markov.hs

module Main (main) where

import Prelude hiding (lookup)
import Data.Map (empty, insertWith', keys, lookup, size)
import System.Random (getStdRandom, randomR)
import Control.Monad (liftM)
import System.Environment (getArgs)

parse (a : b : c : t) = insertWith' comb (a, b) ([c], 1) $ parse $ b : c : t
	where comb (l, m) (r, n) = (l ++ r, m + n)
parse _ = empty

pick (a, len) = liftM ((!!) a) $ getStdRandom $ randomR (0, len - 1)

markov m (x, y)
	| otherwise = case lookup (x, y) m of
		Just e -> pick e >>= \z -> liftM ((++) [x]) $ markov m (y, z)
		otherwise -> return $! [x, y]

main = liftM (parse . words) (liftM head getArgs >>= readFile) >>= \m -> pick (keys m, size m) >>= markov m >>= putStrLn . unwords