Finally fix Trac #3066

[ghc-hetmet.git] / compiler / types / Type.lhs

diff --git a/compiler/types/Type.lhs b/compiler/types/Type.lhs
index 0912a2c..3705914 100644 (file)
--- a/compiler/types/Type.lhs
+++ b/compiler/types/Type.lhs
@@ -41,7 +41,7 @@ module Type (
        applyTy, applyTys, applyTysD, isForAllTy, dropForAlls,
        
        -- (Newtypes)
-       newTyConInstRhs,
+       newTyConInstRhs, carefullySplitNewType_maybe,
        
        -- (Type families)
         tyFamInsts, predFamInsts,
@@ -596,14 +596,9 @@ newtype at outermost level; and bale out if we see it again.
 -- | Looks through:
 --
 --     1. For-alls
---
 --     2. Synonyms
---
 --     3. Predicates
---
---     4. Usage annotations
---
---     5. All newtypes, including recursive ones, but not newtype families
+--     4. All newtypes, including recursive ones, but not newtype families
 --
 -- It's useful in the back end of the compiler.
 repType :: Type -> Type
@@ -618,19 +613,25 @@ repType ty
     go rec_nts (ForAllTy _ ty)                 -- Look through foralls
        = go rec_nts ty
 
-    go rec_nts ty@(TyConApp tc tys)            -- Expand newtypes
-       | Just _co_con <- newTyConCo_maybe tc   -- See Note [Expanding newtypes]
-       = if tc `elem` rec_nts                  --  in Type.lhs
-         then ty
-         else go rec_nts' nt_rhs
-       where
-         nt_rhs = newTyConInstRhs tc tys
-         rec_nts' | isRecursiveTyCon tc = tc:rec_nts
-                  | otherwise           = rec_nts
+    go rec_nts (TyConApp tc tys)               -- Expand newtypes
+      | Just (rec_nts', ty') <- carefullySplitNewType_maybe rec_nts tc tys
+      = go rec_nts' ty'
 
     go _ ty = ty
 
 
+carefullySplitNewType_maybe :: [TyCon] -> TyCon -> [Type] -> Maybe ([TyCon],Type)
+-- Return the representation of a newtype, unless 
+-- we've seen it already: see Note [Expanding newtypes]
+carefullySplitNewType_maybe rec_nts tc tys
+  | isNewTyCon tc
+  , not (tc `elem` rec_nts)  = Just (rec_nts', newTyConInstRhs tc tys)
+  | otherwise               = Nothing
+  where
+    rec_nts' | isRecursiveTyCon tc = tc:rec_nts
+            | otherwise           = rec_nts
+
+
 -- ToDo: this could be moved to the code generator, using splitTyConApp instead
 -- of inspecting the type directly.