automata

import Prelude hiding (init)    -- so we can use the name 'init' later

type Automaton a = [a] -> Bool
type AutomatonPair a = (a, Automaton a)

accept :: Eq a => [AutomatonPair a] -> Automaton a
accept ps = f
  where f [] = True
        f (x:xs) = case lookup x ps of
          Just a -> a xs
          Nothing -> False

v s@('c':_) = init s
  where init = accept [('c', loop)]
        loop = accept [('a', loop),
                       ('d', loop),
                       ('r', end)]
        end = accept [('r', end)]
v s = see0 s
  where see0 = accept [('0', see1)]
        see1 = accept [('1', see0)]