Generator program on Effekt

generator.effekt

module generator

import immutable/option
import immutable/list

effect Replace(x: Int): Unit
effect Reject(): Unit
effect Yield(x: Int): Unit / { Replace, Reject }

def iter(lst: List[Int]): List[Int] / { Yield, Console } = lst match {
  case Nil() => Nil()
  case Cons(x, xs) =>
    val xp = try {
      do Yield(x)
      Some(x)
    }
    with Replace { xp => Some(xp) }
    with Reject { None() }

    val xsp = iter(xs)
    xp match {
      case None() => xsp
      case Some(xpp) => Cons(xpp, xsp)
    }
}

def main() = {
  val lst = [0, 1, 3, 0 - 2, 0 - 8, 9]
  val lst2 = try { iter(lst) }
  with Yield { x =>
    resume { if (x < 0) do Reject() else do Replace(x * 2) }
  }
  println(lst2)
}