[project @ 1999-01-28 14:22:15 by simonpj]

[ghc-hetmet.git] / ghc / compiler / rename / RnEnv.lhs

diff --git a/ghc/compiler/rename/RnEnv.lhs b/ghc/compiler/rename/RnEnv.lhs
index ca8d876..ebe6af2 100644 (file)
--- a/ghc/compiler/rename/RnEnv.lhs
+++ b/ghc/compiler/rename/RnEnv.lhs
@@ -462,8 +462,8 @@ combine_globals :: [Name]   -- Old
 combine_globals ns_old ns_new  -- ns_new is often short
   = foldr add ns_old ns_new
   where
-    add n ns | all (no_conflict n) ns_old = map choose ns      -- Eliminate duplicates
-            | otherwise                  = n:ns
+    add n ns | any (is_duplicate n) ns_old = map choose ns     -- Eliminate duplicates
+            | otherwise                   = n:ns
             where
               choose n' | n==n' && better_provenance n n' = n
                         | otherwise                       = n'
@@ -479,12 +479,16 @@ better_provenance n1 n2
        (NonLocalDef (UserImport _ _ _   ) _, NonLocalDef ImplicitImport _) -> True
        other                                                               -> False
 
-no_conflict :: Name -> Name -> Bool
-no_conflict n1 n2 | isLocallyDefined n1 && isLocallyDefined n2 = False
-                 | otherwise                                  = n1 == n2
-       -- We complain of a conflict if one RdrName maps to two different Names,
-       -- OR if one RdrName maps to the same *locally-defined* Name.  The latter
-       -- case is to catch two separate, local definitions of the same thing.
+is_duplicate :: Name -> Name -> Bool
+is_duplicate n1 n2 | isLocallyDefined n1 && isLocallyDefined n2 = False
+                  | otherwise                                  = n1 == n2
+       -- We treat two bindings of a locally-defined name as a duplicate,
+       -- because they might be two separate, local defns and we want to report
+       -- and error for that, *not* eliminate a duplicate.
+
+       -- On the other hand, if you import the same name from two different
+       -- import statements, we *do* want to eliminate the duplicate, not report
+       -- an error.
        --
        -- If a module imports itself then there might be a local defn and an imported
        -- defn of the same name; in this case the names will compare as equal, but