------------------------------------------------------------------------------
--- |
--- 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