Why is lazy evaluation useful?

Question

I have long been wondering why lazy evaluation is useful. I have yet to have anyone explain to me in a way that makes sense; mostly it ends up boiling down to \"trust me\".<

Answer 1

The most useful exploitation of lazy evaluation that I've used was a function that called a series of sub-functions in a particular order. If any one of these sub-functions failed (returned false), the calling function needed to immediately return. So I could have done it this way:

bool Function(void) {
  if (!SubFunction1())
    return false;
  if (!SubFunction2())
    return false;
  if (!SubFunction3())
    return false;

(etc)

  return true;
}

or, the more elegant solution:

bool Function(void) {
  if (!SubFunction1() || !SubFunction2() || !SubFunction3() || (etc) )
    return false;
  return true;
}

Once you start using it, you'll see opportunities to use it more and more often.