#include <stdbool.h>
#include <stdio.h>

typedef bool (*gen_f)(size_t *i);

gen_f from_to(size_t from, size_t to) {
    size_t i = from;

    bool g(size_t *j) {
        if (i <= to) {
            *j = i++;
            return true;
        } else {
            return false;
        }
    }

    return g;
}

int main(int argc, char **argv) {
    gen_f gen = from_to(5, 7);
    size_t i;

    while (gen(&i)) {
        printf("%ld\n", i);
    }

    return 0;
}