"""
    Regular-expression matching by the Thompson construction.
    Explained in C at http://swtch.com/~rsc/regexp/regexp1.html
    """

    def match(re, s): return run(prepare(re), s)

    def run(states, s):
        for c in s:
            states = set.union(*[state(c) for state in states])
        return accepting_state in states

    def accepting_state(c): return set()
    def expecting_state(char, k): return lambda c: k(set()) if c==char else set()

    def state_node(state): return lambda seen: set([state])
    def alt_node(k1, k2):  return lambda seen: k1(seen) | k2(seen)
    def loop_node(k, make_k):
        def loop(seen):
            if loop in seen: return set()
            seen.add(loop)
            return k(seen) | looping(seen)
        looping = make_k(loop)
        return loop

    def prepare(re): return re(state_node(accepting_state))(set())

    def lit(char):     return lambda k: state_node(expecting_state(char, k))
    def alt(re1, re2): return lambda k: alt_node(re1(k), re2(k))
    def many(re):      return lambda k: loop_node(k, re)
    def empty(k):      return k
    def seq(re1, re2): return lambda k: re1(re2(k))

I'm not sure how the original comes to 14 lines. btw.