State-based oscilator in haskell

state-osci.hs

module Main where

import Control.Monad.State.Lazy

step start stop (currentValue, modifier) = (currentValue, newState)
    where   reverseModifier = (currentValue + modifier > stop) || (currentValue + modifier < start)
            modifier' = if reverseModifier
                        then
                            -modifier
                        else
                            modifier
            newValue = currentValue + modifier'
            newState = (newValue, modifier')

osci :: Int -> Int -> State (Int, Int) Int
osci start stop = state stepper
    where stepper = step start stop


main :: IO ()
main = print $ evalState (replicateM 20 osciFromOneToFive) (1, 1)
    where osciFromOneToFive = osci 1 5