@@ -1,983 +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 DeriveDataTypeable #-}
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−
51−import Language.PureScript.Values
52−import Language.PureScript.Types
53−import Language.PureScript.Kinds
54−import Language.PureScript.Names
55−import Language.PureScript.TypeChecker.Monad
56−import Language.PureScript.TypeChecker.Kinds
57−import Language.PureScript.TypeChecker.Synonyms
58−import Language.PureScript.Pretty
59−
60−import Control.Monad.State
61−import Control.Monad.Error
62−import Control.Monad.Reader
63−import Control.Monad.Unify
64−
65−import Control.Applicative
66−import Control.Arrow (Arrow(..))
67−
68−import qualified Data.Map as M
69−import Data.Function (on)
70−import Debug.Trace (trace)
71−
72−instance Partial Type where
73− unknown = TUnknown
74− isUnknown (TUnknown u) = Just u
75− isUnknown _ = Nothing
76−
77−instance Unifiable Check Type where
78− (=?=) = unifyTypes
79−
80−-- |
81−-- Unify two types, updating the current substitution
82−--
83−unifyTypes :: Type -> Type -> UnifyT Type Check ()
84−unifyTypes t1 t2 = rethrow (\e -> "Error unifying type " ++ prettyPrintType t1 ++ " with type " ++ prettyPrintType t2 ++ ":\n" ++ e) $ do
85− unifyTypes' t1 t2
86− where
87− unifyTypes' (TUnknown u1) (TUnknown u2) | u1 == u2 = return ()
88− unifyTypes' (TUnknown u) t = u =:= t
89− unifyTypes' t (TUnknown u) = u =:= t
90− unifyTypes' (SaturatedTypeSynonym name args) ty = do
91− ty1 <- introduceSkolemScope <=< expandTypeSynonym name $ args
92− ty1 `unifyTypes` ty
93− unifyTypes' ty s@(SaturatedTypeSynonym _ _) = s `unifyTypes` ty
94− unifyTypes' (ForAll ident1 ty1 sc1) (ForAll ident2 ty2 sc2) =
95− case (sc1, sc2) of
96− (Just sc1', Just sc2') -> do
97− sko <- newSkolemConstant
98− let sk1 = skolemize ident1 sko sc1' ty1
99− let sk2 = skolemize ident2 sko sc2' ty2
100− sk1 `unifyTypes` sk2
101− _ -> throwError (prettyPrintType ty1)
102− unifyTypes' (ForAll ident ty1 (Just sc)) ty2 = do
103− sko <- newSkolemConstant
104− let sk = skolemize ident sko sc ty1
105− sk `unifyTypes` ty2
106− unifyTypes' (ForAll _ _ _) _ = throwError "Skolem variable scope is unspecified"
107− unifyTypes' ty f@(ForAll _ _ _) = f `unifyTypes` ty
108− unifyTypes' (Object row1) (Object row2) = row1 =?= row2
109− unifyTypes' (TypeVar v1) (TypeVar v2) | v1 == v2 = return ()
110− unifyTypes' (TypeConstructor c1) (TypeConstructor c2) = do
111− env <- getEnv
112− Just moduleName <- checkCurrentModule <$> get
113− guardWith ("Cannot unify " ++ show c1 ++ " with " ++ show c2 ++ ".") (typeConstructorsAreEqual env moduleName c1 c2)
114− unifyTypes' (TypeApp t3 t4) (TypeApp t5 t6) = do
115− t3 `unifyTypes` t5
116− t4 `unifyTypes` t6
117− unifyTypes' (Skolem s1 _) (Skolem s2 _) | s1 == s2 = return ()
118− unifyTypes' r1@(RCons _ _ _) r2 = unifyRows r1 r2
119− unifyTypes' r1 r2@(RCons _ _ _) = unifyRows r1 r2
120− unifyTypes' r1@REmpty r2 = unifyRows r1 r2
121− unifyTypes' r1 r2@REmpty = unifyRows r1 r2
122− unifyTypes' t3 t4 = throwError $ "Cannot unify " ++ prettyPrintType t3 ++ " with " ++ prettyPrintType t4 ++ "."
123−
124−-- |
125−-- Unify two rows, updating the current substitution
126−--
127−-- Common labels are first identified, and unified. Remaining labels and types are unified with a
128−-- trailing row unification variable, if appropriate, otherwise leftover labels result in a unification
129−-- error.
130−--
131−unifyRows :: Type -> Type -> UnifyT Type Check ()
132−unifyRows r1 r2 =
133− let
134− (s1, r1') = rowToList r1
135− (s2, r2') = rowToList r2
136− int = [ (t1, t2) | (name, t1) <- s1, (name', t2) <- s2, name == name' ]
137− sd1 = [ (name, t1) | (name, t1) <- s1, name `notElem` map fst s2 ]
138− sd2 = [ (name, t2) | (name, t2) <- s2, name `notElem` map fst s1 ]
139− in do
140− forM_ int (uncurry (=?=))
141− unifyRows' sd1 r1' sd2 r2'
142− where
143− unifyRows' :: [(String, Type)] -> Type -> [(String, Type)] -> Type -> UnifyT Type Check ()
144− unifyRows' [] (TUnknown u) sd r = u =:= rowFromList (sd, r)
145− unifyRows' sd r [] (TUnknown u) = u =:= rowFromList (sd, r)
146− unifyRows' ((name, ty):row) r others u@(TUnknown un) = do
147− occursCheck un ty
148− forM_ row $ \(_, t) -> occursCheck un t
149− u' <- fresh
150− u =?= RCons name ty u'
151− unifyRows' row r others u'
152− unifyRows' [] REmpty [] REmpty = return ()
153− unifyRows' [] (TypeVar v1) [] (TypeVar v2) | v1 == v2 = return ()
154− unifyRows' [] (Skolem s1 _) [] (Skolem s2 _) | s1 == s2 = return ()
155− unifyRows' sd3 r3 sd4 r4 = throwError $ "Cannot unify " ++ prettyPrintRow (rowFromList (sd3, r3)) ++ " with " ++ prettyPrintRow (rowFromList (sd4, r4)) ++ "."
156−
157−-- |
158−-- Ensure type constructors are equal after canonicalization
159−--
160−typeConstructorsAreEqual :: Environment -> ModuleName -> Qualified ProperName -> Qualified ProperName -> Bool
161−typeConstructorsAreEqual env moduleName = (==) `on` canonicalizeType moduleName env
162−
163−-- |
164−-- Infer the types of multiple mutually-recursive values, and return elaborated values including
165−-- type class dictionaries and type annotations.
166−--
167−typesOf :: ModuleName -> [(Ident, Value)] -> Check [(Ident, (Value, Type))]
168−typesOf moduleName vals = do
169− tys <- fmap tidyUp . liftUnify $ do
170− let
171− -- Map each declaration to a name/value pair, with an optional type, if the declaration is typed
172− es = map isTyped vals
173− -- Filter the typed and untyped declarations
174− typed = filter (isJust . snd . snd) es
175− untyped = filter (isNothing . snd . snd) es
176− -- Make a map of names to typed declarations
177− typedDict = map (\(ident, (_, Just (ty, _))) -> (ident, ty)) typed
178− -- Create fresh unification variables for the types of untyped declarations
179− untypedNames <- replicateM (length untyped) fresh
180− let
181− -- Make a map of names to the unification variables of untyped declarations
182− untypedDict = zip (map fst untyped) untypedNames
183− -- Create the dictionary of all name/type pairs, which will be added to the environment during type checking
184− dict = M.fromList (map (\(ident, ty) -> ((moduleName, ident), (ty, LocalVariable))) $ typedDict ++ untypedDict)
185− forM es $ \e@(_, (val, _)) -> do
186− -- If the declaration is a function, it has access to other values in the binding group.
187− -- If not, the generated code might fail at runtime since those values might be undefined.
188− let dict' = if isFunction val then dict else M.empty
189− triple@(_, (val, ty)) <- case e of
190− -- Typed declarations
191− (ident, (val, Just (ty, checkType))) -> do
192− -- Kind check
193− kind <- liftCheck $ kindOf moduleName ty
194− guardWith ("Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
195− -- Check the type with the new names in scope
196− ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
197− val' <- bindNames dict' $ if checkType
198− then TypedValue True <$> check val ty' <*> pure ty'
199− else return (TypedValue False val ty')
200− return (ident, (val', ty'))
201− -- Untyped declarations
202− (ident, (val, Nothing)) -> do
203− -- Infer the type with the new names in scope
204− TypedValue _ val' ty <- bindNames dict' $ infer val
205− ty =?= fromMaybe (error "name not found in dictionary") (lookup ident untypedDict)
206− return (ident, (TypedValue True val' ty, ty))
207− -- If run-main is enabled, need to check that Main.main has type Eff eff a for some eff, a
208− when (moduleName == ModuleName (ProperName "Main") && fst e == Ident "main") $ do
209− [eff, a] <- replicateM 2 fresh
210− ty =?= TypeApp (TypeApp (TypeConstructor (Qualified (Just (ModuleName (ProperName "Eff"))) (ProperName "Eff"))) eff) a
211− -- Make sure unification variables do not escape
212− escapeCheck val ty
213− return triple
214− forM tys $ \(ident, (val, ty)) -> rethrow (("Error in " ++ show ident ++ ": \n") ++) $ do
215− -- Replace type class dictionary placeholders with actual dictionaries
216− val' <- replaceTypeClassDictionaries moduleName val
217− -- Check skolem variables did not escape their scope
218− skolemEscapeCheck val'
219− --
220− return $ (ident, (overTypes (desaturateAllTypeSynonyms . setifyAll) $ val'
221− , varIfUnknown . desaturateAllTypeSynonyms . setifyAll $ ty))
222− where
223− -- Apply the substitution that was returned from runUnify to both types and (type-annotated) values
224− tidyUp (ts, sub) = map (\(i, (val, ty)) -> (i, (overTypes (sub $?) val, sub $? ty))) ts
225−
226−-- |
227−-- Check if a value introduces a function
228−--
229−isFunction :: Value -> Bool
230−isFunction (Abs _ _) = True
231−isFunction (TypedValue _ val _) = isFunction val
232−isFunction _ = False
233−
234−-- |
235−-- Check if a value contains a type annotation
236−--
237−isTyped :: (Ident, Value) -> (Ident, (Value, Maybe (Type, Bool)))
238−isTyped (name, TypedValue checkType value ty) = (name, (value, Just (ty, checkType)))
239−isTyped (name, value) = (name, (value, Nothing))
240−
241−-- |
242−-- Map a function over type annotations appearing inside a value
243−--
244−overTypes :: (Type -> Type) -> Value -> Value
245−overTypes f = everywhere (mkT f)
246−
247−-- |
248−-- Replace type class dictionary placeholders with inferred type class dictionaries
249−--
250−replaceTypeClassDictionaries :: ModuleName -> Value -> Check Value
251−replaceTypeClassDictionaries mn = everywhereM (mkM go)
252− where
253− go (TypeClassDictionary constraint dicts) = entails mn dicts constraint
254− go other = return other
255−
256−-- |
257−-- Check that the current set of type class dictionaries entail the specified type class goal, and, if so,
258−-- return a type class dictionary reference.
259−--
260−entails :: ModuleName -> [TypeClassDictionaryInScope] -> (Qualified ProperName, Type) -> Check Value
261−entails moduleName context goal@(className, ty) = do
262− env <- getEnv
263− case go env goal of
264− [] -> throwError $ "No " ++ show className ++ " instance found for " ++ prettyPrintType ty
265− (dict : _) -> return dict
266− where
267− go env (className', ty') =
268− [ mkDictionary (canonicalizeDictionary tcd) args
269− | tcd <- context
270− , filterModule tcd
271− , typeConstructorsAreEqual env moduleName className' (tcdClassName tcd)
272− , subst <- maybeToList $ typeHeadsAreEqual moduleName env ty' (tcdInstanceType tcd)
273− , args <- solveSubgoals env subst (tcdDependencies tcd) ]
274− solveSubgoals :: Environment -> [(String, Type)] -> Maybe [(Qualified ProperName, Type)] -> [Maybe [Value]]
275− solveSubgoals _ _ Nothing = return Nothing
276− solveSubgoals env subst (Just subgoals) = do
277− dict <- mapM (go env) (replaceAllTypeVars subst subgoals)
278− return $ Just dict
279− mkDictionary :: Qualified Ident -> Maybe [Value] -> Value
280− mkDictionary fnName Nothing = Var fnName
281− mkDictionary fnName (Just dicts) = foldl App (Var fnName) dicts
282− filterModule :: TypeClassDictionaryInScope -> Bool
283− filterModule (TypeClassDictionaryInScope { tcdName = Qualified (Just mn) _ }) | mn == moduleName = True
284− filterModule (TypeClassDictionaryInScope { tcdName = Qualified Nothing _ }) = True
285− filterModule _ = False
286− canonicalizeDictionary :: TypeClassDictionaryInScope -> Qualified Ident
287− canonicalizeDictionary (TypeClassDictionaryInScope { tcdType = TCDRegular, tcdName = nm }) = nm
288− canonicalizeDictionary (TypeClassDictionaryInScope { tcdType = TCDAlias nm }) = nm
289−
290−-- |
291−-- Check whether the type heads of two types are equal (for the purposes of type class dictionary lookup),
292−-- and return a substitution from type variables to types which makes the type heads unify.
293−--
294−typeHeadsAreEqual :: ModuleName -> Environment -> Type -> Type -> Maybe [(String, Type)]
295−typeHeadsAreEqual _ _ (Skolem s1 _) (Skolem s2 _) | s1 == s2 = Just []
296−typeHeadsAreEqual _ _ (TypeVar v) t = Just [(v, t)]
297−typeHeadsAreEqual _ _ t (TypeVar v) = Just [(v, t)]
298−typeHeadsAreEqual m e (TypeConstructor c1) (TypeConstructor c2) | typeConstructorsAreEqual e m c1 c2 = Just []
299−typeHeadsAreEqual m e (TypeApp h1 (TypeVar v)) (TypeApp h2 arg) = (:) (v, arg) <$> typeHeadsAreEqual m e h1 h2
300−typeHeadsAreEqual m e t1@(TypeApp _ _) t2@(TypeApp _ (TypeVar _)) = typeHeadsAreEqual m e t2 t1
301−typeHeadsAreEqual _ _ _ _ = Nothing
302−
303−-- |
304−-- Ensure unsolved unification variables do not escape
305−--
306−escapeCheck :: Value -> Type -> UnifyT Type Check ()
307−escapeCheck value ty = do
308− subst <- unifyCurrentSubstitution <$> UnifyT get
309− let visibleUnknowns = nub $ unknowns $ subst $? ty
310− let allUnknowns = findAllTypes value
311− forM_ allUnknowns $ \t -> do
312− let unsolvedUnknowns = nub . unknowns $ subst $? t
313− guardWith "Escape check fails" $ null $ unsolvedUnknowns \\ visibleUnknowns
314−
315−-- |
316−-- Find all type annotations occuring inside a value
317−--
318−findAllTypes :: Value -> [Type]
319−findAllTypes = everything (++) (mkQ [] go)
320− where
321− go (TypedValue _ _ ty) = [ty]
322− go _ = []
323−
324−-- |
325−-- Ensure skolem variables do not escape their scope
326−--
327−skolemEscapeCheck :: Value -> Check ()
328−skolemEscapeCheck (TypedValue False _ _) = return ()
329−skolemEscapeCheck root@(TypedValue _ _ _) =
330− case everythingWithContext [] (++) (mkQ ((,) []) go) root of
331− [] -> return ()
332− ((binding, val) : _) -> throwError $ "Rigid/skolem type variable bound by " ++ maybe "<unknown>" prettyPrintValue binding ++ " has escaped at " ++ prettyPrintValue val
333− where
334− go :: Value -> [(SkolemScope, Value)] -> ([(Maybe Value, Value)], [(SkolemScope, Value)])
335− go val@(TypedValue _ _ (ForAll _ _ (Just sco))) scos = ([], (sco, val) : scos)
336− go val@(TypedValue _ _ ty) scos = case collectSkolems ty \\ map fst scos of
337− (sco : _) -> ([(findBindingScope sco, val)], scos)
338− _ -> ([], scos)
339− where
340− collectSkolems :: Type -> [SkolemScope]
341− collectSkolems = nub . everything (++) (mkQ [] collect)
342− where
343− collect (Skolem _ scope) = [scope]
344− collect _ = []
345− go _ scos = ([], scos)
346− findBindingScope :: SkolemScope -> Maybe Value
347− findBindingScope sco = something (mkQ Nothing go) root
348− where
349− go val@(TypedValue _ _ (ForAll _ _ (Just sco'))) | sco == sco' = Just val
350− go _ = Nothing
351−skolemEscapeCheck val = throwError $ "Untyped value passed to skolemEscapeCheck: " ++ prettyPrintValue val
352−
353−-- |
354−-- Ensure a row contains no duplicate labels
355−--
356−setify :: Type -> Type
357−setify = rowFromList . first (M.toList . M.fromList) . rowToList
358−
359−-- |
360−-- \"Setify\" all rows occuring inside a value
361−--
362−setifyAll :: (D.Data d) => d -> d
363−setifyAll = everywhere (mkT setify)
364−
365−-- |
366−-- Replace outermost unsolved unification variables with named type variables
367−--
368−varIfUnknown :: Type -> Type
369−varIfUnknown ty =
370− let unks = nub $ unknowns ty
371− toName = (:) 't' . show
372− ty' = everywhere (mkT typeToVar) $ ty
373− typeToVar :: Type -> Type
374− typeToVar (TUnknown (Unknown u)) = TypeVar (toName u)
375− typeToVar t = t
376− in mkForAll (sort . map (toName . runUnknown) $ unks) ty'
377−
378−-- |
379−-- Replace named type variables with types
380−--
381−replaceAllTypeVars :: (D.Data d) => [(String, Type)] -> d -> d
382−replaceAllTypeVars = foldl' (\f (name, ty) -> replaceTypeVars name ty . f) id
383−
384−-- |
385−-- Replace named type variables with new unification variables
386−--
387−instantiatePolyTypeWithUnknowns :: Value -> Type -> UnifyT Type Check (Value, Type)
388−instantiatePolyTypeWithUnknowns val (ForAll ident ty _) = do
389− ty' <- replaceVarWithUnknown ident ty
390− instantiatePolyTypeWithUnknowns val ty'
391−instantiatePolyTypeWithUnknowns val (ConstrainedType constraints ty) = do
392− env <- getEnv
393− Just moduleName <- checkCurrentModule <$> get
394− dicts <- getTypeClassDictionaries
395− (_, ty') <- instantiatePolyTypeWithUnknowns (error "Types under a constraint cannot themselves be constrained") ty
396− return (foldl App val (map (flip TypeClassDictionary dicts) (qualifyAllUnqualifiedNames moduleName env constraints)), ty')
397−instantiatePolyTypeWithUnknowns val ty = return (val, ty)
398−
399−-- |
400−-- Replace a single type variable with a new unification variable
401−--
402−replaceVarWithUnknown :: String -> Type -> UnifyT Type Check Type
403−replaceVarWithUnknown ident ty = do
404− tu <- fresh
405− return $ replaceTypeVars ident tu $ ty
406−
407−-- |
408−-- Replace fully applied type synonyms with the @SaturatedTypeSynonym@ data constructor, which helps generate
409−-- better error messages during unification.
410−--
411−replaceAllTypeSynonyms :: (Functor m, MonadState CheckState m, MonadError String m) => (D.Data d) => d -> m d
412−replaceAllTypeSynonyms d = do
413− env <- getEnv
414− Just moduleName <- checkCurrentModule <$> get
415− let syns = map (\((path, name), (args, _)) -> ((path, name), length args)) . M.toList $ typeSynonyms env
416− either throwError return $ saturateAllTypeSynonyms env moduleName syns d
417−
418−-- |
419−-- \"Desaturate\" @SaturatedTypeSynonym@s
420−--
421−desaturateAllTypeSynonyms :: (D.Data d) => d -> d
422−desaturateAllTypeSynonyms = everywhere (mkT replaceSaturatedTypeSynonym)
423− where
424− replaceSaturatedTypeSynonym (SaturatedTypeSynonym name args) = foldl TypeApp (TypeConstructor name) args
425− replaceSaturatedTypeSynonym t = t
426−
427−-- |
428−-- Replace a type synonym and its arguments with the aliased type
429−--
430−expandTypeSynonym :: Qualified ProperName -> [Type] -> UnifyT Type Check Type
431−expandTypeSynonym name args = do
432− env <- getEnv
433− Just moduleName <- checkCurrentModule <$> get
434− case M.lookup (canonicalizeType moduleName env name) (typeSynonyms env) of
435− Just (synArgs, body) -> return $ replaceAllTypeVars (zip synArgs args) body
436− Nothing -> error "Type synonym was not defined"
437−
438−-- |
439−-- Ensure a set of property names and value does not contain duplicate labels
440−--
441−ensureNoDuplicateProperties :: (MonadError String m) => [(String, Value)] -> m ()
442−ensureNoDuplicateProperties ps = guardWith "Duplicate property names" $ length (nub . map fst $ ps) == length ps
443−
444−-- |
445−-- Infer a type for a value, rethrowing any error to provide a more useful error message
446−--
447−infer :: Value -> UnifyT Type Check Value
448−infer val = rethrow (\e -> "Error inferring type of term " ++ prettyPrintValue val ++ ":\n" ++ e) $ infer' val
449−
450−-- |
451−-- Infer a type for a value
452−--
453−infer' :: Value -> UnifyT Type Check Value
454−infer' v@(NumericLiteral _) = return $ TypedValue True v tyNumber
455−infer' v@(StringLiteral _) = return $ TypedValue True v tyString
456−infer' v@(BooleanLiteral _) = return $ TypedValue True v tyBoolean
457−infer' (ArrayLiteral vals) = do
458− ts <- mapM infer vals
459− els <- fresh
460− forM_ ts $ \(TypedValue _ _ t) -> els =?= TypeApp tyArray t
461− return $ TypedValue True (ArrayLiteral ts) els
462−infer' (ObjectLiteral ps) = do
463− ensureNoDuplicateProperties ps
464− ts <- mapM (infer . snd) ps
465− let fields = zipWith (\name (TypedValue _ _ t) -> (name, t)) (map fst ps) ts
466− ty = Object $ rowFromList (fields, REmpty)
467− return $ TypedValue True (ObjectLiteral (zip (map fst ps) ts)) ty
468−infer' (ObjectUpdate o ps) = do
469− ensureNoDuplicateProperties ps
470− row <- fresh
471− newVals <- zipWith (\(name, _) t -> (name, t)) ps <$> mapM (infer . snd) ps
472− let newTys = map (\(name, TypedValue _ _ ty) -> (name, ty)) newVals
473− oldTys <- zip (map fst ps) <$> replicateM (length ps) fresh
474− let oldTy = Object $ rowFromList (oldTys, row)
475− o' <- TypedValue True <$> check o oldTy <*> pure oldTy
476− return $ TypedValue True (ObjectUpdate o' newVals) $ Object $ rowFromList (newTys, row)
477−infer' (Accessor prop val) = do
478− typed@(TypedValue _ _ objTy) <- infer val
479− propTy <- inferProperty objTy prop
480− case propTy of
481− Nothing -> do
482− field <- fresh
483− rest <- fresh
484− _ <- subsumes Nothing objTy (Object (RCons prop field rest))
485− return $ TypedValue True (Accessor prop typed) field
486− Just ty -> return $ TypedValue True (Accessor prop typed) ty
487−infer' (Abs arg ret) = do
488− ty <- fresh
489− Just moduleName <- checkCurrentModule <$> get
490− bindLocalVariables moduleName [(arg, ty)] $ do
491− body@(TypedValue _ _ bodyTy) <- infer' ret
492− return $ TypedValue True (Abs arg body) $ function ty bodyTy
493−infer' (App f arg) = do
494− f'@(TypedValue _ _ ft) <- infer f
495− (ret, app) <- checkFunctionApplication f' ft arg
496− return $ TypedValue True app ret
497−infer' (Var var) = do
498− Just moduleName <- checkCurrentModule <$> get
499− ty <- introduceSkolemScope <=< replaceAllTypeSynonyms <=< lookupVariable moduleName $ var
500− case ty of
501− ConstrainedType constraints ty' -> do
502− env <- getEnv
503− dicts <- getTypeClassDictionaries
504− return $ TypedValue True (foldl App (Var var) (map (flip TypeClassDictionary dicts) (qualifyAllUnqualifiedNames moduleName env constraints))) ty'
505− _ -> return $ TypedValue True (Var var) ty
506−infer' (Block ss) = do
507− ret <- fresh
508− (allCodePathsReturn, _, ss') <- checkBlock M.empty ret ss
509− guardWith "Block is missing a return statement" allCodePathsReturn
510− return $ TypedValue True (Block ss') ret
511−infer' v@(Constructor c) = do
512− env <- getEnv
513− Just moduleName <- checkCurrentModule <$> get
514− case M.lookup (qualify moduleName c) (dataConstructors env) of
515− Nothing -> throwError $ "Constructor " ++ show c ++ " is undefined"
516− Just (ty, _) -> do ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
517− return $ TypedValue True v ty'
518−infer' (Case vals binders) = do
519− ts <- mapM infer vals
520− ret <- fresh
521− binders' <- checkBinders (map (\(TypedValue _ _ t) -> t) ts) ret binders
522− return $ TypedValue True (Case ts binders') ret
523−infer' (IfThenElse cond th el) = do
524− cond' <- check cond tyBoolean
525− v2@(TypedValue _ _ t2) <- infer th
526− v3@(TypedValue _ _ t3) <- infer el
527− t2 =?= t3
528− return $ TypedValue True (IfThenElse cond' v2 v3) t2
529−infer' (TypedValue checkType val ty) = do
530− Just moduleName <- checkCurrentModule <$> get
531− kind <- liftCheck $ kindOf moduleName ty
532− guardWith ("Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
533− ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
534− val' <- if checkType then check val ty' else return val
535− return $ TypedValue True val' ty'
536−infer' _ = error "Invalid argument to infer"
537−
538−-- |
539−-- Infer the type of a property inside a record with a given type
540−--
541−inferProperty :: Type -> String -> UnifyT Type Check (Maybe Type)
542−inferProperty (Object row) prop = do
543− let (props, _) = rowToList row
544− return $ lookup prop props
545−inferProperty (SaturatedTypeSynonym name args) prop = do
546− replaced <- introduceSkolemScope <=< expandTypeSynonym name $ args
547− inferProperty replaced prop
548−inferProperty (ForAll ident ty _) prop = do
549− replaced <- replaceVarWithUnknown ident ty
550− inferProperty replaced prop
551−inferProperty _ _ = return Nothing
552−
553−-- |
554−-- Infer the types of variables brought into scope by a binder
555−--
556−inferBinder :: Type -> Binder -> UnifyT Type Check (M.Map Ident Type)
557−inferBinder _ NullBinder = return M.empty
558−inferBinder val (StringBinder _) = val =?= tyString >> return M.empty
559−inferBinder val (NumberBinder _) = val =?= tyNumber >> return M.empty
560−inferBinder val (BooleanBinder _) = val =?= tyBoolean >> return M.empty
561−inferBinder val (VarBinder name) = return $ M.singleton name val
562−inferBinder val (NullaryBinder ctor) = do
563− env <- getEnv
564− Just moduleName <- checkCurrentModule <$> get
565− case M.lookup (qualify moduleName ctor) (dataConstructors env) of
566− Just (ty, _) -> do
567− _ <- subsumes Nothing ty val
568− return M.empty
569− _ -> throwError $ "Constructor " ++ show ctor ++ " is not defined"
570−inferBinder val (UnaryBinder ctor binder) = do
571− env <- getEnv
572− Just moduleName <- checkCurrentModule <$> get
573− case M.lookup (qualify moduleName ctor) (dataConstructors env) of
574− Just (ty, _) -> do
575− (_, fn) <- instantiatePolyTypeWithUnknowns (error "Data constructor types cannot contains constraints") ty
576− case fn of
577− TypeApp (TypeApp t obj) ret | t == tyFunction -> do
578− _ <- subsumes Nothing val ret
579− inferBinder obj binder
580− _ -> throwError $ "Constructor " ++ show ctor ++ " is not a unary constructor"
581− _ -> throwError $ "Constructor " ++ show ctor ++ " is not defined"
582−inferBinder val (ObjectBinder props) = do
583− row <- fresh
584− rest <- fresh
585− m1 <- inferRowProperties row rest props
586− val =?= Object row
587− return m1
588− where
589− inferRowProperties :: Type -> Type -> [(String, Binder)] -> UnifyT Type Check (M.Map Ident Type)
590− inferRowProperties nrow row [] = nrow =?= row >> return M.empty
591− inferRowProperties nrow row ((name, binder):binders) = do
592− propTy <- fresh
593− m1 <- inferBinder propTy binder
594− m2 <- inferRowProperties nrow (RCons name propTy row) binders
595− return $ m1 `M.union` m2
596−inferBinder val (ArrayBinder binders) = do
597− el <- fresh
598− m1 <- M.unions <$> mapM (inferBinder el) binders
599− val =?= TypeApp tyArray el
600− return m1
601−inferBinder val (ConsBinder headBinder tailBinder) = do
602− el <- fresh
603− m1 <- inferBinder el headBinder
604− m2 <- inferBinder val tailBinder
605− val =?= TypeApp tyArray el
606− return $ m1 `M.union` m2
607−inferBinder val (NamedBinder name binder) = do
608− m <- inferBinder val binder
609− return $ M.insert name val m
610−
611−-- |
612−-- Check the types of the return values in a set of binders in a case statement
613−--
614−checkBinders :: [Type] -> Type -> [([Binder], Maybe Guard, Value)] -> UnifyT Type Check [([Binder], Maybe Guard, Value)]
615−checkBinders _ _ [] = return []
616−checkBinders nvals ret ((binders, grd, val):bs) = do
617− Just moduleName <- checkCurrentModule <$> get
618− m1 <- M.unions <$> zipWithM inferBinder nvals binders
619− r <- bindLocalVariables moduleName (M.toList m1) $ do
620− val' <- TypedValue True <$> check val ret <*> pure ret
621− case grd of
622− Nothing -> return (binders, Nothing, val')
623− Just g -> do
624− g' <- check g tyBoolean
625− return (binders, Just g', val')
626− rs <- checkBinders nvals ret bs
627− return $ r : rs
628−
629−-- |
630−-- Check that a local variable name is not already used
631−--
632−assignVariable :: Ident -> UnifyT Type Check ()
633−assignVariable name = do
634− env <- checkEnv <$> get
635− Just moduleName <- checkCurrentModule <$> get
636− case M.lookup (moduleName, name) (names env) of
637− Just _ -> UnifyT . lift . throwError $ "Variable with name " ++ show name ++ " already exists."
638− _ -> return ()
639−
640−-- |
641−-- Check the type of the return values of a statement, returning whether or not the statement returns on
642−-- all code paths
643−--
644−checkStatement :: M.Map Ident Type -> Type -> Statement -> UnifyT Type Check (Bool, M.Map Ident Type, Statement)
645−checkStatement mass _ (VariableIntroduction name val) = do
646− assignVariable name
647− val'@(TypedValue _ _ t) <- infer val
648− return (False, M.insert name t mass, VariableIntroduction name val')
649−checkStatement mass _ (Assignment ident val) = do
650− val'@(TypedValue _ _ t) <- infer val
651− case M.lookup ident mass of
652− Nothing -> throwError $ "No local variable with name " ++ show ident
653− Just ty -> do t =?= ty
654− return (False, mass, Assignment ident val')
655−checkStatement mass ret (While val inner) = do
656− val' <- check val tyBoolean
657− (allCodePathsReturn, _, inner') <- checkBlock mass ret inner
658− return (allCodePathsReturn, mass, While val' inner')
659−checkStatement mass ret (If ifst) = do
660− (allCodePathsReturn, ifst') <- checkIfStatement mass ret ifst
661− return (allCodePathsReturn, mass, If ifst')
662−checkStatement mass ret (For ident start end inner) = do
663− Just moduleName <- checkCurrentModule <$> get
664− assignVariable ident
665− start' <- check start tyNumber
666− end' <- check end tyNumber
667− (allCodePathsReturn, _, inner') <- bindLocalVariables moduleName [(ident, tyNumber)] $ checkBlock mass ret inner
668− return (allCodePathsReturn, mass, For ident start' end' inner')
669−checkStatement mass ret (Return val) = do
670− val' <- check val ret
671− return (True, mass, Return (TypedValue True val' ret))
672−
673−-- |
674−-- Check the type of an if-then-else statement
675−--
676−checkIfStatement :: M.Map Ident Type -> Type -> IfStatement -> UnifyT Type Check (Bool, IfStatement)
677−checkIfStatement mass ret (IfStatement val thens Nothing) = do
678− val' <- check val tyBoolean
679− (_, _, thens') <- checkBlock mass ret thens
680− return (False, IfStatement val' thens' Nothing)
681−checkIfStatement mass ret (IfStatement val thens (Just elses)) = do
682− val' <- check val tyBoolean
683− (allCodePathsReturn1, _, thens') <- checkBlock mass ret thens
684− (allCodePathsReturn2, elses') <- checkElseStatement mass ret elses
685− return (allCodePathsReturn1 && allCodePathsReturn2, IfStatement val' thens' (Just elses'))
686−
687−-- |
688−-- Check the type of an else statement
689−--
690−checkElseStatement :: M.Map Ident Type -> Type -> ElseStatement -> UnifyT Type Check (Bool, ElseStatement)
691−checkElseStatement mass ret (Else elses) = do
692− (allCodePathsReturn, _, elses') <- checkBlock mass ret elses
693− return (allCodePathsReturn, Else elses')
694−checkElseStatement mass ret (ElseIf ifst) = (id *** ElseIf) <$> checkIfStatement mass ret ifst
695−
696−-- |
697−-- Check the type of the return value of a block of statements
698−--
699−checkBlock :: M.Map Ident Type -> Type -> [Statement] -> UnifyT Type Check (Bool, M.Map Ident Type, [Statement])
700−checkBlock mass _ [] = return (False, mass, [])
701−checkBlock mass ret (s:ss) = do
702− Just moduleName <- checkCurrentModule <$> get
703− (b1, mass1, s') <- checkStatement mass ret s
704− bindLocalVariables moduleName (M.toList mass1) $ case (b1, ss) of
705− (True, []) -> return (True, mass1, [s'])
706− (True, _) -> throwError "Unreachable code"
707− (False, ss') -> do
708− (b, m, ss'') <- checkBlock mass1 ret ss'
709− return (b, m, s':ss'')
710−
711−-- |
712−-- Generate a new skolem constant
713−--
714−newSkolemConstant :: UnifyT Type Check Int
715−newSkolemConstant = runUnknown <$> fresh'
716−
717−-- |
718−-- Generate a new skolem scope
719−--
720−newSkolemScope :: UnifyT Type Check SkolemScope
721−newSkolemScope = SkolemScope . runUnknown <$> fresh'
722−
723−-- |
724−-- Skolemize a type variable by replacing its instances with fresh skolem constants
725−--
726−skolemize :: (D.Data d) => String -> Int -> SkolemScope -> d -> d
727−skolemize ident sko scope d = replaceTypeVars ident (Skolem sko scope) d
728−
729−-- |
730−-- Introduce skolem scope at every occurence of a ForAll
731−--
732−introduceSkolemScope :: Type -> UnifyT Type Check Type
733−introduceSkolemScope = everywhereM (mkM go)
734− where
735− go (ForAll ident ty Nothing) = ForAll ident ty <$> (Just <$> newSkolemScope)
736− go other = return other
737−
738−-- |
739−-- Check the type of a value, rethrowing errors to provide a better error message
740−--
741−check :: Value -> Type -> UnifyT Type Check Value
742−check val ty = rethrow errorMessage $ check' val ty
743− where
744− errorMessage msg =
745− "Error checking type of term " ++
746− prettyPrintValue val ++
747− " against type " ++
748− prettyPrintType ty ++
749− ":\n" ++
750− msg
751−
752−-- |
753−-- Check the type of a value
754−--
755−check' :: Value -> Type -> UnifyT Type Check Value
756−check' val t@(ForAll ident ty _) = do
757− scope <- newSkolemScope
758− sko <- newSkolemConstant
759− let sk = skolemize ident sko scope ty
760− val' <- check val sk
761− return $ TypedValue True val' (ForAll ident ty (Just scope))
762−check' val t@(ConstrainedType constraints ty) = do
763− env <- getEnv
764− Just moduleName <- checkCurrentModule <$> get
765− dictNames <- flip mapM constraints $ \(Qualified _ (ProperName className), _) -> do
766− n <- liftCheck freshDictionaryName
767− return $ Ident $ "__dict_" ++ className ++ "_" ++ show n
768− val' <- withTypeClassDictionaries (zipWith (\name (className, instanceTy) ->
769− TypeClassDictionaryInScope name className instanceTy Nothing TCDRegular) (map (Qualified Nothing) dictNames)
770− (qualifyAllUnqualifiedNames moduleName env constraints)) $
771− check val ty
772− return $ TypedValue True (foldr Abs val' dictNames) t
773−check' val t@(SaturatedTypeSynonym name args) = do
774− ty <- introduceSkolemScope <=< expandTypeSynonym name $ args
775− val' <- check val ty
776− return $ TypedValue True val' ty
777−check' val u@(TUnknown _) = do
778− val'@(TypedValue _ _ ty) <- infer val
779− -- Don't unify an unknown with an inferred polytype
780− (val'', ty') <- instantiatePolyTypeWithUnknowns val' ty
781− ty' =?= u
782− return $ TypedValue True val'' ty'
783−check' v@(NumericLiteral _) t | t == tyNumber =
784− return $ TypedValue True v t
785−check' v@(StringLiteral _) t | t == tyString =
786− return $ TypedValue True v t
787−check' v@(BooleanLiteral _) t | t == tyBoolean =
788− return $ TypedValue True v t
789−check' (ArrayLiteral vals) t@(TypeApp a ty) | a == tyArray = do
790− arr <- ArrayLiteral <$> forM vals (\val -> check val ty)
791− return $ TypedValue True arr t
792−check' (Abs arg ret) ty@(TypeApp (TypeApp t argTy) retTy) | t == tyFunction = do
793− Just moduleName <- checkCurrentModule <$> get
794− ret' <- bindLocalVariables moduleName [(arg, argTy)] $ check ret retTy
795− return $ TypedValue True (Abs arg ret') ty
796−check' (App f arg) ret = do
797− f'@(TypedValue _ _ ft) <- infer f
798− (ret', app) <- checkFunctionApplication f' ft arg
799− subsumes Nothing ret' ret
800− return $ TypedValue True app ret
801−check' v@(Var var) ty = do
802− Just moduleName <- checkCurrentModule <$> get
803− repl <- introduceSkolemScope <=< replaceAllTypeSynonyms <=< lookupVariable moduleName $ var
804− ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
805− v' <- subsumes (Just v) repl ty'
806− case v' of
807− Nothing -> throwError "Unable to check type subsumption"
808− Just v'' -> return $ TypedValue True v'' ty'
809−check' (TypedValue checkType val ty1) ty2 = do
810− Just moduleName <- checkCurrentModule <$> get
811− kind <- liftCheck $ kindOf moduleName ty1
812− guardWith ("Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
813− val' <- subsumes (Just val) ty1 ty2
814− case val' of
815− Nothing -> throwError "Unable to check type subsumption"
816− Just val'' -> do
817− val''' <- if checkType then check val'' ty1 else return val''
818− return $ TypedValue checkType (TypedValue True val''' ty1) ty2
819−check' (Case vals binders) ret = do
820− vals' <- mapM infer vals
821− let ts = map (\(TypedValue _ _ t) -> t) vals'
822− binders' <- checkBinders ts ret binders
823− return $ TypedValue True (Case vals' binders') ret
824−check' (IfThenElse cond th el) ty = do
825− cond' <- check cond tyBoolean
826− th' <- check th ty
827− el' <- check el ty
828− return $ TypedValue True (IfThenElse cond' th' el') ty
829−check' (ObjectLiteral ps) t@(Object row) = do
830− ensureNoDuplicateProperties ps
831− ps' <- checkProperties ps row False
832− return $ TypedValue True (ObjectLiteral ps') t
833−check' (ObjectUpdate obj ps) t@(Object row) = do
834− ensureNoDuplicateProperties ps
835− us <- zip (map fst ps) <$> replicateM (length ps) fresh
836− let (propsToCheck, rest) = rowToList row
837− propsToRemove = map fst ps
838− remainingProps = filter (\(p, _) -> p `notElem` propsToRemove) propsToCheck
839− obj' <- check obj (Object (rowFromList (us ++ remainingProps, rest)))
840− ps' <- checkProperties ps row True
841− return $ TypedValue True (ObjectUpdate obj' ps') t
842−check' (Accessor prop val) ty = do
843− rest <- fresh
844− val' <- check val (Object (RCons prop ty rest))
845− return $ TypedValue True (Accessor prop val') ty
846−check' (Block ss) ret = do
847− (allCodePathsReturn, _, ss') <- checkBlock M.empty ret ss
848− guardWith "Block is missing a return statement" allCodePathsReturn
849− return $ TypedValue True (Block ss') ret
850−check' (Constructor c) ty = do
851− env <- getEnv
852− Just moduleName <- checkCurrentModule <$> get
853− case M.lookup (qualify moduleName c) (dataConstructors env) of
854− Nothing -> throwError $ "Constructor " ++ show c ++ " is undefined"
855− Just (ty1, _) -> do
856− repl <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty1
857− _ <- subsumes Nothing repl ty
858− return $ TypedValue True (Constructor c) ty
859−check' val ty = throwError $ prettyPrintValue val ++ " does not have type " ++ prettyPrintType ty
860−
861−-- |
862−-- Check the type of a collection of named record fields
863−--
864−-- The @lax@ parameter controls whether or not every record member has to be provided. For object updates, this is not the case.
865−--
866−checkProperties :: [(String, Value)] -> Type -> Bool -> UnifyT Type Check [(String, Value)]
867−checkProperties ps row lax = let (ts, r') = rowToList row in go ps ts r' where
868− go [] [] REmpty = return []
869− go [] [] u@(TUnknown _) = do u =?= REmpty
870− return []
871− go [] [] (Skolem _ _) | lax = return []
872− go [] ((p, _): _) _ | lax = return []
873− | otherwise = throwError $ prettyPrintValue (ObjectLiteral ps) ++ " does not have property " ++ p
874− go ((p,_):_) [] REmpty = throwError $ "Property " ++ p ++ " is not present in closed object type " ++ prettyPrintRow row
875− go ((p,v):ps') [] u@(TUnknown _) = do
876− v'@(TypedValue _ _ ty) <- infer v
877− rest <- fresh
878− u =?= RCons p ty rest
879− ps'' <- go ps' [] rest
880− return $ (p, v') : ps''
881− go ((p,v):ps') ts r =
882− case lookup p ts of
883− Nothing -> do
884− v'@(TypedValue _ _ ty) <- infer v
885− rest <- fresh
886− r =?= RCons p ty rest
887− ps'' <- go ps' ts rest
888− return $ (p, v') : ps''
889− Just ty -> do
890− v' <- check v ty
891− ps'' <- go ps' (delete (p, ty) ts) r
892− return $ (p, v') : ps''
893− go _ _ _ = throwError $ prettyPrintValue (ObjectLiteral ps) ++ " does not have type " ++ prettyPrintType (Object row)
894−
895−-- |
896−-- Check the type of a function application, rethrowing errors to provide a better error message
897−--
898−checkFunctionApplication :: Value -> Type -> Value -> UnifyT Type Check (Type, Value)
899−checkFunctionApplication fn fnTy arg = rethrow errorMessage $ checkFunctionApplication' fn fnTy arg
900− where
901− errorMessage msg = "Error applying function of type "
902− ++ prettyPrintType fnTy
903− ++ " to argument " ++ prettyPrintValue arg
904− ++ ":\n" ++ msg
905−
906−-- |
907−-- Check the type of a function application
908−--
909−checkFunctionApplication' :: Value -> Type -> Value -> UnifyT Type Check (Type, Value)
910−checkFunctionApplication' fn (TypeApp (TypeApp tyFunction' argTy) retTy) arg = do
911− tyFunction' =?= tyFunction
912− arg' <- check arg argTy
913− return (retTy, App fn arg')
914−checkFunctionApplication' fn (ForAll ident ty _) arg = do
915− replaced <- replaceVarWithUnknown ident ty
916− checkFunctionApplication fn replaced arg
917−checkFunctionApplication' fn u@(TUnknown _) arg = do
918− arg' <- do
919− TypedValue _ v t <- infer arg
920− (v', t') <- instantiatePolyTypeWithUnknowns arg t
921− return $ TypedValue True v' t'
922− let ty = (\(TypedValue _ _ t) -> t) arg'
923− ret <- fresh
924− u =?= function ty ret
925− return (ret, App fn arg')
926−checkFunctionApplication' fn (SaturatedTypeSynonym name tyArgs) arg = do
927− ty <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
928− checkFunctionApplication fn ty arg
929−checkFunctionApplication' fn (ConstrainedType constraints fnTy) arg = do
930− env <- getEnv
931− dicts <- getTypeClassDictionaries
932− Just moduleName <- checkCurrentModule <$> get
933− checkFunctionApplication' (foldl App fn (map (flip TypeClassDictionary dicts) (qualifyAllUnqualifiedNames moduleName env constraints))) fnTy arg
934−checkFunctionApplication' _ fnTy arg = throwError $ "Cannot apply a function of type "
935− ++ prettyPrintType fnTy
936− ++ " to argument " ++ prettyPrintValue arg
937−
938−-- |
939−-- Check whether one type subsumes another, rethrowing errors to provide a better error message
940−--
941−subsumes :: Maybe Value -> Type -> Type -> UnifyT Type Check (Maybe Value)
942−subsumes val ty1 ty2 = rethrow errorMessage $ subsumes' val ty1 ty2
943− where
944− errorMessage msg = "Error checking that type "
945− ++ prettyPrintType ty1
946− ++ " subsumes type "
947− ++ prettyPrintType ty2
948− ++ ":\n" ++ msg
949−
950−-- |
951−-- Check whether one type subsumes another
952−--
953−subsumes' :: Maybe Value -> Type -> Type -> UnifyT Type Check (Maybe Value)
954−subsumes' val (ForAll ident ty1 _) ty2 = do
955− replaced <- replaceVarWithUnknown ident ty1
956− subsumes val replaced ty2
957−subsumes' val ty1 (ForAll ident ty2 sco) =
958− case sco of
959− Just sco' -> do
960− sko <- newSkolemConstant
961− let sk = skolemize ident sko sco' ty2
962− subsumes val ty1 sk
963− Nothing -> throwError "Skolem variable scope is unspecified"
964−subsumes' val (TypeApp (TypeApp f1 arg1) ret1) (TypeApp (TypeApp f2 arg2) ret2) | f1 == tyFunction && f2 == tyFunction = do
965− subsumes Nothing arg2 arg1
966− subsumes Nothing ret1 ret2
967− return val
968−subsumes' val (SaturatedTypeSynonym name tyArgs) ty2 = do
969− ty1 <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
970− subsumes val ty1 ty2
971−subsumes' val ty1 (SaturatedTypeSynonym name tyArgs) = do
972− ty2 <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
973− subsumes val ty1 ty2
974−subsumes' (Just val) (ConstrainedType constraints ty1) ty2 = do
975− env <- getEnv
976− dicts <- getTypeClassDictionaries
977− Just moduleName <- checkCurrentModule <$> get
978− _ <- subsumes' Nothing ty1 ty2
979− return . Just $ foldl App val (map (flip TypeClassDictionary dicts) (qualifyAllUnqualifiedNames moduleName env constraints))
980−subsumes' val ty1 ty2 = do
981− ty1 =?= ty2
982− return val
983−