How Does One Make Scala Control Abstraction in Repeat Until?

Question

I am Peter Pilgrim. I watched Martin Odersky create a control abstraction in Scala. However I can not yet seem to repeat it inside IntelliJ IDEA 9. Is it the IDE?

Answer 1

Here is a solution without the StackOverflowError.

scala>   class ConditionIsTrueException extends RuntimeException
defined class ConditionIsTrueException

scala>   def repeat(body: => Unit) = new {
 |     def until(condition: => Boolean) = { 
 |       try {
 |         while(true) {
 |           body
 |           if (condition) throw new ConditionIsTrueException
 |         }   
 |       } catch {
 |         case e: ConditionIsTrueException =>
 |       }   
 |     
 |     }   
 |   }
repeat: (body: => Unit)java.lang.Object{def until(condition: => Boolean): Unit}

scala> var i = 0              
i: Int = 0

scala> repeat { println(i); i += 1 } until(i == 3)
0
1
2

scala> repeat { i += 1 } until(i == 100000)       

scala> repeat { i += 1 } until(i == 1000000)

scala> repeat { i += 1 } until(i == 10000000)

scala> repeat { i += 1 } until(i == 100000000)

scala> 

According to Jesper and Rex Kerr here is a solution without the Exception.

def repeat(body: => Unit) = new {
  def until(condition: => Boolean) = { 
    do {
      body
    } while (!condition)
  }   
}