Simon Peyton Jones pushed to branch wip/T26543b at Glasgow Haskell Compiler / GHC Commits: 4d072e5d by Simon Peyton Jones at 2026-09-17T14:31:51+01:00 QuickLook only unifies instantiation variables ...and improvements to simpleUnifyCheck - - - - - 2 changed files: - compiler/GHC/Tc/Gen/App.hs - compiler/GHC/Tc/Utils/Unify.hs Changes: ===================================== compiler/GHC/Tc/Gen/App.hs ===================================== @@ -37,6 +37,7 @@ import GHC.Core.ConLike ( ConLike(..) ) import GHC.Core.DataCon ( dataConConcreteTyVars, isNewDataCon, dataConOrigArgTys ) import GHC.Core.TyCon import GHC.Core.TyCo.Rep +import GHC.Core.TyCo.FVs import GHC.Core.TyCo.Ppr import GHC.Core.TyCo.Subst ( substTyWithInScope ) import GHC.Core.Type @@ -2196,9 +2197,9 @@ qlUnify ty1 ty2 -- with qualified types). go' (TyVarTy tv) ty2 - | isMetaTyVar tv = go_kappa tv ty2 + | isQLInstTyVar tv = go_kappa tv ty2 go' ty1 (TyVarTy tv) - | isMetaTyVar tv = go_kappa tv ty1 + | isQLInstTyVar tv = go_kappa tv ty1 go' (CastTy ty1 _) ty2 = go ty1 ty2 go' ty1 (CastTy ty2 _) = go ty1 ty2 @@ -2240,37 +2241,18 @@ qlUnify ty1 ty2 ; go_flexi kappa ty2 } } ---------------- - -- Swap (kappa1[conc] ~ kappa2[tau]) - -- otherwise we'll fail to unify and emit a coercion. - -- Just an optimisation: emitting a coercion is fine - go_flexi kappa (TyVarTy tv2) - | lhsPriority tv2 > lhsPriority kappa - = go_flexi1 tv2 (TyVarTy kappa) - go_flexi kappa ty2 - = go_flexi1 kappa ty2 - - go_flexi1 kappa ty2 -- ty2 is zonked - = do { cur_lvl <- getTcLevel - -- See Note [Unification preconditions], (UNTOUCHABLE) wrinkles - -- Here we are in the TcM monad, which does not track enclosing - -- Given equalities; so for quick-look unification we conservatively - -- treat /any/ level outside this one as untouchable. Hence cur_lvl. - ; traceTc "go_flexi1" (ppr kappa $$ ppr ty2) - ; case simpleUnifyCheck UC_QuickLook cur_lvl kappa ty2 of - -- qlUnify depends, regrettably delicately, on the exact choices made - -- by `simpleUnifyCheck`. See (SUC1) in - -- Note [simpleUnifyCheck] in GHC.Tc.Utils.Unify - SUC_CanUnify -> - do { co <- unifyKind (Just (TypeThing ty2)) ty2_kind kappa_kind - -- unifyKind: see (UQL2) in Note [QuickLook unification] - -- and (MIV2) in Note [Monomorphise instantiation variables] - ; let ty2' = mkCastTy ty2 co - ; traceTc "qlUnify:update" $ - ppr kappa <+> text ":=" <+> ppr ty2 - ; liftZonkM $ writeMetaTyVar kappa ty2' } - suc -> do { traceTc "go_flexi2" (ppr suc $$ ppr kappa $$ ppr ty2) - ; return () } -- e.g. occurs-check or forall-bound variable - } + go_flexi kappa ty2 -- ty2 is zonked + | anyFreeVarsOfType (== kappa) ty2 + = return () -- Occurs check + | otherwise + = do { co <- unifyKind (Just (TypeThing ty2)) ty2_kind kappa_kind + -- unifyKind: see (UQL2) in Note [QuickLook unification] + -- and (MIV2) in Note [Monomorphise instantiation variables] + ; let ty2' = mkCastTy ty2 co + ; traceTc "qlUnify:update" $ + ppr kappa <+> text ":=" <+> ppr ty2 + ; liftZonkM $ writeMetaTyVar kappa ty2' + ; return () } where kappa_kind = tyVarKind kappa ty2_kind = typeKind ty2 ===================================== compiler/GHC/Tc/Utils/Unify.hs ===================================== @@ -3702,7 +3702,7 @@ simpleUnifyCheck caller given_eq_lvl lhs_tv rhs {- Note [simpleUnifyCheck] ~~~~~~~~~~~~~~~~~~~~~~~~~~ -The function `simpleUnifyCheck` is asimple, /fast/ check for unifying (tv ~ rhs). +The function `simpleUnifyCheck` is a simple, /fast/ check for unifying (tv ~ rhs). It can return a definite decision (SUC_CannotUnify of SUC_CanUnify), or uncertainty (SUC_NotSure). In the latter case we will later use `checkTyEqRhs` to resolve. In particular, `simpleUnifyCheck`: View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/4d072e5df8d1da99a40d8d68af546ab8... -- View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/4d072e5df8d1da99a40d8d68af546ab8... You're receiving this email because of your account on gitlab.haskell.org. Manage all notifications: https://gitlab.haskell.org/-/profile/notifications | Help: https://gitlab.haskell.org/help