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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, mkM, mkQ)
51−import Data.Generics.Extras
53−import Language.PureScript.Declarations
54−import Language.PureScript.Types
55−import Language.PureScript.Kinds
56−import Language.PureScript.Names
57−import Language.PureScript.TypeClassDictionaries
58−import Language.PureScript.TypeChecker.Monad
59−import Language.PureScript.TypeChecker.Kinds
60−import Language.PureScript.TypeChecker.Synonyms
61−import Language.PureScript.Pretty
62−import Language.PureScript.Environment
63−import Language.PureScript.Errors
64−import qualified Language.PureScript.Constants as C
66−import Control.Monad.State
67−import Control.Monad.Error
68−import Control.Monad.Unify
70−import Control.Applicative
71−import Control.Arrow (Arrow(..))
73−import qualified Data.Map as M
74−import qualified Data.HashMap.Strict as H
76−instance Partial Type where
78− isUnknown (TUnknown u) = Just u
79− isUnknown _ = Nothing
80− unknowns = everythingOnTypes (++) go
82− go (TUnknown u) = [u]
84− ($?) sub = everywhereOnTypes go
86− go t@(TUnknown u) = case H.lookup u (runSubstitution sub) of
91−instance Unifiable Check Type where
95−-- Unify two types, updating the current substitution
97−unifyTypes :: Type -> Type -> UnifyT Type Check ()
98−unifyTypes t1 t2 = rethrow (mkErrorStack ("Error unifying type " ++ prettyPrintType t1 ++ " with type " ++ prettyPrintType t2) Nothing <>) $
101− unifyTypes' (TUnknown u1) (TUnknown u2) | u1 == u2 = return ()
102− unifyTypes' (TUnknown u) t = u =:= t
103− unifyTypes' t (TUnknown u) = u =:= t
104− unifyTypes' (SaturatedTypeSynonym name args) ty = do
105− ty1 <- introduceSkolemScope <=< expandTypeSynonym name $ args
107− unifyTypes' ty s@(SaturatedTypeSynonym _ _) = s `unifyTypes` ty
108− unifyTypes' (ForAll ident1 ty1 sc1) (ForAll ident2 ty2 sc2) =
110− (Just sc1', Just sc2') -> do
111− sko <- newSkolemConstant
112− let sk1 = skolemize ident1 sko sc1' ty1
113− let sk2 = skolemize ident2 sko sc2' ty2
114− sk1 `unifyTypes` sk2
115− _ -> error "Skolemized type variable was not given a scope"
116− unifyTypes' (ForAll ident ty1 (Just sc)) ty2 = do
117− sko <- newSkolemConstant
118− let sk = skolemize ident sko sc ty1
120− unifyTypes' ForAll{} _ = throwError . strMsg $ "Skolem variable scope is unspecified"
121− unifyTypes' ty f@ForAll{} = f `unifyTypes` ty
122− unifyTypes' (TypeVar v1) (TypeVar v2) | v1 == v2 = return ()
123− unifyTypes' (TypeConstructor c1) (TypeConstructor c2) =
124− guardWith (strMsg ("Cannot unify " ++ show c1 ++ " with " ++ show c2 ++ ".")) (c1 == c2)
125− unifyTypes' (TypeApp t3 t4) (TypeApp t5 t6) = do
128− unifyTypes' (Skolem _ s1 _) (Skolem _ s2 _) | s1 == s2 = return ()
129− unifyTypes' r1@RCons{} r2 = unifyRows r1 r2
130− unifyTypes' r1 r2@RCons{} = unifyRows r1 r2
131− unifyTypes' r1@REmpty r2 = unifyRows r1 r2
132− unifyTypes' r1 r2@REmpty = unifyRows r1 r2
133− unifyTypes' t@(ConstrainedType _ _) _ = throwError . strMsg $ "Attempted to unify a constrained type " ++ prettyPrintType t ++ " with another type."
134− unifyTypes' t3 t4@(ConstrainedType _ _) = unifyTypes' t4 t3
135− unifyTypes' t3 t4 = throwError . strMsg $ "Cannot unify " ++ prettyPrintType t3 ++ " with " ++ prettyPrintType t4 ++ "."
138−-- Unify two rows, updating the current substitution
140−-- Common labels are first identified, and unified. Remaining labels and types are unified with a
141−-- trailing row unification variable, if appropriate, otherwise leftover labels result in a unification
144−unifyRows :: Type -> Type -> UnifyT Type Check ()
147− (s1, r1') = rowToList r1
148− (s2, r2') = rowToList r2
149− int = [ (t1, t2) | (name, t1) <- s1, (name', t2) <- s2, name == name' ]
150− sd1 = [ (name, t1) | (name, t1) <- s1, name `notElem` map fst s2 ]
151− sd2 = [ (name, t2) | (name, t2) <- s2, name `notElem` map fst s1 ]
153− forM_ int (uncurry (=?=))
154− unifyRows' sd1 r1' sd2 r2'
156− unifyRows' :: [(String, Type)] -> Type -> [(String, Type)] -> Type -> UnifyT Type Check ()
157− unifyRows' [] (TUnknown u) sd r = u =:= rowFromList (sd, r)
158− unifyRows' sd r [] (TUnknown u) = u =:= rowFromList (sd, r)
159− unifyRows' ((name, ty):row) r others u@(TUnknown un) = do
161− forM_ row $ \(_, t) -> occursCheck un t
163− u =?= RCons name ty u'
164− unifyRows' row r others u'
165− unifyRows' [] REmpty [] REmpty = return ()
166− unifyRows' [] (TypeVar v1) [] (TypeVar v2) | v1 == v2 = return ()
167− unifyRows' [] (Skolem _ s1 _) [] (Skolem _ s2 _) | s1 == s2 = return ()
168− unifyRows' sd3 r3 sd4 r4 = throwError . strMsg $ "Cannot unify (" ++ prettyPrintRow (rowFromList (sd3, r3)) ++ ") with (" ++ prettyPrintRow (rowFromList (sd4, r4)) ++ ")"
171−-- Infer the types of multiple mutually-recursive values, and return elaborated values including
172−-- type class dictionaries and type annotations.
174−typesOf :: Maybe ModuleName -> ModuleName -> [(Ident, Value)] -> Check [(Ident, (Value, Type))]
175−typesOf mainModuleName moduleName vals = do
176− tys <- fmap tidyUp . liftUnify $ do
177− (es, dict, untypedDict) <- typeDictionaryForBindingGroup moduleName vals
179− triple@(_, (_, ty)) <- typeForBindingGroupElement moduleName e dict untypedDict
180− -- If --main is enabled, need to check that `main` has type Eff eff a for some eff, a
181− when (Just moduleName == mainModuleName && fst e == Ident C.main) $ do
182− [eff, a] <- replicateM 2 fresh
183− ty =?= TypeApp (TypeApp (TypeConstructor (Qualified (Just (ModuleName [ProperName "Control", ProperName "Monad", ProperName "Eff"])) (ProperName "Eff"))) eff) a
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'))
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
200−typeDictionaryForBindingGroup :: ModuleName -> [(Ident, Value)] -> UnifyT Type Check ([(Ident, (Value, Maybe (Type, Bool)))], M.Map (ModuleName, Ident) (Type, NameKind), [(Ident, Type)])
201−typeDictionaryForBindingGroup moduleName vals = do
203− -- Map each declaration to a name/value pair, with an optional type, if the declaration is typed
204− es = map isTyped vals
205− -- Filter the typed and untyped declarations
206− typed = filter (isJust . snd . snd) es
207− untyped = filter (isNothing . snd . snd) es
208− -- Make a map of names to typed declarations
209− typedDict = map (\(ident, (_, Just (ty, _))) -> (ident, ty)) typed
211− -- Create fresh unification variables for the types of untyped declarations
212− untypedNames <- replicateM (length untyped) fresh
215− -- Make a map of names to the unification variables of untyped declarations
216− untypedDict = zip (map fst untyped) untypedNames
217− -- Create the dictionary of all name/type pairs, which will be added to the environment during type checking
218− dict = M.fromList (map (\(ident, ty) -> ((moduleName, ident), (ty, LocalVariable))) $ typedDict ++ untypedDict)
219− return (es, dict, untypedDict)
221−typeForBindingGroupElement :: ModuleName -> (Ident, (Value, Maybe (Type, Bool))) -> M.Map (ModuleName, Ident) (Type, NameKind) -> [(Ident, Type)] -> UnifyT Type Check (Ident, (Value, Type))
222−typeForBindingGroupElement moduleName e@(_, (val, _)) dict untypedDict = do
223− -- If the declaration is a function, it has access to other values in the binding group.
224− -- If not, the generated code might fail at runtime since those values might be undefined.
225− let dict' = if isFunction val then dict else M.empty
227− -- Typed declarations
228− (ident, (val', Just (ty, checkType))) -> do
230− kind <- liftCheck $ kindOf moduleName ty
231− guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
232− -- Check the type with the new names in scope
233− ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
234− val'' <- bindNames dict' $ if checkType
235− then TypedValue True <$> check val' ty' <*> pure ty'
236− else return (TypedValue False val' ty')
237− return (ident, (val'', ty'))
238− -- Untyped declarations
239− (ident, (val', Nothing)) -> do
240− -- Infer the type with the new names in scope
241− TypedValue _ val'' ty <- bindNames dict' $ infer val'
242− ty =?= fromMaybe (error "name not found in dictionary") (lookup ident untypedDict)
243− return (ident, (TypedValue True val'' ty, ty))
246−-- Check if a value introduces a function
248−isFunction :: Value -> Bool
249−isFunction (Abs _ _) = True
250−isFunction (TypedValue _ val _) = isFunction val
251−isFunction (PositionedValue _ val) = isFunction val
255−-- Check if a value contains a type annotation
257−isTyped :: (Ident, Value) -> (Ident, (Value, Maybe (Type, Bool)))
258−isTyped (name, TypedValue checkType value ty) = (name, (value, Just (ty, checkType)))
259−isTyped (name, value) = (name, (value, Nothing))
262−-- Map a function over type annotations appearing inside a value
264−overTypes :: (Type -> Type) -> Value -> Value
265−overTypes f = let (_, f', _) = everywhereOnValues id g id in f'
268− g (TypedValue checkTy val t) = TypedValue checkTy val (f t)
269− g (TypeClassDictionary b (nm, tys) sco) = TypeClassDictionary b (nm, map f tys) sco
273−-- Replace type class dictionary placeholders with inferred type class dictionaries
275−replaceTypeClassDictionaries :: ModuleName -> Value -> Check Value
276−replaceTypeClassDictionaries mn = everywhereM' (mkM go)
278− go (TypeClassDictionary trySuperclasses constraint dicts) = do
280− entails env mn dicts constraint trySuperclasses
281− go other = return other
284−-- A simplified representation of expressions which are used to represent type
285−-- class dictionaries at runtime, which can be compared for equality
289− -- A dictionary which is brought into scope by a local constraint
291− = LocalDictionaryValue (Qualified Ident)
293− -- A dictionary which is brought into scope by an instance declaration
295− | GlobalDictionaryValue (Qualified Ident)
297− -- A dictionary which depends on other dictionaries
299− | DependentDictionaryValue (Qualified Ident) [DictionaryValue]
301− -- A subclass dictionary
303− | SubclassDictionaryValue DictionaryValue (Qualified ProperName) Integer
304− deriving (Show, Ord, Eq)
307−-- Check that the current set of type class dictionaries entail the specified type class goal, and, if so,
308−-- return a type class dictionary reference.
310−entails :: Environment -> ModuleName -> [TypeClassDictionaryInScope] -> (Qualified ProperName, [Type]) -> Bool -> Check Value
311−entails env moduleName context = solve (sortedNubBy canonicalizeDictionary (filter filterModule context))
313− sortedNubBy :: (Ord k) => (v -> k) -> [v] -> [v]
314− sortedNubBy f vs = M.elems (M.fromList (map (f &&& id) vs))
316− -- Filter out type dictionaries which are in scope in the current module
317− filterModule :: TypeClassDictionaryInScope -> Bool
318− filterModule (TypeClassDictionaryInScope { tcdName = Qualified (Just mn) _ }) | mn == moduleName = True
319− filterModule (TypeClassDictionaryInScope { tcdName = Qualified Nothing _ }) = True
320− filterModule _ = False
322− solve context' (className, tys) trySuperclasses =
324− dicts = go trySuperclasses className tys
325− in case sortedNubBy dictTrace (chooseSimplestDictionaries dicts) of
326− [] -> throwError . strMsg $ "No instance found for " ++ show className ++ " " ++ unwords (map prettyPrintTypeAtom tys)
327− [_] -> return $ dictionaryValueToValue $ head dicts
328− _ -> throwError . strMsg $ "Overlapping instances found for " ++ show className ++ " " ++ unwords (map prettyPrintTypeAtom tys)
330− go trySuperclasses' className' tys' =
331− -- Look for regular type instances
332− [ mkDictionary (canonicalizeDictionary tcd) args
334− -- Make sure the type class name matches the one we are trying to satisfy
335− , className' == tcdClassName tcd
336− -- Make sure the type unifies with the type in the type instance definition
337− , subst <- maybeToList . (>>= verifySubstitution) . fmap concat $ zipWithM (typeHeadsAreEqual moduleName env) tys' (tcdInstanceTypes tcd)
338− -- Solve any necessary subgoals
339− , args <- solveSubgoals subst (tcdDependencies tcd) ] ++
341− -- Look for implementations via superclasses
342− [ SubclassDictionaryValue suDict superclass index
344− , (subclassName, (args, _, implies)) <- M.toList (typeClasses env)
345− -- Try each superclass
346− , (index, (superclass, suTyArgs)) <- zip [0..] implies
347− -- Make sure the type class name matches the superclass name
348− , className' == superclass
349− -- Make sure the types unify with the types in the superclass implication
350− , subst <- maybeToList . (>>= verifySubstitution) . fmap concat $ zipWithM (typeHeadsAreEqual moduleName env) tys' suTyArgs
351− -- Finally, satisfy the subclass constraint
352− , args' <- maybeToList $ mapM (applySubst subst . TypeVar) args
353− , suDict <- go True subclassName args' ]
355− -- Create dictionaries for subgoals which still need to be solved by calling go recursively
356− -- E.g. the goal (Show a, Show b) => Show (Either a b) can be satisfied if the current type
357− -- unifies with Either a b, and we can satisfy the subgoals Show a and Show b recursively.
358− solveSubgoals :: [(String, Type)] -> Maybe [(Qualified ProperName, [Type])] -> [Maybe [DictionaryValue]]
359− solveSubgoals _ Nothing = return Nothing
360− solveSubgoals subst (Just subgoals) = do
361− dict <- mapM (uncurry (go True) . second (map (replaceAllTypeVars subst))) subgoals
363− -- Make a dictionary from subgoal dictionaries by applying the correct function
364− mkDictionary :: Qualified Ident -> Maybe [DictionaryValue] -> DictionaryValue
365− mkDictionary fnName Nothing = LocalDictionaryValue fnName
366− mkDictionary fnName (Just []) = GlobalDictionaryValue fnName
367− mkDictionary fnName (Just dicts) = DependentDictionaryValue fnName dicts
368− -- Turn a DictionaryValue into a Value
369− dictionaryValueToValue :: DictionaryValue -> Value
370− dictionaryValueToValue (LocalDictionaryValue fnName) = Var fnName
371− dictionaryValueToValue (GlobalDictionaryValue fnName) = App (Var fnName) (ObjectLiteral [])
372− dictionaryValueToValue (DependentDictionaryValue fnName dicts) = foldl App (Var fnName) (map dictionaryValueToValue dicts)
373− dictionaryValueToValue (SubclassDictionaryValue dict superclassName index) =
374− App (Accessor (show superclassName ++ "_" ++ show index)
375− (Accessor C.__superclasses (dictionaryValueToValue dict)))
377− -- Ensure that a substitution is valid
378− verifySubstitution :: [(String, Type)] -> Maybe [(String, Type)]
379− verifySubstitution subst = do
380− let grps = groupBy ((==) `on` fst) subst
381− guard (all (pairwise (unifiesWith env) . map snd) grps)
382− return $ map head grps
383− -- Apply a substitution to a type
384− applySubst :: [(String, Type)] -> Type -> Maybe Type
385− applySubst subst = everywhereOnTypesM replace
387− replace (TypeVar v) = lookup v subst
388− replace other = Just other
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
401− isSimpleDictionaryValue SubclassDictionaryValue{} = False
402− isSimpleDictionaryValue (DependentDictionaryValue _ ds) = all isSimpleDictionaryValue ds
403− isSimpleDictionaryValue _ = True
405− -- Get the "trace" of a DictionaryValue - that is, remove all SubclassDictionaryValue
406− -- data constructors
408− dictTrace :: DictionaryValue -> DictionaryValue
409− dictTrace (DependentDictionaryValue fnName dicts) = DependentDictionaryValue fnName $ map dictTrace dicts
410− dictTrace (SubclassDictionaryValue dict _ _) = dictTrace dict
411− dictTrace other = other
414−-- Check all values in a list pairwise match a predicate
416−pairwise :: (a -> a -> Bool) -> [a] -> Bool
418−pairwise _ [_] = True
419−pairwise p (x : xs) = all (p x) xs && pairwise p xs
422−-- Check that two types unify
424−unifiesWith :: Environment -> Type -> Type -> Bool
425−unifiesWith _ (TUnknown _) _ = True
426−unifiesWith _ _ (TUnknown _) = True
427−unifiesWith _ (Skolem _ s1 _) (Skolem _ s2 _) | s1 == s2 = True
428−unifiesWith _ (TypeVar v1) (TypeVar v2) | v1 == v2 = True
429−unifiesWith _ (TypeConstructor c1) (TypeConstructor c2) | c1 == c2 = True
430−unifiesWith e (TypeApp h1 t1) (TypeApp h2 t2) = unifiesWith e h1 h2 && unifiesWith e t1 t2
431−unifiesWith e (SaturatedTypeSynonym name args) t2 =
432− case expandTypeSynonym' e name args of
434− Right t1 -> unifiesWith e t1 t2
435−unifiesWith e t1 t2@(SaturatedTypeSynonym _ _) = unifiesWith e t2 t1
436−unifiesWith _ _ _ = False
439−-- Check whether the type heads of two types are equal (for the purposes of type class dictionary lookup),
440−-- and return a substitution from type variables to types which makes the type heads unify.
442−typeHeadsAreEqual :: ModuleName -> Environment -> Type -> Type -> Maybe [(String, Type)]
443−typeHeadsAreEqual _ _ (Skolem _ s1 _) (Skolem _ s2 _) | s1 == s2 = Just []
444−typeHeadsAreEqual _ _ t (TypeVar v) = Just [(v, t)]
445−typeHeadsAreEqual _ _ (TypeConstructor c1) (TypeConstructor c2) | c1 == c2 = Just []
446−typeHeadsAreEqual m e (TypeApp h1 t1) (TypeApp h2 t2) = (++) <$> typeHeadsAreEqual m e h1 h2 <*> typeHeadsAreEqual m e t1 t2
447−typeHeadsAreEqual m e (SaturatedTypeSynonym name args) t2 = case expandTypeSynonym' e name args of
449− Right t1 -> typeHeadsAreEqual m e t1 t2
450−typeHeadsAreEqual _ _ _ _ = Nothing
453−-- Ensure skolem variables do not escape their scope
455−skolemEscapeCheck :: Value -> Check ()
456−skolemEscapeCheck (TypedValue False _ _) = return ()
457−skolemEscapeCheck root@TypedValue{} =
458− -- Every skolem variable is created when a ForAll type is skolemized.
459− -- This determines the scope of that skolem variable, which is copied from the SkolemScope
460− -- field of the ForAll constructor.
461− -- We traverse the tree top-down, and collect any SkolemScopes introduced by ForAlls.
462− -- If a Skolem is encountered whose SkolemScope is not in the current list, we have found
463− -- an escaped skolem variable.
464− case everythingWithContext [] (++) (mkQ ((,) []) go) root of
466− ((binding, val) : _) -> throwError $ mkErrorStack ("Rigid/skolem type variable " ++ maybe "" (("bound by " ++) . prettyPrintValue) binding ++ " has escaped.") (Just (ValueError val))
468− go :: Value -> [(SkolemScope, Value)] -> ([(Maybe Value, Value)], [(SkolemScope, Value)])
469− go val@(TypedValue _ _ (ForAll _ _ (Just sco))) scos = ([], (sco, val) : scos)
470− go val@(TypedValue _ _ ty) scos = case collectSkolems ty \\ map fst scos of
471− (sco : _) -> ([(findBindingScope sco, val)], scos)
474− collectSkolems :: Type -> [SkolemScope]
475− collectSkolems = nub . everythingOnTypes (++) collect
477− collect (Skolem _ _ scope) = [scope]
479− go _ scos = ([], scos)
480− findBindingScope :: SkolemScope -> Maybe Value
481− findBindingScope sco =
482− let (_, f, _, _, _) = everythingOnValues mappend (const mempty) go' (const mempty) (const mempty) (const mempty)
483− in getFirst $ f root
485− go' val@(TypedValue _ _ (ForAll _ _ (Just sco'))) | sco == sco' = First (Just val)
487−skolemEscapeCheck val = throwError $ mkErrorStack "Untyped value passed to skolemEscapeCheck" (Just (ValueError val))
490−-- Ensure a row contains no duplicate labels
492−setify :: Type -> Type
493−setify = rowFromList . first (M.toList . M.fromList) . rowToList
496−-- \"Setify\" all rows occuring inside a value
498−setifyAll :: Type -> Type
499−setifyAll = everywhereOnTypes setify
502−-- Replace outermost unsolved unification variables with named type variables
504−varIfUnknown :: Type -> Type
506− let unks = nub $ unknowns ty
507− toName = (:) 't' . show
508− ty' = everywhereOnTypes typeToVar ty
509− typeToVar :: Type -> Type
510− typeToVar (TUnknown u) = TypeVar (toName u)
512− in mkForAll (sort . map toName $ unks) ty'
515−-- Remove any ForAlls and ConstrainedType constructors in a type by introducing new unknowns
516−-- or TypeClassDictionary values.
518−-- This is necessary during type checking to avoid unifying a polymorphic type with a
519−-- unification variable.
521−instantiatePolyTypeWithUnknowns :: Value -> Type -> UnifyT Type Check (Value, Type)
522−instantiatePolyTypeWithUnknowns val (ForAll ident ty _) = do
523− ty' <- replaceVarWithUnknown ident ty
524− instantiatePolyTypeWithUnknowns val ty'
525−instantiatePolyTypeWithUnknowns val (ConstrainedType constraints ty) = do
526− dicts <- getTypeClassDictionaries
527− (_, ty') <- instantiatePolyTypeWithUnknowns (error "Types under a constraint cannot themselves be constrained") ty
528− return (foldl App val (map (flip (TypeClassDictionary True) dicts) constraints), ty')
529−instantiatePolyTypeWithUnknowns val ty = return (val, ty)
532−-- Replace a single type variable with a new unification variable
534−replaceVarWithUnknown :: String -> Type -> UnifyT Type Check Type
535−replaceVarWithUnknown ident ty = do
537− return $ replaceTypeVars ident tu ty
540−-- Replace fully applied type synonyms with the @SaturatedTypeSynonym@ data constructor, which helps generate
541−-- better error messages during unification.
543−replaceAllTypeSynonyms' :: Environment -> Type -> Either String Type
544−replaceAllTypeSynonyms' env d =
546− syns = map (\(name, (args, _)) -> (name, length args)) . M.toList $ typeSynonyms env
548− saturateAllTypeSynonyms syns d
550−replaceAllTypeSynonyms :: (Error e, Functor m, Monad m, MonadState CheckState m, MonadError e m) => Type -> m Type
551−replaceAllTypeSynonyms d = do
553− either (throwError . strMsg) return $ replaceAllTypeSynonyms' env d
556−-- \"Desaturate\" @SaturatedTypeSynonym@s
558−desaturateAllTypeSynonyms :: Type -> Type
559−desaturateAllTypeSynonyms = everywhereOnTypes replaceSaturatedTypeSynonym
561− replaceSaturatedTypeSynonym (SaturatedTypeSynonym name args) = foldl TypeApp (TypeConstructor name) args
562− replaceSaturatedTypeSynonym t = t
565−-- Replace a type synonym and its arguments with the aliased type
567−expandTypeSynonym' :: Environment -> Qualified ProperName -> [Type] -> Either String Type
568−expandTypeSynonym' env name args =
569− case M.lookup name (typeSynonyms env) of
570− Just (synArgs, body) -> do
571− let repl = replaceAllTypeVars (zip synArgs args) body
572− replaceAllTypeSynonyms' env repl
573− Nothing -> error "Type synonym was not defined"
575−expandTypeSynonym :: (Error e, Functor m, Monad m, MonadState CheckState m, MonadError e m) => Qualified ProperName -> [Type] -> m Type
576−expandTypeSynonym name args = do
578− either (throwError . strMsg) return $ expandTypeSynonym' env name args
580−expandAllTypeSynonyms :: (Error e, Functor m, Applicative m, Monad m, MonadState CheckState m, MonadError e m) => Type -> m Type
581−expandAllTypeSynonyms = everywhereOnTypesTopDownM go
583− go (SaturatedTypeSynonym name args) = expandTypeSynonym name args
584− go other = return other
587−-- Ensure a set of property names and value does not contain duplicate labels
589−ensureNoDuplicateProperties :: (Error e, MonadError e m) => [(String, Value)] -> m ()
590−ensureNoDuplicateProperties ps = guardWith (strMsg "Duplicate property names") $ length (nub . map fst $ ps) == length ps
593−-- Infer a type for a value, rethrowing any error to provide a more useful error message
595−infer :: Value -> UnifyT Type Check Value
596−infer val = rethrow (mkErrorStack "Error inferring type of value" (Just (ValueError val)) <>) $ infer' val
599−-- Infer a type for a value
601−infer' :: Value -> UnifyT Type Check Value
602−infer' v@(NumericLiteral _) = return $ TypedValue True v tyNumber
603−infer' v@(StringLiteral _) = return $ TypedValue True v tyString
604−infer' v@(BooleanLiteral _) = return $ TypedValue True v tyBoolean
605−infer' (ArrayLiteral vals) = do
606− ts <- mapM infer vals
608− forM_ ts $ \(TypedValue _ _ t) -> els =?= TypeApp tyArray t
609− return $ TypedValue True (ArrayLiteral ts) els
610−infer' (ObjectLiteral ps) = do
611− ensureNoDuplicateProperties ps
612− ts <- mapM (infer . snd) ps
613− let fields = zipWith (\name (TypedValue _ _ t) -> (name, t)) (map fst ps) ts
614− ty = TypeApp tyObject $ rowFromList (fields, REmpty)
615− return $ TypedValue True (ObjectLiteral (zip (map fst ps) ts)) ty
616−infer' (ObjectUpdate o ps) = do
617− ensureNoDuplicateProperties ps
619− newVals <- zipWith (\(name, _) t -> (name, t)) ps <$> mapM (infer . snd) ps
620− let newTys = map (\(name, TypedValue _ _ ty) -> (name, ty)) newVals
621− oldTys <- zip (map fst ps) <$> replicateM (length ps) fresh
622− let oldTy = TypeApp tyObject $ rowFromList (oldTys, row)
623− o' <- TypedValue True <$> check o oldTy <*> pure oldTy
624− return $ TypedValue True (ObjectUpdate o' newVals) $ TypeApp tyObject $ rowFromList (newTys, row)
625−infer' (Accessor prop val) = do
626− typed@(TypedValue _ _ objTy) <- infer val
627− propTy <- inferProperty objTy prop
632− _ <- subsumes Nothing objTy (TypeApp tyObject (RCons prop field rest))
633− return $ TypedValue True (Accessor prop typed) field
634− Just ty -> return $ TypedValue True (Accessor prop typed) ty
635−infer' (Abs (Left arg) ret) = do
637− Just moduleName <- checkCurrentModule <$> get
638− bindLocalVariables moduleName [(arg, ty)] $ do
639− body@(TypedValue _ _ bodyTy) <- infer' ret
640− return $ TypedValue True (Abs (Left arg) body) $ function ty bodyTy
641−infer' (Abs (Right _) _) = error "Binder was not desugared"
642−infer' (App f arg) = do
643− f'@(TypedValue _ _ ft) <- infer f
644− (ret, app) <- checkFunctionApplication f' ft arg Nothing
645− return $ TypedValue True app ret
646−infer' (Var var) = do
647− Just moduleName <- checkCurrentModule <$> get
648− ty <- introduceSkolemScope <=< replaceAllTypeSynonyms <=< lookupVariable moduleName $ var
650− ConstrainedType constraints ty' -> do
651− dicts <- getTypeClassDictionaries
652− return $ TypedValue True (foldl App (Var var) (map (flip (TypeClassDictionary True) dicts) constraints)) ty'
653− _ -> return $ TypedValue True (Var var) ty
654−infer' v@(Constructor c) = do
656− case M.lookup c (dataConstructors env) of
657− Nothing -> throwError . strMsg $ "Constructor " ++ show c ++ " is undefined"
658− Just (_, ty) -> do ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
659− return $ TypedValue True v ty'
660−infer' (Case vals binders) = do
661− ts <- mapM infer vals
663− binders' <- checkBinders (map (\(TypedValue _ _ t) -> t) ts) ret binders
664− return $ TypedValue True (Case ts binders') ret
665−infer' (IfThenElse cond th el) = do
666− cond' <- check cond tyBoolean
667− v2@(TypedValue _ _ t2) <- infer th
668− v3@(TypedValue _ _ t3) <- infer el
670− return $ TypedValue True (IfThenElse cond' v2 v3) t2
671−infer' (Let ds val) = do
672− (ds', val'@(TypedValue _ _ valTy)) <- inferLetBinding [] ds val infer
673− return $ TypedValue True (Let ds' val') valTy
674−infer' (SuperClassDictionary className tys) = do
675− dicts <- getTypeClassDictionaries
676− return $ TypeClassDictionary False (className, tys) dicts
677−infer' (TypedValue checkType val ty) = do
678− Just moduleName <- checkCurrentModule <$> get
679− kind <- liftCheck $ kindOf moduleName ty
680− guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
681− ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
682− val' <- if checkType then check val ty' else return val
683− return $ TypedValue True val' ty'
684−infer' (PositionedValue pos val) = rethrowWithPosition pos $ infer' val
685−infer' _ = error "Invalid argument to infer"
687−inferLetBinding :: [Declaration] -> [Declaration] -> Value -> (Value -> UnifyT Type Check Value) -> UnifyT Type Check ([Declaration], Value)
688−inferLetBinding seen [] ret j = (,) seen <$> j ret
689−inferLetBinding seen (ValueDeclaration ident nameKind [] Nothing tv@(TypedValue checkType val ty) : rest) ret j = do
690− Just moduleName <- checkCurrentModule <$> get
691− kind <- liftCheck $ kindOf moduleName ty
692− guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
693− let dict = if isFunction val then M.singleton (moduleName, ident) (ty, nameKind) else M.empty
694− TypedValue _ val' ty' <- if checkType then bindNames dict (check val ty) else return tv
695− bindNames (M.singleton (moduleName, ident) (ty', nameKind)) $ inferLetBinding (seen ++ [ValueDeclaration ident nameKind [] Nothing (TypedValue checkType val' ty')]) rest ret j
696−inferLetBinding seen (ValueDeclaration ident nameKind [] Nothing val : rest) ret j = do
698− Just moduleName <- checkCurrentModule <$> get
699− let dict = if isFunction val then M.singleton (moduleName, ident) (valTy, nameKind) else M.empty
700− TypedValue _ val' valTy' <- bindNames dict $ infer val
702− bindNames (M.singleton (moduleName, ident) (valTy', nameKind)) $ inferLetBinding (seen ++ [ValueDeclaration ident nameKind [] Nothing val']) rest ret j
703−inferLetBinding seen (BindingGroupDeclaration ds : rest) ret j = do
704− Just moduleName <- checkCurrentModule <$> get
705− (es, dict, untypedDict) <- typeDictionaryForBindingGroup moduleName (map (\(i, _, v) -> (i, v)) ds)
706− ds' <- forM es $ \e -> do
707− (ident, (val', _)) <- typeForBindingGroupElement moduleName e dict untypedDict
708− return $ (ident, LocalVariable, val')
709− bindNames dict $ inferLetBinding (seen ++ [BindingGroupDeclaration ds']) rest ret j
710−inferLetBinding seen (PositionedDeclaration pos d : ds) ret j = rethrowWithPosition pos $ do
711− ((d' : ds'), val') <- inferLetBinding seen (d : ds) ret j
712− return (PositionedDeclaration pos d' : ds', val')
713−inferLetBinding _ _ _ _ = error "Invalid argument to inferLetBinding"
716−-- Infer the type of a property inside a record with a given type
718−inferProperty :: Type -> String -> UnifyT Type Check (Maybe Type)
719−inferProperty (TypeApp obj row) prop | obj == tyObject = do
720− let (props, _) = rowToList row
721− return $ lookup prop props
722−inferProperty (SaturatedTypeSynonym name args) prop = do
723− replaced <- introduceSkolemScope <=< expandTypeSynonym name $ args
724− inferProperty replaced prop
725−inferProperty (ForAll ident ty _) prop = do
726− replaced <- replaceVarWithUnknown ident ty
727− inferProperty replaced prop
728−inferProperty _ _ = return Nothing
731−-- Infer the types of variables brought into scope by a binder
733−inferBinder :: Type -> Binder -> UnifyT Type Check (M.Map Ident Type)
734−inferBinder _ NullBinder = return M.empty
735−inferBinder val (StringBinder _) = val =?= tyString >> return M.empty
736−inferBinder val (NumberBinder _) = val =?= tyNumber >> return M.empty
737−inferBinder val (BooleanBinder _) = val =?= tyBoolean >> return M.empty
738−inferBinder val (VarBinder name) = return $ M.singleton name val
739−inferBinder val (ConstructorBinder ctor binders) = do
741− case M.lookup ctor (dataConstructors env) of
743− (_, fn) <- instantiatePolyTypeWithUnknowns (error "Data constructor types cannot contain constraints") ty
744− fn' <- replaceAllTypeSynonyms fn
748− _ <- subsumes Nothing val ty'
750− go (binder : binders') (TypeApp (TypeApp t obj) ret) | t == tyFunction =
751− M.union <$> inferBinder obj binder <*> go binders' ret
752− go _ _ = throwError . strMsg $ "Wrong number of arguments to constructor " ++ show ctor
753− _ -> throwError . strMsg $ "Constructor " ++ show ctor ++ " is not defined"
754−inferBinder val (ObjectBinder props) = do
757− m1 <- inferRowProperties row rest props
758− val =?= TypeApp tyObject row
761− inferRowProperties :: Type -> Type -> [(String, Binder)] -> UnifyT Type Check (M.Map Ident Type)
762− inferRowProperties nrow row [] = nrow =?= row >> return M.empty
763− inferRowProperties nrow row ((name, binder):binders) = do
765− m1 <- inferBinder propTy binder
766− m2 <- inferRowProperties nrow (RCons name propTy row) binders
767− return $ m1 `M.union` m2
768−inferBinder val (ArrayBinder binders) = do
770− m1 <- M.unions <$> mapM (inferBinder el) binders
771− val =?= TypeApp tyArray el
773−inferBinder val (ConsBinder headBinder tailBinder) = do
775− m1 <- inferBinder el headBinder
776− m2 <- inferBinder val tailBinder
777− val =?= TypeApp tyArray el
778− return $ m1 `M.union` m2
779−inferBinder val (NamedBinder name binder) = do
780− m <- inferBinder val binder
781− return $ M.insert name val m
782−inferBinder val (PositionedBinder pos binder) =
783− rethrowWithPosition pos $ inferBinder val binder
786−-- Check the types of the return values in a set of binders in a case statement
788−checkBinders :: [Type] -> Type -> [CaseAlternative] -> UnifyT Type Check [CaseAlternative]
789−checkBinders _ _ [] = return []
790−checkBinders nvals ret (CaseAlternative binders grd val : bs) = do
791− Just moduleName <- checkCurrentModule <$> get
792− m1 <- M.unions <$> zipWithM inferBinder nvals binders
793− r <- bindLocalVariables moduleName (M.toList m1) $ do
794− val' <- TypedValue True <$> check val ret <*> pure ret
796− Nothing -> return $ CaseAlternative binders Nothing val'
798− g' <- check g tyBoolean
799− return $ CaseAlternative binders (Just g') val'
800− rs <- checkBinders nvals ret bs
804−-- Generate a new skolem constant
806−newSkolemConstant :: UnifyT Type Check Int
807−newSkolemConstant = fresh'
810−-- Generate a new skolem scope
812−newSkolemScope :: UnifyT Type Check SkolemScope
813−newSkolemScope = SkolemScope <$> fresh'
816−-- Skolemize a type variable by replacing its instances with fresh skolem constants
818−skolemize :: String -> Int -> SkolemScope -> Type -> Type
819−skolemize ident sko scope = replaceTypeVars ident (Skolem ident sko scope)
822−-- This function has one purpose - to skolemize type variables appearing in a
823−-- SuperClassDictionary placeholder. These type variables are somewhat unique since they are the
824−-- only example of scoped type variables.
826−skolemizeTypesInValue :: String -> Int -> SkolemScope -> Value -> Value
827−skolemizeTypesInValue ident sko scope = let (_, f, _) = everywhereOnValues id go id in f
829− go (SuperClassDictionary c ts) = SuperClassDictionary c (map (skolemize ident sko scope) ts)
833−-- Introduce skolem scope at every occurence of a ForAll
835−introduceSkolemScope :: Type -> UnifyT Type Check Type
836−introduceSkolemScope = everywhereOnTypesM go
838− go (ForAll ident ty Nothing) = ForAll ident ty <$> (Just <$> newSkolemScope)
839− go other = return other
842−-- Check the type of a value, rethrowing errors to provide a better error message
844−check :: Value -> Type -> UnifyT Type Check Value
845−check val ty = rethrow (mkErrorStack errorMessage (Just (ValueError val)) <>) $ check' val ty
848− "Error checking type of term " ++
849− prettyPrintValue val ++
854−-- Check the type of a value
856−check' :: Value -> Type -> UnifyT Type Check Value
857−check' val (ForAll ident ty _) = do
858− scope <- newSkolemScope
859− sko <- newSkolemConstant
860− let sk = skolemize ident sko scope ty
861− let skVal = skolemizeTypesInValue ident sko scope val
862− val' <- check skVal sk
863− return $ TypedValue True val' (ForAll ident ty (Just scope))
864−check' val t@(ConstrainedType constraints ty) = do
865− dictNames <- forM constraints $ \(Qualified _ (ProperName className), _) -> do
866− n <- liftCheck freshDictionaryName
867− return $ Ident $ "__dict_" ++ className ++ "_" ++ show n
868− val' <- withTypeClassDictionaries (zipWith (\name (className, instanceTy) ->
869− TypeClassDictionaryInScope name className instanceTy Nothing TCDRegular) (map (Qualified Nothing) dictNames)
870− constraints) $ check val ty
871− return $ TypedValue True (foldr (Abs . Left) val' dictNames) t
872−check' val (SaturatedTypeSynonym name args) = do
873− ty <- introduceSkolemScope <=< expandTypeSynonym name $ args
875−check' val u@(TUnknown _) = do
876− val'@(TypedValue _ _ ty) <- infer val
877− -- Don't unify an unknown with an inferred polytype
878− (val'', ty') <- instantiatePolyTypeWithUnknowns val' ty
880− return $ TypedValue True val'' ty'
881−check' v@(NumericLiteral _) t | t == tyNumber =
882− return $ TypedValue True v t
883−check' v@(StringLiteral _) t | t == tyString =
884− return $ TypedValue True v t
885−check' v@(BooleanLiteral _) t | t == tyBoolean =
886− return $ TypedValue True v t
887−check' (ArrayLiteral vals) t@(TypeApp a ty) = do
889− array <- ArrayLiteral <$> forM vals (`check` ty)
890− return $ TypedValue True array t
891−check' (Abs (Left arg) ret) ty@(TypeApp (TypeApp t argTy) retTy) | t == tyFunction = do
892− Just moduleName <- checkCurrentModule <$> get
893− ret' <- bindLocalVariables moduleName [(arg, argTy)] $ check ret retTy
894− return $ TypedValue True (Abs (Left arg) ret') ty
895−check' (Abs (Right _) _) _ = error "Binder was not desugared"
896−check' (App f arg) ret = do
897− f'@(TypedValue _ _ ft) <- infer f
898− (_, app) <- checkFunctionApplication f' ft arg (Just ret)
899− return $ TypedValue True app ret
900−check' v@(Var var) ty = do
901− Just moduleName <- checkCurrentModule <$> get
902− repl <- introduceSkolemScope <=< replaceAllTypeSynonyms <=< lookupVariable moduleName $ var
903− ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
904− v' <- subsumes (Just v) repl ty'
906− Nothing -> throwError . strMsg $ "Unable to check type subsumption"
907− Just v'' -> return $ TypedValue True v'' ty'
908−check' (SuperClassDictionary className tys) _ = do
910− -- Here, we replace a placeholder for a superclass dictionary with a regular
911− -- TypeClassDictionary placeholder. The reason we do this is that it is necessary to have the
912− -- correct super instance dictionaries in scope, and these are not available when the type class
913− -- declaration gets desugared.
915− -- Note also that the first argument to TypeClassDictionary is False, meaning we _do not_ want
916− -- to consider superclass instances when searching for this dictionary - doing so might lead
917− -- to traversing a cycle in the instance graph.
919− dicts <- getTypeClassDictionaries
920− return $ TypeClassDictionary False (className, tys) dicts
921−check' (TypedValue checkType val ty1) ty2 = do
922− Just moduleName <- checkCurrentModule <$> get
923− kind <- liftCheck $ kindOf moduleName ty1
924− guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
925− ty1' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty1
926− val' <- subsumes (Just val) ty1' ty2
928− Nothing -> throwError . strMsg $ "Unable to check type subsumption"
930− val''' <- if checkType then check val'' ty1' else return val''
931− return $ TypedValue checkType (TypedValue True val''' ty1) ty2
932−check' (Case vals binders) ret = do
933− vals' <- mapM infer vals
934− let ts = map (\(TypedValue _ _ t) -> t) vals'
935− binders' <- checkBinders ts ret binders
936− return $ TypedValue True (Case vals' binders') ret
937−check' (IfThenElse cond th el) ty = do
938− cond' <- check cond tyBoolean
941− return $ TypedValue True (IfThenElse cond' th' el') ty
942−check' (ObjectLiteral ps) t@(TypeApp obj row) | obj == tyObject = do
943− ensureNoDuplicateProperties ps
944− ps' <- checkProperties ps row False
945− return $ TypedValue True (ObjectLiteral ps') t
946−check' (ObjectUpdate obj ps) t@(TypeApp o row) | o == tyObject = do
947− ensureNoDuplicateProperties ps
948− us <- zip (map fst ps) <$> replicateM (length ps) fresh
949− let (propsToCheck, rest) = rowToList row
950− propsToRemove = map fst ps
951− remainingProps = filter (\(p, _) -> p `notElem` propsToRemove) propsToCheck
952− obj' <- check obj (TypeApp tyObject (rowFromList (us ++ remainingProps, rest)))
953− ps' <- checkProperties ps row True
954− return $ TypedValue True (ObjectUpdate obj' ps') t
955−check' (Accessor prop val) ty = do
957− val' <- check val (TypeApp tyObject (RCons prop ty rest))
958− return $ TypedValue True (Accessor prop val') ty
959−check' (Constructor c) ty = do
961− case M.lookup c (dataConstructors env) of
962− Nothing -> throwError . strMsg $ "Constructor " ++ show c ++ " is undefined"
964− repl <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty1
965− _ <- subsumes Nothing repl ty
966− return $ TypedValue True (Constructor c) ty
967−check' (Let ds val) ty = do
968− (ds', val') <- inferLetBinding [] ds val (flip check ty)
969− return $ TypedValue True (Let ds' val') ty
970−check' val ty | containsTypeSynonyms ty = do
971− ty' <- introduceSkolemScope <=< expandAllTypeSynonyms $ ty
973−check' (PositionedValue pos val) ty =
974− rethrowWithPosition pos $ check val ty
975−check' val ty = throwError $ mkErrorStack ("Value does not have type " ++ prettyPrintType ty) (Just (ValueError val))
977−containsTypeSynonyms :: Type -> Bool
978−containsTypeSynonyms = everythingOnTypes (||) go where
979− go (SaturatedTypeSynonym _ _) = True
983−-- Check the type of a collection of named record fields
985−-- The @lax@ parameter controls whether or not every record member has to be provided. For object updates, this is not the case.
987−checkProperties :: [(String, Value)] -> Type -> Bool -> UnifyT Type Check [(String, Value)]
988−checkProperties ps row lax = let (ts, r') = rowToList row in go ps ts r' where
989− go [] [] REmpty = return []
990− go [] [] u@(TUnknown _) = do u =?= REmpty
992− go [] [] (Skolem _ _ _) | lax = return []
993− go [] ((p, _): _) _ | lax = return []
994− | otherwise = throwError $ mkErrorStack ("Object does not have property " ++ p) (Just (ValueError (ObjectLiteral ps)))
995− go ((p,_):_) [] REmpty = throwError $ mkErrorStack ("Property " ++ p ++ " is not present in closed object type " ++ prettyPrintRow row) (Just (ValueError (ObjectLiteral ps)))
996− go ((p,v):ps') [] u@(TUnknown _) = do
997− v'@(TypedValue _ _ ty) <- infer v
999− u =?= RCons p ty rest
1000− ps'' <- go ps' [] rest
1001− return $ (p, v') : ps''
1002− go ((p,v):ps') ts r =
1003− case lookup p ts of
1005− v'@(TypedValue _ _ ty) <- infer v
1007− r =?= RCons p ty rest
1008− ps'' <- go ps' ts rest
1009− return $ (p, v') : ps''
1012− ps'' <- go ps' (delete (p, ty) ts) r
1013− return $ (p, v') : ps''
1014− go _ _ _ = throwError $ mkErrorStack ("Object does not have type " ++ prettyPrintType (TypeApp tyObject row)) (Just (ValueError (ObjectLiteral ps)))
1017−-- Check the type of a function application, rethrowing errors to provide a better error message
1019−checkFunctionApplication :: Value -> Type -> Value -> Maybe Type -> UnifyT Type Check (Type, Value)
1020−checkFunctionApplication fn fnTy arg ret = rethrow (mkErrorStack errorMessage (Just (ValueError fn)) <>) $ checkFunctionApplication' fn fnTy arg ret
1022− errorMessage = "Error applying function of type "
1023− ++ prettyPrintType fnTy
1024− ++ " to argument " ++ prettyPrintValue arg
1027−-- Check the type of a function application
1029−checkFunctionApplication' :: Value -> Type -> Value -> Maybe Type -> UnifyT Type Check (Type, Value)
1030−checkFunctionApplication' fn (TypeApp (TypeApp tyFunction' argTy) retTy) arg ret = do
1031− tyFunction' =?= tyFunction
1032− _ <- maybe (return Nothing) (subsumes Nothing retTy) ret
1033− subst <- unifyCurrentSubstitution <$> UnifyT get
1034− arg' <- check arg (subst $? argTy)
1035− return (retTy, App fn arg')
1036−checkFunctionApplication' fn (ForAll ident ty _) arg ret = do
1037− replaced <- replaceVarWithUnknown ident ty
1038− checkFunctionApplication fn replaced arg ret
1039−checkFunctionApplication' fn u@(TUnknown _) arg ret = do
1041− TypedValue _ arg' t <- infer arg
1042− (arg'', t') <- instantiatePolyTypeWithUnknowns arg' t
1043− return $ TypedValue True arg'' t'
1044− let ty = (\(TypedValue _ _ t) -> t) arg'
1045− ret' <- maybe fresh return ret
1046− u =?= function ty ret'
1047− return (ret', App fn arg')
1048−checkFunctionApplication' fn (SaturatedTypeSynonym name tyArgs) arg ret = do
1049− ty <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
1050− checkFunctionApplication fn ty arg ret
1051−checkFunctionApplication' fn (ConstrainedType constraints fnTy) arg ret = do
1052− dicts <- getTypeClassDictionaries
1053− checkFunctionApplication' (foldl App fn (map (flip (TypeClassDictionary True) dicts) constraints)) fnTy arg ret
1054−checkFunctionApplication' _ fnTy arg _ = throwError . strMsg $ "Cannot apply a function of type "
1055− ++ prettyPrintType fnTy
1056− ++ " to argument " ++ prettyPrintValue arg
1059−-- Check whether one type subsumes another, rethrowing errors to provide a better error message
1061−subsumes :: Maybe Value -> Type -> Type -> UnifyT Type Check (Maybe Value)
1062−subsumes val ty1 ty2 = rethrow (mkErrorStack errorMessage (ValueError <$> val) <>) $ subsumes' val ty1 ty2
1064− errorMessage = "Error checking that type "
1065− ++ prettyPrintType ty1
1066− ++ " subsumes type "
1067− ++ prettyPrintType ty2
1070−-- Check whether one type subsumes another
1072−subsumes' :: Maybe Value -> Type -> Type -> UnifyT Type Check (Maybe Value)
1073−subsumes' val (ForAll ident ty1 _) ty2 = do
1074− replaced <- replaceVarWithUnknown ident ty1
1075− subsumes val replaced ty2
1076−subsumes' val ty1 (ForAll ident ty2 sco) =
1079− sko <- newSkolemConstant
1080− let sk = skolemize ident sko sco' ty2
1081− subsumes val ty1 sk
1082− Nothing -> throwError . strMsg $ "Skolem variable scope is unspecified"
1083−subsumes' val (TypeApp (TypeApp f1 arg1) ret1) (TypeApp (TypeApp f2 arg2) ret2) | f1 == tyFunction && f2 == tyFunction = do
1084− _ <- subsumes Nothing arg2 arg1
1085− _ <- subsumes Nothing ret1 ret2
1087−subsumes' val (SaturatedTypeSynonym name tyArgs) ty2 = do
1088− ty1 <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
1089− subsumes val ty1 ty2
1090−subsumes' val ty1 (SaturatedTypeSynonym name tyArgs) = do
1091− ty2 <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
1092− subsumes val ty1 ty2
1093−subsumes' (Just val) (ConstrainedType constraints ty1) ty2 = do
1094− dicts <- getTypeClassDictionaries
1095− _ <- subsumes' Nothing ty1 ty2
1096− return . Just $ foldl App val (map (flip (TypeClassDictionary True) dicts) constraints)
1097−subsumes' val (TypeApp f1 r1) (TypeApp f2 r2) | f1 == tyObject && f2 == tyObject = do
1099− (ts1, r1') = rowToList r1
1100− (ts2, r2') = rowToList r2
1101− ts1' = sortBy (comparing fst) ts1
1102− ts2' = sortBy (comparing fst) ts2
1103− go ts1' ts2' r1' r2'
1106− go [] ts2 r1' r2' = r1' =?= rowFromList (ts2, r2')
1107− go ts1 [] r1' r2' = r2' =?= rowFromList (ts1, r1')
1108− go ((p1, ty1) : ts1) ((p2, ty2) : ts2) r1' r2'
1109− | p1 == p2 = do _ <- subsumes Nothing ty1 ty2
1111− | p1 < p2 = do rest <- fresh
1112− r2' =?= RCons p1 ty1 rest
1113− go ts1 ((p2, ty2) : ts2) r1' rest
1114− | otherwise = do rest <- fresh
1115− r1' =?= RCons p2 ty2 rest
1116− go ((p1, ty1) : ts1) ts2 rest r2'
1117−subsumes' val ty1 ty2@(TypeApp obj _) | obj == tyObject = subsumes val ty2 ty1
1118−subsumes' val ty1 ty2 = do