tcLookupLocatedTyCon = addLocM tcLookupTyCon
-- Look up the representation tycon of a family instance.
---
-tcLookupFamInst :: TyCon -> [Type] -> TcM TyCon
+-- Return the rep tycon and the corresponding rep args
+tcLookupFamInst :: TyCon -> [Type] -> TcM (TyCon, [Type])
tcLookupFamInst tycon tys
+ | not (isOpenTyCon tycon)
+ = return (tycon, tys)
+ | otherwise
= do { env <- getGblEnv
; eps <- getEps
; let instEnv = (eps_fam_inst_env eps, tcg_fam_inst_env env)
- ; case lookupFamInstEnvExact instEnv tycon tys of
- Nothing -> famInstNotFound tycon tys
- Just famInst -> return $ famInstTyCon famInst
+ ; case lookupFamInstEnv instEnv tycon tys of
+
+ [(subst, fam_inst)] | variable_only_subst ->
+ return (rep_tc, substTyVars subst (tyConTyVars rep_tc))
+ where -- NB: assumption is that (tyConTyVars rep_tc) is in
+ -- the domain of the substitution
+ rep_tc = famInstTyCon fam_inst
+ subst_domain = varEnvElts . getTvSubstEnv $ subst
+ tvs = map (Type.getTyVar "tcLookupFamInst")
+ subst_domain
+ variable_only_subst = all Type.isTyVarTy subst_domain &&
+ sizeVarSet (mkVarSet tvs) == length tvs
+ -- renaming may have no repetitions
+
+ other -> famInstNotFound tycon tys other
}
\end{code}
newDFunName clas [] loc = pprPanic "newDFunName" (ppr clas <+> ppr loc)
\end{code}
-Make a name for the representation tycon of a data/newtype instance. It's an
+Make a name for the representation tycon of a family instance. It's an
*external* name, like otber top-level names, and hence must be made with
newGlobalBinder.
= failWithTc (pprTcTyThingCategory thing <+> quotes (ppr name) <+>
ptext SLIT("used as a") <+> text expected)
-famInstNotFound tycon tys
- = failWithTc (quotes famInst <+> ptext SLIT("is not in scope"))
+famInstNotFound tycon tys what
+ = failWithTc (msg <+> quotes (pprTypeApp (ppr tycon) tys))
where
- famInst = ppr tycon <+> hsep (map pprParendType tys)
+ msg = ptext $ if length what > 1
+ then SLIT("More than one family instance for")
+ else SLIT("No family instance exactly matching")
\end{code}