Generators in C

generator.c

#include <stdio.h>

#define FIRST(N, ...) (N)
#define foreach(X, F, ...) \
	for (init_##F(__VA_ARGS__), X = F(FIRST(__VA_ARGS__));\
	     FIRST(__VA_ARGS__)->_running;\
	     X = F(FIRST(__VA_ARGS__)))

struct count_state {
	int _running;
	int n;
};

void
init_count(struct count_state *g, int start)
{
	g->_running = 1;
	g->n = start;
}

int
count(struct count_state *g)
{
	return g->n++;
}

struct range_state {
	int _running;
	int n;
	int start;
	int end;
	int step;
};

void
init_range(struct range_state *g, int start, int end, int step)
{
	g->_running = g->n < g->end;
	g->start = start;
	g->end = end;
	g->step = step;
	g->n = start;
}

struct list_iter_state {
	int _running;
	int *p;
	size_t n;
};

int
range(struct range_state *g)
{
	int r = g->n;
	g->_running = g->n < g->end;
	g->n += g->step;
	return r;
}

void
init_list_iter(struct list_iter_state *g, int *p, size_t n)
{
	g->_running = g->n > 0;
	g->p = p;
	g->n = n;
}

int
list_iter(struct list_iter_state *g)
{
	g->_running = g->n > 0;
	g->n--;
	return *(g->p++);
}

int
main(void)
{
	struct range_state g;
	int x;

	foreach (x, range, &g, 1, 10, 3) {
		printf("%d\n", x);
	}

	printf("\n");

	struct list_iter_state h;
	int xs[] = {2, 3, 5, 7, 11};

	foreach (x, list_iter, &h, xs, sizeof(xs)/sizeof(xs[0])) {
		printf("%d\n", x);
	}

	return 0;
}