Fix building HashTable: Use ord rather than fromEnum

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

diff --git a/Data/Typeable.hs b/Data/Typeable.hs
index e9b0673..f548dc9 100644 (file)
--- a/Data/Typeable.hs
+++ b/Data/Typeable.hs
@@ -40,6 +40,7 @@ module Data.Typeable
        -- * Type representations
        TypeRep,        -- abstract, instance of: Eq, Show, Typeable
        TyCon,          -- abstract, instance of: Eq, Show, Typeable
+       showsTypeRep,
 
        -- * Construction of type representations
        mkTyCon,        -- :: String  -> TyCon
@@ -53,6 +54,7 @@ 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.
@@ -85,6 +87,7 @@ import Data.Either
 import Data.Int
 import Data.Word
 import Data.List( foldl )
+import Unsafe.Coerce
 
 #ifdef __GLASGOW_HASKELL__
 import GHC.Base
@@ -118,19 +121,13 @@ import Hugs.Prelude       ( Key(..), TypeRep(..), TyCon(..), Ratio,
                          ArrayException, AsyncException, Handle,
                          Ptr, FunPtr, ForeignPtr, StablePtr )
 import Hugs.IORef      ( IORef, newIORef, readIORef, writeIORef )
-import Hugs.IOExts     ( unsafePerformIO, unsafeCoerce )
+import Hugs.IOExts     ( unsafePerformIO )
        -- For the Typeable instance
 import Hugs.Array      ( Array )
 import Hugs.ConcBase   ( MVar )
 #endif
 
-#ifdef __GLASGOW_HASKELL__
-unsafeCoerce :: a -> b
-unsafeCoerce = unsafeCoerce#
-#endif
-
 #ifdef __NHC__
-import NonStdUnsafeCoerce (unsafeCoerce)
 import NHC.IOExtras (IORef,newIORef,readIORef,writeIORef,unsafePerformIO)
 import IO (Handle)
 import Ratio (Ratio)
@@ -163,9 +160,21 @@ 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])
@@ -267,6 +276,9 @@ instance Show TypeRep where
            showChar ' '      . 
            showArgs tys
 
+showsTypeRep :: TypeRep -> ShowS
+showsTypeRep = shows
+
 instance Show TyCon where
   showsPrec _ (TyCon _ s) = showString s