[project @ 2003-11-13 19:23:12 by panne]

[ghc-base.git] / Data / Typeable.hs

diff --git a/Data/Typeable.hs b/Data/Typeable.hs
index 6f38656..2be2ae1 100644 (file)
--- a/Data/Typeable.hs
+++ b/Data/Typeable.hs
@@ -241,7 +241,7 @@ cast x = r
               else Nothing
 
 
--- | A convenient variation for kind "* -> *"
+-- | A convenient variation for kind \"* -> *\"
 castss :: (Typeable a, Typeable b) => t a -> Maybe (t b)
 castss x = r
        where
@@ -414,9 +414,28 @@ cache = unsafePerformIO $ do
                                ap_tbl = empty_ap_tbl })
 
 newKey :: IORef Key -> IO Key
+#ifdef __GLASGOW_HASKELL__
+newKey kloc = do i <- genSym; return (Key i)
+#else
 newKey kloc = do { k@(Key i) <- readIORef kloc ;
                   writeIORef kloc (Key (i+1)) ;
                   return k }
+#endif
+
+#ifdef __GLASGOW_HASKELL__
+-- In GHC we use the RTS's genSym function to get a new unique,
+-- because in GHCi we might have two copies of the Data.Typeable
+-- library running (one in the compiler and one in the running
+-- program), and we need to make sure they don't share any keys.  
+--
+-- This is really a hack.  A better solution would be to centralise the
+-- whole mutable state used by this module, i.e. both hashtables.  But
+-- the current solution solves the immediate problem, which is that
+-- dynamics generated in one world with one type were erroneously
+-- being recognised by the other world as having a different type.
+foreign import ccall unsafe "genSymZh"
+  genSym :: IO Int
+#endif
 
 mkTyConKey :: String -> Key
 mkTyConKey str