Any difference between Lazy evaluation and Short-circuit evaluation?

Question

From Wikipedia:

In programming language theory, lazy evaluation or call-by-need is an evaluation strategy which delays the evaluation of an expression until its value is needed

Short-circuit evaluation is:

Short-circuit evaluation, minimal evaluation, or McCarthy evaluation denotes the semantics of some Boolean operators in some programming languages in which the second argument is only executed or evaluated if the first argument does not suffice to determine the value of the expression

So what's the difference between them for example when I have:

if(false && true && true) {
    //boo
}

As far as I know, compiler doesn't execute expressions after false because I have && so the whole expression will be false finally. (right?)

So is that behavior called Lazy evaluation or Short-circuit evaluation?

You have some misunderstanding of what parsing actually refers to. — Gumbo
@Gumbo Edited, I think executing is the correct word, isn't it? — Afshin Mehrabani

Artem Sobolev Artem Sobolev · Accepted Answer · 2013-02-16T09:27:06

The difference is that in case of lazy evaluation an expression is evaluated only when it is needed, while in case of short-circuit evaluation expression evaluation stops right after you know the result. It's sort of orthogonal notions.

Lazy evaluation can be applied to any computation (short-circuit scheme usually is used only with bools). It doesn't cut-off useless computation, but delays the whole computation until its result is required.

variable = bigAndSlowFunc() or evenSlowerFnc()
if (carry out heavy computations)
  print "Here it is: ", variable
else
  print "As you wish :-)"

If evaluation is lazy, variable will be computed only if we choose to go into the first (then) branch of if, otherwise it won't. At the evaluation stage (when we prepare arguments for print) short-circuit scheme can be used to decide if we need to call evenSlowerFnc.

So in your example, it's short-circuit evaluation since no delay of computation happen.

Any difference between Lazy evaluation and Short-circuit evaluation?

1 Answers