fix bugs, add boolean flag to identify coercion variables

[ghc-hetmet.git] / compiler / iface / BuildTyCl.lhs

diff --git a/compiler/iface/BuildTyCl.lhs b/compiler/iface/BuildTyCl.lhs
index e4c392b..d1118c0 100644 (file)
--- a/compiler/iface/BuildTyCl.lhs
+++ b/compiler/iface/BuildTyCl.lhs
@@ -82,13 +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 = 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 
@@ -116,9 +127,8 @@ mkNewTyConRep :: TyCon              -- The original type constructor
 -- Remember that the representation type is the *ultimate* representation
 -- type, looking through other newtypes.
 -- 
--- The non-recursive newtypes are easy, because they look transparent
--- to splitTyConApp_maybe, but recursive ones really are represented as
--- TyConApps (see TypeRep).
+-- splitTyConApp_maybe no longer looks through newtypes, so we must
+-- deal explicitly with this case
 -- 
 -- The trick is to to deal correctly with recursive newtypes
 -- such as     newtype T = MkT T
@@ -133,10 +143,11 @@ mkNewTyConRep tc rhs_ty
        = case splitTyConApp_maybe rep_ty of
            Just (tc, tys)
                | tc `elem` tcs -> unitTy       -- Recursive loop
-               | isNewTyCon tc -> ASSERT( isRecursiveTyCon tc )
-                                       -- Non-recursive ones have been 
-                                       -- dealt with by splitTyConApp_maybe
-                                  go (tc:tcs) (substTyWith tvs tys rhs_ty)
+               | isNewTyCon tc -> 
+                    if isRecursiveTyCon tc then
+                       go (tc:tcs) (substTyWith tvs tys rhs_ty)
+                    else
+                        substTyWith tvs tys rhs_ty
                where
                  (tvs, rhs_ty) = newTyConRhs tc