state.hs

import Control.Monad.State
import System.Random

first  lst = first' lst [] []
first' [] _ result = reverse result
first' (h:t) found result = 
       if any (== h) found then first' t found (False:result)
       else first' t (h:found) (True:result)


state_first' []    = return []
state_first' (h:t) = do current <- get
                        let found = (any (== h) current)
                        put (if found then current else (h:current))
                        rest <- state_first' t
                        return $ (not found):rest

-- isfound h = do current <- get
--                return (any (== h) current)

state_first lst = evalState (state_first' lst) []