Haskell Regex - Backtracking (...?)

gistfile1.hs

import Control.Applicative

data Regex =
    Literal Char
  | Concat Regex Regex
  | Altern Regex Regex
  | Star Regex

match :: Regex -> String -> Bool
match r s = "" `elem` (consume r s)

consume :: Regex -> String -> [String]
consume (Literal c) [] = []
consume (Literal c) (c':cs) = if c == c' then [cs] else []
consume (Concat r1 r2) s = concat $ consume r2 <$> consume r1 s
consume (Altern r1 r2) s = (consume r1 s) ++ (consume r2 s)
consume (Star r) s = s : (concat $ consume (Star r) <$> consume r s)