Pattern matching bits

Bits.hs

{-# LANGUAGE ViewPatterns #-}
{-# LANGUAGE PatternSynonyms #-}

-- | Demonstration of pattern matching on bits in a byte.

module X where

import Data.Bits

pattern Byte a b c d <- (byte -> (ByteBits a b c d))
data ByteBits = ByteBits Bool Bool Bool Bool
byte :: Bits a => a -> ByteBits
byte n = ByteBits (testBit n 3) (testBit n 2) (testBit n 1) (testBit n 0)