Delimit and Rejoin List

Delimit.hs

module Delimit where
import Data.Char (isLetter)

delimit :: (a -> Bool) -> [a] -> ([a], [[a]])
delimit p = foldr step ([], [[]]) where
  step c (ds, w:ws) = if p c then (c:ds, []:w:ws) else (ds, (c:w):ws)

rejoin :: [a] -> [[a]] -> [a]
rejoin ds ws = foldr (\(w, d) acc -> w ++ d:acc) [] (zip ws ds) ++ last ws

example :: String
example = "this is some mad, silly-ass shit"

test :: IO ()
test = if uncurry rejoin (delimit (not.isLetter) example) == example
  then putStrLn "Test Passed!"
  else error "Test Failed!"

I need this so frequently that I'll just put it here for safe keeping ^_^;