implement Execlib;

include "sys.m"; sys: Sys;
include "draw.m";

Execlib: module {
	init: fn(ctxt: ref Draw->Context, args: list of string);
	hailstone: fn(i: big): list of big;
};

init(nil: ref Draw->Context, nil: list of string)
{
	sys = load Sys Sys->PATH;

	seq := hailstone(big 27);
	l := len seq;

	sys->print("hailstone(27):  ");
	for(i := 0; i < 4; i++) {
		sys->print("%bd, ", hd seq);
		seq = tl seq;
	}
	sys->print("⋯");
	
	while(len seq > 4)
		seq = tl seq;

	while(seq != nil) {
		sys->print(", %bd", hd seq);
		seq = tl seq;
	}
	sys->print(" (length %d)\n", l);

	max := 1;
	maxn := big 1;
	for(n := big 2; n < big 100000; n++) {
		cur := len hailstone(n);
		if(cur > max) {
			max = cur;
			maxn = n;
		}
	}
	sys->print("hailstone(%bd) has length %d\n", maxn, max);
}

hailstone(i: big): list of big
{
	if(i == big 1)
		return big 1 :: nil;
	if(i % big 2 == big 0)
		return i :: hailstone(i / big 2);
	return i :: hailstone(big 3 * i + big 1);
}