/* Factorial function using continuations in C.
 * This time without setjmp() and longjmp().
 * Copyright (C) 2008, Ertugrul Söylemez
 */


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


void fact(int x, void (*e)(char *), void (*k)(int)) {
	void mulCont(int y) {
		k(x*y);
	}

	if (x < 0) e("Factorial of negative number.");
	if (x > 12) e("Number too big.");

	if (!x) k(1);
	fact(x-1, e, mulCont);
}


void readInt(char *str, void (*e)(char *), void (*k)(int)) {
	char *endp;
	int res;

	res = strtol(str, &endp, 0);
	if (str[0] && !endp[0]) k(res);
	e("Invalid integer.");
}


void error(char *msg) { printf("Error: %s\n", msg); exit(1); }
void final(int x) { printf("%i\n", x); exit(0); }


int main(int argc, char **argv) {
	void factCont(int x) {
		fact(x, error, final);
	}

	if (argc != 2) error("Expecting one argument.");
	readInt(argv[1], error, factCont);
}