Data/Word.hs

    {-# LANGUAGE CPP, PackageImports #-}
    #if __GLASGOW_HASKELL__ >= 701
    {-# LANGUAGE Safe #-}
    #endif

    module Data.Word (
            -- * Unsigned integral types

            -- $notes

            Word,
            Word8, Word16, Word32, Word64,

      ) where
    import "base" Data.Word

    -- SDM: removed after 'Prelude.fromIntegral':
    -- ..., which is specialized for all the common cases
    -- so should be fast enough

    -- SDM: removed: 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.

    -- SDM: removed, after "All arithmetic is performed module 2^n...".  Neither
    -- Ian Lynagh nor I understand what this means:
    --   One non-obvious consequence of this is that 'Prelude.negate'
    --   should /not/ raise an error on negative arguments.

    {- $notes

    This module provides unsigned integer types of unspecified width ('Word')
    and fixed widths ('Word8', 'Word16', 'Word32' and 'Word64').  All
    arithmetic is performed modulo 2^n, where @n@ is the number of bits in
    the type.

    For coercing between any two integer types, use
    'Prelude.fromIntegral'.  Coercing word types to and from integer
    types preserves representation, not sign.

    The rules that hold for 'Prelude.Enum' instances over a bounded type
    such as 'Prelude.Int' (see the section of the Haskell language 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.

    -}