@@ -1,936 +0,0 @@
1−-----------------------------------------------------------------------------
3−-- Module : Language.PureScript.TypeChecker.Types
4−-- Copyright : (c) Phil Freeman 2013
7−-- Maintainer : Phil Freeman <paf31@cantab.net>
8−-- Stability : experimental
12−-- This module implements the type checker
14−-----------------------------------------------------------------------------
16−{-# OPTIONS_GHC -fno-warn-orphans #-}
17−{-# LANGUAGE DeriveDataTypeable #-}
18−{-# LANGUAGE FlexibleContexts #-}
19−{-# LANGUAGE MultiParamTypeClasses #-}
21−module Language.PureScript.TypeChecker.Types (
26− The following functions represent the corresponding type checking judgements:
29− Synthesize a type for a value
32− Check a value has a given type
35− Check an object with a given type contains specified properties
37− checkFunctionApplication
38− Check a function of a given type returns a value of another type when applied to its arguments
41− Check a type subsumes another type
45−import Data.Maybe (maybeToList, isNothing, isJust, fromMaybe)
46−import qualified Data.Data as D
48− (everythingWithContext, mkM, everywhereM, everything, mkT,
49− something, everywhere, mkQ)
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
60−import Control.Monad.State
61−import Control.Monad.Error
62−import Control.Monad.Reader
63−import Control.Monad.Unify
65−import Control.Applicative
66−import Control.Arrow (Arrow(..))
68−import qualified Data.Map as M
69−import Data.Function (on)
71−instance Partial Type where
73− isUnknown (TUnknown u) = Just u
74− isUnknown _ = Nothing
76−instance Unifiable Check Type where
80−-- Unify two types, updating the current substitution
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
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
92− unifyTypes' ty s@(SaturatedTypeSynonym _ _) = s `unifyTypes` ty
93− unifyTypes' (ForAll ident1 ty1 sc1) (ForAll ident2 ty2 sc2) =
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
100− _ -> throwError (prettyPrintType ty1)
101− unifyTypes' (ForAll ident ty1 (Just sc)) ty2 = do
102− sko <- newSkolemConstant
103− let sk = skolemize ident sko sc ty1
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
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
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 ++ "."
124−-- Unify two rows, updating the current substitution
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
130−unifyRows :: Type -> Type -> UnifyT Type Check ()
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 ]
139− forM_ int (uncurry (=?=))
140− unifyRows' sd1 r1' sd2 r2'
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
147− forM_ row $ \(_, t) -> occursCheck un t
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)) ++ "."
157−-- Ensure type constructors are equal after canonicalization
159−typeConstructorsAreEqual :: Environment -> ModuleName -> Qualified ProperName -> Qualified ProperName -> Bool
160−typeConstructorsAreEqual env moduleName = (==) `on` canonicalizeType moduleName env
163−-- Infer the types of multiple mutually-recursive values, and return elaborated values including
164−-- type class dictionaries and type annotations.
166−typesOf :: ModuleName -> [(Ident, Value)] -> Check [(Ident, (Value, Type))]
167−typesOf moduleName vals = do
168− tys <- fmap tidyUp . liftUnify $ do
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
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
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
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'))
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
228−-- Check if a value introduces a function
230−isFunction :: Value -> Bool
231−isFunction (Abs _ _) = True
232−isFunction (TypedValue _ val _) = isFunction val
236−-- Check if a value contains a type annotation
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))
243−-- Map a function over type annotations appearing inside a value
245−overTypes :: (Type -> Type) -> Value -> Value
246−overTypes f = everywhere (mkT f)
249−-- Replace type class dictionary placeholders with inferred type class dictionaries
251−replaceTypeClassDictionaries :: ModuleName -> Value -> Check Value
252−replaceTypeClassDictionaries mn = everywhereM (mkM go)
254− go (TypeClassDictionary constraint dicts) = entails mn dicts constraint
255− go other = return other
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.
261−entails :: ModuleName -> [TypeClassDictionaryInScope] -> (Qualified ProperName, Type) -> Check Value
262−entails moduleName context goal@(className, ty) = do
265− [] -> throwError $ "No " ++ show className ++ " instance found for " ++ prettyPrintType ty
266− (dict : _) -> return dict
268− go env (className', ty') =
269− [ mkDictionary (canonicalizeDictionary tcd) args
271− -- Choose type class dictionaries in scope in the current module
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)
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
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.
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) <$> typeHeadsAreEqual m e h1 h2
313−typeHeadsAreEqual m e t1@(TypeApp _ _) t2@(TypeApp _ (TypeVar _)) = typeHeadsAreEqual m e t2 t1
314−typeHeadsAreEqual m e (SaturatedTypeSynonym name args) t2 = case expandTypeSynonym' e m name args of
316− Right t1 -> typeHeadsAreEqual m e t1 t2
317−typeHeadsAreEqual _ _ _ _ = Nothing
320−-- Ensure unsolved unification variables do not escape
322−escapeCheck :: Value -> Type -> UnifyT Type Check ()
323−escapeCheck value ty = do
324− subst <- unifyCurrentSubstitution <$> 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
332−-- Find all type annotations occuring inside a value
334−findAllTypes :: Value -> [Type]
335−findAllTypes = everything (++) (mkQ [] go)
337− go (TypedValue _ _ ty) = [ty]
341−-- Ensure skolem variables do not escape their scope
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
354− ((binding, val) : _) -> throwError $ "Rigid/skolem type variable bound by " ++ maybe "<unknown>" prettyPrintValue binding ++ " has escaped at " ++ prettyPrintValue val
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)
362− collectSkolems :: Type -> [SkolemScope]
363− collectSkolems = nub . everything (++) (mkQ [] collect)
365− collect (Skolem _ scope) = [scope]
367− go _ scos = ([], scos)
368− findBindingScope :: SkolemScope -> Maybe Value
369− findBindingScope sco = something (mkQ Nothing go) root
371− go val@(TypedValue _ _ (ForAll _ _ (Just sco'))) | sco == sco' = Just val
373−skolemEscapeCheck val = throwError $ "Untyped value passed to skolemEscapeCheck: " ++ prettyPrintValue val
376−-- Ensure a row contains no duplicate labels
378−setify :: Type -> Type
379−setify = rowFromList . first (M.toList . M.fromList) . rowToList
382−-- \"Setify\" all rows occuring inside a value
384−setifyAll :: (D.Data d) => d -> d
385−setifyAll = everywhere (mkT setify)
388−-- Replace outermost unsolved unification variables with named type variables
390−varIfUnknown :: Type -> Type
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)
398− in mkForAll (sort . map (toName . runUnknown) $ unks) ty'
401−-- Replace named type variables with types
403−replaceAllTypeVars :: [(String, Type)] -> Type -> Type
404−replaceAllTypeVars = foldl' (\f (name, ty) -> replaceTypeVars name ty . f) id
407−-- Remove any ForAlls and ConstrainedType constructors in a type by introducing new unknowns
408−-- or TypeClassDictionary values.
410−-- This is necessary during type checking to avoid unifying a polymorphic type with a
411−-- unification variable.
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
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)
426−-- Replace a single type variable with a new unification variable
428−replaceVarWithUnknown :: String -> Type -> UnifyT Type Check Type
429−replaceVarWithUnknown ident ty = do
431− return $ replaceTypeVars ident tu $ ty
434−-- Replace fully applied type synonyms with the @SaturatedTypeSynonym@ data constructor, which helps generate
435−-- better error messages during unification.
437−replaceAllTypeSynonyms' :: (D.Data d) => Environment -> ModuleName -> d -> Either String d
438−replaceAllTypeSynonyms' env moduleName d =
440− syns = map (\((path, name), (args, _)) -> ((path, name), length args)) . M.toList $ typeSynonyms env
442− saturateAllTypeSynonyms env moduleName syns d
444−replaceAllTypeSynonyms :: (Functor m, Monad m, MonadState CheckState m, MonadError String m) => (D.Data d) => d -> m d
445−replaceAllTypeSynonyms d = do
447− Just moduleName <- checkCurrentModule <$> get
448− either throwError return $ replaceAllTypeSynonyms' env moduleName d
451−-- \"Desaturate\" @SaturatedTypeSynonym@s
453−desaturateAllTypeSynonyms :: (D.Data d) => d -> d
454−desaturateAllTypeSynonyms = everywhere (mkT replaceSaturatedTypeSynonym)
456− replaceSaturatedTypeSynonym (SaturatedTypeSynonym name args) = foldl TypeApp (TypeConstructor name) args
457− replaceSaturatedTypeSynonym t = t
460−-- Replace a type synonym and its arguments with the aliased type
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"
470−expandTypeSynonym :: (Functor m, Monad m, MonadState CheckState m, MonadError String m) => Qualified ProperName -> [Type] -> m Type
471−expandTypeSynonym name args = do
473− Just moduleName <- checkCurrentModule <$> get
474− either throwError return $ expandTypeSynonym' env moduleName name args
477−-- Ensure a set of property names and value does not contain duplicate labels
479−ensureNoDuplicateProperties :: (MonadError String m) => [(String, Value)] -> m ()
480−ensureNoDuplicateProperties ps = guardWith "Duplicate property names" $ length (nub . map fst $ ps) == length ps
483−-- Infer a type for a value, rethrowing any error to provide a more useful error message
485−infer :: Value -> UnifyT Type Check Value
486−infer val = rethrow (\e -> "Error inferring type of term " ++ prettyPrintValue val ++ ":\n" ++ e) $ infer' val
489−-- Infer a type for a value
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
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
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
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
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
539− ConstrainedType constraints ty' -> do
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' v@(Constructor c) = do
546− Just moduleName <- checkCurrentModule <$> get
547− case M.lookup (qualify moduleName c) (dataConstructors env) of
548− Nothing -> throwError $ "Constructor " ++ show c ++ " is undefined"
549− Just (ty, _) -> do ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
550− return $ TypedValue True v ty'
551−infer' (Case vals binders) = do
552− ts <- mapM infer vals
554− binders' <- checkBinders (map (\(TypedValue _ _ t) -> t) ts) ret binders
555− return $ TypedValue True (Case ts binders') ret
556−infer' (IfThenElse cond th el) = do
557− cond' <- check cond tyBoolean
558− v2@(TypedValue _ _ t2) <- infer th
559− v3@(TypedValue _ _ t3) <- infer el
561− return $ TypedValue True (IfThenElse cond' v2 v3) t2
562−infer' (TypedValue checkType val ty) = do
563− Just moduleName <- checkCurrentModule <$> get
564− kind <- liftCheck $ kindOf moduleName ty
565− guardWith ("Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
566− ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
567− val' <- if checkType then check val ty' else return val
568− return $ TypedValue True val' ty'
569−infer' _ = error "Invalid argument to infer"
572−-- Infer the type of a property inside a record with a given type
574−inferProperty :: Type -> String -> UnifyT Type Check (Maybe Type)
575−inferProperty (Object row) prop = do
576− let (props, _) = rowToList row
577− return $ lookup prop props
578−inferProperty (SaturatedTypeSynonym name args) prop = do
579− replaced <- introduceSkolemScope <=< expandTypeSynonym name $ args
580− inferProperty replaced prop
581−inferProperty (ForAll ident ty _) prop = do
582− replaced <- replaceVarWithUnknown ident ty
583− inferProperty replaced prop
584−inferProperty _ _ = return Nothing
587−-- Infer the types of variables brought into scope by a binder
589−inferBinder :: Type -> Binder -> UnifyT Type Check (M.Map Ident Type)
590−inferBinder _ NullBinder = return M.empty
591−inferBinder val (StringBinder _) = val =?= tyString >> return M.empty
592−inferBinder val (NumberBinder _) = val =?= tyNumber >> return M.empty
593−inferBinder val (BooleanBinder _) = val =?= tyBoolean >> return M.empty
594−inferBinder val (VarBinder name) = return $ M.singleton name val
595−inferBinder val (ConstructorBinder ctor binders) = do
597− Just moduleName <- checkCurrentModule <$> get
598− case M.lookup (qualify moduleName ctor) (dataConstructors env) of
600− (_, fn) <- instantiatePolyTypeWithUnknowns (error "Data constructor types cannot contains constraints") ty
604− subsumes Nothing val ty
606− go (binder : binders) (TypeApp (TypeApp t obj) ret) | t == tyFunction =
607− M.union <$> inferBinder obj binder <*> go binders ret
608− go _ _ = throwError $ "Wrong number of arguments to constructor " ++ show ctor
609− _ -> throwError $ "Constructor " ++ show ctor ++ " is not defined"
610−inferBinder val (ObjectBinder props) = do
613− m1 <- inferRowProperties row rest props
617− inferRowProperties :: Type -> Type -> [(String, Binder)] -> UnifyT Type Check (M.Map Ident Type)
618− inferRowProperties nrow row [] = nrow =?= row >> return M.empty
619− inferRowProperties nrow row ((name, binder):binders) = do
621− m1 <- inferBinder propTy binder
622− m2 <- inferRowProperties nrow (RCons name propTy row) binders
623− return $ m1 `M.union` m2
624−inferBinder val (ArrayBinder binders) = do
626− m1 <- M.unions <$> mapM (inferBinder el) binders
627− val =?= TypeApp tyArray el
629−inferBinder val (ConsBinder headBinder tailBinder) = do
631− m1 <- inferBinder el headBinder
632− m2 <- inferBinder val tailBinder
633− val =?= TypeApp tyArray el
634− return $ m1 `M.union` m2
635−inferBinder val (NamedBinder name binder) = do
636− m <- inferBinder val binder
637− return $ M.insert name val m
640−-- Check the types of the return values in a set of binders in a case statement
642−checkBinders :: [Type] -> Type -> [([Binder], Maybe Guard, Value)] -> UnifyT Type Check [([Binder], Maybe Guard, Value)]
643−checkBinders _ _ [] = return []
644−checkBinders nvals ret ((binders, grd, val):bs) = do
645− Just moduleName <- checkCurrentModule <$> get
646− m1 <- M.unions <$> zipWithM inferBinder nvals binders
647− r <- bindLocalVariables moduleName (M.toList m1) $ do
648− val' <- TypedValue True <$> check val ret <*> pure ret
650− Nothing -> return (binders, Nothing, val')
652− g' <- check g tyBoolean
653− return (binders, Just g', val')
654− rs <- checkBinders nvals ret bs
658−-- Check that a local variable name is not already used
660−assignVariable :: Ident -> UnifyT Type Check ()
661−assignVariable name = do
662− env <- checkEnv <$> get
663− Just moduleName <- checkCurrentModule <$> get
664− case M.lookup (moduleName, name) (names env) of
665− Just _ -> UnifyT . lift . throwError $ "Variable with name " ++ show name ++ " already exists."
669−-- Generate a new skolem constant
671−newSkolemConstant :: UnifyT Type Check Int
672−newSkolemConstant = runUnknown <$> fresh'
675−-- Generate a new skolem scope
677−newSkolemScope :: UnifyT Type Check SkolemScope
678−newSkolemScope = SkolemScope . runUnknown <$> fresh'
681−-- Skolemize a type variable by replacing its instances with fresh skolem constants
683−skolemize :: String -> Int -> SkolemScope -> Type -> Type
684−skolemize ident sko scope = replaceTypeVars ident (Skolem sko scope)
687−-- Introduce skolem scope at every occurence of a ForAll
689−introduceSkolemScope :: Type -> UnifyT Type Check Type
690−introduceSkolemScope = everywhereM (mkM go)
692− go (ForAll ident ty Nothing) = ForAll ident ty <$> (Just <$> newSkolemScope)
693− go other = return other
696−-- Check the type of a value, rethrowing errors to provide a better error message
698−check :: Value -> Type -> UnifyT Type Check Value
699−check val ty = rethrow errorMessage $ check' val ty
702− "Error checking type of term " ++
703− prettyPrintValue val ++
705− prettyPrintType ty ++
710−-- Check the type of a value
712−check' :: Value -> Type -> UnifyT Type Check Value
713−check' val t@(ForAll ident ty _) = do
714− scope <- newSkolemScope
715− sko <- newSkolemConstant
716− let sk = skolemize ident sko scope ty
717− val' <- check val sk
718− return $ TypedValue True val' (ForAll ident ty (Just scope))
719−check' val t@(ConstrainedType constraints ty) = do
721− Just moduleName <- checkCurrentModule <$> get
722− dictNames <- flip mapM constraints $ \(Qualified _ (ProperName className), _) -> do
723− n <- liftCheck freshDictionaryName
724− return $ Ident $ "__dict_" ++ className ++ "_" ++ show n
725− val' <- withTypeClassDictionaries (zipWith (\name (className, instanceTy) ->
726− TypeClassDictionaryInScope name className instanceTy Nothing TCDRegular) (map (Qualified Nothing) dictNames)
727− (qualifyAllUnqualifiedNames moduleName env constraints)) $
729− return $ TypedValue True (foldr Abs val' dictNames) t
730−check' val t@(SaturatedTypeSynonym name args) = do
731− ty <- introduceSkolemScope <=< expandTypeSynonym name $ args
732− val' <- check val ty
733− return $ TypedValue True val' ty
734−check' val u@(TUnknown _) = do
735− val'@(TypedValue _ _ ty) <- infer val
736− -- Don't unify an unknown with an inferred polytype
737− (val'', ty') <- instantiatePolyTypeWithUnknowns val' ty
739− return $ TypedValue True val'' ty'
740−check' v@(NumericLiteral _) t | t == tyNumber =
741− return $ TypedValue True v t
742−check' v@(StringLiteral _) t | t == tyString =
743− return $ TypedValue True v t
744−check' v@(BooleanLiteral _) t | t == tyBoolean =
745− return $ TypedValue True v t
746−check' (ArrayLiteral vals) t@(TypeApp a ty) | a == tyArray = do
747− arr <- ArrayLiteral <$> forM vals (\val -> check val ty)
748− return $ TypedValue True arr t
749−check' (Abs arg ret) ty@(TypeApp (TypeApp t argTy) retTy) | t == tyFunction = do
750− Just moduleName <- checkCurrentModule <$> get
751− ret' <- bindLocalVariables moduleName [(arg, argTy)] $ check ret retTy
752− return $ TypedValue True (Abs arg ret') ty
753−check' (App f arg) ret = do
754− f'@(TypedValue _ _ ft) <- infer f
755− (ret', app) <- checkFunctionApplication f' ft arg
756− subsumes Nothing ret' ret
757− return $ TypedValue True app ret
758−check' v@(Var var) ty = do
759− Just moduleName <- checkCurrentModule <$> get
760− repl <- introduceSkolemScope <=< replaceAllTypeSynonyms <=< lookupVariable moduleName $ var
761− ty' <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty
762− v' <- subsumes (Just v) repl ty'
764− Nothing -> throwError "Unable to check type subsumption"
765− Just v'' -> return $ TypedValue True v'' ty'
766−check' (TypedValue checkType val ty1) ty2 = do
767− Just moduleName <- checkCurrentModule <$> get
768− kind <- liftCheck $ kindOf moduleName ty1
769− guardWith ("Expected type of kind *, was " ++ prettyPrintKind kind) $ kind == Star
770− val' <- subsumes (Just val) ty1 ty2
772− Nothing -> throwError "Unable to check type subsumption"
774− val''' <- if checkType then check val'' ty1 else return val''
775− return $ TypedValue checkType (TypedValue True val''' ty1) ty2
776−check' (Case vals binders) ret = do
777− vals' <- mapM infer vals
778− let ts = map (\(TypedValue _ _ t) -> t) vals'
779− binders' <- checkBinders ts ret binders
780− return $ TypedValue True (Case vals' binders') ret
781−check' (IfThenElse cond th el) ty = do
782− cond' <- check cond tyBoolean
785− return $ TypedValue True (IfThenElse cond' th' el') ty
786−check' (ObjectLiteral ps) t@(Object row) = do
787− ensureNoDuplicateProperties ps
788− ps' <- checkProperties ps row False
789− return $ TypedValue True (ObjectLiteral ps') t
790−check' (ObjectUpdate obj ps) t@(Object row) = do
791− ensureNoDuplicateProperties ps
792− us <- zip (map fst ps) <$> replicateM (length ps) fresh
793− let (propsToCheck, rest) = rowToList row
794− propsToRemove = map fst ps
795− remainingProps = filter (\(p, _) -> p `notElem` propsToRemove) propsToCheck
796− obj' <- check obj (Object (rowFromList (us ++ remainingProps, rest)))
797− ps' <- checkProperties ps row True
798− return $ TypedValue True (ObjectUpdate obj' ps') t
799−check' (Accessor prop val) ty = do
801− val' <- check val (Object (RCons prop ty rest))
802− return $ TypedValue True (Accessor prop val') ty
803−check' (Constructor c) ty = do
805− Just moduleName <- checkCurrentModule <$> get
806− case M.lookup (qualify moduleName c) (dataConstructors env) of
807− Nothing -> throwError $ "Constructor " ++ show c ++ " is undefined"
809− repl <- introduceSkolemScope <=< replaceAllTypeSynonyms $ ty1
810− _ <- subsumes Nothing repl ty
811− return $ TypedValue True (Constructor c) ty
812−check' val ty = throwError $ prettyPrintValue val ++ " does not have type " ++ prettyPrintType ty
815−-- Check the type of a collection of named record fields
817−-- The @lax@ parameter controls whether or not every record member has to be provided. For object updates, this is not the case.
819−checkProperties :: [(String, Value)] -> Type -> Bool -> UnifyT Type Check [(String, Value)]
820−checkProperties ps row lax = let (ts, r') = rowToList row in go ps ts r' where
821− go [] [] REmpty = return []
822− go [] [] u@(TUnknown _) = do u =?= REmpty
824− go [] [] (Skolem _ _) | lax = return []
825− go [] ((p, _): _) _ | lax = return []
826− | otherwise = throwError $ prettyPrintValue (ObjectLiteral ps) ++ " does not have property " ++ p
827− go ((p,_):_) [] REmpty = throwError $ "Property " ++ p ++ " is not present in closed object type " ++ prettyPrintRow row
828− go ((p,v):ps') [] u@(TUnknown _) = do
829− v'@(TypedValue _ _ ty) <- infer v
831− u =?= RCons p ty rest
832− ps'' <- go ps' [] rest
833− return $ (p, v') : ps''
834− go ((p,v):ps') ts r =
837− v'@(TypedValue _ _ ty) <- infer v
839− r =?= RCons p ty rest
840− ps'' <- go ps' ts rest
841− return $ (p, v') : ps''
844− ps'' <- go ps' (delete (p, ty) ts) r
845− return $ (p, v') : ps''
846− go _ _ _ = throwError $ prettyPrintValue (ObjectLiteral ps) ++ " does not have type " ++ prettyPrintType (Object row)
849−-- Check the type of a function application, rethrowing errors to provide a better error message
851−checkFunctionApplication :: Value -> Type -> Value -> UnifyT Type Check (Type, Value)
852−checkFunctionApplication fn fnTy arg = rethrow errorMessage $ checkFunctionApplication' fn fnTy arg
854− errorMessage msg = "Error applying function of type "
855− ++ prettyPrintType fnTy
856− ++ " to argument " ++ prettyPrintValue arg
860−-- Check the type of a function application
862−checkFunctionApplication' :: Value -> Type -> Value -> UnifyT Type Check (Type, Value)
863−checkFunctionApplication' fn (TypeApp (TypeApp tyFunction' argTy) retTy) arg = do
864− tyFunction' =?= tyFunction
865− arg' <- check arg argTy
866− return (retTy, App fn arg')
867−checkFunctionApplication' fn (ForAll ident ty _) arg = do
868− replaced <- replaceVarWithUnknown ident ty
869− checkFunctionApplication fn replaced arg
870−checkFunctionApplication' fn u@(TUnknown _) arg = do
872− TypedValue _ v t <- infer arg
873− (v', t') <- instantiatePolyTypeWithUnknowns arg t
874− return $ TypedValue True v' t'
875− let ty = (\(TypedValue _ _ t) -> t) arg'
877− u =?= function ty ret
878− return (ret, App fn arg')
879−checkFunctionApplication' fn (SaturatedTypeSynonym name tyArgs) arg = do
880− ty <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
881− checkFunctionApplication fn ty arg
882−checkFunctionApplication' fn (ConstrainedType constraints fnTy) arg = do
884− dicts <- getTypeClassDictionaries
885− Just moduleName <- checkCurrentModule <$> get
886− checkFunctionApplication' (foldl App fn (map (flip TypeClassDictionary dicts) (qualifyAllUnqualifiedNames moduleName env constraints))) fnTy arg
887−checkFunctionApplication' _ fnTy arg = throwError $ "Cannot apply a function of type "
888− ++ prettyPrintType fnTy
889− ++ " to argument " ++ prettyPrintValue arg
892−-- Check whether one type subsumes another, rethrowing errors to provide a better error message
894−subsumes :: Maybe Value -> Type -> Type -> UnifyT Type Check (Maybe Value)
895−subsumes val ty1 ty2 = rethrow errorMessage $ subsumes' val ty1 ty2
897− errorMessage msg = "Error checking that type "
898− ++ prettyPrintType ty1
899− ++ " subsumes type "
900− ++ prettyPrintType ty2
904−-- Check whether one type subsumes another
906−subsumes' :: Maybe Value -> Type -> Type -> UnifyT Type Check (Maybe Value)
907−subsumes' val (ForAll ident ty1 _) ty2 = do
908− replaced <- replaceVarWithUnknown ident ty1
909− subsumes val replaced ty2
910−subsumes' val ty1 (ForAll ident ty2 sco) =
913− sko <- newSkolemConstant
914− let sk = skolemize ident sko sco' ty2
916− Nothing -> throwError "Skolem variable scope is unspecified"
917−subsumes' val (TypeApp (TypeApp f1 arg1) ret1) (TypeApp (TypeApp f2 arg2) ret2) | f1 == tyFunction && f2 == tyFunction = do
918− subsumes Nothing arg2 arg1
919− subsumes Nothing ret1 ret2
921−subsumes' val (SaturatedTypeSynonym name tyArgs) ty2 = do
922− ty1 <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
923− subsumes val ty1 ty2
924−subsumes' val ty1 (SaturatedTypeSynonym name tyArgs) = do
925− ty2 <- introduceSkolemScope <=< expandTypeSynonym name $ tyArgs
926− subsumes val ty1 ty2
927−subsumes' (Just val) (ConstrainedType constraints ty1) ty2 = do
929− dicts <- getTypeClassDictionaries
930− Just moduleName <- checkCurrentModule <$> get
931− _ <- subsumes' Nothing ty1 ty2
932− return . Just $ foldl App val (map (flip TypeClassDictionary dicts) (qualifyAllUnqualifiedNames moduleName env constraints))
933−subsumes' val ty1 ty2 = do