaceSaturatedTypeSynonym t = t
580+
581+-- |
582+-- Replace a type synonym and its arguments with the aliased type
583+--
584+expandTypeSynonym' :: Environment -> Qualified ProperName -> [Type] -> Either String Type
585+expandTypeSynonym' env name args =
586+ case M.lookup name (typeSynonyms env) of
587+ Just (synArgs, body) -> do
588+ let repl = replaceAllTypeVars (zip synArgs args) body
589+ replaceAllTypeSynonyms' env repl
590+ Nothing -> error "Type synonym was not defined"
591+
592+expandTypeSynonym :: (Error e, Functor m, Monad m, MonadState CheckState m, MonadError e m) => Qualified ProperName -> [Type] -> m Type
593+expandTypeSynonym name args = do
594+ env <- getEnv
595+ either (throwError . strMsg) return $ expandTypeSynonym' env name args
596+
597+expandAllTypeSynonyms :: (Error e, Functor m, Applicative m, Monad m, MonadState CheckState m, MonadError e m) => Type -> m Type
598+expandAllTypeSynonyms = everywhereOnTypesTopDownM go
599+ where
600+ go (SaturatedTypeSynonym name args) = expandTypeSynonym name args
601+ go other = return other
602+
603+-- |
604+-- Ensure a set of property names and value does not contain duplicate labels
605+--
606+ensureNoDuplicateProperties :: (Error e, MonadError e m) => [(String, Expr)] -> m ()
607+ensureNoDuplicateProperties ps = guardWith (strMsg "Duplicate property names") $ length (nub . map fst $ ps) == length ps
608+
609+-- |
610+-- Infer a type for a value, rethrowing any error to provide a more useful error message
611+--
612+infer :: Expr -> UnifyT Type Check Expr
613+infer val = rethrow (mkErrorStack "Error inferring type of value" (Just (ExprError val)) <>) $ infer' val
614+
615+-- |
616+-- Infer a type for a value
617+--
618+infer' :: Expr -> UnifyT Type Check Expr
619+infer' v@(NumericLiteral _) = return $ TypedValue True v tyNumber
620+infer' v@(StringLiteral _) = return $ TypedValue True v tyString
621+infer' v@(BooleanLiteral _) = return $ TypedValue True v tyBoolean
622+infer' (ArrayLiteral vals) = do
623+ ts <- mapM infer vals
624+ els <- fresh
625+ forM_ ts $ \(TypedValue _ _ t) -> els =?= t
626+ return $ TypedValue True (ArrayLiteral ts) (TypeApp tyArray els)
627+infer' (ObjectLiteral ps) = do
628+ ensureNoDuplicateProperties ps
629+ ts <- mapM (infer . snd) ps
630+ let fields = zipWith (\name (TypedValue _ _ t) -> (name, t)) (map fst ps) ts
631+ ty = TypeApp tyObject $ rowFromList (fields, REmpty)
632+ return $ TypedValue True (ObjectLiteral (zip (map fst ps) ts)) ty
633+infer' (ObjectUpdate o ps) = do
634+ ensureNoDuplicateProperties ps
635+ row <- fresh
636+ newVals <- zipWith (\(name, _) t -> (name, t)) ps <$> mapM (infer . snd) ps
637+ let newTys = map (\(name, TypedValue _ _ ty) -> (name, ty)) newVals
638+ oldTys <- zip (map fst ps) <$> replicateM (length ps) fresh
639+ let oldTy = TypeApp tyObject $ rowFromList (oldTys, row)
640+ o' <- TypedValue True <$> check o oldTy <*> pure oldTy
641+ return $ TypedValue True (ObjectUpdate o' newVals) $ TypeApp tyObject $ rowFromList (newTys, row)
642+infer' (Accessor prop val) = do
643+ typed@(TypedValue _ _ objTy) <- infer val
644+ propTy <- inferProperty objTy prop
645+ case propTy of
646+ Nothing -> do
647+ field <- fresh
648+ rest <- fresh
649+ _ <- subsumes Nothing objTy (TypeApp tyObject (RCons prop field rest))
650+ return $ TypedValue True (Accessor prop typed) field
651+ Just ty -> return $ TypedValue True (Accessor prop typed) ty
652+infer' (Abs (Left arg) ret) = do
653+ ty <- fresh
654+ Just moduleName <- checkCurrentModule <$> get
655+ makeBindingGroupVisible $ bindLocalVariables moduleName [(arg, ty, Defined)] $ do
656+ body@(TypedValue _ _ bodyTy) <- infer' ret
657+ return $ TypedValue True (Abs (Left arg) body) $ function ty bodyTy
658+infer' (Abs (Right _) _) = error "Binder was not desugared"
659+infer' (App f arg) = do
660+ f'@(TypedValue _ _ ft) <- infer f
661+ (ret, app) <- checkFunctionApplication f' ft arg Nothing
662+ return $ TypedValue True app ret
663+infer' (Var var) = do
664+ Just moduleName <- checkCurrentModule <$> get
665+ checkVisibility moduleName var
666+ ty <- introduceSkolemScope <=< replaceAllTypeSynonyms <=< lookupVariable moduleName $ var
667+ case ty of
668+ ConstrainedType constraints ty' -> do
669+ dicts <- getTypeClassDictionaries
670+ return $ TypedValue True (foldl App (Var var) (map (flip (TypeClassDictionary True) dicts) constraints)) ty'
671+ _ -> return $ TypedValue True (Var var) ty
672+infer' v@(Constructor c) = do
673+ env <- getEnv
674+ case M.lookup c (dataConstructors env) of
675+ Nothing -> throwError . strMsg $ "Constructor " ++ show c ++ " is undefined"
676+ Just (_, _, ty) -> do ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
677+ return $ TypedValue True v ty'
678+infer' (Case vals binders) = do
679+ ts <- mapM infer vals
680+ ret <- fresh
681+ binders' <- checkBinders (map (\(TypedValue _ _ t) -> t) ts) ret binders
682+ return $ TypedValue True (Case ts binders') ret
683+infer' (IfThenElse cond th el) = do
684+ cond' <- check cond tyBoolean
685+ v2@(TypedValue _ _ t2) <- infer th
686+ v3@(TypedValue _ _ t3) <- infer el
687+ (v2', v3', t) <- meet v2 v3 t2 t3
688+ return $ TypedValue True (IfThenElse cond' v2' v3') t
689+infer' (Let ds val) = do
690+ (ds', val'@(TypedValue _ _ valTy)) <- inferLetBinding [] ds val infer
691+ return $ TypedValue True (Let ds' val') valTy
692+infer' (SuperClassDictionary className tys) = do
693+ dicts <- getTypeClassDictionaries
694+ return $ TypeClassDictionary False (className, tys) dicts
695+infer' (TypedValue checkType val ty) = do
696+ Just moduleName <- checkCurrentModule <$> get
697+ kind <- liftCheck $ kindOf moduleName ty
698+ guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
699+ ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
700+ val' <- if checkType then check val ty' else return val
701+ return $ TypedValue True val' ty'
702+infer' (PositionedValue pos val) = rethrowWithPosition pos $ infer' val
703+infer' _ = error "Invalid argument to infer"
704+
705+inferLetBinding :: [Declaration] -> [Declaration] -> Expr -> (Expr -> UnifyT Type Check Expr) -> UnifyT Type Check ([Declaration], Expr)
706+inferLetBinding seen [] ret j = (,) seen <$> makeBindingGroupVisible (j ret)
707+inferLetBinding seen (ValueDeclaration ident nameKind [] Nothing tv@(TypedValue checkType val ty) : rest) ret j = do
708+ Just moduleName <- checkCurrentModule <$> get
709+ kind <- liftCheck $ kindOf moduleName ty
710+ guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
711+ let dict = M.singleton (moduleName, ident) (ty, nameKind, Undefined)
712+ ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
713+ TypedValue _ val' ty'' <- if checkType then bindNames dict (check val ty') else return tv
714+ bindNames (M.singleton (moduleName, ident) (ty'', nameKind, Defined)) $ inferLetBinding (seen ++ [ValueDeclaration ident nameKind [] Nothing (TypedValue checkType val' ty'')]) rest ret j
715+inferLetBinding seen (ValueDeclaration ident nameKind [] Nothing val : rest) ret j = do
716+ valTy <- fresh
717+ Just moduleName <- checkCurrentModule <$> get
718+ let dict = M.singleton (moduleName, ident) (valTy, nameKind, Undefined)
719+ TypedValue _ val' valTy' <- bindNames dict $ infer val
720+ valTy =?= valTy'
721+ bindNames (M.singleton (moduleName, ident) (valTy', nameKind, Defined)) $ inferLetBinding (seen ++ [ValueDeclaration ident nameKind [] Nothing val']) rest ret j
722+inferLetBinding seen (BindingGroupDeclaration ds : rest) ret j = do
723+ Just moduleName <- checkCurrentModule <$> get
724+ (untyped, typed, dict, untypedDict) <- typeDictionaryForBindingGroup moduleName (map (\(i, _, v) -> (i, v)) ds)
725+ ds1' <- parU typed $ \e -> checkTypedBindingGroupElement moduleName e dict
726+ ds2' <- forM untyped $ \e -> typeForBindingGroupElement e dict untypedDict
727+ let ds' = [(ident, LocalVariable, val') | (ident, (val', _)) <- ds1' ++ ds2']
728+ makeBindingGroupVisible $ bindNames dict $ inferLetBinding (seen ++ [BindingGroupDeclaration ds']) rest ret j
729+inferLetBinding seen (PositionedDeclaration pos d : ds) ret j = rethrowWithPosition pos $ do
730+ ((d' : ds'), val') <- inferLetBinding seen (d : ds) ret j
731+ return (PositionedDeclaration pos d' : ds', val')
732+inferLetBinding _ _ _ _ = error "Invalid argument to inferLetBinding"
733+
734+-- |
735+-- Infer the type of a property inside a record with a given type
736+--
737+inferProperty :: Type -> String -> UnifyT Type Check (Maybe Type)
738+inferProperty (TypeApp obj row) prop | obj == tyObject = do
739+ let (props, _) = rowToList row
740+ return $ lookup prop props
741+inferProperty (SaturatedTypeSynonym name args) prop = do
742+ replaced <- introduceSkolemScope <=< expandTypeSynonym name $ args
743+ inferProperty replaced prop
744+inferProperty (ForAll ident ty _) prop = do
745+ replaced <- replaceVarWithUnknown ident ty
746+ inferProperty replaced prop
747+inferProperty _ _ = return Nothing
748+
749+-- |
750+-- Infer the types of variables brought into scope by a binder
751+--
752+inferBinder :: Type -> Binder -> UnifyT Type Check (M.Map Ident Type)
753+inferBinder _ NullBinder = return M.empty
754+inferBinder val (StringBinder _) = val =?= tyString >> return M.empty
755+inferBinder val (NumberBinder _) = val =?= tyNumber >> return M.empty
756+inferBinder val (BooleanBinder _) = val =?= tyBoolean >> return M.empty
757+inferBinder val (VarBinder name) = return $ M.singleton name val
758+inferBinder val (ConstructorBinder ctor binders) = do
759+ env <- getEnv
760+ case M.lookup ctor (dataConstructors env) of
761+ Just (_, _, ty) -> do
762+ (_, fn) <- instantiatePolyTypeWithUnknowns (error "Data constructor types cannot contain constraints") ty
763+ fn' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ fn
764+ go binders fn'
765+ where
766+ go [] ty' = do
767+ _ <- subsumes Nothing val ty'
768+ return M.empty
769+ go (binder : binders') (TypeApp (TypeApp t obj) ret) | t == tyFunction =
770+ M.union <$> inferBinder obj binder <*> go binders' ret
771+ go _ _ = throwError . strMsg $ "Wrong number of arguments to constructor " ++ show ctor
772+ _ -> throwError . strMsg $ "Constructor " ++ show ctor ++ " is not defined"
773+inferBinder val (ObjectBinder props) = do
774+ row <- fresh
775+ rest <- fresh
776+ m1 <- inferRowProperties row rest props
777+ val =?= TypeApp tyObject row
778+ return m1
779+ where
780+ inferRowProperties :: Type -> Type -> [(String, Binder)] -> UnifyT Type Check (M.Map Ident Type)
781+ inferRowProperties nrow row [] = nrow =?= row >> return M.empty
782+ inferRowProperties nrow row ((name, binder):binders) = do
783+ propTy <- fresh
784+ m1 <- inferBinder propTy binder
785+ m2 <- inferRowProperties nrow (RCons name propTy row) binders
786+ return $ m1 `M.union` m2
787+inferBinder val (ArrayBinder binders) = do
788+ el <- fresh
789+ m1 <- M.unions <$> mapM (inferBinder el) binders
790+ val =?= TypeApp tyArray el
791+ return m1
792+inferBinder val (ConsBinder headBinder tailBinder) = do
793+ el <- fresh
794+ m1 <- inferBinder el headBinder
795+ m2 <- inferBinder val tailBinder
796+ val =?= TypeApp tyArray el
797+ return $ m1 `M.union` m2
798+inferBinder val (NamedBinder name binder) = do
799+ m <- inferBinder val binder
800+ return $ M.insert name val m
801+inferBinder val (PositionedBinder pos binder) =
802+ rethrowWithPosition pos $ inferBinder val binder
803+
804+-- |
805+-- Check the types of the return values in a set of binders in a case statement
806+--
807+checkBinders :: [Type] -> Type -> [CaseAlternative] -> UnifyT Type Check [CaseAlternative]
808+checkBinders _ _ [] = return []
809+checkBinders nvals ret (CaseAlternative binders grd val : bs) = do
810+ guardWith (strMsg "Overlapping binders in case statement") $
811+ let ns = concatMap binderNames binders in length (nub ns) == length ns
812+ Just moduleName <- checkCurrentModule <$> get
813+ m1 <- M.unions <$> zipWithM inferBinder nvals binders
814+ r <- bindLocalVariables moduleName [ (name, ty, Defined) | (name, ty) <- M.toList m1 ] $ do
815+ val' <- TypedValue True <$> check val ret <*> pure ret
816+ case grd of
817+ Nothing -> return $ CaseAlternative binders Nothing val'
818+ Just g -> do
819+ g' <- check g tyBoolean
820+ return $ CaseAlternative binders (Just g') val'
821+ rs <- checkBinders nvals ret bs
822+ return $ r : rs
823+
824+-- |
825+-- Generate a new skolem constant
826+--
827+newSkolemConstant :: UnifyT Type Check Int
828+newSkolemConstant = fresh'
829+
830+-- |
831+-- Generate a new skolem scope
832+--
833+newSkolemScope :: UnifyT Type Check SkolemScope
834+newSkolemScope = SkolemScope <$> fresh'
835+
836+-- |
837+-- Skolemize a type variable by replacing its instances with fresh skolem constants
838+--
839+skolemize :: String -> Int -> SkolemScope -> Type -> Type
840+skolemize ident sko scope = replaceTypeVars ident (Skolem ident sko scope)
841+
842+-- |
843+-- This function has one purpose - to skolemize type variables appearing in a
844+-- SuperClassDictionary placeholder. These type variables are somewhat unique since they are the
845+-- only example of scoped type variables.
846+--
847+skolemizeTypesInValue :: String -> Int -> SkolemScope -> Expr -> Expr
848+skolemizeTypesInValue ident sko scope = let (_, f, _) = everywhereOnValues id go id in f
849+ where
850+ go (SuperClassDictionary c ts) = SuperClassDictionary c (map (skolemize ident sko scope) ts)
851+ go other = other
852+
853+-- |
854+-- Introduce skolem scope at every occurence of a ForAll
855+--
856+introduceSkolemScope :: Type -> UnifyT Type Check Type
857+introduceSkolemScope = everywhereOnTypesM go
858+ where
859+ go (ForAll ident ty Nothing) = ForAll ident ty <$> (Just <$> newSkolemScope)
860+ go other = return other
861+
862+-- |
863+-- Check the type of a value, rethrowing errors to provide a better error message
864+--
865+check :: Expr -> Type -> UnifyT Type Check Expr
866+check val ty = rethrow (mkErrorStack errorMessage (Just (ExprError val)) <>) $ check' val ty
867+ where
868+ errorMessage =
869+ "Error checking type of term " ++
870+ prettyPrintValue val ++
871+ " against type " ++
872+ prettyPrintType ty
873+
874+-- |
875+-- Check the type of a value
876+--
877+check' :: Expr -> Type -> UnifyT Type Check Expr
878+check' val (ForAll ident ty _) = do
879+ scope <- newSkolemScope
880+ sko <- newSkolemConstant
881+ let sk = skolemize ident sko scope ty
882+ let skVal = skolemizeTypesInValue ident sko scope val
883+ val' <- check skVal sk
884+ return $ TypedValue True val' (ForAll ident ty (Just scope))
885+check' val t@(ConstrainedType constraints ty) = do
886+ dictNames <- forM constraints $ \(Qualified _ (ProperName className), _) -> do
887+ n <- liftCheck freshDictionaryName
888+ return $ Ident $ "__dict_" ++ className ++ "_" ++ show n
889+ val' <- makeBindingGroupVisible $ withTypeClassDictionaries (zipWith (\name (className, instanceTy) ->
890+ TypeClassDictionaryInScope name className instanceTy Nothing TCDRegular False) (map (Qualified Nothing) dictNames)
891+ constraints) $ check val ty
892+ return $ TypedValue True (foldr (Abs . Left) val' dictNames) t
893+check' val (SaturatedTypeSynonym name args) = do
894+ ty <- introduceSkolemScope <=< expandTypeSynonym name $ args
895+ check val ty
896+check' val u@(TUnknown _) = do
897+ val'@(TypedValue _ _ ty) <- infer val
898+ -- Don't unify an unknown with an inferred polytype
899+ (val'', ty') <- instantiatePolyTypeWithUnknowns val' ty
900+ ty' =?= u
901+ return $ TypedValue True val'' ty'
902+check' v@(NumericLiteral _) t | t == tyNumber =
903+ return $ TypedValue True v t
904+check' v@(StringLiteral _) t | t == tyString =
905+ return $ TypedValue True v t
906+check' v@(BooleanLiteral _) t | t == tyBoolean =
907+ return $ TypedValue True v t
908+check' (ArrayLiteral vals) t@(TypeApp a ty) = do
909+ a =?= tyArray
910+ array <- ArrayLiteral <$> forM vals (`check` ty)
911+ return $ TypedValue True array t
912+check' (Abs (Left arg) ret) ty@(TypeApp (TypeApp t argTy) retTy) | t == tyFunction = do
913+ Just moduleName <- checkCurrentModule <$> get
914+ ret' <- makeBindingGroupVisible $ bindLocalVariables moduleName [(arg, argTy, Defined)] $ check ret retTy
915+ return $ TypedValue True (Abs (Left arg) ret') ty
916+check' (Abs (Right _) _) _ = error "Binder was not desugared"
917+check' (App f arg) ret = do
918+ f'@(TypedValue _ _ ft) <- infer f
919+ (_, app) <- checkFunctionApplication f' ft arg (Just ret)
920+ return $ TypedValue True app ret
921+check' v@(Var var) ty = do
922+ Just moduleName <- checkCurrentModule <$> get
923+ checkVisibility moduleName var
924+ repl <- introduceSkolemScope <=< replaceAllTypeSynonyms <=< lookupVariable moduleName $ var
925+ ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
926+ v' <- subsumes (Just v) repl ty'
927+ case v' of
928+ Nothing -> throwError . strMsg $ "Unable to check type subsumption"
929+ Just v'' -> return $ TypedValue True v'' ty'
930+check' (SuperClassDictionary className tys) _ = do
931+ {-
932+ -- Here, we replace a placeholder for a superclass dictionary with a regular
933+ -- TypeClassDictionary placeholder. The reason we do this is that it is necessary to have the
934+ -- correct super instance dictionaries in scope, and these are not available when the type class
935+ -- declaration gets desugared.
936+ --
937+ -- Note also that the first argument to TypeClassDictionary is False, meaning we _do not_ want
938+ -- to consider superclass instances when searching for this dictionary - doing so might lead
939+ -- to traversing a cycle in the instance graph.
940+ -}
941+ dicts <- getTypeClassDictionaries
942+ return $ TypeClassDictionary False (className, tys) dicts
943+check' (TypedValue checkType val ty1) ty2 = do
944+ Just moduleName <- checkCurrentModule <$> get
945+ kind <- liftCheck $ kindOf moduleName ty1
946+ guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
947+ ty1' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty1
948+ ty2' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty2
949+ val' <- subsumes (Just val) ty1' ty2'
950+ case val' of
951+ Nothing -> throwError . strMsg $ "Unable to check type subsumption"
952+ Just val'' -> do
953+ val''' <- if checkType then check val'' ty2' else return val''
954+ return $ TypedValue checkType (TypedValue True val''' ty1') ty2'
955+check' (Case vals binders) ret = do
956+ vals' <- mapM infer vals
957+ let ts = map (\(TypedValue _ _ t) -> t) vals'
958+ binders' <- checkBinders ts ret binders
959+ return $ TypedValue True (Case vals' binders') ret
960+check' (IfThenElse cond th el) ty = do
961+ cond' <- check cond tyBoolean
962+ th' <- check th ty
963+ el' <- check el ty
964+ return $ TypedValue True (IfThenElse cond' th' el') ty
965+check' (ObjectLiteral ps) t@(TypeApp obj row) | obj == tyObject = do
966+ ensureNoDuplicateProperties ps
967+ ps' <- checkProperties ps row False
968+ return $ TypedValue True (ObjectLiteral ps') t
969+check' (TypeClassDictionaryConstructorApp name ps) t = do
970+ ps' <- check' ps t
971+ return $ TypedValue True (TypeClassDictionaryConstructorApp name ps') t
972+check' (ObjectUpdate obj ps) t@(TypeApp o row) | o == tyObject = do
973+ ensureNoDuplicateProperties ps
974+ us <- zip (map fst ps) <$> replicateM (length ps) fresh
975+ let (propsToCheck, rest) = rowToList row
976+ propsToRemove = map fst ps
977+ remainingProps = filter (\(p, _) -> p `notElem` propsToRemove) propsToCheck
978+ obj' <- check obj (TypeApp tyObject (rowFromList (us ++ remainingProps, rest)))
979+ ps' <- checkProperties ps row True
980+ return $ TypedValue True (ObjectUpdate obj' ps') t
981+check' (Accessor prop val) ty = do
982+ rest <- fresh
983+ val' <- check val (TypeApp tyObject (RCons prop ty rest))
984+ return $ TypedValue True (Accessor prop val') ty
985+check' (Constructor c) ty = do
986+ env <- getEnv
987+ case M.lookup c (dataConstructors env) of
988+ Nothing -> throwError . strMsg $ "Constructor " ++ show c ++ " is undefined"
989+ Just (_, _, ty1) -> do
990+ repl <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty1
991+ _ <- subsumes Nothing repl ty
992+ return $ TypedValue True (Constructor c) ty
993+check' (Let ds val) ty = do
994+ (ds', val') <- inferLetBinding [] ds val (flip check ty)
995+ return $ TypedValue True (Let ds' val') ty
996+check' val ty | containsTypeSynonyms ty = do
997+ ty' <- introduceSkolemScope <=< expandAllTypeSynonyms $ ty
998+ check val ty'
999+check' (PositionedValue pos val) ty =
1000+ rethrowWithPosition pos $ check val ty
1001+check' val ty = throwError $ mkErrorStack ("Expr does not have type " ++ prettyPrintType ty) (Just (ExprError val))
1002+
1003+containsTypeSynonyms :: Type -> Bool
1004+containsTypeSynonyms = everythingOnTypes (||) go where
1005+ go (SaturatedTypeSynonym _ _) = True
1006+ go _ = False
1007+
1008+-- |
1009+-- Check the type of a collection of named record fields
1010+--
1011+-- The @lax@ parameter controls whether or not every record member has to be provided. For object updates, this is not the case.
1012+--
1013+checkProperties :: [(String, Expr)] -> Type -> Bool -> UnifyT Type Check [(String, Expr)]
1014+checkProperties ps row lax = let (ts, r') = rowToList row in go ps ts r' where
1015+ go [] [] REmpty = return []
1016+ go [] [] u@(TUnknown _) = do u =?= REmpty
1017+ return []
1018+ go [] [] (Skolem _ _ _) | lax = return []
1019+ go [] ((p, _): _) _ | lax = return []
1020+ | otherwise = throwError $ mkErrorStack ("Object does not have property " ++ p) (Just (ExprError (ObjectLiteral ps)))
1021+ go ((p,_):_) [] REmpty = throwError $ mkErrorStack ("Property " ++ p ++ " is not present in closed object type " ++ prettyPrintRow row) (Just (ExprError (ObjectLiteral ps)))
1022+ go ((p,v):ps') [] u@(TUnknown _) = do
1023+ v'@(TypedValue _ _ ty) <- infer v
1024+ rest <- fresh
1025+ u =?= RCons p ty rest
1026+ ps'' <- go ps' [] rest
1027+ return $ (p, v') : ps''
1028+ go ((p,v):ps') ts r =
1029+ case lookup p ts of
1030+ Nothing -> do
1031+ v'@(TypedValue _ _ ty) <- infer v
1032+ rest <- fresh
1033+ r =?= RCons p ty rest
1034+ ps'' <- go ps' ts rest
1035+ return $ (p, v') : ps''
1036+ Just ty -> do
1037+ v' <- check v ty
1038+ ps'' <- go ps' (delete (p, ty) ts) r
1039+ return $ (p, v') : ps''
1040+ go _ _ _ = throwError $ mkErrorStack ("Object does not have type " ++ prettyPrintType (TypeApp tyObject row)) (Just (ExprError (ObjectLiteral ps)))
1041+
1042+-- |
1043+-- Check the type of a function application, rethrowing errors to provide a better error message
1044+--
1045+checkFunctionApplication :: Expr -> Type -> Expr -> Maybe Type -> UnifyT Type Check (Type, Expr)
1046+checkFunctionApplication fn fnTy arg ret = rethrow (mkErrorStack errorMessage (Just (ExprError fn)) <>) $ do
1047+ subst <- unifyCurrentSubstitution <$> UnifyT get
1048+ checkFunctionApplication' fn (subst $? fnTy) arg (($?) subst <$> ret)
1049+ where
1050+ errorMessage = "Error applying function of type "
1051+ ++ prettyPrintType fnTy
1052+ ++ " to argument " ++ prettyPrintValue arg
1053+
1054+-- |
1055+-- Check the type of a function application
1056+--
1057+checkFunctionApplication' :: Expr -> Type -> Expr -> Maybe Type -> UnifyT Type Check (Type, Expr)
1058+checkFunctionApplication' fn (TypeApp (TypeApp tyFunction' argTy) retTy) arg ret = do
1059+ tyFunction' =?= tyFunction
1060+ arg' <- check arg argTy
1061+ case ret of
1062+ Nothing -> return (retTy, App fn arg')
1063+ Just ret' -> do
1064+ Just app' <- subsumes (Just (App fn arg')) retTy ret'
1065+ return (retTy, app')
1066+checkFunctionApplication' fn (ForAll ident ty _) arg ret = do
1067+ replaced <- replaceVarWithUnknown ident ty
1068+ checkFunctionApplication fn replaced arg ret
1069+checkFunctionApplication' fn u@(TUnknown _) arg ret = do
1070+ arg' <- do
1071+ TypedValue _ arg' t <- infer arg
1072+ (arg'', t') <- instantiatePolyTypeWithUnknowns arg' t
1073+ return $ TypedValue True arg'' t'
1074+ let ty = (\(TypedValue _ _ t) -> t) arg'
1075+ ret' <- maybe fresh return ret
1076+ u =?= function ty ret'
1077+ return (ret', App fn arg')
1078+checkFunctionApplication' fn (SaturatedTypeSynonym name tyArgs) arg ret = do
1079+ ty <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
1080+ checkFunctionApplication fn ty arg ret
1081+checkFunctionApplication' fn (ConstrainedType constraints fnTy) arg ret = do
1082+ dicts <- getTypeClassDictionaries
1083+ checkFunctionApplication' (foldl App fn (map (flip (TypeClassDictionary True) dicts) constraints)) fnTy arg ret
1084+checkFunctionApplication' fn fnTy dict@(TypeClassDictionary _ _ _) _ =
1085+ return (fnTy, App fn dict)
1086+checkFunctionApplication' _ fnTy arg _ = throwError . strMsg $ "Cannot apply a function of type "
1087+ ++ prettyPrintType fnTy
1088+ ++ " to argument " ++ prettyPrintValue arg
1089+
1090+-- |
1091+-- Check whether one type subsumes another, rethrowing errors to provide a better error message
1092+--
1093+subsumes :: Maybe Expr -> Type -> Type -> UnifyT Type Check (Maybe Expr)
1094+subsumes val ty1 ty2 = rethrow (mkErrorStack errorMessage (ExprError <$> val) <>) $ subsumes' val ty1 ty2
1095+ where
1096+ errorMessage = "Error checking that type "
1097+ ++ prettyPrintType ty1
1098+ ++ " subsumes type "
1099+ ++ prettyPrintType ty2
1100+
1101+-- |
1102+-- Check whether one type subsumes another
1103+--
1104+subsumes' :: Maybe Expr -> Type -> Type -> UnifyT Type Check (Maybe Expr)
1105+subsumes' val (ForAll ident ty1 _) ty2 = do
1106+ replaced <- replaceVarWithUnknown ident ty1
1107+ subsumes val replaced ty2
1108+subsumes' val ty1 (ForAll ident ty2 sco) =
1109+ case sco of
1110+ Just sco' -> do
1111+ sko <- newSkolemConstant
1112+ let sk = skolemize ident sko sco' ty2
1113+ subsumes val ty1 sk
1114+ Nothing -> throwError . strMsg $ "Skolem variable scope is unspecified"
1115+subsumes' val (TypeApp (TypeApp f1 arg1) ret1) (TypeApp (TypeApp f2 arg2) ret2) | f1 == tyFunction && f2 == tyFunction = do
1116+ _ <- subsumes Nothing arg2 arg1
1117+ _ <- subsumes Nothing ret1 ret2
1118+ return val
1119+subsumes' val (SaturatedTypeSynonym name tyArgs) ty2 = do
1120+ ty1 <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
1121+ subsumes val ty1 ty2
1122+subsumes' val ty1 (SaturatedTypeSynonym name tyArgs) = do
1123+ ty2 <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
1124+ subsumes val ty1 ty2
1125+subsumes' (Just val) (ConstrainedType constraints ty1) ty2 = do
1126+ dicts <- getTypeClassDictionaries
1127+ subsumes' (Just $ foldl App val (map (flip (TypeClassDictionary True) dicts) constraints)) ty1 ty2
1128+subsumes' val (TypeApp f1 r1) (TypeApp f2 r2) | f1 == tyObject && f2 == tyObject = do
1129+ let
1130+ (ts1, r1') = rowToList r1
1131+ (ts2, r2') = rowToList r2
1132+ ts1' = sortBy (comparing fst) ts1
1133+ ts2' = sortBy (comparing fst) ts2
1134+ go ts1' ts2' r1' r2'
1135+ return val
1136+ where
1137+ go [] ts2 r1' r2' = r1' =?= rowFromList (ts2, r2')
1138+ go ts1 [] r1' r2' = r2' =?= rowFromList (ts1, r1')
1139+ go ((p1, ty1) : ts1) ((p2, ty2) : ts2) r1' r2'
1140+ | p1 == p2 = do _ <- subsumes Nothing ty1 ty2
1141+ go ts1 ts2 r1' r2'
1142+ | p1 < p2 = do rest <- fresh
1143+ r2' =?= RCons p1 ty1 rest
1144+ go ts1 ((p2, ty2) : ts2) r1' rest
1145+ | otherwise = do rest <- fresh
1146+ r1' =?= RCons p2 ty2 rest
1147+ go ((p1, ty1) : ts1) ts2 rest r2'
1148+subsumes' val ty1 ty2@(TypeApp obj _) | obj == tyObject = subsumes val ty2 ty1
1149+subsumes' val ty1 ty2 = do
1150+ ty1 =?= ty2
1151+ return val
1152+
1153+-- |
1154+-- Compute the meet of two types, i.e. the most general type which both types subsume.
1155+-- TODO: handle constrained types
1156+--
1157+meet :: Expr -> Expr -> Type -> Type -> UnifyT Type Check (Expr, Expr, Type)
1158+meet e1 e2 (ForAll ident t1 _) t2 = do
1159+ t1' <- replaceVarWithUnknown ident t1
1160+ meet e1 e2 t1' t2
1161+meet e1 e2 t1 (ForAll ident t2 _) = do
1162+ t2' <- replaceVarWithUnknown ident t2
1163+ meet e1 e2 t1 t2'
1164+meet e1 e2 t1 t2 = do
1165+ t1 =?= t2
1166+ return (e1, e2, t1)
1167+
1168+
1169+
1170+
1171+
1172+
1173+