Scala By Example Chapter 11 Solutions - Exercise 11.2.1

Exercise 11.2.1 Write a function repeatLoop with also additional syntax for an until clause.

The repeat { command } until (condition) was tricky. The trick is to realize that "until" would be a method call, and for it to be a method call, "repeat {command}" would have to be an object. Since objects are created using new, we could wrap this object creation with a method. The result is below. Note that the second method has been changed to repeatUntilLoop since it would conflict with the previous method repeatUntil.

	object FunctionalLoops {
	def repeatLoop(command: => Unit)(condition: => Boolean) {
	command
	if (condition) {
	repeatLoop(command)(condition)
	} else ()
	}
	def repeatUntilLoop(command: => Unit) = {
	class RepeatUntilLoopClass(command: => Unit) {
	def until(condition: => Boolean): Unit = {
	command
	if (!condition) {
	until(condition)
	} else ()
	}
	}
	new RepeatUntilLoopClass(command)
	}
	def main(args: Array[String]) {
	var i = 10;
	repeatLoop { i -= 1; println(i) } (i > 0)
	var j = 1;
	repeatUntilLoop { j += 10; println(j) } until (j >= 100)
	}
	}

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