A simple NFA in Haskell

nfa.hs

-- See: http://swizec.com/blog/strangest-line-of-python-you-have-ever-seen/swizec/3012

import Control.Monad
import Data.Maybe
import System.Environment

data NFA s i = NFA s [s] [((s,i),[s])]

runNFA (NFA i f t) = any (`elem` f) . foldM step i where
    step s c = fromMaybe [] $ lookup (s,c) t

parseNFA s = NFA i fs t where
    [_,i]:(_:fs):ts = map words $ lines s
    t = map (\(s:[i]:_:s') -> ((s,i),s')) ts

main = do
    nfa  <- fmap parseNFA $ readFile "machine.txt"
    getArgs >>= mapM_ (\i -> print (i, if runNFA nfa i then "YES" else "NO"))