Simple option type in C

c_option_type.c

//usr/bin/make -s "${0%.*}" CFLAGS="-O2 -Wall -Werror" && ./"${0%.*}" "$@"; s=$?; rm ./"${0%.*}"; exit $s

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

enum option_tag { OPTION_SOME, OPTION_NONE };

#define option_type(T) { enum option_tag tag; T some; }
#define SOME(S) { .tag = OPTION_SOME, .some = S }
#define NONE() { .tag = OPTION_NONE }

#define if_some(A, X) for (bool _once = true; _once; _once = false) /* execute only once */ \
  for (typeof(A) _a = (A); _once; _once = false) /* only evaluate A once */\
  if (_a.tag == OPTION_SOME) /* check tag */\
  for (X = _a.some; _once; _once = false) /* we match! so assign local binding */


struct option_int option_type(int);

static struct option_int compute_a_thing(void) {
	printf("computing things!\n");

	struct option_int a_thing = SOME(5);
	//a_thing = (struct option_int)NONE();
	return a_thing;
}

int main(int argc, char const *argv[])
{
	if_some(compute_a_thing(), int x) {
		// x is locally scoped here and assigned the unwrapped result 
		printf("we have a thing: %d\n", x);
	} else {
		printf("nope\n");
	}
	return 0;
}