@@ -1,1013 +0,0 @@
1−-----------------------------------------------------------------------------
2−--
3−-- Module : Language.PureScript.TypeChecker.Types
4−-- Copyright : (c) Phil Freeman 2013
5−-- License : MIT
6−--
7−-- Maintainer : Phil Freeman <paf31@cantab.net>
8−-- Stability : experimental
9−-- Portability :
10−--
11−-- |
12−-- This module implements the type checker
13−--
14−-----------------------------------------------------------------------------
15−
16−{-# OPTIONS_GHC -fno-warn-orphans #-}
17−{-# LANGUAGE FlexibleInstances #-}
18−{-# LANGUAGE FlexibleContexts #-}
19−{-# LANGUAGE MultiParamTypeClasses #-}
20−
21−module Language.PureScript.TypeChecker.Types (
22− typesOf
23−) where
24−
25−{-
26− The following functions represent the corresponding type checking judgements:
27−
28− infer
29− Synthesize a type for a value
30−
31− check
32− Check a value has a given type
33−
34− checkProperties
35− Check an object with a given type contains specified properties
36−
37− checkFunctionApplication
38− Check a function of a given type returns a value of another type when applied to its arguments
39−
40− subsumes
41− Check a type subsumes another type
42−-}
43−
44−import Data.List
45−import Data.Maybe (maybeToList, isNothing, isJust, fromMaybe)
46−import qualified Data.Data as D
47−import Data.Generics
48− (everythingWithContext, mkM, everywhereM, everything, mkT,
49− something, everywhere, mkQ)
50−import Data.Generics.Extras
51−
52−import Language.PureScript.Declarations
53−import Language.PureScript.Types
54−import Language.PureScript.Kinds
55−import Language.PureScript.Names
56−import Language.PureScript.TypeClassDictionaries
57−import Language.PureScript.TypeChecker.Monad
58−import Language.PureScript.TypeChecker.Kinds
59−import Language.PureScript.TypeChecker.Synonyms
60−import Language.PureScript.Pretty
61−import Language.PureScript.Environment
62−import Language.PureScript.Errors
63−import qualified Language.PureScript.Constants as C
64−
65−import Control.Monad.State
66−import Control.Monad.Error
67−import Control.Monad.Unify
68−
69−import Control.Applicative
70−import Control.Arrow (Arrow(..))
71−
72−import qualified Data.Map as M
73−import Data.Function (on)
74−import Data.Ord (comparing)
75−import Data.Monoid ((<>))
76−
77−instance Partial Type where
78− unknown = TUnknown
79− isUnknown (TUnknown u) = Just u
80− isUnknown _ = Nothing
81−
82−instance Unifiable Check Type where
83− (=?=) = unifyTypes
84−
85−-- |
86−-- Unify two types, updating the current substitution
87−--
88−unifyTypes :: Type -> Type -> UnifyT Type Check ()
89−unifyTypes t1 t2 = rethrow (mkErrorStack ("Error unifying type " ++ prettyPrintType t1 ++ " with type " ++ prettyPrintType t2) Nothing <>) $
90− unifyTypes' t1 t2
91− where
92− unifyTypes' (TUnknown u1) (TUnknown u2) | u1 == u2 = return ()
93− unifyTypes' (TUnknown u) t = u =:= t
94− unifyTypes' t (TUnknown u) = u =:= t
95− unifyTypes' (SaturatedTypeSynonym name args) ty = do
96− ty1 <- introduceSkolemScope <=< expandTypeSynonym name $ args
97− ty1 `unifyTypes` ty
98− unifyTypes' ty s@(SaturatedTypeSynonym _ _) = s `unifyTypes` ty
99− unifyTypes' (ForAll ident1 ty1 sc1) (ForAll ident2 ty2 sc2) =
100− case (sc1, sc2) of
101− (Just sc1', Just sc2') -> do
102− sko <- newSkolemConstant
103− let sk1 = skolemize ident1 sko sc1' ty1
104− let sk2 = skolemize ident2 sko sc2' ty2
105− sk1 `unifyTypes` sk2
106− _ -> error "Skolemized type variable was not given a scope"
107− unifyTypes' (ForAll ident ty1 (Just sc)) ty2 = do
108− sko <- newSkolemConstant
109− let sk = skolemize ident sko sc ty1
110− sk `unifyTypes` ty2
111− unifyTypes' ForAll{} _ = throwError . strMsg $ "Skolem variable scope is unspecified"
112− unifyTypes' ty f@ForAll{} = f `unifyTypes` ty
113− unifyTypes' (TypeVar v1) (TypeVar v2) | v1 == v2 = return ()
114− unifyTypes' (TypeConstructor c1) (TypeConstructor c2) =
115− guardWith (strMsg ("Cannot unify " ++ show c1 ++ " with " ++ show c2 ++ ".")) (c1 == c2)
116− unifyTypes' (TypeApp t3 t4) (TypeApp t5 t6) = do
117− t3 `unifyTypes` t5
118− t4 `unifyTypes` t6
119− unifyTypes' (Skolem s1 _) (Skolem s2 _) | s1 == s2 = return ()
120− unifyTypes' r1@RCons{} r2 = unifyRows r1 r2
121− unifyTypes' r1 r2@RCons{} = unifyRows r1 r2
122− unifyTypes' r1@REmpty r2 = unifyRows r1 r2
123− unifyTypes' r1 r2@REmpty = unifyRows r1 r2
124− unifyTypes' t@(ConstrainedType _ _) _ = throwError . strMsg $ "Attempted to unify a constrained type " ++ prettyPrintType t ++ " with another type."
125− unifyTypes' t3 t4@(ConstrainedType _ _) = unifyTypes' t4 t3
126− unifyTypes' t3 t4 = throwError . strMsg $ "Cannot unify " ++ prettyPrintType t3 ++ " with " ++ prettyPrintType t4 ++ "."
127−
128−-- |
129−-- Unify two rows, updating the current substitution
130−--
131−-- Common labels are first identified, and unified. Remaining labels and types are unified with a
132−-- trailing row unification variable, if appropriate, otherwise leftover labels result in a unification
133−-- error.
134−--
135−unifyRows :: Type -> Type -> UnifyT Type Check ()
136−unifyRows r1 r2 =
137− let
138− (s1, r1') = rowToList r1
139− (s2, r2') = rowToList r2
140− int = [ (t1, t2) | (name, t1) <- s1, (name', t2) <- s2, name == name' ]
141− sd1 = [ (name, t1) | (name, t1) <- s1, name `notElem` map fst s2 ]
142− sd2 = [ (name, t2) | (name, t2) <- s2, name `notElem` map fst s1 ]
143− in do
144− forM_ int (uncurry (=?=))
145− unifyRows' sd1 r1' sd2 r2'
146− where
147− unifyRows' :: [(String, Type)] -> Type -> [(String, Type)] -> Type -> UnifyT Type Check ()
148− unifyRows' [] (TUnknown u) sd r = u =:= rowFromList (sd, r)
149− unifyRows' sd r [] (TUnknown u) = u =:= rowFromList (sd, r)
150− unifyRows' ((name, ty):row) r others u@(TUnknown un) = do
151− occursCheck un ty
152− forM_ row $ \(_, t) -> occursCheck un t
153− u' <- fresh
154− u =?= RCons name ty u'
155− unifyRows' row r others u'
156− unifyRows' [] REmpty [] REmpty = return ()
157− unifyRows' [] (TypeVar v1) [] (TypeVar v2) | v1 == v2 = return ()
158− unifyRows' [] (Skolem s1 _) [] (Skolem s2 _) | s1 == s2 = return ()
159− unifyRows' sd3 r3 sd4 r4 = throwError . strMsg $ "Cannot unify (" ++ prettyPrintRow (rowFromList (sd3, r3)) ++ ") with (" ++ prettyPrintRow (rowFromList (sd4, r4)) ++ ")"
160−
161−-- |
162−-- Infer the types of multiple mutually-recursive values, and return elaborated values including
163−-- type class dictionaries and type annotations.
164−--
165−typesOf :: Maybe ModuleName -> ModuleName -> [(Ident, Value)] -> Check [(Ident, (Value, Type))]
166−typesOf mainModuleName moduleName vals = do
167− tys <- fmap tidyUp . liftUnify $ do
168− (es, dict, untypedDict) <- typeDictionaryForBindingGroup moduleName vals
169− forM es $ \e -> do
170− triple@(_, (_, ty)) <- typeForBindingGroupElement moduleName e dict untypedDict
171− -- If --main is enabled, need to check that `main` has type Eff eff a for some eff, a
172− when (Just moduleName == mainModuleName && fst e == Ident C.main) $ do
173− [eff, a] <- replicateM 2 fresh
174− ty =?= TypeApp (TypeApp (TypeConstructor (Qualified (Just (ModuleName [ProperName "Control", ProperName "Monad", ProperName "Eff"])) (ProperName "Eff"))) eff) a
175− return triple
176−
177− forM tys $ \(ident, (val, ty)) -> do
178− -- Replace type class dictionary placeholders with actual dictionaries
179− val' <- replaceTypeClassDictionaries moduleName val
180− -- Check skolem variables did not escape their scope
181− skolemEscapeCheck val'
182− -- Remove type synonyms placeholders, remove duplicate row fields, and replace
183− -- top-level unification variables with named type variables.
184− let val'' = overTypes (desaturateAllTypeSynonyms . setifyAll) val'
185− ty' = varIfUnknown . desaturateAllTypeSynonyms . setifyAll $ ty
186− return (ident, (val'', ty'))
187− where
188− -- Apply the substitution that was returned from runUnify to both types and (type-annotated) values
189− tidyUp (ts, sub) = map (\(i, (val, ty)) -> (i, (overTypes (sub $?) val, sub $? ty))) ts
190−
191−typeDictionaryForBindingGroup :: ModuleName -> [(Ident, Value)] -> UnifyT Type Check ([(Ident, (Value, Maybe (Type, Bool)))], M.Map (ModuleName, Ident) (Type, NameKind), [(Ident, Type)])
192−typeDictionaryForBindingGroup moduleName vals = do
193− let
194− -- Map each declaration to a name/value pair, with an optional type, if the declaration is typed
195− es = map isTyped vals
196− -- Filter the typed and untyped declarations
197− typed = filter (isJust . snd . snd) es
198− untyped = filter (isNothing . snd . snd) es
199− -- Make a map of names to typed declarations
200− typedDict = map (\(ident, (_, Just (ty, _))) -> (ident, ty)) typed
201−
202− -- Create fresh unification variables for the types of untyped declarations
203− untypedNames <- replicateM (length untyped) fresh
204−
205− let
206− -- Make a map of names to the unification variables of untyped declarations
207− untypedDict = zip (map fst untyped) untypedNames
208− -- Create the dictionary of all name/type pairs, which will be added to the environment during type checking
209− dict = M.fromList (map (\(ident, ty) -> ((moduleName, ident), (ty, LocalVariable))) $ typedDict ++ untypedDict)
210− return (es, dict, untypedDict)
211−
212−typeForBindingGroupElement :: ModuleName -> (Ident, (Value, Maybe (Type, Bool))) -> M.Map (ModuleName, Ident) (Type, NameKind) -> [(Ident, Type)] -> UnifyT Type Check (Ident, (Value, Type))
213−typeForBindingGroupElement moduleName e@(_, (val, _)) dict untypedDict = do
214− -- If the declaration is a function, it has access to other values in the binding group.
215− -- If not, the generated code might fail at runtime since those values might be undefined.
216− let dict' = if isFunction val then dict else M.empty
217− case e of
218− -- Typed declarations
219− (ident, (val', Just (ty, checkType))) -> do
220− -- Kind check
221− kind <- liftCheck $ kindOf moduleName ty
222− guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
223− -- Check the type with the new names in scope
224− ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
225− val'' <- bindNames dict' $ if checkType
226− then TypedValue True <$> check val' ty' <*> pure ty'
227− else return (TypedValue False val' ty')
228− return (ident, (val'', ty'))
229− -- Untyped declarations
230− (ident, (val', Nothing)) -> do
231− -- Infer the type with the new names in scope
232− TypedValue _ val'' ty <- bindNames dict' $ infer val'
233− ty =?= fromMaybe (error "name not found in dictionary") (lookup ident untypedDict)
234− return (ident, (TypedValue True val'' ty, ty))
235−
236−-- |
237−-- Check if a value introduces a function
238−--
239−isFunction :: Value -> Bool
240−isFunction (Abs _ _) = True
241−isFunction (TypedValue _ val _) = isFunction val
242−isFunction (PositionedValue _ val) = isFunction val
243−isFunction _ = False
244−
245−-- |
246−-- Check if a value contains a type annotation
247−--
248−isTyped :: (Ident, Value) -> (Ident, (Value, Maybe (Type, Bool)))
249−isTyped (name, TypedValue checkType value ty) = (name, (value, Just (ty, checkType)))
250−isTyped (name, value) = (name, (value, Nothing))
251−
252−-- |
253−-- Map a function over type annotations appearing inside a value
254−--
255−overTypes :: (Type -> Type) -> Value -> Value
256−overTypes f = everywhere (mkT f)
257−
258−-- |
259−-- Replace type class dictionary placeholders with inferred type class dictionaries
260−--
261−replaceTypeClassDictionaries :: ModuleName -> Value -> Check Value
262−replaceTypeClassDictionaries mn = everywhereM' (mkM go)
263− where
264− go (TypeClassDictionary 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− deriving (Show, Eq)
287−
288−-- |
289−-- Check that the current set of type class dictionaries entail the specified type class goal, and, if so,
290−-- return a type class dictionary reference.
291−--
292−entails :: Environment -> ModuleName -> [TypeClassDictionaryInScope] -> (Qualified ProperName, [Type]) -> Check Value
293−entails env moduleName context goal@(className, tys) = do
294− case nub (go goal) of
295− [] -> throwError . strMsg $ "No instance found for " ++ show className ++ " " ++ unwords (map prettyPrintTypeAtom tys)
296− [dict] -> return (dictionaryValueToValue dict)
297− _ -> throwError . strMsg $ "Overlapping instances found for " ++ show className ++ " " ++ unwords (map prettyPrintTypeAtom tys)
298− where
299− go (className', tys') =
300− [ mkDictionary (canonicalizeDictionary tcd) args
301− | tcd <- context
302− -- Choose type class dictionaries in scope in the current module
303− , filterModule tcd
304− -- Make sure the type class name matches the one we are trying to satisfy
305− , className' == tcdClassName tcd
306− -- Make sure the type unifies with the type in the type instance definition
307− , subst <- maybeToList . (>>= verifySubstitution) . fmap concat $ zipWithM (typeHeadsAreEqual moduleName env) tys' (tcdInstanceTypes tcd)
308− -- Solve any necessary subgoals
309− , args <- solveSubgoals subst (tcdDependencies tcd) ]
310− -- Create dictionaries for subgoals which still need to be solved by calling go recursively
311− -- E.g. the goal (Show a, Show b) => Show (Either a b) can be satisfied if the current type
312− -- unifies with Either a b, and we can satisfy the subgoals Show a and Show b recursively.
313− solveSubgoals :: [(String, Type)] -> Maybe [(Qualified ProperName, [Type])] -> [Maybe [DictionaryValue]]
314− solveSubgoals _ Nothing = return Nothing
315− solveSubgoals subst (Just subgoals) = do
316− dict <- mapM (go . second (map (replaceAllTypeVars subst))) subgoals
317− return $ Just dict
318− -- Make a dictionary from subgoal dictionaries by applying the correct function
319− mkDictionary :: Qualified Ident -> Maybe [DictionaryValue] -> DictionaryValue
320− mkDictionary fnName Nothing = LocalDictionaryValue fnName
321− mkDictionary fnName (Just []) = GlobalDictionaryValue fnName
322− mkDictionary fnName (Just dicts) = DependentDictionaryValue fnName dicts
323− -- Turn a DictionaryValue into a Value
324− dictionaryValueToValue :: DictionaryValue -> Value
325− dictionaryValueToValue (LocalDictionaryValue fnName) = Var fnName
326− dictionaryValueToValue (GlobalDictionaryValue fnName) = App (Var fnName) (ObjectLiteral [])
327− dictionaryValueToValue (DependentDictionaryValue fnName dicts) = foldl App (Var fnName) (map dictionaryValueToValue dicts)
328− -- Filter out type dictionaries which are in scope in the current module
329− filterModule :: TypeClassDictionaryInScope -> Bool
330− filterModule (TypeClassDictionaryInScope { tcdName = Qualified (Just mn) _ }) | mn == moduleName = True
331− filterModule (TypeClassDictionaryInScope { tcdName = Qualified Nothing _ }) = True
332− filterModule _ = False
333− -- Ensure that a substitution is valid
334− verifySubstitution :: [(String, Type)] -> Maybe [(String, Type)]
335− verifySubstitution subst = do
336− let grps = groupBy ((==) `on` fst) subst
337− guard (all (pairwise (unifiesWith env) . map snd) grps)
338− return $ map head grps
339−
340−-- |
341−-- Check all values in a list pairwise match a predicate
342−--
343−pairwise :: (a -> a -> Bool) -> [a] -> Bool
344−pairwise _ [] = True
345−pairwise _ [_] = True
346−pairwise p (x : xs) = all (p x) xs && pairwise p xs
347−
348−-- |
349−-- Check that two types unify
350−--
351−unifiesWith :: Environment -> Type -> Type -> Bool
352−unifiesWith _ (TUnknown _) _ = True
353−unifiesWith _ _ (TUnknown _) = True
354−unifiesWith _ (Skolem s1 _) (Skolem s2 _) | s1 == s2 = True
355−unifiesWith _ (TypeVar v1) (TypeVar v2) | v1 == v2 = True
356−unifiesWith _ (TypeConstructor c1) (TypeConstructor c2) | c1 == c2 = True
357−unifiesWith e (TypeApp h1 t1) (TypeApp h2 t2) = unifiesWith e h1 h2 && unifiesWith e t1 t2
358−unifiesWith e (SaturatedTypeSynonym name args) t2 =
359− case expandTypeSynonym' e name args of
360− Left _ -> False
361− Right t1 -> unifiesWith e t1 t2
362−unifiesWith e t1 t2@(SaturatedTypeSynonym _ _) = unifiesWith e t2 t1
363−unifiesWith _ _ _ = False
364−
365−-- |
366−-- Check whether the type heads of two types are equal (for the purposes of type class dictionary lookup),
367−-- and return a substitution from type variables to types which makes the type heads unify.
368−--
369−typeHeadsAreEqual :: ModuleName -> Environment -> Type -> Type -> Maybe [(String, Type)]
370−typeHeadsAreEqual _ _ (Skolem s1 _) (Skolem s2 _) | s1 == s2 = Just []
371−typeHeadsAreEqual _ _ t (TypeVar v) = Just [(v, t)]
372−typeHeadsAreEqual _ _ (TypeConstructor c1) (TypeConstructor c2) | c1 == c2 = Just []
373−typeHeadsAreEqual m e (TypeApp h1 t1) (TypeApp h2 t2) = (++) <$> typeHeadsAreEqual m e h1 h2 <*> typeHeadsAreEqual m e t1 t2
374−typeHeadsAreEqual m e (SaturatedTypeSynonym name args) t2 = case expandTypeSynonym' e name args of
375− Left _ -> Nothing
376− Right t1 -> typeHeadsAreEqual m e t1 t2
377−typeHeadsAreEqual _ _ _ _ = Nothing
378−
379−-- |
380−-- Ensure skolem variables do not escape their scope
381−--
382−skolemEscapeCheck :: Value -> Check ()
383−skolemEscapeCheck (TypedValue False _ _) = return ()
384−skolemEscapeCheck root@TypedValue{} =
385− -- Every skolem variable is created when a ForAll type is skolemized.
386− -- This determines the scope of that skolem variable, which is copied from the SkolemScope
387− -- field of the ForAll constructor.
388− -- We traverse the tree top-down, and collect any SkolemScopes introduced by ForAlls.
389− -- If a Skolem is encountered whose SkolemScope is not in the current list, we have found
390− -- an escaped skolem variable.
391− case everythingWithContext [] (++) (mkQ ((,) []) go) root of
392− [] -> return ()
393− ((binding, val) : _) -> throwError $ mkErrorStack ("Rigid/skolem type variable " ++ maybe "" (("bound by " ++) . prettyPrintValue) binding ++ " has escaped.") (Just (ValueError val))
394− where
395− go :: Value -> [(SkolemScope, Value)] -> ([(Maybe Value, Value)], [(SkolemScope, Value)])
396− go val@(TypedValue _ _ (ForAll _ _ (Just sco))) scos = ([], (sco, val) : scos)
397− go val@(TypedValue _ _ ty) scos = case collectSkolems ty \\ map fst scos of
398− (sco : _) -> ([(findBindingScope sco, val)], scos)
399− _ -> ([], scos)
400− where
401− collectSkolems :: Type -> [SkolemScope]
402− collectSkolems = nub . everything (++) (mkQ [] collect)
403− where
404− collect (Skolem _ scope) = [scope]
405− collect _ = []
406− go _ scos = ([], scos)
407− findBindingScope :: SkolemScope -> Maybe Value
408− findBindingScope sco = something (mkQ Nothing go') root
409− where
410− go' val@(TypedValue _ _ (ForAll _ _ (Just sco'))) | sco == sco' = Just val
411− go' _ = Nothing
412−skolemEscapeCheck val = throwError $ mkErrorStack "Untyped value passed to skolemEscapeCheck" (Just (ValueError val))
413−
414−-- |
415−-- Ensure a row contains no duplicate labels
416−--
417−setify :: Type -> Type
418−setify = rowFromList . first (M.toList . M.fromList) . rowToList
419−
420−-- |
421−-- \"Setify\" all rows occuring inside a value
422−--
423−setifyAll :: (D.Data d) => d -> d
424−setifyAll = everywhere (mkT setify)
425−
426−-- |
427−-- Replace outermost unsolved unification variables with named type variables
428−--
429−varIfUnknown :: Type -> Type
430−varIfUnknown ty =
431− let unks = nub $ unknowns ty
432− toName = (:) 't' . show
433− ty' = everywhere (mkT typeToVar) ty
434− typeToVar :: Type -> Type
435− typeToVar (TUnknown (Unknown u)) = TypeVar (toName u)
436− typeToVar t = t
437− in mkForAll (sort . map (toName . runUnknown) $ unks) ty'
438−
439−-- |
440−-- Remove any ForAlls and ConstrainedType constructors in a type by introducing new unknowns
441−-- or TypeClassDictionary values.
442−--
443−-- This is necessary during type checking to avoid unifying a polymorphic type with a
444−-- unification variable.
445−--
446−instantiatePolyTypeWithUnknowns :: Value -> Type -> UnifyT Type Check (Value, Type)
447−instantiatePolyTypeWithUnknowns val (ForAll ident ty _) = do
448− ty' <- replaceVarWithUnknown ident ty
449− instantiatePolyTypeWithUnknowns val ty'
450−instantiatePolyTypeWithUnknowns val (ConstrainedType constraints ty) = do
451− dicts <- getTypeClassDictionaries
452− (_, ty') <- instantiatePolyTypeWithUnknowns (error "Types under a constraint cannot themselves be constrained") ty
453− return (foldl App val (map (flip TypeClassDictionary dicts) constraints), ty')
454−instantiatePolyTypeWithUnknowns val ty = return (val, ty)
455−
456−-- |
457−-- Replace a single type variable with a new unification variable
458−--
459−replaceVarWithUnknown :: String -> Type -> UnifyT Type Check Type
460−replaceVarWithUnknown ident ty = do
461− tu <- fresh
462− return $ replaceTypeVars ident tu ty
463−
464−-- |
465−-- Replace fully applied type synonyms with the @SaturatedTypeSynonym@ data constructor, which helps generate
466−-- better error messages during unification.
467−--
468−replaceAllTypeSynonyms' :: (D.Data d) => Environment -> d -> Either String d
469−replaceAllTypeSynonyms' env d =
470− let
471− syns = map (\(name, (args, _)) -> (name, length args)) . M.toList $ typeSynonyms env
472− in
473− saturateAllTypeSynonyms syns d
474−
475−replaceAllTypeSynonyms :: (Error e, Functor m, Monad m, MonadState CheckState m, MonadError e m) => (D.Data d) => d -> m d
476−replaceAllTypeSynonyms d = do
477− env <- getEnv
478− either (throwError . strMsg) return $ replaceAllTypeSynonyms' env d
479−
480−-- |
481−-- \"Desaturate\" @SaturatedTypeSynonym@s
482−--
483−desaturateAllTypeSynonyms :: (D.Data d) => d -> d
484−desaturateAllTypeSynonyms = everywhere (mkT replaceSaturatedTypeSynonym)
485− where
486− replaceSaturatedTypeSynonym (SaturatedTypeSynonym name args) = foldl TypeApp (TypeConstructor name) args
487− replaceSaturatedTypeSynonym t = t
488−
489−-- |
490−-- Replace a type synonym and its arguments with the aliased type
491−--
492−expandTypeSynonym' :: Environment -> Qualified ProperName -> [Type] -> Either String Type
493−expandTypeSynonym' env name args =
494− case M.lookup name (typeSynonyms env) of
495− Just (synArgs, body) -> do
496− let repl = replaceAllTypeVars (zip synArgs args) body
497− replaceAllTypeSynonyms' env repl
498− Nothing -> error "Type synonym was not defined"
499−
500−expandTypeSynonym :: (Error e, Functor m, Monad m, MonadState CheckState m, MonadError e m) => Qualified ProperName -> [Type] -> m Type
501−expandTypeSynonym name args = do
502− env <- getEnv
503− either (throwError . strMsg) return $ expandTypeSynonym' env name args
504−
505−expandAllTypeSynonyms :: (Error e, Functor m, Monad m, MonadState CheckState m, MonadError e m) => Type -> m Type
506−expandAllTypeSynonyms = everywhereM' (mkM go)
507− where
508− go (SaturatedTypeSynonym name args) = expandTypeSynonym name args
509− go other = return other
510−
511−-- |
512−-- Ensure a set of property names and value does not contain duplicate labels
513−--
514−ensureNoDuplicateProperties :: (Error e, MonadError e m) => [(String, Value)] -> m ()
515−ensureNoDuplicateProperties ps = guardWith (strMsg "Duplicate property names") $ length (nub . map fst $ ps) == length ps
516−
517−-- |
518−-- Infer a type for a value, rethrowing any error to provide a more useful error message
519−--
520−infer :: Value -> UnifyT Type Check Value
521−infer val = rethrow (mkErrorStack "Error inferring type of value" (Just (ValueError val)) <>) $ infer' val
522−
523−-- |
524−-- Infer a type for a value
525−--
526−infer' :: Value -> UnifyT Type Check Value
527−infer' v@(NumericLiteral _) = return $ TypedValue True v tyNumber
528−infer' v@(StringLiteral _) = return $ TypedValue True v tyString
529−infer' v@(BooleanLiteral _) = return $ TypedValue True v tyBoolean
530−infer' (ArrayLiteral vals) = do
531− ts <- mapM infer vals
532− els <- fresh
533− forM_ ts $ \(TypedValue _ _ t) -> els =?= TypeApp tyArray t
534− return $ TypedValue True (ArrayLiteral ts) els
535−infer' (ObjectLiteral ps) = do
536− ensureNoDuplicateProperties ps
537− ts <- mapM (infer . snd) ps
538− let fields = zipWith (\name (TypedValue _ _ t) -> (name, t)) (map fst ps) ts
539− ty = TypeApp tyObject $ rowFromList (fields, REmpty)
540− return $ TypedValue True (ObjectLiteral (zip (map fst ps) ts)) ty
541−infer' (ObjectUpdate o ps) = do
542− ensureNoDuplicateProperties ps
543− row <- fresh
544− newVals <- zipWith (\(name, _) t -> (name, t)) ps <$> mapM (infer . snd) ps
545− let newTys = map (\(name, TypedValue _ _ ty) -> (name, ty)) newVals
546− oldTys <- zip (map fst ps) <$> replicateM (length ps) fresh
547− let oldTy = TypeApp tyObject $ rowFromList (oldTys, row)
548− o' <- TypedValue True <$> check o oldTy <*> pure oldTy
549− return $ TypedValue True (ObjectUpdate o' newVals) $ TypeApp tyObject $ rowFromList (newTys, row)
550−infer' (Accessor prop val) = do
551− typed@(TypedValue _ _ objTy) <- infer val
552− propTy <- inferProperty objTy prop
553− case propTy of
554− Nothing -> do
555− field <- fresh
556− rest <- fresh
557− _ <- subsumes Nothing objTy (TypeApp tyObject (RCons prop field rest))
558− return $ TypedValue True (Accessor prop typed) field
559− Just ty -> return $ TypedValue True (Accessor prop typed) ty
560−infer' (Abs (Left arg) ret) = do
561− ty <- fresh
562− Just moduleName <- checkCurrentModule <$> get
563− bindLocalVariables moduleName [(arg, ty)] $ do
564− body@(TypedValue _ _ bodyTy) <- infer' ret
565− return $ TypedValue True (Abs (Left arg) body) $ function ty bodyTy
566−infer' (Abs (Right _) _) = error "Binder was not desugared"
567−infer' (App f arg) = do
568− f'@(TypedValue _ _ ft) <- infer f
569− (ret, app) <- checkFunctionApplication f' ft arg Nothing
570− return $ TypedValue True app ret
571−infer' (Var var) = do
572− Just moduleName <- checkCurrentModule <$> get
573− ty <- introduceSkolemScope <=< replaceAllTypeSynonyms <=< lookupVariable moduleName $ var
574− case ty of
575− ConstrainedType constraints ty' -> do
576− dicts <- getTypeClassDictionaries
577− return $ TypedValue True (foldl App (Var var) (map (flip TypeClassDictionary dicts) constraints)) ty'
578− _ -> return $ TypedValue True (Var var) ty
579−infer' v@(Constructor c) = do
580− env <- getEnv
581− case M.lookup c (dataConstructors env) of
582− Nothing -> throwError . strMsg $ "Constructor " ++ show c ++ " is undefined"
583− Just (_, ty) -> do ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
584− return $ TypedValue True v ty'
585−infer' (Case vals binders) = do
586− ts <- mapM infer vals
587− ret <- fresh
588− binders' <- checkBinders (map (\(TypedValue _ _ t) -> t) ts) ret binders
589− return $ TypedValue True (Case ts binders') ret
590−infer' (IfThenElse cond th el) = do
591− cond' <- check cond tyBoolean
592− v2@(TypedValue _ _ t2) <- infer th
593− v3@(TypedValue _ _ t3) <- infer el
594− t2 =?= t3
595− return $ TypedValue True (IfThenElse cond' v2 v3) t2
596−infer' (Let ds val) = do
597− (ds', val'@(TypedValue _ _ valTy)) <- inferLetBinding [] ds val infer
598− return $ TypedValue True (Let ds' val') valTy
599−infer' (TypedValue checkType val ty) = do
600− Just moduleName <- checkCurrentModule <$> get
601− kind <- liftCheck $ kindOf moduleName ty
602− guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
603− ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
604− val' <- if checkType then check val ty' else return val
605− return $ TypedValue True val' ty'
606−infer' (PositionedValue pos val) = rethrowWithPosition pos $ infer' val
607−infer' _ = error "Invalid argument to infer"
608−
609−inferLetBinding :: [Declaration] -> [Declaration] -> Value -> (Value -> UnifyT Type Check Value) -> UnifyT Type Check ([Declaration], Value)
610−inferLetBinding seen [] ret j = (,) seen <$> j ret
611−inferLetBinding seen (ValueDeclaration ident nameKind [] Nothing val : rest) ret j = do
612− valTy <- fresh
613− Just moduleName <- checkCurrentModule <$> get
614− let dict = if isFunction val then M.singleton (moduleName, ident) (valTy, nameKind) else M.empty
615− TypedValue _ val' valTy' <- bindNames dict $ infer val
616− valTy =?= valTy'
617− bindNames (M.singleton (moduleName, ident) (valTy', nameKind)) $ inferLetBinding (seen ++ [ValueDeclaration ident nameKind [] Nothing val']) rest ret j
618−inferLetBinding seen (BindingGroupDeclaration ds : rest) ret j = do
619− Just moduleName <- checkCurrentModule <$> get
620− (es, dict, untypedDict) <- typeDictionaryForBindingGroup moduleName (map (\(i, _, v) -> (i, v)) ds)
621− ds' <- forM es $ \e -> do
622− (ident, (val', _)) <- typeForBindingGroupElement moduleName e dict untypedDict
623− return $ (ident, LocalVariable, val')
624− bindNames dict $ inferLetBinding (seen ++ [BindingGroupDeclaration ds']) rest ret j
625−inferLetBinding seen (PositionedDeclaration pos d : ds) ret j = do
626− ((d' : ds'), val') <- inferLetBinding seen (d : ds) ret j
627− return (PositionedDeclaration pos d' : ds', val')
628−inferLetBinding _ _ _ _ = error "Invalid argument to inferLetBinding"
629−
630−-- |
631−-- Infer the type of a property inside a record with a given type
632−--
633−inferProperty :: Type -> String -> UnifyT Type Check (Maybe Type)
634−inferProperty (TypeApp obj row) prop | obj == tyObject = do
635− let (props, _) = rowToList row
636− return $ lookup prop props
637−inferProperty (SaturatedTypeSynonym name args) prop = do
638− replaced <- introduceSkolemScope <=< expandTypeSynonym name $ args
639− inferProperty replaced prop
640−inferProperty (ForAll ident ty _) prop = do
641− replaced <- replaceVarWithUnknown ident ty
642− inferProperty replaced prop
643−inferProperty _ _ = return Nothing
644−
645−-- |
646−-- Infer the types of variables brought into scope by a binder
647−--
648−inferBinder :: Type -> Binder -> UnifyT Type Check (M.Map Ident Type)
649−inferBinder _ NullBinder = return M.empty
650−inferBinder val (StringBinder _) = val =?= tyString >> return M.empty
651−inferBinder val (NumberBinder _) = val =?= tyNumber >> return M.empty
652−inferBinder val (BooleanBinder _) = val =?= tyBoolean >> return M.empty
653−inferBinder val (VarBinder name) = return $ M.singleton name val
654−inferBinder val (ConstructorBinder ctor binders) = do
655− env <- getEnv
656− case M.lookup ctor (dataConstructors env) of
657− Just (_, ty) -> do
658− (_, fn) <- instantiatePolyTypeWithUnknowns (error "Data constructor types cannot contain constraints") ty
659− fn' <- replaceAllTypeSynonyms fn
660− go binders fn'
661− where
662− go [] ty' = do
663− _ <- subsumes Nothing val ty'
664− return M.empty
665− go (binder : binders') (TypeApp (TypeApp t obj) ret) | t == tyFunction =
666− M.union <$> inferBinder obj binder <*> go binders' ret
667− go _ _ = throwError . strMsg $ "Wrong number of arguments to constructor " ++ show ctor
668− _ -> throwError . strMsg $ "Constructor " ++ show ctor ++ " is not defined"
669−inferBinder val (ObjectBinder props) = do
670− row <- fresh
671− rest <- fresh
672− m1 <- inferRowProperties row rest props
673− val =?= TypeApp tyObject row
674− return m1
675− where
676− inferRowProperties :: Type -> Type -> [(String, Binder)] -> UnifyT Type Check (M.Map Ident Type)
677− inferRowProperties nrow row [] = nrow =?= row >> return M.empty
678− inferRowProperties nrow row ((name, binder):binders) = do
679− propTy <- fresh
680− m1 <- inferBinder propTy binder
681− m2 <- inferRowProperties nrow (RCons name propTy row) binders
682− return $ m1 `M.union` m2
683−inferBinder val (ArrayBinder binders) = do
684− el <- fresh
685− m1 <- M.unions <$> mapM (inferBinder el) binders
686− val =?= TypeApp tyArray el
687− return m1
688−inferBinder val (ConsBinder headBinder tailBinder) = do
689− el <- fresh
690− m1 <- inferBinder el headBinder
691− m2 <- inferBinder val tailBinder
692− val =?= TypeApp tyArray el
693− return $ m1 `M.union` m2
694−inferBinder val (NamedBinder name binder) = do
695− m <- inferBinder val binder
696− return $ M.insert name val m
697−inferBinder val (PositionedBinder pos binder) =
698− rethrowWithPosition pos $ inferBinder val binder
699−
700−-- |
701−-- Check the types of the return values in a set of binders in a case statement
702−--
703−checkBinders :: [Type] -> Type -> [CaseAlternative] -> UnifyT Type Check [CaseAlternative]
704−checkBinders _ _ [] = return []
705−checkBinders nvals ret (CaseAlternative binders grd val : bs) = do
706− Just moduleName <- checkCurrentModule <$> get
707− m1 <- M.unions <$> zipWithM inferBinder nvals binders
708− r <- bindLocalVariables moduleName (M.toList m1) $ do
709− val' <- TypedValue True <$> check val ret <*> pure ret
710− case grd of
711− Nothing -> return $ CaseAlternative binders Nothing val'
712− Just g -> do
713− g' <- check g tyBoolean
714− return $ CaseAlternative binders (Just g') val'
715− rs <- checkBinders nvals ret bs
716− return $ r : rs
717−
718−-- |
719−-- Generate a new skolem constant
720−--
721−newSkolemConstant :: UnifyT Type Check Int
722−newSkolemConstant = runUnknown <$> fresh'
723−
724−-- |
725−-- Generate a new skolem scope
726−--
727−newSkolemScope :: UnifyT Type Check SkolemScope
728−newSkolemScope = SkolemScope . runUnknown <$> fresh'
729−
730−-- |
731−-- Skolemize a type variable by replacing its instances with fresh skolem constants
732−--
733−skolemize :: String -> Int -> SkolemScope -> Type -> Type
734−skolemize ident sko scope = replaceTypeVars ident (Skolem sko scope)
735−
736−-- |
737−-- Introduce skolem scope at every occurence of a ForAll
738−--
739−introduceSkolemScope :: Type -> UnifyT Type Check Type
740−introduceSkolemScope = everywhereM (mkM go)
741− where
742− go (ForAll ident ty Nothing) = ForAll ident ty <$> (Just <$> newSkolemScope)
743− go other = return other
744−
745−-- |
746−-- Check the type of a value, rethrowing errors to provide a better error message
747−--
748−check :: Value -> Type -> UnifyT Type Check Value
749−check val ty = rethrow (mkErrorStack errorMessage (Just (ValueError val)) <>) $ check' val ty
750− where
751− errorMessage =
752− "Error checking type of term " ++
753− prettyPrintValue val ++
754− " against type " ++
755− prettyPrintType ty
756−
757−-- |
758−-- Check the type of a value
759−--
760−check' :: Value -> Type -> UnifyT Type Check Value
761−check' val (ForAll ident ty _) = do
762− scope <- newSkolemScope
763− sko <- newSkolemConstant
764− let sk = skolemize ident sko scope ty
765− val' <- check val sk
766− return $ TypedValue True val' (ForAll ident ty (Just scope))
767−check' val t@(ConstrainedType constraints ty) = do
768− dictNames <- forM constraints $ \(Qualified _ (ProperName className), _) -> do
769− n <- liftCheck freshDictionaryName
770− return $ Ident $ "__dict_" ++ className ++ "_" ++ show n
771− val' <- withTypeClassDictionaries (zipWith (\name (className, instanceTy) ->
772− TypeClassDictionaryInScope name className instanceTy Nothing TCDRegular) (map (Qualified Nothing) dictNames)
773− constraints) $ check val ty
774− return $ TypedValue True (foldr (Abs . Left) val' dictNames) t
775−check' val (SaturatedTypeSynonym name args) = do
776− ty <- introduceSkolemScope <=< expandTypeSynonym name $ args
777− check val ty
778−check' val u@(TUnknown _) = do
779− val'@(TypedValue _ _ ty) <- infer val
780− -- Don't unify an unknown with an inferred polytype
781− (val'', ty') <- instantiatePolyTypeWithUnknowns val' ty
782− ty' =?= u
783− return $ TypedValue True val'' ty'
784−check' v@(NumericLiteral _) t | t == tyNumber =
785− return $ TypedValue True v t
786−check' v@(StringLiteral _) t | t == tyString =
787− return $ TypedValue True v t
788−check' v@(BooleanLiteral _) t | t == tyBoolean =
789− return $ TypedValue True v t
790−check' (ArrayLiteral vals) t@(TypeApp a ty) = do
791− a =?= tyArray
792− array <- ArrayLiteral <$> forM vals (`check` ty)
793− return $ TypedValue True array t
794−check' (Abs (Left arg) ret) ty@(TypeApp (TypeApp t argTy) retTy) | t == tyFunction = do
795− Just moduleName <- checkCurrentModule <$> get
796− ret' <- bindLocalVariables moduleName [(arg, argTy)] $ check ret retTy
797− return $ TypedValue True (Abs (Left arg) ret') ty
798−check' (Abs (Right _) _) _ = error "Binder was not desugared"
799−check' (App f arg) ret = do
800− f'@(TypedValue _ _ ft) <- infer f
801− (_, app) <- checkFunctionApplication f' ft arg (Just ret)
802− return $ TypedValue True app ret
803−check' v@(Var var) ty = do
804− Just moduleName <- checkCurrentModule <$> get
805− repl <- introduceSkolemScope <=< replaceAllTypeSynonyms <=< lookupVariable moduleName $ var
806− ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
807− v' <- subsumes (Just v) repl ty'
808− case v' of
809− Nothing -> throwError . strMsg $ "Unable to check type subsumption"
810− Just v'' -> return $ TypedValue True v'' ty'
811−check' (TypedValue checkType val ty1) ty2 = do
812− Just moduleName <- checkCurrentModule <$> get
813− kind <- liftCheck $ kindOf moduleName ty1
814− guardWith (strMsg $ "Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
815− ty1' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty1
816− val' <- subsumes (Just val) ty1' ty2
817− case val' of
818− Nothing -> throwError . strMsg $ "Unable to check type subsumption"
819− Just val'' -> do
820− val''' <- if checkType then check val'' ty1' else return val''
821− return $ TypedValue checkType (TypedValue True val''' ty1) ty2
822−check' (Case vals binders) ret = do
823− vals' <- mapM infer vals
824− let ts = map (\(TypedValue _ _ t) -> t) vals'
825− binders' <- checkBinders ts ret binders
826− return $ TypedValue True (Case vals' binders') ret
827−check' (IfThenElse cond th el) ty = do
828− cond' <- check cond tyBoolean
829− th' <- check th ty
830− el' <- check el ty
831− return $ TypedValue True (IfThenElse cond' th' el') ty
832−check' (ObjectLiteral ps) t@(TypeApp obj row) | obj == tyObject = do
833− ensureNoDuplicateProperties ps
834− ps' <- checkProperties ps row False
835− return $ TypedValue True (ObjectLiteral ps') t
836−check' (ObjectUpdate obj ps) t@(TypeApp o row) | o == tyObject = do
837− ensureNoDuplicateProperties ps
838− us <- zip (map fst ps) <$> replicateM (length ps) fresh
839− let (propsToCheck, rest) = rowToList row
840− propsToRemove = map fst ps
841− remainingProps = filter (\(p, _) -> p `notElem` propsToRemove) propsToCheck
842− obj' <- check obj (TypeApp tyObject (rowFromList (us ++ remainingProps, rest)))
843− ps' <- checkProperties ps row True
844− return $ TypedValue True (ObjectUpdate obj' ps') t
845−check' (Accessor prop val) ty = do
846− rest <- fresh
847− val' <- check val (TypeApp tyObject (RCons prop ty rest))
848− return $ TypedValue True (Accessor prop val') ty
849−check' (Constructor c) ty = do
850− env <- getEnv
851− case M.lookup c (dataConstructors env) of
852− Nothing -> throwError . strMsg $ "Constructor " ++ show c ++ " is undefined"
853− Just (_, ty1) -> do
854− repl <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty1
855− _ <- subsumes Nothing repl ty
856− return $ TypedValue True (Constructor c) ty
857−check' (Let ds val) ty = do
858− (ds', val') <- inferLetBinding [] ds val (flip check ty)
859− return $ TypedValue True (Let ds' val') ty
860−check' val ty | containsTypeSynonyms ty = do
861− ty' <- introduceSkolemScope <=< expandAllTypeSynonyms $ ty
862− check val ty'
863−check' (PositionedValue pos val) ty =
864− rethrowWithPosition pos $ check val ty
865−check' val ty = throwError $ mkErrorStack ("Value does not have type " ++ prettyPrintType ty) (Just (ValueError val))
866−
867−containsTypeSynonyms :: Type -> Bool
868−containsTypeSynonyms = everything (||) (mkQ False go) where
869− go (SaturatedTypeSynonym _ _) = True
870− go _ = False
871−
872−-- |
873−-- Check the type of a collection of named record fields
874−--
875−-- The @lax@ parameter controls whether or not every record member has to be provided. For object updates, this is not the case.
876−--
877−checkProperties :: [(String, Value)] -> Type -> Bool -> UnifyT Type Check [(String, Value)]
878−checkProperties ps row lax = let (ts, r') = rowToList row in go ps ts r' where
879− go [] [] REmpty = return []
880− go [] [] u@(TUnknown _) = do u =?= REmpty
881− return []
882− go [] [] (Skolem _ _) | lax = return []
883− go [] ((p, _): _) _ | lax = return []
884− | otherwise = throwError $ mkErrorStack ("Object does not have property " ++ p) (Just (ValueError (ObjectLiteral ps)))
885− go ((p,_):_) [] REmpty = throwError $ mkErrorStack ("Property " ++ p ++ " is not present in closed object type " ++ prettyPrintRow row) (Just (ValueError (ObjectLiteral ps)))
886− go ((p,v):ps') [] u@(TUnknown _) = do
887− v'@(TypedValue _ _ ty) <- infer v
888− rest <- fresh
889− u =?= RCons p ty rest
890− ps'' <- go ps' [] rest
891− return $ (p, v') : ps''
892− go ((p,v):ps') ts r =
893− case lookup p ts of
894− Nothing -> do
895− v'@(TypedValue _ _ ty) <- infer v
896− rest <- fresh
897− r =?= RCons p ty rest
898− ps'' <- go ps' ts rest
899− return $ (p, v') : ps''
900− Just ty -> do
901− v' <- check v ty
902− ps'' <- go ps' (delete (p, ty) ts) r
903− return $ (p, v') : ps''
904− go _ _ _ = throwError $ mkErrorStack ("Object does not have type " ++ prettyPrintType (TypeApp tyObject row)) (Just (ValueError (ObjectLiteral ps)))
905−
906−-- |
907−-- Check the type of a function application, rethrowing errors to provide a better error message
908−--
909−checkFunctionApplication :: Value -> Type -> Value -> Maybe Type -> UnifyT Type Check (Type, Value)
910−checkFunctionApplication fn fnTy arg ret = rethrow (mkErrorStack errorMessage (Just (ValueError fn)) <>) $ checkFunctionApplication' fn fnTy arg ret
911− where
912− errorMessage = "Error applying function of type "
913− ++ prettyPrintType fnTy
914− ++ " to argument " ++ prettyPrintValue arg
915−
916−-- |
917−-- Check the type of a function application
918−--
919−checkFunctionApplication' :: Value -> Type -> Value -> Maybe Type -> UnifyT Type Check (Type, Value)
920−checkFunctionApplication' fn (TypeApp (TypeApp tyFunction' argTy) retTy) arg ret = do
921− tyFunction' =?= tyFunction
922− _ <- maybe (return Nothing) (subsumes Nothing retTy) ret
923− subst <- unifyCurrentSubstitution <$> UnifyT get
924− arg' <- check arg (subst $? argTy)
925− return (retTy, App fn arg')
926−checkFunctionApplication' fn (ForAll ident ty _) arg ret = do
927− replaced <- replaceVarWithUnknown ident ty
928− checkFunctionApplication fn replaced arg ret
929−checkFunctionApplication' fn u@(TUnknown _) arg ret = do
930− arg' <- do
931− TypedValue _ arg' t <- infer arg
932− (arg'', t') <- instantiatePolyTypeWithUnknowns arg' t
933− return $ TypedValue True arg'' t'
934− let ty = (\(TypedValue _ _ t) -> t) arg'
935− ret' <- maybe fresh return ret
936− u =?= function ty ret'
937− return (ret', App fn arg')
938−checkFunctionApplication' fn (SaturatedTypeSynonym name tyArgs) arg ret = do
939− ty <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
940− checkFunctionApplication fn ty arg ret
941−checkFunctionApplication' fn (ConstrainedType constraints fnTy) arg ret = do
942− dicts <- getTypeClassDictionaries
943− checkFunctionApplication' (foldl App fn (map (flip TypeClassDictionary dicts) constraints)) fnTy arg ret
944−checkFunctionApplication' _ fnTy arg _ = throwError . strMsg $ "Cannot apply a function of type "
945− ++ prettyPrintType fnTy
946− ++ " to argument " ++ prettyPrintValue arg
947−
948−-- |
949−-- Check whether one type subsumes another, rethrowing errors to provide a better error message
950−--
951−subsumes :: Maybe Value -> Type -> Type -> UnifyT Type Check (Maybe Value)
952−subsumes val ty1 ty2 = rethrow (mkErrorStack errorMessage (ValueError <$> val) <>) $ subsumes' val ty1 ty2
953− where
954− errorMessage = "Error checking that type "
955− ++ prettyPrintType ty1
956− ++ " subsumes type "
957− ++ prettyPrintType ty2
958−
959−-- |
960−-- Check whether one type subsumes another
961−--
962−subsumes' :: Maybe Value -> Type -> Type -> UnifyT Type Check (Maybe Value)
963−subsumes' val (ForAll ident ty1 _) ty2 = do
964− replaced <- replaceVarWithUnknown ident ty1
965− subsumes val replaced ty2
966−subsumes' val ty1 (ForAll ident ty2 sco) =
967− case sco of
968− Just sco' -> do
969− sko <- newSkolemConstant
970− let sk = skolemize ident sko sco' ty2
971− subsumes val ty1 sk
972− Nothing -> throwError . strMsg $ "Skolem variable scope is unspecified"
973−subsumes' val (TypeApp (TypeApp f1 arg1) ret1) (TypeApp (TypeApp f2 arg2) ret2) | f1 == tyFunction && f2 == tyFunction = do
974− _ <- subsumes Nothing arg2 arg1
975− _ <- subsumes Nothing ret1 ret2
976− return val
977−subsumes' val (SaturatedTypeSynonym name tyArgs) ty2 = do
978− ty1 <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
979− subsumes val ty1 ty2
980−subsumes' val ty1 (SaturatedTypeSynonym name tyArgs) = do
981− ty2 <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
982− subsumes val ty1 ty2
983−subsumes' (Just val) (ConstrainedType constraints ty1) ty2 = do
984− dicts <- getTypeClassDictionaries
985− _ <- subsumes' Nothing ty1 ty2
986− return . Just $ foldl App val (map (flip TypeClassDictionary dicts) constraints)
987−subsumes' val (TypeApp f1 r1) (TypeApp f2 r2) | f1 == tyObject && f2 == tyObject = do
988− let
989− (ts1, r1') = rowToList r1
990− (ts2, r2') = rowToList r2
991− ts1' = sortBy (comparing fst) ts1
992− ts2' = sortBy (comparing fst) ts2
993− go ts1' ts2' r1' r2'
994− return val
995− where
996− go [] ts2 r1' r2' = r1' =?= rowFromList (ts2, r2')
997− go ts1 [] r1' r2' = r2' =?= rowFromList (ts1, r1')
998− go ((p1, ty1) : ts1) ((p2, ty2) : ts2) r1' r2'
999− | p1 == p2 = do _ <- subsumes Nothing ty1 ty2
1000− go ts1 ts2 r1' r2'
1001− | p1 < p2 = do rest <- fresh
1002− r2' =?= RCons p1 ty1 rest
1003− go ts1 ((p2, ty2) : ts2) r1' rest
1004− | otherwise = do rest <- fresh
1005− r1' =?= RCons p2 ty2 rest
1006− go ((p1, ty1) : ts1) ts2 rest r2'
1007−subsumes' val ty1 ty2@(TypeApp obj _) | obj == tyObject = subsumes val ty2 ty1
1008−subsumes' val ty1 ty2 = do
1009− ty1 =?= ty2
1010− return val
1011−
1012−
1013−