The `gc()` function allows controlling the garbage collector of the VM.
It takes the requested operation as first argument and an optional,
operation specific second argument.

Returns `null` if the given operation is invalid or if the operation
specific argument is invalid.

Returns `false` if the requested operation would not result in any
changes.

Returns `true` if the requested oepration succeeded (e.g. starting
the GC when it was previously stopped).

Returns an object count if the given operation is `count`.

-- Testcase --
{%
	printf("Count #1: %d\n", gc("count"));

	// create an unreachable cyclic structure
	let o = {};
	o.cycle = o;
	o = null;

	printf("Count #2: %d\n", gc("count"));

	// invoking gc without any argument defaults to "collect"
	gc();

	printf("Count #3: %d\n", gc("count"));


	// create another unreachable cyclic structure
	o = {};
	o.cycle = o;
	o = null;

	printf("Count #4: %d\n", gc("count"));

	// invoking gc with explicit collect argument
	gc("collect");

	printf("Count #5: %d\n", gc("count"));
%}
-- End --

-- Expect stdout --
Count #1: 5
Count #2: 6
Count #3: 5
Count #4: 6
Count #5: 5
-- End --


Testing enabling the automatic collector.

-- Testcase --
{%
	// start GC, trigger every 10 object allocations
	gc("start", 10);

	for (let i = 0; i < 100; i++) {
		let o = {};
		o.cyle = o;
		o = null;

		if ((i % 10) == 0)
			printf("Count #%d: %d\n", (i / 10) + 1, gc("count"));
	}

	// stop GC
	gc("stop");

	for (let i = 100; i < 200; i++) {
		let o = {};
		o.cyle = o;
		o = null;

		if ((i % 10) == 0)
			printf("Count #%d: %d\n", (i / 10) + 1, gc("count"));
	}
%}
-- End --

-- Expect stdout --
Count #1: 6
Count #2: 12
Count #3: 12
Count #4: 12
Count #5: 12
Count #6: 12
Count #7: 12
Count #8: 12
Count #9: 12
Count #10: 12
Count #11: 12
Count #12: 22
Count #13: 32
Count #14: 42
Count #15: 52
Count #16: 62
Count #17: 72
Count #18: 82
Count #19: 92
Count #20: 102
-- End --