diff options
Diffstat (limited to 'compiler/GHC/Tc/Utils/Instantiate.hs')
| -rw-r--r-- | compiler/GHC/Tc/Utils/Instantiate.hs | 26 |
1 files changed, 20 insertions, 6 deletions
diff --git a/compiler/GHC/Tc/Utils/Instantiate.hs b/compiler/GHC/Tc/Utils/Instantiate.hs index 0b6b519028..b8249bc363 100644 --- a/compiler/GHC/Tc/Utils/Instantiate.hs +++ b/compiler/GHC/Tc/Utils/Instantiate.hs @@ -1,4 +1,4 @@ -{-# LANGUAGE FlexibleContexts #-} +{-# LANGUAGE FlexibleContexts, RecursiveDo #-} {-# LANGUAGE DisambiguateRecordFields #-} {-# OPTIONS_GHC -Wno-incomplete-uni-patterns #-} @@ -446,12 +446,24 @@ tcInstTypeBndrs poly_ty ; return (subst', Bndr tv' spec) } -------------------------- -tcSkolDFunType :: SkolemInfo -> DFunId -> TcM ([TcTyVar], TcThetaType, TcType) +tcSkolDFunType :: Type -> TcM (SkolemInfoAnon, [TcTyVar], TcThetaType, Class, [TcType]) -- Instantiate a type signature with skolem constants. -- This freshens the names, but no need to do so -tcSkolDFunType skol_info dfun - = do { (tv_prs, theta, tau) <- tcInstType (tcInstSuperSkolTyVars skol_info) dfun - ; return (map snd tv_prs, theta, tau) } +tcSkolDFunType dfun_ty + = do { let (tvs, theta, cls, tys) = tcSplitDFunTy dfun_ty + + -- rec {..}: see Note [Keeping SkolemInfo inside a SkolemTv] + -- in GHC.Tc.Utils.TcType + ; rec { skol_info <- mkSkolemInfo skol_info_anon + ; (subst, inst_tvs) <- tcInstSuperSkolTyVars skol_info tvs + -- We instantiate the dfun_tyd with superSkolems. + -- See Note [Subtle interaction of recursion and overlap] + -- and Note [Binding when looking up instances] + ; let inst_tys = substTys subst tys + skol_info_anon = mkClsInstSkol cls inst_tys } + + ; let inst_theta = substTheta subst theta + ; return (skol_info_anon, inst_tvs, inst_theta, cls, inst_tys) } tcSuperSkolTyVars :: TcLevel -> SkolemInfo -> [TyVar] -> (Subst, [TcTyVar]) -- Make skolem constants, but do *not* give them new names, as above @@ -483,7 +495,9 @@ tcInstSkolTyVarsX skol_info = tcInstSkolTyVarsPushLevel skol_info False tcInstSuperSkolTyVars :: SkolemInfo -> [TyVar] -> TcM (Subst, [TcTyVar]) -- See Note [Skolemising type variables] -- This version freshens the names and creates "super skolems"; --- see comments around superSkolemTv. +-- see comments around superSkolemTv. +-- Must be lazy in skol_info: +-- see Note [Keeping SkolemInfo inside a SkolemTv] in GHC.Tc.Utils.TcType tcInstSuperSkolTyVars skol_info = tcInstSuperSkolTyVarsX skol_info emptySubst tcInstSuperSkolTyVarsX :: SkolemInfo -> Subst -> [TyVar] -> TcM (Subst, [TcTyVar]) |