Re-work the newtype-deriving support

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

diff --git a/compiler/iface/BuildTyCl.lhs b/compiler/iface/BuildTyCl.lhs
index 6384ddc..077edb2 100644 (file)
--- a/compiler/iface/BuildTyCl.lhs
+++ b/compiler/iface/BuildTyCl.lhs
@@ -130,21 +130,20 @@ 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
-              cocon_maybe 
-                | all_coercions || isRecursiveTyCon tycon 
-                = Just co_tycon
-                | otherwise              
-                = Nothing
-       ; return (NewTyCon { data_con = con, 
+       ; let co_tycon = mkNewTypeCoercion co_tycon_name tycon etad_rhs
+              cocon_maybe | all_coercions || isRecursiveTyCon tycon 
+                         = Just co_tycon
+                         | otherwise              
+                         = Nothing
+       ; return (NewTyCon { data_con    = con, 
+                            nt_rhs      = rhs_ty,
+                            nt_etad_rhs = etad_rhs,
                             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
+        -- 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
@@ -153,18 +152,20 @@ mkNewTyConRhs tycon_name tycon con
        -- Instantiate the data con with the 
        -- type variables from the tycon
 
-    eta_reduce [] ty = ([], ty)
-    eta_reduce (a:as) ty | null as', 
-                          Just (fun, arg) <- splitAppTy_maybe ty',
+    etad_rhs :: ([TyVar], Type)
+    etad_rhs = eta_reduce (reverse tvs) rhs_ty
+
+    eta_reduce :: [TyVar]              -- Reversed
+              -> Type                  -- Rhs type
+              -> ([TyVar], Type)       -- Eta-reduced version (tyvars in normal order)
+    eta_reduce (a:as) ty | Just (fun, arg) <- splitAppTy_maybe ty,
                           Just tv <- getTyVar_maybe arg,
                           tv == a,
                           not (a `elemVarSet` tyVarsOfType fun)
-                        = ([], fun)    -- Successful eta reduction
-                        | otherwise
-                        = (a:as', ty')
-       where
-         (as', ty') = eta_reduce as ty
+                        = eta_reduce as fun
+    eta_reduce tvs ty = (reverse tvs, ty)
                                
+
 mkNewTyConRep :: TyCon         -- The original type constructor
              -> Type           -- The arg type of its constructor
              -> Type           -- Chosen representation type