X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2Ftypes%2FInstEnv.lhs;h=1be556b22187e0833b6cd28cc6b0370412a31980;hb=4c46b43215295868b332c40ba0d63520e6433536;hp=44f2db313d4b5c47918ddfffc8271ff2717bf6e0;hpb=98744cef7b82e7eefbb1c6f1d8b9e28c415939c4;p=ghc-hetmet.git diff --git a/ghc/compiler/types/InstEnv.lhs b/ghc/compiler/types/InstEnv.lhs index 44f2db3..1be556b 100644 --- a/ghc/compiler/types/InstEnv.lhs +++ b/ghc/compiler/types/InstEnv.lhs @@ -9,27 +9,27 @@ The bits common to TcInstDcls and TcDeriv. module InstEnv ( DFunId, InstEnv, - emptyInstEnv, extendInstEnv, - lookupInstEnv, - classInstEnv, simpleDFunClassTyCon, checkFunDeps + emptyInstEnv, extendInstEnv, extendInstEnvList, + lookupInstEnv, instEnvElts, + classInstances, simpleDFunClassTyCon, checkFunDeps ) where #include "HsVersions.h" import Class ( Class, classTvsFds ) -import Var ( Id ) +import Var ( Id, isTcTyVar ) import VarSet -import VarEnv -import TcType ( Type, tcTyConAppTyCon, - tcSplitDFunTy, tyVarsOfTypes, - matchTys, unifyTyListsX +import Type ( TvSubst ) +import TcType ( Type, tcTyConAppTyCon, tcIsTyVarTy, + tcSplitDFunTy, tyVarsOfTypes, isExistentialTyVar ) +import Unify ( tcMatchTys, tcUnifyTys, BindFlag(..) ) import FunDeps ( checkClsFD ) import TyCon ( TyCon ) import Outputable -import UniqFM ( UniqFM, lookupWithDefaultUFM, emptyUFM, eltsUFM, addToUFM_C ) +import UniqFM ( UniqFM, lookupUFM, emptyUFM, addToUFM_C, eltsUFM ) import Id ( idType ) -import CmdLineOpts +import DynFlags import Util ( notNull ) import Maybe ( isJust ) \end{code} @@ -41,34 +41,78 @@ import Maybe ( isJust ) %* * %************************************************************************ +A @ClsInstEnv@ all the instances of that class. The @Id@ inside a +ClsInstEnv mapping is the dfun for that instance. + +If class C maps to a list containing the item ([a,b], [t1,t2,t3], dfun), then + + forall a b, C t1 t2 t3 can be constructed by dfun + +or, to put it another way, we have + + instance (...) => C t1 t2 t3, witnessed by dfun + \begin{code} type DFunId = Id type InstEnv = UniqFM ClsInstEnv -- Maps Class to instances for that class -type ClsInstEnv = [InstEnvElt] -- The instances for a particular class + +data ClsInstEnv + = ClsIE [InstEnvElt] -- The instances for a particular class, in any order + Bool -- True <=> there is an instance of form C a b c + -- If *not* then the common case of looking up + -- (C a b c) can fail immediately + -- NB: use tcIsTyVarTy: don't look through newtypes!! + type InstEnvElt = (TyVarSet, [Type], DFunId) - -- INVARIANTs: see notes below + +-- INVARIANTS: +-- * [a,b] must be a superset of the free vars of [t1,t2,t3] +-- +-- * The dfun must itself be quantified over [a,b] +-- +-- * The template type variables [a,b] are distinct in each item +-- of a ClsInstEnv (so we can safely unify them) + +-- Thus, the @ClassInstEnv@ for @Eq@ might contain the following entry: +-- [a] ===> dfun_Eq_List :: forall a. Eq a => Eq [a] +-- The "a" in the pattern must be one of the forall'd variables in +-- the dfun type. + emptyInstEnv :: InstEnv emptyInstEnv = emptyUFM -classInstEnv :: InstEnv -> Class -> ClsInstEnv -classInstEnv env cls = lookupWithDefaultUFM env [] cls +instEnvElts :: InstEnv -> [InstEnvElt] +instEnvElts ie = [elt | ClsIE elts _ <- eltsUFM ie, elt <- elts] + +classInstances :: (InstEnv,InstEnv) -> Class -> [InstEnvElt] +classInstances (pkg_ie, home_ie) cls + = get home_ie ++ get pkg_ie + where + get env = case lookupUFM env cls of + Just (ClsIE insts _) -> insts + Nothing -> [] + +extendInstEnvList :: InstEnv -> [DFunId] -> InstEnv +extendInstEnvList inst_env dfuns = foldl extendInstEnv inst_env dfuns extendInstEnv :: InstEnv -> DFunId -> InstEnv extendInstEnv inst_env dfun_id - = addToUFM_C add inst_env clas [ins_item] + = addToUFM_C add inst_env clas (ClsIE [ins_item] ins_tyvar) where - add old _ = ins_item : old + add (ClsIE cur_insts cur_tyvar) _ = ClsIE (ins_item : cur_insts) + (ins_tyvar || cur_tyvar) (ins_tvs, _, clas, ins_tys) = tcSplitDFunTy (idType dfun_id) ins_tv_set = mkVarSet ins_tvs ins_item = (ins_tv_set, ins_tys, dfun_id) + ins_tyvar = all tcIsTyVarTy ins_tys #ifdef UNUSED pprInstEnv :: InstEnv -> SDoc pprInstEnv env = vcat [ brackets (pprWithCommas ppr (varSetElems tyvars)) <+> brackets (pprWithCommas ppr tys) <+> ppr dfun - | cls_inst_env <- eltsUFM env + | ClsIE cls_inst_env _ <- eltsUFM env , (tyvars, tys, dfun) <- cls_inst_env ] #endif @@ -87,32 +131,6 @@ simpleDFunClassTyCon dfun %* * %************************************************************************ -A @ClsInstEnv@ all the instances of that class. The @Id@ inside a -ClsInstEnv mapping is the dfun for that instance. - -If class C maps to a list containing the item ([a,b], [t1,t2,t3], dfun), then - - forall a b, C t1 t2 t3 can be constructed by dfun - -or, to put it another way, we have - - instance (...) => C t1 t2 t3, witnessed by dfun - -There is an important consistency constraint in the elements of a ClsInstEnv: - - * [a,b] must be a superset of the free vars of [t1,t2,t3] - - * The dfun must itself be quantified over [a,b] - - * More specific instances come before less specific ones, - where they overlap - -Thus, the @ClassInstEnv@ for @Eq@ might contain the following entry: - [a] ===> dfun_Eq_List :: forall a. Eq a => Eq [a] -The "a" in the pattern must be one of the forall'd variables in -the dfun type. - - Notes on overlapping instances ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ @@ -253,9 +271,9 @@ thing we are looking up can have an arbitrary "flexi" part. lookupInstEnv :: DynFlags -> (InstEnv -- External package inst-env ,InstEnv) -- Home-package inst-env - -> Class -> [Type] -- What we are looking for - -> ([(TyVarSubstEnv, InstEnvElt)], -- Successful matches - [Id]) -- These don't match but do unify + -> Class -> [Type] -- What we are looking for + -> ([(TvSubst, InstEnvElt)], -- Successful matches + [Id]) -- These don't match but do unify -- The second component of the tuple happens when we look up -- Foo [a] -- in an InstEnv that has entries for @@ -271,10 +289,11 @@ lookupInstEnv dflags (pkg_ie, home_ie) cls tys -- so don't attempt to pune the matches | otherwise = (pruned_matches, []) where + all_tvs = all tcIsTyVarTy tys incoherent_ok = dopt Opt_AllowIncoherentInstances dflags overlap_ok = dopt Opt_AllowOverlappingInstances dflags - (home_matches, home_unifs) = lookup_inst_env home_ie cls tys - (pkg_matches, pkg_unifs) = lookup_inst_env pkg_ie cls tys + (home_matches, home_unifs) = lookup_inst_env home_ie cls tys all_tvs + (pkg_matches, pkg_unifs) = lookup_inst_env pkg_ie cls tys all_tvs all_matches = home_matches ++ pkg_matches all_unifs | incoherent_ok = [] -- Don't worry about these if incoherent is ok! | otherwise = home_unifs ++ pkg_unifs @@ -282,29 +301,59 @@ lookupInstEnv dflags (pkg_ie, home_ie) cls tys pruned_matches | overlap_ok = foldr insert_overlapping [] all_matches | otherwise = all_matches -lookup_inst_env :: InstEnv -- The envt - -> Class -> [Type] -- What we are looking for - -> ([(TyVarSubstEnv, InstEnvElt)], -- Successful matches - [Id]) -- These don't match but do unify -lookup_inst_env env key_cls key_tys - = find (classInstEnv env key_cls) [] [] +lookup_inst_env :: InstEnv -- The envt + -> Class -> [Type] -- What we are looking for + -> Bool -- All the [Type] are tyvars + -> ([(TvSubst, InstEnvElt)], -- Successful matches + [Id]) -- These don't match but do unify +lookup_inst_env env key_cls key_tys key_all_tvs + = case lookupUFM env key_cls of + Nothing -> ([],[]) -- No instances for this class + Just (ClsIE insts has_tv_insts) + | key_all_tvs && not has_tv_insts -> ([],[]) -- Short cut for common case + -- The thing we are looking up is of form (C a b c), and + -- the ClsIE has no instances of that form, so don't bother to search + | otherwise -> find insts [] [] where - key_vars = tyVarsOfTypes key_tys - find [] ms us = (ms, us) find (item@(tpl_tyvars, tpl, dfun_id) : rest) ms us - = case matchTys tpl_tyvars tpl key_tys of - Just (subst, leftovers) -> ASSERT( null leftovers ) - find rest ((subst,item):ms) us + = case tcMatchTys tpl_tyvars tpl key_tys of + Just subst -> find rest ((subst,item):ms) us Nothing -- Does not match, so next check whether the things unify -- [see notes about overlapping instances above] - -> case unifyTyListsX (key_vars `unionVarSet` tpl_tyvars) key_tys tpl of + -> ASSERT2( not (tyVarsOfTypes key_tys `intersectsVarSet` tpl_tyvars), + (ppr key_cls <+> ppr key_tys <+> ppr key_all_tvs) $$ + (ppr dfun_id <+> ppr tpl_tyvars <+> ppr tpl) + ) + -- Unification will break badly if the variables overlap + -- They shouldn't because we allocate separate uniques for them + case tcUnifyTys bind_fn tpl key_tys of Just _ -> find rest ms (dfun_id:us) Nothing -> find rest ms us -insert_overlapping :: (TyVarSubstEnv, InstEnvElt) -> [(TyVarSubstEnv, InstEnvElt)] - -> [(TyVarSubstEnv, InstEnvElt)] + bind_fn tv | isTcTyVar tv && isExistentialTyVar tv = Skolem + | otherwise = BindMe + -- The key_tys can contain skolem constants, and we can guarantee that those + -- are never going to be instantiated to anything, so we should not involve + -- them in the unification test. Example: + -- class Foo a where { op :: a -> Int } + -- instance Foo a => Foo [a] -- NB overlap + -- instance Foo [Int] -- NB overlap + -- data T = forall a. Foo a => MkT a + -- f :: T -> Int + -- f (MkT x) = op [x,x] + -- The op [x,x] means we need (Foo [a]). Without the filterVarSet we'd + -- complain, saying that the choice of instance depended on the instantiation + -- of 'a'; but of course it isn't *going* to be instantiated. + -- + -- We do this only for pattern-bound skolems. For example we reject + -- g :: forall a => [a] -> Int + -- g x = op x + -- on the grounds that the correct instance depends on the instantiation of 'a' + +insert_overlapping :: (TvSubst, InstEnvElt) -> [(TvSubst, InstEnvElt)] + -> [(TvSubst, InstEnvElt)] -- Add a new solution, knocking out strictly less specific ones insert_overlapping new_item [] = [new_item] insert_overlapping new_item (item:items) @@ -314,14 +363,14 @@ insert_overlapping new_item (item:items) -- Keep new one | old_beats_new = item : items -- Keep old one - | otherwise = item : insert_overlapping new_item items + | otherwise = item : insert_overlapping new_item items -- Keep both where new_beats_old = new_item `beats` item old_beats_new = item `beats` new_item (_, (tvs1, tys1, _)) `beats` (_, (tvs2, tys2, _)) - = isJust (matchTys tvs2 tys2 tys1) -- A beats B if A is more specific than B + = isJust (tcMatchTys tvs2 tys2 tys1) -- A beats B if A is more specific than B -- I.e. if B can be instantiated to match A \end{code} @@ -363,16 +412,16 @@ checkFunDeps :: (InstEnv, InstEnv) -> DFunId -> Maybe [DFunId] -- Nothing <=> ok -- Just dfs <=> conflict with dfs -- Check wheher adding DFunId would break functional-dependency constraints -checkFunDeps (pkg_ie, home_ie) dfun +checkFunDeps inst_envs dfun | null bad_fundeps = Nothing | otherwise = Just bad_fundeps where (ins_tvs, _, clas, ins_tys) = tcSplitDFunTy (idType dfun) ins_tv_set = mkVarSet ins_tvs - cls_inst_env = classInstEnv home_ie clas ++ classInstEnv pkg_ie clas + cls_inst_env = classInstances inst_envs clas bad_fundeps = badFunDeps cls_inst_env clas ins_tv_set ins_tys -badFunDeps :: ClsInstEnv -> Class +badFunDeps :: [InstEnvElt] -> Class -> TyVarSet -> [Type] -- Proposed new instance type -> [DFunId] badFunDeps cls_inst_env clas ins_tv_set ins_tys