X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypecheck%2FTcTyFuns.lhs;h=1e654710437f123d4a707e8c47a5c2ce247454c8;hb=5479f1a02fae9141c02a7873c57af80323b0fc0d;hp=bed053d2d654e4f1ec1949f47f6ba96cc55d8040;hpb=654d07dd0fb679d014ac363e13c004b0086d0d6e;p=ghc-hetmet.git diff --git a/compiler/typecheck/TcTyFuns.lhs b/compiler/typecheck/TcTyFuns.lhs index bed053d..1e65471 100644 --- a/compiler/typecheck/TcTyFuns.lhs +++ b/compiler/typecheck/TcTyFuns.lhs @@ -37,7 +37,9 @@ import Name import Bag import Outputable import SrcLoc ( Located(..) ) +import Util ( debugIsOn ) import Maybes +import MonadUtils import FastString -- standard @@ -69,21 +71,16 @@ tcUnfoldSynFamInst (TyConApp tycon tys) | not (isOpenSynTyCon tycon) -- unfold *only* _synonym_ family instances = return Nothing | otherwise - = do { -- we only use the indexing arguments for matching, - -- not the additional ones - ; maybeFamInst <- tcLookupFamInst tycon idxTys + = do { -- The TyCon might be over-saturated, but that's ok for tcLookupFamInst + ; maybeFamInst <- tcLookupFamInst tycon tys ; case maybeFamInst of Nothing -> return Nothing - Just (rep_tc, rep_tys) -> return $ Just (mkTyConApp rep_tc tys', - mkTyConApp coe_tc tys') + Just (rep_tc, rep_tys) -> return $ Just (mkTyConApp rep_tc rep_tys, + mkTyConApp coe_tc rep_tys) where - tys' = rep_tys ++ restTys coe_tc = expectJust "TcTyFuns.tcUnfoldSynFamInst" (tyConFamilyCoercion_maybe rep_tc) } - where - n = tyConArity tycon - (idxTys, restTys) = splitAt n tys tcUnfoldSynFamInst _other = return Nothing \end{code} @@ -231,9 +228,6 @@ tcReduceEqs locals wanteds We maintain normalised equalities together with the skolems introduced as intermediates during flattening of equalities as well as -!!!TODO: We probably now can do without the skolem set. It's not used during -finalisation in the current code. - \begin{code} -- |Configuration of normalised equalities used during solving. -- @@ -286,7 +280,15 @@ no further propoagation is possible. -- normaliseEqs :: [Inst] -> TcM EqConfig normaliseEqs eqs - = do { ASSERTM2( allM isValidWantedEqInst eqs, ppr eqs ) + = do { if debugIsOn then do { all_unsolved <- allM wantedEqInstIsUnsolved eqs + ; let msg = ptext (sLit "(This warning is harmless; for Simon & Manuel)") + ; WARN( not all_unsolved, msg $$ ppr eqs ) return () } + else return () + -- This is just a warning (not an error) because a current + -- harmless bug means that we sometimes solve the same + -- equality more than once It'll go away with the new + -- solver. See Trac #2999 for example + ; traceTc $ ptext (sLit "Entering normaliseEqs") ; (eqss, skolemss) <- mapAndUnzipM normEqInst eqs @@ -303,10 +305,15 @@ normaliseEqs eqs -- normaliseDicts :: Bool -> [Inst] -> TcM EqConfig normaliseDicts isWanted insts - = do { traceTc $ ptext (sLit "Entering normaliseDicts") <+> - ptext (if isWanted then sLit "[Wanted]" else sLit "[Local]") + = do { traceTc $ hang (ptext (sLit "Entering normaliseDicts") <+> + ptext (if isWanted then sLit "[Wanted] for" + else sLit "[Local] for")) + 4 (ppr insts) ; (insts', eqss, bindss, skolemss) <- mapAndUnzip4M (normDict isWanted) insts + + ; traceTc $ hang (ptext (sLit "normaliseDicts returns")) + 4 (ppr insts' $$ ppr eqss) ; return $ emptyEqConfig { eqs = concat eqss , locals = if isWanted then [] else insts' , wanteds = if isWanted then insts' else [] @@ -347,7 +354,7 @@ finaliseEqsAndDicts (EqConfig { eqs = eqs -- Assert that all cotvs of wanted equalities are still unfilled, and -- zonk all final insts, to make any improvement visible - ; ASSERTM2( allM isValidWantedEqInst eqs'', ppr eqs'' ) + ; ASSERTM2( allM wantedEqInstIsUnsolved eqs'', ppr eqs'' ) ; zonked_locals <- zonkInsts locals' ; zonked_wanteds <- zonkInsts (eqs'' ++ wanteds') ; return (zonked_locals, zonked_wanteds, final_binds, improved) @@ -363,7 +370,7 @@ finaliseEqsAndDicts (EqConfig { eqs = eqs A normal equality is a properly oriented equality with associated coercion that contains at most one family equality (in its left-hand side) is oriented -such that it may be used as a reqrite rule. It has one of the following two +such that it may be used as a rewrite rule. It has one of the following two forms: (1) co :: F t1..tn ~ t (family equalities) @@ -376,11 +383,10 @@ Variable equalities fall again in two classes: The types t, t1, ..., tn may not contain any occurrences of synonym families. Moreover, in Forms (2) & (3), the left-hand side may not occur in -the right-hand side, and the relation x > y is an arbitrary, but total order -on type variables - -!!!TODO: We may need to keep track of swapping for error messages (and to -re-orient on finilisation). +the right-hand side, and the relation x > y is an (nearly) arbitrary, but +total order on type variables. The only restriction that we impose on that +order is that for x > y, we are happy to instantiate x with y taking into +account kinds, signature skolems etc (cf, TcUnify.uUnfilledVars). \begin{code} data RewriteInst @@ -593,15 +599,14 @@ checkOrientation ty1 ty2 co inst ; return [] } - -- two tvs, left greater => unchanged + -- two tvs (distinct tvs, due to previous equation) go ty1@(TyVarTy tv1) ty2@(TyVarTy tv2) - | tv1 > tv2 - = mkRewriteVar False tv1 ty2 co - - -- two tvs, right greater => swap - | otherwise - = do { co' <- mkSymEqInstCo co (ty2, ty1) - ; mkRewriteVar True tv2 ty1 co' + = do { isBigger <- tv1 `tvIsBigger` tv2 + ; if isBigger -- left greater + then mkRewriteVar False tv1 ty2 co -- => unchanged + else do { co' <- mkSymEqInstCo co (ty2, ty1) -- right greater + ; mkRewriteVar True tv2 ty1 co' -- => swap + } } -- only lhs is a tv => unchanged @@ -620,6 +625,26 @@ checkOrientation ty1 ty2 co inst ; mkRewriteVar True tv2 ty1 co' } + -- data type constructor application => decompose + -- NB: Special cased for efficiency - could be handled as type application + go (TyConApp con1 args1) (TyConApp con2 args2) + | con1 == con2 + && not (isOpenSynTyCon con1) -- don't match family synonym apps + = do { co_args <- mkTyConEqInstCo co con1 (zip args1 args2) + ; eqss <- zipWith3M (\ty1 ty2 co -> checkOrientation ty1 ty2 co inst) + args1 args2 co_args + ; return $ concat eqss + } + + -- function type => decompose + -- NB: Special cased for efficiency - could be handled as type application + go (FunTy ty1_l ty1_r) (FunTy ty2_l ty2_r) + = do { (co_l, co_r) <- mkFunEqInstCo co (ty1_l, ty2_l) (ty1_r, ty2_r) + ; eqs_l <- checkOrientation ty1_l ty2_l co_l inst + ; eqs_r <- checkOrientation ty1_r ty2_r co_r inst + ; return $ eqs_l ++ eqs_r + } + -- type applications => decompose go ty1 ty2 | Just (ty1_l, ty1_r) <- repSplitAppTy_maybe ty1 -- won't split fam apps @@ -629,8 +654,6 @@ checkOrientation ty1 ty2 co inst ; eqs_r <- checkOrientation ty1_r ty2_r co_r inst ; return $ eqs_l ++ eqs_r } --- !!!TODO: would be more efficient to handle the FunApp and the data --- constructor application explicitly. -- inconsistency => type error go ty1 ty2 @@ -646,6 +669,55 @@ checkOrientation ty1 ty2 co inst , rwi_swapped = swapped }] + -- if tv1 `tvIsBigger` tv2, we make a rewrite rule tv1 ~> tv2 + tvIsBigger :: TcTyVar -> TcTyVar -> TcM Bool + tvIsBigger tv1 tv2 + = isBigger tv1 (tcTyVarDetails tv1) tv2 (tcTyVarDetails tv2) + where + isBigger tv1 (SkolemTv _) tv2 (SkolemTv _) + = return $ tv1 > tv2 + isBigger _ (MetaTv _ _) _ (SkolemTv _) + = return True + isBigger _ (SkolemTv _) _ (MetaTv _ _) + = return False + isBigger tv1 (MetaTv info1 _) tv2 (MetaTv info2 _) + -- meta variable meets meta variable + -- => be clever about which of the two to update + -- (from TcUnify.uUnfilledVars minus boxy stuff) + = case (info1, info2) of + -- Avoid SigTvs if poss + (SigTv _, SigTv _) -> return $ tv1 > tv2 + (SigTv _, _ ) | k1_sub_k2 -> return False + (_, SigTv _) | k2_sub_k1 -> return True + + (_, _) + | k1_sub_k2 && + k2_sub_k1 + -> case (nicer_to_update tv1, nicer_to_update tv2) of + (True, False) -> return True + (False, True) -> return False + _ -> return $ tv1 > tv2 + | k1_sub_k2 -> return False + | k2_sub_k1 -> return True + | otherwise -> kind_err >> return True + -- Update the variable with least kind info + -- See notes on type inference in Kind.lhs + -- The "nicer to" part only applies if the two kinds are the same, + -- so we can choose which to do. + where + kind_err = addErrCtxtM (unifyKindCtxt False tv1 (mkTyVarTy tv2)) $ + unifyKindMisMatch k1 k2 + + k1 = tyVarKind tv1 + k2 = tyVarKind tv2 + k1_sub_k2 = k1 `isSubKind` k2 + k2_sub_k1 = k2 `isSubKind` k1 + + nicer_to_update tv = isSystemName (Var.varName tv) + -- Try to update sys-y type variables in preference to ones + -- gotten (say) by instantiating a polymorphic function with + -- a user-written type sig + flattenType :: Inst -- context to get location & name -> Type -- the type to flatten -> TcM (Type, -- the flattened type @@ -809,17 +881,23 @@ mkDictBind dict isWanted rewriteCo pred where loc = tci_loc dict --- gamma :: Fam args ~ alpha --- => alpha :: Fam args ~ alpha, with alpha := Fam args +-- gamma ::^l Fam args ~ alpha +-- => gamma ::^w Fam args ~ alpha, with alpha := Fam args & gamma := Fam args -- (the update of alpha will not be apparent during propagation, as we -- never follow the indirections of meta variables; it will be revealed -- when the equality is zonked) +-- +-- NB: It's crucial to update *both* alpha and gamma, as gamma may already +-- have escaped into some other coercions during normalisation. +-- wantedToLocal :: RewriteInst -> TcM RewriteInst wantedToLocal eq@(RewriteFam {rwi_fam = fam, rwi_args = args, - rwi_right = alphaTy@(TyVarTy alpha)}) + rwi_right = TyVarTy alpha, + rwi_co = Left gamma}) = do { writeMetaTyVar alpha (mkTyConApp fam args) - ; return $ eq {rwi_co = mkGivenCo alphaTy} + ; writeMetaTyVar gamma (mkTyConApp fam args) + ; return $ eq {rwi_co = mkGivenCo $ mkTyVarTy gamma} } wantedToLocal _ = panic "TcTyFuns.wantedToLocal" \end{code} @@ -873,8 +951,11 @@ mapSubstRules eq eqs } where substRules eq1 eq2 - = do { -- try the SubstFam rule - optEqs <- applySubstFam eq1 eq2 + = do {traceTc $ hang (ptext (sLit "Trying subst rules with")) + 4 (ppr eq1 $$ ppr eq2) + + -- try the SubstFam rule + ; optEqs <- applySubstFam eq1 eq2 ; case optEqs of Just (eqs, skolems) -> return (eqs, [], skolems) Nothing -> do @@ -942,20 +1023,26 @@ applySubstFam :: RewriteInst -> TcM (Maybe ([RewriteInst], TyVarSet)) applySubstFam eq1@(RewriteFam {rwi_fam = fam1, rwi_args = args1}) eq2@(RewriteFam {rwi_fam = fam2, rwi_args = args2}) + + -- rule matches => rewrite | fam1 == fam2 && tcEqTypes args1 args2 && (isWantedRewriteInst eq2 || not (isWantedRewriteInst eq1)) --- !!!TODO: tcEqTypes is insufficient as it does not look through type synonyms --- !!!Check whether anything breaks by making tcEqTypes look through synonyms. --- !!!Should be ok and we don't want three type equalities. = do { co2' <- mkRightTransEqInstCo co2 co1 (lhs, rhs) ; eq2' <- deriveEqInst eq2 lhs rhs co2' ; liftM Just $ normEqInst eq2' } + + -- rule would match with eq1 and eq2 swapped => put eq2 into todo list + | fam1 == fam2 && tcEqTypes args1 args2 && + (isWantedRewriteInst eq1 || not (isWantedRewriteInst eq2)) + = return $ Just ([eq2], emptyVarSet) + where lhs = rwi_right eq1 rhs = rwi_right eq2 co1 = eqInstCoType (rwi_co eq1) co2 = rwi_co eq2 + applySubstFam _ _ = return Nothing \end{code} @@ -977,17 +1064,26 @@ applySubstVarVar :: RewriteInst -> TcM (Maybe ([RewriteInst], TyVarSet)) applySubstVarVar eq1@(RewriteVar {rwi_var = tv1}) eq2@(RewriteVar {rwi_var = tv2}) + + -- rule matches => rewrite | tv1 == tv2 && (isWantedRewriteInst eq2 || not (isWantedRewriteInst eq1)) = do { co2' <- mkRightTransEqInstCo co2 co1 (lhs, rhs) ; eq2' <- deriveEqInst eq2 lhs rhs co2' ; liftM Just $ normEqInst eq2' } + + -- rule would match with eq1 and eq2 swapped => put eq2 into todo list + | tv1 == tv2 && + (isWantedRewriteInst eq1 || not (isWantedRewriteInst eq2)) + = return $ Just ([eq2], emptyVarSet) + where lhs = rwi_right eq1 rhs = rwi_right eq2 co1 = eqInstCoType (rwi_co eq1) co2 = rwi_co eq2 + applySubstVarVar _ _ = return Nothing \end{code} @@ -1005,6 +1101,8 @@ co2' is returned. (The equality co1 is not returned as it remain unaltered.) \begin{code} applySubstVarFam :: RewriteInst -> RewriteInst -> TcM (Maybe RewriteInst) + + -- rule matches => rewrite applySubstVarFam eq1@(RewriteVar {rwi_var = tv1}) eq2@(RewriteFam {rwi_fam = fam2, rwi_args = args2}) | tv1 `elemVarSet` tyVarsOfTypes args2 @@ -1019,6 +1117,13 @@ applySubstVarFam eq1@(RewriteVar {rwi_var = tv1}) rhs2 = rwi_right eq2 co1 = eqInstCoType (rwi_co eq1) co2 = rwi_co eq2 + + -- rule would match with eq1 and eq2 swapped => put eq2 into todo list +applySubstVarFam (RewriteFam {rwi_args = args1}) + eq2@(RewriteVar {rwi_var = tv2}) + | tv2 `elemVarSet` tyVarsOfTypes args1 + = return $ Just eq2 + applySubstVarFam _ _ = return Nothing \end{code} @@ -1153,44 +1258,72 @@ Return all remaining wanted equalities. The Boolean result component is True if at least one instantiation of a flexible that is *not* a skolem from flattening was performed. +We need to instantiate all flexibles that arose as skolems during flattening +of wanteds before we instantiate any other flexibles. Consider F delta ~ +alpha, F alpha ~ delta, where alpha is a skolem and delta a free flexible. We +need to produce F (F delta) ~ delta (and not F (F alpha) ~ alpha). Otherwise, +we may wrongly claim to having performed an improvement, which can lead to +non-termination of the combined class-family solver. + \begin{code} instantiateAndExtract :: [RewriteInst] -> Bool -> TyVarSet -> TcM ([Inst], Bool) instantiateAndExtract eqs localsEmpty skolems - = do { results <- mapM inst wanteds - ; let residuals = [eq | Left eq <- results] - only_skolems = and [tv `elemVarSet` skolems | Right tv <- results] + = do { traceTc $ hang (ptext (sLit "instantiateAndExtract:")) + 4 (ppr eqs $$ ppr skolems) + -- start by *only* instantiating skolem flexibles from flattening + ; unflat_wanteds <- liftM catMaybes $ + mapM (inst (`elemVarSet` skolems)) wanteds + -- only afterwards instantiate free flexibles + ; residuals <- liftM catMaybes $ mapM (inst (const True)) unflat_wanteds + ; let improvement = length residuals < length unflat_wanteds ; residuals' <- mapM rewriteInstToInst residuals - ; return (residuals', not only_skolems) + ; return (residuals', improvement) } where wanteds = filter (isWantedCo . rwi_co) eqs checkingMode = length eqs > length wanteds || not localsEmpty -- no local equalities or dicts => checking mode - inst eq@(RewriteVar {rwi_var = tv1, rwi_right = ty2, rwi_co = co}) - - -- co :: alpha ~ t - | isMetaTyVar tv1 - = doInst (rwi_swapped eq) tv1 ty2 co eq - - -- co :: a ~ alpha - | Just tv2 <- tcGetTyVar_maybe ty2 - , isMetaTyVar tv2 - = doInst (not $ rwi_swapped eq) tv2 (mkTyVarTy tv1) co eq + -- co :: alpha ~ t or co :: a ~ alpha + inst mayInst eq@(RewriteVar {rwi_var = tv1, rwi_right = ty2, rwi_co = co}) + = do { flexi_tv1 <- isFlexible mayInst tv1 + ; maybe_flexi_tv2 <- isFlexibleTy mayInst ty2 + ; case (flexi_tv1, maybe_flexi_tv2) of + (True, _) + -> -- co :: alpha ~ t + doInst (rwi_swapped eq) tv1 ty2 co eq + (False, Just tv2) + -> -- co :: a ~ alpha + doInst (not $ rwi_swapped eq) tv2 (mkTyVarTy tv1) co eq + _ -> return $ Just eq + } -- co :: F args ~ alpha, and we are in checking mode (ie, no locals) - inst eq@(RewriteFam {rwi_fam = fam, rwi_args = args, rwi_right = ty2, - rwi_co = co}) + inst mayInst eq@(RewriteFam {rwi_fam = fam, rwi_args = args, + rwi_right = ty2, rwi_co = co}) | Just tv2 <- tcGetTyVar_maybe ty2 , isMetaTyVar tv2 - , checkingMode || tv2 `elemVarSet` skolems - -- !!!TODO: this is too liberal, even if tv2 is in + , mayInst tv2 && (checkingMode || tv2 `elemVarSet` skolems) + -- !!!FIXME: this is too liberal, even if tv2 is in -- skolems we shouldn't instantiate if tvs occurs -- in other equalities that may propagate it into the -- environment = doInst (not $ rwi_swapped eq) tv2 (mkTyConApp fam args) co eq - inst eq = return $ Left eq + inst _mayInst eq = return $ Just eq + + -- tv is a meta var and not filled + isFlexible mayInst tv + | isMetaTyVar tv && mayInst tv = liftM isFlexi $ readMetaTyVar tv + | otherwise = return False + + -- type is a tv that is a meta var and not filled + isFlexibleTy mayInst ty + | Just tv <- tcGetTyVar_maybe ty = do {flexi <- isFlexible mayInst tv + ; if flexi then return $ Just tv + else return Nothing + } + | otherwise = return Nothing doInst _swapped _tv _ty (Right ty) _eq = pprPanic "TcTyFuns.doInst: local eq: " (ppr ty) @@ -1199,6 +1332,20 @@ instantiateAndExtract eqs localsEmpty skolems ; uMeta swapped tv lookupTV ty cotv } where + -- Try to fill in a meta variable. There is *no* need to consider + -- reorienting the underlying equality; `checkOrientation' makes sure + -- that we get variable-variable equalities only in the appropriate + -- orientation. + -- + uMeta :: Bool -- is this a swapped equality? + -> TcTyVar -- tyvar to instantiate + -> LookupTyVarResult -- lookup result of that tyvar + -> TcType -- to to instantiate tyvar with + -> TcTyVar -- coercion tyvar of current equality + -> TcM (Maybe RewriteInst) -- returns the original equality if + -- the tyvar could not be instantiated, + -- and hence, the equality must be kept + -- meta variable has been filled already -- => keep the equality uMeta _swapped tv (IndirectTv fill_ty) ty _cotv @@ -1206,103 +1353,55 @@ instantiateAndExtract eqs localsEmpty skolems ptext (sLit "flexible") <+> ppr tv <+> ptext (sLit "already filled with") <+> ppr fill_ty <+> ptext (sLit "meant to fill with") <+> ppr ty - ; return $ Left eq + ; return $ Just eq } - -- type variable meets type variable - -- => check that tv2 hasn't been updated yet and choose which to update - uMeta swapped tv1 (DoneTv details1) (TyVarTy tv2) cotv - | tv1 == tv2 - = panic "TcTyFuns.uMeta: normalisation shouldn't allow x ~ x" + -- signature skolem + -- => cannot update (retain the equality)! + uMeta _swapped _tv (DoneTv (MetaTv (SigTv _) _)) _non_tv_ty _cotv + = return $ Just eq - | otherwise + -- type variable meets type variable + -- => `checkOrientation' already ensures that it is fine to instantiate + -- tv1 with tv2, but chase tv2's instantiations if necessary + -- NB: tv's instantiations won't alter the orientation in which we + -- want to instantiate as they either constitute a family + -- application or are themselves due to a properly oriented + -- instantiation + uMeta swapped tv1 details1@(DoneTv (MetaTv _ ref)) ty@(TyVarTy tv2) cotv = do { lookupTV2 <- lookupTcTyVar tv2 ; case lookupTV2 of - IndirectTv ty -> - uMeta swapped tv1 (DoneTv details1) ty cotv - DoneTv details2 -> - uMetaVar swapped tv1 details1 tv2 details2 cotv + IndirectTv ty' -> + uMeta swapped tv1 details1 ty' cotv + DoneTv _ -> + uMetaInst swapped tv1 ref ty cotv } - ------ Beyond this point we know that ty2 is not a type variable - - -- signature skolem meets non-variable type - -- => cannot update (retain the equality)! - uMeta _swapped _tv (DoneTv (MetaTv (SigTv _) _)) _non_tv_ty _cotv - = return $ Left eq - -- updatable meta variable meets non-variable type -- => occurs check, monotype check, and kinds match check, then update uMeta swapped tv (DoneTv (MetaTv _ ref)) non_tv_ty cotv + = uMetaInst swapped tv ref non_tv_ty cotv + + uMeta _ _ _ _ _ = panic "TcTyFuns.uMeta" + + -- We know `tv' can be instantiated; check that `ty' is alright for + -- instantiating `tv' with and then do it; otherwise, return the original + -- equality. + uMetaInst swapped tv ref ty cotv = do { -- occurs + monotype check - ; mb_ty' <- checkTauTvUpdate tv non_tv_ty + ; mb_ty' <- checkTauTvUpdate tv ty ; case mb_ty' of Nothing -> - -- normalisation shouldn't leave families in non_tv_ty - panic "TcTyFuns.uMeta: unexpected synonym family" + -- there may be a family in non_tv_ty due to an unzonked, + -- but updated skolem for a local equality + return $ Just eq Just ty' -> do { checkUpdateMeta swapped tv ref ty' -- update meta var ; writeMetaTyVar cotv ty' -- update co var - ; return $ Right tv + ; return Nothing } } - - uMeta _ _ _ _ _ = panic "TcTyFuns.uMeta" - - -- uMetaVar: unify two type variables - -- meta variable meets skolem - -- => just update - uMetaVar swapped tv1 (MetaTv _ ref) tv2 (SkolemTv _) cotv - = do { checkUpdateMeta swapped tv1 ref (mkTyVarTy tv2) - ; writeMetaTyVar cotv (mkTyVarTy tv2) - ; return $ Right tv1 - } - - -- meta variable meets meta variable - -- => be clever about which of the two to update - -- (from TcUnify.uUnfilledVars minus boxy stuff) - uMetaVar swapped tv1 (MetaTv info1 ref1) tv2 (MetaTv info2 ref2) cotv - = do { tv <- case (info1, info2) of - -- Avoid SigTvs if poss - (SigTv _, _ ) | k1_sub_k2 -> update_tv2 - (_, SigTv _) | k2_sub_k1 -> update_tv1 - - (_, _) | k1_sub_k2 -> if k2_sub_k1 && - nicer_to_update_tv1 - then update_tv1 -- Same kinds - else update_tv2 - | k2_sub_k1 -> update_tv1 - | otherwise -> kind_err >> return tv1 - -- Update the variable with least kind info - -- See notes on type inference in Kind.lhs - -- The "nicer to" part only applies if the two kinds are the same, - -- so we can choose which to do. - - ; writeMetaTyVar cotv (mkTyVarTy tv2) - ; return $ Right tv - } - where - -- Kinds should be guaranteed ok at this point - update_tv1 = updateMeta tv1 ref1 (mkTyVarTy tv2) - >> return tv1 - update_tv2 = updateMeta tv2 ref2 (mkTyVarTy tv1) - >> return tv2 - - kind_err = addErrCtxtM (unifyKindCtxt swapped tv1 (mkTyVarTy tv2)) $ - unifyKindMisMatch k1 k2 - - k1 = tyVarKind tv1 - k2 = tyVarKind tv2 - k1_sub_k2 = k1 `isSubKind` k2 - k2_sub_k1 = k2 `isSubKind` k1 - - nicer_to_update_tv1 = isSystemName (Var.varName tv1) - -- Try to update sys-y type variables in preference to ones - -- gotten (say) by instantiating a polymorphic function with - -- a user-written type sig - - uMetaVar _ _ _ _ _ _ = panic "uMetaVar" \end{code}