Loops

Effekt includes a (almost standard) built-in while loop expression as its sole native looping construct.

def fib(n: Int): Int = {
  var last = 0
  var current = 1
  var iters = 0
  while (iters < n) {
    val next = last + current
    last = current
    current = next
    iters = iters + 1
  } else { println("ran for " ++ show(iters) ++ " iterations") }
  last
}

fib(10)

A while loop consists of a condition on which to continue the loop, the body, and an optional else branch that is run when the while loop ended.

Furthermore, there is a loop function defined in the standard library, you can use for infinite, breakable loops.

interface Event[A] {
  def receive(): Option[A]
}
record Job()

def worker() = loop { {l} =>
  val packet = do receive[Job]()
  packet match {
    case Some(p) => println("processing request")
    case None() => l.break()
  }
}

The operations break and continue have their usual semantics, except that they are handled by loop as operations of the algebraic effect Control.

Additionally, the standard library also includes the functions each and repeat.

each(1, 11) { (n) => if (n.mod(2) == 0) println(n)  }

each expects two value arguments: an inclusive starting index and an exclusive end index. At each iteration, the current index is passed to the block argument of each. You may also use the operations break and continue when binding a label (here l):

each(1, 11) { (n) {l} => if (n.mod(2) == 0) println(n) else l.continue() }

repeat just expects one value argument that controls how often the passed block argument is to be executed. Again, you may bind a label to use the operations of the Control effect here.

repeat(2) { println("Effekt!") }