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1−-----------------------------------------------------------------------------
2−--
3−-- Module : Language.PureScript.TypeChecker.Types
4−-- Copyright : (c) Phil Freeman 2013
5−-- License : MIT
6−--
7−-- Maintainer : Phil Freeman <paf31@cantab.net>
8−-- Stability : experimental
9−-- Portability :
10−--
11−-- |
12−-- This module implements the type checker
13−--
14−-----------------------------------------------------------------------------
15−
16−{-# OPTIONS_GHC -fno-warn-orphans #-}
17−{-# LANGUAGE FlexibleInstances #-}
18−{-# LANGUAGE FlexibleContexts #-}
19−{-# LANGUAGE MultiParamTypeClasses #-}
20−
21−module Language.PureScript.TypeChecker.Types (
22− typesOf
23−) where
24−
25−{-
26− The following functions represent the corresponding type checking judgements:
27−
28− infer
29− Synthesize a type for a value
30−
31− check
32− Check a value has a given type
33−
34− checkProperties
35− Check an object with a given type contains specified properties
36−
37− checkFunctionApplication
38− Check a function of a given type returns a value of another type when applied to its arguments
39−
40− subsumes
41− Check a type subsumes another type
42−-}
43−
44−import Data.List
45−import Data.Maybe (maybeToList, isNothing, isJust, fromMaybe)
46−import qualified Data.Data as D
47−import Data.Generics
48− (everythingWithContext, mkM, everywhereM, everything, mkT,
49− something, everywhere, mkQ)
50−import Data.Generics.Extras
51−
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
64−
65−import Control.Monad.State
66−import Control.Monad.Error
67−import Control.Monad.Unify
68−
69−import Control.Applicative
70−import Control.Arrow (Arrow(..))
71−
72−import qualified Data.Map as M
73−import Data.Function (on)
74−import Data.Ord (comparing)
75−import Data.Monoid ((<>))
76−
77−instance Partial Type where
78− unknown = TUnknown
79− isUnknown (TUnknown u) = Just u
80− isUnknown _ = Nothing
81−
82−instance Unifiable Check Type where
83− (=?=) = unifyTypes
84−
85−-- |
86−-- Unify two types, updating the current substitution
87−--
88−unifyTypes :: Type -> Type -> UnifyT Type Check ()
89−unifyTypes t1 t2 = rethrow (mkErrorStack ("Error unifying type " ++ prettyPrintType t1 ++ " with type " ++ prettyPrintType t2) Nothing <>) $
90− unifyTypes' t1 t2
91− where
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
97− ty1 `unifyTypes` ty
98− unifyTypes' ty s@(SaturatedTypeSynonym _ _) = s `unifyTypes` ty
99− unifyTypes' (ForAll ident1 ty1 sc1) (ForAll ident2 ty2 sc2) =
100− case (sc1, sc2) of
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
110− sk `unifyTypes` ty2
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
117− t3 `unifyTypes` t5
118− t4 `unifyTypes` t6
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 ++ "."
127−
128−-- |
129−-- Unify two rows, updating the current substitution
130−--
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
133−-- error.
134−--
135−unifyRows :: Type -> Type -> UnifyT Type Check ()
136−unifyRows r1 r2 =
137− let
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 ]
143− in do
144− forM_ int (uncurry (=?=))
145− unifyRows' sd1 r1' sd2 r2'
146− where
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
151− occursCheck un ty
152− forM_ row $ \(_, t) -> occursCheck un t
153− u' <- fresh
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)) ++ ")"
160−
161−-- |
162−-- Infer the types of multiple mutually-recursive values, and return elaborated values including
163−-- type class dictionaries and type annotations.
164−--
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
169− forM es $ \e -> do
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
175− return triple
176−
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'))
187− where
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
190−
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
193− let
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
201−
202− -- Create fresh unification variables for the types of untyped declarations
203− untypedNames <- replicateM (length untyped) fresh
204−
205− let
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)
211−
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
217− case e of
218− -- Typed declarations
219− (ident, (val', Just (ty, checkType))) -> do
220− -- Kind check
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))
235−
236−-- |
237−-- Check if a value introduces a function
238−--
239−isFunction :: Value -> Bool
240−isFunction (Abs _ _) = True
241−isFunction (TypedValue _ val _) = isFunction val
242−isFunction (PositionedValue _ val) = isFunction val
243−isFunction _ = False
244−
245−-- |
246−-- Check if a value contains a type annotation
247−--
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))
251−
252−-- |
253−-- Map a function over type annotations appearing inside a value
254−--
255−overTypes :: (Type -> Type) -> Value -> Value
256−overTypes f = everywhere (mkT f)
257−
258−-- |
259−-- Replace type class dictionary placeholders with inferred type class dictionaries
260−--
261−replaceTypeClassDictionaries :: ModuleName -> Value -> Check Value
262−replaceTypeClassDictionaries mn = everywhereM' (mkM go)
263− where
264− go (TypeClassDictionary trySuperclasses constraint dicts) = do
265− env <- getEnv
266− let dicts' = fromMaybe (typeClassDictionaries env) dicts
267− entails env mn dicts' constraint trySuperclasses
268− go other = return other
269−
270−-- |
271−-- A simplified representation of expressions which are used to represent type
272−-- class dictionaries at runtime, which can be compared for equality
273−--
274−data DictionaryValue
275− -- |
276− -- A dictionary which is brought into scope by a local constraint
277− --
278− = LocalDictionaryValue (Qualified Ident)
279− -- |
280− -- A dictionary which is brought into scope by an instance declaration
281− --
282− | GlobalDictionaryValue (Qualified Ident)
283− -- |
284− -- A dictionary which depends on other dictionaries
285− --
286− | DependentDictionaryValue (Qualified Ident) [DictionaryValue]
287− -- |
288− -- A subclass dictionary
289− --
290− | SubclassDictionaryValue DictionaryValue Integer
291− deriving (Show, Ord, Eq)
292−
293−-- |
294−-- Check that the current set of type class dictionaries entail the specified type class goal, and, if so,
295−-- return a type class dictionary reference.
296−--
297−entails :: Environment -> ModuleName -> [TypeClassDictionaryInScope] -> (Qualified ProperName, [Type]) -> Bool -> Check Value
298−entails env moduleName context = solve (sortedNubBy canonicalizeDictionary (filter filterModule context))
299− where
300− sortedNubBy :: (Ord k) => (v -> k) -> [v] -> [v]
301− sortedNubBy f vs = M.elems (M.fromList (map (f &&& id) vs))
302−
303− -- Filter out type dictionaries which are in scope in the current module
304− filterModule :: TypeClassDictionaryInScope -> Bool
305− filterModule (TypeClassDictionaryInScope { tcdName = Qualified (Just mn) _ }) | mn == moduleName = True
306− filterModule (TypeClassDictionaryInScope { tcdName = Qualified Nothing _ }) = True
307− filterModule _ = False
308−
309− solve context' (className, tys) trySuperclasses =
310− case chooseSimplestDictionaries (go className tys) of
311− [] -> throwError . strMsg $ "No instance found for " ++ show className ++ " " ++ unwords (map prettyPrintTypeAtom tys)
312− [dict] -> return (dictionaryValueToValue dict)
313− _ -> throwError . strMsg $ "Overlapping instances found for " ++ show className ++ " " ++ unwords (map prettyPrintTypeAtom tys)
314− where
315− go className' tys' =
316− -- Look for regular type instances
317− [ mkDictionary (canonicalizeDictionary tcd) args
318− | tcd <- context'
319− -- Make sure the type class name matches the one we are trying to satisfy
320− , className' == tcdClassName tcd
321− -- Make sure the type unifies with the type in the type instance definition
322− , subst <- maybeToList . (>>= verifySubstitution) . fmap concat $ zipWithM (typeHeadsAreEqual moduleName env) tys' (tcdInstanceTypes tcd)
323− -- Solve any necessary subgoals
324− , args <- solveSubgoals subst (tcdDependencies tcd) ] ++
325−
326− -- Look for implementations via superclasses
327− [ SubclassDictionaryValue suDict index
328− | trySuperclasses
329− , (subclassName, (args, _, implies)) <- M.toList (typeClasses env)
330− -- Try each superclass
331− , (index, (superclass, suTyArgs)) <- zip [0..] implies
332− -- Make sure the type class name matches the superclass name
333− , className' == superclass
334− -- Make sure the types unify with the types in the superclass implication
335− , subst <- maybeToList . (>>= verifySubstitution) . fmap concat $ zipWithM (typeHeadsAreEqual moduleName env) tys' suTyArgs
336− -- Finally, satisfy the subclass constraint
337− , suDict <- go subclassName (map (applySubst subst . TypeVar) args) ]
338−
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 . second (map (replaceAllTypeVars subst))) subgoals
346− return $ Just dict
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 index) =
358− App (App (Var (Qualified (Just (ModuleName [ProperName C.prelude])) (Ident (C.!!))))
359− (Accessor C.__superclasses (dictionaryValueToValue dict)))
360− (NumericLiteral (Left index))
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 -> Type
369− applySubst subst = everywhere (mkT replace)
370− where
371− replace t@(TypeVar v) = fromMaybe t $ lookup v subst
372− replace other = 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
383− [] -> ds
384− simple -> simple
385− isSimpleDictionaryValue SubclassDictionaryValue{} = False
386− isSimpleDictionaryValue _ = True
387−
388−-- |
389−-- Check all values in a list pairwise match a predicate
390−--
391−pairwise :: (a -> a -> Bool) -> [a] -> Bool
392−pairwise _ [] = True
393−pairwise _ [_] = True
394−pairwise p (x : xs) = all (p x) xs && pairwise p xs
395−
396−-- |
397−-- Check that two types unify
398−--
399−unifiesWith :: Environment -> Type -> Type -> Bool
400−unifiesWith _ (TUnknown _) _ = True
401−unifiesWith _ _ (TUnknown _) = True
402−unifiesWith _ (Skolem s1 _) (Skolem s2 _) | s1 == s2 = True
403−unifiesWith _ (TypeVar v1) (TypeVar v2) | v1 == v2 = True
404−unifiesWith _ (TypeConstructor c1) (TypeConstructor c2) | c1 == c2 = True
405−unifiesWith e (TypeApp h1 t1) (TypeApp h2 t2) = unifiesWith e h1 h2 && unifiesWith e t1 t2
406−unifiesWith e (SaturatedTypeSynonym name args) t2 =
407− case expandTypeSynonym' e name args of
408− Left _ -> False
409− Right t1 -> unifiesWith e t1 t2
410−unifiesWith e t1 t2@(SaturatedTypeSynonym _ _) = unifiesWith e t2 t1
411−unifiesWith _ _ _ = False
412−
413−-- |
414−-- Check whether the type heads of two types are equal (for the purposes of type class dictionary lookup),
415−-- and return a substitution from type variables to types which makes the type heads unify.
416−--
417−typeHeadsAreEqual :: ModuleName -> Environment -> Type -> Type -> Maybe [(String, Type)]
418−typeHeadsAreEqual _ _ (Skolem s1 _) (Skolem s2 _) | s1 == s2 = Just []
419−typeHeadsAreEqual _ _ t (TypeVar v) = Just [(v, t)]
420−typeHeadsAreEqual _ _ (TypeConstructor c1) (TypeConstructor c2) | c1 == c2 = Just []
421−typeHeadsAreEqual m e (TypeApp h1 t1) (TypeApp h2 t2) = (++) <$> typeHeadsAreEqual m e h1 h2 <*> typeHeadsAreEqual m e t1 t2
422−typeHeadsAreEqual m e (SaturatedTypeSynonym name args) t2 = case expandTypeSynonym' e name args of
423− Left _ -> Nothing
424− Right t1 -> typeHeadsAreEqual m e t1 t2
425−typeHeadsAreEqual _ _ _ _ = Nothing
426−
427−-- |
428−-- Ensure skolem variables do not escape their scope
429−--
430−skolemEscapeCheck :: Value -> Check ()
431−skolemEscapeCheck (TypedValue False _ _) = return ()
432−skolemEscapeCheck root@TypedValue{} =
433− -- Every skolem variable is created when a ForAll type is skolemized.
434− -- This determines the scope of that skolem variable, which is copied from the SkolemScope
435− -- field of the ForAll constructor.
436− -- We traverse the tree top-down, and collect any SkolemScopes introduced by ForAlls.
437− -- If a Skolem is encountered whose SkolemScope is not in the current list, we have found
438− -- an escaped skolem variable.
439− case everythingWithContext [] (++) (mkQ ((,) []) go) root of
440− [] -> return ()
441− ((binding, val) : _) -> throwError $ mkErrorStack ("Rigid/skolem type variable " ++ maybe "" (("bound by " ++) . prettyPrintValue) binding ++ " has escaped.") (Just (ValueError val))
442− where
443− go :: Value -> [(SkolemScope, Value)] -> ([(Maybe Value, Value)], [(SkolemScope, Value)])
444− go val@(TypedValue _ _ (ForAll _ _ (Just sco))) scos = ([], (sco, val) : scos)
445− go val@(TypedValue _ _ ty) scos = case collectSkolems ty \\ map fst scos of
446− (sco : _) -> ([(findBindingScope sco, val)], scos)
447− _ -> ([], scos)
448− where
449− collectSkolems :: Type -> [SkolemScope]
450− collectSkolems = nub . everything (++) (mkQ [] collect)
451− where
452− collect (Skolem _ scope) = [scope]
453− collect _ = []
454− go _ scos = ([], scos)
455− findBindingScope :: SkolemScope -> Maybe Value
456− findBindingScope sco = something (mkQ Nothing go') root
457− where
458− go' val@(TypedValue _ _ (ForAll _ _ (Just sco'))) | sco == sco' = Just val
459− go' _ = Nothing
460−skolemEscapeCheck val = throwError $ mkErrorStack "Untyped value passed to skolemEscapeCheck" (Just (ValueError val))
461−
462−-- |
463−-- Ensure a row contains no duplicate labels
464−--
465−setify :: Type -> Type
466−setify = rowFromList . first (M.toList . M.fromList) . rowToList
467−
468−-- |
469−-- \"Setify\" all rows occuring inside a value
470−--
471−setifyAll :: (D.Data d) => d -> d
472−setifyAll = everywhere (mkT setify)
473−
474−-- |
475−-- Replace outermost unsolved unification variables with named type variables
476−--
477−varIfUnknown :: Type -> Type
478−varIfUnknown ty =
479− let unks = nub $ unknowns ty
480− toName = (:) 't' . show
481− ty' = everywhere (mkT typeToVar) ty
482− typeToVar :: Type -> Type
483− typeToVar (TUnknown (Unknown u)) = TypeVar (toName u)
484− typeToVar t = t
485− in mkForAll (sort . map (toName . runUnknown) $ unks) ty'
486−
487−-- |
488−-- Remove any ForAlls and ConstrainedType constructors in a type by introducing new unknowns
489−-- or TypeClassDictionary values.
490−--
491−-- This is necessary during type checking to avoid unifying a polymorphic type with a
492−-- unification variable.
493−--
494−instantiatePolyTypeWithUnknowns :: Value -> Type -> UnifyT Type Check (Value, Type)
495−instantiatePolyTypeWithUnknowns val (ForAll ident ty _) = do
496− ty' <- replaceVarWithUnknown ident ty
497− instantiatePolyTypeWithUnknowns val ty'
498−instantiatePolyTypeWithUnknowns val (ConstrainedType constraints ty) = do
499− dicts <- getTypeClassDictionaries
500− (_, ty') <- instantiatePolyTypeWithUnknowns (error "Types under a constraint cannot themselves be constrained") ty
501− return (foldl App val (map (flip (TypeClassDictionary True) (Just dicts)) constraints), ty')
502−instantiatePolyTypeWithUnknowns val ty = return (val, ty)
503−
504−-- |
505−-- Replace a single type variable with a new unification variable
506−--
507−replaceVarWithUnknown :: String -> Type -> UnifyT Type Check Type
508−replaceVarWithUnknown ident ty = do
509− tu <- fresh
510− return $ replaceTypeVars ident tu ty
511−
512−-- |
513−-- Replace fully applied type synonyms with the @SaturatedTypeSynonym@ data constructor, which helps generate
514−-- better error messages during unification.
515−--
516−replaceAllTypeSynonyms' :: (D.Data d) => Environment -> d -> Either String d
517−replaceAllTypeSynonyms' env d =
518− let
519− syns = map (\(name, (args, _)) -> (name, length args)) . M.toList $ typeSynonyms env
520− in
521− saturateAllTypeSynonyms syns d
522−
523−replaceAllTypeSynonyms :: (Error e, Functor m, Monad m, MonadState CheckState m, MonadError e m) => (D.Data d) => d -> m d
524−replaceAllTypeSynonyms d = do
525− env <- getEnv
526− either (throwError . strMsg) return $ replaceAllTypeSynonyms' env d
527−
528−-- |
529−-- \"Desaturate\" @SaturatedTypeSynonym@s
530−--
531−desaturateAllTypeSynonyms :: (D.Data d) => d -> d
532−desaturateAllTypeSynonyms = everywhere (mkT replaceSaturatedTypeSynonym)
533− where
534− replaceSaturatedTypeSynonym (SaturatedTypeSynonym name args) = foldl TypeApp (TypeConstructor name) args
535− replaceSaturatedTypeSynonym t = t
536−
537−-- |
538−-- Replace a type synonym and its arguments with the aliased type
539−--
540−expandTypeSynonym' :: Environment -> Qualified ProperName -> [Type] -> Either String Type
541−expandTypeSynonym' env name args =
542− case M.lookup name (typeSynonyms env) of
543− Just (synArgs, body) -> do
544− let repl = replaceAllTypeVars (zip synArgs args) body
545− replaceAllTypeSynonyms' env repl
546− Nothing -> error "Type synonym was not defined"
547−
548−expandTypeSynonym :: (Error e, Functor m, Monad m, MonadState CheckState m, MonadError e m) => Qualified ProperName -> [Type] -> m Type
549−expandTypeSynonym name args = do
550− env <- getEnv
551− either (throwError . strMsg) return $ expandTypeSynonym' env name args
552−
553−expandAllTypeSynonyms :: (Error e, Functor m, Monad m, MonadState CheckState m, MonadError e m) => Type -> m Type
554−expandAllTypeSynonyms = everywhereM' (mkM go)
555− where
556− go (SaturatedTypeSynonym name args) = expandTypeSynonym name args
557− go other = return other
558−
559−-- |
560−-- Ensure a set of property names and value does not contain duplicate labels
561−--
562−ensureNoDuplicateProperties :: (Error e, MonadError e m) => [(String, Value)] -> m ()
563−ensureNoDuplicateProperties ps = guardWith (strMsg "Duplicate property names") $ length (nub . map fst $ ps) == length ps
564−
565−-- |
566−-- Infer a type for a value, rethrowing any error to provide a more useful error message
567−--
568−infer :: Value -> UnifyT Type Check Value
569−infer val = rethrow (mkErrorStack "Error inferring type of value" (Just (ValueError val)) <>) $ infer' val
570−
571−-- |
572−-- Infer a type for a value
573−--
574−infer' :: Value -> UnifyT Type Check Value
575−infer' v@(NumericLiteral _) = return $ TypedValue True v tyNumber
576−infer' v@(StringLiteral _) = return $ TypedValue True v tyString
577−infer' v@(BooleanLiteral _) = return $ TypedValue True v tyBoolean
578−infer' (ArrayLiteral vals) = do
579− ts <- mapM infer vals
580− els <- fresh
581− forM_ ts $ \(TypedValue _ _ t) -> els =?= TypeApp tyArray t
582− return $ TypedValue True (ArrayLiteral ts) els
583−infer' (ObjectLiteral ps) = do
584− ensureNoDuplicateProperties ps
585− ts <- mapM (infer . snd) ps
586− let fields = zipWith (\name (TypedValue _ _ t) -> (name, t)) (map fst ps) ts
587− ty = TypeApp tyObject $ rowFromList (fields, REmpty)
588− return $ TypedValue True (ObjectLiteral (zip (map fst ps) ts)) ty
589−infer' (ObjectUpdate o ps) = do
590− ensureNoDuplicateProperties ps
591− row <- fresh
592− newVals <- zipWith (\(name, _) t -> (name, t)) ps <$> mapM (infer . snd) ps
593− let newTys = map (\(name, TypedValue _ _ ty) -> (name, ty)) newVals
594− oldTys <- zip (map fst ps) <$> replicateM (length ps) fresh
595− let oldTy = TypeApp tyObject $ rowFromList (oldTys, row)
596− o' <- TypedValue True <$> check o oldTy <*> pure oldTy
597− return $ TypedValue True (ObjectUpdate o' newVals) $ TypeApp tyObject $ rowFromList (newTys, row)
598−infer' (Accessor prop val) = do
599− typed@(TypedValue _ _ objTy) <- infer val
600− propTy <- inferProperty objTy prop
601− case propTy of
602− Nothing -> do
603− field <- fresh
604− rest <- fresh
605− _ <- subsumes Nothing objTy (TypeApp tyObject (RCons prop field rest))
606− return $ TypedValue True (Accessor prop typed) field
607− Just ty -> return $ TypedValue True (Accessor prop typed) ty
608−infer' (Abs (Left arg) ret) = do
609− ty <- fresh
610− Just moduleName <- checkCurrentModule <$> get
611− bindLocalVariables moduleName [(arg, ty)] $ do
612− body@(TypedValue _ _ bodyTy) <- infer' ret
613− return $ TypedValue True (Abs (Left arg) body) $ function ty bodyTy
614−infer' (Abs (Right _) _) = error "Binder was not desugared"
615−infer' (App f arg) = do
616− f'@(TypedValue _ _ ft) <- infer f
617− (ret, app) <- checkFunctionApplication f' ft arg Nothing
618− return $ TypedValue True app ret
619−infer' (Var var) = do
620− Just moduleName <- checkCurrentModule <$> get
621− ty <- introduceSkolemScope <=< replaceAllTypeSynonyms <=< lookupVariable moduleName $ var
622− case ty of
623− ConstrainedType constraints ty' -> do
624− dicts <- getTypeClassDictionaries
625− return $ TypedValue True (foldl App (Var var) (map (flip (TypeClassDictionary True) (Just dicts)) constraints)) ty'
626− _ -> return $ TypedValue True (Var var) ty
627−infer' v@(Constructor c) = do
628− env <- getEnv
629− case M.lookup c (dataConstructors env) of
630− Nothing -> throwError . strMsg $ "Constructor " ++ show c ++ " is undefined"
631− Just (_, ty) -> do ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
632− return $ TypedValue True v ty'
633−infer' (Case vals binders) = do
634− ts <- mapM infer vals
635− ret <- fresh
636− binders' <- checkBinders (map (\(TypedValue _ _ t) -> t) ts) ret binders
637− return $ TypedValue True (Case ts binders') ret
638−infer' (IfThenElse cond th el) = do
639− cond' <- check cond tyBoolean
640− v2@(TypedValue _ _ t2) <- infer th
641− v3@(TypedValue _ _ t3) <- infer el
642− t2 =?= t3
643− return $ TypedValue True (IfThenElse cond' v2 v3) t2
644−infer' (Let ds val) = do
645− (ds', val'@(TypedValue _ _ valTy)) <- inferLetBinding [] ds val infer
646− return $ TypedValue True (Let ds' val') valTy
647−infer' (TypedValue checkType val ty) = do
648− Just moduleName <- checkCurrentModule <$> get
649− kind <- liftCheck $ kindOf moduleName ty
650− guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
651− ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
652− val' <- if checkType then check val ty' else return val
653− return $ TypedValue True val' ty'
654−infer' (PositionedValue pos val) = rethrowWithPosition pos $ infer' val
655−infer' _ = error "Invalid argument to infer"
656−
657−inferLetBinding :: [Declaration] -> [Declaration] -> Value -> (Value -> UnifyT Type Check Value) -> UnifyT Type Check ([Declaration], Value)
658−inferLetBinding seen [] ret j = (,) seen <$> j ret
659−inferLetBinding seen (ValueDeclaration ident nameKind [] Nothing val : rest) ret j = do
660− valTy <- fresh
661− Just moduleName <- checkCurrentModule <$> get
662− let dict = if isFunction val then M.singleton (moduleName, ident) (valTy, nameKind) else M.empty
663− TypedValue _ val' valTy' <- bindNames dict $ infer val
664− valTy =?= valTy'
665− bindNames (M.singleton (moduleName, ident) (valTy', nameKind)) $ inferLetBinding (seen ++ [ValueDeclaration ident nameKind [] Nothing val']) rest ret j
666−inferLetBinding seen (BindingGroupDeclaration ds : rest) ret j = do
667− Just moduleName <- checkCurrentModule <$> get
668− (es, dict, untypedDict) <- typeDictionaryForBindingGroup moduleName (map (\(i, _, v) -> (i, v)) ds)
669− ds' <- forM es $ \e -> do
670− (ident, (val', _)) <- typeForBindingGroupElement moduleName e dict untypedDict
671− return $ (ident, LocalVariable, val')
672− bindNames dict $ inferLetBinding (seen ++ [BindingGroupDeclaration ds']) rest ret j
673−inferLetBinding seen (PositionedDeclaration pos d : ds) ret j = do
674− ((d' : ds'), val') <- inferLetBinding seen (d : ds) ret j
675− return (PositionedDeclaration pos d' : ds', val')
676−inferLetBinding _ _ _ _ = error "Invalid argument to inferLetBinding"
677−
678−-- |
679−-- Infer the type of a property inside a record with a given type
680−--
681−inferProperty :: Type -> String -> UnifyT Type Check (Maybe Type)
682−inferProperty (TypeApp obj row) prop | obj == tyObject = do
683− let (props, _) = rowToList row
684− return $ lookup prop props
685−inferProperty (SaturatedTypeSynonym name args) prop = do
686− replaced <- introduceSkolemScope <=< expandTypeSynonym name $ args
687− inferProperty replaced prop
688−inferProperty (ForAll ident ty _) prop = do
689− replaced <- replaceVarWithUnknown ident ty
690− inferProperty replaced prop
691−inferProperty _ _ = return Nothing
692−
693−-- |
694−-- Infer the types of variables brought into scope by a binder
695−--
696−inferBinder :: Type -> Binder -> UnifyT Type Check (M.Map Ident Type)
697−inferBinder _ NullBinder = return M.empty
698−inferBinder val (StringBinder _) = val =?= tyString >> return M.empty
699−inferBinder val (NumberBinder _) = val =?= tyNumber >> return M.empty
700−inferBinder val (BooleanBinder _) = val =?= tyBoolean >> return M.empty
701−inferBinder val (VarBinder name) = return $ M.singleton name val
702−inferBinder val (ConstructorBinder ctor binders) = do
703− env <- getEnv
704− case M.lookup ctor (dataConstructors env) of
705− Just (_, ty) -> do
706− (_, fn) <- instantiatePolyTypeWithUnknowns (error "Data constructor types cannot contain constraints") ty
707− fn' <- replaceAllTypeSynonyms fn
708− go binders fn'
709− where
710− go [] ty' = do
711− _ <- subsumes Nothing val ty'
712− return M.empty
713− go (binder : binders') (TypeApp (TypeApp t obj) ret) | t == tyFunction =
714− M.union <$> inferBinder obj binder <*> go binders' ret
715− go _ _ = throwError . strMsg $ "Wrong number of arguments to constructor " ++ show ctor
716− _ -> throwError . strMsg $ "Constructor " ++ show ctor ++ " is not defined"
717−inferBinder val (ObjectBinder props) = do
718− row <- fresh
719− rest <- fresh
720− m1 <- inferRowProperties row rest props
721− val =?= TypeApp tyObject row
722− return m1
723− where
724− inferRowProperties :: Type -> Type -> [(String, Binder)] -> UnifyT Type Check (M.Map Ident Type)
725− inferRowProperties nrow row [] = nrow =?= row >> return M.empty
726− inferRowProperties nrow row ((name, binder):binders) = do
727− propTy <- fresh
728− m1 <- inferBinder propTy binder
729− m2 <- inferRowProperties nrow (RCons name propTy row) binders
730− return $ m1 `M.union` m2
731−inferBinder val (ArrayBinder binders) = do
732− el <- fresh
733− m1 <- M.unions <$> mapM (inferBinder el) binders
734− val =?= TypeApp tyArray el
735− return m1
736−inferBinder val (ConsBinder headBinder tailBinder) = do
737− el <- fresh
738− m1 <- inferBinder el headBinder
739− m2 <- inferBinder val tailBinder
740− val =?= TypeApp tyArray el
741− return $ m1 `M.union` m2
742−inferBinder val (NamedBinder name binder) = do
743− m <- inferBinder val binder
744− return $ M.insert name val m
745−inferBinder val (PositionedBinder pos binder) =
746− rethrowWithPosition pos $ inferBinder val binder
747−
748−-- |
749−-- Check the types of the return values in a set of binders in a case statement
750−--
751−checkBinders :: [Type] -> Type -> [CaseAlternative] -> UnifyT Type Check [CaseAlternative]
752−checkBinders _ _ [] = return []
753−checkBinders nvals ret (CaseAlternative binders grd val : bs) = do
754− Just moduleName <- checkCurrentModule <$> get
755− m1 <- M.unions <$> zipWithM inferBinder nvals binders
756− r <- bindLocalVariables moduleName (M.toList m1) $ do
757− val' <- TypedValue True <$> check val ret <*> pure ret
758− case grd of
759− Nothing -> return $ CaseAlternative binders Nothing val'
760− Just g -> do
761− g' <- check g tyBoolean
762− return $ CaseAlternative binders (Just g') val'
763− rs <- checkBinders nvals ret bs
764− return $ r : rs
765−
766−-- |
767−-- Generate a new skolem constant
768−--
769−newSkolemConstant :: UnifyT Type Check Int
770−newSkolemConstant = runUnknown <$> fresh'
771−
772−-- |
773−-- Generate a new skolem scope
774−--
775−newSkolemScope :: UnifyT Type Check SkolemScope
776−newSkolemScope = SkolemScope . runUnknown <$> fresh'
777−
778−-- |
779−-- Skolemize a type variable by replacing its instances with fresh skolem constants
780−--
781−skolemize :: String -> Int -> SkolemScope -> Type -> Type
782−skolemize ident sko scope = replaceTypeVars ident (Skolem sko scope)
783−
784−-- |
785−-- Introduce skolem scope at every occurence of a ForAll
786−--
787−introduceSkolemScope :: Type -> UnifyT Type Check Type
788−introduceSkolemScope = everywhereM (mkM go)
789− where
790− go (ForAll ident ty Nothing) = ForAll ident ty <$> (Just <$> newSkolemScope)
791− go other = return other
792−
793−-- |
794−-- Check the type of a value, rethrowing errors to provide a better error message
795−--
796−check :: Value -> Type -> UnifyT Type Check Value
797−check val ty = rethrow (mkErrorStack errorMessage (Just (ValueError val)) <>) $ check' val ty
798− where
799− errorMessage =
800− "Error checking type of term " ++
801− prettyPrintValue val ++
802− " against type " ++
803− prettyPrintType ty
804−
805−-- |
806−-- Check the type of a value
807−--
808−check' :: Value -> Type -> UnifyT Type Check Value
809−check' val (ForAll ident ty _) = do
810− scope <- newSkolemScope
811− sko <- newSkolemConstant
812− let sk = skolemize ident sko scope ty
813− val' <- check val sk
814− return $ TypedValue True val' (ForAll ident ty (Just scope))
815−check' val t@(ConstrainedType constraints ty) = do
816− dictNames <- forM constraints $ \(Qualified _ (ProperName className), _) -> do
817− n <- liftCheck freshDictionaryName
818− return $ Ident $ "__dict_" ++ className ++ "_" ++ show n
819− val' <- withTypeClassDictionaries (zipWith (\name (className, instanceTy) ->
820− TypeClassDictionaryInScope name className instanceTy Nothing TCDRegular) (map (Qualified Nothing) dictNames)
821− constraints) $ check val ty
822− return $ TypedValue True (foldr (Abs . Left) val' dictNames) t
823−check' val (SaturatedTypeSynonym name args) = do
824− ty <- introduceSkolemScope <=< expandTypeSynonym name $ args
825− check val ty
826−check' val u@(TUnknown _) = do
827− val'@(TypedValue _ _ ty) <- infer val
828− -- Don't unify an unknown with an inferred polytype
829− (val'', ty') <- instantiatePolyTypeWithUnknowns val' ty
830− ty' =?= u
831− return $ TypedValue True val'' ty'
832−check' v@(NumericLiteral _) t | t == tyNumber =
833− return $ TypedValue True v t
834−check' v@(StringLiteral _) t | t == tyString =
835− return $ TypedValue True v t
836−check' v@(BooleanLiteral _) t | t == tyBoolean =
837− return $ TypedValue True v t
838−check' (ArrayLiteral vals) t@(TypeApp a ty) = do
839− a =?= tyArray
840− array <- ArrayLiteral <$> forM vals (`check` ty)
841− return $ TypedValue True array t
842−check' (Abs (Left arg) ret) ty@(TypeApp (TypeApp t argTy) retTy) | t == tyFunction = do
843− Just moduleName <- checkCurrentModule <$> get
844− ret' <- bindLocalVariables moduleName [(arg, argTy)] $ check ret retTy
845− return $ TypedValue True (Abs (Left arg) ret') ty
846−check' (Abs (Right _) _) _ = error "Binder was not desugared"
847−check' (App f arg) ret = do
848− f'@(TypedValue _ _ ft) <- infer f
849− (_, app) <- checkFunctionApplication f' ft arg (Just ret)
850− return $ TypedValue True app ret
851−check' v@(Var var) ty = do
852− Just moduleName <- checkCurrentModule <$> get
853− repl <- introduceSkolemScope <=< replaceAllTypeSynonyms <=< lookupVariable moduleName $ var
854− ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
855− v' <- subsumes (Just v) repl ty'
856− case v' of
857− Nothing -> throwError . strMsg $ "Unable to check type subsumption"
858− Just v'' -> return $ TypedValue True v'' ty'
859−check' (TypedValue checkType val ty1) ty2 = do
860− Just moduleName <- checkCurrentModule <$> get
861− kind <- liftCheck $ kindOf moduleName ty1
862− guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
863− ty1' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty1
864− val' <- subsumes (Just val) ty1' ty2
865− case val' of
866− Nothing -> throwError . strMsg $ "Unable to check type subsumption"
867− Just val'' -> do
868− val''' <- if checkType then check val'' ty1' else return val''
869− return $ TypedValue checkType (TypedValue True val''' ty1) ty2
870−check' (Case vals binders) ret = do
871− vals' <- mapM infer vals
872− let ts = map (\(TypedValue _ _ t) -> t) vals'
873− binders' <- checkBinders ts ret binders
874− return $ TypedValue True (Case vals' binders') ret
875−check' (IfThenElse cond th el) ty = do
876− cond' <- check cond tyBoolean
877− th' <- check th ty
878− el' <- check el ty
879− return $ TypedValue True (IfThenElse cond' th' el') ty
880−check' (ObjectLiteral ps) t@(TypeApp obj row) | obj == tyObject = do
881− ensureNoDuplicateProperties ps
882− ps' <- checkProperties ps row False
883− return $ TypedValue True (ObjectLiteral ps') t
884−check' (ObjectUpdate obj ps) t@(TypeApp o row) | o == tyObject = do
885− ensureNoDuplicateProperties ps
886− us <- zip (map fst ps) <$> replicateM (length ps) fresh
887− let (propsToCheck, rest) = rowToList row
888− propsToRemove = map fst ps
889− remainingProps = filter (\(p, _) -> p `notElem` propsToRemove) propsToCheck
890− obj' <- check obj (TypeApp tyObject (rowFromList (us ++ remainingProps, rest)))
891− ps' <- checkProperties ps row True
892− return $ TypedValue True (ObjectUpdate obj' ps') t
893−check' (Accessor prop val) ty = do
894− rest <- fresh
895− val' <- check val (TypeApp tyObject (RCons prop ty rest))
896− return $ TypedValue True (Accessor prop val') ty
897−check' (Constructor c) ty = do
898− env <- getEnv
899− case M.lookup c (dataConstructors env) of
900− Nothing -> throwError . strMsg $ "Constructor " ++ show c ++ " is undefined"
901− Just (_, ty1) -> do
902− repl <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty1
903− _ <- subsumes Nothing repl ty
904− return $ TypedValue True (Constructor c) ty
905−check' (Let ds val) ty = do
906− (ds', val') <- inferLetBinding [] ds val (flip check ty)
907− return $ TypedValue True (Let ds' val') ty
908−check' val ty | containsTypeSynonyms ty = do
909− ty' <- introduceSkolemScope <=< expandAllTypeSynonyms $ ty
910− check val ty'
911−check' (PositionedValue pos val) ty =
912− rethrowWithPosition pos $ check val ty
913−check' val ty = throwError $ mkErrorStack ("Value does not have type " ++ prettyPrintType ty) (Just (ValueError val))
914−
915−containsTypeSynonyms :: Type -> Bool
916−containsTypeSynonyms = everything (||) (mkQ False go) where
917− go (SaturatedTypeSynonym _ _) = True
918− go _ = False
919−
920−-- |
921−-- Check the type of a collection of named record fields
922−--
923−-- The @lax@ parameter controls whether or not every record member has to be provided. For object updates, this is not the case.
924−--
925−checkProperties :: [(String, Value)] -> Type -> Bool -> UnifyT Type Check [(String, Value)]
926−checkProperties ps row lax = let (ts, r') = rowToList row in go ps ts r' where
927− go [] [] REmpty = return []
928− go [] [] u@(TUnknown _) = do u =?= REmpty
929− return []
930− go [] [] (Skolem _ _) | lax = return []
931− go [] ((p, _): _) _ | lax = return []
932− | otherwise = throwError $ mkErrorStack ("Object does not have property " ++ p) (Just (ValueError (ObjectLiteral ps)))
933− go ((p,_):_) [] REmpty = throwError $ mkErrorStack ("Property " ++ p ++ " is not present in closed object type " ++ prettyPrintRow row) (Just (ValueError (ObjectLiteral ps)))
934− go ((p,v):ps') [] u@(TUnknown _) = do
935− v'@(TypedValue _ _ ty) <- infer v
936− rest <- fresh
937− u =?= RCons p ty rest
938− ps'' <- go ps' [] rest
939− return $ (p, v') : ps''
940− go ((p,v):ps') ts r =
941− case lookup p ts of
942− Nothing -> do
943− v'@(TypedValue _ _ ty) <- infer v
944− rest <- fresh
945− r =?= RCons p ty rest
946− ps'' <- go ps' ts rest
947− return $ (p, v') : ps''
948− Just ty -> do
949− v' <- check v ty
950− ps'' <- go ps' (delete (p, ty) ts) r
951− return $ (p, v') : ps''
952− go _ _ _ = throwError $ mkErrorStack ("Object does not have type " ++ prettyPrintType (TypeApp tyObject row)) (Just (ValueError (ObjectLiteral ps)))
953−
954−-- |
955−-- Check the type of a function application, rethrowing errors to provide a better error message
956−--
957−checkFunctionApplication :: Value -> Type -> Value -> Maybe Type -> UnifyT Type Check (Type, Value)
958−checkFunctionApplication fn fnTy arg ret = rethrow (mkErrorStack errorMessage (Just (ValueError fn)) <>) $ checkFunctionApplication' fn fnTy arg ret
959− where
960− errorMessage = "Error applying function of type "
961− ++ prettyPrintType fnTy
962− ++ " to argument " ++ prettyPrintValue arg
963−
964−-- |
965−-- Check the type of a function application
966−--
967−checkFunctionApplication' :: Value -> Type -> Value -> Maybe Type -> UnifyT Type Check (Type, Value)
968−checkFunctionApplication' fn (TypeApp (TypeApp tyFunction' argTy) retTy) arg ret = do
969− tyFunction' =?= tyFunction
970− _ <- maybe (return Nothing) (subsumes Nothing retTy) ret
971− subst <- unifyCurrentSubstitution <$> UnifyT get
972− arg' <- check arg (subst $? argTy)
973− return (retTy, App fn arg')
974−checkFunctionApplication' fn (ForAll ident ty _) arg ret = do
975− replaced <- replaceVarWithUnknown ident ty
976− checkFunctionApplication fn replaced arg ret
977−checkFunctionApplication' fn u@(TUnknown _) arg ret = do
978− arg' <- do
979− TypedValue _ arg' t <- infer arg
980− (arg'', t') <- instantiatePolyTypeWithUnknowns arg' t
981− return $ TypedValue True arg'' t'
982− let ty = (\(TypedValue _ _ t) -> t) arg'
983− ret' <- maybe fresh return ret
984− u =?= function ty ret'
985− return (ret', App fn arg')
986−checkFunctionApplication' fn (SaturatedTypeSynonym name tyArgs) arg ret = do
987− ty <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
988− checkFunctionApplication fn ty arg ret
989−checkFunctionApplication' fn (ConstrainedType constraints fnTy) arg ret = do
990− dicts <- getTypeClassDictionaries
991− checkFunctionApplication' (foldl App fn (map (flip (TypeClassDictionary True) (Just dicts)) constraints)) fnTy arg ret
992−checkFunctionApplication' _ fnTy arg _ = throwError . strMsg $ "Cannot apply a function of type "
993− ++ prettyPrintType fnTy
994− ++ " to argument " ++ prettyPrintValue arg
995−
996−-- |
997−-- Check whether one type subsumes another, rethrowing errors to provide a better error message
998−--
999−subsumes :: Maybe Value -> Type -> Type -> UnifyT Type Check (Maybe Value)
1000−subsumes val ty1 ty2 = rethrow (mkErrorStack errorMessage (ValueError <$> val) <>) $ subsumes' val ty1 ty2
1001− where
1002− errorMessage = "Error checking that type "
1003− ++ prettyPrintType ty1
1004− ++ " subsumes type "
1005− ++ prettyPrintType ty2
1006−
1007−-- |
1008−-- Check whether one type subsumes another
1009−--
1010−subsumes' :: Maybe Value -> Type -> Type -> UnifyT Type Check (Maybe Value)
1011−subsumes' val (ForAll ident ty1 _) ty2 = do
1012− replaced <- replaceVarWithUnknown ident ty1
1013− subsumes val replaced ty2
1014−subsumes' val ty1 (ForAll ident ty2 sco) =
1015− case sco of
1016− Just sco' -> do
1017− sko <- newSkolemConstant
1018− let sk = skolemize ident sko sco' ty2
1019− subsumes val ty1 sk
1020− Nothing -> throwError . strMsg $ "Skolem variable scope is unspecified"
1021−subsumes' val (TypeApp (TypeApp f1 arg1) ret1) (TypeApp (TypeApp f2 arg2) ret2) | f1 == tyFunction && f2 == tyFunction = do
1022− _ <- subsumes Nothing arg2 arg1
1023− _ <- subsumes Nothing ret1 ret2
1024− return val
1025−subsumes' val (SaturatedTypeSynonym name tyArgs) ty2 = do
1026− ty1 <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
1027− subsumes val ty1 ty2
1028−subsumes' val ty1 (SaturatedTypeSynonym name tyArgs) = do
1029− ty2 <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
1030− subsumes val ty1 ty2
1031−subsumes' (Just val) (ConstrainedType constraints ty1) ty2 = do
1032− dicts <- getTypeClassDictionaries
1033− _ <- subsumes' Nothing ty1 ty2
1034− return . Just $ foldl App val (map (flip (TypeClassDictionary True) (Just dicts)) constraints)
1035−subsumes' val (TypeApp f1 r1) (TypeApp f2 r2) | f1 == tyObject && f2 == tyObject = do
1036− let
1037− (ts1, r1') = rowToList r1
1038− (ts2, r2') = rowToList r2
1039− ts1' = sortBy (comparing fst) ts1
1040− ts2' = sortBy (comparing fst) ts2
1041− go ts1' ts2' r1' r2'
1042− return val
1043− where
1044− go [] ts2 r1' r2' = r1' =?= rowFromList (ts2, r2')
1045− go ts1 [] r1' r2' = r2' =?= rowFromList (ts1, r1')
1046− go ((p1, ty1) : ts1) ((p2, ty2) : ts2) r1' r2'
1047− | p1 == p2 = do _ <- subsumes Nothing ty1 ty2
1048− go ts1 ts2 r1' r2'
1049− | p1 < p2 = do rest <- fresh
1050− r2' =?= RCons p1 ty1 rest
1051− go ts1 ((p2, ty2) : ts2) r1' rest
1052− | otherwise = do rest <- fresh
1053− r1' =?= RCons p2 ty2 rest
1054− go ((p1, ty1) : ts1) ts2 rest r2'
1055−subsumes' val ty1 ty2@(TypeApp obj _) | obj == tyObject = subsumes val ty2 ty1
1056−subsumes' val ty1 ty2 = do
1057− ty1 =?= ty2
1058− return val
1059−
1060−
1061−