Haskell Bytestrings: How to pattern match?

Question

I\'m a Haskell newbie, and having a bit of trouble figuring out how to pattern match a ByteString. The [Char] version of my function looks like:

Answer 1

You can use view patterns for such things

{-# LANGUAGE ViewPatterns #-}    
import Data.ByteString (ByteString, cons, uncons, singleton, empty)
import Data.ByteString.Internal (c2w) 

dropR :: ByteString -> ByteString
dropR (uncons -> Nothing) = empty
dropR (uncons -> Just (x,uncons -> Nothing)) = singleton x
dropR (uncons -> Just (x,uncons -> Just(y,xs))) =
    if x == c2w 'a' && y == c2w 'b'
    then dropR xs
    else cons x (dropR $ cons y xs)