Another Slang example. As there are no mutable members / variables (yet), we must use functional concepts for things like iteration. This program prints 12345 twice. Due to use of names like next() and hasNext(), the content of the loop should be before the while statement. The loop will be continued with the Range returned from i.next() and so …

Range.sl

╒═════════════════════════╕
╎ Range class             ╎
╘═════════════════════════╛
val class Range (from: Int, to: Int) {
  def hasNext() = from < to
  def valid() = from <= to
  def current() = from
  def next() = Range(from + 1, to)
}

extending Int {
  def to(that: Int) = Range(this, that)
} 
╒═════════════════════════╕
╎ Range example           ╎
╘═════════════════════════╛
def main() = {
  /* This is more like a do-while loop. It assumes ranges are never empty. */
  loop(i := 1 to 5) {
    printNumber(i.current());
    while (i.hasNext()) do i.next()
  }
  /* This is like a normal while loop. If I could come up with better names, this might be better. */
  loop(i := 1 to 5) while i.valid() do {
    printNumber(i.current());
    i.next()
  }
  /* Once I add some kind of for-comprehensions, it could generate a similar loop with syntax like below */
  //for (i <- 1 to 5) printNumber(i);
}

You can also think of the loop as a tail-recursive anonymous function, except it never compiles to a function. Actually it gets expanded to:

loop(i: Range := 1 to 5)
if i.valid() then {
printNumber(i.current());
continue(i.next())
} else break()

Where continue and break are magic functions that are only available inside loop bodies.