X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Fiface%2FBuildTyCl.lhs;h=d1118c01286375ae1cca62c81235d0ee599cd1c8;hb=0b86bc9b022a5965d2b35f143ff4b919f784e676;hp=ad580289c518a037e5fbac75b80c5f51e8076474;hpb=c94408e522e5af3b79a5beadc7e6d15cee553ee7;p=ghc-hetmet.git

diff --git a/compiler/iface/BuildTyCl.lhs b/compiler/iface/BuildTyCl.lhs
index ad58028..d1118c0 100644
--- a/compiler/iface/BuildTyCl.lhs
+++ b/compiler/iface/BuildTyCl.lhs
@@ -82,15 +82,24 @@ mkNewTyConRhs :: Name -> TyCon -> DataCon -> TcRnIf m n AlgTyConRhs
 -- because the latter is part of a knot, whereas the former is not.
 mkNewTyConRhs tycon_name tycon con 
   = do	{ co_tycon_name <- newImplicitBinder tycon_name mkNewTyCoOcc
-	; let co_tycon = mkNewTypeCoercion co_tycon_name tycon tvs rhs_ty 
+	; let co_tycon = mkNewTypeCoercion co_tycon_name tycon tvs rhs_ty
+              cocon_maybe 
+                | all_coercions || isRecursiveTyCon tycon 
+                = Just co_tycon
+                | otherwise              
+                = Nothing
 	; return (NewTyCon { data_con = con, 
- 		       	     nt_co = Just co_tycon, 
+ 		       	     nt_co = cocon_maybe, 
                              -- Coreview looks through newtypes with a Nothing
                              -- for nt_co, or uses explicit coercions otherwise
 		       	     nt_rhs = rhs_ty,
 		       	     nt_etad_rhs = eta_reduce tvs rhs_ty,
 		       	     nt_rep = mkNewTyConRep tycon rhs_ty }) }
   where
+        -- if all_coercions is True then we use coercions for all newtypes
+        -- otherwise we use coercions for recursive newtypes and look through
+        -- non-recursive newtypes
+    all_coercions = True
     tvs    = tyConTyVars tycon
     rhs_ty = head (dataConInstOrigArgTys con (mkTyVarTys tvs))
 	-- Instantiate the data con with the 
@@ -138,7 +147,7 @@ mkNewTyConRep tc rhs_ty
                     if isRecursiveTyCon tc then
 			go (tc:tcs) (substTyWith tvs tys rhs_ty)
                     else
-                        go tcs (head tys)
+                        substTyWith tvs tys rhs_ty
 		where
 		  (tvs, rhs_ty) = newTyConRhs tc