X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypecheck%2FTcEnv.lhs;h=ff49db6af6b04448f5a032cbb551f2d397b58b4a;hb=cdce647711c0f46f5799b24de087622cb77e647f;hp=d59278a26357a881769db37943203ea7f17addf2;hpb=380512de6eef0cbb17431d9e64007a9320914e23;p=ghc-hetmet.git

diff --git a/compiler/typecheck/TcEnv.lhs b/compiler/typecheck/TcEnv.lhs
index d59278a..ff49db6 100644
--- a/compiler/typecheck/TcEnv.lhs
+++ b/compiler/typecheck/TcEnv.lhs
@@ -160,15 +160,30 @@ tcLookupLocatedTyCon :: Located Name -> TcM TyCon
 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}
 
@@ -670,8 +685,10 @@ wrongThingErr expected thing name
   = 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}