2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1998
6 Type - public interface
9 {-# OPTIONS -fno-warn-incomplete-patterns #-}
10 -- The above warning supression flag is a temporary kludge.
11 -- While working on this module you are encouraged to remove it and fix
12 -- any warnings in the module. See
13 -- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
16 -- | Main functions for manipulating types and type-related things
18 -- Note some of this is just re-exports from TyCon..
20 -- * Main data types representing Types
21 -- $type_classification
23 -- $representation_types
24 TyThing(..), Type, PredType(..), ThetaType,
26 -- ** Constructing and deconstructing types
27 mkTyVarTy, mkTyVarTys, getTyVar, getTyVar_maybe,
29 mkAppTy, mkAppTys, splitAppTy, splitAppTys,
30 splitAppTy_maybe, repSplitAppTy_maybe,
32 mkFunTy, mkFunTys, splitFunTy, splitFunTy_maybe,
33 splitFunTys, splitFunTysN,
34 funResultTy, funArgTy, zipFunTys,
36 mkTyConApp, mkTyConTy,
37 tyConAppTyCon, tyConAppArgs,
38 splitTyConApp_maybe, splitTyConApp,
40 mkForAllTy, mkForAllTys, splitForAllTy_maybe, splitForAllTys,
41 applyTy, applyTys, applyTysD, isForAllTy, dropForAlls,
44 newTyConInstRhs, carefullySplitNewType_maybe,
47 tyFamInsts, predFamInsts,
50 mkPredTy, mkPredTys, mkFamilyTyConApp, isEqPred,
52 -- ** Common type constructors
55 -- ** Predicates on types
58 -- (Lifting and boxity)
59 isUnLiftedType, isUnboxedTupleType, isAlgType, isClosedAlgType,
60 isPrimitiveType, isStrictType, isStrictPred,
62 -- * Main data types representing Kinds
64 Kind, SimpleKind, KindVar,
66 -- ** Common Kinds and SuperKinds
67 liftedTypeKind, unliftedTypeKind, openTypeKind,
68 argTypeKind, ubxTupleKind,
70 tySuperKind, coSuperKind,
72 -- ** Common Kind type constructors
73 liftedTypeKindTyCon, openTypeKindTyCon, unliftedTypeKindTyCon,
74 argTypeKindTyCon, ubxTupleKindTyCon,
76 -- * Type free variables
77 tyVarsOfType, tyVarsOfTypes, tyVarsOfPred, tyVarsOfTheta,
80 -- * Tidying type related things up for printing
82 tidyOpenType, tidyOpenTypes,
83 tidyTyVarBndr, tidyFreeTyVars,
84 tidyOpenTyVar, tidyOpenTyVars,
85 tidyTopType, tidyPred,
89 coreEqType, coreEqType2,
90 tcEqType, tcEqTypes, tcCmpType, tcCmpTypes,
91 tcEqPred, tcEqPredX, tcCmpPred, tcEqTypeX, tcPartOfType, tcPartOfPred,
93 -- * Forcing evaluation of types
96 -- * Other views onto Types
97 coreView, tcView, kindView,
101 -- * Type representation for the code generator
104 typePrimRep, predTypeRep,
106 -- * Main type substitution data types
107 TvSubstEnv, -- Representation widely visible
108 TvSubst(..), -- Representation visible to a few friends
110 -- ** Manipulating type substitutions
111 emptyTvSubstEnv, emptyTvSubst,
113 mkTvSubst, mkOpenTvSubst, zipOpenTvSubst, zipTopTvSubst, mkTopTvSubst, notElemTvSubst,
114 getTvSubstEnv, setTvSubstEnv, zapTvSubstEnv, getTvInScope,
115 extendTvInScope, extendTvInScopeList,
116 extendTvSubst, extendTvSubstList, isInScope, composeTvSubst, zipTyEnv,
119 -- ** Performing substitution on types
120 substTy, substTys, substTyWith, substTysWith, substTheta,
121 substPred, substTyVar, substTyVars, substTyVarBndr, deShadowTy, lookupTyVar,
124 pprType, pprParendType, pprTypeApp, pprTyThingCategory, pprTyThing, pprForAll,
125 pprPred, pprEqPred, pprTheta, pprThetaArrow, pprClassPred, pprKind, pprParendKind,
130 #include "HsVersions.h"
132 -- We import the representation and primitive functions from TypeRep.
133 -- Many things are reexported, but not the representation!
153 import Data.Maybe ( isJust )
157 -- $type_classification
158 -- #type_classification#
162 -- [Unboxed] Iff its representation is other than a pointer
163 -- Unboxed types are also unlifted.
165 -- [Lifted] Iff it has bottom as an element.
166 -- Closures always have lifted types: i.e. any
167 -- let-bound identifier in Core must have a lifted
168 -- type. Operationally, a lifted object is one that
170 -- Only lifted types may be unified with a type variable.
172 -- [Algebraic] Iff it is a type with one or more constructors, whether
173 -- declared with @data@ or @newtype@.
174 -- An algebraic type is one that can be deconstructed
175 -- with a case expression. This is /not/ the same as
176 -- lifted types, because we also include unboxed
177 -- tuples in this classification.
179 -- [Data] Iff it is a type declared with @data@, or a boxed tuple.
181 -- [Primitive] Iff it is a built-in type that can't be expressed in Haskell.
183 -- Currently, all primitive types are unlifted, but that's not necessarily
184 -- the case: for example, @Int@ could be primitive.
186 -- Some primitive types are unboxed, such as @Int#@, whereas some are boxed
187 -- but unlifted (such as @ByteArray#@). The only primitive types that we
188 -- classify as algebraic are the unboxed tuples.
190 -- Some examples of type classifications that may make this a bit clearer are:
193 -- Type primitive boxed lifted algebraic
194 -- -----------------------------------------------------------------------------
196 -- ByteArray# Yes Yes No No
197 -- (\# a, b \#) Yes No No Yes
198 -- ( a, b ) No Yes Yes Yes
199 -- [a] No Yes Yes Yes
202 -- $representation_types
203 -- A /source type/ is a type that is a separate type as far as the type checker is
204 -- concerned, but which has a more low-level representation as far as Core-to-Core
205 -- passes and the rest of the back end is concerned. Notably, 'PredTy's are removed
206 -- from the representation type while they do exist in the source types.
208 -- You don't normally have to worry about this, as the utility functions in
209 -- this module will automatically convert a source into a representation type
210 -- if they are spotted, to the best of it's abilities. If you don't want this
211 -- to happen, use the equivalent functions from the "TcType" module.
214 %************************************************************************
218 %************************************************************************
221 {-# INLINE coreView #-}
222 coreView :: Type -> Maybe Type
223 -- ^ In Core, we \"look through\" non-recursive newtypes and 'PredTypes': this
224 -- function tries to obtain a different view of the supplied type given this
226 -- Strips off the /top layer only/ of a type to give
227 -- its underlying representation type.
228 -- Returns Nothing if there is nothing to look through.
230 -- In the case of @newtype@s, it returns one of:
232 -- 1) A vanilla 'TyConApp' (recursive newtype, or non-saturated)
234 -- 2) The newtype representation (otherwise), meaning the
235 -- type written in the RHS of the newtype declaration,
236 -- which may itself be a newtype
238 -- For example, with:
240 -- > newtype R = MkR S
241 -- > newtype S = MkS T
242 -- > newtype T = MkT (T -> T)
244 -- 'expandNewTcApp' on:
246 -- * @R@ gives @Just S@
247 -- * @S@ gives @Just T@
248 -- * @T@ gives @Nothing@ (no expansion)
250 -- By being non-recursive and inlined, this case analysis gets efficiently
251 -- joined onto the case analysis that the caller is already doing
253 | isEqPred p = Nothing
254 | otherwise = Just (predTypeRep p)
255 coreView (TyConApp tc tys) | Just (tenv, rhs, tys') <- coreExpandTyCon_maybe tc tys
256 = Just (mkAppTys (substTy (mkTopTvSubst tenv) rhs) tys')
257 -- Its important to use mkAppTys, rather than (foldl AppTy),
258 -- because the function part might well return a
259 -- partially-applied type constructor; indeed, usually will!
264 -----------------------------------------------
265 {-# INLINE tcView #-}
266 tcView :: Type -> Maybe Type
267 -- ^ Similar to 'coreView', but for the type checker, which just looks through synonyms
268 tcView (TyConApp tc tys) | Just (tenv, rhs, tys') <- tcExpandTyCon_maybe tc tys
269 = Just (mkAppTys (substTy (mkTopTvSubst tenv) rhs) tys')
272 -----------------------------------------------
273 expandTypeSynonyms :: Type -> Type
274 -- ^ Expand out all type synonyms. Actually, it'd suffice to expand out
275 -- just the ones that discard type variables (e.g. type Funny a = Int)
276 -- But we don't know which those are currently, so we just expand all.
277 expandTypeSynonyms ty
281 | Just (tenv, rhs, tys') <- tcExpandTyCon_maybe tc tys
282 = go (mkAppTys (substTy (mkTopTvSubst tenv) rhs) tys')
284 = TyConApp tc (map go tys)
285 go (TyVarTy tv) = TyVarTy tv
286 go (AppTy t1 t2) = AppTy (go t1) (go t2)
287 go (FunTy t1 t2) = FunTy (go t1) (go t2)
288 go (ForAllTy tv t) = ForAllTy tv (go t)
289 go (PredTy p) = PredTy (go_pred p)
291 go_pred (ClassP c ts) = ClassP c (map go ts)
292 go_pred (IParam ip t) = IParam ip (go t)
293 go_pred (EqPred t1 t2) = EqPred (go t1) (go t2)
295 -----------------------------------------------
296 {-# INLINE kindView #-}
297 kindView :: Kind -> Maybe Kind
298 -- ^ Similar to 'coreView' or 'tcView', but works on 'Kind's
300 -- For the moment, we don't even handle synonyms in kinds
305 %************************************************************************
307 \subsection{Constructor-specific functions}
309 %************************************************************************
312 ---------------------------------------------------------------------
316 mkTyVarTy :: TyVar -> Type
319 mkTyVarTys :: [TyVar] -> [Type]
320 mkTyVarTys = map mkTyVarTy -- a common use of mkTyVarTy
322 -- | Attempts to obtain the type variable underlying a 'Type', and panics with the
323 -- given message if this is not a type variable type. See also 'getTyVar_maybe'
324 getTyVar :: String -> Type -> TyVar
325 getTyVar msg ty = case getTyVar_maybe ty of
327 Nothing -> panic ("getTyVar: " ++ msg)
329 isTyVarTy :: Type -> Bool
330 isTyVarTy ty = isJust (getTyVar_maybe ty)
332 -- | Attempts to obtain the type variable underlying a 'Type'
333 getTyVar_maybe :: Type -> Maybe TyVar
334 getTyVar_maybe ty | Just ty' <- coreView ty = getTyVar_maybe ty'
335 getTyVar_maybe (TyVarTy tv) = Just tv
336 getTyVar_maybe _ = Nothing
341 ---------------------------------------------------------------------
344 We need to be pretty careful with AppTy to make sure we obey the
345 invariant that a TyConApp is always visibly so. mkAppTy maintains the
349 -- | Applies a type to another, as in e.g. @k a@
350 mkAppTy :: Type -> Type -> Type
351 mkAppTy orig_ty1 orig_ty2
354 mk_app (TyConApp tc tys) = mkTyConApp tc (tys ++ [orig_ty2])
355 mk_app _ = AppTy orig_ty1 orig_ty2
356 -- Note that the TyConApp could be an
357 -- under-saturated type synonym. GHC allows that; e.g.
358 -- type Foo k = k a -> k a
360 -- foo :: Foo Id -> Foo Id
362 -- Here Id is partially applied in the type sig for Foo,
363 -- but once the type synonyms are expanded all is well
365 mkAppTys :: Type -> [Type] -> Type
366 mkAppTys orig_ty1 [] = orig_ty1
367 -- This check for an empty list of type arguments
368 -- avoids the needless loss of a type synonym constructor.
369 -- For example: mkAppTys Rational []
370 -- returns to (Ratio Integer), which has needlessly lost
371 -- the Rational part.
372 mkAppTys orig_ty1 orig_tys2
375 mk_app (TyConApp tc tys) = mkTyConApp tc (tys ++ orig_tys2)
376 -- mkTyConApp: see notes with mkAppTy
377 mk_app _ = foldl AppTy orig_ty1 orig_tys2
380 splitAppTy_maybe :: Type -> Maybe (Type, Type)
381 -- ^ Attempt to take a type application apart, whether it is a
382 -- function, type constructor, or plain type application. Note
383 -- that type family applications are NEVER unsaturated by this!
384 splitAppTy_maybe ty | Just ty' <- coreView ty
385 = splitAppTy_maybe ty'
386 splitAppTy_maybe ty = repSplitAppTy_maybe ty
389 repSplitAppTy_maybe :: Type -> Maybe (Type,Type)
390 -- ^ Does the AppTy split as in 'splitAppTy_maybe', but assumes that
391 -- any Core view stuff is already done
392 repSplitAppTy_maybe (FunTy ty1 ty2) = Just (TyConApp funTyCon [ty1], ty2)
393 repSplitAppTy_maybe (AppTy ty1 ty2) = Just (ty1, ty2)
394 repSplitAppTy_maybe (TyConApp tc tys)
395 | isDecomposableTyCon tc || length tys > tyConArity tc
396 = case snocView tys of -- never create unsaturated type family apps
397 Just (tys', ty') -> Just (TyConApp tc tys', ty')
399 repSplitAppTy_maybe _other = Nothing
401 splitAppTy :: Type -> (Type, Type)
402 -- ^ Attempts to take a type application apart, as in 'splitAppTy_maybe',
403 -- and panics if this is not possible
404 splitAppTy ty = case splitAppTy_maybe ty of
406 Nothing -> panic "splitAppTy"
409 splitAppTys :: Type -> (Type, [Type])
410 -- ^ Recursively splits a type as far as is possible, leaving a residual
411 -- type being applied to and the type arguments applied to it. Never fails,
412 -- even if that means returning an empty list of type applications.
413 splitAppTys ty = split ty ty []
415 split orig_ty ty args | Just ty' <- coreView ty = split orig_ty ty' args
416 split _ (AppTy ty arg) args = split ty ty (arg:args)
417 split _ (TyConApp tc tc_args) args
418 = let -- keep type families saturated
419 n | isDecomposableTyCon tc = 0
420 | otherwise = tyConArity tc
421 (tc_args1, tc_args2) = splitAt n tc_args
423 (TyConApp tc tc_args1, tc_args2 ++ args)
424 split _ (FunTy ty1 ty2) args = ASSERT( null args )
425 (TyConApp funTyCon [], [ty1,ty2])
426 split orig_ty _ args = (orig_ty, args)
431 ---------------------------------------------------------------------
436 mkFunTy :: Type -> Type -> Type
437 -- ^ Creates a function type from the given argument and result type
438 mkFunTy arg@(PredTy (EqPred {})) res = ForAllTy (mkWildCoVar arg) res
439 mkFunTy arg res = FunTy arg res
441 mkFunTys :: [Type] -> Type -> Type
442 mkFunTys tys ty = foldr mkFunTy ty tys
444 isFunTy :: Type -> Bool
445 isFunTy ty = isJust (splitFunTy_maybe ty)
447 splitFunTy :: Type -> (Type, Type)
448 -- ^ Attempts to extract the argument and result types from a type, and
449 -- panics if that is not possible. See also 'splitFunTy_maybe'
450 splitFunTy ty | Just ty' <- coreView ty = splitFunTy ty'
451 splitFunTy (FunTy arg res) = (arg, res)
452 splitFunTy other = pprPanic "splitFunTy" (ppr other)
454 splitFunTy_maybe :: Type -> Maybe (Type, Type)
455 -- ^ Attempts to extract the argument and result types from a type
456 splitFunTy_maybe ty | Just ty' <- coreView ty = splitFunTy_maybe ty'
457 splitFunTy_maybe (FunTy arg res) = Just (arg, res)
458 splitFunTy_maybe _ = Nothing
460 splitFunTys :: Type -> ([Type], Type)
461 splitFunTys ty = split [] ty ty
463 split args orig_ty ty | Just ty' <- coreView ty = split args orig_ty ty'
464 split args _ (FunTy arg res) = split (arg:args) res res
465 split args orig_ty _ = (reverse args, orig_ty)
467 splitFunTysN :: Int -> Type -> ([Type], Type)
468 -- ^ Split off exactly the given number argument types, and panics if that is not possible
469 splitFunTysN 0 ty = ([], ty)
470 splitFunTysN n ty = case splitFunTy ty of { (arg, res) ->
471 case splitFunTysN (n-1) res of { (args, res) ->
474 -- | Splits off argument types from the given type and associating
475 -- them with the things in the input list from left to right. The
476 -- final result type is returned, along with the resulting pairs of
477 -- objects and types, albeit with the list of pairs in reverse order.
478 -- Panics if there are not enough argument types for the input list.
479 zipFunTys :: Outputable a => [a] -> Type -> ([(a, Type)], Type)
480 zipFunTys orig_xs orig_ty = split [] orig_xs orig_ty orig_ty
482 split acc [] nty _ = (reverse acc, nty)
484 | Just ty' <- coreView ty = split acc xs nty ty'
485 split acc (x:xs) _ (FunTy arg res) = split ((x,arg):acc) xs res res
486 split _ _ _ _ = pprPanic "zipFunTys" (ppr orig_xs <+> ppr orig_ty)
488 funResultTy :: Type -> Type
489 -- ^ Extract the function result type and panic if that is not possible
490 funResultTy ty | Just ty' <- coreView ty = funResultTy ty'
491 funResultTy (FunTy _arg res) = res
492 funResultTy ty = pprPanic "funResultTy" (ppr ty)
494 funArgTy :: Type -> Type
495 -- ^ Extract the function argument type and panic if that is not possible
496 funArgTy ty | Just ty' <- coreView ty = funArgTy ty'
497 funArgTy (FunTy arg _res) = arg
498 funArgTy ty = pprPanic "funArgTy" (ppr ty)
501 ---------------------------------------------------------------------
506 -- | A key function: builds a 'TyConApp' or 'FunTy' as apppropriate to its arguments.
507 -- Applies its arguments to the constructor from left to right
508 mkTyConApp :: TyCon -> [Type] -> Type
510 | isFunTyCon tycon, [ty1,ty2] <- tys
516 -- | Create the plain type constructor type which has been applied to no type arguments at all.
517 mkTyConTy :: TyCon -> Type
518 mkTyConTy tycon = mkTyConApp tycon []
520 -- splitTyConApp "looks through" synonyms, because they don't
521 -- mean a distinct type, but all other type-constructor applications
522 -- including functions are returned as Just ..
524 -- | The same as @fst . splitTyConApp@
525 tyConAppTyCon :: Type -> TyCon
526 tyConAppTyCon ty = fst (splitTyConApp ty)
528 -- | The same as @snd . splitTyConApp@
529 tyConAppArgs :: Type -> [Type]
530 tyConAppArgs ty = snd (splitTyConApp ty)
532 -- | Attempts to tease a type apart into a type constructor and the application
533 -- of a number of arguments to that constructor. Panics if that is not possible.
534 -- See also 'splitTyConApp_maybe'
535 splitTyConApp :: Type -> (TyCon, [Type])
536 splitTyConApp ty = case splitTyConApp_maybe ty of
538 Nothing -> pprPanic "splitTyConApp" (ppr ty)
540 -- | Attempts to tease a type apart into a type constructor and the application
541 -- of a number of arguments to that constructor
542 splitTyConApp_maybe :: Type -> Maybe (TyCon, [Type])
543 splitTyConApp_maybe ty | Just ty' <- coreView ty = splitTyConApp_maybe ty'
544 splitTyConApp_maybe (TyConApp tc tys) = Just (tc, tys)
545 splitTyConApp_maybe (FunTy arg res) = Just (funTyCon, [arg,res])
546 splitTyConApp_maybe _ = Nothing
548 newTyConInstRhs :: TyCon -> [Type] -> Type
549 -- ^ Unwrap one 'layer' of newtype on a type constructor and its arguments, using an
550 -- eta-reduced version of the @newtype@ if possible
551 newTyConInstRhs tycon tys
552 = ASSERT2( equalLength tvs tys1, ppr tycon $$ ppr tys $$ ppr tvs )
553 mkAppTys (substTyWith tvs tys1 ty) tys2
555 (tvs, ty) = newTyConEtadRhs tycon
556 (tys1, tys2) = splitAtList tvs tys
560 ---------------------------------------------------------------------
564 Notes on type synonyms
565 ~~~~~~~~~~~~~~~~~~~~~~
566 The various "split" functions (splitFunTy, splitRhoTy, splitForAllTy) try
567 to return type synonyms whereever possible. Thus
572 splitFunTys (a -> Foo a) = ([a], Foo a)
575 The reason is that we then get better (shorter) type signatures in
576 interfaces. Notably this plays a role in tcTySigs in TcBinds.lhs.
579 Note [Expanding newtypes]
580 ~~~~~~~~~~~~~~~~~~~~~~~~~
581 When expanding a type to expose a data-type constructor, we need to be
582 careful about newtypes, lest we fall into an infinite loop. Here are
585 newtype Id x = MkId x
586 newtype Fix f = MkFix (f (Fix f))
587 newtype T = MkT (T -> T)
590 --------------------------
592 Fix Maybe Maybe (Fix Maybe)
596 Notice that we can expand T, even though it's recursive.
597 And we can expand Id (Id Int), even though the Id shows up
598 twice at the outer level.
600 So, when expanding, we keep track of when we've seen a recursive
601 newtype at outermost level; and bale out if we see it again.
613 -- 4. All newtypes, including recursive ones, but not newtype families
615 -- It's useful in the back end of the compiler.
616 repType :: Type -> Type
617 -- Only applied to types of kind *; hence tycons are saturated
621 go :: [TyCon] -> Type -> Type
622 go rec_nts ty | Just ty' <- coreView ty -- Expand synonyms
625 go rec_nts (ForAllTy _ ty) -- Look through foralls
628 go rec_nts (TyConApp tc tys) -- Expand newtypes
629 | Just (rec_nts', ty') <- carefullySplitNewType_maybe rec_nts tc tys
635 carefullySplitNewType_maybe :: [TyCon] -> TyCon -> [Type] -> Maybe ([TyCon],Type)
636 -- Return the representation of a newtype, unless
637 -- we've seen it already: see Note [Expanding newtypes]
638 carefullySplitNewType_maybe rec_nts tc tys
640 , not (tc `elem` rec_nts) = Just (rec_nts', newTyConInstRhs tc tys)
641 | otherwise = Nothing
643 rec_nts' | isRecursiveTyCon tc = tc:rec_nts
644 | otherwise = rec_nts
647 -- ToDo: this could be moved to the code generator, using splitTyConApp instead
648 -- of inspecting the type directly.
650 -- | Discovers the primitive representation of a more abstract 'Type'
651 typePrimRep :: Type -> PrimRep
652 typePrimRep ty = case repType ty of
653 TyConApp tc _ -> tyConPrimRep tc
655 AppTy _ _ -> PtrRep -- See note below
657 _ -> pprPanic "typePrimRep" (ppr ty)
658 -- Types of the form 'f a' must be of kind *, not *#, so
659 -- we are guaranteed that they are represented by pointers.
660 -- The reason is that f must have kind *->*, not *->*#, because
661 -- (we claim) there is no way to constrain f's kind any other
666 ---------------------------------------------------------------------
671 mkForAllTy :: TyVar -> Type -> Type
675 -- | Wraps foralls over the type using the provided 'TyVar's from left to right
676 mkForAllTys :: [TyVar] -> Type -> Type
677 mkForAllTys tyvars ty = foldr ForAllTy ty tyvars
679 isForAllTy :: Type -> Bool
680 isForAllTy (ForAllTy _ _) = True
683 -- | Attempts to take a forall type apart, returning the bound type variable
684 -- and the remainder of the type
685 splitForAllTy_maybe :: Type -> Maybe (TyVar, Type)
686 splitForAllTy_maybe ty = splitFAT_m ty
688 splitFAT_m ty | Just ty' <- coreView ty = splitFAT_m ty'
689 splitFAT_m (ForAllTy tyvar ty) = Just(tyvar, ty)
690 splitFAT_m _ = Nothing
692 -- | Attempts to take a forall type apart, returning all the immediate such bound
693 -- type variables and the remainder of the type. Always suceeds, even if that means
694 -- returning an empty list of 'TyVar's
695 splitForAllTys :: Type -> ([TyVar], Type)
696 splitForAllTys ty = split ty ty []
698 split orig_ty ty tvs | Just ty' <- coreView ty = split orig_ty ty' tvs
699 split _ (ForAllTy tv ty) tvs = split ty ty (tv:tvs)
700 split orig_ty _ tvs = (reverse tvs, orig_ty)
702 -- | Equivalent to @snd . splitForAllTys@
703 dropForAlls :: Type -> Type
704 dropForAlls ty = snd (splitForAllTys ty)
707 -- (mkPiType now in CoreUtils)
713 -- | Instantiate a forall type with one or more type arguments.
714 -- Used when we have a polymorphic function applied to type args:
718 -- We use @applyTys type-of-f [t1,t2]@ to compute the type of the expression.
719 -- Panics if no application is possible.
720 applyTy :: Type -> Type -> Type
721 applyTy ty arg | Just ty' <- coreView ty = applyTy ty' arg
722 applyTy (ForAllTy tv ty) arg = substTyWith [tv] [arg] ty
723 applyTy _ _ = panic "applyTy"
725 applyTys :: Type -> [Type] -> Type
726 -- ^ This function is interesting because:
728 -- 1. The function may have more for-alls than there are args
730 -- 2. Less obviously, it may have fewer for-alls
732 -- For case 2. think of:
734 -- > applyTys (forall a.a) [forall b.b, Int]
736 -- This really can happen, via dressing up polymorphic types with newtype
737 -- clothing. Here's an example:
739 -- > newtype R = R (forall a. a->a)
740 -- > foo = case undefined :: R of
743 applyTys ty args = applyTysD empty ty args
745 applyTysD :: SDoc -> Type -> [Type] -> Type -- Debug version
746 applyTysD _ orig_fun_ty [] = orig_fun_ty
747 applyTysD doc orig_fun_ty arg_tys
748 | n_tvs == n_args -- The vastly common case
749 = substTyWith tvs arg_tys rho_ty
750 | n_tvs > n_args -- Too many for-alls
751 = substTyWith (take n_args tvs) arg_tys
752 (mkForAllTys (drop n_args tvs) rho_ty)
753 | otherwise -- Too many type args
754 = ASSERT2( n_tvs > 0, doc $$ ppr orig_fun_ty ) -- Zero case gives infnite loop!
755 applyTysD doc (substTyWith tvs (take n_tvs arg_tys) rho_ty)
758 (tvs, rho_ty) = splitForAllTys orig_fun_ty
760 n_args = length arg_tys
764 %************************************************************************
766 \subsection{Source types}
768 %************************************************************************
770 Source types are always lifted.
772 The key function is predTypeRep which gives the representation of a source type:
775 mkPredTy :: PredType -> Type
776 mkPredTy pred = PredTy pred
778 mkPredTys :: ThetaType -> [Type]
779 mkPredTys preds = map PredTy preds
781 isEqPred :: PredType -> Bool
782 isEqPred (EqPred _ _) = True
785 predTypeRep :: PredType -> Type
786 -- ^ Convert a 'PredType' to its representation type. However, it unwraps
787 -- only the outermost level; for example, the result might be a newtype application
788 predTypeRep (IParam _ ty) = ty
789 predTypeRep (ClassP clas tys) = mkTyConApp (classTyCon clas) tys
790 -- Result might be a newtype application, but the consumer will
791 -- look through that too if necessary
792 predTypeRep (EqPred ty1 ty2) = pprPanic "predTypeRep" (ppr (EqPred ty1 ty2))
794 mkFamilyTyConApp :: TyCon -> [Type] -> Type
795 -- ^ Given a family instance TyCon and its arg types, return the
796 -- corresponding family type. E.g:
799 -- > data instance T (Maybe b) = MkT b
801 -- Where the instance tycon is :RTL, so:
803 -- > mkFamilyTyConApp :RTL Int = T (Maybe Int)
804 mkFamilyTyConApp tc tys
805 | Just (fam_tc, fam_tys) <- tyConFamInst_maybe tc
806 , let fam_subst = zipTopTvSubst (tyConTyVars tc) tys
807 = mkTyConApp fam_tc (substTys fam_subst fam_tys)
811 -- | Pretty prints a 'TyCon', using the family instance in case of a
812 -- representation tycon. For example:
814 -- > data T [a] = ...
816 -- In that case we want to print @T [a]@, where @T@ is the family 'TyCon'
817 pprSourceTyCon :: TyCon -> SDoc
819 | Just (fam_tc, tys) <- tyConFamInst_maybe tycon
820 = ppr $ fam_tc `TyConApp` tys -- can't be FunTyCon
826 %************************************************************************
828 The free variables of a type
830 %************************************************************************
833 tyVarsOfType :: Type -> TyVarSet
834 -- ^ NB: for type synonyms tyVarsOfType does /not/ expand the synonym
835 tyVarsOfType (TyVarTy tv) = unitVarSet tv
836 tyVarsOfType (TyConApp _ tys) = tyVarsOfTypes tys
837 tyVarsOfType (PredTy sty) = tyVarsOfPred sty
838 tyVarsOfType (FunTy arg res) = tyVarsOfType arg `unionVarSet` tyVarsOfType res
839 tyVarsOfType (AppTy fun arg) = tyVarsOfType fun `unionVarSet` tyVarsOfType arg
840 tyVarsOfType (ForAllTy tyvar ty) = delVarSet (tyVarsOfType ty) tyvar
842 tyVarsOfTypes :: [Type] -> TyVarSet
843 tyVarsOfTypes tys = foldr (unionVarSet.tyVarsOfType) emptyVarSet tys
845 tyVarsOfPred :: PredType -> TyVarSet
846 tyVarsOfPred (IParam _ ty) = tyVarsOfType ty
847 tyVarsOfPred (ClassP _ tys) = tyVarsOfTypes tys
848 tyVarsOfPred (EqPred ty1 ty2) = tyVarsOfType ty1 `unionVarSet` tyVarsOfType ty2
850 tyVarsOfTheta :: ThetaType -> TyVarSet
851 tyVarsOfTheta = foldr (unionVarSet . tyVarsOfPred) emptyVarSet
855 %************************************************************************
857 \subsection{Type families}
859 %************************************************************************
862 -- | Finds type family instances occuring in a type after expanding synonyms.
863 tyFamInsts :: Type -> [(TyCon, [Type])]
865 | Just exp_ty <- tcView ty = tyFamInsts exp_ty
866 tyFamInsts (TyVarTy _) = []
867 tyFamInsts (TyConApp tc tys)
868 | isOpenSynTyCon tc = [(tc, tys)]
869 | otherwise = concat (map tyFamInsts tys)
870 tyFamInsts (FunTy ty1 ty2) = tyFamInsts ty1 ++ tyFamInsts ty2
871 tyFamInsts (AppTy ty1 ty2) = tyFamInsts ty1 ++ tyFamInsts ty2
872 tyFamInsts (ForAllTy _ ty) = tyFamInsts ty
873 tyFamInsts (PredTy pty) = predFamInsts pty
875 -- | Finds type family instances occuring in a predicate type after expanding
877 predFamInsts :: PredType -> [(TyCon, [Type])]
878 predFamInsts (ClassP _cla tys) = concat (map tyFamInsts tys)
879 predFamInsts (IParam _ ty) = tyFamInsts ty
880 predFamInsts (EqPred ty1 ty2) = tyFamInsts ty1 ++ tyFamInsts ty2
884 %************************************************************************
886 \subsection{TidyType}
888 %************************************************************************
891 -- | This tidies up a type for printing in an error message, or in
892 -- an interface file.
894 -- It doesn't change the uniques at all, just the print names.
895 tidyTyVarBndr :: TidyEnv -> TyVar -> (TidyEnv, TyVar)
896 tidyTyVarBndr env@(tidy_env, subst) tyvar
897 = case tidyOccName tidy_env (getOccName name) of
898 (tidy', occ') -> ((tidy', subst'), tyvar'')
900 subst' = extendVarEnv subst tyvar tyvar''
901 tyvar' = setTyVarName tyvar name'
902 name' = tidyNameOcc name occ'
903 -- Don't forget to tidy the kind for coercions!
904 tyvar'' | isCoVar tyvar = setTyVarKind tyvar' kind'
906 kind' = tidyType env (tyVarKind tyvar)
908 name = tyVarName tyvar
910 tidyFreeTyVars :: TidyEnv -> TyVarSet -> TidyEnv
911 -- ^ Add the free 'TyVar's to the env in tidy form,
912 -- so that we can tidy the type they are free in
913 tidyFreeTyVars env tyvars = fst (tidyOpenTyVars env (varSetElems tyvars))
915 tidyOpenTyVars :: TidyEnv -> [TyVar] -> (TidyEnv, [TyVar])
916 tidyOpenTyVars env tyvars = mapAccumL tidyOpenTyVar env tyvars
918 tidyOpenTyVar :: TidyEnv -> TyVar -> (TidyEnv, TyVar)
919 -- ^ Treat a new 'TyVar' as a binder, and give it a fresh tidy name
920 -- using the environment if one has not already been allocated. See
921 -- also 'tidyTyVarBndr'
922 tidyOpenTyVar env@(_, subst) tyvar
923 = case lookupVarEnv subst tyvar of
924 Just tyvar' -> (env, tyvar') -- Already substituted
925 Nothing -> tidyTyVarBndr env tyvar -- Treat it as a binder
927 tidyType :: TidyEnv -> Type -> Type
928 tidyType env@(_, subst) ty
931 go (TyVarTy tv) = case lookupVarEnv subst tv of
932 Nothing -> TyVarTy tv
933 Just tv' -> TyVarTy tv'
934 go (TyConApp tycon tys) = let args = map go tys
935 in args `seqList` TyConApp tycon args
936 go (PredTy sty) = PredTy (tidyPred env sty)
937 go (AppTy fun arg) = (AppTy $! (go fun)) $! (go arg)
938 go (FunTy fun arg) = (FunTy $! (go fun)) $! (go arg)
939 go (ForAllTy tv ty) = ForAllTy tvp $! (tidyType envp ty)
941 (envp, tvp) = tidyTyVarBndr env tv
943 tidyTypes :: TidyEnv -> [Type] -> [Type]
944 tidyTypes env tys = map (tidyType env) tys
946 tidyPred :: TidyEnv -> PredType -> PredType
947 tidyPred env (IParam n ty) = IParam n (tidyType env ty)
948 tidyPred env (ClassP clas tys) = ClassP clas (tidyTypes env tys)
949 tidyPred env (EqPred ty1 ty2) = EqPred (tidyType env ty1) (tidyType env ty2)
954 -- | Grabs the free type variables, tidies them
955 -- and then uses 'tidyType' to work over the type itself
956 tidyOpenType :: TidyEnv -> Type -> (TidyEnv, Type)
958 = (env', tidyType env' ty)
960 env' = tidyFreeTyVars env (tyVarsOfType ty)
962 tidyOpenTypes :: TidyEnv -> [Type] -> (TidyEnv, [Type])
963 tidyOpenTypes env tys = mapAccumL tidyOpenType env tys
965 -- | Calls 'tidyType' on a top-level type (i.e. with an empty tidying environment)
966 tidyTopType :: Type -> Type
967 tidyTopType ty = tidyType emptyTidyEnv ty
972 tidyKind :: TidyEnv -> Kind -> (TidyEnv, Kind)
973 tidyKind env k = tidyOpenType env k
978 %************************************************************************
980 \subsection{Liftedness}
982 %************************************************************************
985 -- | See "Type#type_classification" for what an unlifted type is
986 isUnLiftedType :: Type -> Bool
987 -- isUnLiftedType returns True for forall'd unlifted types:
988 -- x :: forall a. Int#
989 -- I found bindings like these were getting floated to the top level.
990 -- They are pretty bogus types, mind you. It would be better never to
993 isUnLiftedType ty | Just ty' <- coreView ty = isUnLiftedType ty'
994 isUnLiftedType (ForAllTy _ ty) = isUnLiftedType ty
995 isUnLiftedType (TyConApp tc _) = isUnLiftedTyCon tc
996 isUnLiftedType _ = False
998 isUnboxedTupleType :: Type -> Bool
999 isUnboxedTupleType ty = case splitTyConApp_maybe ty of
1000 Just (tc, _ty_args) -> isUnboxedTupleTyCon tc
1003 -- | See "Type#type_classification" for what an algebraic type is.
1004 -- Should only be applied to /types/, as opposed to e.g. partially
1005 -- saturated type constructors
1006 isAlgType :: Type -> Bool
1008 = case splitTyConApp_maybe ty of
1009 Just (tc, ty_args) -> ASSERT( ty_args `lengthIs` tyConArity tc )
1013 -- | See "Type#type_classification" for what an algebraic type is.
1014 -- Should only be applied to /types/, as opposed to e.g. partially
1015 -- saturated type constructors. Closed type constructors are those
1016 -- with a fixed right hand side, as opposed to e.g. associated types
1017 isClosedAlgType :: Type -> Bool
1019 = case splitTyConApp_maybe ty of
1020 Just (tc, ty_args) -> ASSERT( ty_args `lengthIs` tyConArity tc )
1021 isAlgTyCon tc && not (isOpenTyCon tc)
1026 -- | Computes whether an argument (or let right hand side) should
1027 -- be computed strictly or lazily, based only on its type.
1028 -- Works just like 'isUnLiftedType', except that it has a special case
1029 -- for dictionaries (i.e. does not work purely on representation types)
1031 -- Since it takes account of class 'PredType's, you might think
1032 -- this function should be in 'TcType', but 'isStrictType' is used by 'DataCon',
1033 -- which is below 'TcType' in the hierarchy, so it's convenient to put it here.
1034 isStrictType :: Type -> Bool
1035 isStrictType (PredTy pred) = isStrictPred pred
1036 isStrictType ty | Just ty' <- coreView ty = isStrictType ty'
1037 isStrictType (ForAllTy _ ty) = isStrictType ty
1038 isStrictType (TyConApp tc _) = isUnLiftedTyCon tc
1039 isStrictType _ = False
1041 -- | We may be strict in dictionary types, but only if it
1042 -- has more than one component.
1044 -- (Being strict in a single-component dictionary risks
1045 -- poking the dictionary component, which is wrong.)
1046 isStrictPred :: PredType -> Bool
1047 isStrictPred (ClassP clas _) = opt_DictsStrict && not (isNewTyCon (classTyCon clas))
1048 isStrictPred _ = False
1052 isPrimitiveType :: Type -> Bool
1053 -- ^ Returns true of types that are opaque to Haskell.
1054 -- Most of these are unlifted, but now that we interact with .NET, we
1055 -- may have primtive (foreign-imported) types that are lifted
1056 isPrimitiveType ty = case splitTyConApp_maybe ty of
1057 Just (tc, ty_args) -> ASSERT( ty_args `lengthIs` tyConArity tc )
1063 %************************************************************************
1065 \subsection{Sequencing on types}
1067 %************************************************************************
1070 seqType :: Type -> ()
1071 seqType (TyVarTy tv) = tv `seq` ()
1072 seqType (AppTy t1 t2) = seqType t1 `seq` seqType t2
1073 seqType (FunTy t1 t2) = seqType t1 `seq` seqType t2
1074 seqType (PredTy p) = seqPred p
1075 seqType (TyConApp tc tys) = tc `seq` seqTypes tys
1076 seqType (ForAllTy tv ty) = tv `seq` seqType ty
1078 seqTypes :: [Type] -> ()
1080 seqTypes (ty:tys) = seqType ty `seq` seqTypes tys
1082 seqPred :: PredType -> ()
1083 seqPred (ClassP c tys) = c `seq` seqTypes tys
1084 seqPred (IParam n ty) = n `seq` seqType ty
1085 seqPred (EqPred ty1 ty2) = seqType ty1 `seq` seqType ty2
1089 %************************************************************************
1091 Equality for Core types
1092 (We don't use instances so that we know where it happens)
1094 %************************************************************************
1096 Note that eqType works right even for partial applications of newtypes.
1097 See Note [Newtype eta] in TyCon.lhs
1100 -- | Type equality test for Core types (i.e. ignores predicate-types, synonyms etc.)
1101 coreEqType :: Type -> Type -> Bool
1102 coreEqType t1 t2 = coreEqType2 rn_env t1 t2
1104 rn_env = mkRnEnv2 (mkInScopeSet (tyVarsOfType t1 `unionVarSet` tyVarsOfType t2))
1106 coreEqType2 :: RnEnv2 -> Type -> Type -> Bool
1107 coreEqType2 rn_env t1 t2
1110 eq env (TyVarTy tv1) (TyVarTy tv2) = rnOccL env tv1 == rnOccR env tv2
1111 eq env (ForAllTy tv1 t1) (ForAllTy tv2 t2) = eq (rnBndr2 env tv1 tv2) t1 t2
1112 eq env (AppTy s1 t1) (AppTy s2 t2) = eq env s1 s2 && eq env t1 t2
1113 eq env (FunTy s1 t1) (FunTy s2 t2) = eq env s1 s2 && eq env t1 t2
1114 eq env (TyConApp tc1 tys1) (TyConApp tc2 tys2)
1115 | tc1 == tc2, all2 (eq env) tys1 tys2 = True
1116 -- The lengths should be equal because
1117 -- the two types have the same kind
1118 -- NB: if the type constructors differ that does not
1119 -- necessarily mean that the types aren't equal
1120 -- (synonyms, newtypes)
1121 -- Even if the type constructors are the same, but the arguments
1122 -- differ, the two types could be the same (e.g. if the arg is just
1123 -- ignored in the RHS). In both these cases we fall through to an
1124 -- attempt to expand one side or the other.
1126 -- Now deal with newtypes, synonyms, pred-tys
1127 eq env t1 t2 | Just t1' <- coreView t1 = eq env t1' t2
1128 | Just t2' <- coreView t2 = eq env t1 t2'
1130 -- Fall through case; not equal!
1135 %************************************************************************
1137 Comparision for source types
1138 (We don't use instances so that we know where it happens)
1140 %************************************************************************
1143 tcEqType :: Type -> Type -> Bool
1144 -- ^ Type equality on source types. Does not look through @newtypes@ or
1145 -- 'PredType's, but it does look through type synonyms.
1146 tcEqType t1 t2 = isEqual $ cmpType t1 t2
1148 tcEqTypes :: [Type] -> [Type] -> Bool
1149 tcEqTypes tys1 tys2 = isEqual $ cmpTypes tys1 tys2
1151 tcCmpType :: Type -> Type -> Ordering
1152 -- ^ Type ordering on source types. Does not look through @newtypes@ or
1153 -- 'PredType's, but it does look through type synonyms.
1154 tcCmpType t1 t2 = cmpType t1 t2
1156 tcCmpTypes :: [Type] -> [Type] -> Ordering
1157 tcCmpTypes tys1 tys2 = cmpTypes tys1 tys2
1159 tcEqPred :: PredType -> PredType -> Bool
1160 tcEqPred p1 p2 = isEqual $ cmpPred p1 p2
1162 tcEqPredX :: RnEnv2 -> PredType -> PredType -> Bool
1163 tcEqPredX env p1 p2 = isEqual $ cmpPredX env p1 p2
1165 tcCmpPred :: PredType -> PredType -> Ordering
1166 tcCmpPred p1 p2 = cmpPred p1 p2
1168 tcEqTypeX :: RnEnv2 -> Type -> Type -> Bool
1169 tcEqTypeX env t1 t2 = isEqual $ cmpTypeX env t1 t2
1173 -- | Checks whether the second argument is a subterm of the first. (We don't care
1174 -- about binders, as we are only interested in syntactic subterms.)
1175 tcPartOfType :: Type -> Type -> Bool
1177 | tcEqType t1 t2 = True
1179 | Just t2' <- tcView t2 = tcPartOfType t1 t2'
1180 tcPartOfType _ (TyVarTy _) = False
1181 tcPartOfType t1 (ForAllTy _ t2) = tcPartOfType t1 t2
1182 tcPartOfType t1 (AppTy s2 t2) = tcPartOfType t1 s2 || tcPartOfType t1 t2
1183 tcPartOfType t1 (FunTy s2 t2) = tcPartOfType t1 s2 || tcPartOfType t1 t2
1184 tcPartOfType t1 (PredTy p2) = tcPartOfPred t1 p2
1185 tcPartOfType t1 (TyConApp _ ts) = any (tcPartOfType t1) ts
1187 tcPartOfPred :: Type -> PredType -> Bool
1188 tcPartOfPred t1 (IParam _ t2) = tcPartOfType t1 t2
1189 tcPartOfPred t1 (ClassP _ ts) = any (tcPartOfType t1) ts
1190 tcPartOfPred t1 (EqPred s2 t2) = tcPartOfType t1 s2 || tcPartOfType t1 t2
1193 Now here comes the real worker
1196 cmpType :: Type -> Type -> Ordering
1197 cmpType t1 t2 = cmpTypeX rn_env t1 t2
1199 rn_env = mkRnEnv2 (mkInScopeSet (tyVarsOfType t1 `unionVarSet` tyVarsOfType t2))
1201 cmpTypes :: [Type] -> [Type] -> Ordering
1202 cmpTypes ts1 ts2 = cmpTypesX rn_env ts1 ts2
1204 rn_env = mkRnEnv2 (mkInScopeSet (tyVarsOfTypes ts1 `unionVarSet` tyVarsOfTypes ts2))
1206 cmpPred :: PredType -> PredType -> Ordering
1207 cmpPred p1 p2 = cmpPredX rn_env p1 p2
1209 rn_env = mkRnEnv2 (mkInScopeSet (tyVarsOfPred p1 `unionVarSet` tyVarsOfPred p2))
1211 cmpTypeX :: RnEnv2 -> Type -> Type -> Ordering -- Main workhorse
1212 cmpTypeX env t1 t2 | Just t1' <- tcView t1 = cmpTypeX env t1' t2
1213 | Just t2' <- tcView t2 = cmpTypeX env t1 t2'
1215 cmpTypeX env (TyVarTy tv1) (TyVarTy tv2) = rnOccL env tv1 `compare` rnOccR env tv2
1216 cmpTypeX env (ForAllTy tv1 t1) (ForAllTy tv2 t2) = cmpTypeX (rnBndr2 env tv1 tv2) t1 t2
1217 cmpTypeX env (AppTy s1 t1) (AppTy s2 t2) = cmpTypeX env s1 s2 `thenCmp` cmpTypeX env t1 t2
1218 cmpTypeX env (FunTy s1 t1) (FunTy s2 t2) = cmpTypeX env s1 s2 `thenCmp` cmpTypeX env t1 t2
1219 cmpTypeX env (PredTy p1) (PredTy p2) = cmpPredX env p1 p2
1220 cmpTypeX env (TyConApp tc1 tys1) (TyConApp tc2 tys2) = (tc1 `compare` tc2) `thenCmp` cmpTypesX env tys1 tys2
1222 -- Deal with the rest: TyVarTy < AppTy < FunTy < TyConApp < ForAllTy < PredTy
1223 cmpTypeX _ (AppTy _ _) (TyVarTy _) = GT
1225 cmpTypeX _ (FunTy _ _) (TyVarTy _) = GT
1226 cmpTypeX _ (FunTy _ _) (AppTy _ _) = GT
1228 cmpTypeX _ (TyConApp _ _) (TyVarTy _) = GT
1229 cmpTypeX _ (TyConApp _ _) (AppTy _ _) = GT
1230 cmpTypeX _ (TyConApp _ _) (FunTy _ _) = GT
1232 cmpTypeX _ (ForAllTy _ _) (TyVarTy _) = GT
1233 cmpTypeX _ (ForAllTy _ _) (AppTy _ _) = GT
1234 cmpTypeX _ (ForAllTy _ _) (FunTy _ _) = GT
1235 cmpTypeX _ (ForAllTy _ _) (TyConApp _ _) = GT
1237 cmpTypeX _ (PredTy _) _ = GT
1242 cmpTypesX :: RnEnv2 -> [Type] -> [Type] -> Ordering
1243 cmpTypesX _ [] [] = EQ
1244 cmpTypesX env (t1:tys1) (t2:tys2) = cmpTypeX env t1 t2 `thenCmp` cmpTypesX env tys1 tys2
1245 cmpTypesX _ [] _ = LT
1246 cmpTypesX _ _ [] = GT
1249 cmpPredX :: RnEnv2 -> PredType -> PredType -> Ordering
1250 cmpPredX env (IParam n1 ty1) (IParam n2 ty2) = (n1 `compare` n2) `thenCmp` cmpTypeX env ty1 ty2
1251 -- Compare names only for implicit parameters
1252 -- This comparison is used exclusively (I believe)
1253 -- for the Avails finite map built in TcSimplify
1254 -- If the types differ we keep them distinct so that we see
1255 -- a distinct pair to run improvement on
1256 cmpPredX env (ClassP c1 tys1) (ClassP c2 tys2) = (c1 `compare` c2) `thenCmp` (cmpTypesX env tys1 tys2)
1257 cmpPredX env (EqPred ty1 ty2) (EqPred ty1' ty2') = (cmpTypeX env ty1 ty1') `thenCmp` (cmpTypeX env ty2 ty2')
1259 -- Constructor order: IParam < ClassP < EqPred
1260 cmpPredX _ (IParam {}) _ = LT
1261 cmpPredX _ (ClassP {}) (IParam {}) = GT
1262 cmpPredX _ (ClassP {}) (EqPred {}) = LT
1263 cmpPredX _ (EqPred {}) _ = GT
1266 PredTypes are used as a FM key in TcSimplify,
1267 so we take the easy path and make them an instance of Ord
1270 instance Eq PredType where { (==) = tcEqPred }
1271 instance Ord PredType where { compare = tcCmpPred }
1275 %************************************************************************
1279 %************************************************************************
1282 -- | Type substitution
1284 -- #tvsubst_invariant#
1285 -- The following invariants must hold of a 'TvSubst':
1287 -- 1. The in-scope set is needed /only/ to
1288 -- guide the generation of fresh uniques
1290 -- 2. In particular, the /kind/ of the type variables in
1291 -- the in-scope set is not relevant
1293 -- 3. The substition is only applied ONCE! This is because
1294 -- in general such application will not reached a fixed point.
1296 = TvSubst InScopeSet -- The in-scope type variables
1297 TvSubstEnv -- The substitution itself
1298 -- See Note [Apply Once]
1299 -- and Note [Extending the TvSubstEnv]
1301 {- ----------------------------------------------------------
1305 We use TvSubsts to instantiate things, and we might instantiate
1309 So the substition might go [a->b, b->a]. A similar situation arises in Core
1310 when we find a beta redex like
1311 (/\ a /\ b -> e) b a
1312 Then we also end up with a substition that permutes type variables. Other
1313 variations happen to; for example [a -> (a, b)].
1315 ***************************************************
1316 *** So a TvSubst must be applied precisely once ***
1317 ***************************************************
1319 A TvSubst is not idempotent, but, unlike the non-idempotent substitution
1320 we use during unifications, it must not be repeatedly applied.
1322 Note [Extending the TvSubst]
1323 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1324 See #tvsubst_invariant# for the invariants that must hold.
1326 This invariant allows a short-cut when the TvSubstEnv is empty:
1327 if the TvSubstEnv is empty --- i.e. (isEmptyTvSubt subst) holds ---
1328 then (substTy subst ty) does nothing.
1330 For example, consider:
1331 (/\a. /\b:(a~Int). ...b..) Int
1332 We substitute Int for 'a'. The Unique of 'b' does not change, but
1333 nevertheless we add 'b' to the TvSubstEnv, because b's type does change
1335 This invariant has several crucial consequences:
1337 * In substTyVarBndr, we need extend the TvSubstEnv
1338 - if the unique has changed
1339 - or if the kind has changed
1341 * In substTyVar, we do not need to consult the in-scope set;
1342 the TvSubstEnv is enough
1344 * In substTy, substTheta, we can short-circuit when the TvSubstEnv is empty
1347 -------------------------------------------------------------- -}
1349 -- | A substitition of 'Type's for 'TyVar's
1350 type TvSubstEnv = TyVarEnv Type
1351 -- A TvSubstEnv is used both inside a TvSubst (with the apply-once
1352 -- invariant discussed in Note [Apply Once]), and also independently
1353 -- in the middle of matching, and unification (see Types.Unify)
1354 -- So you have to look at the context to know if it's idempotent or
1355 -- apply-once or whatever
1357 emptyTvSubstEnv :: TvSubstEnv
1358 emptyTvSubstEnv = emptyVarEnv
1360 composeTvSubst :: InScopeSet -> TvSubstEnv -> TvSubstEnv -> TvSubstEnv
1361 -- ^ @(compose env1 env2)(x)@ is @env1(env2(x))@; i.e. apply @env2@ then @env1@.
1362 -- It assumes that both are idempotent.
1363 -- Typically, @env1@ is the refinement to a base substitution @env2@
1364 composeTvSubst in_scope env1 env2
1365 = env1 `plusVarEnv` mapVarEnv (substTy subst1) env2
1366 -- First apply env1 to the range of env2
1367 -- Then combine the two, making sure that env1 loses if
1368 -- both bind the same variable; that's why env1 is the
1369 -- *left* argument to plusVarEnv, because the right arg wins
1371 subst1 = TvSubst in_scope env1
1373 emptyTvSubst :: TvSubst
1374 emptyTvSubst = TvSubst emptyInScopeSet emptyVarEnv
1376 isEmptyTvSubst :: TvSubst -> Bool
1377 -- See Note [Extending the TvSubstEnv]
1378 isEmptyTvSubst (TvSubst _ env) = isEmptyVarEnv env
1380 mkTvSubst :: InScopeSet -> TvSubstEnv -> TvSubst
1383 getTvSubstEnv :: TvSubst -> TvSubstEnv
1384 getTvSubstEnv (TvSubst _ env) = env
1386 getTvInScope :: TvSubst -> InScopeSet
1387 getTvInScope (TvSubst in_scope _) = in_scope
1389 isInScope :: Var -> TvSubst -> Bool
1390 isInScope v (TvSubst in_scope _) = v `elemInScopeSet` in_scope
1392 notElemTvSubst :: TyVar -> TvSubst -> Bool
1393 notElemTvSubst tv (TvSubst _ env) = not (tv `elemVarEnv` env)
1395 setTvSubstEnv :: TvSubst -> TvSubstEnv -> TvSubst
1396 setTvSubstEnv (TvSubst in_scope _) env = TvSubst in_scope env
1398 zapTvSubstEnv :: TvSubst -> TvSubst
1399 zapTvSubstEnv (TvSubst in_scope _) = TvSubst in_scope emptyVarEnv
1401 extendTvInScope :: TvSubst -> Var -> TvSubst
1402 extendTvInScope (TvSubst in_scope env) var = TvSubst (extendInScopeSet in_scope var) env
1404 extendTvInScopeList :: TvSubst -> [Var] -> TvSubst
1405 extendTvInScopeList (TvSubst in_scope env) vars = TvSubst (extendInScopeSetList in_scope vars) env
1407 extendTvSubst :: TvSubst -> TyVar -> Type -> TvSubst
1408 extendTvSubst (TvSubst in_scope env) tv ty = TvSubst in_scope (extendVarEnv env tv ty)
1410 extendTvSubstList :: TvSubst -> [TyVar] -> [Type] -> TvSubst
1411 extendTvSubstList (TvSubst in_scope env) tvs tys
1412 = TvSubst in_scope (extendVarEnvList env (tvs `zip` tys))
1414 -- mkOpenTvSubst and zipOpenTvSubst generate the in-scope set from
1415 -- the types given; but it's just a thunk so with a bit of luck
1416 -- it'll never be evaluated
1418 -- Note [Generating the in-scope set for a substitution]
1419 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1420 -- If we want to substitute [a -> ty1, b -> ty2] I used to
1421 -- think it was enough to generate an in-scope set that includes
1422 -- fv(ty1,ty2). But that's not enough; we really should also take the
1423 -- free vars of the type we are substituting into! Example:
1424 -- (forall b. (a,b,x)) [a -> List b]
1425 -- Then if we use the in-scope set {b}, there is a danger we will rename
1426 -- the forall'd variable to 'x' by mistake, getting this:
1427 -- (forall x. (List b, x, x)
1428 -- Urk! This means looking at all the calls to mkOpenTvSubst....
1431 -- | Generates the in-scope set for the 'TvSubst' from the types in the incoming
1432 -- environment, hence "open"
1433 mkOpenTvSubst :: TvSubstEnv -> TvSubst
1434 mkOpenTvSubst env = TvSubst (mkInScopeSet (tyVarsOfTypes (varEnvElts env))) env
1436 -- | Generates the in-scope set for the 'TvSubst' from the types in the incoming
1437 -- environment, hence "open"
1438 zipOpenTvSubst :: [TyVar] -> [Type] -> TvSubst
1439 zipOpenTvSubst tyvars tys
1440 | debugIsOn && (length tyvars /= length tys)
1441 = pprTrace "zipOpenTvSubst" (ppr tyvars $$ ppr tys) emptyTvSubst
1443 = TvSubst (mkInScopeSet (tyVarsOfTypes tys)) (zipTyEnv tyvars tys)
1445 -- | Called when doing top-level substitutions. Here we expect that the
1446 -- free vars of the range of the substitution will be empty.
1447 mkTopTvSubst :: [(TyVar, Type)] -> TvSubst
1448 mkTopTvSubst prs = TvSubst emptyInScopeSet (mkVarEnv prs)
1450 zipTopTvSubst :: [TyVar] -> [Type] -> TvSubst
1451 zipTopTvSubst tyvars tys
1452 | debugIsOn && (length tyvars /= length tys)
1453 = pprTrace "zipTopTvSubst" (ppr tyvars $$ ppr tys) emptyTvSubst
1455 = TvSubst emptyInScopeSet (zipTyEnv tyvars tys)
1457 zipTyEnv :: [TyVar] -> [Type] -> TvSubstEnv
1459 | debugIsOn && (length tyvars /= length tys)
1460 = pprTrace "mkTopTvSubst" (ppr tyvars $$ ppr tys) emptyVarEnv
1462 = zip_ty_env tyvars tys emptyVarEnv
1464 -- Later substitutions in the list over-ride earlier ones,
1465 -- but there should be no loops
1466 zip_ty_env :: [TyVar] -> [Type] -> TvSubstEnv -> TvSubstEnv
1467 zip_ty_env [] [] env = env
1468 zip_ty_env (tv:tvs) (ty:tys) env = zip_ty_env tvs tys (extendVarEnv env tv ty)
1469 -- There used to be a special case for when
1471 -- (a not-uncommon case) in which case the substitution was dropped.
1472 -- But the type-tidier changes the print-name of a type variable without
1473 -- changing the unique, and that led to a bug. Why? Pre-tidying, we had
1474 -- a type {Foo t}, where Foo is a one-method class. So Foo is really a newtype.
1475 -- And it happened that t was the type variable of the class. Post-tiding,
1476 -- it got turned into {Foo t2}. The ext-core printer expanded this using
1477 -- sourceTypeRep, but that said "Oh, t == t2" because they have the same unique,
1478 -- and so generated a rep type mentioning t not t2.
1480 -- Simplest fix is to nuke the "optimisation"
1481 zip_ty_env tvs tys env = pprTrace "Var/Type length mismatch: " (ppr tvs $$ ppr tys) env
1482 -- zip_ty_env _ _ env = env
1484 instance Outputable TvSubst where
1485 ppr (TvSubst ins env)
1486 = brackets $ sep[ ptext (sLit "TvSubst"),
1487 nest 2 (ptext (sLit "In scope:") <+> ppr ins),
1488 nest 2 (ptext (sLit "Env:") <+> ppr env) ]
1491 %************************************************************************
1493 Performing type substitutions
1495 %************************************************************************
1498 -- | Type substitution making use of an 'TvSubst' that
1499 -- is assumed to be open, see 'zipOpenTvSubst'
1500 substTyWith :: [TyVar] -> [Type] -> Type -> Type
1501 substTyWith tvs tys = ASSERT( length tvs == length tys )
1502 substTy (zipOpenTvSubst tvs tys)
1504 -- | Type substitution making use of an 'TvSubst' that
1505 -- is assumed to be open, see 'zipOpenTvSubst'
1506 substTysWith :: [TyVar] -> [Type] -> [Type] -> [Type]
1507 substTysWith tvs tys = ASSERT( length tvs == length tys )
1508 substTys (zipOpenTvSubst tvs tys)
1510 -- | Substitute within a 'Type'
1511 substTy :: TvSubst -> Type -> Type
1512 substTy subst ty | isEmptyTvSubst subst = ty
1513 | otherwise = subst_ty subst ty
1515 -- | Substitute within several 'Type's
1516 substTys :: TvSubst -> [Type] -> [Type]
1517 substTys subst tys | isEmptyTvSubst subst = tys
1518 | otherwise = map (subst_ty subst) tys
1520 -- | Substitute within a 'ThetaType'
1521 substTheta :: TvSubst -> ThetaType -> ThetaType
1522 substTheta subst theta
1523 | isEmptyTvSubst subst = theta
1524 | otherwise = map (substPred subst) theta
1526 -- | Substitute within a 'PredType'
1527 substPred :: TvSubst -> PredType -> PredType
1528 substPred subst (IParam n ty) = IParam n (subst_ty subst ty)
1529 substPred subst (ClassP clas tys) = ClassP clas (map (subst_ty subst) tys)
1530 substPred subst (EqPred ty1 ty2) = EqPred (subst_ty subst ty1) (subst_ty subst ty2)
1532 -- | Remove any nested binders mentioning the 'TyVar's in the 'TyVarSet'
1533 deShadowTy :: TyVarSet -> Type -> Type
1535 = subst_ty (mkTvSubst in_scope emptyTvSubstEnv) ty
1537 in_scope = mkInScopeSet tvs
1539 subst_ty :: TvSubst -> Type -> Type
1540 -- subst_ty is the main workhorse for type substitution
1542 -- Note that the in_scope set is poked only if we hit a forall
1543 -- so it may often never be fully computed
1547 go (TyVarTy tv) = substTyVar subst tv
1548 go (TyConApp tc tys) = let args = map go tys
1549 in args `seqList` TyConApp tc args
1551 go (PredTy p) = PredTy $! (substPred subst p)
1553 go (FunTy arg res) = (FunTy $! (go arg)) $! (go res)
1554 go (AppTy fun arg) = mkAppTy (go fun) $! (go arg)
1555 -- The mkAppTy smart constructor is important
1556 -- we might be replacing (a Int), represented with App
1557 -- by [Int], represented with TyConApp
1558 go (ForAllTy tv ty) = case substTyVarBndr subst tv of
1560 ForAllTy tv' $! (subst_ty subst' ty)
1562 substTyVar :: TvSubst -> TyVar -> Type
1563 substTyVar subst@(TvSubst _ _) tv
1564 = case lookupTyVar subst tv of {
1565 Nothing -> TyVarTy tv;
1566 Just ty -> ty -- See Note [Apply Once]
1569 substTyVars :: TvSubst -> [TyVar] -> [Type]
1570 substTyVars subst tvs = map (substTyVar subst) tvs
1572 lookupTyVar :: TvSubst -> TyVar -> Maybe Type
1573 -- See Note [Extending the TvSubst]
1574 lookupTyVar (TvSubst _ env) tv = lookupVarEnv env tv
1576 substTyVarBndr :: TvSubst -> TyVar -> (TvSubst, TyVar)
1577 substTyVarBndr subst@(TvSubst in_scope env) old_var
1578 = (TvSubst (in_scope `extendInScopeSet` new_var) new_env, new_var)
1580 is_co_var = isCoVar old_var
1582 new_env | no_change = delVarEnv env old_var
1583 | otherwise = extendVarEnv env old_var (TyVarTy new_var)
1585 no_change = new_var == old_var && not is_co_var
1586 -- no_change means that the new_var is identical in
1587 -- all respects to the old_var (same unique, same kind)
1588 -- See Note [Extending the TvSubst]
1590 -- In that case we don't need to extend the substitution
1591 -- to map old to new. But instead we must zap any
1592 -- current substitution for the variable. For example:
1593 -- (\x.e) with id_subst = [x |-> e']
1594 -- Here we must simply zap the substitution for x
1596 new_var = uniqAway in_scope subst_old_var
1597 -- The uniqAway part makes sure the new variable is not already in scope
1599 subst_old_var -- subst_old_var is old_var with the substitution applied to its kind
1600 -- It's only worth doing the substitution for coercions,
1601 -- becuase only they can have free type variables
1602 | is_co_var = setTyVarKind old_var (substTy subst (tyVarKind old_var))
1603 | otherwise = old_var
1606 ----------------------------------------------------
1615 -- There's a little subtyping at the kind level:
1625 -- Where: \* [LiftedTypeKind] means boxed type
1626 -- \# [UnliftedTypeKind] means unboxed type
1627 -- (\#) [UbxTupleKind] means unboxed tuple
1628 -- ?? [ArgTypeKind] is the lub of {\*, \#}
1629 -- ? [OpenTypeKind] means any type at all
1634 -- > error :: forall a:?. String -> a
1635 -- > (->) :: ?? -> ? -> \*
1636 -- > (\\(x::t) -> ...)
1638 -- Where in the last example @t :: ??@ (i.e. is not an unboxed tuple)
1640 type KindVar = TyVar -- invariant: KindVar will always be a
1641 -- TcTyVar with details MetaTv TauTv ...
1642 -- kind var constructors and functions are in TcType
1644 type SimpleKind = Kind
1649 During kind inference, a kind variable unifies only with
1651 sk ::= * | sk1 -> sk2
1653 data T a = MkT a (T Int#)
1654 fails. We give T the kind (k -> *), and the kind variable k won't unify
1655 with # (the kind of Int#).
1659 When creating a fresh internal type variable, we give it a kind to express
1660 constraints on it. E.g. in (\x->e) we make up a fresh type variable for x,
1663 During unification we only bind an internal type variable to a type
1664 whose kind is lower in the sub-kind hierarchy than the kind of the tyvar.
1666 When unifying two internal type variables, we collect their kind constraints by
1667 finding the GLB of the two. Since the partial order is a tree, they only
1668 have a glb if one is a sub-kind of the other. In that case, we bind the
1669 less-informative one to the more informative one. Neat, eh?