X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypecheck%2FTcUnify.lhs;h=e8fb134c31dab85f84f646019443ab452781d617;hb=e656c6e3aaa827c51cd39c9cd9f0a6461db1d4c2;hp=1a618228ebe9d85954f376bba70bd717653a64c8;hpb=6493f9d3305d5af08ad92c8f32b8b6410404eb46;p=ghc-hetmet.git diff --git a/compiler/typecheck/TcUnify.lhs b/compiler/typecheck/TcUnify.lhs index 1a61822..e8fb134 100644 --- a/compiler/typecheck/TcUnify.lhs +++ b/compiler/typecheck/TcUnify.lhs @@ -13,7 +13,7 @@ module TcUnify ( unifyType, unifyTypeList, unifyTheta, unifyKind, unifyKinds, unifyFunKind, checkExpectedKind, - boxySubMatchType, boxyMatchTypes, + preSubType, boxyMatchTypes, -------------------------------- -- Holes @@ -29,8 +29,8 @@ import HsSyn ( ExprCoFn(..), idCoercion, isIdCoercion, (<.>) ) import TypeRep ( Type(..), PredType(..) ) import TcMType ( lookupTcTyVar, LookupTyVarResult(..), - tcInstSkolType, newKindVar, newMetaTyVar, - tcInstBoxy, newBoxyTyVar, newBoxyTyVarTys, readFilledBox, + tcInstSkolType, tcInstBoxyTyVar, newKindVar, newMetaTyVar, + newBoxyTyVar, newBoxyTyVarTys, readFilledBox, readMetaTyVar, writeMetaTyVar, newFlexiTyVarTy, tcInstSkolTyVars, tcInstTyVar, zonkTcKind, zonkType, zonkTcType, zonkTcTyVarsAndFV, @@ -46,11 +46,13 @@ import TcType ( TcKind, TcType, TcTyVar, BoxyTyVar, TcTauType, pprSkolTvBinding, isTauTy, isTauTyCon, isSigmaTy, mkFunTy, mkFunTys, mkTyConApp, isMetaTyVar, tcSplitForAllTys, tcSplitAppTy_maybe, tcSplitFunTys, mkTyVarTys, - tyVarsOfType, mkPhiTy, mkTyVarTy, mkPredTy, + tcSplitSigmaTy, tyVarsOfType, mkPhiTy, mkTyVarTy, mkPredTy, typeKind, mkForAllTys, mkAppTy, isBoxyTyVar, + exactTyVarsOfType, tidyOpenType, tidyOpenTyVar, tidyOpenTyVars, pprType, tidyKind, tidySkolemTyVar, isSkolemTyVar, tcView, - TvSubst, mkTvSubst, zipTyEnv, substTy, emptyTvSubst, + TvSubst, mkTvSubst, zipTyEnv, zipOpenTvSubst, emptyTvSubst, + substTy, substTheta, lookupTyVar, extendTvSubst ) import Kind ( Kind(..), SimpleKind, KindVar, isArgTypeKind, openTypeKind, liftedTypeKind, unliftedTypeKind, @@ -63,8 +65,7 @@ import TyCon ( TyCon, tyConArity, tyConTyVars, isSynTyCon ) import TysWiredIn ( listTyCon ) import Id ( Id, mkSysLocal ) import Var ( Var, varName, tyVarKind, isTcTyVar, tcTyVarDetails ) -import VarSet ( emptyVarSet, mkVarSet, unitVarSet, unionVarSet, elemVarSet, varSetElems, - extendVarSet, intersectsVarSet ) +import VarSet import VarEnv import Name ( Name, isSystemName ) import ErrUtils ( Message ) @@ -166,7 +167,7 @@ subFunTys error_herald n_pats res_ty thing_inside loop n args_so_far res_ty@(AppTy _ _) = do { [arg_ty',res_ty'] <- newBoxyTyVarTys [argTypeKind, openTypeKind] ; (_, mb_unit) <- tryTcErrs $ boxyUnify res_ty (FunTy arg_ty' res_ty') - ; if isNothing mb_unit then bale_out args_so_far res_ty + ; if isNothing mb_unit then bale_out args_so_far else loop n args_so_far (FunTy arg_ty' res_ty') } loop n args_so_far (TyVarTy tv) @@ -183,9 +184,9 @@ subFunTys error_herald n_pats res_ty thing_inside -- Note argTypeKind: the args can have an unboxed type, -- but not an unboxed tuple. - loop n args_so_far res_ty = bale_out args_so_far res_ty + loop n args_so_far res_ty = bale_out args_so_far - bale_out args_so_far res_ty + bale_out args_so_far = do { env0 <- tcInitTidyEnv ; res_ty' <- zonkTcType res_ty ; let (env1, res_ty'') = tidyOpenType env0 res_ty' @@ -334,16 +335,108 @@ withBox kind thing_inside %************************************************************************ \begin{code} +preSubType :: [TcTyVar] -- Quantified type variables + -> TcTyVarSet -- Subset of quantified type variables + -- that can be instantiated with boxy types + -> TcType -- The rho-type part; quantified tyvars scopes over this + -> BoxySigmaType -- Matching type from the context + -> TcM [TcType] -- Types to instantiate the tyvars +-- Perform pre-subsumption, and return suitable types +-- to instantiate the quantified type varibles: +-- info from the pre-subsumption, if there is any +-- a boxy type variable otherwise +-- +-- The 'btvs' are a subset of 'qtvs'. They are the ones we can +-- instantiate to a boxy type variable, because they'll definitely be +-- filled in later. This isn't always the case; sometimes we have type +-- variables mentioned in the context of the type, but not the body; +-- f :: forall a b. C a b => a -> a +-- Then we may land up with an unconstrained 'b', so we want to +-- instantiate it to a monotype (non-boxy) type variable + +preSubType qtvs btvs qty expected_ty + = do { tys <- mapM inst_tv qtvs + ; traceTc (text "preSubType" <+> (ppr qtvs $$ ppr btvs $$ ppr qty $$ ppr expected_ty $$ ppr pre_subst $$ ppr tys)) + ; return tys } + where + pre_subst = boxySubMatchType (mkVarSet qtvs) qty expected_ty + inst_tv tv + | Just boxy_ty <- lookupTyVar pre_subst tv = return boxy_ty + | tv `elemVarSet` btvs = do { tv' <- tcInstBoxyTyVar tv + ; return (mkTyVarTy tv') } + | otherwise = do { tv' <- tcInstTyVar tv + ; return (mkTyVarTy tv') } + boxySubMatchType :: TcTyVarSet -> TcType -- The "template"; the tyvars are skolems -> BoxyRhoType -- Type to match (note a *Rho* type) -> TvSubst -- Substitution of the [TcTyVar] to BoxySigmaTypes +-- boxySubMatchType implements the Pre-subsumption judgement, in Fig 5 of the paper +-- "Boxy types: inference for higher rank types and impredicativity" + +boxySubMatchType tmpl_tvs tmpl_ty boxy_ty + = go tmpl_tvs tmpl_ty emptyVarSet boxy_ty + where + go t_tvs t_ty b_tvs b_ty + | Just t_ty' <- tcView t_ty = go t_tvs t_ty' b_tvs b_ty + | Just b_ty' <- tcView b_ty = go t_tvs t_ty b_tvs b_ty' + + go t_tvs (TyVarTy _) b_tvs b_ty = emptyTvSubst -- Rule S-ANY; no bindings + -- Rule S-ANY covers (a) type variables and (b) boxy types + -- in the template. Both look like a TyVarTy. + -- See Note [Sub-match] below + + go t_tvs t_ty b_tvs b_ty + | isSigmaTy t_ty, (tvs, _, t_tau) <- tcSplitSigmaTy t_ty + = go (t_tvs `delVarSetList` tvs) t_tau b_tvs b_ty -- Rule S-SPEC + -- Under a forall on the left, if there is shadowing, + -- do not bind! Hence the delVarSetList. + | isSigmaTy b_ty, (tvs, _, b_tau) <- tcSplitSigmaTy b_ty + = go t_tvs t_ty (extendVarSetList b_tvs tvs) b_tau -- Rule S-SKOL + -- Add to the variables we must not bind to + -- NB: it's *important* to discard the theta part. Otherwise + -- consider (forall a. Eq a => a -> b) ~<~ (Int -> Int -> Bool) + -- and end up with a completely bogus binding (b |-> Bool), by lining + -- up the (Eq a) with the Int, whereas it should be (b |-> (Int->Bool)). + -- This pre-subsumption stuff can return too few bindings, but it + -- must *never* return bogus info. + + go t_tvs (FunTy arg1 res1) b_tvs (FunTy arg2 res2) -- Rule S-FUN + = boxy_match t_tvs arg1 b_tvs arg2 (go t_tvs res1 b_tvs res2) + -- Match the args, and sub-match the results + + go t_tvs t_ty b_tvs b_ty = boxy_match t_tvs t_ty b_tvs b_ty emptyTvSubst + -- Otherwise defer to boxy matching + -- This covers TyConApp, AppTy, PredTy +\end{code} + +Note [Sub-match] +~~~~~~~~~~~~~~~~ +Consider this + head :: [a] -> a + |- head xs : +We will do a boxySubMatchType between a ~ +But we *don't* want to match [a |-> ] because + (a) The box should be filled in with a rho-type, but + but the returned substitution maps TyVars to boxy + *sigma* types + (b) In any case, the right final answer might be *either* + instantiate 'a' with a rho-type or a sigma type + head xs : Int vs head xs : forall b. b->b +So the matcher MUST NOT make a choice here. In general, we only +bind a template type variable in boxyMatchType, not in boxySubMatchType. + + +\begin{code} boxyMatchTypes :: TcTyVarSet -> [TcType] -- The "template"; the tyvars are skolems -> [BoxySigmaType] -- Type to match -> TvSubst -- Substitution of the [TcTyVar] to BoxySigmaTypes +-- boxyMatchTypes implements the Pre-matching judgement, in Fig 5 of the paper +-- "Boxy types: inference for higher rank types and impredicativity" + -- Find a *boxy* substitution that makes the template look as much -- like the BoxySigmaType as possible. -- It's always ok to return an empty substitution; @@ -352,57 +445,10 @@ boxyMatchTypes -- NB1: This is a pure, non-monadic function. -- It does no unification, and cannot fail -- --- Note [Matching kinds] --- The target type might legitimately not be a sub-kind of template. --- For example, suppose the target is simply a box with an OpenTypeKind, --- and the template is a type variable with LiftedTypeKind. --- Then it's ok (because the target type will later be refined). --- We simply don't bind the template type variable. --- --- It might also be that the kind mis-match is an error. For example, --- suppose we match the template (a -> Int) against (Int# -> Int), --- where the template type variable 'a' has LiftedTypeKind. This --- matching function does not fail; it simply doesn't bind the template. --- Later stuff will fail. --- -- Precondition: the arg lengths are equal --- Precondition: none of the template type variables appear in the [BoxySigmaType] --- Precondition: any nested quantifiers in either type differ from --- the template type variables passed as arguments +-- Precondition: none of the template type variables appear anywhere in the [BoxySigmaType] -- --- Note [Sub-match] --- ~~~~~~~~~~~~~~~~ --- Consider this --- head :: [a] -> a --- |- head xs : --- We will do a boxySubMatchType between a ~ --- But we *don't* want to match [a |-> ] because --- (a) The box should be filled in with a rho-type, but --- but the returned substitution maps TyVars to boxy *sigma* --- types --- (b) In any case, the right final answer might be *either* --- instantiate 'a' with a rho-type or a sigma type --- head xs : Int vs head xs : forall b. b->b --- So the matcher MUST NOT make a choice here. In general, we only --- bind a template type variable in boxyMatchType, not in boxySubMatchType. -boxySubMatchType tmpl_tvs tmpl_ty boxy_ty - = go tmpl_ty boxy_ty - where - go t_ty b_ty - | Just t_ty' <- tcView t_ty = go t_ty' b_ty - | Just b_ty' <- tcView b_ty = go t_ty b_ty' - - go (FunTy arg1 res1) (FunTy arg2 res2) - = do_match arg1 arg2 (go res1 res2) - -- Match the args, and sub-match the results - - go (TyVarTy _) b_ty = emptyTvSubst -- Do not bind! See Note [Sub-match] - - go t_ty b_ty = do_match t_ty b_ty emptyTvSubst -- Otherwise we are safe to bind - - do_match t_ty b_ty subst = boxy_match tmpl_tvs t_ty emptyVarSet b_ty subst - ------------ boxyMatchTypes tmpl_tvs tmpl_tys boxy_tys = ASSERT( length tmpl_tys == length boxy_tys ) @@ -412,8 +458,9 @@ boxyMatchTypes tmpl_tvs tmpl_tys boxy_tys boxy_match_s tmpl_tvs [] boxy_tvs [] subst = subst boxy_match_s tmpl_tvs (t_ty:t_tys) boxy_tvs (b_ty:b_tys) subst - = boxy_match_s tmpl_tvs t_tys boxy_tvs b_tys $ - boxy_match tmpl_tvs t_ty boxy_tvs b_ty subst + = boxy_match tmpl_tvs t_ty boxy_tvs b_ty $ + boxy_match_s tmpl_tvs t_tys boxy_tvs b_tys subst + ------------ boxy_match :: TcTyVarSet -> TcType -- Template @@ -434,8 +481,13 @@ boxy_match tmpl_tvs orig_tmpl_ty boxy_tvs orig_boxy_ty subst | Just t_ty' <- tcView t_ty = go t_ty' b_ty | Just b_ty' <- tcView b_ty = go t_ty b_ty' - go (ForAllTy _ ty1) (ForAllTy tv2 ty2) - = boxy_match tmpl_tvs ty1 (boxy_tvs `extendVarSet` tv2) ty2 subst + go ty1 ty2 -- C.f. the isSigmaTy case for boxySubMatchType + | isSigmaTy ty1 + , (tvs1, _, tau1) <- tcSplitSigmaTy ty1 + , (tvs2, _, tau2) <- tcSplitSigmaTy ty2 + , equalLength tvs1 tvs2 + = boxy_match (tmpl_tvs `delVarSetList` tvs1) tau1 + (boxy_tvs `extendVarSetList` tvs2) tau2 subst go (TyConApp tc1 tys1) (TyConApp tc2 tys2) | tc1 == tc2 = go_s tys1 tys2 @@ -452,14 +504,22 @@ boxy_match tmpl_tvs orig_tmpl_ty boxy_tvs orig_boxy_ty subst go (TyVarTy tv) b_ty | tv `elemVarSet` tmpl_tvs -- Template type variable in the template , not (intersectsVarSet boxy_tvs (tyVarsOfType orig_boxy_ty)) - , typeKind b_ty `isSubKind` tyVarKind tv + , typeKind b_ty `isSubKind` tyVarKind tv -- See Note [Matching kinds] = extendTvSubst subst tv boxy_ty' + | otherwise + = subst -- Ignore others where boxy_ty' = case lookupTyVar subst tv of Nothing -> orig_boxy_ty Just ty -> ty `boxyLub` orig_boxy_ty - go _ _ = subst -- Always safe + go _ _ = emptyTvSubst -- It's important to *fail* by returning the empty substitution + -- Example: Tree a ~ Maybe Int + -- We do not want to bind (a |-> Int) in pre-matching, because that can give very + -- misleading error messages. An even more confusing case is + -- a -> b ~ Maybe Int + -- Then we do not want to bind (b |-> Int)! It's always safe to discard bindings + -- from this pre-matching phase. -------- go_s tys1 tys2 = boxy_match_s tmpl_tvs tys1 boxy_tvs tys2 subst @@ -489,6 +549,19 @@ boxyLub orig_ty1 orig_ty2 go ty1 ty2 = orig_ty1 -- Default \end{code} +Note [Matching kinds] +~~~~~~~~~~~~~~~~~~~~~ +The target type might legitimately not be a sub-kind of template. +For example, suppose the target is simply a box with an OpenTypeKind, +and the template is a type variable with LiftedTypeKind. +Then it's ok (because the target type will later be refined). +We simply don't bind the template type variable. + +It might also be that the kind mis-match is an error. For example, +suppose we match the template (a -> Int) against (Int# -> Int), +where the template type variable 'a' has LiftedTypeKind. This +matching function does not fail; it simply doesn't bind the template. +Later stuff will fail. %************************************************************************ %* * @@ -563,8 +636,8 @@ tc_sub outer act_sty act_ty exp_sty exp_ty ; return (gen_fn <.> co_fn) } where act_tvs = tyVarsOfType act_ty - -- It's really important to check for escape wrt the free vars of - -- both expected_ty *and* actual_ty + -- It's really important to check for escape wrt + -- the free vars of both expected_ty *and* actual_ty ----------------------------------- -- Specialisation case (rule ASPEC): @@ -573,13 +646,31 @@ tc_sub outer act_sty act_ty exp_sty exp_ty -- co_fn e = e Int dOrdInt tc_sub outer act_sty actual_ty exp_sty expected_ty +-- Implements the new SPEC rule in the Appendix of the paper +-- "Boxy types: inference for higher rank types and impredicativity" +-- (This appendix isn't in the published version.) +-- The idea is to *first* do pre-subsumption, and then full subsumption +-- Example: forall a. a->a <= Int -> (forall b. Int) +-- Pre-subsumpion finds a|->Int, and that works fine, whereas +-- just running full subsumption would fail. | isSigmaTy actual_ty - = do { (tyvars, theta, tau) <- tcInstBoxy actual_ty - ; dicts <- newDicts InstSigOrigin theta + = do { -- Perform pre-subsumption, and instantiate + -- the type with info from the pre-subsumption; + -- boxy tyvars if pre-subsumption gives no info + let (tyvars, theta, tau) = tcSplitSigmaTy actual_ty + tau_tvs = exactTyVarsOfType tau + ; inst_tys <- preSubType tyvars tau_tvs tau expected_ty + ; let subst' = zipOpenTvSubst tyvars inst_tys + tau' = substTy subst' tau + + -- Perform a full subsumption check + ; co_fn <- tc_sub False tau' tau' exp_sty expected_ty + + -- Deal with the dictionaries + ; dicts <- newDicts InstSigOrigin (substTheta subst' theta) ; extendLIEs dicts - ; let inst_fn = CoApps (CoTyApps CoHole (mkTyVarTys tyvars)) + ; let inst_fn = CoApps (CoTyApps CoHole inst_tys) (map instToId dicts) - ; co_fn <- tc_sub False tau tau exp_sty expected_ty ; return (co_fn <.> inst_fn) } ----------------------------------- @@ -1288,7 +1379,7 @@ unBox :: BoxyType -> TcM TcType -- |- s' ~ box(s) -- with input s', and result s -- --- It remove all boxes from the input type, returning a non-boxy type. +-- It removes all boxes from the input type, returning a non-boxy type. -- A filled box in the type can only contain a monotype; unBox fails if not -- The type can have empty boxes, which unBox fills with a monotype --