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|
-----------------------------------------------------------------------------
-- |
-- Module : Data.Unique
-- Copyright : (c) The University of Glasgow 2001
-- License : BSD-style (see the file libraries/base/LICENSE)
--
-- Maintainer : libraries@haskell.org
-- Stability : experimental
-- Portability : non-portable
--
-- An abstract interface to a unique symbol generator.
--
-----------------------------------------------------------------------------
module Data.Unique (
-- * Unique objects
Unique, -- instance (Eq, Ord)
newUnique, -- :: IO Unique
hashUnique -- :: Unique -> Int
) where
import Prelude
import Control.Concurrent.MVar
import System.IO.Unsafe (unsafePerformIO)
#ifdef __GLASGOW_HASKELL__
import GHC.Base
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
let next = val+1
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) = fromInteger (u `mod` (toInteger (maxBound :: Int) + 1))
#endif
|
