How would one implement Lazy Evaluation in C?

Question

Take for example,

The follow python code:

def multiples_of_2():
  i = 0
  while True:
    i = i + 2
    yield i

How do we translate thi

Answer 1

The basic approach is to not do it. In Python (and C#) the 'yield' method stores local state between calls, whereas in C/C++ and most other languages the local state stored on the stack is not preserved between calls and this is a fundemental implementation difference. So in C you'd have to store the state between calls in some variable explicitly - either a global variable or a function parameter to your sequence generator. So either:

int multiples_of_2() {
   static int i = 0;
   i += 2;
   return i;
}

or

int multiples_of_2(int i) {
   i += 2;
   return i;
}

depending upon if there's one global sequence or many.

I've quickly considered longjmp and GCC computed gotos and other non-standard things, and I can't say I'd recommend any of them for this! In C, do it the C way.