@@ -1,978 +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 FlexibleContexts #-}
18−{-# LANGUAGE MultiParamTypeClasses #-}
19−
20−module Language.PureScript.TypeChecker.Types (
21− typesOf
22−) where
23−
24−{-
25− The following functions represent the corresponding type checking judgements:
26−
27− infer
28− Synthesize a type for a value
29−
30− check
31− Check a value has a given type
32−
33− checkProperties
34− Check an object with a given type contains specified properties
35−
36− checkFunctionApplication
37− Check a function of a given type returns a value of another type when applied to its arguments
38−
39− subsumes
40− Check a type subsumes another type
41−-}
42−
43−import Data.List
44−import Data.Maybe (maybeToList, isNothing, isJust, fromMaybe)
45−import qualified Data.Data as D
46−import Data.Generics
47− (everythingWithContext, mkM, everywhereM, everything, mkT,
48− something, everywhere, mkQ)
49−import Data.Generics.Extras
50−
51−import Language.PureScript.Declarations
52−import Language.PureScript.Types
53−import Language.PureScript.Kinds
54−import Language.PureScript.Names
55−import Language.PureScript.TypeClassDictionaries
56−import Language.PureScript.TypeChecker.Monad
57−import Language.PureScript.TypeChecker.Kinds
58−import Language.PureScript.TypeChecker.Synonyms
59−import Language.PureScript.Pretty
60−import Language.PureScript.Environment
61−import qualified Language.PureScript.Constants as C
62−
63−import Control.Monad.State
64−import Control.Monad.Error
65−import Control.Monad.Unify
66−
67−import Control.Applicative
68−import Control.Arrow (Arrow(..))
69−
70−import qualified Data.Map as M
71−import Data.Function (on)
72−import Data.Ord (comparing)
73−
74−instance Partial Type where
75− unknown = TUnknown
76− isUnknown (TUnknown u) = Just u
77− isUnknown _ = Nothing
78−
79−instance Unifiable Check Type where
80− (=?=) = unifyTypes
81−
82−-- |
83−-- Unify two types, updating the current substitution
84−--
85−unifyTypes :: Type -> Type -> UnifyT Type Check ()
86−unifyTypes t1 t2 = rethrow (\e -> "Error unifying type " ++ prettyPrintType t1 ++ " with type " ++ prettyPrintType t2 ++ ":\n" ++ e) $
87− unifyTypes' t1 t2
88− where
89− unifyTypes' (TUnknown u1) (TUnknown u2) | u1 == u2 = return ()
90− unifyTypes' (TUnknown u) t = u =:= t
91− unifyTypes' t (TUnknown u) = u =:= t
92− unifyTypes' (SaturatedTypeSynonym name args) ty = do
93− ty1 <- introduceSkolemScope <=< expandTypeSynonym name $ args
94− ty1 `unifyTypes` ty
95− unifyTypes' ty s@(SaturatedTypeSynonym _ _) = s `unifyTypes` ty
96− unifyTypes' (ForAll ident1 ty1 sc1) (ForAll ident2 ty2 sc2) =
97− case (sc1, sc2) of
98− (Just sc1', Just sc2') -> do
99− sko <- newSkolemConstant
100− let sk1 = skolemize ident1 sko sc1' ty1
101− let sk2 = skolemize ident2 sko sc2' ty2
102− sk1 `unifyTypes` sk2
103− _ -> throwError (prettyPrintType ty1)
104− unifyTypes' (ForAll ident ty1 (Just sc)) ty2 = do
105− sko <- newSkolemConstant
106− let sk = skolemize ident sko sc ty1
107− sk `unifyTypes` ty2
108− unifyTypes' ForAll{} _ = throwError "Skolem variable scope is unspecified"
109− unifyTypes' ty f@ForAll{} = f `unifyTypes` ty
110− unifyTypes' (TypeVar v1) (TypeVar v2) | v1 == v2 = return ()
111− unifyTypes' (TypeConstructor c1) (TypeConstructor c2) =
112− guardWith ("Cannot unify " ++ show c1 ++ " with " ++ show c2 ++ ".") (c1 == c2)
113− unifyTypes' (TypeApp t3 t4) (TypeApp t5 t6) = do
114− t3 `unifyTypes` t5
115− t4 `unifyTypes` t6
116− unifyTypes' (Skolem s1 _) (Skolem s2 _) | s1 == s2 = return ()
117− unifyTypes' r1@RCons{} r2 = unifyRows r1 r2
118− unifyTypes' r1 r2@RCons{} = unifyRows r1 r2
119− unifyTypes' r1@REmpty r2 = unifyRows r1 r2
120− unifyTypes' r1 r2@REmpty = unifyRows r1 r2
121− unifyTypes' t@(ConstrainedType _ _) _ = throwError $ "Attempted to unify a constrained type " ++ prettyPrintType t ++
122− " with another type."
123− unifyTypes' t3 t4@(ConstrainedType _ _) = unifyTypes' t4 t3
124− unifyTypes' t3 t4 = throwError $ "Cannot unify " ++ prettyPrintType t3 ++ " with " ++ prettyPrintType t4 ++ "."
125−
126−-- |
127−-- Unify two rows, updating the current substitution
128−--
129−-- Common labels are first identified, and unified. Remaining labels and types are unified with a
130−-- trailing row unification variable, if appropriate, otherwise leftover labels result in a unification
131−-- error.
132−--
133−unifyRows :: Type -> Type -> UnifyT Type Check ()
134−unifyRows r1 r2 =
135− let
136− (s1, r1') = rowToList r1
137− (s2, r2') = rowToList r2
138− int = [ (t1, t2) | (name, t1) <- s1, (name', t2) <- s2, name == name' ]
139− sd1 = [ (name, t1) | (name, t1) <- s1, name `notElem` map fst s2 ]
140− sd2 = [ (name, t2) | (name, t2) <- s2, name `notElem` map fst s1 ]
141− in do
142− forM_ int (uncurry (=?=))
143− unifyRows' sd1 r1' sd2 r2'
144− where
145− unifyRows' :: [(String, Type)] -> Type -> [(String, Type)] -> Type -> UnifyT Type Check ()
146− unifyRows' [] (TUnknown u) sd r = u =:= rowFromList (sd, r)
147− unifyRows' sd r [] (TUnknown u) = u =:= rowFromList (sd, r)
148− unifyRows' ((name, ty):row) r others u@(TUnknown un) = do
149− occursCheck un ty
150− forM_ row $ \(_, t) -> occursCheck un t
151− u' <- fresh
152− u =?= RCons name ty u'
153− unifyRows' row r others u'
154− unifyRows' [] REmpty [] REmpty = return ()
155− unifyRows' [] (TypeVar v1) [] (TypeVar v2) | v1 == v2 = return ()
156− unifyRows' [] (Skolem s1 _) [] (Skolem s2 _) | s1 == s2 = return ()
157− unifyRows' sd3 r3 sd4 r4 = throwError $ "Cannot unify (" ++ prettyPrintRow (rowFromList (sd3, r3)) ++ ") with (" ++ prettyPrintRow (rowFromList (sd4, r4)) ++ ")."
158−
159−-- |
160−-- Infer the types of multiple mutually-recursive values, and return elaborated values including
161−-- type class dictionaries and type annotations.
162−--
163−typesOf :: Maybe ModuleName -> ModuleName -> [(Ident, Value)] -> Check [(Ident, (Value, Type))]
164−typesOf mainModuleName moduleName vals = do
165− tys <- fmap tidyUp . liftUnify $ do
166− (es, dict, untypedDict) <- typeDictionaryForBindingGroup moduleName vals
167− forM es $ \e -> do
168− triple@(_, (_, ty)) <- typeForBindingGroupElement moduleName e dict untypedDict
169− -- If --main is enabled, need to check that `main` has type Eff eff a for some eff, a
170− when (Just moduleName == mainModuleName && fst e == Ident C.main) $ do
171− [eff, a] <- replicateM 2 fresh
172− ty =?= TypeApp (TypeApp (TypeConstructor (Qualified (Just (ModuleName [ProperName "Control", ProperName "Monad", ProperName "Eff"])) (ProperName "Eff"))) eff) a
173− return triple
174−
175− forM tys $ \(ident, (val, ty)) -> do
176− -- Replace type class dictionary placeholders with actual dictionaries
177− val' <- replaceTypeClassDictionaries moduleName val
178− -- Check skolem variables did not escape their scope
179− skolemEscapeCheck val'
180− -- Remove type synonyms placeholders, remove duplicate row fields, and replace
181− -- top-level unification variables with named type variables.
182− let val'' = overTypes (desaturateAllTypeSynonyms . setifyAll) val'
183− ty' = varIfUnknown . desaturateAllTypeSynonyms . setifyAll $ ty
184− return (ident, (val'', ty'))
185− where
186− -- Apply the substitution that was returned from runUnify to both types and (type-annotated) values
187− tidyUp (ts, sub) = map (\(i, (val, ty)) -> (i, (overTypes (sub $?) val, sub $? ty))) ts
188−
189−typeDictionaryForBindingGroup :: ModuleName -> [(Ident, Value)] -> UnifyT Type Check ([(Ident, (Value, Maybe (Type, Bool)))], M.Map (ModuleName, Ident) (Type, NameKind), [(Ident, Type)])
190−typeDictionaryForBindingGroup moduleName vals = do
191− let
192− -- Map each declaration to a name/value pair, with an optional type, if the declaration is typed
193− es = map isTyped vals
194− -- Filter the typed and untyped declarations
195− typed = filter (isJust . snd . snd) es
196− untyped = filter (isNothing . snd . snd) es
197− -- Make a map of names to typed declarations
198− typedDict = map (\(ident, (_, Just (ty, _))) -> (ident, ty)) typed
199−
200− -- Create fresh unification variables for the types of untyped declarations
201− untypedNames <- replicateM (length untyped) fresh
202−
203− let
204− -- Make a map of names to the unification variables of untyped declarations
205− untypedDict = zip (map fst untyped) untypedNames
206− -- Create the dictionary of all name/type pairs, which will be added to the environment during type checking
207− dict = M.fromList (map (\(ident, ty) -> ((moduleName, ident), (ty, LocalVariable))) $ typedDict ++ untypedDict)
208− return (es, dict, untypedDict)
209−
210−typeForBindingGroupElement :: ModuleName -> (Ident, (Value, Maybe (Type, Bool))) -> M.Map (ModuleName, Ident) (Type, NameKind) -> [(Ident, Type)] -> UnifyT Type Check (Ident, (Value, Type))
211−typeForBindingGroupElement moduleName e@(_, (val, _)) dict untypedDict = do
212− -- If the declaration is a function, it has access to other values in the binding group.
213− -- If not, the generated code might fail at runtime since those values might be undefined.
214− let dict' = if isFunction val then dict else M.empty
215− case e of
216− -- Typed declarations
217− (ident, (val', Just (ty, checkType))) -> do
218− -- Kind check
219− kind <- liftCheck $ kindOf moduleName ty
220− guardWith ("Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
221− -- Check the type with the new names in scope
222− ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
223− val'' <- bindNames dict' $ if checkType
224− then TypedValue True <$> check val' ty' <*> pure ty'
225− else return (TypedValue False val' ty')
226− return (ident, (val'', ty'))
227− -- Untyped declarations
228− (ident, (val', Nothing)) -> do
229− -- Infer the type with the new names in scope
230− TypedValue _ val'' ty <- bindNames dict' $ infer val'
231− ty =?= fromMaybe (error "name not found in dictionary") (lookup ident untypedDict)
232− return (ident, (TypedValue True val'' ty, ty))
233−
234−-- |
235−-- Check if a value introduces a function
236−--
237−isFunction :: Value -> Bool
238−isFunction (Abs _ _) = True
239−isFunction (TypedValue _ val _) = isFunction val
240−isFunction _ = False
241−
242−-- |
243−-- Check if a value contains a type annotation
244−--
245−isTyped :: (Ident, Value) -> (Ident, (Value, Maybe (Type, Bool)))
246−isTyped (name, TypedValue checkType value ty) = (name, (value, Just (ty, checkType)))
247−isTyped (name, value) = (name, (value, Nothing))
248−
249−-- |
250−-- Map a function over type annotations appearing inside a value
251−--
252−overTypes :: (Type -> Type) -> Value -> Value
253−overTypes f = everywhere (mkT f)
254−
255−-- |
256−-- Replace type class dictionary placeholders with inferred type class dictionaries
257−--
258−replaceTypeClassDictionaries :: ModuleName -> Value -> Check Value
259−replaceTypeClassDictionaries mn = everywhereM' (mkM go)
260− where
261− go (TypeClassDictionary constraint dicts) = do
262− env <- getEnv
263− entails env mn dicts constraint
264− go other = return other
265−
266−-- |
267−-- Check that the current set of type class dictionaries entail the specified type class goal, and, if so,
268−-- return a type class dictionary reference.
269−--
270−entails :: Environment -> ModuleName -> [TypeClassDictionaryInScope] -> (Qualified ProperName, [Type]) -> Check Value
271−entails env moduleName context goal@(className, tys) = do
272− case go goal of
273− [] -> throwError $ "No " ++ show className ++ " instance found for " ++ intercalate ", " (map prettyPrintType tys)
274− (dict : _) -> return dict
275− where
276− go (className', tys') =
277− [ mkDictionary (canonicalizeDictionary tcd) args
278− | tcd <- context
279− -- Choose type class dictionaries in scope in the current module
280− , filterModule tcd
281− -- Make sure the type class name matches the one we are trying to satisfy
282− , className' == tcdClassName tcd
283− -- Make sure the type unifies with the type in the type instance definition
284− , subst <- maybeToList . (>>= verifySubstitution) . fmap concat $ zipWithM (typeHeadsAreEqual moduleName env) tys' (tcdInstanceTypes tcd)
285− -- Solve any necessary subgoals
286− , args <- solveSubgoals subst (tcdDependencies tcd) ]
287− -- Create dictionaries for subgoals which still need to be solved by calling go recursively
288− -- E.g. the goal (Show a, Show b) => Show (Either a b) can be satisfied if the current type
289− -- unifies with Either a b, and we can satisfy the subgoals Show a and Show b recursively.
290− solveSubgoals :: [(String, Type)] -> Maybe [(Qualified ProperName, [Type])] -> [Maybe [Value]]
291− solveSubgoals _ Nothing = return Nothing
292− solveSubgoals subst (Just subgoals) = do
293− dict <- mapM (go . second (map (replaceAllTypeVars subst))) subgoals
294− return $ Just dict
295− -- Make a dictionary from subgoal dictionaries by applying the correct function
296− mkDictionary :: Qualified Ident -> Maybe [Value] -> Value
297− mkDictionary fnName Nothing = Var fnName
298− mkDictionary fnName (Just []) = App (Var fnName) (ObjectLiteral [])
299− mkDictionary fnName (Just dicts) = foldl App (Var fnName) dicts
300− -- Filter out type dictionaries which are in scope in the current module
301− filterModule :: TypeClassDictionaryInScope -> Bool
302− filterModule (TypeClassDictionaryInScope { tcdName = Qualified (Just mn) _ }) | mn == moduleName = True
303− filterModule (TypeClassDictionaryInScope { tcdName = Qualified Nothing _ }) = True
304− filterModule _ = False
305− -- Ensure that a substitution is valid
306− verifySubstitution :: [(String, Type)] -> Maybe [(String, Type)]
307− verifySubstitution subst = do
308− let grps = groupBy ((==) `on` fst) subst
309− guard (all (pairwise (unifiesWith env) . map snd) grps)
310− return $ map head grps
311−
312−-- |
313−-- Check all values in a list pairwise match a predicate
314−--
315−pairwise :: (a -> a -> Bool) -> [a] -> Bool
316−pairwise _ [] = True
317−pairwise _ [_] = True
318−pairwise p (x : xs) = all (p x) xs && pairwise p xs
319−
320−-- |
321−-- Check that two types unify
322−--
323−unifiesWith :: Environment -> Type -> Type -> Bool
324−unifiesWith _ (TUnknown _) _ = True
325−unifiesWith _ _ (TUnknown _) = True
326−unifiesWith _ (Skolem s1 _) (Skolem s2 _) | s1 == s2 = True
327−unifiesWith _ (TypeVar v1) (TypeVar v2) | v1 == v2 = True
328−unifiesWith _ (TypeConstructor c1) (TypeConstructor c2) | c1 == c2 = True
329−unifiesWith e (TypeApp h1 t1) (TypeApp h2 t2) = unifiesWith e h1 h2 && unifiesWith e t1 t2
330−unifiesWith e (SaturatedTypeSynonym name args) t2 =
331− case expandTypeSynonym' e name args of
332− Left _ -> False
333− Right t1 -> unifiesWith e t1 t2
334−unifiesWith e t1 t2@(SaturatedTypeSynonym _ _) = unifiesWith e t2 t1
335−unifiesWith _ _ _ = False
336−
337−-- |
338−-- Check whether the type heads of two types are equal (for the purposes of type class dictionary lookup),
339−-- and return a substitution from type variables to types which makes the type heads unify.
340−--
341−typeHeadsAreEqual :: ModuleName -> Environment -> Type -> Type -> Maybe [(String, Type)]
342−typeHeadsAreEqual _ _ (Skolem s1 _) (Skolem s2 _) | s1 == s2 = Just []
343−typeHeadsAreEqual _ _ t (TypeVar v) = Just [(v, t)]
344−typeHeadsAreEqual _ _ (TypeConstructor c1) (TypeConstructor c2) | c1 == c2 = Just []
345−typeHeadsAreEqual m e (TypeApp h1 t1) (TypeApp h2 t2) = (++) <$> typeHeadsAreEqual m e h1 h2 <*> typeHeadsAreEqual m e t1 t2
346−typeHeadsAreEqual m e (SaturatedTypeSynonym name args) t2 = case expandTypeSynonym' e name args of
347− Left _ -> Nothing
348− Right t1 -> typeHeadsAreEqual m e t1 t2
349−typeHeadsAreEqual _ _ _ _ = Nothing
350−
351−-- |
352−-- Ensure skolem variables do not escape their scope
353−--
354−skolemEscapeCheck :: Value -> Check ()
355−skolemEscapeCheck (TypedValue False _ _) = return ()
356−skolemEscapeCheck root@TypedValue{} =
357− -- Every skolem variable is created when a ForAll type is skolemized.
358− -- This determines the scope of that skolem variable, which is copied from the SkolemScope
359− -- field of the ForAll constructor.
360− -- We traverse the tree top-down, and collect any SkolemScopes introduced by ForAlls.
361− -- If a Skolem is encountered whose SkolemScope is not in the current list, we have found
362− -- an escaped skolem variable.
363− case everythingWithContext [] (++) (mkQ ((,) []) go) root of
364− [] -> return ()
365− ((binding, val) : _) -> throwError $ "Rigid/skolem type variable bound by " ++ maybe "<unknown>" prettyPrintValue binding ++ " has escaped at " ++ prettyPrintValue val
366− where
367− go :: Value -> [(SkolemScope, Value)] -> ([(Maybe Value, Value)], [(SkolemScope, Value)])
368− go val@(TypedValue _ _ (ForAll _ _ (Just sco))) scos = ([], (sco, val) : scos)
369− go val@(TypedValue _ _ ty) scos = case collectSkolems ty \\ map fst scos of
370− (sco : _) -> ([(findBindingScope sco, val)], scos)
371− _ -> ([], scos)
372− where
373− collectSkolems :: Type -> [SkolemScope]
374− collectSkolems = nub . everything (++) (mkQ [] collect)
375− where
376− collect (Skolem _ scope) = [scope]
377− collect _ = []
378− go _ scos = ([], scos)
379− findBindingScope :: SkolemScope -> Maybe Value
380− findBindingScope sco = something (mkQ Nothing go') root
381− where
382− go' val@(TypedValue _ _ (ForAll _ _ (Just sco'))) | sco == sco' = Just val
383− go' _ = Nothing
384−skolemEscapeCheck val = throwError $ "Untyped value passed to skolemEscapeCheck: " ++ prettyPrintValue val
385−
386−-- |
387−-- Ensure a row contains no duplicate labels
388−--
389−setify :: Type -> Type
390−setify = rowFromList . first (M.toList . M.fromList) . rowToList
391−
392−-- |
393−-- \"Setify\" all rows occuring inside a value
394−--
395−setifyAll :: (D.Data d) => d -> d
396−setifyAll = everywhere (mkT setify)
397−
398−-- |
399−-- Replace outermost unsolved unification variables with named type variables
400−--
401−varIfUnknown :: Type -> Type
402−varIfUnknown ty =
403− let unks = nub $ unknowns ty
404− toName = (:) 't' . show
405− ty' = everywhere (mkT typeToVar) ty
406− typeToVar :: Type -> Type
407− typeToVar (TUnknown (Unknown u)) = TypeVar (toName u)
408− typeToVar t = t
409− in mkForAll (sort . map (toName . runUnknown) $ unks) ty'
410−
411−-- |
412−-- Remove any ForAlls and ConstrainedType constructors in a type by introducing new unknowns
413−-- or TypeClassDictionary values.
414−--
415−-- This is necessary during type checking to avoid unifying a polymorphic type with a
416−-- unification variable.
417−--
418−instantiatePolyTypeWithUnknowns :: Value -> Type -> UnifyT Type Check (Value, Type)
419−instantiatePolyTypeWithUnknowns val (ForAll ident ty _) = do
420− ty' <- replaceVarWithUnknown ident ty
421− instantiatePolyTypeWithUnknowns val ty'
422−instantiatePolyTypeWithUnknowns val (ConstrainedType constraints ty) = do
423− dicts <- getTypeClassDictionaries
424− (_, ty') <- instantiatePolyTypeWithUnknowns (error "Types under a constraint cannot themselves be constrained") ty
425− return (foldl App val (map (flip TypeClassDictionary dicts) constraints), ty')
426−instantiatePolyTypeWithUnknowns val ty = return (val, ty)
427−
428−-- |
429−-- Replace a single type variable with a new unification variable
430−--
431−replaceVarWithUnknown :: String -> Type -> UnifyT Type Check Type
432−replaceVarWithUnknown ident ty = do
433− tu <- fresh
434− return $ replaceTypeVars ident tu ty
435−
436−-- |
437−-- Replace fully applied type synonyms with the @SaturatedTypeSynonym@ data constructor, which helps generate
438−-- better error messages during unification.
439−--
440−replaceAllTypeSynonyms' :: (D.Data d) => Environment -> d -> Either String d
441−replaceAllTypeSynonyms' env d =
442− let
443− syns = map (\(name, (args, _)) -> (name, length args)) . M.toList $ typeSynonyms env
444− in
445− saturateAllTypeSynonyms syns d
446−
447−replaceAllTypeSynonyms :: (Functor m, Monad m, MonadState CheckState m, MonadError String m) => (D.Data d) => d -> m d
448−replaceAllTypeSynonyms d = do
449− env <- getEnv
450− either throwError return $ replaceAllTypeSynonyms' env d
451−
452−-- |
453−-- \"Desaturate\" @SaturatedTypeSynonym@s
454−--
455−desaturateAllTypeSynonyms :: (D.Data d) => d -> d
456−desaturateAllTypeSynonyms = everywhere (mkT replaceSaturatedTypeSynonym)
457− where
458− replaceSaturatedTypeSynonym (SaturatedTypeSynonym name args) = foldl TypeApp (TypeConstructor name) args
459− replaceSaturatedTypeSynonym t = t
460−
461−-- |
462−-- Replace a type synonym and its arguments with the aliased type
463−--
464−expandTypeSynonym' :: Environment -> Qualified ProperName -> [Type] -> Either String Type
465−expandTypeSynonym' env name args =
466− case M.lookup name (typeSynonyms env) of
467− Just (synArgs, body) -> do
468− let repl = replaceAllTypeVars (zip synArgs args) body
469− replaceAllTypeSynonyms' env repl
470− Nothing -> error "Type synonym was not defined"
471−
472−expandTypeSynonym :: (Functor m, Monad m, MonadState CheckState m, MonadError String m) => Qualified ProperName -> [Type] -> m Type
473−expandTypeSynonym name args = do
474− env <- getEnv
475− either throwError return $ expandTypeSynonym' env name args
476−
477−expandAllTypeSynonyms :: (Functor m, Monad m, MonadState CheckState m, MonadError String m) => Type -> m Type
478−expandAllTypeSynonyms = everywhereM' (mkM go)
479− where
480− go (SaturatedTypeSynonym name args) = expandTypeSynonym name args
481− go other = return other
482−
483−-- |
484−-- Ensure a set of property names and value does not contain duplicate labels
485−--
486−ensureNoDuplicateProperties :: (MonadError String m) => [(String, Value)] -> m ()
487−ensureNoDuplicateProperties ps = guardWith "Duplicate property names" $ length (nub . map fst $ ps) == length ps
488−
489−-- |
490−-- Infer a type for a value, rethrowing any error to provide a more useful error message
491−--
492−infer :: Value -> UnifyT Type Check Value
493−infer val = rethrow (\e -> "Error inferring type of term " ++ prettyPrintValue val ++ ":\n" ++ e) $ infer' val
494−
495−-- |
496−-- Infer a type for a value
497−--
498−infer' :: Value -> UnifyT Type Check Value
499−infer' v@(NumericLiteral _) = return $ TypedValue True v tyNumber
500−infer' v@(StringLiteral _) = return $ TypedValue True v tyString
501−infer' v@(BooleanLiteral _) = return $ TypedValue True v tyBoolean
502−infer' (ArrayLiteral vals) = do
503− ts <- mapM infer vals
504− els <- fresh
505− forM_ ts $ \(TypedValue _ _ t) -> els =?= TypeApp tyArray t
506− return $ TypedValue True (ArrayLiteral ts) els
507−infer' (ObjectLiteral ps) = do
508− ensureNoDuplicateProperties ps
509− ts <- mapM (infer . snd) ps
510− let fields = zipWith (\name (TypedValue _ _ t) -> (name, t)) (map fst ps) ts
511− ty = TypeApp tyObject $ rowFromList (fields, REmpty)
512− return $ TypedValue True (ObjectLiteral (zip (map fst ps) ts)) ty
513−infer' (ObjectUpdate o ps) = do
514− ensureNoDuplicateProperties ps
515− row <- fresh
516− newVals <- zipWith (\(name, _) t -> (name, t)) ps <$> mapM (infer . snd) ps
517− let newTys = map (\(name, TypedValue _ _ ty) -> (name, ty)) newVals
518− oldTys <- zip (map fst ps) <$> replicateM (length ps) fresh
519− let oldTy = TypeApp tyObject $ rowFromList (oldTys, row)
520− o' <- TypedValue True <$> check o oldTy <*> pure oldTy
521− return $ TypedValue True (ObjectUpdate o' newVals) $ TypeApp tyObject $ rowFromList (newTys, row)
522−infer' (Accessor prop val) = do
523− typed@(TypedValue _ _ objTy) <- infer val
524− propTy <- inferProperty objTy prop
525− case propTy of
526− Nothing -> do
527− field <- fresh
528− rest <- fresh
529− _ <- subsumes Nothing objTy (TypeApp tyObject (RCons prop field rest))
530− return $ TypedValue True (Accessor prop typed) field
531− Just ty -> return $ TypedValue True (Accessor prop typed) ty
532−infer' (Abs (Left arg) ret) = do
533− ty <- fresh
534− Just moduleName <- checkCurrentModule <$> get
535− bindLocalVariables moduleName [(arg, ty)] $ do
536− body@(TypedValue _ _ bodyTy) <- infer' ret
537− return $ TypedValue True (Abs (Left arg) body) $ function ty bodyTy
538−infer' (Abs (Right _) _) = error "Binder was not desugared"
539−infer' (App f arg) = do
540− f'@(TypedValue _ _ ft) <- infer f
541− (ret, app) <- checkFunctionApplication f' ft arg Nothing
542− return $ TypedValue True app ret
543−infer' (Var var) = do
544− Just moduleName <- checkCurrentModule <$> get
545− ty <- introduceSkolemScope <=< replaceAllTypeSynonyms <=< lookupVariable moduleName $ var
546− case ty of
547− ConstrainedType constraints ty' -> do
548− dicts <- getTypeClassDictionaries
549− return $ TypedValue True (foldl App (Var var) (map (flip TypeClassDictionary dicts) constraints)) ty'
550− _ -> return $ TypedValue True (Var var) ty
551−infer' v@(Constructor c) = do
552− env <- getEnv
553− case M.lookup c (dataConstructors env) of
554− Nothing -> throwError $ "Constructor " ++ show c ++ " is undefined"
555− Just (_, ty) -> do ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
556− return $ TypedValue True v ty'
557−infer' (Case vals binders) = do
558− ts <- mapM infer vals
559− ret <- fresh
560− binders' <- checkBinders (map (\(TypedValue _ _ t) -> t) ts) ret binders
561− return $ TypedValue True (Case ts binders') ret
562−infer' (IfThenElse cond th el) = do
563− cond' <- check cond tyBoolean
564− v2@(TypedValue _ _ t2) <- infer th
565− v3@(TypedValue _ _ t3) <- infer el
566− t2 =?= t3
567− return $ TypedValue True (IfThenElse cond' v2 v3) t2
568−infer' (Let ds val) = do
569− (ds', val'@(TypedValue _ _ valTy)) <- inferLetBinding [] ds val infer
570− return $ TypedValue True (Let ds' val') valTy
571−infer' (TypedValue checkType val ty) = do
572− Just moduleName <- checkCurrentModule <$> get
573− kind <- liftCheck $ kindOf moduleName ty
574− guardWith ("Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
575− ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
576− val' <- if checkType then check val ty' else return val
577− return $ TypedValue True val' ty'
578−infer' _ = error "Invalid argument to infer"
579−
580−inferLetBinding :: [Declaration] -> [Declaration] -> Value -> (Value -> UnifyT Type Check Value) -> UnifyT Type Check ([Declaration], Value)
581−inferLetBinding seen [] ret j = (,) seen <$> j ret
582−inferLetBinding seen (ValueDeclaration ident nameKind [] Nothing val : rest) ret j = do
583− valTy <- fresh
584− Just moduleName <- checkCurrentModule <$> get
585− TypedValue _ val' valTy' <- bindNames (M.singleton (moduleName, ident) (valTy, nameKind)) $ infer val
586− valTy =?= valTy'
587− bindNames (M.singleton (moduleName, ident) (valTy', nameKind)) $ inferLetBinding (seen ++ [ValueDeclaration ident nameKind [] Nothing val']) rest ret j
588−inferLetBinding seen (BindingGroupDeclaration ds : rest) ret j = do
589− Just moduleName <- checkCurrentModule <$> get
590− (es, dict, untypedDict) <- typeDictionaryForBindingGroup moduleName (map (\(i, _, v) -> (i, v)) ds)
591− ds' <- forM es $ \e -> do
592− (ident, (val', _)) <- typeForBindingGroupElement moduleName e dict untypedDict
593− return $ (ident, LocalVariable, val')
594− bindNames dict $ inferLetBinding (seen ++ [BindingGroupDeclaration ds']) rest ret j
595−inferLetBinding _ _ _ _ = error "Invalid argument to fromValueDeclaration"
596−
597−-- |
598−-- Infer the type of a property inside a record with a given type
599−--
600−inferProperty :: Type -> String -> UnifyT Type Check (Maybe Type)
601−inferProperty (TypeApp obj row) prop | obj == tyObject = do
602− let (props, _) = rowToList row
603− return $ lookup prop props
604−inferProperty (SaturatedTypeSynonym name args) prop = do
605− replaced <- introduceSkolemScope <=< expandTypeSynonym name $ args
606− inferProperty replaced prop
607−inferProperty (ForAll ident ty _) prop = do
608− replaced <- replaceVarWithUnknown ident ty
609− inferProperty replaced prop
610−inferProperty _ _ = return Nothing
611−
612−-- |
613−-- Infer the types of variables brought into scope by a binder
614−--
615−inferBinder :: Type -> Binder -> UnifyT Type Check (M.Map Ident Type)
616−inferBinder _ NullBinder = return M.empty
617−inferBinder val (StringBinder _) = val =?= tyString >> return M.empty
618−inferBinder val (NumberBinder _) = val =?= tyNumber >> return M.empty
619−inferBinder val (BooleanBinder _) = val =?= tyBoolean >> return M.empty
620−inferBinder val (VarBinder name) = return $ M.singleton name val
621−inferBinder val (ConstructorBinder ctor binders) = do
622− env <- getEnv
623− case M.lookup ctor (dataConstructors env) of
624− Just (_, ty) -> do
625− (_, fn) <- instantiatePolyTypeWithUnknowns (error "Data constructor types cannot contain constraints") ty
626− fn' <- replaceAllTypeSynonyms fn
627− go binders fn'
628− where
629− go [] ty' = do
630− _ <- subsumes Nothing val ty'
631− return M.empty
632− go (binder : binders') (TypeApp (TypeApp t obj) ret) | t == tyFunction =
633− M.union <$> inferBinder obj binder <*> go binders' ret
634− go _ _ = throwError $ "Wrong number of arguments to constructor " ++ show ctor
635− _ -> throwError $ "Constructor " ++ show ctor ++ " is not defined"
636−inferBinder val (ObjectBinder props) = do
637− row <- fresh
638− rest <- fresh
639− m1 <- inferRowProperties row rest props
640− val =?= TypeApp tyObject row
641− return m1
642− where
643− inferRowProperties :: Type -> Type -> [(String, Binder)] -> UnifyT Type Check (M.Map Ident Type)
644− inferRowProperties nrow row [] = nrow =?= row >> return M.empty
645− inferRowProperties nrow row ((name, binder):binders) = do
646− propTy <- fresh
647− m1 <- inferBinder propTy binder
648− m2 <- inferRowProperties nrow (RCons name propTy row) binders
649− return $ m1 `M.union` m2
650−inferBinder val (ArrayBinder binders) = do
651− el <- fresh
652− m1 <- M.unions <$> mapM (inferBinder el) binders
653− val =?= TypeApp tyArray el
654− return m1
655−inferBinder val (ConsBinder headBinder tailBinder) = do
656− el <- fresh
657− m1 <- inferBinder el headBinder
658− m2 <- inferBinder val tailBinder
659− val =?= TypeApp tyArray el
660− return $ m1 `M.union` m2
661−inferBinder val (NamedBinder name binder) = do
662− m <- inferBinder val binder
663− return $ M.insert name val m
664−
665−-- |
666−-- Check the types of the return values in a set of binders in a case statement
667−--
668−checkBinders :: [Type] -> Type -> [CaseAlternative] -> UnifyT Type Check [CaseAlternative]
669−checkBinders _ _ [] = return []
670−checkBinders nvals ret (CaseAlternative binders grd val : bs) = do
671− Just moduleName <- checkCurrentModule <$> get
672− m1 <- M.unions <$> zipWithM inferBinder nvals binders
673− r <- bindLocalVariables moduleName (M.toList m1) $ do
674− val' <- TypedValue True <$> check val ret <*> pure ret
675− case grd of
676− Nothing -> return $ CaseAlternative binders Nothing val'
677− Just g -> do
678− g' <- check g tyBoolean
679− return $ CaseAlternative binders (Just g') val'
680− rs <- checkBinders nvals ret bs
681− return $ r : rs
682−
683−-- |
684−-- Generate a new skolem constant
685−--
686−newSkolemConstant :: UnifyT Type Check Int
687−newSkolemConstant = runUnknown <$> fresh'
688−
689−-- |
690−-- Generate a new skolem scope
691−--
692−newSkolemScope :: UnifyT Type Check SkolemScope
693−newSkolemScope = SkolemScope . runUnknown <$> fresh'
694−
695−-- |
696−-- Skolemize a type variable by replacing its instances with fresh skolem constants
697−--
698−skolemize :: String -> Int -> SkolemScope -> Type -> Type
699−skolemize ident sko scope = replaceTypeVars ident (Skolem sko scope)
700−
701−-- |
702−-- Introduce skolem scope at every occurence of a ForAll
703−--
704−introduceSkolemScope :: Type -> UnifyT Type Check Type
705−introduceSkolemScope = everywhereM (mkM go)
706− where
707− go (ForAll ident ty Nothing) = ForAll ident ty <$> (Just <$> newSkolemScope)
708− go other = return other
709−
710−-- |
711−-- Check the type of a value, rethrowing errors to provide a better error message
712−--
713−check :: Value -> Type -> UnifyT Type Check Value
714−check val ty = rethrow errorMessage $ check' val ty
715− where
716− errorMessage msg =
717− "Error checking type of term " ++
718− prettyPrintValue val ++
719− " against type " ++
720− prettyPrintType ty ++
721− ":\n" ++
722− msg
723−
724−-- |
725−-- Check the type of a value
726−--
727−check' :: Value -> Type -> UnifyT Type Check Value
728−check' val (ForAll ident ty _) = do
729− scope <- newSkolemScope
730− sko <- newSkolemConstant
731− let sk = skolemize ident sko scope ty
732− val' <- check val sk
733− return $ TypedValue True val' (ForAll ident ty (Just scope))
734−check' val t@(ConstrainedType constraints ty) = do
735− dictNames <- forM constraints $ \(Qualified _ (ProperName className), _) -> do
736− n <- liftCheck freshDictionaryName
737− return $ Ident $ "__dict_" ++ className ++ "_" ++ show n
738− val' <- withTypeClassDictionaries (zipWith (\name (className, instanceTy) ->
739− TypeClassDictionaryInScope name className instanceTy Nothing TCDRegular) (map (Qualified Nothing) dictNames)
740− constraints) $ check val ty
741− return $ TypedValue True (foldr (Abs . Left) val' dictNames) t
742−check' val (SaturatedTypeSynonym name args) = do
743− ty <- introduceSkolemScope <=< expandTypeSynonym name $ args
744− check val ty
745−check' val u@(TUnknown _) = do
746− val'@(TypedValue _ _ ty) <- infer val
747− -- Don't unify an unknown with an inferred polytype
748− (val'', ty') <- instantiatePolyTypeWithUnknowns val' ty
749− ty' =?= u
750− return $ TypedValue True val'' ty'
751−check' v@(NumericLiteral _) t | t == tyNumber =
752− return $ TypedValue True v t
753−check' v@(StringLiteral _) t | t == tyString =
754− return $ TypedValue True v t
755−check' v@(BooleanLiteral _) t | t == tyBoolean =
756− return $ TypedValue True v t
757−check' (ArrayLiteral vals) t@(TypeApp a ty) = do
758− a =?= tyArray
759− array <- ArrayLiteral <$> forM vals (`check` ty)
760− return $ TypedValue True array t
761−check' (Abs (Left arg) ret) ty@(TypeApp (TypeApp t argTy) retTy) | t == tyFunction = do
762− Just moduleName <- checkCurrentModule <$> get
763− ret' <- bindLocalVariables moduleName [(arg, argTy)] $ check ret retTy
764− return $ TypedValue True (Abs (Left arg) ret') ty
765−check' (Abs (Right _) _) _ = error "Binder was not desugared"
766−check' (App f arg) ret = do
767− f'@(TypedValue _ _ ft) <- infer f
768− (_, app) <- checkFunctionApplication f' ft arg (Just ret)
769− return $ TypedValue True app ret
770−check' v@(Var var) ty = do
771− Just moduleName <- checkCurrentModule <$> get
772− repl <- introduceSkolemScope <=< replaceAllTypeSynonyms <=< lookupVariable moduleName $ var
773− ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
774− v' <- subsumes (Just v) repl ty'
775− case v' of
776− Nothing -> throwError "Unable to check type subsumption"
777− Just v'' -> return $ TypedValue True v'' ty'
778−check' (TypedValue checkType val ty1) ty2 = do
779− Just moduleName <- checkCurrentModule <$> get
780− kind <- liftCheck $ kindOf moduleName ty1
781− guardWith ("Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
782− ty1' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty1
783− val' <- subsumes (Just val) ty1' ty2
784− case val' of
785− Nothing -> throwError "Unable to check type subsumption"
786− Just val'' -> do
787− val''' <- if checkType then check val'' ty1' else return val''
788− return $ TypedValue checkType (TypedValue True val''' ty1) ty2
789−check' (Case vals binders) ret = do
790− vals' <- mapM infer vals
791− let ts = map (\(TypedValue _ _ t) -> t) vals'
792− binders' <- checkBinders ts ret binders
793− return $ TypedValue True (Case vals' binders') ret
794−check' (IfThenElse cond th el) ty = do
795− cond' <- check cond tyBoolean
796− th' <- check th ty
797− el' <- check el ty
798− return $ TypedValue True (IfThenElse cond' th' el') ty
799−check' (ObjectLiteral ps) t@(TypeApp obj row) | obj == tyObject = do
800− ensureNoDuplicateProperties ps
801− ps' <- checkProperties ps row False
802− return $ TypedValue True (ObjectLiteral ps') t
803−check' (ObjectUpdate obj ps) t@(TypeApp o row) | o == tyObject = do
804− ensureNoDuplicateProperties ps
805− us <- zip (map fst ps) <$> replicateM (length ps) fresh
806− let (propsToCheck, rest) = rowToList row
807− propsToRemove = map fst ps
808− remainingProps = filter (\(p, _) -> p `notElem` propsToRemove) propsToCheck
809− obj' <- check obj (TypeApp tyObject (rowFromList (us ++ remainingProps, rest)))
810− ps' <- checkProperties ps row True
811− return $ TypedValue True (ObjectUpdate obj' ps') t
812−check' (Accessor prop val) ty = do
813− rest <- fresh
814− val' <- check val (TypeApp tyObject (RCons prop ty rest))
815− return $ TypedValue True (Accessor prop val') ty
816−check' (Constructor c) ty = do
817− env <- getEnv
818− case M.lookup c (dataConstructors env) of
819− Nothing -> throwError $ "Constructor " ++ show c ++ " is undefined"
820− Just (_, ty1) -> do
821− repl <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty1
822− _ <- subsumes Nothing repl ty
823− return $ TypedValue True (Constructor c) ty
824−check' (Let ds val) ty = do
825− (ds', val') <- inferLetBinding [] ds val (flip check ty)
826− return $ TypedValue True (Let ds' val') ty
827−check' val ty | containsTypeSynonyms ty = do
828− ty' <- introduceSkolemScope <=< expandAllTypeSynonyms $ ty
829− check val ty'
830−check' val ty = throwError $ prettyPrintValue val ++ " does not have type " ++ prettyPrintType ty
831−
832−containsTypeSynonyms :: Type -> Bool
833−containsTypeSynonyms = everything (||) (mkQ False go) where
834− go (SaturatedTypeSynonym _ _) = True
835− go _ = False
836−
837−-- |
838−-- Check the type of a collection of named record fields
839−--
840−-- The @lax@ parameter controls whether or not every record member has to be provided. For object updates, this is not the case.
841−--
842−checkProperties :: [(String, Value)] -> Type -> Bool -> UnifyT Type Check [(String, Value)]
843−checkProperties ps row lax = let (ts, r') = rowToList row in go ps ts r' where
844− go [] [] REmpty = return []
845− go [] [] u@(TUnknown _) = do u =?= REmpty
846− return []
847− go [] [] (Skolem _ _) | lax = return []
848− go [] ((p, _): _) _ | lax = return []
849− | otherwise = throwError $ prettyPrintValue (ObjectLiteral ps) ++ " does not have property " ++ p
850− go ((p,_):_) [] REmpty = throwError $ "Property " ++ p ++ " is not present in closed object type " ++ prettyPrintRow row
851− go ((p,v):ps') [] u@(TUnknown _) = do
852− v'@(TypedValue _ _ ty) <- infer v
853− rest <- fresh
854− u =?= RCons p ty rest
855− ps'' <- go ps' [] rest
856− return $ (p, v') : ps''
857− go ((p,v):ps') ts r =
858− case lookup p ts of
859− Nothing -> do
860− v'@(TypedValue _ _ ty) <- infer v
861− rest <- fresh
862− r =?= RCons p ty rest
863− ps'' <- go ps' ts rest
864− return $ (p, v') : ps''
865− Just ty -> do
866− v' <- check v ty
867− ps'' <- go ps' (delete (p, ty) ts) r
868− return $ (p, v') : ps''
869− go _ _ _ = throwError $ prettyPrintValue (ObjectLiteral ps) ++ " does not have type " ++ prettyPrintType (TypeApp tyObject row)
870−
871−-- |
872−-- Check the type of a function application, rethrowing errors to provide a better error message
873−--
874−checkFunctionApplication :: Value -> Type -> Value -> Maybe Type -> UnifyT Type Check (Type, Value)
875−checkFunctionApplication fn fnTy arg ret = rethrow errorMessage $ checkFunctionApplication' fn fnTy arg ret
876− where
877− errorMessage msg = "Error applying function of type "
878− ++ prettyPrintType fnTy
879− ++ " to argument " ++ prettyPrintValue arg
880− ++ ":\n" ++ msg
881−
882−-- |
883−-- Check the type of a function application
884−--
885−checkFunctionApplication' :: Value -> Type -> Value -> Maybe Type -> UnifyT Type Check (Type, Value)
886−checkFunctionApplication' fn (TypeApp (TypeApp tyFunction' argTy) retTy) arg ret = do
887− tyFunction' =?= tyFunction
888− _ <- maybe (return Nothing) (subsumes Nothing retTy) ret
889− subst <- unifyCurrentSubstitution <$> UnifyT get
890− arg' <- check arg (subst $? argTy)
891− return (retTy, App fn arg')
892−checkFunctionApplication' fn (ForAll ident ty _) arg ret = do
893− replaced <- replaceVarWithUnknown ident ty
894− checkFunctionApplication fn replaced arg ret
895−checkFunctionApplication' fn u@(TUnknown _) arg ret = do
896− arg' <- do
897− TypedValue _ arg' t <- infer arg
898− (arg'', t') <- instantiatePolyTypeWithUnknowns arg' t
899− return $ TypedValue True arg'' t'
900− let ty = (\(TypedValue _ _ t) -> t) arg'
901− ret' <- maybe fresh return ret
902− u =?= function ty ret'
903− return (ret', App fn arg')
904−checkFunctionApplication' fn (SaturatedTypeSynonym name tyArgs) arg ret = do
905− ty <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
906− checkFunctionApplication fn ty arg ret
907−checkFunctionApplication' fn (ConstrainedType constraints fnTy) arg ret = do
908− dicts <- getTypeClassDictionaries
909− checkFunctionApplication' (foldl App fn (map (flip TypeClassDictionary dicts) constraints)) fnTy arg ret
910−checkFunctionApplication' _ fnTy arg _ = throwError $ "Cannot apply a function of type "
911− ++ prettyPrintType fnTy
912− ++ " to argument " ++ prettyPrintValue arg
913−
914−-- |
915−-- Check whether one type subsumes another, rethrowing errors to provide a better error message
916−--
917−subsumes :: Maybe Value -> Type -> Type -> UnifyT Type Check (Maybe Value)
918−subsumes val ty1 ty2 = rethrow errorMessage $ subsumes' val ty1 ty2
919− where
920− errorMessage msg = "Error checking that type "
921− ++ prettyPrintType ty1
922− ++ " subsumes type "
923− ++ prettyPrintType ty2
924− ++ ":\n" ++ msg
925−
926−-- |
927−-- Check whether one type subsumes another
928−--
929−subsumes' :: Maybe Value -> Type -> Type -> UnifyT Type Check (Maybe Value)
930−subsumes' val (ForAll ident ty1 _) ty2 = do
931− replaced <- replaceVarWithUnknown ident ty1
932− subsumes val replaced ty2
933−subsumes' val ty1 (ForAll ident ty2 sco) =
934− case sco of
935− Just sco' -> do
936− sko <- newSkolemConstant
937− let sk = skolemize ident sko sco' ty2
938− subsumes val ty1 sk
939− Nothing -> throwError "Skolem variable scope is unspecified"
940−subsumes' val (TypeApp (TypeApp f1 arg1) ret1) (TypeApp (TypeApp f2 arg2) ret2) | f1 == tyFunction && f2 == tyFunction = do
941− _ <- subsumes Nothing arg2 arg1
942− _ <- subsumes Nothing ret1 ret2
943− return val
944−subsumes' val (SaturatedTypeSynonym name tyArgs) ty2 = do
945− ty1 <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
946− subsumes val ty1 ty2
947−subsumes' val ty1 (SaturatedTypeSynonym name tyArgs) = do
948− ty2 <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
949− subsumes val ty1 ty2
950−subsumes' (Just val) (ConstrainedType constraints ty1) ty2 = do
951− dicts <- getTypeClassDictionaries
952− _ <- subsumes' Nothing ty1 ty2
953− return . Just $ foldl App val (map (flip TypeClassDictionary dicts) constraints)
954−subsumes' val (TypeApp f1 r1) (TypeApp f2 r2) | f1 == tyObject && f2 == tyObject = do
955− let
956− (ts1, r1') = rowToList r1
957− (ts2, r2') = rowToList r2
958− ts1' = sortBy (comparing fst) ts1
959− ts2' = sortBy (comparing fst) ts2
960− go ts1' ts2' r1' r2'
961− return val
962− where
963− go [] ts2 r1' r2' = r1' =?= rowFromList (ts2, r2')
964− go ts1 [] r1' r2' = r2' =?= rowFromList (ts1, r1')
965− go ((p1, ty1) : ts1) ((p2, ty2) : ts2) r1' r2'
966− | p1 == p2 = do _ <- subsumes Nothing ty1 ty2
967− go ts1 ts2 r1' r2'
968− | p1 < p2 = do rest <- fresh
969− r2' =?= RCons p1 ty1 rest
970− go ts1 ((p2, ty2) : ts2) r1' rest
971− | otherwise = do rest <- fresh
972− r1' =?= RCons p2 ty2 rest
973− go ((p1, ty1) : ts1) ts2 rest r2'
974−subsumes' val ty1 ty2@(TypeApp obj _) | obj == tyObject = subsumes val ty2 ty1
975−subsumes' val ty1 ty2 = do
976− ty1 =?= ty2
977− return val
978−