Answering to http://stackoverflow.com/a/6160080/53974.

TailRec.scala

import annotation.tailrec

object TailRec {
  // A tail-recursive function, from
  // http://stackoverflow.com/a/6160080/53974
  @tailrec def isDivis(x:Int, i:Int):Boolean =
    if(i > 20) true
    else if(x % i != 0) false
    else isDivis(x, i+1)

  // The same code, written using && and || (in a more readable way):
  // since && and || are short-circuiting, this code means the same
  // thing. So much the same that isDivis2 is also tail-recursive.
  @tailrec def isDivis2(x: Int, i: Int): Boolean =
    (i > 20) || (x % i == 0) && isDivis2(x, i+1)

  // I compared the generated bytecode, and noticed that there is a
  // minor difference - similar to the difference between if (cond)
  // branch1 branch2 and if (!cond) branch2 branch1, that is the order
  // of branches is different.
}