[project @ 2001-07-04 10:48:39 by simonmar]

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

diff --git a/Data/Unique.hs b/Data/Unique.hs
new file mode 100644 (file)
index 0000000..97251ff
--- /dev/null
+++ b/Data/Unique.hs
@@ -0,0 +1,53 @@
+-----------------------------------------------------------------------------
+-- 
+-- Module      :  Data.Unique
+-- Copyright   :  (c) The University of Glasgow 2001
+-- License     :  BSD-style (see the file libraries/core/LICENSE)
+-- 
+-- Maintainer  :  libraries@haskell.org
+-- Stability   :  experimental
+-- Portability :  non-portable
+--
+-- $Id: Unique.hs,v 1.1 2001/07/04 10:48:39 simonmar Exp $
+--
+-- An infinite supply of unique objects, supporting ordering and equality.
+--
+-----------------------------------------------------------------------------
+
+module Data.Unique (
+   Unique,             -- instance (Eq, Ord)
+   newUnique,          -- :: IO Unique
+   hashUnique          -- :: Unique -> Int
+ ) where
+
+import Prelude
+
+import Control.Concurrent
+import System.IO.Unsafe (unsafePerformIO)
+
+#ifdef __GLASGOW_HASKELL__
+import GHC.Base
+import GHC.Num         ( Integer(..) )
+#endif
+
+newtype Unique = Unique Integer deriving (Eq,Ord)
+
+uniqSource :: MVar Integer
+uniqSource = unsafePerformIO (newMVar 0)
+{-# NOINLINE uniqSource #-}
+
+newUnique :: IO Unique
+newUnique = do
+   val <- takeMVar uniqSource
+   let next = val+1
+   putMVar uniqSource next
+   return (Unique next)
+
+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)
+#endif