Playing around with flattening nested if-then-else

FirstWhereM.hs

module Main where

import System.FilePath
import System.Directory

main = firstWhereM check ["a", "x", "b"] >>= print
  where check = doesFileExist . (</>"z"</>"y")

firstWhereM :: (Monad m) => (a -> m Bool) -> [a] -> m (Maybe a)
firstWhereM pred ins = case ins of
  []    -> return Nothing
  a:as  -> pred a >>= \b ->
           if b then return (Just a)
                else firstWhereM pred as