match.c

#include <stdio.h>

typedef struct {
	int tag;
	union {
		int l;
		struct {
			char* fst;
			float snd;
		} r;
	} payload;
} either;

#define tag_left 1

void
mk_left(either *e, int l)
{
	e->tag = tag_left;
	e->payload.l = l;
}
void
from_left(either e, void f(int))
{
	f(e.payload.l);
}

#define tag_right 2

void
mk_right(either* e, char* r, float f)
{
	e->tag = tag_right;
	e->payload.r.fst = r;
	e->payload.r.snd = f;
}
void
from_right(either e, void f(char*, float))
{
	f(e.payload.r.fst, e.payload.r.snd);
}

#define match(expr) { typeof(expr) _expr = expr; switch(_expr.tag) {
#define end_match } }
#define case_(constr, bindings) } break; case(tag_##constr): { auto void _handler bindings; from_##constr(_expr, _handler); void _handler bindings

int main(int argc, char* argv[])
{
	either e1, e2;
	mk_right(&e1, "argl", 7.0);
	mk_left(&e2, 22);

	match(e1) {
		case_(left, (int n)) {
			printf("left %d\n", n);
		}
		case_(right, (char* s, float f)) {
			printf("right %s %f\n", s, f);
		}
	} end_match;

	match(e2) {
		case_(left, (int n)) {
			printf("left %d\n", n);
		}
		case_(right, (char* s, float f)) {
			printf("right %s %f\n", s, f);
		}
	} end_match;

	return 0;
}