@@ -1,1021 +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−
71−instance Partial Type where
72− unknown = TUnknown
73− isUnknown (TUnknown u) = Just u
74− isUnknown _ = Nothing
75−
76−instance Unifiable Check Type where
77− (=?=) = unifyTypes
78−
79−-- |
80−-- Unify two types, updating the current substitution
81−--
82−unifyTypes :: Type -> Type -> UnifyT Type Check ()
83−unifyTypes t1 t2 = rethrow (\e -> "Error unifying type " ++ prettyPrintType t1 ++ " with type " ++ prettyPrintType t2 ++ ":\n" ++ e) $ do
84− unifyTypes' t1 t2
85− where
86− unifyTypes' (TUnknown u1) (TUnknown u2) | u1 == u2 = return ()
87− unifyTypes' (TUnknown u) t = u =:= t
88− unifyTypes' t (TUnknown u) = u =:= t
89− unifyTypes' (SaturatedTypeSynonym name args) ty = do
90− ty1 <- introduceSkolemScope <=< expandTypeSynonym name $ args
91− ty1 `unifyTypes` ty
92− unifyTypes' ty s@(SaturatedTypeSynonym _ _) = s `unifyTypes` ty
93− unifyTypes' (ForAll ident1 ty1 sc1) (ForAll ident2 ty2 sc2) =
94− case (sc1, sc2) of
95− (Just sc1', Just sc2') -> do
96− sko <- newSkolemConstant
97− let sk1 = skolemize ident1 sko sc1' ty1
98− let sk2 = skolemize ident2 sko sc2' ty2
99− sk1 `unifyTypes` sk2
100− _ -> throwError (prettyPrintType ty1)
101− unifyTypes' (ForAll ident ty1 (Just sc)) ty2 = do
102− sko <- newSkolemConstant
103− let sk = skolemize ident sko sc ty1
104− sk `unifyTypes` ty2
105− unifyTypes' (ForAll _ _ _) _ = throwError "Skolem variable scope is unspecified"
106− unifyTypes' ty f@(ForAll _ _ _) = f `unifyTypes` ty
107− unifyTypes' (Object row1) (Object row2) = row1 =?= row2
108− unifyTypes' (TypeVar v1) (TypeVar v2) | v1 == v2 = return ()
109− unifyTypes' (TypeConstructor c1) (TypeConstructor c2) = do
110− env <- getEnv
111− Just moduleName <- checkCurrentModule <$> get
112− guardWith ("Cannot unify " ++ show c1 ++ " with " ++ show c2 ++ ".") (typeConstructorsAreEqual env moduleName 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' t3 t4 = throwError $ "Cannot unify " ++ prettyPrintType t3 ++ " with " ++ prettyPrintType t4 ++ "."
122−
123−-- |
124−-- Unify two rows, updating the current substitution
125−--
126−-- Common labels are first identified, and unified. Remaining labels and types are unified with a
127−-- trailing row unification variable, if appropriate, otherwise leftover labels result in a unification
128−-- error.
129−--
130−unifyRows :: Type -> Type -> UnifyT Type Check ()
131−unifyRows r1 r2 =
132− let
133− (s1, r1') = rowToList r1
134− (s2, r2') = rowToList r2
135− int = [ (t1, t2) | (name, t1) <- s1, (name', t2) <- s2, name == name' ]
136− sd1 = [ (name, t1) | (name, t1) <- s1, name `notElem` map fst s2 ]
137− sd2 = [ (name, t2) | (name, t2) <- s2, name `notElem` map fst s1 ]
138− in do
139− forM_ int (uncurry (=?=))
140− unifyRows' sd1 r1' sd2 r2'
141− where
142− unifyRows' :: [(String, Type)] -> Type -> [(String, Type)] -> Type -> UnifyT Type Check ()
143− unifyRows' [] (TUnknown u) sd r = u =:= rowFromList (sd, r)
144− unifyRows' sd r [] (TUnknown u) = u =:= rowFromList (sd, r)
145− unifyRows' ((name, ty):row) r others u@(TUnknown un) = do
146− occursCheck un ty
147− forM_ row $ \(_, t) -> occursCheck un t
148− u' <- fresh
149− u =?= RCons name ty u'
150− unifyRows' row r others u'
151− unifyRows' [] REmpty [] REmpty = return ()
152− unifyRows' [] (TypeVar v1) [] (TypeVar v2) | v1 == v2 = return ()
153− unifyRows' [] (Skolem s1 _) [] (Skolem s2 _) | s1 == s2 = return ()
154− unifyRows' sd3 r3 sd4 r4 = throwError $ "Cannot unify " ++ prettyPrintRow (rowFromList (sd3, r3)) ++ " with " ++ prettyPrintRow (rowFromList (sd4, r4)) ++ "."
155−
156−-- |
157−-- Ensure type constructors are equal after canonicalization
158−--
159−typeConstructorsAreEqual :: Environment -> ModuleName -> Qualified ProperName -> Qualified ProperName -> Bool
160−typeConstructorsAreEqual env moduleName = (==) `on` canonicalizeType moduleName env
161−
162−-- |
163−-- Infer the types of multiple mutually-recursive values, and return elaborated values including
164−-- type class dictionaries and type annotations.
165−--
166−typesOf :: ModuleName -> [(Ident, Value)] -> Check [(Ident, (Value, Type))]
167−typesOf moduleName vals = do
168− tys <- fmap tidyUp . liftUnify $ do
169− let
170− -- Map each declaration to a name/value pair, with an optional type, if the declaration is typed
171− es = map isTyped vals
172− -- Filter the typed and untyped declarations
173− typed = filter (isJust . snd . snd) es
174− untyped = filter (isNothing . snd . snd) es
175− -- Make a map of names to typed declarations
176− typedDict = map (\(ident, (_, Just (ty, _))) -> (ident, ty)) typed
177− -- Create fresh unification variables for the types of untyped declarations
178− untypedNames <- replicateM (length untyped) fresh
179− let
180− -- Make a map of names to the unification variables of untyped declarations
181− untypedDict = zip (map fst untyped) untypedNames
182− -- Create the dictionary of all name/type pairs, which will be added to the environment during type checking
183− dict = M.fromList (map (\(ident, ty) -> ((moduleName, ident), (ty, LocalVariable))) $ typedDict ++ untypedDict)
184− forM es $ \e@(_, (val, _)) -> do
185− -- If the declaration is a function, it has access to other values in the binding group.
186− -- If not, the generated code might fail at runtime since those values might be undefined.
187− let dict' = if isFunction val then dict else M.empty
188− triple@(_, (val, ty)) <- case e of
189− -- Typed declarations
190− (ident, (val, Just (ty, checkType))) -> do
191− -- Kind check
192− kind <- liftCheck $ kindOf moduleName ty
193− guardWith ("Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
194− -- Check the type with the new names in scope
195− ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
196− val' <- bindNames dict' $ if checkType
197− then TypedValue True <$> check val ty' <*> pure ty'
198− else return (TypedValue False val ty')
199− return (ident, (val', ty'))
200− -- Untyped declarations
201− (ident, (val, Nothing)) -> do
202− -- Infer the type with the new names in scope
203− TypedValue _ val' ty <- bindNames dict' $ infer val
204− ty =?= fromMaybe (error "name not found in dictionary") (lookup ident untypedDict)
205− return (ident, (TypedValue True val' ty, ty))
206− -- If run-main is enabled, need to check that Main.main has type Eff eff a for some eff, a
207− when (moduleName == ModuleName (ProperName "Main") && fst e == Ident "main") $ do
208− [eff, a] <- replicateM 2 fresh
209− ty =?= TypeApp (TypeApp (TypeConstructor (Qualified (Just (ModuleName (ProperName "Eff"))) (ProperName "Eff"))) eff) a
210− -- Make sure unification variables do not escape
211− escapeCheck val ty
212− return triple
213− forM tys $ \(ident, (val, ty)) -> do
214− -- Replace type class dictionary placeholders with actual dictionaries
215− val' <- replaceTypeClassDictionaries moduleName val
216− -- Check skolem variables did not escape their scope
217− skolemEscapeCheck val'
218− -- Remove type synonyms placeholders, remove duplicate row fields, and replace
219− -- top-level unification variables with named type variables.
220− let val'' = overTypes (desaturateAllTypeSynonyms . setifyAll) val'
221− ty' = varIfUnknown . desaturateAllTypeSynonyms . setifyAll $ ty
222− return $ (ident, (val'', ty'))
223− where
224− -- Apply the substitution that was returned from runUnify to both types and (type-annotated) values
225− tidyUp (ts, sub) = map (\(i, (val, ty)) -> (i, (overTypes (sub $?) val, sub $? ty))) ts
226−
227−-- |
228−-- Check if a value introduces a function
229−--
230−isFunction :: Value -> Bool
231−isFunction (Abs _ _) = True
232−isFunction (TypedValue _ val _) = isFunction val
233−isFunction _ = False
234−
235−-- |
236−-- Check if a value contains a type annotation
237−--
238−isTyped :: (Ident, Value) -> (Ident, (Value, Maybe (Type, Bool)))
239−isTyped (name, TypedValue checkType value ty) = (name, (value, Just (ty, checkType)))
240−isTyped (name, value) = (name, (value, Nothing))
241−
242−-- |
243−-- Map a function over type annotations appearing inside a value
244−--
245−overTypes :: (Type -> Type) -> Value -> Value
246−overTypes f = everywhere (mkT f)
247−
248−-- |
249−-- Replace type class dictionary placeholders with inferred type class dictionaries
250−--
251−replaceTypeClassDictionaries :: ModuleName -> Value -> Check Value
252−replaceTypeClassDictionaries mn = everywhereM (mkM go)
253− where
254− go (TypeClassDictionary constraint dicts) = entails mn dicts constraint
255− go other = return other
256−
257−-- |
258−-- Check that the current set of type class dictionaries entail the specified type class goal, and, if so,
259−-- return a type class dictionary reference.
260−--
261−entails :: ModuleName -> [TypeClassDictionaryInScope] -> (Qualified ProperName, Type) -> Check Value
262−entails moduleName context goal@(className, ty) = do
263− env <- getEnv
264− case go env goal of
265− [] -> throwError $ "No " ++ show className ++ " instance found for " ++ prettyPrintType ty
266− (dict : _) -> return dict
267− where
268− go env (className', ty') =
269− [ mkDictionary (canonicalizeDictionary tcd) args
270− | tcd <- context
271− -- Choose type class dictionaries in scope in the current module
272− , filterModule tcd
273− -- Make sure the type class name matches the one we are trying to satisfy
274− , typeConstructorsAreEqual env moduleName className' (tcdClassName tcd)
275− -- Make sure the type unifies with the type in the type instance definition
276− , subst <- maybeToList $ typeHeadsAreEqual moduleName env ty' (tcdInstanceType tcd)
277− -- Solve any necessary subgoals
278− , args <- solveSubgoals env subst (tcdDependencies tcd) ]
279− -- Create dictionaries for subgoals which still need to be solved by calling go recursively
280− -- E.g. the goal (Show a, Show b) => Show (Either a b) can be satisfied if the current type
281− -- unifies with Either a b, and we can satisfy the subgoals Show a and Show b recursively.
282− solveSubgoals :: Environment -> [(String, Type)] -> Maybe [(Qualified ProperName, Type)] -> [Maybe [Value]]
283− solveSubgoals _ _ Nothing = return Nothing
284− solveSubgoals env subst (Just subgoals) = do
285− dict <- mapM (go env) (map (id *** replaceAllTypeVars subst) subgoals)
286− return $ Just dict
287− -- Make a dictionary from subgoal dictionaries by applying the correct function
288− mkDictionary :: Qualified Ident -> Maybe [Value] -> Value
289− mkDictionary fnName Nothing = Var fnName
290− mkDictionary fnName (Just []) = App (Var fnName) (ObjectLiteral [])
291− mkDictionary fnName (Just dicts) = foldl App (Var fnName) dicts
292− -- Filter out type dictionaries which are in scope in the current module
293− filterModule :: TypeClassDictionaryInScope -> Bool
294− filterModule (TypeClassDictionaryInScope { tcdName = Qualified (Just mn) _ }) | mn == moduleName = True
295− filterModule (TypeClassDictionaryInScope { tcdName = Qualified Nothing _ }) = True
296− filterModule _ = False
297− -- Resolve a type class dictionary in scope to an actual value by following any (TCDAlias) pointers
298− -- which originated from module imports
299− canonicalizeDictionary :: TypeClassDictionaryInScope -> Qualified Ident
300− canonicalizeDictionary (TypeClassDictionaryInScope { tcdType = TCDRegular, tcdName = nm }) = nm
301− canonicalizeDictionary (TypeClassDictionaryInScope { tcdType = TCDAlias nm }) = nm
302−
303−-- |
304−-- Check whether the type heads of two types are equal (for the purposes of type class dictionary lookup),
305−-- and return a substitution from type variables to types which makes the type heads unify.
306−--
307−typeHeadsAreEqual :: ModuleName -> Environment -> Type -> Type -> Maybe [(String, Type)]
308−typeHeadsAreEqual _ _ (Skolem s1 _) (Skolem s2 _) | s1 == s2 = Just []
309−typeHeadsAreEqual _ _ (TypeVar v) t = Just [(v, t)]
310−typeHeadsAreEqual _ _ t (TypeVar v) = Just [(v, t)]
311−typeHeadsAreEqual m e (TypeConstructor c1) (TypeConstructor c2) | typeConstructorsAreEqual e m c1 c2 = Just []
312−typeHeadsAreEqual m e (TypeApp h1 (TypeVar v)) (TypeApp h2 arg) = (:) (v, arg) <$> typeHeadsAreEqual m e h1 h2
313−typeHeadsAreEqual m e t1@(TypeApp _ _) t2@(TypeApp _ (TypeVar _)) = typeHeadsAreEqual m e t2 t1
314−typeHeadsAreEqual m e (SaturatedTypeSynonym name args) t2 = case expandTypeSynonym' e m name args of
315− Left err -> Nothing
316− Right t1 -> typeHeadsAreEqual m e t1 t2
317−typeHeadsAreEqual _ _ _ _ = Nothing
318−
319−-- |
320−-- Ensure unsolved unification variables do not escape
321−--
322−escapeCheck :: Value -> Type -> UnifyT Type Check ()
323−escapeCheck value ty = do
324− subst <- unifyCurrentSubstitution <$> UnifyT get
325− let visibleUnknowns = nub $ unknowns $ subst $? ty
326− let allUnknowns = findAllTypes value
327− forM_ allUnknowns $ \t -> do
328− let unsolvedUnknowns = nub . unknowns $ subst $? t
329− guardWith "Escape check fails" $ null $ unsolvedUnknowns \\ visibleUnknowns
330−
331−-- |
332−-- Find all type annotations occuring inside a value
333−--
334−findAllTypes :: Value -> [Type]
335−findAllTypes = everything (++) (mkQ [] go)
336− where
337− go (TypedValue _ _ ty) = [ty]
338− go _ = []
339−
340−-- |
341−-- Ensure skolem variables do not escape their scope
342−--
343−skolemEscapeCheck :: Value -> Check ()
344−skolemEscapeCheck (TypedValue False _ _) = return ()
345−skolemEscapeCheck root@(TypedValue _ _ _) =
346− -- Every skolem variable is created when a ForAll type is skolemized.
347− -- This determines the scope of that skolem variable, which is copied from the SkolemScope
348− -- field of the ForAll constructor.
349− -- We traverse the tree top-down, and collect any SkolemScopes introduced by ForAlls.
350− -- If a Skolem is encountered whose SkolemScope is not in the current list, we have found
351− -- an escaped skolem variable.
352− case everythingWithContext [] (++) (mkQ ((,) []) go) root of
353− [] -> return ()
354− ((binding, val) : _) -> throwError $ "Rigid/skolem type variable bound by " ++ maybe "<unknown>" prettyPrintValue binding ++ " has escaped at " ++ prettyPrintValue val
355− where
356− go :: Value -> [(SkolemScope, Value)] -> ([(Maybe Value, Value)], [(SkolemScope, Value)])
357− go val@(TypedValue _ _ (ForAll _ _ (Just sco))) scos = ([], (sco, val) : scos)
358− go val@(TypedValue _ _ ty) scos = case collectSkolems ty \\ map fst scos of
359− (sco : _) -> ([(findBindingScope sco, val)], scos)
360− _ -> ([], scos)
361− where
362− collectSkolems :: Type -> [SkolemScope]
363− collectSkolems = nub . everything (++) (mkQ [] collect)
364− where
365− collect (Skolem _ scope) = [scope]
366− collect _ = []
367− go _ scos = ([], scos)
368− findBindingScope :: SkolemScope -> Maybe Value
369− findBindingScope sco = something (mkQ Nothing go) root
370− where
371− go val@(TypedValue _ _ (ForAll _ _ (Just sco'))) | sco == sco' = Just val
372− go _ = Nothing
373−skolemEscapeCheck val = throwError $ "Untyped value passed to skolemEscapeCheck: " ++ prettyPrintValue val
374−
375−-- |
376−-- Ensure a row contains no duplicate labels
377−--
378−setify :: Type -> Type
379−setify = rowFromList . first (M.toList . M.fromList) . rowToList
380−
381−-- |
382−-- \"Setify\" all rows occuring inside a value
383−--
384−setifyAll :: (D.Data d) => d -> d
385−setifyAll = everywhere (mkT setify)
386−
387−-- |
388−-- Replace outermost unsolved unification variables with named type variables
389−--
390−varIfUnknown :: Type -> Type
391−varIfUnknown ty =
392− let unks = nub $ unknowns ty
393− toName = (:) 't' . show
394− ty' = everywhere (mkT typeToVar) $ ty
395− typeToVar :: Type -> Type
396− typeToVar (TUnknown (Unknown u)) = TypeVar (toName u)
397− typeToVar t = t
398− in mkForAll (sort . map (toName . runUnknown) $ unks) ty'
399−
400−-- |
401−-- Replace named type variables with types
402−--
403−replaceAllTypeVars :: [(String, Type)] -> Type -> Type
404−replaceAllTypeVars = foldl' (\f (name, ty) -> replaceTypeVars name ty . f) id
405−
406−-- |
407−-- Remove any ForAlls and ConstrainedType constructors in a type by introducing new unknowns
408−-- or TypeClassDictionary values.
409−--
410−-- This is necessary during type checking to avoid unifying a polymorphic type with a
411−-- unification variable.
412−--
413−instantiatePolyTypeWithUnknowns :: Value -> Type -> UnifyT Type Check (Value, Type)
414−instantiatePolyTypeWithUnknowns val (ForAll ident ty _) = do
415− ty' <- replaceVarWithUnknown ident ty
416− instantiatePolyTypeWithUnknowns val ty'
417−instantiatePolyTypeWithUnknowns val (ConstrainedType constraints ty) = do
418− env <- getEnv
419− Just moduleName <- checkCurrentModule <$> get
420− dicts <- getTypeClassDictionaries
421− (_, ty') <- instantiatePolyTypeWithUnknowns (error "Types under a constraint cannot themselves be constrained") ty
422− return (foldl App val (map (flip TypeClassDictionary dicts) (qualifyAllUnqualifiedNames moduleName env constraints)), ty')
423−instantiatePolyTypeWithUnknowns val ty = return (val, ty)
424−
425−-- |
426−-- Replace a single type variable with a new unification variable
427−--
428−replaceVarWithUnknown :: String -> Type -> UnifyT Type Check Type
429−replaceVarWithUnknown ident ty = do
430− tu <- fresh
431− return $ replaceTypeVars ident tu $ ty
432−
433−-- |
434−-- Replace fully applied type synonyms with the @SaturatedTypeSynonym@ data constructor, which helps generate
435−-- better error messages during unification.
436−--
437−replaceAllTypeSynonyms' :: (D.Data d) => Environment -> ModuleName -> d -> Either String d
438−replaceAllTypeSynonyms' env moduleName d =
439− let
440− syns = map (\((path, name), (args, _)) -> ((path, name), length args)) . M.toList $ typeSynonyms env
441− in
442− saturateAllTypeSynonyms env moduleName syns d
443−
444−replaceAllTypeSynonyms :: (Functor m, Monad m, MonadState CheckState m, MonadError String m) => (D.Data d) => d -> m d
445−replaceAllTypeSynonyms d = do
446− env <- getEnv
447− Just moduleName <- checkCurrentModule <$> get
448− either throwError return $ replaceAllTypeSynonyms' env moduleName d
449−
450−-- |
451−-- \"Desaturate\" @SaturatedTypeSynonym@s
452−--
453−desaturateAllTypeSynonyms :: (D.Data d) => d -> d
454−desaturateAllTypeSynonyms = everywhere (mkT replaceSaturatedTypeSynonym)
455− where
456− replaceSaturatedTypeSynonym (SaturatedTypeSynonym name args) = foldl TypeApp (TypeConstructor name) args
457− replaceSaturatedTypeSynonym t = t
458−
459−-- |
460−-- Replace a type synonym and its arguments with the aliased type
461−--
462−expandTypeSynonym' :: Environment -> ModuleName -> Qualified ProperName -> [Type] -> Either String Type
463−expandTypeSynonym' env moduleName name args =
464− case M.lookup (canonicalizeType moduleName env name) (typeSynonyms env) of
465− Just (synArgs, body) -> do
466− let repl = replaceAllTypeVars (zip synArgs args) body
467− replaceAllTypeSynonyms' env moduleName repl
468− Nothing -> error "Type synonym was not defined"
469−
470−expandTypeSynonym :: (Functor m, Monad m, MonadState CheckState m, MonadError String m) => Qualified ProperName -> [Type] -> m Type
471−expandTypeSynonym name args = do
472− env <- getEnv
473− Just moduleName <- checkCurrentModule <$> get
474− either throwError return $ expandTypeSynonym' env moduleName name args
475−
476−-- |
477−-- Ensure a set of property names and value does not contain duplicate labels
478−--
479−ensureNoDuplicateProperties :: (MonadError String m) => [(String, Value)] -> m ()
480−ensureNoDuplicateProperties ps = guardWith "Duplicate property names" $ length (nub . map fst $ ps) == length ps
481−
482−-- |
483−-- Infer a type for a value, rethrowing any error to provide a more useful error message
484−--
485−infer :: Value -> UnifyT Type Check Value
486−infer val = rethrow (\e -> "Error inferring type of term " ++ prettyPrintValue val ++ ":\n" ++ e) $ infer' val
487−
488−-- |
489−-- Infer a type for a value
490−--
491−infer' :: Value -> UnifyT Type Check Value
492−infer' v@(NumericLiteral _) = return $ TypedValue True v tyNumber
493−infer' v@(StringLiteral _) = return $ TypedValue True v tyString
494−infer' v@(BooleanLiteral _) = return $ TypedValue True v tyBoolean
495−infer' (ArrayLiteral vals) = do
496− ts <- mapM infer vals
497− els <- fresh
498− forM_ ts $ \(TypedValue _ _ t) -> els =?= TypeApp tyArray t
499− return $ TypedValue True (ArrayLiteral ts) els
500−infer' (ObjectLiteral ps) = do
501− ensureNoDuplicateProperties ps
502− ts <- mapM (infer . snd) ps
503− let fields = zipWith (\name (TypedValue _ _ t) -> (name, t)) (map fst ps) ts
504− ty = Object $ rowFromList (fields, REmpty)
505− return $ TypedValue True (ObjectLiteral (zip (map fst ps) ts)) ty
506−infer' (ObjectUpdate o ps) = do
507− ensureNoDuplicateProperties ps
508− row <- fresh
509− newVals <- zipWith (\(name, _) t -> (name, t)) ps <$> mapM (infer . snd) ps
510− let newTys = map (\(name, TypedValue _ _ ty) -> (name, ty)) newVals
511− oldTys <- zip (map fst ps) <$> replicateM (length ps) fresh
512− let oldTy = Object $ rowFromList (oldTys, row)
513− o' <- TypedValue True <$> check o oldTy <*> pure oldTy
514− return $ TypedValue True (ObjectUpdate o' newVals) $ Object $ rowFromList (newTys, row)
515−infer' (Accessor prop val) = do
516− typed@(TypedValue _ _ objTy) <- infer val
517− propTy <- inferProperty objTy prop
518− case propTy of
519− Nothing -> do
520− field <- fresh
521− rest <- fresh
522− _ <- subsumes Nothing objTy (Object (RCons prop field rest))
523− return $ TypedValue True (Accessor prop typed) field
524− Just ty -> return $ TypedValue True (Accessor prop typed) ty
525−infer' (Abs arg ret) = do
526− ty <- fresh
527− Just moduleName <- checkCurrentModule <$> get
528− bindLocalVariables moduleName [(arg, ty)] $ do
529− body@(TypedValue _ _ bodyTy) <- infer' ret
530− return $ TypedValue True (Abs arg body) $ function ty bodyTy
531−infer' (App f arg) = do
532− f'@(TypedValue _ _ ft) <- infer f
533− (ret, app) <- checkFunctionApplication f' ft arg
534− return $ TypedValue True app ret
535−infer' (Var var) = do
536− Just moduleName <- checkCurrentModule <$> get
537− ty <- introduceSkolemScope <=< replaceAllTypeSynonyms <=< lookupVariable moduleName $ var
538− case ty of
539− ConstrainedType constraints ty' -> do
540− env <- getEnv
541− dicts <- getTypeClassDictionaries
542− return $ TypedValue True (foldl App (Var var) (map (flip TypeClassDictionary dicts) (qualifyAllUnqualifiedNames moduleName env constraints))) ty'
543− _ -> return $ TypedValue True (Var var) ty
544−infer' (Block ss) = do
545− ret <- fresh
546− (allCodePathsReturn, _, ss') <- checkBlock M.empty ret ss
547− guardWith "Block is missing a return statement" allCodePathsReturn
548− return $ TypedValue True (Block ss') ret
549−infer' v@(Constructor c) = do
550− env <- getEnv
551− Just moduleName <- checkCurrentModule <$> get
552− case M.lookup (qualify moduleName c) (dataConstructors env) of
553− Nothing -> throwError $ "Constructor " ++ show c ++ " is undefined"
554− Just (ty, _) -> do ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
555− return $ TypedValue True v ty'
556−infer' (Case vals binders) = do
557− ts <- mapM infer vals
558− ret <- fresh
559− binders' <- checkBinders (map (\(TypedValue _ _ t) -> t) ts) ret binders
560− return $ TypedValue True (Case ts binders') ret
561−infer' (IfThenElse cond th el) = do
562− cond' <- check cond tyBoolean
563− v2@(TypedValue _ _ t2) <- infer th
564− v3@(TypedValue _ _ t3) <- infer el
565− t2 =?= t3
566− return $ TypedValue True (IfThenElse cond' v2 v3) t2
567−infer' (TypedValue checkType val ty) = do
568− Just moduleName <- checkCurrentModule <$> get
569− kind <- liftCheck $ kindOf moduleName ty
570− guardWith ("Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
571− ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
572− val' <- if checkType then check val ty' else return val
573− return $ TypedValue True val' ty'
574−infer' _ = error "Invalid argument to infer"
575−
576−-- |
577−-- Infer the type of a property inside a record with a given type
578−--
579−inferProperty :: Type -> String -> UnifyT Type Check (Maybe Type)
580−inferProperty (Object row) prop = do
581− let (props, _) = rowToList row
582− return $ lookup prop props
583−inferProperty (SaturatedTypeSynonym name args) prop = do
584− replaced <- introduceSkolemScope <=< expandTypeSynonym name $ args
585− inferProperty replaced prop
586−inferProperty (ForAll ident ty _) prop = do
587− replaced <- replaceVarWithUnknown ident ty
588− inferProperty replaced prop
589−inferProperty _ _ = return Nothing
590−
591−-- |
592−-- Infer the types of variables brought into scope by a binder
593−--
594−inferBinder :: Type -> Binder -> UnifyT Type Check (M.Map Ident Type)
595−inferBinder _ NullBinder = return M.empty
596−inferBinder val (StringBinder _) = val =?= tyString >> return M.empty
597−inferBinder val (NumberBinder _) = val =?= tyNumber >> return M.empty
598−inferBinder val (BooleanBinder _) = val =?= tyBoolean >> return M.empty
599−inferBinder val (VarBinder name) = return $ M.singleton name val
600−inferBinder val (NullaryBinder ctor) = do
601− env <- getEnv
602− Just moduleName <- checkCurrentModule <$> get
603− case M.lookup (qualify moduleName ctor) (dataConstructors env) of
604− Just (ty, _) -> do
605− _ <- subsumes Nothing ty val
606− return M.empty
607− _ -> throwError $ "Constructor " ++ show ctor ++ " is not defined"
608−inferBinder val (UnaryBinder ctor binder) = do
609− env <- getEnv
610− Just moduleName <- checkCurrentModule <$> get
611− case M.lookup (qualify moduleName ctor) (dataConstructors env) of
612− Just (ty, _) -> do
613− (_, fn) <- instantiatePolyTypeWithUnknowns (error "Data constructor types cannot contains constraints") ty
614− case fn of
615− TypeApp (TypeApp t obj) ret | t == tyFunction -> do
616− _ <- subsumes Nothing val ret
617− inferBinder obj binder
618− _ -> throwError $ "Constructor " ++ show ctor ++ " is not a unary constructor"
619− _ -> throwError $ "Constructor " ++ show ctor ++ " is not defined"
620−inferBinder val (ObjectBinder props) = do
621− row <- fresh
622− rest <- fresh
623− m1 <- inferRowProperties row rest props
624− val =?= Object row
625− return m1
626− where
627− inferRowProperties :: Type -> Type -> [(String, Binder)] -> UnifyT Type Check (M.Map Ident Type)
628− inferRowProperties nrow row [] = nrow =?= row >> return M.empty
629− inferRowProperties nrow row ((name, binder):binders) = do
630− propTy <- fresh
631− m1 <- inferBinder propTy binder
632− m2 <- inferRowProperties nrow (RCons name propTy row) binders
633− return $ m1 `M.union` m2
634−inferBinder val (ArrayBinder binders) = do
635− el <- fresh
636− m1 <- M.unions <$> mapM (inferBinder el) binders
637− val =?= TypeApp tyArray el
638− return m1
639−inferBinder val (ConsBinder headBinder tailBinder) = do
640− el <- fresh
641− m1 <- inferBinder el headBinder
642− m2 <- inferBinder val tailBinder
643− val =?= TypeApp tyArray el
644− return $ m1 `M.union` m2
645−inferBinder val (NamedBinder name binder) = do
646− m <- inferBinder val binder
647− return $ M.insert name val m
648−
649−-- |
650−-- Check the types of the return values in a set of binders in a case statement
651−--
652−checkBinders :: [Type] -> Type -> [([Binder], Maybe Guard, Value)] -> UnifyT Type Check [([Binder], Maybe Guard, Value)]
653−checkBinders _ _ [] = return []
654−checkBinders nvals ret ((binders, grd, val):bs) = do
655− Just moduleName <- checkCurrentModule <$> get
656− m1 <- M.unions <$> zipWithM inferBinder nvals binders
657− r <- bindLocalVariables moduleName (M.toList m1) $ do
658− val' <- TypedValue True <$> check val ret <*> pure ret
659− case grd of
660− Nothing -> return (binders, Nothing, val')
661− Just g -> do
662− g' <- check g tyBoolean
663− return (binders, Just g', val')
664− rs <- checkBinders nvals ret bs
665− return $ r : rs
666−
667−-- |
668−-- Check that a local variable name is not already used
669−--
670−assignVariable :: Ident -> UnifyT Type Check ()
671−assignVariable name = do
672− env <- checkEnv <$> get
673− Just moduleName <- checkCurrentModule <$> get
674− case M.lookup (moduleName, name) (names env) of
675− Just _ -> UnifyT . lift . throwError $ "Variable with name " ++ show name ++ " already exists."
676− _ -> return ()
677−
678−-- |
679−-- Check the type of the return values of a statement, returning whether or not the statement returns on
680−-- all code paths
681−--
682−checkStatement :: M.Map Ident Type -> Type -> Statement -> UnifyT Type Check (Bool, M.Map Ident Type, Statement)
683−checkStatement mass _ (VariableIntroduction name val) = do
684− assignVariable name
685− val'@(TypedValue _ _ t) <- infer val
686− return (False, M.insert name t mass, VariableIntroduction name val')
687−checkStatement mass _ (Assignment ident val) = do
688− val'@(TypedValue _ _ t) <- infer val
689− case M.lookup ident mass of
690− Nothing -> throwError $ "No local variable with name " ++ show ident
691− Just ty -> do t =?= ty
692− return (False, mass, Assignment ident val')
693−checkStatement mass ret (While val inner) = do
694− val' <- check val tyBoolean
695− (allCodePathsReturn, _, inner') <- checkBlock mass ret inner
696− return (allCodePathsReturn, mass, While val' inner')
697−checkStatement mass ret (If ifst) = do
698− (allCodePathsReturn, ifst') <- checkIfStatement mass ret ifst
699− return (allCodePathsReturn, mass, If ifst')
700−checkStatement mass ret (For ident start end inner) = do
701− Just moduleName <- checkCurrentModule <$> get
702− assignVariable ident
703− start' <- check start tyNumber
704− end' <- check end tyNumber
705− (allCodePathsReturn, _, inner') <- bindLocalVariables moduleName [(ident, tyNumber)] $ checkBlock mass ret inner
706− return (allCodePathsReturn, mass, For ident start' end' inner')
707−checkStatement mass ret (Return val) = do
708− val' <- check val ret
709− return (True, mass, Return (TypedValue True val' ret))
710−
711−-- |
712−-- Check the type of an if-then-else statement
713−--
714−checkIfStatement :: M.Map Ident Type -> Type -> IfStatement -> UnifyT Type Check (Bool, IfStatement)
715−checkIfStatement mass ret (IfStatement val thens Nothing) = do
716− val' <- check val tyBoolean
717− (_, _, thens') <- checkBlock mass ret thens
718− return (False, IfStatement val' thens' Nothing)
719−checkIfStatement mass ret (IfStatement val thens (Just elses)) = do
720− val' <- check val tyBoolean
721− (allCodePathsReturn1, _, thens') <- checkBlock mass ret thens
722− (allCodePathsReturn2, elses') <- checkElseStatement mass ret elses
723− return (allCodePathsReturn1 && allCodePathsReturn2, IfStatement val' thens' (Just elses'))
724−
725−-- |
726−-- Check the type of an else statement
727−--
728−checkElseStatement :: M.Map Ident Type -> Type -> ElseStatement -> UnifyT Type Check (Bool, ElseStatement)
729−checkElseStatement mass ret (Else elses) = do
730− (allCodePathsReturn, _, elses') <- checkBlock mass ret elses
731− return (allCodePathsReturn, Else elses')
732−checkElseStatement mass ret (ElseIf ifst) = (id *** ElseIf) <$> checkIfStatement mass ret ifst
733−
734−-- |
735−-- Check the type of the return value of a block of statements
736−--
737−checkBlock :: M.Map Ident Type -> Type -> [Statement] -> UnifyT Type Check (Bool, M.Map Ident Type, [Statement])
738−checkBlock mass _ [] = return (False, mass, [])
739−checkBlock mass ret (s:ss) = do
740− Just moduleName <- checkCurrentModule <$> get
741− (b1, mass1, s') <- checkStatement mass ret s
742− bindLocalVariables moduleName (M.toList mass1) $ case (b1, ss) of
743− (True, []) -> return (True, mass1, [s'])
744− (True, _) -> throwError "Unreachable code"
745− (False, ss') -> do
746− (b, m, ss'') <- checkBlock mass1 ret ss'
747− return (b, m, s':ss'')
748−
749−-- |
750−-- Generate a new skolem constant
751−--
752−newSkolemConstant :: UnifyT Type Check Int
753−newSkolemConstant = runUnknown <$> fresh'
754−
755−-- |
756−-- Generate a new skolem scope
757−--
758−newSkolemScope :: UnifyT Type Check SkolemScope
759−newSkolemScope = SkolemScope . runUnknown <$> fresh'
760−
761−-- |
762−-- Skolemize a type variable by replacing its instances with fresh skolem constants
763−--
764−skolemize :: String -> Int -> SkolemScope -> Type -> Type
765−skolemize ident sko scope = replaceTypeVars ident (Skolem sko scope)
766−
767−-- |
768−-- Introduce skolem scope at every occurence of a ForAll
769−--
770−introduceSkolemScope :: Type -> UnifyT Type Check Type
771−introduceSkolemScope = everywhereM (mkM go)
772− where
773− go (ForAll ident ty Nothing) = ForAll ident ty <$> (Just <$> newSkolemScope)
774− go other = return other
775−
776−-- |
777−-- Check the type of a value, rethrowing errors to provide a better error message
778−--
779−check :: Value -> Type -> UnifyT Type Check Value
780−check val ty = rethrow errorMessage $ check' val ty
781− where
782− errorMessage msg =
783− "Error checking type of term " ++
784− prettyPrintValue val ++
785− " against type " ++
786− prettyPrintType ty ++
787− ":\n" ++
788− msg
789−
790−-- |
791−-- Check the type of a value
792−--
793−check' :: Value -> Type -> UnifyT Type Check Value
794−check' val t@(ForAll ident ty _) = do
795− scope <- newSkolemScope
796− sko <- newSkolemConstant
797− let sk = skolemize ident sko scope ty
798− val' <- check val sk
799− return $ TypedValue True val' (ForAll ident ty (Just scope))
800−check' val t@(ConstrainedType constraints ty) = do
801− env <- getEnv
802− Just moduleName <- checkCurrentModule <$> get
803− dictNames <- flip mapM constraints $ \(Qualified _ (ProperName className), _) -> do
804− n <- liftCheck freshDictionaryName
805− return $ Ident $ "__dict_" ++ className ++ "_" ++ show n
806− val' <- withTypeClassDictionaries (zipWith (\name (className, instanceTy) ->
807− TypeClassDictionaryInScope name className instanceTy Nothing TCDRegular) (map (Qualified Nothing) dictNames)
808− (qualifyAllUnqualifiedNames moduleName env constraints)) $
809− check val ty
810− return $ TypedValue True (foldr Abs val' dictNames) t
811−check' val t@(SaturatedTypeSynonym name args) = do
812− ty <- introduceSkolemScope <=< expandTypeSynonym name $ args
813− val' <- check val ty
814− return $ TypedValue True val' ty
815−check' val u@(TUnknown _) = do
816− val'@(TypedValue _ _ ty) <- infer val
817− -- Don't unify an unknown with an inferred polytype
818− (val'', ty') <- instantiatePolyTypeWithUnknowns val' ty
819− ty' =?= u
820− return $ TypedValue True val'' ty'
821−check' v@(NumericLiteral _) t | t == tyNumber =
822− return $ TypedValue True v t
823−check' v@(StringLiteral _) t | t == tyString =
824− return $ TypedValue True v t
825−check' v@(BooleanLiteral _) t | t == tyBoolean =
826− return $ TypedValue True v t
827−check' (ArrayLiteral vals) t@(TypeApp a ty) | a == tyArray = do
828− arr <- ArrayLiteral <$> forM vals (\val -> check val ty)
829− return $ TypedValue True arr t
830−check' (Abs arg ret) ty@(TypeApp (TypeApp t argTy) retTy) | t == tyFunction = do
831− Just moduleName <- checkCurrentModule <$> get
832− ret' <- bindLocalVariables moduleName [(arg, argTy)] $ check ret retTy
833− return $ TypedValue True (Abs arg ret') ty
834−check' (App f arg) ret = do
835− f'@(TypedValue _ _ ft) <- infer f
836− (ret', app) <- checkFunctionApplication f' ft arg
837− subsumes Nothing ret' ret
838− return $ TypedValue True app ret
839−check' v@(Var var) ty = do
840− Just moduleName <- checkCurrentModule <$> get
841− repl <- introduceSkolemScope <=< replaceAllTypeSynonyms <=< lookupVariable moduleName $ var
842− ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
843− v' <- subsumes (Just v) repl ty'
844− case v' of
845− Nothing -> throwError "Unable to check type subsumption"
846− Just v'' -> return $ TypedValue True v'' ty'
847−check' (TypedValue checkType val ty1) ty2 = do
848− Just moduleName <- checkCurrentModule <$> get
849− kind <- liftCheck $ kindOf moduleName ty1
850− guardWith ("Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
851− val' <- subsumes (Just val) ty1 ty2
852− case val' of
853− Nothing -> throwError "Unable to check type subsumption"
854− Just val'' -> do
855− val''' <- if checkType then check val'' ty1 else return val''
856− return $ TypedValue checkType (TypedValue True val''' ty1) ty2
857−check' (Case vals binders) ret = do
858− vals' <- mapM infer vals
859− let ts = map (\(TypedValue _ _ t) -> t) vals'
860− binders' <- checkBinders ts ret binders
861− return $ TypedValue True (Case vals' binders') ret
862−check' (IfThenElse cond th el) ty = do
863− cond' <- check cond tyBoolean
864− th' <- check th ty
865− el' <- check el ty
866− return $ TypedValue True (IfThenElse cond' th' el') ty
867−check' (ObjectLiteral ps) t@(Object row) = do
868− ensureNoDuplicateProperties ps
869− ps' <- checkProperties ps row False
870− return $ TypedValue True (ObjectLiteral ps') t
871−check' (ObjectUpdate obj ps) t@(Object row) = do
872− ensureNoDuplicateProperties ps
873− us <- zip (map fst ps) <$> replicateM (length ps) fresh
874− let (propsToCheck, rest) = rowToList row
875− propsToRemove = map fst ps
876− remainingProps = filter (\(p, _) -> p `notElem` propsToRemove) propsToCheck
877− obj' <- check obj (Object (rowFromList (us ++ remainingProps, rest)))
878− ps' <- checkProperties ps row True
879− return $ TypedValue True (ObjectUpdate obj' ps') t
880−check' (Accessor prop val) ty = do
881− rest <- fresh
882− val' <- check val (Object (RCons prop ty rest))
883− return $ TypedValue True (Accessor prop val') ty
884−check' (Block ss) ret = do
885− (allCodePathsReturn, _, ss') <- checkBlock M.empty ret ss
886− guardWith "Block is missing a return statement" allCodePathsReturn
887− return $ TypedValue True (Block ss') ret
888−check' (Constructor c) ty = do
889− env <- getEnv
890− Just moduleName <- checkCurrentModule <$> get
891− case M.lookup (qualify moduleName c) (dataConstructors env) of
892− Nothing -> throwError $ "Constructor " ++ show c ++ " is undefined"
893− Just (ty1, _) -> do
894− repl <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty1
895− _ <- subsumes Nothing repl ty
896− return $ TypedValue True (Constructor c) ty
897−check' val ty = throwError $ prettyPrintValue val ++ " does not have type " ++ prettyPrintType ty
898−
899−-- |
900−-- Check the type of a collection of named record fields
901−--
902−-- The @lax@ parameter controls whether or not every record member has to be provided. For object updates, this is not the case.
903−--
904−checkProperties :: [(String, Value)] -> Type -> Bool -> UnifyT Type Check [(String, Value)]
905−checkProperties ps row lax = let (ts, r') = rowToList row in go ps ts r' where
906− go [] [] REmpty = return []
907− go [] [] u@(TUnknown _) = do u =?= REmpty
908− return []
909− go [] [] (Skolem _ _) | lax = return []
910− go [] ((p, _): _) _ | lax = return []
911− | otherwise = throwError $ prettyPrintValue (ObjectLiteral ps) ++ " does not have property " ++ p
912− go ((p,_):_) [] REmpty = throwError $ "Property " ++ p ++ " is not present in closed object type " ++ prettyPrintRow row
913− go ((p,v):ps') [] u@(TUnknown _) = do
914− v'@(TypedValue _ _ ty) <- infer v
915− rest <- fresh
916− u =?= RCons p ty rest
917− ps'' <- go ps' [] rest
918− return $ (p, v') : ps''
919− go ((p,v):ps') ts r =
920− case lookup p ts of
921− Nothing -> do
922− v'@(TypedValue _ _ ty) <- infer v
923− rest <- fresh
924− r =?= RCons p ty rest
925− ps'' <- go ps' ts rest
926− return $ (p, v') : ps''
927− Just ty -> do
928− v' <- check v ty
929− ps'' <- go ps' (delete (p, ty) ts) r
930− return $ (p, v') : ps''
931− go _ _ _ = throwError $ prettyPrintValue (ObjectLiteral ps) ++ " does not have type " ++ prettyPrintType (Object row)
932−
933−-- |
934−-- Check the type of a function application, rethrowing errors to provide a better error message
935−--
936−checkFunctionApplication :: Value -> Type -> Value -> UnifyT Type Check (Type, Value)
937−checkFunctionApplication fn fnTy arg = rethrow errorMessage $ checkFunctionApplication' fn fnTy arg
938− where
939− errorMessage msg = "Error applying function of type "
940− ++ prettyPrintType fnTy
941− ++ " to argument " ++ prettyPrintValue arg
942− ++ ":\n" ++ msg
943−
944−-- |
945−-- Check the type of a function application
946−--
947−checkFunctionApplication' :: Value -> Type -> Value -> UnifyT Type Check (Type, Value)
948−checkFunctionApplication' fn (TypeApp (TypeApp tyFunction' argTy) retTy) arg = do
949− tyFunction' =?= tyFunction
950− arg' <- check arg argTy
951− return (retTy, App fn arg')
952−checkFunctionApplication' fn (ForAll ident ty _) arg = do
953− replaced <- replaceVarWithUnknown ident ty
954− checkFunctionApplication fn replaced arg
955−checkFunctionApplication' fn u@(TUnknown _) arg = do
956− arg' <- do
957− TypedValue _ v t <- infer arg
958− (v', t') <- instantiatePolyTypeWithUnknowns arg t
959− return $ TypedValue True v' t'
960− let ty = (\(TypedValue _ _ t) -> t) arg'
961− ret <- fresh
962− u =?= function ty ret
963− return (ret, App fn arg')
964−checkFunctionApplication' fn (SaturatedTypeSynonym name tyArgs) arg = do
965− ty <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
966− checkFunctionApplication fn ty arg
967−checkFunctionApplication' fn (ConstrainedType constraints fnTy) arg = do
968− env <- getEnv
969− dicts <- getTypeClassDictionaries
970− Just moduleName <- checkCurrentModule <$> get
971− checkFunctionApplication' (foldl App fn (map (flip TypeClassDictionary dicts) (qualifyAllUnqualifiedNames moduleName env constraints))) fnTy arg
972−checkFunctionApplication' _ fnTy arg = throwError $ "Cannot apply a function of type "
973− ++ prettyPrintType fnTy
974− ++ " to argument " ++ prettyPrintValue arg
975−
976−-- |
977−-- Check whether one type subsumes another, rethrowing errors to provide a better error message
978−--
979−subsumes :: Maybe Value -> Type -> Type -> UnifyT Type Check (Maybe Value)
980−subsumes val ty1 ty2 = rethrow errorMessage $ subsumes' val ty1 ty2
981− where
982− errorMessage msg = "Error checking that type "
983− ++ prettyPrintType ty1
984− ++ " subsumes type "
985− ++ prettyPrintType ty2
986− ++ ":\n" ++ msg
987−
988−-- |
989−-- Check whether one type subsumes another
990−--
991−subsumes' :: Maybe Value -> Type -> Type -> UnifyT Type Check (Maybe Value)
992−subsumes' val (ForAll ident ty1 _) ty2 = do
993− replaced <- replaceVarWithUnknown ident ty1
994− subsumes val replaced ty2
995−subsumes' val ty1 (ForAll ident ty2 sco) =
996− case sco of
997− Just sco' -> do
998− sko <- newSkolemConstant
999− let sk = skolemize ident sko sco' ty2
1000− subsumes val ty1 sk
1001− Nothing -> throwError "Skolem variable scope is unspecified"
1002−subsumes' val (TypeApp (TypeApp f1 arg1) ret1) (TypeApp (TypeApp f2 arg2) ret2) | f1 == tyFunction && f2 == tyFunction = do
1003− subsumes Nothing arg2 arg1
1004− subsumes Nothing ret1 ret2
1005− return val
1006−subsumes' val (SaturatedTypeSynonym name tyArgs) ty2 = do
1007− ty1 <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
1008− subsumes val ty1 ty2
1009−subsumes' val ty1 (SaturatedTypeSynonym name tyArgs) = do
1010− ty2 <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
1011− subsumes val ty1 ty2
1012−subsumes' (Just val) (ConstrainedType constraints ty1) ty2 = do
1013− env <- getEnv
1014− dicts <- getTypeClassDictionaries
1015− Just moduleName <- checkCurrentModule <$> get
1016− _ <- subsumes' Nothing ty1 ty2
1017− return . Just $ foldl App val (map (flip TypeClassDictionary dicts) (qualifyAllUnqualifiedNames moduleName env constraints))
1018−subsumes' val ty1 ty2 = do
1019− ty1 =?= ty2
1020− return val
1021−