C continuation passing

gistfile1.c

#include <stdio.h>
#include <stdlib.h>

#define NEXT(n) ((n)->next(n))

typedef struct co_fib {
    int (*next)(struct co_fib *);
    int a;
    int b;
} * co_fib_t;

int co_fib_next(struct co_fib *state) {
    int t = state->a + state->b;
    state->a = state->b;
    state->b = t;
    return state->a;
}

co_fib_t co_fib_new() {
    co_fib_t f = (co_fib_t)malloc(sizeof(struct co_fib));
    f->a = 0;
    f->b = 1;
    f->next = co_fib_next;
}

void co_fib_del(co_fib_t f) {
    free(f);
}

int main() {
    co_fib_t f = co_fib_new();
    int k;

    for (k = 0; k < 30; k++) {
        printf("%d\n", NEXT(f));
    }

    co_fib_del(f);
}