FactorialAutomaton.elm

module Main (..) where

import Automaton
import Dict
import Graphics.Element exposing (show)


main =
    Automaton.step 5 factorialAutomaton |> snd |> show


type alias State =
    Dict.Dict Int Int


factorialAutomaton : Automaton.Automaton Int Int
factorialAutomaton =
    let
        factorial : Int -> State -> ( Int, State )
        factorial i state =
            case Dict.get i state of
                Just n ->
                    ( n, state )

                Nothing ->
                    let
                        ( n, state' ) = factorial (i - 1) state
                    in
                        ( i * n, Dict.insert i n state' )
    in
        Automaton.hiddenState (Dict.fromList [ ( 0, 1 ) ]) factorial