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1−-----------------------------------------------------------------------------
3−-- Module : Language.PureScript.TypeChecker.Types
4−-- Copyright : (c) Phil Freeman 2013
7−-- Maintainer : Phil Freeman <paf31@cantab.net>
8−-- Stability : experimental
12−-- This module implements the type checker
14−-----------------------------------------------------------------------------
16−{-# OPTIONS_GHC -fno-warn-orphans #-}
17−{-# LANGUAGE FlexibleInstances #-}
18−{-# LANGUAGE FlexibleContexts #-}
19−{-# LANGUAGE MultiParamTypeClasses #-}
21−module Language.PureScript.TypeChecker.Types (
26− The following functions represent the corresponding type checking judgements:
29− Synthesize a type for a value
32− Check a value has a given type
35− Check an object with a given type contains specified properties
37− checkFunctionApplication
38− Check a function of a given type returns a value of another type when applied to its arguments
41− Check a type subsumes another type
45−import Data.Maybe (maybeToList, isNothing, isJust, fromMaybe)
46−import Data.Function (on)
47−import Data.Ord (comparing)
50− (everythingWithContext, mkQ)
52−import Language.PureScript.Declarations
53−import Language.PureScript.Types
54−import Language.PureScript.Kinds
55−import Language.PureScript.Names
56−import Language.PureScript.TypeClassDictionaries
57−import Language.PureScript.TypeChecker.Monad
58−import Language.PureScript.TypeChecker.Kinds
59−import Language.PureScript.TypeChecker.Synonyms
60−import Language.PureScript.Pretty
61−import Language.PureScript.Environment
62−import Language.PureScript.Errors
63−import qualified Language.PureScript.Constants as C
65−import Control.Monad.State
66−import Control.Monad.Error
67−import Control.Monad.Unify
69−import Control.Applicative
70−import Control.Arrow (Arrow(..))
72−import qualified Data.Map as M
73−import qualified Data.HashMap.Strict as H
75−instance Partial Type where
77− isUnknown (TUnknown u) = Just u
78− isUnknown _ = Nothing
79− unknowns = everythingOnTypes (++) go
81− go (TUnknown u) = [u]
83− ($?) sub = everywhereOnTypes go
85− go t@(TUnknown u) = case H.lookup u (runSubstitution sub) of
90−instance Unifiable Check Type where
94−-- Unify two types, updating the current substitution
96−unifyTypes :: Type -> Type -> UnifyT Type Check ()
97−unifyTypes t1 t2 = rethrow (mkErrorStack ("Error unifying type " ++ prettyPrintType t1 ++ " with type " ++ prettyPrintType t2) Nothing <>) $
100− unifyTypes' (TUnknown u1) (TUnknown u2) | u1 == u2 = return ()
101− unifyTypes' (TUnknown u) t = u =:= t
102− unifyTypes' t (TUnknown u) = u =:= t
103− unifyTypes' (SaturatedTypeSynonym name args) ty = do
104− ty1 <- introduceSkolemScope <=< expandTypeSynonym name $ args
106− unifyTypes' ty s@(SaturatedTypeSynonym _ _) = s `unifyTypes` ty
107− unifyTypes' (ForAll ident1 ty1 sc1) (ForAll ident2 ty2 sc2) =
109− (Just sc1', Just sc2') -> do
110− sko <- newSkolemConstant
111− let sk1 = skolemize ident1 sko sc1' ty1
112− let sk2 = skolemize ident2 sko sc2' ty2
113− sk1 `unifyTypes` sk2
114− _ -> error "Skolemized type variable was not given a scope"
115− unifyTypes' (ForAll ident ty1 (Just sc)) ty2 = do
116− sko <- newSkolemConstant
117− let sk = skolemize ident sko sc ty1
119− unifyTypes' ForAll{} _ = throwError . strMsg $ "Skolem variable scope is unspecified"
120− unifyTypes' ty f@ForAll{} = f `unifyTypes` ty
121− unifyTypes' (TypeVar v1) (TypeVar v2) | v1 == v2 = return ()
122− unifyTypes' (TypeConstructor c1) (TypeConstructor c2) =
123− guardWith (strMsg ("Cannot unify " ++ show c1 ++ " with " ++ show c2 ++ ".")) (c1 == c2)
124− unifyTypes' (TypeApp t3 t4) (TypeApp t5 t6) = do
127− unifyTypes' (Skolem _ s1 _) (Skolem _ s2 _) | s1 == s2 = return ()
128− unifyTypes' r1@RCons{} r2 = unifyRows r1 r2
129− unifyTypes' r1 r2@RCons{} = unifyRows r1 r2
130− unifyTypes' r1@REmpty r2 = unifyRows r1 r2
131− unifyTypes' r1 r2@REmpty = unifyRows r1 r2
132− unifyTypes' t@(ConstrainedType _ _) _ = throwError . strMsg $ "Attempted to unify a constrained type " ++ prettyPrintType t ++ " with another type."
133− unifyTypes' t3 t4@(ConstrainedType _ _) = unifyTypes' t4 t3
134− unifyTypes' t3 t4 = throwError . strMsg $ "Cannot unify " ++ prettyPrintType t3 ++ " with " ++ prettyPrintType t4 ++ "."
137−-- Unify two rows, updating the current substitution
139−-- Common labels are first identified, and unified. Remaining labels and types are unified with a
140−-- trailing row unification variable, if appropriate, otherwise leftover labels result in a unification
143−unifyRows :: Type -> Type -> UnifyT Type Check ()
146− (s1, r1') = rowToList r1
147− (s2, r2') = rowToList r2
148− int = [ (t1, t2) | (name, t1) <- s1, (name', t2) <- s2, name == name' ]
149− sd1 = [ (name, t1) | (name, t1) <- s1, name `notElem` map fst s2 ]
150− sd2 = [ (name, t2) | (name, t2) <- s2, name `notElem` map fst s1 ]
152− forM_ int (uncurry (=?=))
153− unifyRows' sd1 r1' sd2 r2'
155− unifyRows' :: [(String, Type)] -> Type -> [(String, Type)] -> Type -> UnifyT Type Check ()
156− unifyRows' [] (TUnknown u) sd r = u =:= rowFromList (sd, r)
157− unifyRows' sd r [] (TUnknown u) = u =:= rowFromList (sd, r)
158− unifyRows' ((name, ty):row) r others u@(TUnknown un) = do
160− forM_ row $ \(_, t) -> occursCheck un t
162− u =?= RCons name ty u'
163− unifyRows' row r others u'
164− unifyRows' [] REmpty [] REmpty = return ()
165− unifyRows' [] (TypeVar v1) [] (TypeVar v2) | v1 == v2 = return ()
166− unifyRows' [] (Skolem _ s1 _) [] (Skolem _ s2 _) | s1 == s2 = return ()
167− unifyRows' sd3 r3 sd4 r4 = throwError . strMsg $ "Cannot unify (" ++ prettyPrintRow (rowFromList (sd3, r3)) ++ ") with (" ++ prettyPrintRow (rowFromList (sd4, r4)) ++ ")"
170−-- Infer the types of multiple mutually-recursive values, and return elaborated values including
171−-- type class dictionaries and type annotations.
173−typesOf :: Maybe ModuleName -> ModuleName -> [(Ident, Value)] -> Check [(Ident, (Value, Type))]
174−typesOf mainModuleName moduleName vals = do
175− tys <- fmap tidyUp . liftUnify $ do
176− (es, dict, untypedDict) <- typeDictionaryForBindingGroup moduleName vals
178− triple@(_, (_, ty)) <- typeForBindingGroupElement moduleName e dict untypedDict
179− -- If --main is enabled, need to check that `main` has type Eff eff a for some eff, a
180− when (Just moduleName == mainModuleName && fst e == Ident C.main) $ do
181− [eff, a] <- replicateM 2 fresh
182− ty =?= TypeApp (TypeApp (TypeConstructor (Qualified (Just (ModuleName [ProperName "Control", ProperName "Monad", ProperName "Eff"])) (ProperName "Eff"))) eff) a
185− forM tys $ \(ident, (val, ty)) -> do
186− -- Replace type class dictionary placeholders with actual dictionaries
187− val' <- replaceTypeClassDictionaries moduleName val
188− -- Check skolem variables did not escape their scope
189− skolemEscapeCheck val'
190− -- Remove type synonyms placeholders, remove duplicate row fields, and replace
191− -- top-level unification variables with named type variables.
192− let val'' = overTypes (desaturateAllTypeSynonyms . setifyAll) val'
193− ty' = varIfUnknown . desaturateAllTypeSynonyms . setifyAll $ ty
194− return (ident, (val'', ty'))
196− -- Apply the substitution that was returned from runUnify to both types and (type-annotated) values
197− tidyUp (ts, sub) = map (\(i, (val, ty)) -> (i, (overTypes (sub $?) val, sub $? ty))) ts
199−typeDictionaryForBindingGroup :: ModuleName -> [(Ident, Value)] -> UnifyT Type Check ([(Ident, (Value, Maybe (Type, Bool)))], M.Map (ModuleName, Ident) (Type, NameKind), [(Ident, Type)])
200−typeDictionaryForBindingGroup moduleName vals = do
202− -- Map each declaration to a name/value pair, with an optional type, if the declaration is typed
203− es = map isTyped vals
204− -- Filter the typed and untyped declarations
205− typed = filter (isJust . snd . snd) es
206− untyped = filter (isNothing . snd . snd) es
207− -- Make a map of names to typed declarations
208− typedDict = map (\(ident, (_, Just (ty, _))) -> (ident, ty)) typed
210− -- Create fresh unification variables for the types of untyped declarations
211− untypedNames <- replicateM (length untyped) fresh
214− -- Make a map of names to the unification variables of untyped declarations
215− untypedDict = zip (map fst untyped) untypedNames
216− -- Create the dictionary of all name/type pairs, which will be added to the environment during type checking
217− dict = M.fromList (map (\(ident, ty) -> ((moduleName, ident), (ty, LocalVariable))) $ typedDict ++ untypedDict)
218− return (es, dict, untypedDict)
220−typeForBindingGroupElement :: ModuleName -> (Ident, (Value, Maybe (Type, Bool))) -> M.Map (ModuleName, Ident) (Type, NameKind) -> [(Ident, Type)] -> UnifyT Type Check (Ident, (Value, Type))
221−typeForBindingGroupElement moduleName e@(_, (val, _)) dict untypedDict = do
222− -- If the declaration is a function, it has access to other values in the binding group.
223− -- If not, the generated code might fail at runtime since those values might be undefined.
224− let dict' = if isFunction val then dict else M.empty
226− -- Typed declarations
227− (ident, (val', Just (ty, checkType))) -> do
229− kind <- liftCheck $ kindOf moduleName ty
230− guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
231− -- Check the type with the new names in scope
232− ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
233− val'' <- bindNames dict' $ if checkType
234− then TypedValue True <$> check val' ty' <*> pure ty'
235− else return (TypedValue False val' ty')
236− return (ident, (val'', ty'))
237− -- Untyped declarations
238− (ident, (val', Nothing)) -> do
239− -- Infer the type with the new names in scope
240− TypedValue _ val'' ty <- bindNames dict' $ infer val'
241− ty =?= fromMaybe (error "name not found in dictionary") (lookup ident untypedDict)
242− return (ident, (TypedValue True val'' ty, ty))
245−-- Check if a value introduces a function
247−isFunction :: Value -> Bool
248−isFunction (Abs _ _) = True
249−isFunction (TypedValue _ val _) = isFunction val
250−isFunction (PositionedValue _ val) = isFunction val
254−-- Check if a value contains a type annotation
256−isTyped :: (Ident, Value) -> (Ident, (Value, Maybe (Type, Bool)))
257−isTyped (name, TypedValue checkType value ty) = (name, (value, Just (ty, checkType)))
258−isTyped (name, value) = (name, (value, Nothing))
261−-- Map a function over type annotations appearing inside a value
263−overTypes :: (Type -> Type) -> Value -> Value
264−overTypes f = let (_, f', _) = everywhereOnValues id g id in f'
267− g (TypedValue checkTy val t) = TypedValue checkTy val (f t)
268− g (TypeClassDictionary b (nm, tys) sco) = TypeClassDictionary b (nm, map f tys) sco
272−-- Replace type class dictionary placeholders with inferred type class dictionaries
274−replaceTypeClassDictionaries :: ModuleName -> Value -> Check Value
275−replaceTypeClassDictionaries mn =
276− let (_, f, _) = everywhereOnValuesTopDownM return go return
279− go (TypeClassDictionary trySuperclasses constraint dicts) = do
281− entails env mn dicts constraint trySuperclasses
282− go other = return other
285−-- A simplified representation of expressions which are used to represent type
286−-- class dictionaries at runtime, which can be compared for equality
290− -- A dictionary which is brought into scope by a local constraint
292− = LocalDictionaryValue (Qualified Ident)
294− -- A dictionary which is brought into scope by an instance declaration
296− | GlobalDictionaryValue (Qualified Ident)
298− -- A dictionary which depends on other dictionaries
300− | DependentDictionaryValue (Qualified Ident) [DictionaryValue]
302− -- A subclass dictionary
304− | SubclassDictionaryValue DictionaryValue (Qualified ProperName) Integer
305− deriving (Show, Ord, Eq)
308−-- Check that the current set of type class dictionaries entail the specified type class goal, and, if so,
309−-- return a type class dictionary reference.
311−entails :: Environment -> ModuleName -> [TypeClassDictionaryInScope] -> (Qualified ProperName, [Type]) -> Bool -> Check Value
312−entails env moduleName context = solve (sortedNubBy canonicalizeDictionary (filter filterModule context))
314− sortedNubBy :: (Ord k) => (v -> k) -> [v] -> [v]
315− sortedNubBy f vs = M.elems (M.fromList (map (f &&& id) vs))
317− -- Filter out type dictionaries which are in scope in the current module
318− filterModule :: TypeClassDictionaryInScope -> Bool
319− filterModule (TypeClassDictionaryInScope { tcdName = Qualified (Just mn) _ }) | mn == moduleName = True
320− filterModule (TypeClassDictionaryInScope { tcdName = Qualified Nothing _ }) = True
321− filterModule _ = False
323− solve context' (className, tys) trySuperclasses =
325− dicts = go trySuperclasses className tys
326− in case sortedNubBy dictTrace (chooseSimplestDictionaries dicts) of
327− [] -> throwError . strMsg $ "No instance found for " ++ show className ++ " " ++ unwords (map prettyPrintTypeAtom tys)
328− [_] -> return $ dictionaryValueToValue $ head dicts
329− _ -> throwError . strMsg $ "Overlapping instances found for " ++ show className ++ " " ++ unwords (map prettyPrintTypeAtom tys)
331− go trySuperclasses' className' tys' =
332− -- Look for regular type instances
333− [ mkDictionary (canonicalizeDictionary tcd) args
335− -- Make sure the type class name matches the one we are trying to satisfy
336− , className' == tcdClassName tcd
337− -- Make sure the type unifies with the type in the type instance definition
338− , subst <- maybeToList . (>>= verifySubstitution) . fmap concat $ zipWithM (typeHeadsAreEqual moduleName env) tys' (tcdInstanceTypes tcd)
339− -- Solve any necessary subgoals
340− , args <- solveSubgoals subst (tcdDependencies tcd) ] ++
342− -- Look for implementations via superclasses
343− [ SubclassDictionaryValue suDict superclass index
345− , (subclassName, (args, _, implies)) <- M.toList (typeClasses env)
346− -- Try each superclass
347− , (index, (superclass, suTyArgs)) <- zip [0..] implies
348− -- Make sure the type class name matches the superclass name
349− , className' == superclass
350− -- Make sure the types unify with the types in the superclass implication
351− , subst <- maybeToList . (>>= verifySubstitution) . fmap concat $ zipWithM (typeHeadsAreEqual moduleName env) tys' suTyArgs
352− -- Finally, satisfy the subclass constraint
353− , args' <- maybeToList $ mapM (applySubst subst . TypeVar) args
354− , suDict <- go True subclassName args' ]
356− -- Create dictionaries for subgoals which still need to be solved by calling go recursively
357− -- E.g. the goal (Show a, Show b) => Show (Either a b) can be satisfied if the current type
358− -- unifies with Either a b, and we can satisfy the subgoals Show a and Show b recursively.
359− solveSubgoals :: [(String, Type)] -> Maybe [(Qualified ProperName, [Type])] -> [Maybe [DictionaryValue]]
360− solveSubgoals _ Nothing = return Nothing
361− solveSubgoals subst (Just subgoals) = do
362− dict <- mapM (uncurry (go True) . second (map (replaceAllTypeVars subst))) subgoals
364− -- Make a dictionary from subgoal dictionaries by applying the correct function
365− mkDictionary :: Qualified Ident -> Maybe [DictionaryValue] -> DictionaryValue
366− mkDictionary fnName Nothing = LocalDictionaryValue fnName
367− mkDictionary fnName (Just []) = GlobalDictionaryValue fnName
368− mkDictionary fnName (Just dicts) = DependentDictionaryValue fnName dicts
369− -- Turn a DictionaryValue into a Value
370− dictionaryValueToValue :: DictionaryValue -> Value
371− dictionaryValueToValue (LocalDictionaryValue fnName) = Var fnName
372− dictionaryValueToValue (GlobalDictionaryValue fnName) = App (Var fnName) (ObjectLiteral [])
373− dictionaryValueToValue (DependentDictionaryValue fnName dicts) = foldl App (Var fnName) (map dictionaryValueToValue dicts)
374− dictionaryValueToValue (SubclassDictionaryValue dict superclassName index) =
375− App (Accessor (show superclassName ++ "_" ++ show index)
376− (Accessor C.__superclasses (dictionaryValueToValue dict)))
378− -- Ensure that a substitution is valid
379− verifySubstitution :: [(String, Type)] -> Maybe [(String, Type)]
380− verifySubstitution subst = do
381− let grps = groupBy ((==) `on` fst) subst
382− guard (all (pairwise (unifiesWith env) . map snd) grps)
383− return $ map head grps
384− -- Apply a substitution to a type
385− applySubst :: [(String, Type)] -> Type -> Maybe Type
386− applySubst subst = everywhereOnTypesM replace
388− replace (TypeVar v) = lookup v subst
389− replace other = Just other
390− -- Choose the simplest DictionaryValues from a list of candidates
391− -- The reason for this function is as follows:
392− -- When considering overlapping instances, we don't want to consider the same dictionary
393− -- to be an overlap of itself when obtained as a superclass of another class.
394− -- Observing that we probably don't want to select a superclass instance when an instance
395− -- is available directly, and that there is no way for a superclass instance to actually
396− -- introduce an overlap that wouldn't have been there already, we simply remove dictionaries
397− -- obtained as superclass instances if there are simpler instances available.
398− chooseSimplestDictionaries :: [DictionaryValue] -> [DictionaryValue]
399− chooseSimplestDictionaries ds = case filter isSimpleDictionaryValue ds of
402− isSimpleDictionaryValue SubclassDictionaryValue{} = False
403− isSimpleDictionaryValue (DependentDictionaryValue _ ds) = all isSimpleDictionaryValue ds
404− isSimpleDictionaryValue _ = True
406− -- Get the "trace" of a DictionaryValue - that is, remove all SubclassDictionaryValue
407− -- data constructors
409− dictTrace :: DictionaryValue -> DictionaryValue
410− dictTrace (DependentDictionaryValue fnName dicts) = DependentDictionaryValue fnName $ map dictTrace dicts
411− dictTrace (SubclassDictionaryValue dict _ _) = dictTrace dict
412− dictTrace other = other
415−-- Check all values in a list pairwise match a predicate
417−pairwise :: (a -> a -> Bool) -> [a] -> Bool
419−pairwise _ [_] = True
420−pairwise p (x : xs) = all (p x) xs && pairwise p xs
423−-- Check that two types unify
425−unifiesWith :: Environment -> Type -> Type -> Bool
426−unifiesWith _ (TUnknown _) _ = True
427−unifiesWith _ _ (TUnknown _) = True
428−unifiesWith _ (Skolem _ s1 _) (Skolem _ s2 _) | s1 == s2 = True
429−unifiesWith _ (TypeVar v1) (TypeVar v2) | v1 == v2 = True
430−unifiesWith _ (TypeConstructor c1) (TypeConstructor c2) | c1 == c2 = True
431−unifiesWith e (TypeApp h1 t1) (TypeApp h2 t2) = unifiesWith e h1 h2 && unifiesWith e t1 t2
432−unifiesWith e (SaturatedTypeSynonym name args) t2 =
433− case expandTypeSynonym' e name args of
435− Right t1 -> unifiesWith e t1 t2
436−unifiesWith e t1 t2@(SaturatedTypeSynonym _ _) = unifiesWith e t2 t1
437−unifiesWith _ _ _ = False
440−-- Check whether the type heads of two types are equal (for the purposes of type class dictionary lookup),
441−-- and return a substitution from type variables to types which makes the type heads unify.
443−typeHeadsAreEqual :: ModuleName -> Environment -> Type -> Type -> Maybe [(String, Type)]
444−typeHeadsAreEqual _ _ (Skolem _ s1 _) (Skolem _ s2 _) | s1 == s2 = Just []
445−typeHeadsAreEqual _ _ t (TypeVar v) = Just [(v, t)]
446−typeHeadsAreEqual _ _ (TypeConstructor c1) (TypeConstructor c2) | c1 == c2 = Just []
447−typeHeadsAreEqual m e (TypeApp h1 t1) (TypeApp h2 t2) = (++) <$> typeHeadsAreEqual m e h1 h2 <*> typeHeadsAreEqual m e t1 t2
448−typeHeadsAreEqual m e (SaturatedTypeSynonym name args) t2 = case expandTypeSynonym' e name args of
450− Right t1 -> typeHeadsAreEqual m e t1 t2
451−typeHeadsAreEqual _ _ _ _ = Nothing
454−-- Ensure skolem variables do not escape their scope
456−skolemEscapeCheck :: Value -> Check ()
457−skolemEscapeCheck (TypedValue False _ _) = return ()
458−skolemEscapeCheck root@TypedValue{} =
459− -- Every skolem variable is created when a ForAll type is skolemized.
460− -- This determines the scope of that skolem variable, which is copied from the SkolemScope
461− -- field of the ForAll constructor.
462− -- We traverse the tree top-down, and collect any SkolemScopes introduced by ForAlls.
463− -- If a Skolem is encountered whose SkolemScope is not in the current list, we have found
464− -- an escaped skolem variable.
465− case everythingWithContext [] (++) (mkQ ((,) []) go) root of
467− ((binding, val) : _) -> throwError $ mkErrorStack ("Rigid/skolem type variable " ++ maybe "" (("bound by " ++) . prettyPrintValue) binding ++ " has escaped.") (Just (ValueError val))
469− go :: Value -> [(SkolemScope, Value)] -> ([(Maybe Value, Value)], [(SkolemScope, Value)])
470− go val@(TypedValue _ _ (ForAll _ _ (Just sco))) scos = ([], (sco, val) : scos)
471− go val@(TypedValue _ _ ty) scos = case collectSkolems ty \\ map fst scos of
472− (sco : _) -> ([(findBindingScope sco, val)], scos)
475− collectSkolems :: Type -> [SkolemScope]
476− collectSkolems = nub . everythingOnTypes (++) collect
478− collect (Skolem _ _ scope) = [scope]
480− go _ scos = ([], scos)
481− findBindingScope :: SkolemScope -> Maybe Value
482− findBindingScope sco =
483− let (_, f, _, _, _) = everythingOnValues mappend (const mempty) go' (const mempty) (const mempty) (const mempty)
484− in getFirst $ f root
486− go' val@(TypedValue _ _ (ForAll _ _ (Just sco'))) | sco == sco' = First (Just val)
488−skolemEscapeCheck val = throwError $ mkErrorStack "Untyped value passed to skolemEscapeCheck" (Just (ValueError val))
491−-- Ensure a row contains no duplicate labels
493−setify :: Type -> Type
494−setify = rowFromList . first (M.toList . M.fromList) . rowToList
497−-- \"Setify\" all rows occuring inside a value
499−setifyAll :: Type -> Type
500−setifyAll = everywhereOnTypes setify
503−-- Replace outermost unsolved unification variables with named type variables
505−varIfUnknown :: Type -> Type
507− let unks = nub $ unknowns ty
508− toName = (:) 't' . show
509− ty' = everywhereOnTypes typeToVar ty
510− typeToVar :: Type -> Type
511− typeToVar (TUnknown u) = TypeVar (toName u)
513− in mkForAll (sort . map toName $ unks) ty'
516−-- Remove any ForAlls and ConstrainedType constructors in a type by introducing new unknowns
517−-- or TypeClassDictionary values.
519−-- This is necessary during type checking to avoid unifying a polymorphic type with a
520−-- unification variable.
522−instantiatePolyTypeWithUnknowns :: Value -> Type -> UnifyT Type Check (Value, Type)
523−instantiatePolyTypeWithUnknowns val (ForAll ident ty _) = do
524− ty' <- replaceVarWithUnknown ident ty
525− instantiatePolyTypeWithUnknowns val ty'
526−instantiatePolyTypeWithUnknowns val (ConstrainedType constraints ty) = do
527− dicts <- getTypeClassDictionaries
528− (_, ty') <- instantiatePolyTypeWithUnknowns (error "Types under a constraint cannot themselves be constrained") ty
529− return (foldl App val (map (flip (TypeClassDictionary True) dicts) constraints), ty')
530−instantiatePolyTypeWithUnknowns val ty = return (val, ty)
533−-- Replace a single type variable with a new unification variable
535−replaceVarWithUnknown :: String -> Type -> UnifyT Type Check Type
536−replaceVarWithUnknown ident ty = do
538− return $ replaceTypeVars ident tu ty
541−-- Replace fully applied type synonyms with the @SaturatedTypeSynonym@ data constructor, which helps generate
542−-- better error messages during unification.
544−replaceAllTypeSynonyms' :: Environment -> Type -> Either String Type
545−replaceAllTypeSynonyms' env d =
547− syns = map (\(name, (args, _)) -> (name, length args)) . M.toList $ typeSynonyms env
549− saturateAllTypeSynonyms syns d
551−replaceAllTypeSynonyms :: (Error e, Functor m, Monad m, MonadState CheckState m, MonadError e m) => Type -> m Type
552−replaceAllTypeSynonyms d = do
554− either (throwError . strMsg) return $ replaceAllTypeSynonyms' env d
557−-- \"Desaturate\" @SaturatedTypeSynonym@s
559−desaturateAllTypeSynonyms :: Type -> Type
560−desaturateAllTypeSynonyms = everywhereOnTypes replaceSaturatedTypeSynonym
562− replaceSaturatedTypeSynonym (SaturatedTypeSynonym name args) = foldl TypeApp (TypeConstructor name) args
563− replaceSaturatedTypeSynonym t = t
566−-- Replace a type synonym and its arguments with the aliased type
568−expandTypeSynonym' :: Environment -> Qualified ProperName -> [Type] -> Either String Type
569−expandTypeSynonym' env name args =
570− case M.lookup name (typeSynonyms env) of
571− Just (synArgs, body) -> do
572− let repl = replaceAllTypeVars (zip synArgs args) body
573− replaceAllTypeSynonyms' env repl
574− Nothing -> error "Type synonym was not defined"
576−expandTypeSynonym :: (Error e, Functor m, Monad m, MonadState CheckState m, MonadError e m) => Qualified ProperName -> [Type] -> m Type
577−expandTypeSynonym name args = do
579− either (throwError . strMsg) return $ expandTypeSynonym' env name args
581−expandAllTypeSynonyms :: (Error e, Functor m, Applicative m, Monad m, MonadState CheckState m, MonadError e m) => Type -> m Type
582−expandAllTypeSynonyms = everywhereOnTypesTopDownM go
584− go (SaturatedTypeSynonym name args) = expandTypeSynonym name args
585− go other = return other
588−-- Ensure a set of property names and value does not contain duplicate labels
590−ensureNoDuplicateProperties :: (Error e, MonadError e m) => [(String, Value)] -> m ()
591−ensureNoDuplicateProperties ps = guardWith (strMsg "Duplicate property names") $ length (nub . map fst $ ps) == length ps
594−-- Infer a type for a value, rethrowing any error to provide a more useful error message
596−infer :: Value -> UnifyT Type Check Value
597−infer val = rethrow (mkErrorStack "Error inferring type of value" (Just (ValueError val)) <>) $ infer' val
600−-- Infer a type for a value
602−infer' :: Value -> UnifyT Type Check Value
603−infer' v@(NumericLiteral _) = return $ TypedValue True v tyNumber
604−infer' v@(StringLiteral _) = return $ TypedValue True v tyString
605−infer' v@(BooleanLiteral _) = return $ TypedValue True v tyBoolean
606−infer' (ArrayLiteral vals) = do
607− ts <- mapM infer vals
609− forM_ ts $ \(TypedValue _ _ t) -> els =?= TypeApp tyArray t
610− return $ TypedValue True (ArrayLiteral ts) els
611−infer' (ObjectLiteral ps) = do
612− ensureNoDuplicateProperties ps
613− ts <- mapM (infer . snd) ps
614− let fields = zipWith (\name (TypedValue _ _ t) -> (name, t)) (map fst ps) ts
615− ty = TypeApp tyObject $ rowFromList (fields, REmpty)
616− return $ TypedValue True (ObjectLiteral (zip (map fst ps) ts)) ty
617−infer' (ObjectUpdate o ps) = do
618− ensureNoDuplicateProperties ps
620− newVals <- zipWith (\(name, _) t -> (name, t)) ps <$> mapM (infer . snd) ps
621− let newTys = map (\(name, TypedValue _ _ ty) -> (name, ty)) newVals
622− oldTys <- zip (map fst ps) <$> replicateM (length ps) fresh
623− let oldTy = TypeApp tyObject $ rowFromList (oldTys, row)
624− o' <- TypedValue True <$> check o oldTy <*> pure oldTy
625− return $ TypedValue True (ObjectUpdate o' newVals) $ TypeApp tyObject $ rowFromList (newTys, row)
626−infer' (Accessor prop val) = do
627− typed@(TypedValue _ _ objTy) <- infer val
628− propTy <- inferProperty objTy prop
633− _ <- subsumes Nothing objTy (TypeApp tyObject (RCons prop field rest))
634− return $ TypedValue True (Accessor prop typed) field
635− Just ty -> return $ TypedValue True (Accessor prop typed) ty
636−infer' (Abs (Left arg) ret) = do
638− Just moduleName <- checkCurrentModule <$> get
639− bindLocalVariables moduleName [(arg, ty)] $ do
640− body@(TypedValue _ _ bodyTy) <- infer' ret
641− return $ TypedValue True (Abs (Left arg) body) $ function ty bodyTy
642−infer' (Abs (Right _) _) = error "Binder was not desugared"
643−infer' (App f arg) = do
644− f'@(TypedValue _ _ ft) <- infer f
645− (ret, app) <- checkFunctionApplication f' ft arg Nothing
646− return $ TypedValue True app ret
647−infer' (Var var) = do
648− Just moduleName <- checkCurrentModule <$> get
649− ty <- introduceSkolemScope <=< replaceAllTypeSynonyms <=< lookupVariable moduleName $ var
651− ConstrainedType constraints ty' -> do
652− dicts <- getTypeClassDictionaries
653− return $ TypedValue True (foldl App (Var var) (map (flip (TypeClassDictionary True) dicts) constraints)) ty'
654− _ -> return $ TypedValue True (Var var) ty
655−infer' v@(Constructor c) = do
657− case M.lookup c (dataConstructors env) of
658− Nothing -> throwError . strMsg $ "Constructor " ++ show c ++ " is undefined"
659− Just (_, ty) -> do ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
660− return $ TypedValue True v ty'
661−infer' (Case vals binders) = do
662− ts <- mapM infer vals
664− binders' <- checkBinders (map (\(TypedValue _ _ t) -> t) ts) ret binders
665− return $ TypedValue True (Case ts binders') ret
666−infer' (IfThenElse cond th el) = do
667− cond' <- check cond tyBoolean
668− v2@(TypedValue _ _ t2) <- infer th
669− v3@(TypedValue _ _ t3) <- infer el
671− return $ TypedValue True (IfThenElse cond' v2 v3) t2
672−infer' (Let ds val) = do
673− (ds', val'@(TypedValue _ _ valTy)) <- inferLetBinding [] ds val infer
674− return $ TypedValue True (Let ds' val') valTy
675−infer' (SuperClassDictionary className tys) = do
676− dicts <- getTypeClassDictionaries
677− return $ TypeClassDictionary False (className, tys) dicts
678−infer' (TypedValue checkType val ty) = 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− ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
683− val' <- if checkType then check val ty' else return val
684− return $ TypedValue True val' ty'
685−infer' (PositionedValue pos val) = rethrowWithPosition pos $ infer' val
686−infer' _ = error "Invalid argument to infer"
688−inferLetBinding :: [Declaration] -> [Declaration] -> Value -> (Value -> UnifyT Type Check Value) -> UnifyT Type Check ([Declaration], Value)
689−inferLetBinding seen [] ret j = (,) seen <$> j ret
690−inferLetBinding seen (ValueDeclaration ident nameKind [] Nothing tv@(TypedValue checkType val ty) : rest) ret j = do
691− Just moduleName <- checkCurrentModule <$> get
692− kind <- liftCheck $ kindOf moduleName ty
693− guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
694− let dict = if isFunction val then M.singleton (moduleName, ident) (ty, nameKind) else M.empty
695− TypedValue _ val' ty' <- if checkType then bindNames dict (check val ty) else return tv
696− bindNames (M.singleton (moduleName, ident) (ty', nameKind)) $ inferLetBinding (seen ++ [ValueDeclaration ident nameKind [] Nothing (TypedValue checkType val' ty')]) rest ret j
697−inferLetBinding seen (ValueDeclaration ident nameKind [] Nothing val : rest) ret j = do
699− Just moduleName <- checkCurrentModule <$> get
700− let dict = if isFunction val then M.singleton (moduleName, ident) (valTy, nameKind) else M.empty
701− TypedValue _ val' valTy' <- bindNames dict $ infer val
703− bindNames (M.singleton (moduleName, ident) (valTy', nameKind)) $ inferLetBinding (seen ++ [ValueDeclaration ident nameKind [] Nothing val']) rest ret j
704−inferLetBinding seen (BindingGroupDeclaration ds : rest) ret j = do
705− Just moduleName <- checkCurrentModule <$> get
706− (es, dict, untypedDict) <- typeDictionaryForBindingGroup moduleName (map (\(i, _, v) -> (i, v)) ds)
707− ds' <- forM es $ \e -> do
708− (ident, (val', _)) <- typeForBindingGroupElement moduleName e dict untypedDict
709− return $ (ident, LocalVariable, val')
710− bindNames dict $ inferLetBinding (seen ++ [BindingGroupDeclaration ds']) rest ret j
711−inferLetBinding seen (PositionedDeclaration pos d : ds) ret j = rethrowWithPosition pos $ do
712− ((d' : ds'), val') <- inferLetBinding seen (d : ds) ret j
713− return (PositionedDeclaration pos d' : ds', val')
714−inferLetBinding _ _ _ _ = error "Invalid argument to inferLetBinding"
717−-- Infer the type of a property inside a record with a given type
719−inferProperty :: Type -> String -> UnifyT Type Check (Maybe Type)
720−inferProperty (TypeApp obj row) prop | obj == tyObject = do
721− let (props, _) = rowToList row
722− return $ lookup prop props
723−inferProperty (SaturatedTypeSynonym name args) prop = do
724− replaced <- introduceSkolemScope <=< expandTypeSynonym name $ args
725− inferProperty replaced prop
726−inferProperty (ForAll ident ty _) prop = do
727− replaced <- replaceVarWithUnknown ident ty
728− inferProperty replaced prop
729−inferProperty _ _ = return Nothing
732−-- Infer the types of variables brought into scope by a binder
734−inferBinder :: Type -> Binder -> UnifyT Type Check (M.Map Ident Type)
735−inferBinder _ NullBinder = return M.empty
736−inferBinder val (StringBinder _) = val =?= tyString >> return M.empty
737−inferBinder val (NumberBinder _) = val =?= tyNumber >> return M.empty
738−inferBinder val (BooleanBinder _) = val =?= tyBoolean >> return M.empty
739−inferBinder val (VarBinder name) = return $ M.singleton name val
740−inferBinder val (ConstructorBinder ctor binders) = do
742− case M.lookup ctor (dataConstructors env) of
744− (_, fn) <- instantiatePolyTypeWithUnknowns (error "Data constructor types cannot contain constraints") ty
745− fn' <- replaceAllTypeSynonyms fn
749− _ <- subsumes Nothing val ty'
751− go (binder : binders') (TypeApp (TypeApp t obj) ret) | t == tyFunction =
752− M.union <$> inferBinder obj binder <*> go binders' ret
753− go _ _ = throwError . strMsg $ "Wrong number of arguments to constructor " ++ show ctor
754− _ -> throwError . strMsg $ "Constructor " ++ show ctor ++ " is not defined"
755−inferBinder val (ObjectBinder props) = do
758− m1 <- inferRowProperties row rest props
759− val =?= TypeApp tyObject row
762− inferRowProperties :: Type -> Type -> [(String, Binder)] -> UnifyT Type Check (M.Map Ident Type)
763− inferRowProperties nrow row [] = nrow =?= row >> return M.empty
764− inferRowProperties nrow row ((name, binder):binders) = do
766− m1 <- inferBinder propTy binder
767− m2 <- inferRowProperties nrow (RCons name propTy row) binders
768− return $ m1 `M.union` m2
769−inferBinder val (ArrayBinder binders) = do
771− m1 <- M.unions <$> mapM (inferBinder el) binders
772− val =?= TypeApp tyArray el
774−inferBinder val (ConsBinder headBinder tailBinder) = do
776− m1 <- inferBinder el headBinder
777− m2 <- inferBinder val tailBinder
778− val =?= TypeApp tyArray el
779− return $ m1 `M.union` m2
780−inferBinder val (NamedBinder name binder) = do
781− m <- inferBinder val binder
782− return $ M.insert name val m
783−inferBinder val (PositionedBinder pos binder) =
784− rethrowWithPosition pos $ inferBinder val binder
787−-- Check the types of the return values in a set of binders in a case statement
789−checkBinders :: [Type] -> Type -> [CaseAlternative] -> UnifyT Type Check [CaseAlternative]
790−checkBinders _ _ [] = return []
791−checkBinders nvals ret (CaseAlternative binders grd val : bs) = do
792− Just moduleName <- checkCurrentModule <$> get
793− m1 <- M.unions <$> zipWithM inferBinder nvals binders
794− r <- bindLocalVariables moduleName (M.toList m1) $ do
795− val' <- TypedValue True <$> check val ret <*> pure ret
797− Nothing -> return $ CaseAlternative binders Nothing val'
799− g' <- check g tyBoolean
800− return $ CaseAlternative binders (Just g') val'
801− rs <- checkBinders nvals ret bs
805−-- Generate a new skolem constant
807−newSkolemConstant :: UnifyT Type Check Int
808−newSkolemConstant = fresh'
811−-- Generate a new skolem scope
813−newSkolemScope :: UnifyT Type Check SkolemScope
814−newSkolemScope = SkolemScope <$> fresh'
817−-- Skolemize a type variable by replacing its instances with fresh skolem constants
819−skolemize :: String -> Int -> SkolemScope -> Type -> Type
820−skolemize ident sko scope = replaceTypeVars ident (Skolem ident sko scope)
823−-- This function has one purpose - to skolemize type variables appearing in a
824−-- SuperClassDictionary placeholder. These type variables are somewhat unique since they are the
825−-- only example of scoped type variables.
827−skolemizeTypesInValue :: String -> Int -> SkolemScope -> Value -> Value
828−skolemizeTypesInValue ident sko scope = let (_, f, _) = everywhereOnValues id go id in f
830− go (SuperClassDictionary c ts) = SuperClassDictionary c (map (skolemize ident sko scope) ts)
834−-- Introduce skolem scope at every occurence of a ForAll
836−introduceSkolemScope :: Type -> UnifyT Type Check Type
837−introduceSkolemScope = everywhereOnTypesM go
839− go (ForAll ident ty Nothing) = ForAll ident ty <$> (Just <$> newSkolemScope)
840− go other = return other
843−-- Check the type of a value, rethrowing errors to provide a better error message
845−check :: Value -> Type -> UnifyT Type Check Value
846−check val ty = rethrow (mkErrorStack errorMessage (Just (ValueError val)) <>) $ check' val ty
849− "Error checking type of term " ++
850− prettyPrintValue val ++
855−-- Check the type of a value
857−check' :: Value -> Type -> UnifyT Type Check Value
858−check' val (ForAll ident ty _) = do
859− scope <- newSkolemScope
860− sko <- newSkolemConstant
861− let sk = skolemize ident sko scope ty
862− let skVal = skolemizeTypesInValue ident sko scope val
863− val' <- check skVal sk
864− return $ TypedValue True val' (ForAll ident ty (Just scope))
865−check' val t@(ConstrainedType constraints ty) = do
866− dictNames <- forM constraints $ \(Qualified _ (ProperName className), _) -> do
867− n <- liftCheck freshDictionaryName
868− return $ Ident $ "__dict_" ++ className ++ "_" ++ show n
869− val' <- withTypeClassDictionaries (zipWith (\name (className, instanceTy) ->
870− TypeClassDictionaryInScope name className instanceTy Nothing TCDRegular) (map (Qualified Nothing) dictNames)
871− constraints) $ check val ty
872− return $ TypedValue True (foldr (Abs . Left) val' dictNames) t
873−check' val (SaturatedTypeSynonym name args) = do
874− ty <- introduceSkolemScope <=< expandTypeSynonym name $ args
876−check' val u@(TUnknown _) = do
877− val'@(TypedValue _ _ ty) <- infer val
878− -- Don't unify an unknown with an inferred polytype
879− (val'', ty') <- instantiatePolyTypeWithUnknowns val' ty
881− return $ TypedValue True val'' ty'
882−check' v@(NumericLiteral _) t | t == tyNumber =
883− return $ TypedValue True v t
884−check' v@(StringLiteral _) t | t == tyString =
885− return $ TypedValue True v t
886−check' v@(BooleanLiteral _) t | t == tyBoolean =
887− return $ TypedValue True v t
888−check' (ArrayLiteral vals) t@(TypeApp a ty) = do
890− array <- ArrayLiteral <$> forM vals (`check` ty)
891− return $ TypedValue True array t
892−check' (Abs (Left arg) ret) ty@(TypeApp (TypeApp t argTy) retTy) | t == tyFunction = do
893− Just moduleName <- checkCurrentModule <$> get
894− ret' <- bindLocalVariables moduleName [(arg, argTy)] $ check ret retTy
895− return $ TypedValue True (Abs (Left arg) ret') ty
896−check' (Abs (Right _) _) _ = error "Binder was not desugared"
897−check' (App f arg) ret = do
898− f'@(TypedValue _ _ ft) <- infer f
899− (_, app) <- checkFunctionApplication f' ft arg (Just ret)
900− return $ TypedValue True app ret
901−check' v@(Var var) ty = do
902− Just moduleName <- checkCurrentModule <$> get
903− repl <- introduceSkolemScope <=< replaceAllTypeSynonyms <=< lookupVariable moduleName $ var
904− ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
905− v' <- subsumes (Just v) repl ty'
907− Nothing -> throwError . strMsg $ "Unable to check type subsumption"
908− Just v'' -> return $ TypedValue True v'' ty'
909−check' (SuperClassDictionary className tys) _ = do
911− -- Here, we replace a placeholder for a superclass dictionary with a regular
912− -- TypeClassDictionary placeholder. The reason we do this is that it is necessary to have the
913− -- correct super instance dictionaries in scope, and these are not available when the type class
914− -- declaration gets desugared.
916− -- Note also that the first argument to TypeClassDictionary is False, meaning we _do not_ want
917− -- to consider superclass instances when searching for this dictionary - doing so might lead
918− -- to traversing a cycle in the instance graph.
920− dicts <- getTypeClassDictionaries
921− return $ TypeClassDictionary False (className, tys) dicts
922−check' (TypedValue checkType val ty1) ty2 = do
923− Just moduleName <- checkCurrentModule <$> get
924− kind <- liftCheck $ kindOf moduleName ty1
925− guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
926− ty1' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty1
927− val' <- subsumes (Just val) ty1' ty2
929− Nothing -> throwError . strMsg $ "Unable to check type subsumption"
931− val''' <- if checkType then check val'' ty1' else return val''
932− return $ TypedValue checkType (TypedValue True val''' ty1) ty2
933−check' (Case vals binders) ret = do
934− vals' <- mapM infer vals
935− let ts = map (\(TypedValue _ _ t) -> t) vals'
936− binders' <- checkBinders ts ret binders
937− return $ TypedValue True (Case vals' binders') ret
938−check' (IfThenElse cond th el) ty = do
939− cond' <- check cond tyBoolean
942− return $ TypedValue True (IfThenElse cond' th' el') ty
943−check' (ObjectLiteral ps) t@(TypeApp obj row) | obj == tyObject = do
944− ensureNoDuplicateProperties ps
945− ps' <- checkProperties ps row False
946− return $ TypedValue True (ObjectLiteral ps') t
947−check' (ObjectUpdate obj ps) t@(TypeApp o row) | o == tyObject = do
948− ensureNoDuplicateProperties ps
949− us <- zip (map fst ps) <$> replicateM (length ps) fresh
950− let (propsToCheck, rest) = rowToList row
951− propsToRemove = map fst ps
952− remainingProps = filter (\(p, _) -> p `notElem` propsToRemove) propsToCheck
953− obj' <- check obj (TypeApp tyObject (rowFromList (us ++ remainingProps, rest)))
954− ps' <- checkProperties ps row True
955− return $ TypedValue True (ObjectUpdate obj' ps') t
956−check' (Accessor prop val) ty = do
958− val' <- check val (TypeApp tyObject (RCons prop ty rest))
959− return $ TypedValue True (Accessor prop val') ty
960−check' (Constructor c) ty = do
962− case M.lookup c (dataConstructors env) of
963− Nothing -> throwError . strMsg $ "Constructor " ++ show c ++ " is undefined"
965− repl <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty1
966− _ <- subsumes Nothing repl ty
967− return $ TypedValue True (Constructor c) ty
968−check' (Let ds val) ty = do
969− (ds', val') <- inferLetBinding [] ds val (flip check ty)
970− return $ TypedValue True (Let ds' val') ty
971−check' val ty | containsTypeSynonyms ty = do
972− ty' <- introduceSkolemScope <=< expandAllTypeSynonyms $ ty
974−check' (PositionedValue pos val) ty =
975− rethrowWithPosition pos $ check val ty
976−check' val ty = throwError $ mkErrorStack ("Value does not have type " ++ prettyPrintType ty) (Just (ValueError val))
978−containsTypeSynonyms :: Type -> Bool
979−containsTypeSynonyms = everythingOnTypes (||) go where
980− go (SaturatedTypeSynonym _ _) = True
984−-- Check the type of a collection of named record fields
986−-- The @lax@ parameter controls whether or not every record member has to be provided. For object updates, this is not the case.
988−checkProperties :: [(String, Value)] -> Type -> Bool -> UnifyT Type Check [(String, Value)]
989−checkProperties ps row lax = let (ts, r') = rowToList row in go ps ts r' where
990− go [] [] REmpty = return []
991− go [] [] u@(TUnknown _) = do u =?= REmpty
993− go [] [] (Skolem _ _ _) | lax = return []
994− go [] ((p, _): _) _ | lax = return []
995− | otherwise = throwError $ mkErrorStack ("Object does not have property " ++ p) (Just (ValueError (ObjectLiteral ps)))
996− go ((p,_):_) [] REmpty = throwError $ mkErrorStack ("Property " ++ p ++ " is not present in closed object type " ++ prettyPrintRow row) (Just (ValueError (ObjectLiteral ps)))
997− go ((p,v):ps') [] u@(TUnknown _) = do
998− v'@(TypedValue _ _ ty) <- infer v
1000− u =?= RCons p ty rest
1001− ps'' <- go ps' [] rest
1002− return $ (p, v') : ps''
1003− go ((p,v):ps') ts r =
1004− case lookup p ts of
1006− v'@(TypedValue _ _ ty) <- infer v
1008− r =?= RCons p ty rest
1009− ps'' <- go ps' ts rest
1010− return $ (p, v') : ps''
1013− ps'' <- go ps' (delete (p, ty) ts) r
1014− return $ (p, v') : ps''
1015− go _ _ _ = throwError $ mkErrorStack ("Object does not have type " ++ prettyPrintType (TypeApp tyObject row)) (Just (ValueError (ObjectLiteral ps)))
1018−-- Check the type of a function application, rethrowing errors to provide a better error message
1020−checkFunctionApplication :: Value -> Type -> Value -> Maybe Type -> UnifyT Type Check (Type, Value)
1021−checkFunctionApplication fn fnTy arg ret = rethrow (mkErrorStack errorMessage (Just (ValueError fn)) <>) $ checkFunctionApplication' fn fnTy arg ret
1023− errorMessage = "Error applying function of type "
1024− ++ prettyPrintType fnTy
1025− ++ " to argument " ++ prettyPrintValue arg
1028−-- Check the type of a function application
1030−checkFunctionApplication' :: Value -> Type -> Value -> Maybe Type -> UnifyT Type Check (Type, Value)
1031−checkFunctionApplication' fn (TypeApp (TypeApp tyFunction' argTy) retTy) arg ret = do
1032− tyFunction' =?= tyFunction
1033− _ <- maybe (return Nothing) (subsumes Nothing retTy) ret
1034− subst <- unifyCurrentSubstitution <$> UnifyT get
1035− arg' <- check arg (subst $? argTy)
1036− return (retTy, App fn arg')
1037−checkFunctionApplication' fn (ForAll ident ty _) arg ret = do
1038− replaced <- replaceVarWithUnknown ident ty
1039− checkFunctionApplication fn replaced arg ret
1040−checkFunctionApplication' fn u@(TUnknown _) arg ret = do
1042− TypedValue _ arg' t <- infer arg
1043− (arg'', t') <- instantiatePolyTypeWithUnknowns arg' t
1044− return $ TypedValue True arg'' t'
1045− let ty = (\(TypedValue _ _ t) -> t) arg'
1046− ret' <- maybe fresh return ret
1047− u =?= function ty ret'
1048− return (ret', App fn arg')
1049−checkFunctionApplication' fn (SaturatedTypeSynonym name tyArgs) arg ret = do
1050− ty <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
1051− checkFunctionApplication fn ty arg ret
1052−checkFunctionApplication' fn (ConstrainedType constraints fnTy) arg ret = do
1053− dicts <- getTypeClassDictionaries
1054− checkFunctionApplication' (foldl App fn (map (flip (TypeClassDictionary True) dicts) constraints)) fnTy arg ret
1055−checkFunctionApplication' _ fnTy arg _ = throwError . strMsg $ "Cannot apply a function of type "
1056− ++ prettyPrintType fnTy
1057− ++ " to argument " ++ prettyPrintValue arg
1060−-- Check whether one type subsumes another, rethrowing errors to provide a better error message
1062−subsumes :: Maybe Value -> Type -> Type -> UnifyT Type Check (Maybe Value)
1063−subsumes val ty1 ty2 = rethrow (mkErrorStack errorMessage (ValueError <$> val) <>) $ subsumes' val ty1 ty2
1065− errorMessage = "Error checking that type "
1066− ++ prettyPrintType ty1
1067− ++ " subsumes type "
1068− ++ prettyPrintType ty2
1071−-- Check whether one type subsumes another
1073−subsumes' :: Maybe Value -> Type -> Type -> UnifyT Type Check (Maybe Value)
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) =
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
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' Nothing ty1 ty2
1097− return . Just $ foldl App val (map (flip (TypeClassDictionary True) dicts) constraints)
1098−subsumes' val (TypeApp f1 r1) (TypeApp f2 r2) | f1 == tyObject && f2 == tyObject = do
1100− (ts1, r1') = rowToList r1
1101− (ts2, r2') = rowToList r2
1102− ts1' = sortBy (comparing fst) ts1
1103− ts2' = sortBy (comparing fst) ts2
1104− go ts1' ts2' r1' r2'
1107− go [] ts2 r1' r2' = r1' =?= rowFromList (ts2, r2')
1108− go ts1 [] r1' r2' = r2' =?= rowFromList (ts1, r1')
1109− go ((p1, ty1) : ts1) ((p2, ty2) : ts2) r1' r2'
1110− | p1 == p2 = do _ <- subsumes Nothing ty1 ty2
1112− | p1 < p2 = do rest <- fresh
1113− r2' =?= RCons p1 ty1 rest
1114− go ts1 ((p2, ty2) : ts2) r1' rest
1115− | otherwise = do rest <- fresh
1116− r1' =?= RCons p2 ty2 rest
1117− go ((p1, ty1) : ts1) ts2 rest r2'
1118−subsumes' val ty1 ty2@(TypeApp obj _) | obj == tyObject = subsumes val ty2 ty1
1119−subsumes' val ty1 ty2 = do