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| author | Simon Peyton Jones <simonpj@microsoft.com> | 2013-05-30 22:03:24 +0100 |
|---|---|---|
| committer | Simon Peyton Jones <simonpj@microsoft.com> | 2013-05-30 22:03:48 +0100 |
| commit | d0ecba6d98c5fae1df8b63632557a44a09c559f8 (patch) | |
| tree | 1eb7f77034508e3b575048258d865f1ee55911c7 /compiler | |
| parent | 3d81b68d48e86f9dff032321aff20b76ad3ea081 (diff) | |
| download | haskell-d0ecba6d98c5fae1df8b63632557a44a09c559f8.tar.gz | |
Fix a trailing case in making FamInstTyCon,
where the invariant didn't hold, leading to
subsequent chaos. Happily an ASSERT caught it.
Diffstat (limited to 'compiler')
| -rw-r--r-- | compiler/iface/TcIface.lhs | 17 |
1 files changed, 12 insertions, 5 deletions
diff --git a/compiler/iface/TcIface.lhs b/compiler/iface/TcIface.lhs index 89d9807a37..4c7435a554 100644 --- a/compiler/iface/TcIface.lhs +++ b/compiler/iface/TcIface.lhs @@ -461,15 +461,22 @@ tc_iface_decl parent _ (IfaceData {ifName = occ_name, ; let fam_tc = coAxiomTyCon ax ax_unbr = toUnbranchedAxiom ax -- data families don't have branches: - branch = coAxiomSingleBranch ax_unbr - ax_tvs = coAxBranchTyVars branch - ax_lhs = coAxBranchLHS branch - subst = zipTopTvSubst ax_tvs (mkTyVarTys tyvars) + branch = coAxiomSingleBranch ax_unbr + ax_tvs = coAxBranchTyVars branch + ax_lhs = coAxBranchLHS branch + tycon_tys = mkTyVarTys tyvars + subst = mkTopTvSubst (ax_tvs `zip` tycon_tys) -- The subst matches the tyvar of the TyCon -- with those from the CoAxiom. They aren't -- necessarily the same, since the two may be -- gotten from separate interface-file declarations - ; return (FamInstTyCon ax_unbr fam_tc (substTys subst ax_lhs)) } + -- NB: ax_tvs may be shorter because of eta-reduction + -- See Note [Eta reduction for data family axioms] in TcInstDcls + lhs_tys = substTys subst ax_lhs `chkAppend` + dropList ax_tvs tycon_tys + -- The 'lhs_tys' should be 1-1 with the 'tyvars' + -- but ax_tvs maybe shorter because of eta-reduction + ; return (FamInstTyCon ax_unbr fam_tc lhs_tys) } tc_iface_decl parent _ (IfaceSyn {ifName = occ_name, ifTyVars = tv_bndrs, ifSynRhs = mb_rhs_ty, |