2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1998
6 Type - public interface
10 -- re-exports from TypeRep
11 TyThing(..), Type, PredType(..), ThetaType,
15 Kind, SimpleKind, KindVar,
16 kindFunResult, splitKindFunTys, splitKindFunTysN,
18 liftedTypeKindTyCon, openTypeKindTyCon, unliftedTypeKindTyCon,
19 argTypeKindTyCon, ubxTupleKindTyCon,
21 liftedTypeKind, unliftedTypeKind, openTypeKind,
22 argTypeKind, ubxTupleKind,
24 tySuperKind, coSuperKind,
26 isLiftedTypeKind, isUnliftedTypeKind, isOpenTypeKind,
27 isUbxTupleKind, isArgTypeKind, isKind, isTySuperKind,
28 isCoSuperKind, isSuperKind, isCoercionKind, isEqPred,
29 mkArrowKind, mkArrowKinds,
31 isSubArgTypeKind, isSubOpenTypeKind, isSubKind, defaultKind, eqKind,
34 -- Re-exports from TyCon
37 mkTyVarTy, mkTyVarTys, getTyVar, getTyVar_maybe, isTyVarTy,
39 mkAppTy, mkAppTys, splitAppTy, splitAppTys,
40 splitAppTy_maybe, repSplitAppTy_maybe,
42 mkFunTy, mkFunTys, splitFunTy, splitFunTy_maybe,
43 splitFunTys, splitFunTysN,
44 funResultTy, funArgTy, zipFunTys, isFunTy,
46 mkTyConApp, mkTyConTy,
47 tyConAppTyCon, tyConAppArgs,
48 splitTyConApp_maybe, splitTyConApp,
49 splitNewTyConApp_maybe, splitNewTyConApp,
51 repType, repType', typePrimRep, coreView, tcView, kindView,
53 mkForAllTy, mkForAllTys, splitForAllTy_maybe, splitForAllTys,
54 applyTy, applyTys, isForAllTy, dropForAlls,
57 predTypeRep, mkPredTy, mkPredTys,
58 tyConOrigHead, pprSourceTyCon,
61 splitRecNewType_maybe, newTyConInstRhs,
64 isUnLiftedType, isUnboxedTupleType, isAlgType, isPrimitiveType,
65 isStrictType, isStrictPred,
68 tyVarsOfType, tyVarsOfTypes, tyVarsOfPred, tyVarsOfTheta,
69 typeKind, addFreeTyVars,
71 -- Tidying up for printing
73 tidyOpenType, tidyOpenTypes,
74 tidyTyVarBndr, tidyFreeTyVars,
75 tidyOpenTyVar, tidyOpenTyVars,
76 tidyTopType, tidyPred,
80 coreEqType, tcEqType, tcEqTypes, tcCmpType, tcCmpTypes,
81 tcEqPred, tcCmpPred, tcEqTypeX,
87 TvSubstEnv, emptyTvSubstEnv, -- Representation widely visible
88 TvSubst(..), emptyTvSubst, -- Representation visible to a few friends
89 mkTvSubst, mkOpenTvSubst, zipOpenTvSubst, zipTopTvSubst, mkTopTvSubst, notElemTvSubst,
90 getTvSubstEnv, setTvSubstEnv, getTvInScope, extendTvInScope,
91 extendTvSubst, extendTvSubstList, isInScope, composeTvSubst, zipTyEnv,
94 -- Performing substitution on types
95 substTy, substTys, substTyWith, substTheta,
96 substPred, substTyVar, substTyVars, substTyVarBndr, deShadowTy, lookupTyVar,
99 pprType, pprParendType, pprTypeApp, pprTyThingCategory, pprForAll,
100 pprPred, pprTheta, pprThetaArrow, pprClassPred, pprKind, pprParendKind
103 #include "HsVersions.h"
105 -- We import the representation and primitive functions from TypeRep.
106 -- Many things are reexported, but not the representation!
126 import Data.Maybe ( isJust )
130 %************************************************************************
134 %************************************************************************
136 In Core, we "look through" non-recursive newtypes and PredTypes.
139 {-# INLINE coreView #-}
140 coreView :: Type -> Maybe Type
141 -- Strips off the *top layer only* of a type to give
142 -- its underlying representation type.
143 -- Returns Nothing if there is nothing to look through.
145 -- In the case of newtypes, it returns
146 -- *either* a vanilla TyConApp (recursive newtype, or non-saturated)
147 -- *or* the newtype representation (otherwise), meaning the
148 -- type written in the RHS of the newtype decl,
149 -- which may itself be a newtype
151 -- Example: newtype R = MkR S
153 -- newtype T = MkT (T -> T)
154 -- expandNewTcApp on R gives Just S
156 -- on T gives Nothing (no expansion)
158 -- By being non-recursive and inlined, this case analysis gets efficiently
159 -- joined onto the case analysis that the caller is already doing
160 coreView (NoteTy _ ty) = Just ty
162 | isEqPred p = Nothing
163 | otherwise = Just (predTypeRep p)
164 coreView (TyConApp tc tys) | Just (tenv, rhs, tys') <- coreExpandTyCon_maybe tc tys
165 = Just (mkAppTys (substTy (mkTopTvSubst tenv) rhs) tys')
166 -- Its important to use mkAppTys, rather than (foldl AppTy),
167 -- because the function part might well return a
168 -- partially-applied type constructor; indeed, usually will!
169 coreView ty = Nothing
173 -----------------------------------------------
174 {-# INLINE tcView #-}
175 tcView :: Type -> Maybe Type
176 -- Same, but for the type checker, which just looks through synonyms
177 tcView (NoteTy _ ty) = Just ty
178 tcView (TyConApp tc tys) | Just (tenv, rhs, tys') <- tcExpandTyCon_maybe tc tys
179 = Just (mkAppTys (substTy (mkTopTvSubst tenv) rhs) tys')
182 -----------------------------------------------
183 {-# INLINE kindView #-}
184 kindView :: Kind -> Maybe Kind
185 -- C.f. coreView, tcView
186 -- For the moment, we don't even handle synonyms in kinds
187 kindView (NoteTy _ k) = Just k
188 kindView other = Nothing
192 %************************************************************************
194 \subsection{Constructor-specific functions}
196 %************************************************************************
199 ---------------------------------------------------------------------
203 mkTyVarTy :: TyVar -> Type
206 mkTyVarTys :: [TyVar] -> [Type]
207 mkTyVarTys = map mkTyVarTy -- a common use of mkTyVarTy
209 getTyVar :: String -> Type -> TyVar
210 getTyVar msg ty = case getTyVar_maybe ty of
212 Nothing -> panic ("getTyVar: " ++ msg)
214 isTyVarTy :: Type -> Bool
215 isTyVarTy ty = isJust (getTyVar_maybe ty)
217 getTyVar_maybe :: Type -> Maybe TyVar
218 getTyVar_maybe ty | Just ty' <- coreView ty = getTyVar_maybe ty'
219 getTyVar_maybe (TyVarTy tv) = Just tv
220 getTyVar_maybe other = Nothing
225 ---------------------------------------------------------------------
228 We need to be pretty careful with AppTy to make sure we obey the
229 invariant that a TyConApp is always visibly so. mkAppTy maintains the
233 mkAppTy orig_ty1 orig_ty2
236 mk_app (NoteTy _ ty1) = mk_app ty1
237 mk_app (TyConApp tc tys) = mkTyConApp tc (tys ++ [orig_ty2])
238 mk_app ty1 = AppTy orig_ty1 orig_ty2
239 -- Note that the TyConApp could be an
240 -- under-saturated type synonym. GHC allows that; e.g.
241 -- type Foo k = k a -> k a
243 -- foo :: Foo Id -> Foo Id
245 -- Here Id is partially applied in the type sig for Foo,
246 -- but once the type synonyms are expanded all is well
248 mkAppTys :: Type -> [Type] -> Type
249 mkAppTys orig_ty1 [] = orig_ty1
250 -- This check for an empty list of type arguments
251 -- avoids the needless loss of a type synonym constructor.
252 -- For example: mkAppTys Rational []
253 -- returns to (Ratio Integer), which has needlessly lost
254 -- the Rational part.
255 mkAppTys orig_ty1 orig_tys2
258 mk_app (NoteTy _ ty1) = mk_app ty1
259 mk_app (TyConApp tc tys) = mkTyConApp tc (tys ++ orig_tys2)
260 -- mkTyConApp: see notes with mkAppTy
261 mk_app ty1 = foldl AppTy orig_ty1 orig_tys2
264 splitAppTy_maybe :: Type -> Maybe (Type, Type)
265 splitAppTy_maybe ty | Just ty' <- coreView ty
266 = splitAppTy_maybe ty'
267 splitAppTy_maybe ty = repSplitAppTy_maybe ty
270 repSplitAppTy_maybe :: Type -> Maybe (Type,Type)
271 -- Does the AppTy split, but assumes that any view stuff is already done
272 repSplitAppTy_maybe (FunTy ty1 ty2) = Just (TyConApp funTyCon [ty1], ty2)
273 repSplitAppTy_maybe (AppTy ty1 ty2) = Just (ty1, ty2)
274 repSplitAppTy_maybe (TyConApp tc tys) = case snocView tys of
275 Just (tys', ty') -> Just (TyConApp tc tys', ty')
277 repSplitAppTy_maybe other = Nothing
279 splitAppTy :: Type -> (Type, Type)
280 splitAppTy ty = case splitAppTy_maybe ty of
282 Nothing -> panic "splitAppTy"
285 splitAppTys :: Type -> (Type, [Type])
286 splitAppTys ty = split ty ty []
288 split orig_ty ty args | Just ty' <- coreView ty = split orig_ty ty' args
289 split orig_ty (AppTy ty arg) args = split ty ty (arg:args)
290 split orig_ty (TyConApp tc tc_args) args = (TyConApp tc [], tc_args ++ args)
291 split orig_ty (FunTy ty1 ty2) args = ASSERT( null args )
292 (TyConApp funTyCon [], [ty1,ty2])
293 split orig_ty ty args = (orig_ty, args)
298 ---------------------------------------------------------------------
303 mkFunTy :: Type -> Type -> Type
304 mkFunTy (PredTy (EqPred ty1 ty2)) res = mkForAllTy (mkWildCoVar (PredTy (EqPred ty1 ty2))) res
305 mkFunTy arg res = FunTy arg res
307 mkFunTys :: [Type] -> Type -> Type
308 mkFunTys tys ty = foldr mkFunTy ty tys
310 isFunTy :: Type -> Bool
311 isFunTy ty = isJust (splitFunTy_maybe ty)
313 splitFunTy :: Type -> (Type, Type)
314 splitFunTy ty | Just ty' <- coreView ty = splitFunTy ty'
315 splitFunTy (FunTy arg res) = (arg, res)
316 splitFunTy other = pprPanic "splitFunTy" (ppr other)
318 splitFunTy_maybe :: Type -> Maybe (Type, Type)
319 splitFunTy_maybe ty | Just ty' <- coreView ty = splitFunTy_maybe ty'
320 splitFunTy_maybe (FunTy arg res) = Just (arg, res)
321 splitFunTy_maybe other = Nothing
323 splitFunTys :: Type -> ([Type], Type)
324 splitFunTys ty = split [] ty ty
326 split args orig_ty ty | Just ty' <- coreView ty = split args orig_ty ty'
327 split args orig_ty (FunTy arg res) = split (arg:args) res res
328 split args orig_ty ty = (reverse args, orig_ty)
330 splitFunTysN :: Int -> Type -> ([Type], Type)
331 -- Split off exactly n arg tys
332 splitFunTysN 0 ty = ([], ty)
333 splitFunTysN n ty = case splitFunTy ty of { (arg, res) ->
334 case splitFunTysN (n-1) res of { (args, res) ->
337 zipFunTys :: Outputable a => [a] -> Type -> ([(a,Type)], Type)
338 zipFunTys orig_xs orig_ty = split [] orig_xs orig_ty orig_ty
340 split acc [] nty ty = (reverse acc, nty)
342 | Just ty' <- coreView ty = split acc xs nty ty'
343 split acc (x:xs) nty (FunTy arg res) = split ((x,arg):acc) xs res res
344 split acc (x:xs) nty ty = pprPanic "zipFunTys" (ppr orig_xs <+> ppr orig_ty)
346 funResultTy :: Type -> Type
347 funResultTy ty | Just ty' <- coreView ty = funResultTy ty'
348 funResultTy (FunTy arg res) = res
349 funResultTy ty = pprPanic "funResultTy" (ppr ty)
351 funArgTy :: Type -> Type
352 funArgTy ty | Just ty' <- coreView ty = funArgTy ty'
353 funArgTy (FunTy arg res) = arg
354 funArgTy ty = pprPanic "funArgTy" (ppr ty)
358 ---------------------------------------------------------------------
361 @mkTyConApp@ is a key function, because it builds a TyConApp, FunTy or PredTy,
365 mkTyConApp :: TyCon -> [Type] -> Type
367 | isFunTyCon tycon, [ty1,ty2] <- tys
373 mkTyConTy :: TyCon -> Type
374 mkTyConTy tycon = mkTyConApp tycon []
376 -- splitTyConApp "looks through" synonyms, because they don't
377 -- mean a distinct type, but all other type-constructor applications
378 -- including functions are returned as Just ..
380 tyConAppTyCon :: Type -> TyCon
381 tyConAppTyCon ty = fst (splitTyConApp ty)
383 tyConAppArgs :: Type -> [Type]
384 tyConAppArgs ty = snd (splitTyConApp ty)
386 splitTyConApp :: Type -> (TyCon, [Type])
387 splitTyConApp ty = case splitTyConApp_maybe ty of
389 Nothing -> pprPanic "splitTyConApp" (ppr ty)
391 splitTyConApp_maybe :: Type -> Maybe (TyCon, [Type])
392 splitTyConApp_maybe ty | Just ty' <- coreView ty = splitTyConApp_maybe ty'
393 splitTyConApp_maybe (TyConApp tc tys) = Just (tc, tys)
394 splitTyConApp_maybe (FunTy arg res) = Just (funTyCon, [arg,res])
395 splitTyConApp_maybe other = Nothing
397 -- Sometimes we do NOT want to look throught a newtype. When case matching
398 -- on a newtype we want a convenient way to access the arguments of a newty
399 -- constructor so as to properly form a coercion.
400 splitNewTyConApp :: Type -> (TyCon, [Type])
401 splitNewTyConApp ty = case splitNewTyConApp_maybe ty of
403 Nothing -> pprPanic "splitNewTyConApp" (ppr ty)
404 splitNewTyConApp_maybe :: Type -> Maybe (TyCon, [Type])
405 splitNewTyConApp_maybe ty | Just ty' <- tcView ty = splitNewTyConApp_maybe ty'
406 splitNewTyConApp_maybe (TyConApp tc tys) = Just (tc, tys)
407 splitNewTyConApp_maybe (FunTy arg res) = Just (funTyCon, [arg,res])
408 splitNewTyConApp_maybe other = Nothing
410 -- get instantiated newtype rhs, the arguments had better saturate
412 newTyConInstRhs :: TyCon -> [Type] -> Type
413 newTyConInstRhs tycon tys =
414 let (tvs, ty) = newTyConRhs tycon in substTyWith tvs tys ty
418 ---------------------------------------------------------------------
422 Notes on type synonyms
423 ~~~~~~~~~~~~~~~~~~~~~~
424 The various "split" functions (splitFunTy, splitRhoTy, splitForAllTy) try
425 to return type synonyms whereever possible. Thus
430 splitFunTys (a -> Foo a) = ([a], Foo a)
433 The reason is that we then get better (shorter) type signatures in
434 interfaces. Notably this plays a role in tcTySigs in TcBinds.lhs.
439 repType looks through
443 (d) usage annotations
444 (e) all newtypes, including recursive ones, but not newtype families
445 It's useful in the back end.
448 repType :: Type -> Type
449 -- Only applied to types of kind *; hence tycons are saturated
450 repType ty | Just ty' <- coreView ty = repType ty'
451 repType (ForAllTy _ ty) = repType ty
452 repType (TyConApp tc tys)
453 | isClosedNewTyCon tc = -- Recursive newtypes are opaque to coreView
454 -- but we must expand them here. Sure to
455 -- be saturated because repType is only applied
456 -- to types of kind *
457 ASSERT( {- isRecursiveTyCon tc && -} tys `lengthIs` tyConArity tc )
458 repType (new_type_rep tc tys)
461 -- repType' aims to be a more thorough version of repType
462 -- For now it simply looks through the TyConApp args too
463 repType' ty -- | pprTrace "repType'" (ppr ty $$ ppr (go1 ty)) False = undefined
467 go (TyConApp tc tys) = mkTyConApp tc (map repType' tys)
471 -- new_type_rep doesn't ask any questions:
472 -- it just expands newtype, whether recursive or not
473 new_type_rep new_tycon tys = ASSERT( tys `lengthIs` tyConArity new_tycon )
474 case newTyConRep new_tycon of
475 (tvs, rep_ty) -> substTyWith tvs tys rep_ty
477 -- ToDo: this could be moved to the code generator, using splitTyConApp instead
478 -- of inspecting the type directly.
479 typePrimRep :: Type -> PrimRep
480 typePrimRep ty = case repType ty of
481 TyConApp tc _ -> tyConPrimRep tc
483 AppTy _ _ -> PtrRep -- See note below
485 other -> pprPanic "typePrimRep" (ppr ty)
486 -- Types of the form 'f a' must be of kind *, not *#, so
487 -- we are guaranteed that they are represented by pointers.
488 -- The reason is that f must have kind *->*, not *->*#, because
489 -- (we claim) there is no way to constrain f's kind any other
495 ---------------------------------------------------------------------
500 mkForAllTy :: TyVar -> Type -> Type
502 = mkForAllTys [tyvar] ty
504 mkForAllTys :: [TyVar] -> Type -> Type
505 mkForAllTys tyvars ty = foldr ForAllTy ty tyvars
507 isForAllTy :: Type -> Bool
508 isForAllTy (NoteTy _ ty) = isForAllTy ty
509 isForAllTy (ForAllTy _ _) = True
510 isForAllTy other_ty = False
512 splitForAllTy_maybe :: Type -> Maybe (TyVar, Type)
513 splitForAllTy_maybe ty = splitFAT_m ty
515 splitFAT_m ty | Just ty' <- coreView ty = splitFAT_m ty'
516 splitFAT_m (ForAllTy tyvar ty) = Just(tyvar, ty)
517 splitFAT_m _ = Nothing
519 splitForAllTys :: Type -> ([TyVar], Type)
520 splitForAllTys ty = split ty ty []
522 split orig_ty ty tvs | Just ty' <- coreView ty = split orig_ty ty' tvs
523 split orig_ty (ForAllTy tv ty) tvs = split ty ty (tv:tvs)
524 split orig_ty t tvs = (reverse tvs, orig_ty)
526 dropForAlls :: Type -> Type
527 dropForAlls ty = snd (splitForAllTys ty)
530 -- (mkPiType now in CoreUtils)
534 Instantiate a for-all type with one or more type arguments.
535 Used when we have a polymorphic function applied to type args:
537 Then we use (applyTys type-of-f [t1,t2]) to compute the type of
541 applyTy :: Type -> Type -> Type
542 applyTy ty arg | Just ty' <- coreView ty = applyTy ty' arg
543 applyTy (ForAllTy tv ty) arg = substTyWith [tv] [arg] ty
544 applyTy other arg = panic "applyTy"
546 applyTys :: Type -> [Type] -> Type
547 -- This function is interesting because
548 -- a) the function may have more for-alls than there are args
549 -- b) less obviously, it may have fewer for-alls
550 -- For case (b) think of
551 -- applyTys (forall a.a) [forall b.b, Int]
552 -- This really can happen, via dressing up polymorphic types with newtype
553 -- clothing. Here's an example:
554 -- newtype R = R (forall a. a->a)
555 -- foo = case undefined :: R of
558 applyTys orig_fun_ty [] = orig_fun_ty
559 applyTys orig_fun_ty arg_tys
560 | n_tvs == n_args -- The vastly common case
561 = substTyWith tvs arg_tys rho_ty
562 | n_tvs > n_args -- Too many for-alls
563 = substTyWith (take n_args tvs) arg_tys
564 (mkForAllTys (drop n_args tvs) rho_ty)
565 | otherwise -- Too many type args
566 = ASSERT2( n_tvs > 0, ppr orig_fun_ty ) -- Zero case gives infnite loop!
567 applyTys (substTyWith tvs (take n_tvs arg_tys) rho_ty)
570 (tvs, rho_ty) = splitForAllTys orig_fun_ty
572 n_args = length arg_tys
576 %************************************************************************
578 \subsection{Source types}
580 %************************************************************************
582 A "source type" is a type that is a separate type as far as the type checker is
583 concerned, but which has low-level representation as far as the back end is concerned.
585 Source types are always lifted.
587 The key function is predTypeRep which gives the representation of a source type:
590 mkPredTy :: PredType -> Type
591 mkPredTy pred = PredTy pred
593 mkPredTys :: ThetaType -> [Type]
594 mkPredTys preds = map PredTy preds
596 predTypeRep :: PredType -> Type
597 -- Convert a PredType to its "representation type";
598 -- the post-type-checking type used by all the Core passes of GHC.
599 -- Unwraps only the outermost level; for example, the result might
600 -- be a newtype application
601 predTypeRep (IParam _ ty) = ty
602 predTypeRep (ClassP clas tys) = mkTyConApp (classTyCon clas) tys
603 -- Result might be a newtype application, but the consumer will
604 -- look through that too if necessary
605 predTypeRep (EqPred ty1 ty2) = pprPanic "predTypeRep" (ppr (EqPred ty1 ty2))
607 -- The original head is the tycon and its variables for a vanilla tycon and it
608 -- is the family tycon and its type indexes for a family instance.
609 tyConOrigHead :: TyCon -> (TyCon, [Type])
610 tyConOrigHead tycon = case tyConFamInst_maybe tycon of
611 Nothing -> (tycon, mkTyVarTys (tyConTyVars tycon))
612 Just famInst -> famInst
614 -- Pretty prints a tycon, using the family instance in case of a
615 -- representation tycon. For example
616 -- e.g. data T [a] = ...
617 -- In that case we want to print `T [a]', where T is the family TyCon
619 | Just (repTyCon, tys) <- tyConFamInst_maybe tycon
620 = ppr $ repTyCon `TyConApp` tys -- can't be FunTyCon
626 %************************************************************************
630 %************************************************************************
633 splitRecNewType_maybe :: Type -> Maybe Type
634 -- Sometimes we want to look through a recursive newtype, and that's what happens here
635 -- It only strips *one layer* off, so the caller will usually call itself recursively
636 -- Only applied to types of kind *, hence the newtype is always saturated
637 splitRecNewType_maybe ty | Just ty' <- coreView ty = splitRecNewType_maybe ty'
638 splitRecNewType_maybe (TyConApp tc tys)
639 | isClosedNewTyCon tc
640 = ASSERT( tys `lengthIs` tyConArity tc ) -- splitRecNewType_maybe only be applied
641 -- to *types* (of kind *)
642 ASSERT( isRecursiveTyCon tc ) -- Guaranteed by coreView
643 case newTyConRhs tc of
644 (tvs, rep_ty) -> ASSERT( length tvs == length tys )
645 Just (substTyWith tvs tys rep_ty)
647 splitRecNewType_maybe other = Nothing
654 %************************************************************************
656 \subsection{Kinds and free variables}
658 %************************************************************************
660 ---------------------------------------------------------------------
661 Finding the kind of a type
662 ~~~~~~~~~~~~~~~~~~~~~~~~~~
664 typeKind :: Type -> Kind
665 typeKind (TyConApp tycon tys) = ASSERT( not (isCoercionTyCon tycon) )
666 -- We should be looking for the coercion kind,
668 foldr (\_ k -> kindFunResult k) (tyConKind tycon) tys
669 typeKind (NoteTy _ ty) = typeKind ty
670 typeKind (PredTy pred) = predKind pred
671 typeKind (AppTy fun arg) = kindFunResult (typeKind fun)
672 typeKind (ForAllTy tv ty) = typeKind ty
673 typeKind (TyVarTy tyvar) = tyVarKind tyvar
674 typeKind (FunTy arg res)
675 -- Hack alert. The kind of (Int -> Int#) is liftedTypeKind (*),
676 -- not unliftedTypKind (#)
677 -- The only things that can be after a function arrow are
678 -- (a) types (of kind openTypeKind or its sub-kinds)
679 -- (b) kinds (of super-kind TY) (e.g. * -> (* -> *))
680 | isTySuperKind k = k
681 | otherwise = ASSERT( isSubOpenTypeKind k) liftedTypeKind
685 predKind :: PredType -> Kind
686 predKind (EqPred {}) = coSuperKind -- A coercion kind!
687 predKind (ClassP {}) = liftedTypeKind -- Class and implicitPredicates are
688 predKind (IParam {}) = liftedTypeKind -- always represented by lifted types
692 ---------------------------------------------------------------------
693 Free variables of a type
694 ~~~~~~~~~~~~~~~~~~~~~~~~
696 tyVarsOfType :: Type -> TyVarSet
697 -- NB: for type synonyms tyVarsOfType does *not* expand the synonym
698 tyVarsOfType (TyVarTy tv) = unitVarSet tv
699 tyVarsOfType (TyConApp tycon tys) = tyVarsOfTypes tys
700 tyVarsOfType (NoteTy (FTVNote tvs) ty2) = tvs
701 tyVarsOfType (PredTy sty) = tyVarsOfPred sty
702 tyVarsOfType (FunTy arg res) = tyVarsOfType arg `unionVarSet` tyVarsOfType res
703 tyVarsOfType (AppTy fun arg) = tyVarsOfType fun `unionVarSet` tyVarsOfType arg
704 tyVarsOfType (ForAllTy tyvar ty) = delVarSet (tyVarsOfType ty) tyvar
706 tyVarsOfTypes :: [Type] -> TyVarSet
707 tyVarsOfTypes tys = foldr (unionVarSet.tyVarsOfType) emptyVarSet tys
709 tyVarsOfPred :: PredType -> TyVarSet
710 tyVarsOfPred (IParam _ ty) = tyVarsOfType ty
711 tyVarsOfPred (ClassP _ tys) = tyVarsOfTypes tys
712 tyVarsOfPred (EqPred ty1 ty2) = tyVarsOfType ty1 `unionVarSet` tyVarsOfType ty2
714 tyVarsOfTheta :: ThetaType -> TyVarSet
715 tyVarsOfTheta = foldr (unionVarSet . tyVarsOfPred) emptyVarSet
717 -- Add a Note with the free tyvars to the top of the type
718 addFreeTyVars :: Type -> Type
719 addFreeTyVars ty@(NoteTy (FTVNote _) _) = ty
720 addFreeTyVars ty = NoteTy (FTVNote (tyVarsOfType ty)) ty
724 %************************************************************************
726 \subsection{TidyType}
728 %************************************************************************
730 tidyTy tidies up a type for printing in an error message, or in
733 It doesn't change the uniques at all, just the print names.
736 tidyTyVarBndr :: TidyEnv -> TyVar -> (TidyEnv, TyVar)
737 tidyTyVarBndr env@(tidy_env, subst) tyvar
738 = case tidyOccName tidy_env (getOccName name) of
739 (tidy', occ') -> ((tidy', subst'), tyvar'')
741 subst' = extendVarEnv subst tyvar tyvar''
742 tyvar' = setTyVarName tyvar name'
743 name' = tidyNameOcc name occ'
744 -- Don't forget to tidy the kind for coercions!
745 tyvar'' | isCoVar tyvar = setTyVarKind tyvar' kind'
747 kind' = tidyType env (tyVarKind tyvar)
749 name = tyVarName tyvar
751 tidyFreeTyVars :: TidyEnv -> TyVarSet -> TidyEnv
752 -- Add the free tyvars to the env in tidy form,
753 -- so that we can tidy the type they are free in
754 tidyFreeTyVars env tyvars = fst (tidyOpenTyVars env (varSetElems tyvars))
756 tidyOpenTyVars :: TidyEnv -> [TyVar] -> (TidyEnv, [TyVar])
757 tidyOpenTyVars env tyvars = mapAccumL tidyOpenTyVar env tyvars
759 tidyOpenTyVar :: TidyEnv -> TyVar -> (TidyEnv, TyVar)
760 -- Treat a new tyvar as a binder, and give it a fresh tidy name
761 tidyOpenTyVar env@(tidy_env, subst) tyvar
762 = case lookupVarEnv subst tyvar of
763 Just tyvar' -> (env, tyvar') -- Already substituted
764 Nothing -> tidyTyVarBndr env tyvar -- Treat it as a binder
766 tidyType :: TidyEnv -> Type -> Type
767 tidyType env@(tidy_env, subst) ty
770 go (TyVarTy tv) = case lookupVarEnv subst tv of
771 Nothing -> TyVarTy tv
772 Just tv' -> TyVarTy tv'
773 go (TyConApp tycon tys) = let args = map go tys
774 in args `seqList` TyConApp tycon args
775 go (NoteTy note ty) = (NoteTy $! (go_note note)) $! (go ty)
776 go (PredTy sty) = PredTy (tidyPred env sty)
777 go (AppTy fun arg) = (AppTy $! (go fun)) $! (go arg)
778 go (FunTy fun arg) = (FunTy $! (go fun)) $! (go arg)
779 go (ForAllTy tv ty) = ForAllTy tvp $! (tidyType envp ty)
781 (envp, tvp) = tidyTyVarBndr env tv
783 go_note note@(FTVNote ftvs) = note -- No need to tidy the free tyvars
785 tidyTypes env tys = map (tidyType env) tys
787 tidyPred :: TidyEnv -> PredType -> PredType
788 tidyPred env (IParam n ty) = IParam n (tidyType env ty)
789 tidyPred env (ClassP clas tys) = ClassP clas (tidyTypes env tys)
790 tidyPred env (EqPred ty1 ty2) = EqPred (tidyType env ty1) (tidyType env ty2)
794 @tidyOpenType@ grabs the free type variables, tidies them
795 and then uses @tidyType@ to work over the type itself
798 tidyOpenType :: TidyEnv -> Type -> (TidyEnv, Type)
800 = (env', tidyType env' ty)
802 env' = tidyFreeTyVars env (tyVarsOfType ty)
804 tidyOpenTypes :: TidyEnv -> [Type] -> (TidyEnv, [Type])
805 tidyOpenTypes env tys = mapAccumL tidyOpenType env tys
807 tidyTopType :: Type -> Type
808 tidyTopType ty = tidyType emptyTidyEnv ty
813 tidyKind :: TidyEnv -> Kind -> (TidyEnv, Kind)
814 tidyKind env k = tidyOpenType env k
819 %************************************************************************
821 \subsection{Liftedness}
823 %************************************************************************
826 isUnLiftedType :: Type -> Bool
827 -- isUnLiftedType returns True for forall'd unlifted types:
828 -- x :: forall a. Int#
829 -- I found bindings like these were getting floated to the top level.
830 -- They are pretty bogus types, mind you. It would be better never to
833 isUnLiftedType ty | Just ty' <- coreView ty = isUnLiftedType ty'
834 isUnLiftedType (ForAllTy tv ty) = isUnLiftedType ty
835 isUnLiftedType (TyConApp tc _) = isUnLiftedTyCon tc
836 isUnLiftedType other = False
838 isUnboxedTupleType :: Type -> Bool
839 isUnboxedTupleType ty = case splitTyConApp_maybe ty of
840 Just (tc, ty_args) -> isUnboxedTupleTyCon tc
843 -- Should only be applied to *types*; hence the assert
844 isAlgType :: Type -> Bool
845 isAlgType ty = case splitTyConApp_maybe ty of
846 Just (tc, ty_args) -> ASSERT( ty_args `lengthIs` tyConArity tc )
851 @isStrictType@ computes whether an argument (or let RHS) should
852 be computed strictly or lazily, based only on its type.
853 Works just like isUnLiftedType, except that it has a special case
854 for dictionaries. Since it takes account of ClassP, you might think
855 this function should be in TcType, but isStrictType is used by DataCon,
856 which is below TcType in the hierarchy, so it's convenient to put it here.
859 isStrictType (PredTy pred) = isStrictPred pred
860 isStrictType ty | Just ty' <- coreView ty = isStrictType ty'
861 isStrictType (ForAllTy tv ty) = isStrictType ty
862 isStrictType (TyConApp tc _) = isUnLiftedTyCon tc
863 isStrictType other = False
865 isStrictPred (ClassP clas _) = opt_DictsStrict && not (isNewTyCon (classTyCon clas))
866 isStrictPred other = False
867 -- We may be strict in dictionary types, but only if it
868 -- has more than one component.
869 -- [Being strict in a single-component dictionary risks
870 -- poking the dictionary component, which is wrong.]
874 isPrimitiveType :: Type -> Bool
875 -- Returns types that are opaque to Haskell.
876 -- Most of these are unlifted, but now that we interact with .NET, we
877 -- may have primtive (foreign-imported) types that are lifted
878 isPrimitiveType ty = case splitTyConApp_maybe ty of
879 Just (tc, ty_args) -> ASSERT( ty_args `lengthIs` tyConArity tc )
885 %************************************************************************
887 \subsection{Sequencing on types
889 %************************************************************************
892 seqType :: Type -> ()
893 seqType (TyVarTy tv) = tv `seq` ()
894 seqType (AppTy t1 t2) = seqType t1 `seq` seqType t2
895 seqType (FunTy t1 t2) = seqType t1 `seq` seqType t2
896 seqType (NoteTy note t2) = seqNote note `seq` seqType t2
897 seqType (PredTy p) = seqPred p
898 seqType (TyConApp tc tys) = tc `seq` seqTypes tys
899 seqType (ForAllTy tv ty) = tv `seq` seqType ty
901 seqTypes :: [Type] -> ()
903 seqTypes (ty:tys) = seqType ty `seq` seqTypes tys
905 seqNote :: TyNote -> ()
906 seqNote (FTVNote set) = sizeUniqSet set `seq` ()
908 seqPred :: PredType -> ()
909 seqPred (ClassP c tys) = c `seq` seqTypes tys
910 seqPred (IParam n ty) = n `seq` seqType ty
911 seqPred (EqPred ty1 ty2) = seqType ty1 `seq` seqType ty2
915 %************************************************************************
917 Equality for Core types
918 (We don't use instances so that we know where it happens)
920 %************************************************************************
922 Note that eqType works right even for partial applications of newtypes.
923 See Note [Newtype eta] in TyCon.lhs
926 coreEqType :: Type -> Type -> Bool
930 rn_env = mkRnEnv2 (mkInScopeSet (tyVarsOfType t1 `unionVarSet` tyVarsOfType t2))
932 eq env (TyVarTy tv1) (TyVarTy tv2) = rnOccL env tv1 == rnOccR env tv2
933 eq env (ForAllTy tv1 t1) (ForAllTy tv2 t2) = eq (rnBndr2 env tv1 tv2) t1 t2
934 eq env (AppTy s1 t1) (AppTy s2 t2) = eq env s1 s2 && eq env t1 t2
935 eq env (FunTy s1 t1) (FunTy s2 t2) = eq env s1 s2 && eq env t1 t2
936 eq env (TyConApp tc1 tys1) (TyConApp tc2 tys2)
937 | tc1 == tc2, all2 (eq env) tys1 tys2 = True
938 -- The lengths should be equal because
939 -- the two types have the same kind
940 -- NB: if the type constructors differ that does not
941 -- necessarily mean that the types aren't equal
942 -- (synonyms, newtypes)
943 -- Even if the type constructors are the same, but the arguments
944 -- differ, the two types could be the same (e.g. if the arg is just
945 -- ignored in the RHS). In both these cases we fall through to an
946 -- attempt to expand one side or the other.
948 -- Now deal with newtypes, synonyms, pred-tys
949 eq env t1 t2 | Just t1' <- coreView t1 = eq env t1' t2
950 | Just t2' <- coreView t2 = eq env t1 t2'
952 -- Fall through case; not equal!
957 %************************************************************************
959 Comparision for source types
960 (We don't use instances so that we know where it happens)
962 %************************************************************************
966 do *not* look through newtypes, PredTypes
969 tcEqType :: Type -> Type -> Bool
970 tcEqType t1 t2 = isEqual $ cmpType t1 t2
972 tcEqTypes :: [Type] -> [Type] -> Bool
973 tcEqTypes tys1 tys2 = isEqual $ cmpTypes tys1 tys2
975 tcCmpType :: Type -> Type -> Ordering
976 tcCmpType t1 t2 = cmpType t1 t2
978 tcCmpTypes :: [Type] -> [Type] -> Ordering
979 tcCmpTypes tys1 tys2 = cmpTypes tys1 tys2
981 tcEqPred :: PredType -> PredType -> Bool
982 tcEqPred p1 p2 = isEqual $ cmpPred p1 p2
984 tcCmpPred :: PredType -> PredType -> Ordering
985 tcCmpPred p1 p2 = cmpPred p1 p2
987 tcEqTypeX :: RnEnv2 -> Type -> Type -> Bool
988 tcEqTypeX env t1 t2 = isEqual $ cmpTypeX env t1 t2
991 Now here comes the real worker
994 cmpType :: Type -> Type -> Ordering
995 cmpType t1 t2 = cmpTypeX rn_env t1 t2
997 rn_env = mkRnEnv2 (mkInScopeSet (tyVarsOfType t1 `unionVarSet` tyVarsOfType t2))
999 cmpTypes :: [Type] -> [Type] -> Ordering
1000 cmpTypes ts1 ts2 = cmpTypesX rn_env ts1 ts2
1002 rn_env = mkRnEnv2 (mkInScopeSet (tyVarsOfTypes ts1 `unionVarSet` tyVarsOfTypes ts2))
1004 cmpPred :: PredType -> PredType -> Ordering
1005 cmpPred p1 p2 = cmpPredX rn_env p1 p2
1007 rn_env = mkRnEnv2 (mkInScopeSet (tyVarsOfPred p1 `unionVarSet` tyVarsOfPred p2))
1009 cmpTypeX :: RnEnv2 -> Type -> Type -> Ordering -- Main workhorse
1010 cmpTypeX env t1 t2 | Just t1' <- tcView t1 = cmpTypeX env t1' t2
1011 | Just t2' <- tcView t2 = cmpTypeX env t1 t2'
1013 cmpTypeX env (TyVarTy tv1) (TyVarTy tv2) = rnOccL env tv1 `compare` rnOccR env tv2
1014 cmpTypeX env (ForAllTy tv1 t1) (ForAllTy tv2 t2) = cmpTypeX (rnBndr2 env tv1 tv2) t1 t2
1015 cmpTypeX env (AppTy s1 t1) (AppTy s2 t2) = cmpTypeX env s1 s2 `thenCmp` cmpTypeX env t1 t2
1016 cmpTypeX env (FunTy s1 t1) (FunTy s2 t2) = cmpTypeX env s1 s2 `thenCmp` cmpTypeX env t1 t2
1017 cmpTypeX env (PredTy p1) (PredTy p2) = cmpPredX env p1 p2
1018 cmpTypeX env (TyConApp tc1 tys1) (TyConApp tc2 tys2) = (tc1 `compare` tc2) `thenCmp` cmpTypesX env tys1 tys2
1019 cmpTypeX env t1 (NoteTy _ t2) = cmpTypeX env t1 t2
1021 -- Deal with the rest: TyVarTy < AppTy < FunTy < TyConApp < ForAllTy < PredTy
1022 cmpTypeX env (AppTy _ _) (TyVarTy _) = GT
1024 cmpTypeX env (FunTy _ _) (TyVarTy _) = GT
1025 cmpTypeX env (FunTy _ _) (AppTy _ _) = GT
1027 cmpTypeX env (TyConApp _ _) (TyVarTy _) = GT
1028 cmpTypeX env (TyConApp _ _) (AppTy _ _) = GT
1029 cmpTypeX env (TyConApp _ _) (FunTy _ _) = GT
1031 cmpTypeX env (ForAllTy _ _) (TyVarTy _) = GT
1032 cmpTypeX env (ForAllTy _ _) (AppTy _ _) = GT
1033 cmpTypeX env (ForAllTy _ _) (FunTy _ _) = GT
1034 cmpTypeX env (ForAllTy _ _) (TyConApp _ _) = GT
1036 cmpTypeX env (PredTy _) t2 = GT
1038 cmpTypeX env _ _ = LT
1041 cmpTypesX :: RnEnv2 -> [Type] -> [Type] -> Ordering
1042 cmpTypesX env [] [] = EQ
1043 cmpTypesX env (t1:tys1) (t2:tys2) = cmpTypeX env t1 t2 `thenCmp` cmpTypesX env tys1 tys2
1044 cmpTypesX env [] tys = LT
1045 cmpTypesX env ty [] = GT
1048 cmpPredX :: RnEnv2 -> PredType -> PredType -> Ordering
1049 cmpPredX env (IParam n1 ty1) (IParam n2 ty2) = (n1 `compare` n2) `thenCmp` cmpTypeX env ty1 ty2
1050 -- Compare names only for implicit parameters
1051 -- This comparison is used exclusively (I believe)
1052 -- for the Avails finite map built in TcSimplify
1053 -- If the types differ we keep them distinct so that we see
1054 -- a distinct pair to run improvement on
1055 cmpPredX env (ClassP c1 tys1) (ClassP c2 tys2) = (c1 `compare` c2) `thenCmp` (cmpTypesX env tys1 tys2)
1056 cmpPredX env (EqPred ty1 ty2) (EqPred ty1' ty2') = (cmpTypeX env ty1 ty1') `thenCmp` (cmpTypeX env ty2 ty2')
1058 -- Constructor order: IParam < ClassP < EqPred
1059 cmpPredX env (IParam {}) _ = LT
1060 cmpPredX env (ClassP {}) (IParam {}) = GT
1061 cmpPredX env (ClassP {}) (EqPred {}) = LT
1062 cmpPredX env (EqPred {}) _ = GT
1065 PredTypes are used as a FM key in TcSimplify,
1066 so we take the easy path and make them an instance of Ord
1069 instance Eq PredType where { (==) = tcEqPred }
1070 instance Ord PredType where { compare = tcCmpPred }
1074 %************************************************************************
1078 %************************************************************************
1082 = TvSubst InScopeSet -- The in-scope type variables
1083 TvSubstEnv -- The substitution itself
1084 -- See Note [Apply Once]
1085 -- and Note [Extending the TvSubstEnv]
1087 {- ----------------------------------------------------------
1091 We use TvSubsts to instantiate things, and we might instantiate
1095 So the substition might go [a->b, b->a]. A similar situation arises in Core
1096 when we find a beta redex like
1097 (/\ a /\ b -> e) b a
1098 Then we also end up with a substition that permutes type variables. Other
1099 variations happen to; for example [a -> (a, b)].
1101 ***************************************************
1102 *** So a TvSubst must be applied precisely once ***
1103 ***************************************************
1105 A TvSubst is not idempotent, but, unlike the non-idempotent substitution
1106 we use during unifications, it must not be repeatedly applied.
1108 Note [Extending the TvSubst]
1109 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1110 The following invariant should hold of a TvSubst
1112 The in-scope set is needed *only* to
1113 guide the generation of fresh uniques
1115 In particular, the *kind* of the type variables in
1116 the in-scope set is not relevant
1118 This invariant allows a short-cut when the TvSubstEnv is empty:
1119 if the TvSubstEnv is empty --- i.e. (isEmptyTvSubt subst) holds ---
1120 then (substTy subst ty) does nothing.
1122 For example, consider:
1123 (/\a. /\b:(a~Int). ...b..) Int
1124 We substitute Int for 'a'. The Unique of 'b' does not change, but
1125 nevertheless we add 'b' to the TvSubstEnv, because b's type does change
1127 This invariant has several crucial consequences:
1129 * In substTyVarBndr, we need extend the TvSubstEnv
1130 - if the unique has changed
1131 - or if the kind has changed
1133 * In substTyVar, we do not need to consult the in-scope set;
1134 the TvSubstEnv is enough
1136 * In substTy, substTheta, we can short-circuit when the TvSubstEnv is empty
1139 -------------------------------------------------------------- -}
1142 type TvSubstEnv = TyVarEnv Type
1143 -- A TvSubstEnv is used both inside a TvSubst (with the apply-once
1144 -- invariant discussed in Note [Apply Once]), and also independently
1145 -- in the middle of matching, and unification (see Types.Unify)
1146 -- So you have to look at the context to know if it's idempotent or
1147 -- apply-once or whatever
1148 emptyTvSubstEnv :: TvSubstEnv
1149 emptyTvSubstEnv = emptyVarEnv
1151 composeTvSubst :: InScopeSet -> TvSubstEnv -> TvSubstEnv -> TvSubstEnv
1152 -- (compose env1 env2)(x) is env1(env2(x)); i.e. apply env2 then env1
1153 -- It assumes that both are idempotent
1154 -- Typically, env1 is the refinement to a base substitution env2
1155 composeTvSubst in_scope env1 env2
1156 = env1 `plusVarEnv` mapVarEnv (substTy subst1) env2
1157 -- First apply env1 to the range of env2
1158 -- Then combine the two, making sure that env1 loses if
1159 -- both bind the same variable; that's why env1 is the
1160 -- *left* argument to plusVarEnv, because the right arg wins
1162 subst1 = TvSubst in_scope env1
1164 emptyTvSubst = TvSubst emptyInScopeSet emptyVarEnv
1166 isEmptyTvSubst :: TvSubst -> Bool
1167 -- See Note [Extending the TvSubstEnv]
1168 isEmptyTvSubst (TvSubst _ env) = isEmptyVarEnv env
1170 mkTvSubst :: InScopeSet -> TvSubstEnv -> TvSubst
1173 getTvSubstEnv :: TvSubst -> TvSubstEnv
1174 getTvSubstEnv (TvSubst _ env) = env
1176 getTvInScope :: TvSubst -> InScopeSet
1177 getTvInScope (TvSubst in_scope _) = in_scope
1179 isInScope :: Var -> TvSubst -> Bool
1180 isInScope v (TvSubst in_scope _) = v `elemInScopeSet` in_scope
1182 notElemTvSubst :: TyVar -> TvSubst -> Bool
1183 notElemTvSubst tv (TvSubst _ env) = not (tv `elemVarEnv` env)
1185 setTvSubstEnv :: TvSubst -> TvSubstEnv -> TvSubst
1186 setTvSubstEnv (TvSubst in_scope _) env = TvSubst in_scope env
1188 extendTvInScope :: TvSubst -> [Var] -> TvSubst
1189 extendTvInScope (TvSubst in_scope env) vars = TvSubst (extendInScopeSetList in_scope vars) env
1191 extendTvSubst :: TvSubst -> TyVar -> Type -> TvSubst
1192 extendTvSubst (TvSubst in_scope env) tv ty = TvSubst in_scope (extendVarEnv env tv ty)
1194 extendTvSubstList :: TvSubst -> [TyVar] -> [Type] -> TvSubst
1195 extendTvSubstList (TvSubst in_scope env) tvs tys
1196 = TvSubst in_scope (extendVarEnvList env (tvs `zip` tys))
1198 -- mkOpenTvSubst and zipOpenTvSubst generate the in-scope set from
1199 -- the types given; but it's just a thunk so with a bit of luck
1200 -- it'll never be evaluated
1202 mkOpenTvSubst :: TvSubstEnv -> TvSubst
1203 mkOpenTvSubst env = TvSubst (mkInScopeSet (tyVarsOfTypes (varEnvElts env))) env
1205 zipOpenTvSubst :: [TyVar] -> [Type] -> TvSubst
1206 zipOpenTvSubst tyvars tys
1208 | length tyvars /= length tys
1209 = pprTrace "zipOpenTvSubst" (ppr tyvars $$ ppr tys) emptyTvSubst
1212 = TvSubst (mkInScopeSet (tyVarsOfTypes tys)) (zipTyEnv tyvars tys)
1214 -- mkTopTvSubst is called when doing top-level substitutions.
1215 -- Here we expect that the free vars of the range of the
1216 -- substitution will be empty.
1217 mkTopTvSubst :: [(TyVar, Type)] -> TvSubst
1218 mkTopTvSubst prs = TvSubst emptyInScopeSet (mkVarEnv prs)
1220 zipTopTvSubst :: [TyVar] -> [Type] -> TvSubst
1221 zipTopTvSubst tyvars tys
1223 | length tyvars /= length tys
1224 = pprTrace "zipOpenTvSubst" (ppr tyvars $$ ppr tys) emptyTvSubst
1227 = TvSubst emptyInScopeSet (zipTyEnv tyvars tys)
1229 zipTyEnv :: [TyVar] -> [Type] -> TvSubstEnv
1232 | length tyvars /= length tys
1233 = pprTrace "mkTopTvSubst" (ppr tyvars $$ ppr tys) emptyVarEnv
1236 = zip_ty_env tyvars tys emptyVarEnv
1238 -- Later substitutions in the list over-ride earlier ones,
1239 -- but there should be no loops
1240 zip_ty_env [] [] env = env
1241 zip_ty_env (tv:tvs) (ty:tys) env = zip_ty_env tvs tys (extendVarEnv env tv ty)
1242 -- There used to be a special case for when
1244 -- (a not-uncommon case) in which case the substitution was dropped.
1245 -- But the type-tidier changes the print-name of a type variable without
1246 -- changing the unique, and that led to a bug. Why? Pre-tidying, we had
1247 -- a type {Foo t}, where Foo is a one-method class. So Foo is really a newtype.
1248 -- And it happened that t was the type variable of the class. Post-tiding,
1249 -- it got turned into {Foo t2}. The ext-core printer expanded this using
1250 -- sourceTypeRep, but that said "Oh, t == t2" because they have the same unique,
1251 -- and so generated a rep type mentioning t not t2.
1253 -- Simplest fix is to nuke the "optimisation"
1254 zip_ty_env tvs tys env = pprTrace "Var/Type length mismatch: " (ppr tvs $$ ppr tys) env
1255 -- zip_ty_env _ _ env = env
1257 instance Outputable TvSubst where
1258 ppr (TvSubst ins env)
1259 = brackets $ sep[ ptext SLIT("TvSubst"),
1260 nest 2 (ptext SLIT("In scope:") <+> ppr ins),
1261 nest 2 (ptext SLIT("Env:") <+> ppr env) ]
1264 %************************************************************************
1266 Performing type substitutions
1268 %************************************************************************
1271 substTyWith :: [TyVar] -> [Type] -> Type -> Type
1272 substTyWith tvs tys = ASSERT( length tvs == length tys )
1273 substTy (zipOpenTvSubst tvs tys)
1275 substTy :: TvSubst -> Type -> Type
1276 substTy subst ty | isEmptyTvSubst subst = ty
1277 | otherwise = subst_ty subst ty
1279 substTys :: TvSubst -> [Type] -> [Type]
1280 substTys subst tys | isEmptyTvSubst subst = tys
1281 | otherwise = map (subst_ty subst) tys
1283 substTheta :: TvSubst -> ThetaType -> ThetaType
1284 substTheta subst theta
1285 | isEmptyTvSubst subst = theta
1286 | otherwise = map (substPred subst) theta
1288 substPred :: TvSubst -> PredType -> PredType
1289 substPred subst (IParam n ty) = IParam n (subst_ty subst ty)
1290 substPred subst (ClassP clas tys) = ClassP clas (map (subst_ty subst) tys)
1291 substPred subst (EqPred ty1 ty2) = EqPred (subst_ty subst ty1) (subst_ty subst ty2)
1293 deShadowTy :: TyVarSet -> Type -> Type -- Remove any nested binders mentioning tvs
1295 = subst_ty (mkTvSubst in_scope emptyTvSubstEnv) ty
1297 in_scope = mkInScopeSet tvs
1299 subst_ty :: TvSubst -> Type -> Type
1300 -- subst_ty is the main workhorse for type substitution
1302 -- Note that the in_scope set is poked only if we hit a forall
1303 -- so it may often never be fully computed
1307 go (TyVarTy tv) = substTyVar subst tv
1308 go (TyConApp tc tys) = let args = map go tys
1309 in args `seqList` TyConApp tc args
1311 go (PredTy p) = PredTy $! (substPred subst p)
1313 go (NoteTy (FTVNote _) ty2) = go ty2 -- Discard the free tyvar note
1315 go (FunTy arg res) = (FunTy $! (go arg)) $! (go res)
1316 go (AppTy fun arg) = mkAppTy (go fun) $! (go arg)
1317 -- The mkAppTy smart constructor is important
1318 -- we might be replacing (a Int), represented with App
1319 -- by [Int], represented with TyConApp
1320 go (ForAllTy tv ty) = case substTyVarBndr subst tv of
1321 (subst', tv') -> ForAllTy tv' $! (subst_ty subst' ty)
1323 substTyVar :: TvSubst -> TyVar -> Type
1324 substTyVar subst@(TvSubst in_scope env) tv
1325 = case lookupTyVar subst tv of {
1326 Nothing -> TyVarTy tv;
1327 Just ty -> ty -- See Note [Apply Once]
1330 substTyVars :: TvSubst -> [TyVar] -> [Type]
1331 substTyVars subst tvs = map (substTyVar subst) tvs
1333 lookupTyVar :: TvSubst -> TyVar -> Maybe Type
1334 -- See Note [Extending the TvSubst]
1335 lookupTyVar (TvSubst in_scope env) tv = lookupVarEnv env tv
1337 substTyVarBndr :: TvSubst -> TyVar -> (TvSubst, TyVar)
1338 substTyVarBndr subst@(TvSubst in_scope env) old_var
1339 = (TvSubst (in_scope `extendInScopeSet` new_var) new_env, new_var)
1341 is_co_var = isCoVar old_var
1343 new_env | no_change = delVarEnv env old_var
1344 | otherwise = extendVarEnv env old_var (TyVarTy new_var)
1346 no_change = new_var == old_var && not is_co_var
1347 -- no_change means that the new_var is identical in
1348 -- all respects to the old_var (same unique, same kind)
1349 -- See Note [Extending the TvSubst]
1351 -- In that case we don't need to extend the substitution
1352 -- to map old to new. But instead we must zap any
1353 -- current substitution for the variable. For example:
1354 -- (\x.e) with id_subst = [x |-> e']
1355 -- Here we must simply zap the substitution for x
1357 new_var = uniqAway in_scope subst_old_var
1358 -- The uniqAway part makes sure the new variable is not already in scope
1360 subst_old_var -- subst_old_var is old_var with the substitution applied to its kind
1361 -- It's only worth doing the substitution for coercions,
1362 -- becuase only they can have free type variables
1363 | is_co_var = setTyVarKind old_var (substTy subst (tyVarKind old_var))
1364 | otherwise = old_var
1367 ----------------------------------------------------
1372 There's a little subtyping at the kind level:
1381 where * [LiftedTypeKind] means boxed type
1382 # [UnliftedTypeKind] means unboxed type
1383 (#) [UbxTupleKind] means unboxed tuple
1384 ?? [ArgTypeKind] is the lub of *,#
1385 ? [OpenTypeKind] means any type at all
1389 error :: forall a:?. String -> a
1390 (->) :: ?? -> ? -> *
1391 (\(x::t) -> ...) Here t::?? (i.e. not unboxed tuple)
1394 type KindVar = TyVar -- invariant: KindVar will always be a
1395 -- TcTyVar with details MetaTv TauTv ...
1396 -- kind var constructors and functions are in TcType
1398 type SimpleKind = Kind
1403 During kind inference, a kind variable unifies only with
1405 sk ::= * | sk1 -> sk2
1407 data T a = MkT a (T Int#)
1408 fails. We give T the kind (k -> *), and the kind variable k won't unify
1409 with # (the kind of Int#).
1413 When creating a fresh internal type variable, we give it a kind to express
1414 constraints on it. E.g. in (\x->e) we make up a fresh type variable for x,
1417 During unification we only bind an internal type variable to a type
1418 whose kind is lower in the sub-kind hierarchy than the kind of the tyvar.
1420 When unifying two internal type variables, we collect their kind constraints by
1421 finding the GLB of the two. Since the partial order is a tree, they only
1422 have a glb if one is a sub-kind of the other. In that case, we bind the
1423 less-informative one to the more informative one. Neat, eh?
1430 %************************************************************************
1432 Functions over Kinds
1434 %************************************************************************
1437 kindFunResult :: Kind -> Kind
1438 kindFunResult k = funResultTy k
1440 splitKindFunTys :: Kind -> ([Kind],Kind)
1441 splitKindFunTys k = splitFunTys k
1443 splitKindFunTysN :: Int -> Kind -> ([Kind],Kind)
1444 splitKindFunTysN k = splitFunTysN k
1446 isUbxTupleKind, isOpenTypeKind, isArgTypeKind, isUnliftedTypeKind :: Kind -> Bool
1448 isOpenTypeKindCon tc = tyConUnique tc == openTypeKindTyConKey
1450 isOpenTypeKind (TyConApp tc _) = isOpenTypeKindCon tc
1451 isOpenTypeKind other = False
1453 isUbxTupleKindCon tc = tyConUnique tc == ubxTupleKindTyConKey
1455 isUbxTupleKind (TyConApp tc _) = isUbxTupleKindCon tc
1456 isUbxTupleKind other = False
1458 isArgTypeKindCon tc = tyConUnique tc == argTypeKindTyConKey
1460 isArgTypeKind (TyConApp tc _) = isArgTypeKindCon tc
1461 isArgTypeKind other = False
1463 isUnliftedTypeKindCon tc = tyConUnique tc == unliftedTypeKindTyConKey
1465 isUnliftedTypeKind (TyConApp tc _) = isUnliftedTypeKindCon tc
1466 isUnliftedTypeKind other = False
1468 isSubOpenTypeKind :: Kind -> Bool
1469 -- True of any sub-kind of OpenTypeKind (i.e. anything except arrow)
1470 isSubOpenTypeKind (FunTy k1 k2) = ASSERT2 ( isKind k1, text "isSubOpenTypeKind" <+> ppr k1 <+> text "::" <+> ppr (typeKind k1) )
1471 ASSERT2 ( isKind k2, text "isSubOpenTypeKind" <+> ppr k2 <+> text "::" <+> ppr (typeKind k2) )
1473 isSubOpenTypeKind (TyConApp kc []) = ASSERT( isKind (TyConApp kc []) ) True
1474 isSubOpenTypeKind other = ASSERT( isKind other ) False
1475 -- This is a conservative answer
1476 -- It matters in the call to isSubKind in
1477 -- checkExpectedKind.
1479 isSubArgTypeKindCon kc
1480 | isUnliftedTypeKindCon kc = True
1481 | isLiftedTypeKindCon kc = True
1482 | isArgTypeKindCon kc = True
1485 isSubArgTypeKind :: Kind -> Bool
1486 -- True of any sub-kind of ArgTypeKind
1487 isSubArgTypeKind (TyConApp kc []) = isSubArgTypeKindCon kc
1488 isSubArgTypeKind other = False
1490 isSuperKind :: Type -> Bool
1491 isSuperKind (TyConApp (skc) []) = isSuperKindTyCon skc
1492 isSuperKind other = False
1494 isKind :: Kind -> Bool
1495 isKind k = isSuperKind (typeKind k)
1499 isSubKind :: Kind -> Kind -> Bool
1500 -- (k1 `isSubKind` k2) checks that k1 <: k2
1501 isSubKind (TyConApp kc1 []) (TyConApp kc2 []) = kc1 `isSubKindCon` kc2
1502 isSubKind (FunTy a1 r1) (FunTy a2 r2) = (a2 `isSubKind` a1) && (r1 `isSubKind` r2)
1503 isSubKind (PredTy (EqPred ty1 ty2)) (PredTy (EqPred ty1' ty2'))
1504 = ty1 `tcEqType` ty1' && ty2 `tcEqType` ty2'
1505 isSubKind k1 k2 = False
1507 eqKind :: Kind -> Kind -> Bool
1510 isSubKindCon :: TyCon -> TyCon -> Bool
1511 -- (kc1 `isSubKindCon` kc2) checks that kc1 <: kc2
1512 isSubKindCon kc1 kc2
1513 | isLiftedTypeKindCon kc1 && isLiftedTypeKindCon kc2 = True
1514 | isUnliftedTypeKindCon kc1 && isUnliftedTypeKindCon kc2 = True
1515 | isUbxTupleKindCon kc1 && isUbxTupleKindCon kc2 = True
1516 | isOpenTypeKindCon kc2 = True
1517 -- we already know kc1 is not a fun, its a TyCon
1518 | isArgTypeKindCon kc2 && isSubArgTypeKindCon kc1 = True
1521 defaultKind :: Kind -> Kind
1522 -- Used when generalising: default kind '?' and '??' to '*'
1524 -- When we generalise, we make generic type variables whose kind is
1525 -- simple (* or *->* etc). So generic type variables (other than
1526 -- built-in constants like 'error') always have simple kinds. This is important;
1529 -- We want f to get type
1530 -- f :: forall (a::*). a -> Bool
1532 -- f :: forall (a::??). a -> Bool
1533 -- because that would allow a call like (f 3#) as well as (f True),
1534 --and the calling conventions differ. This defaulting is done in TcMType.zonkTcTyVarBndr.
1536 | isSubOpenTypeKind k = liftedTypeKind
1537 | isSubArgTypeKind k = liftedTypeKind
1540 isEqPred :: PredType -> Bool
1541 isEqPred (EqPred _ _) = True
1542 isEqPred other = False