X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2Ftypes%2FFamInstEnv.lhs;h=89fd193914b502f1ce3ff7b6a0e8ad7cf5c40be7;hp=ba96a55e45fc695e95aec52c4f3b8646a6535cc2;hb=c56450419ef6c819ad86ab01dca6fd2966b11305;hpb=eee94cc7e8e39f84dc61c07461582b9655270d67 diff --git a/compiler/types/FamInstEnv.lhs b/compiler/types/FamInstEnv.lhs index ba96a55..89fd193 100644 --- a/compiler/types/FamInstEnv.lhs +++ b/compiler/types/FamInstEnv.lhs @@ -14,7 +14,7 @@ module FamInstEnv ( extendFamInstEnv, extendFamInstEnvList, famInstEnvElts, familyInstances, - lookupFamInstEnv, lookupFamInstEnvUnify, + lookupFamInstEnv, lookupFamInstEnvConflicts, -- Normalisation topNormaliseType @@ -36,8 +36,6 @@ import Outputable import Maybes import Util import FastString - -import Maybe \end{code} @@ -94,10 +92,11 @@ pprFamInstHdr (FamInst {fi_fam = fam, fi_tys = tys, fi_tycon = tycon}) = pprTyConSort <+> pprHead where pprHead = pprTypeApp fam tys - pprTyConSort | isDataTyCon tycon = ptext (sLit "data instance") - | isNewTyCon tycon = ptext (sLit "newtype instance") - | isSynTyCon tycon = ptext (sLit "type instance") - | otherwise = panic "FamInstEnv.pprFamInstHdr" + pprTyConSort | isDataTyCon tycon = ptext (sLit "data instance") + | isNewTyCon tycon = ptext (sLit "newtype instance") + | isSynTyCon tycon = ptext (sLit "type instance") + | isAbstractTyCon tycon = ptext (sLit "data instance") + | otherwise = panic "FamInstEnv.pprFamInstHdr" pprFamInsts :: [FamInst] -> SDoc pprFamInsts finsts = vcat (map pprFamInst finsts) @@ -220,51 +219,68 @@ we return the matching instance '(FamInst{.., fi_tycon = :R42T}, Int)'. \begin{code} type FamInstMatch = (FamInst, [Type]) -- Matching type instance - -lookupFamInstEnv :: FamInstEnvs - -> TyCon -> [Type] -- What we are looking for - -> [FamInstMatch] -- Successful matches -lookupFamInstEnv (pkg_ie, home_ie) fam tys - | not (isOpenTyCon fam) - = [] - | otherwise - = home_matches ++ pkg_matches + -- See Note [Over-saturated matches] + +lookupFamInstEnv + :: FamInstEnvs + -> TyCon -> [Type] -- What we are looking for + -> [FamInstMatch] -- Successful matches + +lookupFamInstEnv + = lookup_fam_inst_env match True + where + match _ tpl_tvs tpl_tys tys = tcMatchTys tpl_tvs tpl_tys tys + +lookupFamInstEnvConflicts + :: FamInstEnvs + -> FamInst -- Putative new instance + -> [TyVar] -- Unique tyvars, matching arity of FamInst + -> [FamInstMatch] -- Conflicting matches +-- E.g. when we are about to add +-- f : type instance F [a] = a->a +-- we do (lookupFamInstConflicts f [b]) +-- to find conflicting matches +-- The skolem tyvars are needed because we don't have a +-- unique supply to hand + +lookupFamInstEnvConflicts envs fam_inst skol_tvs + = lookup_fam_inst_env my_unify False envs fam tys' where - rough_tcs = roughMatchTcs tys - all_tvs = all isNothing rough_tcs - home_matches = lookup home_ie - pkg_matches = lookup pkg_ie - - -------------- - lookup env = case lookupUFM env fam of - Nothing -> [] -- No instances for this class - Just (FamIE insts has_tv_insts) - -- Short cut for common case: - -- The thing we are looking up is of form (C a - -- b c), and the FamIE has no instances of - -- that form, so don't bother to search - | all_tvs && not has_tv_insts -> [] - | otherwise -> find insts - - -------------- - find [] = [] - find (item@(FamInst { fi_tcs = mb_tcs, fi_tvs = tpl_tvs, - fi_tys = tpl_tys, fi_tycon = tycon }) : rest) - -- Fast check for no match, uses the "rough match" fields - | instanceCantMatch rough_tcs mb_tcs - = find rest - - -- Proper check - | Just subst <- tcMatchTys tpl_tvs tpl_tys tys - = (item, substTyVars subst (tyConTyVars tycon)) : find rest - - -- No match => try next - | otherwise - = find rest + inst_tycon = famInstTyCon fam_inst + (fam, tys) = expectJust "FamInstEnv.lookuFamInstEnvConflicts" + (tyConFamInst_maybe inst_tycon) + skol_tys = mkTyVarTys skol_tvs + tys' = substTys (zipTopTvSubst (tyConTyVars inst_tycon) skol_tys) tys + -- In example above, fam tys' = F [b] + + my_unify old_fam_inst tpl_tvs tpl_tys match_tys + = ASSERT2( tyVarsOfTypes tys `disjointVarSet` tpl_tvs, + (ppr fam <+> ppr tys) $$ + (ppr tpl_tvs <+> ppr tpl_tys) ) + -- Unification will break badly if the variables overlap + -- They shouldn't because we allocate separate uniques for them + case tcUnifyTys instanceBindFun tpl_tys match_tys of + Just subst | conflicting old_fam_inst subst -> Just subst + _other -> Nothing + + -- - In the case of data family instances, any overlap is fundamentally a + -- conflict (as these instances imply injective type mappings). + -- - In the case of type family instances, overlap is admitted as long as + -- the right-hand sides of the overlapping rules coincide under the + -- overlap substitution. We require that they are syntactically equal; + -- anything else would be difficult to test for at this stage. + conflicting old_fam_inst subst + | isAlgTyCon fam = True + | otherwise = not (old_rhs `tcEqType` new_rhs) + where + old_tycon = famInstTyCon old_fam_inst + old_tvs = tyConTyVars old_tycon + old_rhs = mkTyConApp old_tycon (substTyVars subst old_tvs) + new_rhs = mkTyConApp inst_tycon (substTyVars subst skol_tvs) \end{code} While @lookupFamInstEnv@ uses a one-way match, the next function -@lookupFamInstEnvUnify@ uses two-way matching (ie, unification). This is +@lookupFamInstEnvConflicts@ uses two-way matching (ie, unification). This is needed to check for overlapping instances. For class instances, these two variants of lookup are combined into one @@ -274,19 +290,45 @@ Moreover, matching is the wildly more frequently used operation in the case of indexed synonyms and we don't want to slow that down by needless unification. \begin{code} -lookupFamInstEnvUnify :: (FamInstEnv, FamInstEnv) -> TyCon -> [Type] - -> [(FamInstMatch, TvSubst)] -lookupFamInstEnvUnify (pkg_ie, home_ie) fam tys +------------------------------------------------------------ +-- Might be a one-way match or a unifier +type MatchFun = FamInst -- The FamInst template + -> TyVarSet -> [Type] -- fi_tvs, fi_tys of that FamInst + -> [Type] -- Target to match against + -> Maybe TvSubst + +type OneSidedMatch = Bool -- Are optimisations that are only valid for + -- one sided matches allowed? + +lookup_fam_inst_env -- The worker, local to this module + :: MatchFun + -> OneSidedMatch + -> FamInstEnvs + -> TyCon -> [Type] -- What we are looking for + -> [FamInstMatch] -- Successful matches +lookup_fam_inst_env match_fun one_sided (pkg_ie, home_ie) fam tys | not (isOpenTyCon fam) = [] | otherwise - = home_matches ++ pkg_matches + = ASSERT( n_tys >= arity ) -- Family type applications must be saturated + home_matches ++ pkg_matches where - rough_tcs = roughMatchTcs tys - all_tvs = all isNothing rough_tcs home_matches = lookup home_ie pkg_matches = lookup pkg_ie + -- See Note [Over-saturated matches] + arity = tyConArity fam + n_tys = length tys + extra_tys = drop arity tys + (match_tys, add_extra_tys) + | arity > n_tys = (take arity tys, \res_tys -> res_tys ++ extra_tys) + | otherwise = (tys, \res_tys -> res_tys) + -- The second case is the common one, hence functional representation + + -------------- + rough_tcs = roughMatchTcs match_tys + all_tvs = all isNothing rough_tcs && one_sided + -------------- lookup env = case lookupUFM env fam of Nothing -> [] -- No instances for this class @@ -306,20 +348,33 @@ lookupFamInstEnvUnify (pkg_ie, home_ie) fam tys | instanceCantMatch rough_tcs mb_tcs = find rest + -- Proper check + | Just subst <- match_fun item tpl_tvs tpl_tys match_tys + = (item, add_extra_tys $ substTyVars subst (tyConTyVars tycon)) : find rest + + -- No match => try next | otherwise - = ASSERT2( tyVarsOfTypes tys `disjointVarSet` tpl_tvs, - (ppr fam <+> ppr tys <+> ppr all_tvs) $$ - (ppr tycon <+> ppr tpl_tvs <+> ppr tpl_tys) - ) - -- Unification will break badly if the variables overlap - -- They shouldn't because we allocate separate uniques for them - case tcUnifyTys instanceBindFun tpl_tys tys of - Just subst -> let rep_tys = substTyVars subst (tyConTyVars tycon) - in - ((item, rep_tys), subst) : find rest - Nothing -> find rest + = find rest \end{code} +Note [Over-saturated matches] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +It's ok to look up an over-saturated type constructor. E.g. + type family F a :: * -> * + type instance F (a,b) = Either (a->b) + +The type instance gives rise to a newtype TyCon (at a higher kind +which you can't do in Haskell!): + newtype FPair a b = FP (Either (a->b)) + +Then looking up (F (Int,Bool) Char) will return a FamInstMatch + (FPair, [Int,Bool,Char]) + +The "extra" type argument [Char] just stays on the end. + + + + %************************************************************************ %* * Looking up a family instance