X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=Data%2FTypeable.hs;h=d187296faca25b2f75762d32521ef6844e5beb46;hb=93b9a4ab1adffb656b3f65ac5a9ebe89d10adef8;hp=e9b06732b7e120219873cc6e325bff38cab54c6c;hpb=18068216d7d40cba4a39ab4893b752dc818d6b1e;p=haskell-directory.git

diff --git a/Data/Typeable.hs b/Data/Typeable.hs
index e9b0673..d187296 100644
--- a/Data/Typeable.hs
+++ b/Data/Typeable.hs
@@ -53,6 +53,7 @@ module Data.Typeable
 	typeRepTyCon,	-- :: TypeRep -> TyCon
 	typeRepArgs,	-- :: TypeRep -> [TypeRep]
 	tyConString,	-- :: TyCon   -> String
+	typeRepKey,	-- :: TypeRep -> IO Int
 
 	-- * The other Typeable classes
 	-- | /Note:/ The general instances are provided for GHC only.
@@ -163,9 +164,21 @@ data TyCon = TyCon !Key String
 
 instance Eq TyCon where
   (TyCon t1 _) == (TyCon t2 _) = t1 == t2
-
 #endif
 
+-- | Returns a unique integer associated with a 'TypeRep'.  This can
+-- be used for making a mapping ('Data.IntMap.IntMap') with TypeReps
+-- as the keys, for example.  It is guaranteed that @t1 == t2@ if and only if
+-- @typeRepKey t1 == typeRepKey t2@.
+--
+-- It is in the 'IO' monad because the actual value of the key may
+-- vary from run to run of the program.  You should only rely on
+-- the equality property, not any actual key value.  The relative ordering
+-- of keys has no meaning either.
+--
+typeRepKey :: TypeRep -> IO Int
+typeRepKey (TypeRep (Key i) _ _) = return i
+
 	-- 
 	-- let fTy = mkTyCon "Foo" in show (mkTyConApp (mkTyCon ",,")
 	--                                 [fTy,fTy,fTy])