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