dfa.hs

import System.IO
import Data.List.Split (chunksOf)
import Data.List (foldl')
import Control.Monad (forever)
import Data.Set (Set)
import qualified Data.Set as Set
import Data.Map (Map)
import qualified Data.Map as Map

type State = String
type Symbol = String
type TransitionTable = Map (State, Symbol) State

main :: IO ()
main = do
    let start = "q0"
        final = Set.singleton "q0"
        transitions = Map.fromList
          [ (("q0", "0"), "q0")
          , (("q0", "1"), "q1")
          , (("q1", "0"), "q2")
          , (("q1", "1"), "qc")
          , (("q2", "0"), "q1")
          , (("q2", "1"), "q2")
          , (("qc", "0"), "q0")
          , (("qc", "1"), "q1")
          ]
        my_dfa = dfa start final transitions

    let loop = do
          input <- prompt "Enter a string to test >>> "
          print $ my_dfa (chunksOf 1 input)

    forever loop

dfa :: State -> Set State -> TransitionTable -> [Symbol] -> Bool
dfa start final transitions input = Set.member finalState final
  where
    finalState = foldl' getNextState start input
    getNextState cur str = transitions Map.! (cur, str)

prompt :: String -> IO String
prompt str = do
    putStr str
    hFlush stdout
    getLine