-- |
-- 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
--
--- $Id: Unique.hs,v 1.2 2002/04/24 16:31:43 simonmar Exp $
---
--- An infinite supply of unique objects, supporting ordering and equality.
+-- An abstract interface to a unique symbol generator.
--
-----------------------------------------------------------------------------
module Data.Unique (
+ -- * Unique objects
Unique, -- instance (Eq, Ord)
newUnique, -- :: IO Unique
hashUnique -- :: Unique -> Int
import Prelude
-import Control.Concurrent
+import Control.Concurrent.MVar
import System.IO.Unsafe (unsafePerformIO)
#ifdef __GLASGOW_HASKELL__
import GHC.Num ( Integer(..) )
#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
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#)
#else
-hashUnique (Unique u) = u `mod` (fromIntegral (maxBound :: Int) + 1)
+hashUnique (Unique u) = fromInteger (u `mod` (toInteger (maxBound :: Int) + 1))
#endif