X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2Ftypes%2FType.lhs;h=d3b87ffdcc38b6f33d5e46dc2045f03c4ffc38c0;hb=b783b8644d142d12c832e261ba60bc81c19c3a12;hp=ec4160499853f5a13d86560fcdbb65d2c45ec1de;hpb=957bf3756ffd56f5329a2aabe1022d6f996dd641;p=ghc-hetmet.git diff --git a/ghc/compiler/types/Type.lhs b/ghc/compiler/types/Type.lhs index ec41604..d3b87ff 100644 --- a/ghc/compiler/types/Type.lhs +++ b/ghc/compiler/types/Type.lhs @@ -5,29 +5,22 @@ \begin{code} module Type ( - -- re-exports from TypeRep: - Type, PredType, ThetaType, - Kind, TyVarSubst, - - TyThing(..), isTyClThing, - - superKind, superBoxity, -- KX and BX respectively - liftedBoxity, unliftedBoxity, -- :: BX - openKindCon, -- :: KX - typeCon, -- :: BX -> KX - liftedTypeKind, unliftedTypeKind, openTypeKind, -- :: KX - mkArrowKind, mkArrowKinds, -- :: KX -> KX -> KX - isTypeKind, isAnyTypeKind, + -- re-exports from TypeRep + TyThing(..), Type, PredType(..), ThetaType, funTyCon, - -- exports from this module: - hasMoreBoxityInfo, defaultKind, + -- Re-exports from Kind + module Kind, + + -- Re-exports from TyCon + PrimRep(..), mkTyVarTy, mkTyVarTys, getTyVar, getTyVar_maybe, isTyVarTy, mkAppTy, mkAppTys, splitAppTy, splitAppTys, splitAppTy_maybe, - mkFunTy, mkFunTys, splitFunTy, splitFunTy_maybe, splitFunTys, + mkFunTy, mkFunTys, splitFunTy, splitFunTy_maybe, + splitFunTys, splitFunTysN, funResultTy, funArgTy, zipFunTys, isFunTy, mkGenTyConApp, mkTyConApp, mkTyConTy, @@ -36,19 +29,20 @@ module Type ( mkSynTy, - repType, typePrimRep, + repType, typePrimRep, coreView, deepCoreView, mkForAllTy, mkForAllTys, splitForAllTy_maybe, splitForAllTys, applyTy, applyTys, isForAllTy, dropForAlls, -- Source types - SourceType(..), sourceTypeRep, mkPredTy, mkPredTys, + predTypeRep, mkPredTy, mkPredTys, -- Newtypes - splitNewType_maybe, + splitRecNewType_maybe, -- Lifting and boxity - isUnLiftedType, isUnboxedTupleType, isAlgType, isStrictType, isPrimitiveType, + isUnLiftedType, isUnboxedTupleType, isAlgType, isPrimitiveType, + isStrictType, isStrictPred, -- Free variables tyVarsOfType, tyVarsOfTypes, tyVarsOfPred, tyVarsOfTheta, @@ -62,11 +56,26 @@ module Type ( tidyTopType, tidyPred, -- Comparison - eqType, eqKind, + coreEqType, tcEqType, tcEqTypes, tcCmpType, tcCmpTypes, + tcEqPred, tcCmpPred, tcEqTypeX, -- Seq - seqType, seqTypes - + seqType, seqTypes, + + -- Type substitutions + TvSubst(..), -- Representation visible to a few friends + TvSubstEnv, emptyTvSubst, + mkTvSubst, zipTvSubst, zipTopTvSubst, mkTopTvSubst, + getTvSubstEnv, setTvSubstEnv, getTvInScope, extendTvInScope, + extendTvSubst, extendTvSubstList, isInScope, + + -- Performing substitution on types + substTy, substTys, substTyWith, substTheta, substTyVar, + deShadowTy, + + -- Pretty-printing + pprType, pprParendType, pprTyThingCategory, + pprPred, pprTheta, pprThetaArrow, pprClassPred ) where #include "HsVersions.h" @@ -76,13 +85,9 @@ module Type ( import TypeRep --- Other imports: - -import {-# SOURCE #-} PprType( pprType ) -- Only called in debug messages -import {-# SOURCE #-} Subst ( substTyWith ) - -- friends: -import Var ( Id, TyVar, tyVarKind, tyVarName, setTyVarName ) +import Kind +import Var ( Var, TyVar, tyVarKind, tyVarName, setTyVarName ) import VarEnv import VarSet @@ -90,18 +95,16 @@ import Name ( NamedThing(..), mkInternalName, tidyOccName ) import Class ( Class, classTyCon ) import TyCon ( TyCon, isRecursiveTyCon, isPrimTyCon, isUnboxedTupleTyCon, isUnLiftedTyCon, - isFunTyCon, isNewTyCon, newTyConRep, - isAlgTyCon, isSynTyCon, tyConArity, - tyConKind, getSynTyConDefn, - tyConPrimRep, + isFunTyCon, isNewTyCon, newTyConRep, newTyConRhs, + isAlgTyCon, isSynTyCon, tyConArity, newTyConRhs_maybe, + tyConKind, getSynTyConDefn, PrimRep(..), tyConPrimRep, ) -- others import CmdLineOpts ( opt_DictsStrict ) import SrcLoc ( noSrcLoc ) -import PrimRep ( PrimRep(..) ) import Unique ( Uniquable(..) ) -import Util ( mapAccumL, seqList, lengthIs, snocView ) +import Util ( mapAccumL, seqList, lengthIs, snocView, thenCmp, isEqual ) import Outputable import UniqSet ( sizeUniqSet ) -- Should come via VarSet import Maybe ( isJust ) @@ -110,57 +113,55 @@ import Maybe ( isJust ) %************************************************************************ %* * - TyThing + Type representation %* * %************************************************************************ -\begin{code} -data TyThing = AnId Id - | ATyCon TyCon - | AClass Class - -isTyClThing :: TyThing -> Bool -isTyClThing (ATyCon _) = True -isTyClThing (AClass _) = True -isTyClThing (AnId _) = False - -instance NamedThing TyThing where - getName (AnId id) = getName id - getName (ATyCon tc) = getName tc - getName (AClass cl) = getName cl -\end{code} - - -%************************************************************************ -%* * -\subsection{Stuff to do with kinds.} -%* * -%************************************************************************ +In Core, we "look through" non-recursive newtypes and PredTypes. \begin{code} -hasMoreBoxityInfo :: Kind -> Kind -> Bool --- (k1 `hasMoreBoxityInfo` k2) checks that k1 <: k2 -hasMoreBoxityInfo k1 k2 - | k2 `eqKind` openTypeKind = isAnyTypeKind k1 - | otherwise = k1 `eqKind` k2 - where - -isAnyTypeKind :: Kind -> Bool --- True of kind * and *# and ? -isAnyTypeKind (TyConApp tc _) = tc == typeCon || tc == openKindCon -isAnyTypeKind (NoteTy _ k) = isAnyTypeKind k -isAnyTypeKind other = False - -isTypeKind :: Kind -> Bool --- True of kind * and *# -isTypeKind (TyConApp tc _) = tc == typeCon -isTypeKind (NoteTy _ k) = isTypeKind k -isTypeKind other = False - -defaultKind :: Kind -> Kind --- Used when generalising: default kind '?' to '*' -defaultKind kind | kind `eqKind` openTypeKind = liftedTypeKind - | otherwise = kind +{-# INLINE coreView #-} +coreView :: Type -> Maybe Type +-- Srips off the *top layer only* of a type to give +-- its underlying representation type. +-- Returns Nothing if there is nothing to look through. +-- +-- By being non-recursive and inlined, this case analysis gets efficiently +-- joined onto the case analysis that the caller is already doing +coreView (NoteTy _ ty) = Just ty +coreView (PredTy p) = Just (predTypeRep p) +coreView (TyConApp tc tys) = expandNewTcApp tc tys +coreView ty = Nothing + +deepCoreView :: Type -> Type +-- Apply coreView recursively +deepCoreView ty + | Just ty' <- coreView ty = deepCoreView ty' +deepCoreView (TyVarTy tv) = TyVarTy tv +deepCoreView (TyConApp tc tys) = TyConApp tc (map deepCoreView tys) +deepCoreView (AppTy t1 t2) = AppTy (deepCoreView t1) (deepCoreView t2) +deepCoreView (FunTy t1 t2) = FunTy (deepCoreView t1) (deepCoreView t2) +deepCoreView (ForAllTy tv ty) = ForAllTy tv (deepCoreView ty) + -- No NoteTy, no PredTy + +expandNewTcApp :: TyCon -> [Type] -> Maybe Type +-- A local helper function (not exported) +-- Expands *the outermoset level of* a newtype application to +-- *either* a vanilla TyConApp (recursive newtype, or non-saturated) +-- *or* the newtype representation (otherwise), meaning the +-- type written in the RHS of the newtype decl, +-- which may itself be a newtype +-- +-- Example: newtype R = MkR S +-- newtype S = MkS T +-- newtype T = MkT (T -> T) +-- expandNewTcApp on R gives Just S +-- on S gives Just T +-- on T gives Nothing (no expansion) + +expandNewTcApp tc tys = case newTyConRhs_maybe tc tys of + Nothing -> Nothing + Just (tenv, rhs) -> Just (substTy (mkTopTvSubst tenv) rhs) \end{code} @@ -182,22 +183,17 @@ mkTyVarTys :: [TyVar] -> [Type] mkTyVarTys = map mkTyVarTy -- a common use of mkTyVarTy getTyVar :: String -> Type -> TyVar -getTyVar msg (TyVarTy tv) = tv -getTyVar msg (SourceTy p) = getTyVar msg (sourceTypeRep p) -getTyVar msg (NoteTy _ t) = getTyVar msg t -getTyVar msg other = panic ("getTyVar: " ++ msg) - -getTyVar_maybe :: Type -> Maybe TyVar -getTyVar_maybe (TyVarTy tv) = Just tv -getTyVar_maybe (NoteTy _ t) = getTyVar_maybe t -getTyVar_maybe (SourceTy p) = getTyVar_maybe (sourceTypeRep p) -getTyVar_maybe other = Nothing +getTyVar msg ty = case getTyVar_maybe ty of + Just tv -> tv + Nothing -> panic ("getTyVar: " ++ msg) isTyVarTy :: Type -> Bool -isTyVarTy (TyVarTy tv) = True -isTyVarTy (NoteTy _ ty) = isTyVarTy ty -isTyVarTy (SourceTy p) = isTyVarTy (sourceTypeRep p) -isTyVarTy other = False +isTyVarTy ty = isJust (getTyVar_maybe ty) + +getTyVar_maybe :: Type -> Maybe TyVar +getTyVar_maybe ty | Just ty' <- coreView ty = getTyVar_maybe ty' +getTyVar_maybe (TyVarTy tv) = Just tv +getTyVar_maybe other = Nothing \end{code} @@ -210,8 +206,7 @@ invariant: use it. \begin{code} mkAppTy orig_ty1 orig_ty2 - = ASSERT( not (isSourceTy orig_ty1) ) -- Source types are of kind * - mk_app orig_ty1 + = mk_app orig_ty1 where mk_app (NoteTy _ ty1) = mk_app ty1 mk_app (TyConApp tc tys) = mkGenTyConApp tc (tys ++ [orig_ty2]) @@ -233,20 +228,19 @@ mkAppTys orig_ty1 [] = orig_ty1 -- returns to (Ratio Integer), which has needlessly lost -- the Rational part. mkAppTys orig_ty1 orig_tys2 - = ASSERT( not (isSourceTy orig_ty1) ) -- Source types are of kind * - mk_app orig_ty1 + = mk_app orig_ty1 where mk_app (NoteTy _ ty1) = mk_app ty1 - mk_app (TyConApp tc tys) = mkTyConApp tc (tys ++ orig_tys2) + mk_app (TyConApp tc tys) = mkGenTyConApp tc (tys ++ orig_tys2) + -- mkGenTyConApp: see notes with mkAppTy mk_app ty1 = foldl AppTy orig_ty1 orig_tys2 splitAppTy_maybe :: Type -> Maybe (Type, Type) +splitAppTy_maybe ty | Just ty' <- coreView ty = splitAppTy_maybe ty' splitAppTy_maybe (FunTy ty1 ty2) = Just (TyConApp funTyCon [ty1], ty2) splitAppTy_maybe (AppTy ty1 ty2) = Just (ty1, ty2) -splitAppTy_maybe (NoteTy _ ty) = splitAppTy_maybe ty -splitAppTy_maybe (SourceTy p) = splitAppTy_maybe (sourceTypeRep p) splitAppTy_maybe (TyConApp tc tys) = case snocView tys of - Nothing -> Nothing + Nothing -> Nothing Just (tys',ty') -> Just (TyConApp tc tys', ty') splitAppTy_maybe other = Nothing @@ -258,12 +252,11 @@ splitAppTy ty = case splitAppTy_maybe ty of splitAppTys :: Type -> (Type, [Type]) splitAppTys ty = split ty ty [] where + split orig_ty ty args | Just ty' <- coreView ty = split orig_ty ty' args split orig_ty (AppTy ty arg) args = split ty ty (arg:args) - split orig_ty (NoteTy _ ty) args = split orig_ty ty args - split orig_ty (SourceTy p) args = split orig_ty (sourceTypeRep p) args + split orig_ty (TyConApp tc tc_args) args = (TyConApp tc [], tc_args ++ args) split orig_ty (FunTy ty1 ty2) args = ASSERT( null args ) (TyConApp funTyCon [], [ty1,ty2]) - split orig_ty (TyConApp tc tc_args) args = (TyConApp tc [], tc_args ++ args) split orig_ty ty args = (orig_ty, args) \end{code} @@ -283,51 +276,54 @@ isFunTy :: Type -> Bool isFunTy ty = isJust (splitFunTy_maybe ty) splitFunTy :: Type -> (Type, Type) -splitFunTy (FunTy arg res) = (arg, res) -splitFunTy (NoteTy _ ty) = splitFunTy ty -splitFunTy (SourceTy p) = splitFunTy (sourceTypeRep p) +splitFunTy ty | Just ty' <- coreView ty = splitFunTy ty' +splitFunTy (FunTy arg res) = (arg, res) +splitFunTy other = pprPanic "splitFunTy" (ppr other) splitFunTy_maybe :: Type -> Maybe (Type, Type) -splitFunTy_maybe (FunTy arg res) = Just (arg, res) -splitFunTy_maybe (NoteTy _ ty) = splitFunTy_maybe ty -splitFunTy_maybe (SourceTy p) = splitFunTy_maybe (sourceTypeRep p) -splitFunTy_maybe other = Nothing +splitFunTy_maybe ty | Just ty' <- coreView ty = splitFunTy_maybe ty' +splitFunTy_maybe (FunTy arg res) = Just (arg, res) +splitFunTy_maybe other = Nothing splitFunTys :: Type -> ([Type], Type) splitFunTys ty = split [] ty ty where - split args orig_ty (FunTy arg res) = split (arg:args) res res - split args orig_ty (NoteTy _ ty) = split args orig_ty ty - split args orig_ty (SourceTy p) = split args orig_ty (sourceTypeRep p) - split args orig_ty ty = (reverse args, orig_ty) + split args orig_ty ty | Just ty' <- coreView ty = split args orig_ty ty' + split args orig_ty (FunTy arg res) = split (arg:args) res res + split args orig_ty ty = (reverse args, orig_ty) + +splitFunTysN :: Int -> Type -> ([Type], Type) +-- Split off exactly n arg tys +splitFunTysN 0 ty = ([], ty) +splitFunTysN n ty = case splitFunTy ty of { (arg, res) -> + case splitFunTysN (n-1) res of { (args, res) -> + (arg:args, res) }} zipFunTys :: Outputable a => [a] -> Type -> ([(a,Type)], Type) zipFunTys orig_xs orig_ty = split [] orig_xs orig_ty orig_ty where - split acc [] nty ty = (reverse acc, nty) - split acc (x:xs) nty (FunTy arg res) = split ((x,arg):acc) xs res res - split acc xs nty (NoteTy _ ty) = split acc xs nty ty - split acc xs nty (SourceTy p) = split acc xs nty (sourceTypeRep p) - split acc (x:xs) nty ty = pprPanic "zipFunTys" (ppr orig_xs <+> pprType orig_ty) + split acc [] nty ty = (reverse acc, nty) + split acc xs nty ty + | Just ty' <- coreView ty = split acc xs nty ty' + split acc (x:xs) nty (FunTy arg res) = split ((x,arg):acc) xs res res + split acc (x:xs) nty ty = pprPanic "zipFunTys" (ppr orig_xs <+> ppr orig_ty) funResultTy :: Type -> Type -funResultTy (FunTy arg res) = res -funResultTy (NoteTy _ ty) = funResultTy ty -funResultTy (SourceTy p) = funResultTy (sourceTypeRep p) -funResultTy ty = pprPanic "funResultTy" (pprType ty) +funResultTy ty | Just ty' <- coreView ty = funResultTy ty' +funResultTy (FunTy arg res) = res +funResultTy ty = pprPanic "funResultTy" (ppr ty) funArgTy :: Type -> Type -funArgTy (FunTy arg res) = arg -funArgTy (NoteTy _ ty) = funArgTy ty -funArgTy (SourceTy p) = funArgTy (sourceTypeRep p) -funArgTy ty = pprPanic "funArgTy" (pprType ty) +funArgTy ty | Just ty' <- coreView ty = funArgTy ty' +funArgTy (FunTy arg res) = arg +funArgTy ty = pprPanic "funArgTy" (ppr ty) \end{code} --------------------------------------------------------------------- TyConApp ~~~~~~~~ -@mkTyConApp@ is a key function, because it builds a TyConApp, FunTy or SourceTy, +@mkTyConApp@ is a key function, because it builds a TyConApp, FunTy or PredTy, as apppropriate. \begin{code} @@ -342,18 +338,12 @@ mkTyConApp tycon tys | isFunTyCon tycon, [ty1,ty2] <- tys = FunTy ty1 ty2 - | isNewTyCon tycon, -- A saturated newtype application; - not (isRecursiveTyCon tycon), -- Not recursive (we don't use SourceTypes for them) - tys `lengthIs` tyConArity tycon -- use the SourceType form - = SourceTy (NType tycon tys) - | otherwise = ASSERT(not (isSynTyCon tycon)) TyConApp tycon tys mkTyConTy :: TyCon -> Type -mkTyConTy tycon = ASSERT( not (isSynTyCon tycon) ) - TyConApp tycon [] +mkTyConTy tycon = mkTyConApp tycon [] -- splitTyConApp "looks through" synonyms, because they don't -- mean a distinct type, but all other type-constructor applications @@ -368,13 +358,12 @@ tyConAppArgs ty = snd (splitTyConApp ty) splitTyConApp :: Type -> (TyCon, [Type]) splitTyConApp ty = case splitTyConApp_maybe ty of Just stuff -> stuff - Nothing -> pprPanic "splitTyConApp" (pprType ty) + Nothing -> pprPanic "splitTyConApp" (ppr ty) splitTyConApp_maybe :: Type -> Maybe (TyCon, [Type]) +splitTyConApp_maybe ty | Just ty' <- coreView ty = splitTyConApp_maybe ty' splitTyConApp_maybe (TyConApp tc tys) = Just (tc, tys) splitTyConApp_maybe (FunTy arg res) = Just (funTyCon, [arg,res]) -splitTyConApp_maybe (NoteTy _ ty) = splitTyConApp_maybe ty -splitTyConApp_maybe (SourceTy p) = splitTyConApp_maybe (sourceTypeRep p) splitTyConApp_maybe other = Nothing \end{code} @@ -431,33 +420,43 @@ repType looks through (b) synonyms (c) predicates (d) usage annotations - (e) [recursive] newtypes + (e) all newtypes, including recursive ones It's useful in the back end. -Remember, non-recursive newtypes get expanded as part of the SourceTy case, -but recursive ones are represented by TyConApps and have to be expanded -by steam. - \begin{code} repType :: Type -> Type +-- Only applied to types of kind *; hence tycons are saturated repType (ForAllTy _ ty) = repType ty repType (NoteTy _ ty) = repType ty -repType (SourceTy p) = repType (sourceTypeRep p) -repType (TyConApp tc tys) | isNewTyCon tc && tys `lengthIs` tyConArity tc - = repType (newTypeRep tc tys) +repType (PredTy p) = repType (predTypeRep p) +repType (TyConApp tc tys) + | isNewTyCon tc = ASSERT( tys `lengthIs` tyConArity tc ) + repType (new_type_rep tc tys) repType ty = ty - +-- ToDo: this could be moved to the code generator, using splitTyConApp instead +-- of inspecting the type directly. typePrimRep :: Type -> PrimRep typePrimRep ty = case repType ty of TyConApp tc _ -> tyConPrimRep tc FunTy _ _ -> PtrRep - AppTy _ _ -> PtrRep -- ?? + AppTy _ _ -> PtrRep -- See note below TyVarTy _ -> PtrRep + other -> pprPanic "typePrimRep" (ppr ty) + -- Types of the form 'f a' must be of kind *, not *#, so + -- we are guaranteed that they are represented by pointers. + -- The reason is that f must have kind *->*, not *->*#, because + -- (we claim) there is no way to constrain f's kind any other + -- way. + +-- new_type_rep doesn't ask any questions: +-- it just expands newtype, whether recursive or not +new_type_rep new_tycon tys = ASSERT( tys `lengthIs` tyConArity new_tycon ) + case newTyConRep new_tycon of + (tvs, rep_ty) -> substTyWith tvs tys rep_ty \end{code} - --------------------------------------------------------------------- ForAllTy ~~~~~~~~ @@ -478,18 +477,16 @@ isForAllTy other_ty = False splitForAllTy_maybe :: Type -> Maybe (TyVar, Type) splitForAllTy_maybe ty = splitFAT_m ty where - splitFAT_m (NoteTy _ ty) = splitFAT_m ty - splitFAT_m (SourceTy p) = splitFAT_m (sourceTypeRep p) - splitFAT_m (ForAllTy tyvar ty) = Just(tyvar, ty) - splitFAT_m _ = Nothing + splitFAT_m ty | Just ty' <- coreView ty = splitFAT_m ty' + splitFAT_m (ForAllTy tyvar ty) = Just(tyvar, ty) + splitFAT_m _ = Nothing splitForAllTys :: Type -> ([TyVar], Type) splitForAllTys ty = split ty ty [] where - split orig_ty (ForAllTy tv ty) tvs = split ty ty (tv:tvs) - split orig_ty (NoteTy _ ty) tvs = split orig_ty ty tvs - split orig_ty (SourceTy p) tvs = split orig_ty (sourceTypeRep p) tvs - split orig_ty t tvs = (reverse tvs, orig_ty) + split orig_ty ty tvs | Just ty' <- coreView ty = split orig_ty ty' tvs + split orig_ty (ForAllTy tv ty) tvs = split ty ty (tv:tvs) + split orig_ty t tvs = (reverse tvs, orig_ty) dropForAlls :: Type -> Type dropForAlls ty = snd (splitForAllTys ty) @@ -497,28 +494,47 @@ dropForAlls ty = snd (splitForAllTys ty) -- (mkPiType now in CoreUtils) -Applying a for-all to its arguments. Lift usage annotation as required. +applyTy, applyTys +~~~~~~~~~~~~~~~~~ +Instantiate a for-all type with one or more type arguments. +Used when we have a polymorphic function applied to type args: + f t1 t2 +Then we use (applyTys type-of-f [t1,t2]) to compute the type of +the expression. \begin{code} applyTy :: Type -> Type -> Type -applyTy (SourceTy p) arg = applyTy (sourceTypeRep p) arg -applyTy (NoteTy _ fun) arg = applyTy fun arg +applyTy ty arg | Just ty' <- coreView ty = applyTy ty' arg applyTy (ForAllTy tv ty) arg = substTyWith [tv] [arg] ty applyTy other arg = panic "applyTy" applyTys :: Type -> [Type] -> Type -applyTys orig_fun_ty arg_tys - = substTyWith tvs arg_tys ty - where - (tvs, ty) = split orig_fun_ty arg_tys - - split fun_ty [] = ([], fun_ty) - split (NoteTy _ fun_ty) args = split fun_ty args - split (SourceTy p) args = split (sourceTypeRep p) args - split (ForAllTy tv fun_ty) (arg:args) = case split fun_ty args of - (tvs, ty) -> (tv:tvs, ty) - split other_ty args = panic "applyTys" - -- No show instance for Type yet +-- This function is interesting because +-- a) the function may have more for-alls than there are args +-- b) less obviously, it may have fewer for-alls +-- For case (b) think of +-- applyTys (forall a.a) [forall b.b, Int] +-- This really can happen, via dressing up polymorphic types with newtype +-- clothing. Here's an example: +-- newtype R = R (forall a. a->a) +-- foo = case undefined :: R of +-- R f -> f () + +applyTys orig_fun_ty [] = orig_fun_ty +applyTys orig_fun_ty arg_tys + | n_tvs == n_args -- The vastly common case + = substTyWith tvs arg_tys rho_ty + | n_tvs > n_args -- Too many for-alls + = substTyWith (take n_args tvs) arg_tys + (mkForAllTys (drop n_args tvs) rho_ty) + | otherwise -- Too many type args + = ASSERT2( n_tvs > 0, ppr orig_fun_ty ) -- Zero case gives infnite loop! + applyTys (substTyWith tvs (take n_tvs arg_tys) rho_ty) + (drop n_tvs arg_tys) + where + (tvs, rho_ty) = splitForAllTys orig_fun_ty + n_tvs = length tvs + n_args = length arg_tys \end{code} @@ -533,46 +549,48 @@ concerned, but which has low-level representation as far as the back end is conc Source types are always lifted. -The key function is sourceTypeRep which gives the representation of a source type: +The key function is predTypeRep which gives the representation of a source type: \begin{code} mkPredTy :: PredType -> Type -mkPredTy pred = SourceTy pred +mkPredTy pred = PredTy pred mkPredTys :: ThetaType -> [Type] -mkPredTys preds = map SourceTy preds - -sourceTypeRep :: SourceType -> Type --- Convert a predicate to its "representation type"; --- the type of evidence for that predicate, which is actually passed at runtime -sourceTypeRep (IParam _ ty) = ty -sourceTypeRep (ClassP clas tys) = mkTyConApp (classTyCon clas) tys - -- Note the mkTyConApp; the classTyCon might be a newtype! -sourceTypeRep (NType tc tys) = newTypeRep tc tys - -- ToDo: Consider caching this substitution in a NType - -isSourceTy :: Type -> Bool -isSourceTy (NoteTy _ ty) = isSourceTy ty -isSourceTy (SourceTy sty) = True -isSourceTy _ = False - - -splitNewType_maybe :: Type -> Maybe Type --- Newtypes that are recursive are reprsented by TyConApp, just --- as they always were. Occasionally we want to find their representation type. --- NB: remember that in this module, non-recursive newtypes are transparent - -splitNewType_maybe ty - = case splitTyConApp_maybe ty of - Just (tc,tys) | isNewTyCon tc -> ASSERT( tys `lengthIs` tyConArity tc ) - -- The assert should hold because repType should - -- only be applied to *types* (of kind *) - Just (newTypeRep tc tys) - other -> Nothing - --- A local helper function (not exported) -newTypeRep new_tycon tys = case newTyConRep new_tycon of - (tvs, rep_ty) -> substTyWith tvs tys rep_ty +mkPredTys preds = map PredTy preds + +predTypeRep :: PredType -> Type +-- Convert a PredType to its "representation type"; +-- the post-type-checking type used by all the Core passes of GHC. +-- Unwraps only the outermost level; for example, the result might +-- be a newtype application +predTypeRep (IParam _ ty) = ty +predTypeRep (ClassP clas tys) = mkTyConApp (classTyCon clas) tys + -- Result might be a newtype application, but the consumer will + -- look through that too if necessary +\end{code} + + +%************************************************************************ +%* * + NewTypes +%* * +%************************************************************************ + +\begin{code} +splitRecNewType_maybe :: Type -> Maybe Type +-- Sometimes we want to look through a recursive newtype, and that's what happens here +-- It only strips *one layer* off, so the caller will usually call itself recursively +-- Only applied to types of kind *, hence the newtype is always saturated +splitRecNewType_maybe ty | Just ty' <- coreView ty = splitRecNewType_maybe ty' +splitRecNewType_maybe (TyConApp tc tys) + | isNewTyCon tc + = ASSERT( tys `lengthIs` tyConArity tc ) -- splitRecNewType_maybe only be applied + -- to *types* (of kind *) + ASSERT( isRecursiveTyCon tc ) -- Guaranteed by coreView + case newTyConRhs tc of + (tvs, rep_ty) -> Just (substTyWith tvs tys rep_ty) + +splitRecNewType_maybe other = Nothing \end{code} @@ -589,25 +607,12 @@ newTypeRep new_tycon tys = case newTyConRep new_tycon of typeKind :: Type -> Kind typeKind (TyVarTy tyvar) = tyVarKind tyvar -typeKind (TyConApp tycon tys) = foldr (\_ k -> funResultTy k) (tyConKind tycon) tys +typeKind (TyConApp tycon tys) = foldr (\_ k -> kindFunResult k) (tyConKind tycon) tys typeKind (NoteTy _ ty) = typeKind ty -typeKind (SourceTy _) = liftedTypeKind -- Predicates are always +typeKind (PredTy _) = liftedTypeKind -- Predicates are always -- represented by lifted types -typeKind (AppTy fun arg) = funResultTy (typeKind fun) - -typeKind (FunTy arg res) = fix_up (typeKind res) - where - fix_up (TyConApp tycon _) | tycon == typeCon - || tycon == openKindCon = liftedTypeKind - fix_up (NoteTy _ kind) = fix_up kind - fix_up kind = kind - -- The basic story is - -- typeKind (FunTy arg res) = typeKind res - -- But a function is lifted regardless of its result type - -- Hence the strange fix-up. - -- Note that 'res', being the result of a FunTy, can't have - -- a strange kind like (*->*). - +typeKind (AppTy fun arg) = kindFunResult (typeKind fun) +typeKind (FunTy arg res) = liftedTypeKind typeKind (ForAllTy tv ty) = typeKind ty \end{code} @@ -621,7 +626,7 @@ tyVarsOfType (TyVarTy tv) = unitVarSet tv tyVarsOfType (TyConApp tycon tys) = tyVarsOfTypes tys tyVarsOfType (NoteTy (FTVNote tvs) ty2) = tvs tyVarsOfType (NoteTy (SynNote ty1) ty2) = tyVarsOfType ty2 -- See note [Syn] below -tyVarsOfType (SourceTy sty) = tyVarsOfSourceType sty +tyVarsOfType (PredTy sty) = tyVarsOfPred sty tyVarsOfType (FunTy arg res) = tyVarsOfType arg `unionVarSet` tyVarsOfType res tyVarsOfType (AppTy fun arg) = tyVarsOfType fun `unionVarSet` tyVarsOfType arg tyVarsOfType (ForAllTy tyvar ty) = tyVarsOfType ty `minusVarSet` unitVarSet tyvar @@ -645,15 +650,11 @@ tyVarsOfTypes :: [Type] -> TyVarSet tyVarsOfTypes tys = foldr (unionVarSet.tyVarsOfType) emptyVarSet tys tyVarsOfPred :: PredType -> TyVarSet -tyVarsOfPred = tyVarsOfSourceType -- Just a subtype - -tyVarsOfSourceType :: SourceType -> TyVarSet -tyVarsOfSourceType (IParam _ ty) = tyVarsOfType ty -tyVarsOfSourceType (ClassP _ tys) = tyVarsOfTypes tys -tyVarsOfSourceType (NType _ tys) = tyVarsOfTypes tys +tyVarsOfPred (IParam _ ty) = tyVarsOfType ty +tyVarsOfPred (ClassP _ tys) = tyVarsOfTypes tys tyVarsOfTheta :: ThetaType -> TyVarSet -tyVarsOfTheta = foldr (unionVarSet . tyVarsOfSourceType) emptyVarSet +tyVarsOfTheta = foldr (unionVarSet . tyVarsOfPred) emptyVarSet -- Add a Note with the free tyvars to the top of the type addFreeTyVars :: Type -> Type @@ -676,8 +677,7 @@ It doesn't change the uniques at all, just the print names. tidyTyVarBndr :: TidyEnv -> TyVar -> (TidyEnv, TyVar) tidyTyVarBndr (tidy_env, subst) tyvar = case tidyOccName tidy_env (getOccName name) of - (tidy', occ') -> -- New occname reqd - ((tidy', subst'), tyvar') + (tidy', occ') -> ((tidy', subst'), tyvar') where subst' = extendVarEnv subst tyvar tyvar' tyvar' = setTyVarName tyvar name' @@ -712,7 +712,7 @@ tidyType env@(tidy_env, subst) ty go (TyConApp tycon tys) = let args = map go tys in args `seqList` TyConApp tycon args go (NoteTy note ty) = (NoteTy $! (go_note note)) $! (go ty) - go (SourceTy sty) = SourceTy (tidySourceType env sty) + go (PredTy sty) = PredTy (tidyPred env sty) go (AppTy fun arg) = (AppTy $! (go fun)) $! (go arg) go (FunTy fun arg) = (FunTy $! (go fun)) $! (go arg) go (ForAllTy tv ty) = ForAllTy tvp $! (tidyType envp ty) @@ -724,13 +724,9 @@ tidyType env@(tidy_env, subst) ty tidyTypes env tys = map (tidyType env) tys -tidyPred :: TidyEnv -> SourceType -> SourceType -tidyPred = tidySourceType - -tidySourceType :: TidyEnv -> SourceType -> SourceType -tidySourceType env (IParam n ty) = IParam n (tidyType env ty) -tidySourceType env (ClassP clas tys) = ClassP clas (tidyTypes env tys) -tidySourceType env (NType tc tys) = NType tc (tidyTypes env tys) +tidyPred :: TidyEnv -> PredType -> PredType +tidyPred env (IParam n ty) = IParam n (tidyType env ty) +tidyPred env (ClassP clas tys) = ClassP clas (tidyTypes env tys) \end{code} @@ -767,11 +763,10 @@ isUnLiftedType :: Type -> Bool -- They are pretty bogus types, mind you. It would be better never to -- construct them -isUnLiftedType (ForAllTy tv ty) = isUnLiftedType ty -isUnLiftedType (NoteTy _ ty) = isUnLiftedType ty -isUnLiftedType (TyConApp tc _) = isUnLiftedTyCon tc -isUnLiftedType (SourceTy _) = False -- All source types are lifted -isUnLiftedType other = False +isUnLiftedType ty | Just ty' <- coreView ty = isUnLiftedType ty' +isUnLiftedType (ForAllTy tv ty) = isUnLiftedType ty +isUnLiftedType (TyConApp tc _) = isUnLiftedTyCon tc +isUnLiftedType other = False isUnboxedTupleType :: Type -> Bool isUnboxedTupleType ty = case splitTyConApp_maybe ty of @@ -794,15 +789,18 @@ this function should be in TcType, but isStrictType is used by DataCon, which is below TcType in the hierarchy, so it's convenient to put it here. \begin{code} -isStrictType (ForAllTy tv ty) = isStrictType ty -isStrictType (NoteTy _ ty) = isStrictType ty -isStrictType (TyConApp tc _) = isUnLiftedTyCon tc -isStrictType (SourceTy (ClassP clas _)) = opt_DictsStrict && not (isNewTyCon (classTyCon clas)) +isStrictType (PredTy pred) = isStrictPred pred +isStrictType ty | Just ty' <- coreView ty = isStrictType ty' +isStrictType (ForAllTy tv ty) = isStrictType ty +isStrictType (TyConApp tc _) = isUnLiftedTyCon tc +isStrictType other = False + +isStrictPred (ClassP clas _) = opt_DictsStrict && not (isNewTyCon (classTyCon clas)) +isStrictPred other = False -- We may be strict in dictionary types, but only if it -- has more than one component. -- [Being strict in a single-component dictionary risks -- poking the dictionary component, which is wrong.] -isStrictType other = False \end{code} \begin{code} @@ -829,7 +827,7 @@ seqType (TyVarTy tv) = tv `seq` () seqType (AppTy t1 t2) = seqType t1 `seq` seqType t2 seqType (FunTy t1 t2) = seqType t1 `seq` seqType t2 seqType (NoteTy note t2) = seqNote note `seq` seqType t2 -seqType (SourceTy p) = seqPred p +seqType (PredTy p) = seqPred p seqType (TyConApp tc tys) = tc `seq` seqTypes tys seqType (ForAllTy tv ty) = tv `seq` seqType ty @@ -841,58 +839,351 @@ seqNote :: TyNote -> () seqNote (SynNote ty) = seqType ty seqNote (FTVNote set) = sizeUniqSet set `seq` () -seqPred :: SourceType -> () +seqPred :: PredType -> () seqPred (ClassP c tys) = c `seq` seqTypes tys -seqPred (NType tc tys) = tc `seq` seqTypes tys seqPred (IParam n ty) = n `seq` seqType ty \end{code} %************************************************************************ %* * -\subsection{Equality on types} + Comparison of types + (We don't use instances so that we know where it happens) %* * %************************************************************************ -Comparison; don't use instances so that we know where it happens. -Look through newtypes but not usage types. +Two flavours: + +* tcEqType, tcCmpType do *not* look through newtypes, PredTypes +* coreEqType *does* look through them Note that eqType can respond 'False' for partial applications of newtypes. Consider newtype Parser m a = MkParser (Foogle m a) - Does Monad (Parser m) `eqType` Monad (Foogle m) - Well, yes, but eqType won't see that they are the same. I don't think this is harmful, but it's soemthing to watch out for. +First, the external interface + +\begin{code} +coreEqType :: Type -> Type -> Bool +coreEqType t1 t2 = isEqual $ cmpType (deepCoreView t1) (deepCoreView t2) + +tcEqType :: Type -> Type -> Bool +tcEqType t1 t2 = isEqual $ cmpType t1 t2 + +tcEqTypes :: [Type] -> [Type] -> Bool +tcEqTypes tys1 tys2 = isEqual $ cmpTypes tys1 tys2 + +tcCmpType :: Type -> Type -> Ordering +tcCmpType t1 t2 = cmpType t1 t2 + +tcCmpTypes :: [Type] -> [Type] -> Ordering +tcCmpTypes tys1 tys2 = cmpTypes tys1 tys2 + +tcEqPred :: PredType -> PredType -> Bool +tcEqPred p1 p2 = isEqual $ cmpPred p1 p2 + +tcCmpPred :: PredType -> PredType -> Ordering +tcCmpPred p1 p2 = cmpPred p1 p2 + +tcEqTypeX :: RnEnv2 -> Type -> Type -> Bool +tcEqTypeX env t1 t2 = isEqual $ cmpTypeX env t1 t2 +\end{code} + +Now here comes the real worker + +\begin{code} +cmpType :: Type -> Type -> Ordering +cmpType t1 t2 = cmpTypeX rn_env t1 t2 + where + rn_env = mkRnEnv2 (mkInScopeSet (tyVarsOfType t1 `unionVarSet` tyVarsOfType t2)) + +cmpTypes :: [Type] -> [Type] -> Ordering +cmpTypes ts1 ts2 = cmpTypesX rn_env ts1 ts2 + where + rn_env = mkRnEnv2 (mkInScopeSet (tyVarsOfTypes ts1 `unionVarSet` tyVarsOfTypes ts2)) + +cmpPred :: PredType -> PredType -> Ordering +cmpPred p1 p2 = cmpPredX rn_env p1 p2 + where + rn_env = mkRnEnv2 (mkInScopeSet (tyVarsOfPred p1 `unionVarSet` tyVarsOfPred p2)) + +cmpTypeX :: RnEnv2 -> Type -> Type -> Ordering -- Main workhorse + +-- NB: we *cannot* short-cut the newtype comparison thus: +-- eqTypeX env (NewTcApp tc1 tys1) (NewTcApp tc2 tys2) +-- | (tc1 == tc2) = (eqTypeXs env tys1 tys2) +-- +-- Consider: +-- newtype T a = MkT [a] +-- newtype Foo m = MkFoo (forall a. m a -> Int) +-- w1 :: Foo [] +-- w1 = ... +-- +-- w2 :: Foo T +-- w2 = MkFoo (\(MkT x) -> case w1 of MkFoo f -> f x) +-- +-- We end up with w2 = w1; so we need that Foo T = Foo [] +-- but we can only expand saturated newtypes, so just comparing +-- T with [] won't do. + +cmpTypeX env (TyVarTy tv1) (TyVarTy tv2) = rnOccL env tv1 `compare` rnOccR env tv2 +cmpTypeX env (ForAllTy tv1 t1) (ForAllTy tv2 t2) = cmpTypeX (rnBndr2 env tv1 tv2) t1 t2 +cmpTypeX env (AppTy s1 t1) (AppTy s2 t2) = cmpTypeX env s1 s2 `thenCmp` cmpTypeX env t1 t2 +cmpTypeX env (FunTy s1 t1) (FunTy s2 t2) = cmpTypeX env s1 s2 `thenCmp` cmpTypeX env t1 t2 +cmpTypeX env (PredTy p1) (PredTy p2) = cmpPredX env p1 p2 +cmpTypeX env (TyConApp tc1 tys1) (TyConApp tc2 tys2) = (tc1 `compare` tc2) `thenCmp` cmpTypesX env tys1 tys2 +cmpTypeX env (NoteTy _ t1) t2 = cmpTypeX env t1 t2 +cmpTypeX env t1 (NoteTy _ t2) = cmpTypeX env t1 t2 + + -- Deal with the rest: TyVarTy < AppTy < FunTy < TyConApp < ForAllTy < PredTy +cmpTypeX env (AppTy _ _) (TyVarTy _) = GT + +cmpTypeX env (FunTy _ _) (TyVarTy _) = GT +cmpTypeX env (FunTy _ _) (AppTy _ _) = GT + +cmpTypeX env (TyConApp _ _) (TyVarTy _) = GT +cmpTypeX env (TyConApp _ _) (AppTy _ _) = GT +cmpTypeX env (TyConApp _ _) (FunTy _ _) = GT + +cmpTypeX env (ForAllTy _ _) (TyVarTy _) = GT +cmpTypeX env (ForAllTy _ _) (AppTy _ _) = GT +cmpTypeX env (ForAllTy _ _) (FunTy _ _) = GT +cmpTypeX env (ForAllTy _ _) (TyConApp _ _) = GT + +cmpTypeX env (PredTy _) t2 = GT + +cmpTypeX env _ _ = LT + +------------- +cmpTypesX :: RnEnv2 -> [Type] -> [Type] -> Ordering +cmpTypesX env [] [] = EQ +cmpTypesX env (t1:tys1) (t2:tys2) = cmpTypeX env t1 t2 `thenCmp` cmpTypesX env tys1 tys2 +cmpTypesX env [] tys = LT +cmpTypesX env ty [] = GT + +------------- +cmpPredX :: RnEnv2 -> PredType -> PredType -> Ordering +cmpPredX env (IParam n1 ty1) (IParam n2 ty2) = (n1 `compare` n2) `thenCmp` cmpTypeX env ty1 ty2 + -- Compare types as well as names for implicit parameters + -- This comparison is used exclusively (I think) for the + -- finite map built in TcSimplify +cmpPredX env (ClassP c1 tys1) (ClassP c2 tys2) = (c1 `compare` c2) `thenCmp` cmpTypesX env tys1 tys2 +cmpPredX env (IParam _ _) (ClassP _ _) = LT +cmpPredX env (ClassP _ _) (IParam _ _) = GT +\end{code} + +PredTypes are used as a FM key in TcSimplify, +so we take the easy path and make them an instance of Ord + \begin{code} -eqType t1 t2 = eq_ty emptyVarEnv t1 t2 -eqKind = eqType -- No worries about looking - --- Look through Notes -eq_ty env (NoteTy _ t1) t2 = eq_ty env t1 t2 -eq_ty env t1 (NoteTy _ t2) = eq_ty env t1 t2 - --- Look through SourceTy. This is where the looping danger comes from -eq_ty env (SourceTy sty1) t2 = eq_ty env (sourceTypeRep sty1) t2 -eq_ty env t1 (SourceTy sty2) = eq_ty env t1 (sourceTypeRep sty2) - --- The rest is plain sailing -eq_ty env (TyVarTy tv1) (TyVarTy tv2) = case lookupVarEnv env tv1 of - Just tv1a -> tv1a == tv2 - Nothing -> tv1 == tv2 -eq_ty env (ForAllTy tv1 t1) (ForAllTy tv2 t2) - | tv1 == tv2 = eq_ty (delVarEnv env tv1) t1 t2 - | otherwise = eq_ty (extendVarEnv env tv1 tv2) t1 t2 -eq_ty env (AppTy s1 t1) (AppTy s2 t2) = (eq_ty env s1 s2) && (eq_ty env t1 t2) -eq_ty env (FunTy s1 t1) (FunTy s2 t2) = (eq_ty env s1 s2) && (eq_ty env t1 t2) -eq_ty env (TyConApp tc1 tys1) (TyConApp tc2 tys2) = (tc1 == tc2) && (eq_tys env tys1 tys2) -eq_ty env t1 t2 = False - -eq_tys env [] [] = True -eq_tys env (t1:tys1) (t2:tys2) = (eq_ty env t1 t2) && (eq_tys env tys1 tys2) -eq_tys env tys1 tys2 = False +instance Eq PredType where { (==) = tcEqPred } +instance Ord PredType where { compare = tcCmpPred } \end{code} + +%************************************************************************ +%* * + Type substitutions +%* * +%************************************************************************ + +\begin{code} +data TvSubst + = TvSubst InScopeSet -- The in-scope type variables + TvSubstEnv -- The substitution itself; guaranteed idempotent + -- See Note [Apply Once] + +{- ---------------------------------------------------------- + Note [Apply Once] + +We use TvSubsts to instantiate things, and we might instantiate + forall a b. ty +\with the types + [a, b], or [b, a]. +So the substition might go [a->b, b->a]. A similar situation arises in Core +when we find a beta redex like + (/\ a /\ b -> e) b a +Then we also end up with a substition that permutes type variables. Other +variations happen to; for example [a -> (a, b)]. + + *************************************************** + *** So a TvSubst must be applied precisely once *** + *************************************************** + +A TvSubst is not idempotent, but, unlike the non-idempotent substitution +we use during unifications, it must not be repeatedly applied. +-------------------------------------------------------------- -} + + +type TvSubstEnv = TyVarEnv Type + -- A TvSubstEnv is used both inside a TvSubst (with the apply-once + -- invariant discussed in Note [Apply Once]), and also independently + -- in the middle of matching, and unification (see Types.Unify) + -- So you have to look at the context to know if it's idempotent or + -- apply-once or whatever + +emptyTvSubst = TvSubst emptyInScopeSet emptyVarEnv +isEmptyTvSubst :: TvSubst -> Bool +isEmptyTvSubst (TvSubst _ env) = isEmptyVarEnv env + +getTvSubstEnv :: TvSubst -> TvSubstEnv +getTvSubstEnv (TvSubst _ env) = env + +getTvInScope :: TvSubst -> InScopeSet +getTvInScope (TvSubst in_scope _) = in_scope + +isInScope :: Var -> TvSubst -> Bool +isInScope v (TvSubst in_scope _) = v `elemInScopeSet` in_scope + +setTvSubstEnv :: TvSubst -> TvSubstEnv -> TvSubst +setTvSubstEnv (TvSubst in_scope _) env = TvSubst in_scope env + +extendTvInScope :: TvSubst -> [Var] -> TvSubst +extendTvInScope (TvSubst in_scope env) vars = TvSubst (extendInScopeSetList in_scope vars) env + +extendTvSubst :: TvSubst -> TyVar -> Type -> TvSubst +extendTvSubst (TvSubst in_scope env) tv ty = TvSubst in_scope (extendVarEnv env tv ty) + +extendTvSubstList :: TvSubst -> [TyVar] -> [Type] -> TvSubst +extendTvSubstList (TvSubst in_scope env) tvs tys + = TvSubst in_scope (extendVarEnvList env (tvs `zip` tys)) + +-- mkTvSubst and zipTvSubst generate the in-scope set from +-- the types given; but it's just a thunk so with a bit of luck +-- it'll never be evaluated + +mkTvSubst :: TvSubstEnv -> TvSubst +mkTvSubst env + = TvSubst (mkInScopeSet (tyVarsOfTypes (varEnvElts env))) env + +zipTvSubst :: [TyVar] -> [Type] -> TvSubst +zipTvSubst tyvars tys + = TvSubst (mkInScopeSet (tyVarsOfTypes tys)) (zipTyEnv tyvars tys) + +-- mkTopTvSubst is called when doing top-level substitutions. +-- Here we expect that the free vars of the range of the +-- substitution will be empty. +mkTopTvSubst :: [(TyVar, Type)] -> TvSubst +mkTopTvSubst prs = TvSubst emptyInScopeSet (mkVarEnv prs) + +zipTopTvSubst :: [TyVar] -> [Type] -> TvSubst +zipTopTvSubst tyvars tys = TvSubst emptyInScopeSet (zipTyEnv tyvars tys) + +zipTyEnv :: [TyVar] -> [Type] -> TvSubstEnv +zipTyEnv tyvars tys +#ifdef DEBUG + | length tyvars /= length tys + = pprTrace "mkTopTvSubst" (ppr tyvars $$ ppr tys) emptyVarEnv + | otherwise +#endif + = zip_ty_env tyvars tys emptyVarEnv + +-- Later substitutions in the list over-ride earlier ones, +-- but there should be no loops +zip_ty_env [] [] env = env +zip_ty_env (tv:tvs) (ty:tys) env = zip_ty_env tvs tys (extendVarEnv env tv ty) + -- There used to be a special case for when + -- ty == TyVarTy tv + -- (a not-uncommon case) in which case the substitution was dropped. + -- But the type-tidier changes the print-name of a type variable without + -- changing the unique, and that led to a bug. Why? Pre-tidying, we had + -- a type {Foo t}, where Foo is a one-method class. So Foo is really a newtype. + -- And it happened that t was the type variable of the class. Post-tiding, + -- it got turned into {Foo t2}. The ext-core printer expanded this using + -- sourceTypeRep, but that said "Oh, t == t2" because they have the same unique, + -- and so generated a rep type mentioning t not t2. + -- + -- Simplest fix is to nuke the "optimisation" + +instance Outputable TvSubst where + ppr (TvSubst ins env) + = sep[ ptext SLIT(" ppr ins), + nest 2 (ptext SLIT("Env:") <+> ppr env) ] +\end{code} + +%************************************************************************ +%* * + Performing type substitutions +%* * +%************************************************************************ + +\begin{code} +substTyWith :: [TyVar] -> [Type] -> Type -> Type +substTyWith tvs tys = substTy (zipTvSubst tvs tys) + +substTy :: TvSubst -> Type -> Type +substTy subst ty | isEmptyTvSubst subst = ty + | otherwise = subst_ty subst ty + +substTys :: TvSubst -> [Type] -> [Type] +substTys subst tys | isEmptyTvSubst subst = tys + | otherwise = map (subst_ty subst) tys + +deShadowTy :: Type -> Type -- Remove any shadowing from the type +deShadowTy ty = subst_ty emptyTvSubst ty + +substTheta :: TvSubst -> ThetaType -> ThetaType +substTheta subst theta + | isEmptyTvSubst subst = theta + | otherwise = map (substPred subst) theta + +substPred :: TvSubst -> PredType -> PredType +substPred subst (IParam n ty) = IParam n (subst_ty subst ty) +substPred subst (ClassP clas tys) = ClassP clas (map (subst_ty subst) tys) + +-- Note that the in_scope set is poked only if we hit a forall +-- so it may often never be fully computed +subst_ty subst@(TvSubst in_scope env) ty + = go ty + where + go ty@(TyVarTy tv) = case (lookupVarEnv env tv) of + Nothing -> ty + Just ty' -> ty' -- See Note [Apply Once] + + go (TyConApp tc tys) = let args = map go tys + in args `seqList` TyConApp tc args + + go (PredTy p) = PredTy $! (substPred subst p) + + go (NoteTy (SynNote ty1) ty2) = NoteTy (SynNote $! (go ty1)) $! (go ty2) + go (NoteTy (FTVNote _) ty2) = go ty2 -- Discard the free tyvar note + + go (FunTy arg res) = (FunTy $! (go arg)) $! (go res) + go (AppTy fun arg) = mkAppTy (go fun) $! (go arg) + -- The mkAppTy smart constructor is important + -- we might be replacing (a Int), represented with App + -- by [Int], represented with TyConApp + go (ForAllTy tv ty) = case substTyVar subst tv of + (subst', tv') -> ForAllTy tv' $! (subst_ty subst' ty) + +substTyVar :: TvSubst -> TyVar -> (TvSubst, TyVar) +substTyVar subst@(TvSubst in_scope env) old_var + | old_var == new_var -- No need to clone + -- But we *must* zap any current substitution for the variable. + -- For example: + -- (\x.e) with id_subst = [x |-> e'] + -- Here we must simply zap the substitution for x + -- + -- The new_id isn't cloned, but it may have a different type + -- etc, so we must return it, not the old id + = (TvSubst (in_scope `extendInScopeSet` new_var) (delVarEnv env old_var), + new_var) + + | otherwise -- The new binder is in scope so + -- we'd better rename it away from the in-scope variables + -- Extending the substitution to do this renaming also + -- has the (correct) effect of discarding any existing + -- substitution for that variable + = (TvSubst (in_scope `extendInScopeSet` new_var) (extendVarEnv env old_var (TyVarTy new_var)), + new_var) + where + new_var = uniqAway in_scope old_var + -- The uniqAway part makes sure the new variable is not already in scope +\end{code} + +