gistfile1.hs

import Data.Char

atLeastOneFollowedByAndThen f c g []     = False
atLeastOneFollowedByAndThen f c g (x:xs) = f x && yys /= [] && y == c && g ys
	where yys     = dropWhile f xs
          ~(y:ys) = yys

isEmail  = atLeastOneFollowedByAndThen isAlphaNum '@' isDomain
isDomain = atLeastOneFollowedByAndThen isAlphaNum '.' (\t -> isTerminator t || isDomain t)
isTerminator = (`elem` ["com", "net", "org", "ie"])