update Data.Generics import

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

diff --git a/Data/Unique.hs b/Data/Unique.hs
index 3e093d3..6f8c24f 100644 (file)
--- a/Data/Unique.hs
+++ b/Data/Unique.hs
@@ -2,38 +2,45 @@
 -- |
 -- Module      :  Data.Unique
 -- Copyright   :  (c) The University of Glasgow 2001
--- License     :  BSD-style (see the file libraries/core/LICENSE)
+-- License     :  BSD-style (see the file libraries/base/LICENSE)
 -- 
 -- Maintainer  :  libraries@haskell.org
 -- Stability   :  experimental
 -- Portability :  non-portable
 --
--- An infinite supply of unique objects, supporting ordering and equality.
+-- An abstract interface to a unique symbol generator.
 --
 -----------------------------------------------------------------------------
 
 module Data.Unique (
-   Unique,             -- instance (Eq, Ord)
-   newUnique,          -- :: IO Unique
-   hashUnique          -- :: Unique -> Int
+   -- * Unique objects
+   Unique,              -- instance (Eq, Ord)
+   newUnique,           -- :: IO Unique
+   hashUnique           -- :: Unique -> Int
  ) where
 
 import Prelude
 
-import Control.Concurrent
+import Control.Concurrent.MVar
 import System.IO.Unsafe (unsafePerformIO)
 
 #ifdef __GLASGOW_HASKELL__
 import GHC.Base
-import GHC.Num         ( Integer(..) )
+import GHC.Num
 #endif
 
+-- | An abstract unique object.  Objects of type 'Unique' may be
+-- compared for equality and ordering and hashed into 'Int'.
 newtype Unique = Unique Integer deriving (Eq,Ord)
 
 uniqSource :: MVar Integer
 uniqSource = unsafePerformIO (newMVar 0)
 {-# NOINLINE uniqSource #-}
 
+-- | Creates a new object of type 'Unique'.  The value returned will
+-- not compare equal to any other value of type 'Unique' returned by
+-- previous calls to 'newUnique'.  There is no limit on the number of
+-- times 'newUnique' may be called.
 newUnique :: IO Unique
 newUnique = do
    val <- takeMVar uniqSource
@@ -41,11 +48,12 @@ newUnique = do
    putMVar uniqSource next
    return (Unique next)
 
+-- | Hashes a 'Unique' into an 'Int'.  Two 'Unique's may hash to the
+-- same value, although in practice this is unlikely.  The 'Int'
+-- returned makes a good hash key.
 hashUnique :: Unique -> Int
-#ifdef __GLASGOW_HASKELL__ 
-hashUnique (Unique (S# i))   = I# i
-hashUnique (Unique (J# s d)) | s ==# 0#  = 0
-                            | otherwise = I# (indexIntArray# d 0#)
+#if defined(__GLASGOW_HASKELL__)
+hashUnique (Unique i) = I# (hashInteger i)
 #else
-hashUnique (Unique u) = u `mod` (fromIntegral (maxBound :: Int) + 1)
+hashUnique (Unique u) = fromInteger (u `mod` (toInteger (maxBound :: Int) + 1))
 #endif