MultiSource/Benchmarks/Prolangs-C++/primes/primes.cpp

// From Ravi Sethi's book on Programming Languages.

#include <stdio.h>
class item {
public:
	item *source;
	item(item *src) {source = src;}
	virtual int out() {return 0;}
};
class counter : public item {
	int value;
public:
	int out() {return value++;}
	counter(int v) : item(0) {value = v;}
};
class sieve : public item {
public:
	int out();
	sieve(item *src) : item(src) {};
};
class filter : public item {
	int factor;
public:
	int out();
	filter(item *src, int f) : item (src) {factor = f;}
};

int main() {
	counter c(2);
	sieve s(&c);
	int next;
	do {
		next = s.out();
		printf("%d ",next);
	} while (next < 100001);
	printf ("\n");
}
int sieve::out() {
	int n = source->out();
	source = new filter(source,n);
	return n;
}
int filter::out() {
	while (1) {
		int n = source->out();
		if (n % factor)
			return n;
	}
}