diff options
| -rw-r--r-- | compiler/typecheck/TcTyFuns.lhs | 10 |
1 files changed, 7 insertions, 3 deletions
diff --git a/compiler/typecheck/TcTyFuns.lhs b/compiler/typecheck/TcTyFuns.lhs index fc1906172d..f8bf40e19b 100644 --- a/compiler/typecheck/TcTyFuns.lhs +++ b/compiler/typecheck/TcTyFuns.lhs @@ -68,15 +68,19 @@ tcUnfoldSynFamInst (TyConApp tycon tys) | not (isOpenSynTyCon tycon) -- unfold *only* _synonym_ family instances = return Nothing | otherwise - = do { maybeFamInst <- tcLookupFamInst tycon tys + = do { -- we only use the indexing arguments for matching, not the additional ones + maybeFamInst <- tcLookupFamInst tycon idxTys ; case maybeFamInst of Nothing -> return Nothing - Just (rep_tc, rep_tys) -> return $ Just (mkTyConApp rep_tc rep_tys, - mkTyConApp coe_tc rep_tys) + Just (rep_tc, rep_tys) -> return $ Just (mkTyConApp rep_tc (rep_tys ++ restTys), + mkTyConApp coe_tc (rep_tys ++ restTys)) where coe_tc = expectJust "TcTyFun.tcUnfoldSynFamInst" (tyConFamilyCoercion_maybe rep_tc) } + where + n = tyConArity tycon + (idxTys, restTys) = splitAt n tys tcUnfoldSynFamInst _other = return Nothing \end{code} |