@@ -1,1100 +0,0 @@
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− entails env mn dicts constraint trySuperclasses
267− go other = return other
268−
269−-- |
270−-- A simplified representation of expressions which are used to represent type
271−-- class dictionaries at runtime, which can be compared for equality
272−--
273−data DictionaryValue
274− -- |
275− -- A dictionary which is brought into scope by a local constraint
276− --
277− = LocalDictionaryValue (Qualified Ident)
278− -- |
279− -- A dictionary which is brought into scope by an instance declaration
280− --
281− | GlobalDictionaryValue (Qualified Ident)
282− -- |
283− -- A dictionary which depends on other dictionaries
284− --
285− | DependentDictionaryValue (Qualified Ident) [DictionaryValue]
286− -- |
287− -- A subclass dictionary
288− --
289− | SubclassDictionaryValue DictionaryValue (Qualified ProperName) Integer
290− deriving (Show, Ord, Eq)
291−
292−-- |
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.
295−--
296−entails :: Environment -> ModuleName -> [TypeClassDictionaryInScope] -> (Qualified ProperName, [Type]) -> Bool -> Check Value
297−entails env moduleName context = solve (sortedNubBy canonicalizeDictionary (filter filterModule context))
298− where
299− sortedNubBy :: (Ord k) => (v -> k) -> [v] -> [v]
300− sortedNubBy f vs = M.elems (M.fromList (map (f &&& id) vs))
301−
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
307−
308− solve context' (className, tys) trySuperclasses =
309− let
310− dicts = go trySuperclasses className tys
311− in case sortedNubBy dictTrace (chooseSimplestDictionaries dicts) of
312− [] -> throwError . strMsg $ "No instance found for " ++ show className ++ " " ++ unwords (map prettyPrintTypeAtom tys)
313− [_] -> return $ dictionaryValueToValue $ head dicts
314− _ -> throwError . strMsg $ "Overlapping instances found for " ++ show className ++ " " ++ unwords (map prettyPrintTypeAtom tys)
315− where
316− go trySuperclasses' className' tys' =
317− -- Look for regular type instances
318− [ mkDictionary (canonicalizeDictionary tcd) args
319− | tcd <- context'
320− -- Make sure the type class name matches the one we are trying to satisfy
321− , className' == tcdClassName tcd
322− -- Make sure the type unifies with the type in the type instance definition
323− , subst <- maybeToList . (>>= verifySubstitution) . fmap concat $ zipWithM (typeHeadsAreEqual moduleName env) tys' (tcdInstanceTypes tcd)
324− -- Solve any necessary subgoals
325− , args <- solveSubgoals subst (tcdDependencies tcd) ] ++
326−
327− -- Look for implementations via superclasses
328− [ SubclassDictionaryValue suDict superclass index
329− | trySuperclasses'
330− , (subclassName, (args, _, implies)) <- M.toList (typeClasses env)
331− -- Try each superclass
332− , (index, (superclass, suTyArgs)) <- zip [0..] implies
333− -- Make sure the type class name matches the superclass name
334− , className' == superclass
335− -- Make sure the types unify with the types in the superclass implication
336− , subst <- maybeToList . (>>= verifySubstitution) . fmap concat $ zipWithM (typeHeadsAreEqual moduleName env) tys' suTyArgs
337− -- Finally, satisfy the subclass constraint
338− , args' <- maybeToList $ mapM (applySubst subst . TypeVar) args
339− , suDict <- go True subclassName args' ]
340−
341− -- Create dictionaries for subgoals which still need to be solved by calling go recursively
342− -- E.g. the goal (Show a, Show b) => Show (Either a b) can be satisfied if the current type
343− -- unifies with Either a b, and we can satisfy the subgoals Show a and Show b recursively.
344− solveSubgoals :: [(String, Type)] -> Maybe [(Qualified ProperName, [Type])] -> [Maybe [DictionaryValue]]
345− solveSubgoals _ Nothing = return Nothing
346− solveSubgoals subst (Just subgoals) = do
347− dict <- mapM (uncurry (go True) . second (map (replaceAllTypeVars subst))) subgoals
348− return $ Just dict
349− -- Make a dictionary from subgoal dictionaries by applying the correct function
350− mkDictionary :: Qualified Ident -> Maybe [DictionaryValue] -> DictionaryValue
351− mkDictionary fnName Nothing = LocalDictionaryValue fnName
352− mkDictionary fnName (Just []) = GlobalDictionaryValue fnName
353− mkDictionary fnName (Just dicts) = DependentDictionaryValue fnName dicts
354− -- Turn a DictionaryValue into a Value
355− dictionaryValueToValue :: DictionaryValue -> Value
356− dictionaryValueToValue (LocalDictionaryValue fnName) = Var fnName
357− dictionaryValueToValue (GlobalDictionaryValue fnName) = App (Var fnName) (ObjectLiteral [])
358− dictionaryValueToValue (DependentDictionaryValue fnName dicts) = foldl App (Var fnName) (map dictionaryValueToValue dicts)
359− dictionaryValueToValue (SubclassDictionaryValue dict superclassName index) =
360− App (Accessor (show superclassName ++ "_" ++ show index)
361− (Accessor C.__superclasses (dictionaryValueToValue dict)))
362− (ObjectLiteral [])
363− -- Ensure that a substitution is valid
364− verifySubstitution :: [(String, Type)] -> Maybe [(String, Type)]
365− verifySubstitution subst = do
366− let grps = groupBy ((==) `on` fst) subst
367− guard (all (pairwise (unifiesWith env) . map snd) grps)
368− return $ map head grps
369− -- Apply a substitution to a type
370− applySubst :: [(String, Type)] -> Type -> Maybe Type
371− applySubst subst = everywhereM (mkM replace)
372− where
373− replace (TypeVar v) = lookup v subst
374− replace other = Just other
375− -- Choose the simplest DictionaryValues from a list of candidates
376− -- The reason for this function is as follows:
377− -- When considering overlapping instances, we don't want to consider the same dictionary
378− -- to be an overlap of itself when obtained as a superclass of another class.
379− -- Observing that we probably don't want to select a superclass instance when an instance
380− -- is available directly, and that there is no way for a superclass instance to actually
381− -- introduce an overlap that wouldn't have been there already, we simply remove dictionaries
382− -- obtained as superclass instances if there are simpler instances available.
383− chooseSimplestDictionaries :: [DictionaryValue] -> [DictionaryValue]
384− chooseSimplestDictionaries ds = case filter isSimpleDictionaryValue ds of
385− [] -> ds
386− simple -> simple
387− isSimpleDictionaryValue SubclassDictionaryValue{} = False
388− isSimpleDictionaryValue (DependentDictionaryValue _ ds) = all isSimpleDictionaryValue ds
389− isSimpleDictionaryValue _ = True
390− -- |
391− -- Get the "trace" of a DictionaryValue - that is, remove all SubclassDictionaryValue
392− -- data constructors
393− --
394− dictTrace :: DictionaryValue -> DictionaryValue
395− dictTrace (DependentDictionaryValue fnName dicts) = DependentDictionaryValue fnName $ map dictTrace dicts
396− dictTrace (SubclassDictionaryValue dict _ _) = dictTrace dict
397− dictTrace other = other
398−
399−-- |
400−-- Check all values in a list pairwise match a predicate
401−--
402−pairwise :: (a -> a -> Bool) -> [a] -> Bool
403−pairwise _ [] = True
404−pairwise _ [_] = True
405−pairwise p (x : xs) = all (p x) xs && pairwise p xs
406−
407−-- |
408−-- Check that two types unify
409−--
410−unifiesWith :: Environment -> Type -> Type -> Bool
411−unifiesWith _ (TUnknown _) _ = True
412−unifiesWith _ _ (TUnknown _) = True
413−unifiesWith _ (Skolem _ s1 _) (Skolem _ s2 _) | s1 == s2 = True
414−unifiesWith _ (TypeVar v1) (TypeVar v2) | v1 == v2 = True
415−unifiesWith _ (TypeConstructor c1) (TypeConstructor c2) | c1 == c2 = True
416−unifiesWith e (TypeApp h1 t1) (TypeApp h2 t2) = unifiesWith e h1 h2 && unifiesWith e t1 t2
417−unifiesWith e (SaturatedTypeSynonym name args) t2 =
418− case expandTypeSynonym' e name args of
419− Left _ -> False
420− Right t1 -> unifiesWith e t1 t2
421−unifiesWith e t1 t2@(SaturatedTypeSynonym _ _) = unifiesWith e t2 t1
422−unifiesWith _ _ _ = False
423−
424−-- |
425−-- Check whether the type heads of two types are equal (for the purposes of type class dictionary lookup),
426−-- and return a substitution from type variables to types which makes the type heads unify.
427−--
428−typeHeadsAreEqual :: ModuleName -> Environment -> Type -> Type -> Maybe [(String, Type)]
429−typeHeadsAreEqual _ _ (Skolem _ s1 _) (Skolem _ s2 _) | s1 == s2 = Just []
430−typeHeadsAreEqual _ _ t (TypeVar v) = Just [(v, t)]
431−typeHeadsAreEqual _ _ (TypeConstructor c1) (TypeConstructor c2) | c1 == c2 = Just []
432−typeHeadsAreEqual m e (TypeApp h1 t1) (TypeApp h2 t2) = (++) <$> typeHeadsAreEqual m e h1 h2 <*> typeHeadsAreEqual m e t1 t2
433−typeHeadsAreEqual m e (SaturatedTypeSynonym name args) t2 = case expandTypeSynonym' e name args of
434− Left _ -> Nothing
435− Right t1 -> typeHeadsAreEqual m e t1 t2
436−typeHeadsAreEqual _ _ _ _ = Nothing
437−
438−-- |
439−-- Ensure skolem variables do not escape their scope
440−--
441−skolemEscapeCheck :: Value -> Check ()
442−skolemEscapeCheck (TypedValue False _ _) = return ()
443−skolemEscapeCheck root@TypedValue{} =
444− -- Every skolem variable is created when a ForAll type is skolemized.
445− -- This determines the scope of that skolem variable, which is copied from the SkolemScope
446− -- field of the ForAll constructor.
447− -- We traverse the tree top-down, and collect any SkolemScopes introduced by ForAlls.
448− -- If a Skolem is encountered whose SkolemScope is not in the current list, we have found
449− -- an escaped skolem variable.
450− case everythingWithContext [] (++) (mkQ ((,) []) go) root of
451− [] -> return ()
452− ((binding, val) : _) -> throwError $ mkErrorStack ("Rigid/skolem type variable " ++ maybe "" (("bound by " ++) . prettyPrintValue) binding ++ " has escaped.") (Just (ValueError val))
453− where
454− go :: Value -> [(SkolemScope, Value)] -> ([(Maybe Value, Value)], [(SkolemScope, Value)])
455− go val@(TypedValue _ _ (ForAll _ _ (Just sco))) scos = ([], (sco, val) : scos)
456− go val@(TypedValue _ _ ty) scos = case collectSkolems ty \\ map fst scos of
457− (sco : _) -> ([(findBindingScope sco, val)], scos)
458− _ -> ([], scos)
459− where
460− collectSkolems :: Type -> [SkolemScope]
461− collectSkolems = nub . everything (++) (mkQ [] collect)
462− where
463− collect (Skolem _ _ scope) = [scope]
464− collect _ = []
465− go _ scos = ([], scos)
466− findBindingScope :: SkolemScope -> Maybe Value
467− findBindingScope sco = something (mkQ Nothing go') root
468− where
469− go' val@(TypedValue _ _ (ForAll _ _ (Just sco'))) | sco == sco' = Just val
470− go' _ = Nothing
471−skolemEscapeCheck val = throwError $ mkErrorStack "Untyped value passed to skolemEscapeCheck" (Just (ValueError val))
472−
473−-- |
474−-- Ensure a row contains no duplicate labels
475−--
476−setify :: Type -> Type
477−setify = rowFromList . first (M.toList . M.fromList) . rowToList
478−
479−-- |
480−-- \"Setify\" all rows occuring inside a value
481−--
482−setifyAll :: (D.Data d) => d -> d
483−setifyAll = everywhere (mkT setify)
484−
485−-- |
486−-- Replace outermost unsolved unification variables with named type variables
487−--
488−varIfUnknown :: Type -> Type
489−varIfUnknown ty =
490− let unks = nub $ unknowns ty
491− toName = (:) 't' . show
492− ty' = everywhere (mkT typeToVar) ty
493− typeToVar :: Type -> Type
494− typeToVar (TUnknown (Unknown u)) = TypeVar (toName u)
495− typeToVar t = t
496− in mkForAll (sort . map (toName . runUnknown) $ unks) ty'
497−
498−-- |
499−-- Remove any ForAlls and ConstrainedType constructors in a type by introducing new unknowns
500−-- or TypeClassDictionary values.
501−--
502−-- This is necessary during type checking to avoid unifying a polymorphic type with a
503−-- unification variable.
504−--
505−instantiatePolyTypeWithUnknowns :: Value -> Type -> UnifyT Type Check (Value, Type)
506−instantiatePolyTypeWithUnknowns val (ForAll ident ty _) = do
507− ty' <- replaceVarWithUnknown ident ty
508− instantiatePolyTypeWithUnknowns val ty'
509−instantiatePolyTypeWithUnknowns val (ConstrainedType constraints ty) = do
510− dicts <- getTypeClassDictionaries
511− (_, ty') <- instantiatePolyTypeWithUnknowns (error "Types under a constraint cannot themselves be constrained") ty
512− return (foldl App val (map (flip (TypeClassDictionary True) dicts) constraints), ty')
513−instantiatePolyTypeWithUnknowns val ty = return (val, ty)
514−
515−-- |
516−-- Replace a single type variable with a new unification variable
517−--
518−replaceVarWithUnknown :: String -> Type -> UnifyT Type Check Type
519−replaceVarWithUnknown ident ty = do
520− tu <- fresh
521− return $ replaceTypeVars ident tu ty
522−
523−-- |
524−-- Replace fully applied type synonyms with the @SaturatedTypeSynonym@ data constructor, which helps generate
525−-- better error messages during unification.
526−--
527−replaceAllTypeSynonyms' :: (D.Data d) => Environment -> d -> Either String d
528−replaceAllTypeSynonyms' env d =
529− let
530− syns = map (\(name, (args, _)) -> (name, length args)) . M.toList $ typeSynonyms env
531− in
532− saturateAllTypeSynonyms syns d
533−
534−replaceAllTypeSynonyms :: (Error e, Functor m, Monad m, MonadState CheckState m, MonadError e m) => (D.Data d) => d -> m d
535−replaceAllTypeSynonyms d = do
536− env <- getEnv
537− either (throwError . strMsg) return $ replaceAllTypeSynonyms' env d
538−
539−-- |
540−-- \"Desaturate\" @SaturatedTypeSynonym@s
541−--
542−desaturateAllTypeSynonyms :: (D.Data d) => d -> d
543−desaturateAllTypeSynonyms = everywhere (mkT replaceSaturatedTypeSynonym)
544− where
545− replaceSaturatedTypeSynonym (SaturatedTypeSynonym name args) = foldl TypeApp (TypeConstructor name) args
546− replaceSaturatedTypeSynonym t = t
547−
548−-- |
549−-- Replace a type synonym and its arguments with the aliased type
550−--
551−expandTypeSynonym' :: Environment -> Qualified ProperName -> [Type] -> Either String Type
552−expandTypeSynonym' env name args =
553− case M.lookup name (typeSynonyms env) of
554− Just (synArgs, body) -> do
555− let repl = replaceAllTypeVars (zip synArgs args) body
556− replaceAllTypeSynonyms' env repl
557− Nothing -> error "Type synonym was not defined"
558−
559−expandTypeSynonym :: (Error e, Functor m, Monad m, MonadState CheckState m, MonadError e m) => Qualified ProperName -> [Type] -> m Type
560−expandTypeSynonym name args = do
561− env <- getEnv
562− either (throwError . strMsg) return $ expandTypeSynonym' env name args
563−
564−expandAllTypeSynonyms :: (Error e, Functor m, Monad m, MonadState CheckState m, MonadError e m) => Type -> m Type
565−expandAllTypeSynonyms = everywhereM' (mkM go)
566− where
567− go (SaturatedTypeSynonym name args) = expandTypeSynonym name args
568− go other = return other
569−
570−-- |
571−-- Ensure a set of property names and value does not contain duplicate labels
572−--
573−ensureNoDuplicateProperties :: (Error e, MonadError e m) => [(String, Value)] -> m ()
574−ensureNoDuplicateProperties ps = guardWith (strMsg "Duplicate property names") $ length (nub . map fst $ ps) == length ps
575−
576−-- |
577−-- Infer a type for a value, rethrowing any error to provide a more useful error message
578−--
579−infer :: Value -> UnifyT Type Check Value
580−infer val = rethrow (mkErrorStack "Error inferring type of value" (Just (ValueError val)) <>) $ infer' val
581−
582−-- |
583−-- Infer a type for a value
584−--
585−infer' :: Value -> UnifyT Type Check Value
586−infer' v@(NumericLiteral _) = return $ TypedValue True v tyNumber
587−infer' v@(StringLiteral _) = return $ TypedValue True v tyString
588−infer' v@(BooleanLiteral _) = return $ TypedValue True v tyBoolean
589−infer' (ArrayLiteral vals) = do
590− ts <- mapM infer vals
591− els <- fresh
592− forM_ ts $ \(TypedValue _ _ t) -> els =?= TypeApp tyArray t
593− return $ TypedValue True (ArrayLiteral ts) els
594−infer' (ObjectLiteral ps) = do
595− ensureNoDuplicateProperties ps
596− ts <- mapM (infer . snd) ps
597− let fields = zipWith (\name (TypedValue _ _ t) -> (name, t)) (map fst ps) ts
598− ty = TypeApp tyObject $ rowFromList (fields, REmpty)
599− return $ TypedValue True (ObjectLiteral (zip (map fst ps) ts)) ty
600−infer' (ObjectUpdate o ps) = do
601− ensureNoDuplicateProperties ps
602− row <- fresh
603− newVals <- zipWith (\(name, _) t -> (name, t)) ps <$> mapM (infer . snd) ps
604− let newTys = map (\(name, TypedValue _ _ ty) -> (name, ty)) newVals
605− oldTys <- zip (map fst ps) <$> replicateM (length ps) fresh
606− let oldTy = TypeApp tyObject $ rowFromList (oldTys, row)
607− o' <- TypedValue True <$> check o oldTy <*> pure oldTy
608− return $ TypedValue True (ObjectUpdate o' newVals) $ TypeApp tyObject $ rowFromList (newTys, row)
609−infer' (Accessor prop val) = do
610− typed@(TypedValue _ _ objTy) <- infer val
611− propTy <- inferProperty objTy prop
612− case propTy of
613− Nothing -> do
614− field <- fresh
615− rest <- fresh
616− _ <- subsumes Nothing objTy (TypeApp tyObject (RCons prop field rest))
617− return $ TypedValue True (Accessor prop typed) field
618− Just ty -> return $ TypedValue True (Accessor prop typed) ty
619−infer' (Abs (Left arg) ret) = do
620− ty <- fresh
621− Just moduleName <- checkCurrentModule <$> get
622− bindLocalVariables moduleName [(arg, ty)] $ do
623− body@(TypedValue _ _ bodyTy) <- infer' ret
624− return $ TypedValue True (Abs (Left arg) body) $ function ty bodyTy
625−infer' (Abs (Right _) _) = error "Binder was not desugared"
626−infer' (App f arg) = do
627− f'@(TypedValue _ _ ft) <- infer f
628− (ret, app) <- checkFunctionApplication f' ft arg Nothing
629− return $ TypedValue True app ret
630−infer' (Var var) = do
631− Just moduleName <- checkCurrentModule <$> get
632− ty <- introduceSkolemScope <=< replaceAllTypeSynonyms <=< lookupVariable moduleName $ var
633− case ty of
634− ConstrainedType constraints ty' -> do
635− dicts <- getTypeClassDictionaries
636− return $ TypedValue True (foldl App (Var var) (map (flip (TypeClassDictionary True) dicts) constraints)) ty'
637− _ -> return $ TypedValue True (Var var) ty
638−infer' v@(Constructor c) = do
639− env <- getEnv
640− case M.lookup c (dataConstructors env) of
641− Nothing -> throwError . strMsg $ "Constructor " ++ show c ++ " is undefined"
642− Just (_, ty) -> do ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
643− return $ TypedValue True v ty'
644−infer' (Case vals binders) = do
645− ts <- mapM infer vals
646− ret <- fresh
647− binders' <- checkBinders (map (\(TypedValue _ _ t) -> t) ts) ret binders
648− return $ TypedValue True (Case ts binders') ret
649−infer' (IfThenElse cond th el) = do
650− cond' <- check cond tyBoolean
651− v2@(TypedValue _ _ t2) <- infer th
652− v3@(TypedValue _ _ t3) <- infer el
653− t2 =?= t3
654− return $ TypedValue True (IfThenElse cond' v2 v3) t2
655−infer' (Let ds val) = do
656− (ds', val'@(TypedValue _ _ valTy)) <- inferLetBinding [] ds val infer
657− return $ TypedValue True (Let ds' val') valTy
658−infer' (SuperClassDictionary className tys) = do
659− dicts <- getTypeClassDictionaries
660− return $ TypeClassDictionary False (className, tys) dicts
661−infer' (TypedValue checkType val ty) = do
662− Just moduleName <- checkCurrentModule <$> get
663− kind <- liftCheck $ kindOf moduleName ty
664− guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
665− ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
666− val' <- if checkType then check val ty' else return val
667− return $ TypedValue True val' ty'
668−infer' (PositionedValue pos val) = rethrowWithPosition pos $ infer' val
669−infer' _ = error "Invalid argument to infer"
670−
671−inferLetBinding :: [Declaration] -> [Declaration] -> Value -> (Value -> UnifyT Type Check Value) -> UnifyT Type Check ([Declaration], Value)
672−inferLetBinding seen [] ret j = (,) seen <$> j ret
673−inferLetBinding seen (ValueDeclaration ident nameKind [] Nothing val : rest) ret j = do
674− valTy <- fresh
675− Just moduleName <- checkCurrentModule <$> get
676− let dict = if isFunction val then M.singleton (moduleName, ident) (valTy, nameKind) else M.empty
677− TypedValue _ val' valTy' <- bindNames dict $ infer val
678− valTy =?= valTy'
679− bindNames (M.singleton (moduleName, ident) (valTy', nameKind)) $ inferLetBinding (seen ++ [ValueDeclaration ident nameKind [] Nothing val']) rest ret j
680−inferLetBinding seen (BindingGroupDeclaration ds : rest) ret j = do
681− Just moduleName <- checkCurrentModule <$> get
682− (es, dict, untypedDict) <- typeDictionaryForBindingGroup moduleName (map (\(i, _, v) -> (i, v)) ds)
683− ds' <- forM es $ \e -> do
684− (ident, (val', _)) <- typeForBindingGroupElement moduleName e dict untypedDict
685− return $ (ident, LocalVariable, val')
686− bindNames dict $ inferLetBinding (seen ++ [BindingGroupDeclaration ds']) rest ret j
687−inferLetBinding seen (PositionedDeclaration pos d : ds) ret j = do
688− ((d' : ds'), val') <- inferLetBinding seen (d : ds) ret j
689− return (PositionedDeclaration pos d' : ds', val')
690−inferLetBinding _ _ _ _ = error "Invalid argument to inferLetBinding"
691−
692−-- |
693−-- Infer the type of a property inside a record with a given type
694−--
695−inferProperty :: Type -> String -> UnifyT Type Check (Maybe Type)
696−inferProperty (TypeApp obj row) prop | obj == tyObject = do
697− let (props, _) = rowToList row
698− return $ lookup prop props
699−inferProperty (SaturatedTypeSynonym name args) prop = do
700− replaced <- introduceSkolemScope <=< expandTypeSynonym name $ args
701− inferProperty replaced prop
702−inferProperty (ForAll ident ty _) prop = do
703− replaced <- replaceVarWithUnknown ident ty
704− inferProperty replaced prop
705−inferProperty _ _ = return Nothing
706−
707−-- |
708−-- Infer the types of variables brought into scope by a binder
709−--
710−inferBinder :: Type -> Binder -> UnifyT Type Check (M.Map Ident Type)
711−inferBinder _ NullBinder = return M.empty
712−inferBinder val (StringBinder _) = val =?= tyString >> return M.empty
713−inferBinder val (NumberBinder _) = val =?= tyNumber >> return M.empty
714−inferBinder val (BooleanBinder _) = val =?= tyBoolean >> return M.empty
715−inferBinder val (VarBinder name) = return $ M.singleton name val
716−inferBinder val (ConstructorBinder ctor binders) = do
717− env <- getEnv
718− case M.lookup ctor (dataConstructors env) of
719− Just (_, ty) -> do
720− (_, fn) <- instantiatePolyTypeWithUnknowns (error "Data constructor types cannot contain constraints") ty
721− fn' <- replaceAllTypeSynonyms fn
722− go binders fn'
723− where
724− go [] ty' = do
725− _ <- subsumes Nothing val ty'
726− return M.empty
727− go (binder : binders') (TypeApp (TypeApp t obj) ret) | t == tyFunction =
728− M.union <$> inferBinder obj binder <*> go binders' ret
729− go _ _ = throwError . strMsg $ "Wrong number of arguments to constructor " ++ show ctor
730− _ -> throwError . strMsg $ "Constructor " ++ show ctor ++ " is not defined"
731−inferBinder val (ObjectBinder props) = do
732− row <- fresh
733− rest <- fresh
734− m1 <- inferRowProperties row rest props
735− val =?= TypeApp tyObject row
736− return m1
737− where
738− inferRowProperties :: Type -> Type -> [(String, Binder)] -> UnifyT Type Check (M.Map Ident Type)
739− inferRowProperties nrow row [] = nrow =?= row >> return M.empty
740− inferRowProperties nrow row ((name, binder):binders) = do
741− propTy <- fresh
742− m1 <- inferBinder propTy binder
743− m2 <- inferRowProperties nrow (RCons name propTy row) binders
744− return $ m1 `M.union` m2
745−inferBinder val (ArrayBinder binders) = do
746− el <- fresh
747− m1 <- M.unions <$> mapM (inferBinder el) binders
748− val =?= TypeApp tyArray el
749− return m1
750−inferBinder val (ConsBinder headBinder tailBinder) = do
751− el <- fresh
752− m1 <- inferBinder el headBinder
753− m2 <- inferBinder val tailBinder
754− val =?= TypeApp tyArray el
755− return $ m1 `M.union` m2
756−inferBinder val (NamedBinder name binder) = do
757− m <- inferBinder val binder
758− return $ M.insert name val m
759−inferBinder val (PositionedBinder pos binder) =
760− rethrowWithPosition pos $ inferBinder val binder
761−
762−-- |
763−-- Check the types of the return values in a set of binders in a case statement
764−--
765−checkBinders :: [Type] -> Type -> [CaseAlternative] -> UnifyT Type Check [CaseAlternative]
766−checkBinders _ _ [] = return []
767−checkBinders nvals ret (CaseAlternative binders grd val : bs) = do
768− Just moduleName <- checkCurrentModule <$> get
769− m1 <- M.unions <$> zipWithM inferBinder nvals binders
770− r <- bindLocalVariables moduleName (M.toList m1) $ do
771− val' <- TypedValue True <$> check val ret <*> pure ret
772− case grd of
773− Nothing -> return $ CaseAlternative binders Nothing val'
774− Just g -> do
775− g' <- check g tyBoolean
776− return $ CaseAlternative binders (Just g') val'
777− rs <- checkBinders nvals ret bs
778− return $ r : rs
779−
780−-- |
781−-- Generate a new skolem constant
782−--
783−newSkolemConstant :: UnifyT Type Check Int
784−newSkolemConstant = runUnknown <$> fresh'
785−
786−-- |
787−-- Generate a new skolem scope
788−--
789−newSkolemScope :: UnifyT Type Check SkolemScope
790−newSkolemScope = SkolemScope . runUnknown <$> fresh'
791−
792−-- |
793−-- Skolemize a type variable by replacing its instances with fresh skolem constants
794−--
795−skolemize :: String -> Int -> SkolemScope -> Type -> Type
796−skolemize ident sko scope = replaceTypeVars ident (Skolem ident sko scope)
797−
798−-- |
799−-- This function has one purpose - to skolemize type variables appearing in a
800−-- SuperClassDictionary placeholder. These type variables are somewhat unique since they are the
801−-- only example of scoped type variables.
802−--
803−skolemizeTypesInValue :: String -> Int -> SkolemScope -> Value -> Value
804−skolemizeTypesInValue ident sko scope = everywhere (mkT go)
805− where
806− go (SuperClassDictionary c ts) = SuperClassDictionary c (map (skolemize ident sko scope) ts)
807− go other = other
808−
809−-- |
810−-- Introduce skolem scope at every occurence of a ForAll
811−--
812−introduceSkolemScope :: Type -> UnifyT Type Check Type
813−introduceSkolemScope = everywhereM (mkM go)
814− where
815− go (ForAll ident ty Nothing) = ForAll ident ty <$> (Just <$> newSkolemScope)
816− go other = return other
817−
818−-- |
819−-- Check the type of a value, rethrowing errors to provide a better error message
820−--
821−check :: Value -> Type -> UnifyT Type Check Value
822−check val ty = rethrow (mkErrorStack errorMessage (Just (ValueError val)) <>) $ check' val ty
823− where
824− errorMessage =
825− "Error checking type of term " ++
826− prettyPrintValue val ++
827− " against type " ++
828− prettyPrintType ty
829−
830−-- |
831−-- Check the type of a value
832−--
833−check' :: Value -> Type -> UnifyT Type Check Value
834−check' val (ForAll ident ty _) = do
835− scope <- newSkolemScope
836− sko <- newSkolemConstant
837− let sk = skolemize ident sko scope ty
838− let skVal = skolemizeTypesInValue ident sko scope val
839− val' <- check skVal sk
840− return $ TypedValue True val' (ForAll ident ty (Just scope))
841−check' val t@(ConstrainedType constraints ty) = do
842− dictNames <- forM constraints $ \(Qualified _ (ProperName className), _) -> do
843− n <- liftCheck freshDictionaryName
844− return $ Ident $ "__dict_" ++ className ++ "_" ++ show n
845− val' <- withTypeClassDictionaries (zipWith (\name (className, instanceTy) ->
846− TypeClassDictionaryInScope name className instanceTy Nothing TCDRegular) (map (Qualified Nothing) dictNames)
847− constraints) $ check val ty
848− return $ TypedValue True (foldr (Abs . Left) val' dictNames) t
849−check' val (SaturatedTypeSynonym name args) = do
850− ty <- introduceSkolemScope <=< expandTypeSynonym name $ args
851− check val ty
852−check' val u@(TUnknown _) = do
853− val'@(TypedValue _ _ ty) <- infer val
854− -- Don't unify an unknown with an inferred polytype
855− (val'', ty') <- instantiatePolyTypeWithUnknowns val' ty
856− ty' =?= u
857− return $ TypedValue True val'' ty'
858−check' v@(NumericLiteral _) t | t == tyNumber =
859− return $ TypedValue True v t
860−check' v@(StringLiteral _) t | t == tyString =
861− return $ TypedValue True v t
862−check' v@(BooleanLiteral _) t | t == tyBoolean =
863− return $ TypedValue True v t
864−check' (ArrayLiteral vals) t@(TypeApp a ty) = do
865− a =?= tyArray
866− array <- ArrayLiteral <$> forM vals (`check` ty)
867− return $ TypedValue True array t
868−check' (Abs (Left arg) ret) ty@(TypeApp (TypeApp t argTy) retTy) | t == tyFunction = do
869− Just moduleName <- checkCurrentModule <$> get
870− ret' <- bindLocalVariables moduleName [(arg, argTy)] $ check ret retTy
871− return $ TypedValue True (Abs (Left arg) ret') ty
872−check' (Abs (Right _) _) _ = error "Binder was not desugared"
873−check' (App f arg) ret = do
874− f'@(TypedValue _ _ ft) <- infer f
875− (_, app) <- checkFunctionApplication f' ft arg (Just ret)
876− return $ TypedValue True app ret
877−check' v@(Var var) ty = do
878− Just moduleName <- checkCurrentModule <$> get
879− repl <- introduceSkolemScope <=< replaceAllTypeSynonyms <=< lookupVariable moduleName $ var
880− ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
881− v' <- subsumes (Just v) repl ty'
882− case v' of
883− Nothing -> throwError . strMsg $ "Unable to check type subsumption"
884− Just v'' -> return $ TypedValue True v'' ty'
885−check' (SuperClassDictionary className tys) _ = do
886− -- |
887− -- Here, we replace a placeholder for a superclass dictionary with a regular
888− -- TypeClassDictionary placeholder. The reason we do this is that it is necessary to have the
889− -- correct super instance dictionaries in scope, and these are not available when the type class
890− -- declaration gets desugared.
891− --
892− -- Note also that the first argument to TypeClassDictionary is False, meaning we _do not_ want
893− -- to consider superclass instances when searching for this dictionary - doing so might lead
894− -- to traversing a cycle in the instance graph.
895− --
896− dicts <- getTypeClassDictionaries
897− return $ TypeClassDictionary False (className, tys) dicts
898−check' (TypedValue checkType val ty1) ty2 = do
899− Just moduleName <- checkCurrentModule <$> get
900− kind <- liftCheck $ kindOf moduleName ty1
901− guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
902− ty1' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty1
903− val' <- subsumes (Just val) ty1' ty2
904− case val' of
905− Nothing -> throwError . strMsg $ "Unable to check type subsumption"
906− Just val'' -> do
907− val''' <- if checkType then check val'' ty1' else return val''
908− return $ TypedValue checkType (TypedValue True val''' ty1) ty2
909−check' (Case vals binders) ret = do
910− vals' <- mapM infer vals
911− let ts = map (\(TypedValue _ _ t) -> t) vals'
912− binders' <- checkBinders ts ret binders
913− return $ TypedValue True (Case vals' binders') ret
914−check' (IfThenElse cond th el) ty = do
915− cond' <- check cond tyBoolean
916− th' <- check th ty
917− el' <- check el ty
918− return $ TypedValue True (IfThenElse cond' th' el') ty
919−check' (ObjectLiteral ps) t@(TypeApp obj row) | obj == tyObject = do
920− ensureNoDuplicateProperties ps
921− ps' <- checkProperties ps row False
922− return $ TypedValue True (ObjectLiteral ps') t
923−check' (ObjectUpdate obj ps) t@(TypeApp o row) | o == tyObject = do
924− ensureNoDuplicateProperties ps
925− us <- zip (map fst ps) <$> replicateM (length ps) fresh
926− let (propsToCheck, rest) = rowToList row
927− propsToRemove = map fst ps
928− remainingProps = filter (\(p, _) -> p `notElem` propsToRemove) propsToCheck
929− obj' <- check obj (TypeApp tyObject (rowFromList (us ++ remainingProps, rest)))
930− ps' <- checkProperties ps row True
931− return $ TypedValue True (ObjectUpdate obj' ps') t
932−check' (Accessor prop val) ty = do
933− rest <- fresh
934− val' <- check val (TypeApp tyObject (RCons prop ty rest))
935− return $ TypedValue True (Accessor prop val') ty
936−check' (Constructor c) ty = do
937− env <- getEnv
938− case M.lookup c (dataConstructors env) of
939− Nothing -> throwError . strMsg $ "Constructor " ++ show c ++ " is undefined"
940− Just (_, ty1) -> do
941− repl <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty1
942− _ <- subsumes Nothing repl ty
943− return $ TypedValue True (Constructor c) ty
944−check' (Let ds val) ty = do
945− (ds', val') <- inferLetBinding [] ds val (flip check ty)
946− return $ TypedValue True (Let ds' val') ty
947−check' val ty | containsTypeSynonyms ty = do
948− ty' <- introduceSkolemScope <=< expandAllTypeSynonyms $ ty
949− check val ty'
950−check' (PositionedValue pos val) ty =
951− rethrowWithPosition pos $ check val ty
952−check' val ty = throwError $ mkErrorStack ("Value does not have type " ++ prettyPrintType ty) (Just (ValueError val))
953−
954−containsTypeSynonyms :: Type -> Bool
955−containsTypeSynonyms = everything (||) (mkQ False go) where
956− go (SaturatedTypeSynonym _ _) = True
957− go _ = False
958−
959−-- |
960−-- Check the type of a collection of named record fields
961−--
962−-- The @lax@ parameter controls whether or not every record member has to be provided. For object updates, this is not the case.
963−--
964−checkProperties :: [(String, Value)] -> Type -> Bool -> UnifyT Type Check [(String, Value)]
965−checkProperties ps row lax = let (ts, r') = rowToList row in go ps ts r' where
966− go [] [] REmpty = return []
967− go [] [] u@(TUnknown _) = do u =?= REmpty
968− return []
969− go [] [] (Skolem _ _ _) | lax = return []
970− go [] ((p, _): _) _ | lax = return []
971− | otherwise = throwError $ mkErrorStack ("Object does not have property " ++ p) (Just (ValueError (ObjectLiteral ps)))
972− go ((p,_):_) [] REmpty = throwError $ mkErrorStack ("Property " ++ p ++ " is not present in closed object type " ++ prettyPrintRow row) (Just (ValueError (ObjectLiteral ps)))
973− go ((p,v):ps') [] u@(TUnknown _) = do
974− v'@(TypedValue _ _ ty) <- infer v
975− rest <- fresh
976− u =?= RCons p ty rest
977− ps'' <- go ps' [] rest
978− return $ (p, v') : ps''
979− go ((p,v):ps') ts r =
980− case lookup p ts of
981− Nothing -> do
982− v'@(TypedValue _ _ ty) <- infer v
983− rest <- fresh
984− r =?= RCons p ty rest
985− ps'' <- go ps' ts rest
986− return $ (p, v') : ps''
987− Just ty -> do
988− v' <- check v ty
989− ps'' <- go ps' (delete (p, ty) ts) r
990− return $ (p, v') : ps''
991− go _ _ _ = throwError $ mkErrorStack ("Object does not have type " ++ prettyPrintType (TypeApp tyObject row)) (Just (ValueError (ObjectLiteral ps)))
992−
993−-- |
994−-- Check the type of a function application, rethrowing errors to provide a better error message
995−--
996−checkFunctionApplication :: Value -> Type -> Value -> Maybe Type -> UnifyT Type Check (Type, Value)
997−checkFunctionApplication fn fnTy arg ret = rethrow (mkErrorStack errorMessage (Just (ValueError fn)) <>) $ checkFunctionApplication' fn fnTy arg ret
998− where
999− errorMessage = "Error applying function of type "
1000− ++ prettyPrintType fnTy
1001− ++ " to argument " ++ prettyPrintValue arg
1002−
1003−-- |
1004−-- Check the type of a function application
1005−--
1006−checkFunctionApplication' :: Value -> Type -> Value -> Maybe Type -> UnifyT Type Check (Type, Value)
1007−checkFunctionApplication' fn (TypeApp (TypeApp tyFunction' argTy) retTy) arg ret = do
1008− tyFunction' =?= tyFunction
1009− _ <- maybe (return Nothing) (subsumes Nothing retTy) ret
1010− subst <- unifyCurrentSubstitution <$> UnifyT get
1011− arg' <- check arg (subst $? argTy)
1012− return (retTy, App fn arg')
1013−checkFunctionApplication' fn (ForAll ident ty _) arg ret = do
1014− replaced <- replaceVarWithUnknown ident ty
1015− checkFunctionApplication fn replaced arg ret
1016−checkFunctionApplication' fn u@(TUnknown _) arg ret = do
1017− arg' <- do
1018− TypedValue _ arg' t <- infer arg
1019− (arg'', t') <- instantiatePolyTypeWithUnknowns arg' t
1020− return $ TypedValue True arg'' t'
1021− let ty = (\(TypedValue _ _ t) -> t) arg'
1022− ret' <- maybe fresh return ret
1023− u =?= function ty ret'
1024− return (ret', App fn arg')
1025−checkFunctionApplication' fn (SaturatedTypeSynonym name tyArgs) arg ret = do
1026− ty <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
1027− checkFunctionApplication fn ty arg ret
1028−checkFunctionApplication' fn (ConstrainedType constraints fnTy) arg ret = do
1029− dicts <- getTypeClassDictionaries
1030− checkFunctionApplication' (foldl App fn (map (flip (TypeClassDictionary True) dicts) constraints)) fnTy arg ret
1031−checkFunctionApplication' _ fnTy arg _ = throwError . strMsg $ "Cannot apply a function of type "
1032− ++ prettyPrintType fnTy
1033− ++ " to argument " ++ prettyPrintValue arg
1034−
1035−-- |
1036−-- Check whether one type subsumes another, rethrowing errors to provide a better error message
1037−--
1038−subsumes :: Maybe Value -> Type -> Type -> UnifyT Type Check (Maybe Value)
1039−subsumes val ty1 ty2 = rethrow (mkErrorStack errorMessage (ValueError <$> val) <>) $ subsumes' val ty1 ty2
1040− where
1041− errorMessage = "Error checking that type "
1042− ++ prettyPrintType ty1
1043− ++ " subsumes type "
1044− ++ prettyPrintType ty2
1045−
1046−-- |
1047−-- Check whether one type subsumes another
1048−--
1049−subsumes' :: Maybe Value -> Type -> Type -> UnifyT Type Check (Maybe Value)
1050−subsumes' val (ForAll ident ty1 _) ty2 = do
1051− replaced <- replaceVarWithUnknown ident ty1
1052− subsumes val replaced ty2
1053−subsumes' val ty1 (ForAll ident ty2 sco) =
1054− case sco of
1055− Just sco' -> do
1056− sko <- newSkolemConstant
1057− let sk = skolemize ident sko sco' ty2
1058− subsumes val ty1 sk
1059− Nothing -> throwError . strMsg $ "Skolem variable scope is unspecified"
1060−subsumes' val (TypeApp (TypeApp f1 arg1) ret1) (TypeApp (TypeApp f2 arg2) ret2) | f1 == tyFunction && f2 == tyFunction = do
1061− _ <- subsumes Nothing arg2 arg1
1062− _ <- subsumes Nothing ret1 ret2
1063− return val
1064−subsumes' val (SaturatedTypeSynonym name tyArgs) ty2 = do
1065− ty1 <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
1066− subsumes val ty1 ty2
1067−subsumes' val ty1 (SaturatedTypeSynonym name tyArgs) = do
1068− ty2 <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
1069− subsumes val ty1 ty2
1070−subsumes' (Just val) (ConstrainedType constraints ty1) ty2 = do
1071− dicts <- getTypeClassDictionaries
1072− _ <- subsumes' Nothing ty1 ty2
1073− return . Just $ foldl App val (map (flip (TypeClassDictionary True) dicts) constraints)
1074−subsumes' val (TypeApp f1 r1) (TypeApp f2 r2) | f1 == tyObject && f2 == tyObject = do
1075− let
1076− (ts1, r1') = rowToList r1
1077− (ts2, r2') = rowToList r2
1078− ts1' = sortBy (comparing fst) ts1
1079− ts2' = sortBy (comparing fst) ts2
1080− go ts1' ts2' r1' r2'
1081− return val
1082− where
1083− go [] ts2 r1' r2' = r1' =?= rowFromList (ts2, r2')
1084− go ts1 [] r1' r2' = r2' =?= rowFromList (ts1, r1')
1085− go ((p1, ty1) : ts1) ((p2, ty2) : ts2) r1' r2'
1086− | p1 == p2 = do _ <- subsumes Nothing ty1 ty2
1087− go ts1 ts2 r1' r2'
1088− | p1 < p2 = do rest <- fresh
1089− r2' =?= RCons p1 ty1 rest
1090− go ts1 ((p2, ty2) : ts2) r1' rest
1091− | otherwise = do rest <- fresh
1092− r1' =?= RCons p2 ty2 rest
1093− go ((p1, ty1) : ts1) ts2 rest r2'
1094−subsumes' val ty1 ty2@(TypeApp obj _) | obj == tyObject = subsumes val ty2 ty1
1095−subsumes' val ty1 ty2 = do
1096− ty1 =?= ty2
1097− return val
1098−
1099−
1100−