@@ -1,1090 +0,0 @@
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 qualified Data.Data as D
48− (everythingWithContext, mkM, everywhereM, everything, mkT,
49− something, everywhere, mkQ)
50−import Data.Generics.Extras
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 Data.Function (on)
74−import Data.Ord (comparing)
75−import Data.Monoid ((<>))
77−instance Partial Type where
79− isUnknown (TUnknown u) = Just u
80− isUnknown _ = Nothing
82−instance Unifiable Check Type where
86−-- Unify two types, updating the current substitution
88−unifyTypes :: Type -> Type -> UnifyT Type Check ()
89−unifyTypes t1 t2 = rethrow (mkErrorStack ("Error unifying type " ++ prettyPrintType t1 ++ " with type " ++ prettyPrintType t2) Nothing <>) $
92− unifyTypes' (TUnknown u1) (TUnknown u2) | u1 == u2 = return ()
93− unifyTypes' (TUnknown u) t = u =:= t
94− unifyTypes' t (TUnknown u) = u =:= t
95− unifyTypes' (SaturatedTypeSynonym name args) ty = do
96− ty1 <- introduceSkolemScope <=< expandTypeSynonym name $ args
98− unifyTypes' ty s@(SaturatedTypeSynonym _ _) = s `unifyTypes` ty
99− unifyTypes' (ForAll ident1 ty1 sc1) (ForAll ident2 ty2 sc2) =
101− (Just sc1', Just sc2') -> do
102− sko <- newSkolemConstant
103− let sk1 = skolemize ident1 sko sc1' ty1
104− let sk2 = skolemize ident2 sko sc2' ty2
105− sk1 `unifyTypes` sk2
106− _ -> error "Skolemized type variable was not given a scope"
107− unifyTypes' (ForAll ident ty1 (Just sc)) ty2 = do
108− sko <- newSkolemConstant
109− let sk = skolemize ident sko sc ty1
111− unifyTypes' ForAll{} _ = throwError . strMsg $ "Skolem variable scope is unspecified"
112− unifyTypes' ty f@ForAll{} = f `unifyTypes` ty
113− unifyTypes' (TypeVar v1) (TypeVar v2) | v1 == v2 = return ()
114− unifyTypes' (TypeConstructor c1) (TypeConstructor c2) =
115− guardWith (strMsg ("Cannot unify " ++ show c1 ++ " with " ++ show c2 ++ ".")) (c1 == c2)
116− unifyTypes' (TypeApp t3 t4) (TypeApp t5 t6) = do
119− unifyTypes' (Skolem _ s1 _) (Skolem _ s2 _) | s1 == s2 = return ()
120− unifyTypes' r1@RCons{} r2 = unifyRows r1 r2
121− unifyTypes' r1 r2@RCons{} = unifyRows r1 r2
122− unifyTypes' r1@REmpty r2 = unifyRows r1 r2
123− unifyTypes' r1 r2@REmpty = unifyRows r1 r2
124− unifyTypes' t@(ConstrainedType _ _) _ = throwError . strMsg $ "Attempted to unify a constrained type " ++ prettyPrintType t ++ " with another type."
125− unifyTypes' t3 t4@(ConstrainedType _ _) = unifyTypes' t4 t3
126− unifyTypes' t3 t4 = throwError . strMsg $ "Cannot unify " ++ prettyPrintType t3 ++ " with " ++ prettyPrintType t4 ++ "."
129−-- Unify two rows, updating the current substitution
131−-- Common labels are first identified, and unified. Remaining labels and types are unified with a
132−-- trailing row unification variable, if appropriate, otherwise leftover labels result in a unification
135−unifyRows :: Type -> Type -> UnifyT Type Check ()
138− (s1, r1') = rowToList r1
139− (s2, r2') = rowToList r2
140− int = [ (t1, t2) | (name, t1) <- s1, (name', t2) <- s2, name == name' ]
141− sd1 = [ (name, t1) | (name, t1) <- s1, name `notElem` map fst s2 ]
142− sd2 = [ (name, t2) | (name, t2) <- s2, name `notElem` map fst s1 ]
144− forM_ int (uncurry (=?=))
145− unifyRows' sd1 r1' sd2 r2'
147− unifyRows' :: [(String, Type)] -> Type -> [(String, Type)] -> Type -> UnifyT Type Check ()
148− unifyRows' [] (TUnknown u) sd r = u =:= rowFromList (sd, r)
149− unifyRows' sd r [] (TUnknown u) = u =:= rowFromList (sd, r)
150− unifyRows' ((name, ty):row) r others u@(TUnknown un) = do
152− forM_ row $ \(_, t) -> occursCheck un t
154− u =?= RCons name ty u'
155− unifyRows' row r others u'
156− unifyRows' [] REmpty [] REmpty = return ()
157− unifyRows' [] (TypeVar v1) [] (TypeVar v2) | v1 == v2 = return ()
158− unifyRows' [] (Skolem _ s1 _) [] (Skolem _ s2 _) | s1 == s2 = return ()
159− unifyRows' sd3 r3 sd4 r4 = throwError . strMsg $ "Cannot unify (" ++ prettyPrintRow (rowFromList (sd3, r3)) ++ ") with (" ++ prettyPrintRow (rowFromList (sd4, r4)) ++ ")"
162−-- Infer the types of multiple mutually-recursive values, and return elaborated values including
163−-- type class dictionaries and type annotations.
165−typesOf :: Maybe ModuleName -> ModuleName -> [(Ident, Value)] -> Check [(Ident, (Value, Type))]
166−typesOf mainModuleName moduleName vals = do
167− tys <- fmap tidyUp . liftUnify $ do
168− (es, dict, untypedDict) <- typeDictionaryForBindingGroup moduleName vals
170− triple@(_, (_, ty)) <- typeForBindingGroupElement moduleName e dict untypedDict
171− -- If --main is enabled, need to check that `main` has type Eff eff a for some eff, a
172− when (Just moduleName == mainModuleName && fst e == Ident C.main) $ do
173− [eff, a] <- replicateM 2 fresh
174− ty =?= TypeApp (TypeApp (TypeConstructor (Qualified (Just (ModuleName [ProperName "Control", ProperName "Monad", ProperName "Eff"])) (ProperName "Eff"))) eff) a
177− forM tys $ \(ident, (val, ty)) -> do
178− -- Replace type class dictionary placeholders with actual dictionaries
179− val' <- replaceTypeClassDictionaries moduleName val
180− -- Check skolem variables did not escape their scope
181− skolemEscapeCheck val'
182− -- Remove type synonyms placeholders, remove duplicate row fields, and replace
183− -- top-level unification variables with named type variables.
184− let val'' = overTypes (desaturateAllTypeSynonyms . setifyAll) val'
185− ty' = varIfUnknown . desaturateAllTypeSynonyms . setifyAll $ ty
186− return (ident, (val'', ty'))
188− -- Apply the substitution that was returned from runUnify to both types and (type-annotated) values
189− tidyUp (ts, sub) = map (\(i, (val, ty)) -> (i, (overTypes (sub $?) val, sub $? ty))) ts
191−typeDictionaryForBindingGroup :: ModuleName -> [(Ident, Value)] -> UnifyT Type Check ([(Ident, (Value, Maybe (Type, Bool)))], M.Map (ModuleName, Ident) (Type, NameKind), [(Ident, Type)])
192−typeDictionaryForBindingGroup moduleName vals = do
194− -- Map each declaration to a name/value pair, with an optional type, if the declaration is typed
195− es = map isTyped vals
196− -- Filter the typed and untyped declarations
197− typed = filter (isJust . snd . snd) es
198− untyped = filter (isNothing . snd . snd) es
199− -- Make a map of names to typed declarations
200− typedDict = map (\(ident, (_, Just (ty, _))) -> (ident, ty)) typed
202− -- Create fresh unification variables for the types of untyped declarations
203− untypedNames <- replicateM (length untyped) fresh
206− -- Make a map of names to the unification variables of untyped declarations
207− untypedDict = zip (map fst untyped) untypedNames
208− -- Create the dictionary of all name/type pairs, which will be added to the environment during type checking
209− dict = M.fromList (map (\(ident, ty) -> ((moduleName, ident), (ty, LocalVariable))) $ typedDict ++ untypedDict)
210− return (es, dict, untypedDict)
212−typeForBindingGroupElement :: ModuleName -> (Ident, (Value, Maybe (Type, Bool))) -> M.Map (ModuleName, Ident) (Type, NameKind) -> [(Ident, Type)] -> UnifyT Type Check (Ident, (Value, Type))
213−typeForBindingGroupElement moduleName e@(_, (val, _)) dict untypedDict = do
214− -- If the declaration is a function, it has access to other values in the binding group.
215− -- If not, the generated code might fail at runtime since those values might be undefined.
216− let dict' = if isFunction val then dict else M.empty
218− -- Typed declarations
219− (ident, (val', Just (ty, checkType))) -> do
221− kind <- liftCheck $ kindOf moduleName ty
222− guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
223− -- Check the type with the new names in scope
224− ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
225− val'' <- bindNames dict' $ if checkType
226− then TypedValue True <$> check val' ty' <*> pure ty'
227− else return (TypedValue False val' ty')
228− return (ident, (val'', ty'))
229− -- Untyped declarations
230− (ident, (val', Nothing)) -> do
231− -- Infer the type with the new names in scope
232− TypedValue _ val'' ty <- bindNames dict' $ infer val'
233− ty =?= fromMaybe (error "name not found in dictionary") (lookup ident untypedDict)
234− return (ident, (TypedValue True val'' ty, ty))
237−-- Check if a value introduces a function
239−isFunction :: Value -> Bool
240−isFunction (Abs _ _) = True
241−isFunction (TypedValue _ val _) = isFunction val
242−isFunction (PositionedValue _ val) = isFunction val
246−-- Check if a value contains a type annotation
248−isTyped :: (Ident, Value) -> (Ident, (Value, Maybe (Type, Bool)))
249−isTyped (name, TypedValue checkType value ty) = (name, (value, Just (ty, checkType)))
250−isTyped (name, value) = (name, (value, Nothing))
253−-- Map a function over type annotations appearing inside a value
255−overTypes :: (Type -> Type) -> Value -> Value
256−overTypes f = everywhere (mkT f)
259−-- Replace type class dictionary placeholders with inferred type class dictionaries
261−replaceTypeClassDictionaries :: ModuleName -> Value -> Check Value
262−replaceTypeClassDictionaries mn = everywhereM' (mkM go)
264− go (TypeClassDictionary trySuperclasses constraint dicts) = do
266− entails env mn dicts constraint trySuperclasses
267− go other = return other
270−-- A simplified representation of expressions which are used to represent type
271−-- class dictionaries at runtime, which can be compared for equality
275− -- A dictionary which is brought into scope by a local constraint
277− = LocalDictionaryValue (Qualified Ident)
279− -- A dictionary which is brought into scope by an instance declaration
281− | GlobalDictionaryValue (Qualified Ident)
283− -- A dictionary which depends on other dictionaries
285− | DependentDictionaryValue (Qualified Ident) [DictionaryValue]
287− -- A subclass dictionary
289− | SubclassDictionaryValue DictionaryValue (Qualified ProperName) Integer
290− deriving (Show, Ord, Eq)
293−-- Check that the current set of type class dictionaries entail the specified type class goal, and, if so,
294−-- return a type class dictionary reference.
296−entails :: Environment -> ModuleName -> [TypeClassDictionaryInScope] -> (Qualified ProperName, [Type]) -> Bool -> Check Value
297−entails env moduleName context = solve (sortedNubBy canonicalizeDictionary (filter filterModule context))
299− sortedNubBy :: (Ord k) => (v -> k) -> [v] -> [v]
300− sortedNubBy f vs = M.elems (M.fromList (map (f &&& id) vs))
302− -- Filter out type dictionaries which are in scope in the current module
303− filterModule :: TypeClassDictionaryInScope -> Bool
304− filterModule (TypeClassDictionaryInScope { tcdName = Qualified (Just mn) _ }) | mn == moduleName = True
305− filterModule (TypeClassDictionaryInScope { tcdName = Qualified Nothing _ }) = True
306− filterModule _ = False
308− solve context' (className, tys) trySuperclasses =
309− case chooseSimplestDictionaries (go trySuperclasses className tys) of
310− [] -> throwError . strMsg $ "No instance found for " ++ show className ++ " " ++ unwords (map prettyPrintTypeAtom tys)
311− [dict] -> return (dictionaryValueToValue dict)
312− _ -> throwError . strMsg $ "Overlapping instances found for " ++ show className ++ " " ++ unwords (map prettyPrintTypeAtom tys)
314− go trySuperclasses' className' tys' =
315− -- Look for regular type instances
316− [ mkDictionary (canonicalizeDictionary tcd) args
318− -- Make sure the type class name matches the one we are trying to satisfy
319− , className' == tcdClassName tcd
320− -- Make sure the type unifies with the type in the type instance definition
321− , subst <- maybeToList . (>>= verifySubstitution) . fmap concat $ zipWithM (typeHeadsAreEqual moduleName env) tys' (tcdInstanceTypes tcd)
322− -- Solve any necessary subgoals
323− , args <- solveSubgoals subst (tcdDependencies tcd) ] ++
325− -- Look for implementations via superclasses
326− [ SubclassDictionaryValue suDict superclass index
328− , (subclassName, (args, _, implies)) <- M.toList (typeClasses env)
329− -- Try each superclass
330− , (index, (superclass, suTyArgs)) <- zip [0..] implies
331− -- Make sure the type class name matches the superclass name
332− , className' == superclass
333− -- Make sure the types unify with the types in the superclass implication
334− , subst <- maybeToList . (>>= verifySubstitution) . fmap concat $ zipWithM (typeHeadsAreEqual moduleName env) tys' suTyArgs
335− -- Finally, satisfy the subclass constraint
336− , args' <- maybeToList $ mapM (applySubst subst . TypeVar) args
337− , suDict <- go True subclassName args' ]
339− -- Create dictionaries for subgoals which still need to be solved by calling go recursively
340− -- E.g. the goal (Show a, Show b) => Show (Either a b) can be satisfied if the current type
341− -- unifies with Either a b, and we can satisfy the subgoals Show a and Show b recursively.
342− solveSubgoals :: [(String, Type)] -> Maybe [(Qualified ProperName, [Type])] -> [Maybe [DictionaryValue]]
343− solveSubgoals _ Nothing = return Nothing
344− solveSubgoals subst (Just subgoals) = do
345− dict <- mapM (uncurry (go True) . second (map (replaceAllTypeVars subst))) subgoals
347− -- Make a dictionary from subgoal dictionaries by applying the correct function
348− mkDictionary :: Qualified Ident -> Maybe [DictionaryValue] -> DictionaryValue
349− mkDictionary fnName Nothing = LocalDictionaryValue fnName
350− mkDictionary fnName (Just []) = GlobalDictionaryValue fnName
351− mkDictionary fnName (Just dicts) = DependentDictionaryValue fnName dicts
352− -- Turn a DictionaryValue into a Value
353− dictionaryValueToValue :: DictionaryValue -> Value
354− dictionaryValueToValue (LocalDictionaryValue fnName) = Var fnName
355− dictionaryValueToValue (GlobalDictionaryValue fnName) = App (Var fnName) (ObjectLiteral [])
356− dictionaryValueToValue (DependentDictionaryValue fnName dicts) = foldl App (Var fnName) (map dictionaryValueToValue dicts)
357− dictionaryValueToValue (SubclassDictionaryValue dict superclassName index) =
358− App (Accessor (show superclassName ++ "_" ++ show index)
359− (Accessor C.__superclasses (dictionaryValueToValue dict)))
361− -- Ensure that a substitution is valid
362− verifySubstitution :: [(String, Type)] -> Maybe [(String, Type)]
363− verifySubstitution subst = do
364− let grps = groupBy ((==) `on` fst) subst
365− guard (all (pairwise (unifiesWith env) . map snd) grps)
366− return $ map head grps
367− -- Apply a substitution to a type
368− applySubst :: [(String, Type)] -> Type -> Maybe Type
369− applySubst subst = everywhereM (mkM replace)
371− replace (TypeVar v) = lookup v subst
372− replace other = Just other
373− -- Choose the simplest DictionaryValues from a list of candidates
374− -- The reason for this function is as follows:
375− -- When considering overlapping instances, we don't want to consider the same dictionary
376− -- to be an overlap of itself when obtained as a superclass of another class.
377− -- Observing that we probably don't want to select a superclass instance when an instance
378− -- is available directly, and that there is no way for a superclass instance to actually
379− -- introduce an overlap that wouldn't have been there already, we simply remove dictionaries
380− -- obtained as superclass instances if there are simpler instances available.
381− chooseSimplestDictionaries :: [DictionaryValue] -> [DictionaryValue]
382− chooseSimplestDictionaries ds = case filter isSimpleDictionaryValue ds of
385− isSimpleDictionaryValue SubclassDictionaryValue{} = False
386− isSimpleDictionaryValue (DependentDictionaryValue _ ds) = all isSimpleDictionaryValue ds
387− isSimpleDictionaryValue _ = True
390−-- Check all values in a list pairwise match a predicate
392−pairwise :: (a -> a -> Bool) -> [a] -> Bool
394−pairwise _ [_] = True
395−pairwise p (x : xs) = all (p x) xs && pairwise p xs
398−-- Check that two types unify
400−unifiesWith :: Environment -> Type -> Type -> Bool
401−unifiesWith _ (TUnknown _) _ = True
402−unifiesWith _ _ (TUnknown _) = True
403−unifiesWith _ (Skolem _ s1 _) (Skolem _ s2 _) | s1 == s2 = True
404−unifiesWith _ (TypeVar v1) (TypeVar v2) | v1 == v2 = True
405−unifiesWith _ (TypeConstructor c1) (TypeConstructor c2) | c1 == c2 = True
406−unifiesWith e (TypeApp h1 t1) (TypeApp h2 t2) = unifiesWith e h1 h2 && unifiesWith e t1 t2
407−unifiesWith e (SaturatedTypeSynonym name args) t2 =
408− case expandTypeSynonym' e name args of
410− Right t1 -> unifiesWith e t1 t2
411−unifiesWith e t1 t2@(SaturatedTypeSynonym _ _) = unifiesWith e t2 t1
412−unifiesWith _ _ _ = False
415−-- Check whether the type heads of two types are equal (for the purposes of type class dictionary lookup),
416−-- and return a substitution from type variables to types which makes the type heads unify.
418−typeHeadsAreEqual :: ModuleName -> Environment -> Type -> Type -> Maybe [(String, Type)]
419−typeHeadsAreEqual _ _ (Skolem _ s1 _) (Skolem _ s2 _) | s1 == s2 = Just []
420−typeHeadsAreEqual _ _ t (TypeVar v) = Just [(v, t)]
421−typeHeadsAreEqual _ _ (TypeConstructor c1) (TypeConstructor c2) | c1 == c2 = Just []
422−typeHeadsAreEqual m e (TypeApp h1 t1) (TypeApp h2 t2) = (++) <$> typeHeadsAreEqual m e h1 h2 <*> typeHeadsAreEqual m e t1 t2
423−typeHeadsAreEqual m e (SaturatedTypeSynonym name args) t2 = case expandTypeSynonym' e name args of
425− Right t1 -> typeHeadsAreEqual m e t1 t2
426−typeHeadsAreEqual _ _ _ _ = Nothing
429−-- Ensure skolem variables do not escape their scope
431−skolemEscapeCheck :: Value -> Check ()
432−skolemEscapeCheck (TypedValue False _ _) = return ()
433−skolemEscapeCheck root@TypedValue{} =
434− -- Every skolem variable is created when a ForAll type is skolemized.
435− -- This determines the scope of that skolem variable, which is copied from the SkolemScope
436− -- field of the ForAll constructor.
437− -- We traverse the tree top-down, and collect any SkolemScopes introduced by ForAlls.
438− -- If a Skolem is encountered whose SkolemScope is not in the current list, we have found
439− -- an escaped skolem variable.
440− case everythingWithContext [] (++) (mkQ ((,) []) go) root of
442− ((binding, val) : _) -> throwError $ mkErrorStack ("Rigid/skolem type variable " ++ maybe "" (("bound by " ++) . prettyPrintValue) binding ++ " has escaped.") (Just (ValueError val))
444− go :: Value -> [(SkolemScope, Value)] -> ([(Maybe Value, Value)], [(SkolemScope, Value)])
445− go val@(TypedValue _ _ (ForAll _ _ (Just sco))) scos = ([], (sco, val) : scos)
446− go val@(TypedValue _ _ ty) scos = case collectSkolems ty \\ map fst scos of
447− (sco : _) -> ([(findBindingScope sco, val)], scos)
450− collectSkolems :: Type -> [SkolemScope]
451− collectSkolems = nub . everything (++) (mkQ [] collect)
453− collect (Skolem _ _ scope) = [scope]
455− go _ scos = ([], scos)
456− findBindingScope :: SkolemScope -> Maybe Value
457− findBindingScope sco = something (mkQ Nothing go') root
459− go' val@(TypedValue _ _ (ForAll _ _ (Just sco'))) | sco == sco' = Just val
461−skolemEscapeCheck val = throwError $ mkErrorStack "Untyped value passed to skolemEscapeCheck" (Just (ValueError val))
464−-- Ensure a row contains no duplicate labels
466−setify :: Type -> Type
467−setify = rowFromList . first (M.toList . M.fromList) . rowToList
470−-- \"Setify\" all rows occuring inside a value
472−setifyAll :: (D.Data d) => d -> d
473−setifyAll = everywhere (mkT setify)
476−-- Replace outermost unsolved unification variables with named type variables
478−varIfUnknown :: Type -> Type
480− let unks = nub $ unknowns ty
481− toName = (:) 't' . show
482− ty' = everywhere (mkT typeToVar) ty
483− typeToVar :: Type -> Type
484− typeToVar (TUnknown (Unknown u)) = TypeVar (toName u)
486− in mkForAll (sort . map (toName . runUnknown) $ unks) ty'
489−-- Remove any ForAlls and ConstrainedType constructors in a type by introducing new unknowns
490−-- or TypeClassDictionary values.
492−-- This is necessary during type checking to avoid unifying a polymorphic type with a
493−-- unification variable.
495−instantiatePolyTypeWithUnknowns :: Value -> Type -> UnifyT Type Check (Value, Type)
496−instantiatePolyTypeWithUnknowns val (ForAll ident ty _) = do
497− ty' <- replaceVarWithUnknown ident ty
498− instantiatePolyTypeWithUnknowns val ty'
499−instantiatePolyTypeWithUnknowns val (ConstrainedType constraints ty) = do
500− dicts <- getTypeClassDictionaries
501− (_, ty') <- instantiatePolyTypeWithUnknowns (error "Types under a constraint cannot themselves be constrained") ty
502− return (foldl App val (map (flip (TypeClassDictionary True) dicts) constraints), ty')
503−instantiatePolyTypeWithUnknowns val ty = return (val, ty)
506−-- Replace a single type variable with a new unification variable
508−replaceVarWithUnknown :: String -> Type -> UnifyT Type Check Type
509−replaceVarWithUnknown ident ty = do
511− return $ replaceTypeVars ident tu ty
514−-- Replace fully applied type synonyms with the @SaturatedTypeSynonym@ data constructor, which helps generate
515−-- better error messages during unification.
517−replaceAllTypeSynonyms' :: (D.Data d) => Environment -> d -> Either String d
518−replaceAllTypeSynonyms' env d =
520− syns = map (\(name, (args, _)) -> (name, length args)) . M.toList $ typeSynonyms env
522− saturateAllTypeSynonyms syns d
524−replaceAllTypeSynonyms :: (Error e, Functor m, Monad m, MonadState CheckState m, MonadError e m) => (D.Data d) => d -> m d
525−replaceAllTypeSynonyms d = do
527− either (throwError . strMsg) return $ replaceAllTypeSynonyms' env d
530−-- \"Desaturate\" @SaturatedTypeSynonym@s
532−desaturateAllTypeSynonyms :: (D.Data d) => d -> d
533−desaturateAllTypeSynonyms = everywhere (mkT replaceSaturatedTypeSynonym)
535− replaceSaturatedTypeSynonym (SaturatedTypeSynonym name args) = foldl TypeApp (TypeConstructor name) args
536− replaceSaturatedTypeSynonym t = t
539−-- Replace a type synonym and its arguments with the aliased type
541−expandTypeSynonym' :: Environment -> Qualified ProperName -> [Type] -> Either String Type
542−expandTypeSynonym' env name args =
543− case M.lookup name (typeSynonyms env) of
544− Just (synArgs, body) -> do
545− let repl = replaceAllTypeVars (zip synArgs args) body
546− replaceAllTypeSynonyms' env repl
547− Nothing -> error "Type synonym was not defined"
549−expandTypeSynonym :: (Error e, Functor m, Monad m, MonadState CheckState m, MonadError e m) => Qualified ProperName -> [Type] -> m Type
550−expandTypeSynonym name args = do
552− either (throwError . strMsg) return $ expandTypeSynonym' env name args
554−expandAllTypeSynonyms :: (Error e, Functor m, Monad m, MonadState CheckState m, MonadError e m) => Type -> m Type
555−expandAllTypeSynonyms = everywhereM' (mkM go)
557− go (SaturatedTypeSynonym name args) = expandTypeSynonym name args
558− go other = return other
561−-- Ensure a set of property names and value does not contain duplicate labels
563−ensureNoDuplicateProperties :: (Error e, MonadError e m) => [(String, Value)] -> m ()
564−ensureNoDuplicateProperties ps = guardWith (strMsg "Duplicate property names") $ length (nub . map fst $ ps) == length ps
567−-- Infer a type for a value, rethrowing any error to provide a more useful error message
569−infer :: Value -> UnifyT Type Check Value
570−infer val = rethrow (mkErrorStack "Error inferring type of value" (Just (ValueError val)) <>) $ infer' val
573−-- Infer a type for a value
575−infer' :: Value -> UnifyT Type Check Value
576−infer' v@(NumericLiteral _) = return $ TypedValue True v tyNumber
577−infer' v@(StringLiteral _) = return $ TypedValue True v tyString
578−infer' v@(BooleanLiteral _) = return $ TypedValue True v tyBoolean
579−infer' (ArrayLiteral vals) = do
580− ts <- mapM infer vals
582− forM_ ts $ \(TypedValue _ _ t) -> els =?= TypeApp tyArray t
583− return $ TypedValue True (ArrayLiteral ts) els
584−infer' (ObjectLiteral ps) = do
585− ensureNoDuplicateProperties ps
586− ts <- mapM (infer . snd) ps
587− let fields = zipWith (\name (TypedValue _ _ t) -> (name, t)) (map fst ps) ts
588− ty = TypeApp tyObject $ rowFromList (fields, REmpty)
589− return $ TypedValue True (ObjectLiteral (zip (map fst ps) ts)) ty
590−infer' (ObjectUpdate o ps) = do
591− ensureNoDuplicateProperties ps
593− newVals <- zipWith (\(name, _) t -> (name, t)) ps <$> mapM (infer . snd) ps
594− let newTys = map (\(name, TypedValue _ _ ty) -> (name, ty)) newVals
595− oldTys <- zip (map fst ps) <$> replicateM (length ps) fresh
596− let oldTy = TypeApp tyObject $ rowFromList (oldTys, row)
597− o' <- TypedValue True <$> check o oldTy <*> pure oldTy
598− return $ TypedValue True (ObjectUpdate o' newVals) $ TypeApp tyObject $ rowFromList (newTys, row)
599−infer' (Accessor prop val) = do
600− typed@(TypedValue _ _ objTy) <- infer val
601− propTy <- inferProperty objTy prop
606− _ <- subsumes Nothing objTy (TypeApp tyObject (RCons prop field rest))
607− return $ TypedValue True (Accessor prop typed) field
608− Just ty -> return $ TypedValue True (Accessor prop typed) ty
609−infer' (Abs (Left arg) ret) = do
611− Just moduleName <- checkCurrentModule <$> get
612− bindLocalVariables moduleName [(arg, ty)] $ do
613− body@(TypedValue _ _ bodyTy) <- infer' ret
614− return $ TypedValue True (Abs (Left arg) body) $ function ty bodyTy
615−infer' (Abs (Right _) _) = error "Binder was not desugared"
616−infer' (App f arg) = do
617− f'@(TypedValue _ _ ft) <- infer f
618− (ret, app) <- checkFunctionApplication f' ft arg Nothing
619− return $ TypedValue True app ret
620−infer' (Var var) = do
621− Just moduleName <- checkCurrentModule <$> get
622− ty <- introduceSkolemScope <=< replaceAllTypeSynonyms <=< lookupVariable moduleName $ var
624− ConstrainedType constraints ty' -> do
625− dicts <- getTypeClassDictionaries
626− return $ TypedValue True (foldl App (Var var) (map (flip (TypeClassDictionary True) dicts) constraints)) ty'
627− _ -> return $ TypedValue True (Var var) ty
628−infer' v@(Constructor c) = do
630− case M.lookup c (dataConstructors env) of
631− Nothing -> throwError . strMsg $ "Constructor " ++ show c ++ " is undefined"
632− Just (_, ty) -> do ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
633− return $ TypedValue True v ty'
634−infer' (Case vals binders) = do
635− ts <- mapM infer vals
637− binders' <- checkBinders (map (\(TypedValue _ _ t) -> t) ts) ret binders
638− return $ TypedValue True (Case ts binders') ret
639−infer' (IfThenElse cond th el) = do
640− cond' <- check cond tyBoolean
641− v2@(TypedValue _ _ t2) <- infer th
642− v3@(TypedValue _ _ t3) <- infer el
644− return $ TypedValue True (IfThenElse cond' v2 v3) t2
645−infer' (Let ds val) = do
646− (ds', val'@(TypedValue _ _ valTy)) <- inferLetBinding [] ds val infer
647− return $ TypedValue True (Let ds' val') valTy
648−infer' (SuperClassDictionary className tys) = do
649− dicts <- getTypeClassDictionaries
650− return $ TypeClassDictionary False (className, tys) dicts
651−infer' (TypedValue checkType val ty) = do
652− Just moduleName <- checkCurrentModule <$> get
653− kind <- liftCheck $ kindOf moduleName ty
654− guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
655− ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
656− val' <- if checkType then check val ty' else return val
657− return $ TypedValue True val' ty'
658−infer' (PositionedValue pos val) = rethrowWithPosition pos $ infer' val
659−infer' _ = error "Invalid argument to infer"
661−inferLetBinding :: [Declaration] -> [Declaration] -> Value -> (Value -> UnifyT Type Check Value) -> UnifyT Type Check ([Declaration], Value)
662−inferLetBinding seen [] ret j = (,) seen <$> j ret
663−inferLetBinding seen (ValueDeclaration ident nameKind [] Nothing val : rest) ret j = do
665− Just moduleName <- checkCurrentModule <$> get
666− let dict = if isFunction val then M.singleton (moduleName, ident) (valTy, nameKind) else M.empty
667− TypedValue _ val' valTy' <- bindNames dict $ infer val
669− bindNames (M.singleton (moduleName, ident) (valTy', nameKind)) $ inferLetBinding (seen ++ [ValueDeclaration ident nameKind [] Nothing val']) rest ret j
670−inferLetBinding seen (BindingGroupDeclaration ds : rest) ret j = do
671− Just moduleName <- checkCurrentModule <$> get
672− (es, dict, untypedDict) <- typeDictionaryForBindingGroup moduleName (map (\(i, _, v) -> (i, v)) ds)
673− ds' <- forM es $ \e -> do
674− (ident, (val', _)) <- typeForBindingGroupElement moduleName e dict untypedDict
675− return $ (ident, LocalVariable, val')
676− bindNames dict $ inferLetBinding (seen ++ [BindingGroupDeclaration ds']) rest ret j
677−inferLetBinding seen (PositionedDeclaration pos d : ds) ret j = do
678− ((d' : ds'), val') <- inferLetBinding seen (d : ds) ret j
679− return (PositionedDeclaration pos d' : ds', val')
680−inferLetBinding _ _ _ _ = error "Invalid argument to inferLetBinding"
683−-- Infer the type of a property inside a record with a given type
685−inferProperty :: Type -> String -> UnifyT Type Check (Maybe Type)
686−inferProperty (TypeApp obj row) prop | obj == tyObject = do
687− let (props, _) = rowToList row
688− return $ lookup prop props
689−inferProperty (SaturatedTypeSynonym name args) prop = do
690− replaced <- introduceSkolemScope <=< expandTypeSynonym name $ args
691− inferProperty replaced prop
692−inferProperty (ForAll ident ty _) prop = do
693− replaced <- replaceVarWithUnknown ident ty
694− inferProperty replaced prop
695−inferProperty _ _ = return Nothing
698−-- Infer the types of variables brought into scope by a binder
700−inferBinder :: Type -> Binder -> UnifyT Type Check (M.Map Ident Type)
701−inferBinder _ NullBinder = return M.empty
702−inferBinder val (StringBinder _) = val =?= tyString >> return M.empty
703−inferBinder val (NumberBinder _) = val =?= tyNumber >> return M.empty
704−inferBinder val (BooleanBinder _) = val =?= tyBoolean >> return M.empty
705−inferBinder val (VarBinder name) = return $ M.singleton name val
706−inferBinder val (ConstructorBinder ctor binders) = do
708− case M.lookup ctor (dataConstructors env) of
710− (_, fn) <- instantiatePolyTypeWithUnknowns (error "Data constructor types cannot contain constraints") ty
711− fn' <- replaceAllTypeSynonyms fn
715− _ <- subsumes Nothing val ty'
717− go (binder : binders') (TypeApp (TypeApp t obj) ret) | t == tyFunction =
718− M.union <$> inferBinder obj binder <*> go binders' ret
719− go _ _ = throwError . strMsg $ "Wrong number of arguments to constructor " ++ show ctor
720− _ -> throwError . strMsg $ "Constructor " ++ show ctor ++ " is not defined"
721−inferBinder val (ObjectBinder props) = do
724− m1 <- inferRowProperties row rest props
725− val =?= TypeApp tyObject row
728− inferRowProperties :: Type -> Type -> [(String, Binder)] -> UnifyT Type Check (M.Map Ident Type)
729− inferRowProperties nrow row [] = nrow =?= row >> return M.empty
730− inferRowProperties nrow row ((name, binder):binders) = do
732− m1 <- inferBinder propTy binder
733− m2 <- inferRowProperties nrow (RCons name propTy row) binders
734− return $ m1 `M.union` m2
735−inferBinder val (ArrayBinder binders) = do
737− m1 <- M.unions <$> mapM (inferBinder el) binders
738− val =?= TypeApp tyArray el
740−inferBinder val (ConsBinder headBinder tailBinder) = do
742− m1 <- inferBinder el headBinder
743− m2 <- inferBinder val tailBinder
744− val =?= TypeApp tyArray el
745− return $ m1 `M.union` m2
746−inferBinder val (NamedBinder name binder) = do
747− m <- inferBinder val binder
748− return $ M.insert name val m
749−inferBinder val (PositionedBinder pos binder) =
750− rethrowWithPosition pos $ inferBinder val binder
753−-- Check the types of the return values in a set of binders in a case statement
755−checkBinders :: [Type] -> Type -> [CaseAlternative] -> UnifyT Type Check [CaseAlternative]
756−checkBinders _ _ [] = return []
757−checkBinders nvals ret (CaseAlternative binders grd val : bs) = do
758− Just moduleName <- checkCurrentModule <$> get
759− m1 <- M.unions <$> zipWithM inferBinder nvals binders
760− r <- bindLocalVariables moduleName (M.toList m1) $ do
761− val' <- TypedValue True <$> check val ret <*> pure ret
763− Nothing -> return $ CaseAlternative binders Nothing val'
765− g' <- check g tyBoolean
766− return $ CaseAlternative binders (Just g') val'
767− rs <- checkBinders nvals ret bs
771−-- Generate a new skolem constant
773−newSkolemConstant :: UnifyT Type Check Int
774−newSkolemConstant = runUnknown <$> fresh'
777−-- Generate a new skolem scope
779−newSkolemScope :: UnifyT Type Check SkolemScope
780−newSkolemScope = SkolemScope . runUnknown <$> fresh'
783−-- Skolemize a type variable by replacing its instances with fresh skolem constants
785−skolemize :: String -> Int -> SkolemScope -> Type -> Type
786−skolemize ident sko scope = replaceTypeVars ident (Skolem ident sko scope)
789−-- This function has one purpose - to skolemize type variables appearing in a
790−-- SuperClassDictionary placeholder. These type variables are somewhat unique since they are the
791−-- only example of scoped type variables.
793−skolemizeTypesInValue :: String -> Int -> SkolemScope -> Value -> Value
794−skolemizeTypesInValue ident sko scope = everywhere (mkT go)
796− go (SuperClassDictionary c ts) = SuperClassDictionary c (map (skolemize ident sko scope) ts)
800−-- Introduce skolem scope at every occurence of a ForAll
802−introduceSkolemScope :: Type -> UnifyT Type Check Type
803−introduceSkolemScope = everywhereM (mkM go)
805− go (ForAll ident ty Nothing) = ForAll ident ty <$> (Just <$> newSkolemScope)
806− go other = return other
809−-- Check the type of a value, rethrowing errors to provide a better error message
811−check :: Value -> Type -> UnifyT Type Check Value
812−check val ty = rethrow (mkErrorStack errorMessage (Just (ValueError val)) <>) $ check' val ty
815− "Error checking type of term " ++
816− prettyPrintValue val ++
821−-- Check the type of a value
823−check' :: Value -> Type -> UnifyT Type Check Value
824−check' val (ForAll ident ty _) = do
825− scope <- newSkolemScope
826− sko <- newSkolemConstant
827− let sk = skolemize ident sko scope ty
828− let skVal = skolemizeTypesInValue ident sko scope val
829− val' <- check skVal sk
830− return $ TypedValue True val' (ForAll ident ty (Just scope))
831−check' val t@(ConstrainedType constraints ty) = do
832− dictNames <- forM constraints $ \(Qualified _ (ProperName className), _) -> do
833− n <- liftCheck freshDictionaryName
834− return $ Ident $ "__dict_" ++ className ++ "_" ++ show n
835− val' <- withTypeClassDictionaries (zipWith (\name (className, instanceTy) ->
836− TypeClassDictionaryInScope name className instanceTy Nothing TCDRegular) (map (Qualified Nothing) dictNames)
837− constraints) $ check val ty
838− return $ TypedValue True (foldr (Abs . Left) val' dictNames) t
839−check' val (SaturatedTypeSynonym name args) = do
840− ty <- introduceSkolemScope <=< expandTypeSynonym name $ args
842−check' val u@(TUnknown _) = do
843− val'@(TypedValue _ _ ty) <- infer val
844− -- Don't unify an unknown with an inferred polytype
845− (val'', ty') <- instantiatePolyTypeWithUnknowns val' ty
847− return $ TypedValue True val'' ty'
848−check' v@(NumericLiteral _) t | t == tyNumber =
849− return $ TypedValue True v t
850−check' v@(StringLiteral _) t | t == tyString =
851− return $ TypedValue True v t
852−check' v@(BooleanLiteral _) t | t == tyBoolean =
853− return $ TypedValue True v t
854−check' (ArrayLiteral vals) t@(TypeApp a ty) = do
856− array <- ArrayLiteral <$> forM vals (`check` ty)
857− return $ TypedValue True array t
858−check' (Abs (Left arg) ret) ty@(TypeApp (TypeApp t argTy) retTy) | t == tyFunction = do
859− Just moduleName <- checkCurrentModule <$> get
860− ret' <- bindLocalVariables moduleName [(arg, argTy)] $ check ret retTy
861− return $ TypedValue True (Abs (Left arg) ret') ty
862−check' (Abs (Right _) _) _ = error "Binder was not desugared"
863−check' (App f arg) ret = do
864− f'@(TypedValue _ _ ft) <- infer f
865− (_, app) <- checkFunctionApplication f' ft arg (Just ret)
866− return $ TypedValue True app ret
867−check' v@(Var var) ty = do
868− Just moduleName <- checkCurrentModule <$> get
869− repl <- introduceSkolemScope <=< replaceAllTypeSynonyms <=< lookupVariable moduleName $ var
870− ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
871− v' <- subsumes (Just v) repl ty'
873− Nothing -> throwError . strMsg $ "Unable to check type subsumption"
874− Just v'' -> return $ TypedValue True v'' ty'
875−check' (SuperClassDictionary className tys) _ = do
877− -- Here, we replace a placeholder for a superclass dictionary with a regular
878− -- TypeClassDictionary placeholder. The reason we do this is that it is necessary to have the
879− -- correct super instance dictionaries in scope, and these are not available when the type class
880− -- declaration gets desugared.
882− -- Note also that the first argument to TypeClassDictionary is False, meaning we _do not_ want
883− -- to consider superclass instances when searching for this dictionary - doing so might lead
884− -- to traversing a cycle in the instance graph.
886− dicts <- getTypeClassDictionaries
887− return $ TypeClassDictionary False (className, tys) dicts
888−check' (TypedValue checkType val ty1) ty2 = do
889− Just moduleName <- checkCurrentModule <$> get
890− kind <- liftCheck $ kindOf moduleName ty1
891− guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
892− ty1' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty1
893− val' <- subsumes (Just val) ty1' ty2
895− Nothing -> throwError . strMsg $ "Unable to check type subsumption"
897− val''' <- if checkType then check val'' ty1' else return val''
898− return $ TypedValue checkType (TypedValue True val''' ty1) ty2
899−check' (Case vals binders) ret = do
900− vals' <- mapM infer vals
901− let ts = map (\(TypedValue _ _ t) -> t) vals'
902− binders' <- checkBinders ts ret binders
903− return $ TypedValue True (Case vals' binders') ret
904−check' (IfThenElse cond th el) ty = do
905− cond' <- check cond tyBoolean
908− return $ TypedValue True (IfThenElse cond' th' el') ty
909−check' (ObjectLiteral ps) t@(TypeApp obj row) | obj == tyObject = do
910− ensureNoDuplicateProperties ps
911− ps' <- checkProperties ps row False
912− return $ TypedValue True (ObjectLiteral ps') t
913−check' (ObjectUpdate obj ps) t@(TypeApp o row) | o == tyObject = do
914− ensureNoDuplicateProperties ps
915− us <- zip (map fst ps) <$> replicateM (length ps) fresh
916− let (propsToCheck, rest) = rowToList row
917− propsToRemove = map fst ps
918− remainingProps = filter (\(p, _) -> p `notElem` propsToRemove) propsToCheck
919− obj' <- check obj (TypeApp tyObject (rowFromList (us ++ remainingProps, rest)))
920− ps' <- checkProperties ps row True
921− return $ TypedValue True (ObjectUpdate obj' ps') t
922−check' (Accessor prop val) ty = do
924− val' <- check val (TypeApp tyObject (RCons prop ty rest))
925− return $ TypedValue True (Accessor prop val') ty
926−check' (Constructor c) ty = do
928− case M.lookup c (dataConstructors env) of
929− Nothing -> throwError . strMsg $ "Constructor " ++ show c ++ " is undefined"
931− repl <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty1
932− _ <- subsumes Nothing repl ty
933− return $ TypedValue True (Constructor c) ty
934−check' (Let ds val) ty = do
935− (ds', val') <- inferLetBinding [] ds val (flip check ty)
936− return $ TypedValue True (Let ds' val') ty
937−check' val ty | containsTypeSynonyms ty = do
938− ty' <- introduceSkolemScope <=< expandAllTypeSynonyms $ ty
940−check' (PositionedValue pos val) ty =
941− rethrowWithPosition pos $ check val ty
942−check' val ty = throwError $ mkErrorStack ("Value does not have type " ++ prettyPrintType ty) (Just (ValueError val))
944−containsTypeSynonyms :: Type -> Bool
945−containsTypeSynonyms = everything (||) (mkQ False go) where
946− go (SaturatedTypeSynonym _ _) = True
950−-- Check the type of a collection of named record fields
952−-- The @lax@ parameter controls whether or not every record member has to be provided. For object updates, this is not the case.
954−checkProperties :: [(String, Value)] -> Type -> Bool -> UnifyT Type Check [(String, Value)]
955−checkProperties ps row lax = let (ts, r') = rowToList row in go ps ts r' where
956− go [] [] REmpty = return []
957− go [] [] u@(TUnknown _) = do u =?= REmpty
959− go [] [] (Skolem _ _ _) | lax = return []
960− go [] ((p, _): _) _ | lax = return []
961− | otherwise = throwError $ mkErrorStack ("Object does not have property " ++ p) (Just (ValueError (ObjectLiteral ps)))
962− go ((p,_):_) [] REmpty = throwError $ mkErrorStack ("Property " ++ p ++ " is not present in closed object type " ++ prettyPrintRow row) (Just (ValueError (ObjectLiteral ps)))
963− go ((p,v):ps') [] u@(TUnknown _) = do
964− v'@(TypedValue _ _ ty) <- infer v
966− u =?= RCons p ty rest
967− ps'' <- go ps' [] rest
968− return $ (p, v') : ps''
969− go ((p,v):ps') ts r =
972− v'@(TypedValue _ _ ty) <- infer v
974− r =?= RCons p ty rest
975− ps'' <- go ps' ts rest
976− return $ (p, v') : ps''
979− ps'' <- go ps' (delete (p, ty) ts) r
980− return $ (p, v') : ps''
981− go _ _ _ = throwError $ mkErrorStack ("Object does not have type " ++ prettyPrintType (TypeApp tyObject row)) (Just (ValueError (ObjectLiteral ps)))
984−-- Check the type of a function application, rethrowing errors to provide a better error message
986−checkFunctionApplication :: Value -> Type -> Value -> Maybe Type -> UnifyT Type Check (Type, Value)
987−checkFunctionApplication fn fnTy arg ret = rethrow (mkErrorStack errorMessage (Just (ValueError fn)) <>) $ checkFunctionApplication' fn fnTy arg ret
989− errorMessage = "Error applying function of type "
990− ++ prettyPrintType fnTy
991− ++ " to argument " ++ prettyPrintValue arg
994−-- Check the type of a function application
996−checkFunctionApplication' :: Value -> Type -> Value -> Maybe Type -> UnifyT Type Check (Type, Value)
997−checkFunctionApplication' fn (TypeApp (TypeApp tyFunction' argTy) retTy) arg ret = do
998− tyFunction' =?= tyFunction
999− _ <- maybe (return Nothing) (subsumes Nothing retTy) ret
1000− subst <- unifyCurrentSubstitution <$> UnifyT get
1001− arg' <- check arg (subst $? argTy)
1002− return (retTy, App fn arg')
1003−checkFunctionApplication' fn (ForAll ident ty _) arg ret = do
1004− replaced <- replaceVarWithUnknown ident ty
1005− checkFunctionApplication fn replaced arg ret
1006−checkFunctionApplication' fn u@(TUnknown _) arg ret = do
1008− TypedValue _ arg' t <- infer arg
1009− (arg'', t') <- instantiatePolyTypeWithUnknowns arg' t
1010− return $ TypedValue True arg'' t'
1011− let ty = (\(TypedValue _ _ t) -> t) arg'
1012− ret' <- maybe fresh return ret
1013− u =?= function ty ret'
1014− return (ret', App fn arg')
1015−checkFunctionApplication' fn (SaturatedTypeSynonym name tyArgs) arg ret = do
1016− ty <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
1017− checkFunctionApplication fn ty arg ret
1018−checkFunctionApplication' fn (ConstrainedType constraints fnTy) arg ret = do
1019− dicts <- getTypeClassDictionaries
1020− checkFunctionApplication' (foldl App fn (map (flip (TypeClassDictionary True) dicts) constraints)) fnTy arg ret
1021−checkFunctionApplication' _ fnTy arg _ = throwError . strMsg $ "Cannot apply a function of type "
1022− ++ prettyPrintType fnTy
1023− ++ " to argument " ++ prettyPrintValue arg
1026−-- Check whether one type subsumes another, rethrowing errors to provide a better error message
1028−subsumes :: Maybe Value -> Type -> Type -> UnifyT Type Check (Maybe Value)
1029−subsumes val ty1 ty2 = rethrow (mkErrorStack errorMessage (ValueError <$> val) <>) $ subsumes' val ty1 ty2
1031− errorMessage = "Error checking that type "
1032− ++ prettyPrintType ty1
1033− ++ " subsumes type "
1034− ++ prettyPrintType ty2
1037−-- Check whether one type subsumes another
1039−subsumes' :: Maybe Value -> Type -> Type -> UnifyT Type Check (Maybe Value)
1040−subsumes' val (ForAll ident ty1 _) ty2 = do
1041− replaced <- replaceVarWithUnknown ident ty1
1042− subsumes val replaced ty2
1043−subsumes' val ty1 (ForAll ident ty2 sco) =
1046− sko <- newSkolemConstant
1047− let sk = skolemize ident sko sco' ty2
1048− subsumes val ty1 sk
1049− Nothing -> throwError . strMsg $ "Skolem variable scope is unspecified"
1050−subsumes' val (TypeApp (TypeApp f1 arg1) ret1) (TypeApp (TypeApp f2 arg2) ret2) | f1 == tyFunction && f2 == tyFunction = do
1051− _ <- subsumes Nothing arg2 arg1
1052− _ <- subsumes Nothing ret1 ret2
1054−subsumes' val (SaturatedTypeSynonym name tyArgs) ty2 = do
1055− ty1 <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
1056− subsumes val ty1 ty2
1057−subsumes' val ty1 (SaturatedTypeSynonym name tyArgs) = do
1058− ty2 <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
1059− subsumes val ty1 ty2
1060−subsumes' (Just val) (ConstrainedType constraints ty1) ty2 = do
1061− dicts <- getTypeClassDictionaries
1062− _ <- subsumes' Nothing ty1 ty2
1063− return . Just $ foldl App val (map (flip (TypeClassDictionary True) dicts) constraints)
1064−subsumes' val (TypeApp f1 r1) (TypeApp f2 r2) | f1 == tyObject && f2 == tyObject = do
1066− (ts1, r1') = rowToList r1
1067− (ts2, r2') = rowToList r2
1068− ts1' = sortBy (comparing fst) ts1
1069− ts2' = sortBy (comparing fst) ts2
1070− go ts1' ts2' r1' r2'
1073− go [] ts2 r1' r2' = r1' =?= rowFromList (ts2, r2')
1074− go ts1 [] r1' r2' = r2' =?= rowFromList (ts1, r1')
1075− go ((p1, ty1) : ts1) ((p2, ty2) : ts2) r1' r2'
1076− | p1 == p2 = do _ <- subsumes Nothing ty1 ty2
1078− | p1 < p2 = do rest <- fresh
1079− r2' =?= RCons p1 ty1 rest
1080− go ts1 ((p2, ty2) : ts2) r1' rest
1081− | otherwise = do rest <- fresh
1082− r1' =?= RCons p2 ty2 rest
1083− go ((p1, ty1) : ts1) ts2 rest r2'
1084−subsumes' val ty1 ty2@(TypeApp obj _) | obj == tyObject = subsumes val ty2 ty1
1085−subsumes' val ty1 ty2 = do