/* Factorial function using continuations in C.
 * Copyright (C) 2008, Ertugrul Söylemez
 */

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


int factorial(int x, jmp_buf e, jmp_buf k) {
	static int p;
	jmp_buf r;
	int jv;

	p = 1;
	if (x < 0) longjmp(e, 25);
	jv = setjmp(r);
	if (!jv) longjmp(r, x);

	p *= jv;
	if (jv > 1) longjmp(r, jv-1);
	longjmp(k, p);
}


int main(int argc, char **argv) {
	jmp_buf e;
	jmp_buf p;
	int jv;

	jv = setjmp(e);
	if (jv) {
		puts("_Expecting one argument.\0Invalid integer." + jv);
		return jv;
	}

	jv = setjmp(p);
	if (jv) {
		printf("%i\n", jv);
		return 0;
	}

	if (argc != 2) longjmp(e, 1);
	factorial(atoi(argv[1]), e, p);
}