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 this into C code?

Edit: I am looking to translate this python code into a similar generator in C, with next() function. What I am not looking for is how to create a function in C to output multiples of 2. Multiples of 2 is merely an example to illustrate the problem of lazy eval generators in C.

Answer 1

You could try to encapsulate this in a struct:

typedef struct s_generator {
    int current;
    int (*func)(int);
} generator;

int next(generator* gen) {
    int result = gen->current;
    gen->current = (gen->func)(gen->current);
    return result;
}

Then you define you multiples with:

int next_multiple(int current) { return 2 + current; }
generator multiples_of_2 = {0, next_multiple};

You get the next multiple by calling

next(&multiples_of_2);