content: {-# LANGUAGE Safe #-}
  {-# LANGUAGE CPP, NoImplicitPrelude #-}
  
  -----------------------------------------------------------------------------
  -- |
  -- Module      :  Data.Word
  -- Copyright   :  (c) The University of Glasgow 2001
  -- License     :  BSD-style (see the file libraries/base/LICENSE)
  -- 
  -- Maintainer  :  libraries@haskell.org
  -- Stability   :  experimental
  -- Portability :  portable
  --
  -- Unsigned integer types.
  --
  -----------------------------------------------------------------------------
  
  module Data.Word
    (
          -- * Unsigned integral types
  
          Word,
          Word8, Word16, Word32, Word64,
  
          -- * Notes
  
          -- $notes
          ) where
  
  #ifdef __GLASGOW_HASKELL__
  import GHC.Word
  #endif
  
  #ifdef __HUGS__
  import Hugs.Word
  #endif
  
  #ifdef __NHC__
  import NHC.FFI (Word8, Word16, Word32, Word64)
  import NHC.SizedTypes (Word8, Word16, Word32, Word64)   -- instances of Bits
  type Word = Word32
  #endif
  
  {- $notes
  
  * All arithmetic is performed modulo 2^n, where n is the number of
    bits in the type.  One non-obvious consequence of this is that 'Prelude.negate'
    should /not/ raise an error on negative arguments.
  
  * For coercing between any two integer types, use
    'Prelude.fromIntegral', which is specialized for all the
    common cases so should be fast enough.  Coercing word types to and
    from integer types preserves representation, not sign.
  
  * It would be very natural to add a type @Natural@ providing an unbounded 
    size unsigned integer, just as 'Prelude.Integer' provides unbounded
    size signed integers.  We do not do that yet since there is no demand
    for it.
  
  * The rules that hold for 'Prelude.Enum' instances over a bounded type
    such as 'Prelude.Int' (see the section of the Haskell report dealing
    with arithmetic sequences) also hold for the 'Prelude.Enum' instances
    over the various 'Word' types defined here.
  
  * Right and left shifts by amounts greater than or equal to the width
    of the type result in a zero result.  This is contrary to the
    behaviour in C, which is undefined; a common interpretation is to
    truncate the shift count to the width of the type, for example @1 \<\<
    32 == 1@ in some C implementations. 
  -}
  
  