7. Word

This library provides unsigned integers of various sizes. The types supported are as follows:

type number of bits Word8 8 Word16 16 Word32 32 Word64 64

For each type W above, we provide the following functions and instances. The type I refers to the signed integer type of the same size.

data W            -- Unsigned Ints
instance Eq       W
instance Ord      W
instance Show     W
instance Read     W
instance Bounded  W
instance Num      W
instance Real     W
instance Integral W
instance Enum     W
instance Ix       W
instance Bits     W

word8ToWord32  :: Word8  -> Word32
word32ToWord8  :: Word32 -> Word8
word16ToWord32 :: Word16 -> Word32
word32ToWord16 :: Word32 -> Word16

word8ToInt     :: Word8  -> Int
intToWord8     :: Int    -> Word8
word16ToInt    :: Word16 -> Int
intToWord16    :: Int    -> Word16
word32ToInt    :: Word32 -> Int
intToWord32    :: Int    -> Word32

Notes:

• All arithmetic is performed modulo 2^n One non-obvious consequequence of this is that negate should not raise an error on negative arguments.
• The coercion wToI converts an unsigned n-bit value to the signed n-bit value with the same representation. For example, word8ToInt8 0xff = -1. Likewise, iToW converts signed n-bit values to the corresponding unsigned n-bit value.
• ToDo: complete the set of coercion functions.
• Use Prelude.fromIntegral :: (Integral a, Num b) => a -> b to coerce between different sizes or to preserve sign when converting between values of the same size.
• It would be very natural to add a type a type Natural providing an unbounded size unsigned integer --- just as Integer provides unbounded size signed integers. We do not do that yet since there is no demand for it. Doing so would require Bits.bitSize to return Maybe Int.
• The Enum instances stop when they reach their upper or lower bound --- they don't overflow the way the Int and Float instances do.
• It would be useful to provide a function (or a family of functions?) which coerced between any two Word types (without going through Integer).

Hugs only provides Eq, Ord, Read and Show instances for Word64 at the moment.