X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=Data%2FUnique.hs;h=1c1ceb88eef52e2943acb87279adf79525d09ba6;hb=a0d7892da0d00fee781a550ef353df8734be5884;hp=81fe6d87a02f58b1fe2d294b2703f2fefd0fb283;hpb=f7a485978f04e84b086f1974b88887cc72d832d0;p=haskell-directory.git

diff --git a/Data/Unique.hs b/Data/Unique.hs
index 81fe6d8..1c1ceb8 100644
--- a/Data/Unique.hs
+++ b/Data/Unique.hs
@@ -8,11 +8,12 @@
 -- 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 objects
    Unique,		-- instance (Eq, Ord)
    newUnique, 		-- :: IO Unique
    hashUnique 		-- :: Unique -> Int
@@ -20,7 +21,7 @@ module Data.Unique (
 
 import Prelude
 
-import Control.Concurrent
+import Control.Concurrent.MVar
 import System.IO.Unsafe (unsafePerformIO)
 
 #ifdef __GLASGOW_HASKELL__
@@ -28,12 +29,18 @@ 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
@@ -41,11 +48,14 @@ 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#)
 #else
-hashUnique (Unique u) = u `mod` (fromIntegral (maxBound :: Int) + 1)
+hashUnique (Unique u) = fromInteger (u `mod` (toInteger (maxBound :: Int) + 1))
 #endif