--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/util/gc.lua	Mon Jun 15 14:16:10 2020 +0100
@@ -0,0 +1,50 @@
+local array = require "util.array";
+local set = require "util.set";
+
+local known_options = {
+	incremental = set.new { "mode", "threshold", "speed", "step_size" };
+	generational = set.new { "mode", "minor_threshold", "major_threshold" };
+};
+
+if _VERSION ~= "5.4" then
+	known_options.generational = nil;
+	known_options.incremental:remove("step_size");
+end
+
+local function configure(user, defaults)
+	local mode = user.mode or defaults.mode or "incremental";
+	if not known_options[mode] then
+		return nil, "GC mode not supported on ".._VERSION..": "..mode;
+	end
+
+	for k, v in pairs(user) do
+		if not known_options[mode]:contains(k) then
+			return nil, "Unknown GC parameter: "..k;
+		elseif k ~= "mode" and type(v) ~= "number" then
+			return nil, "parameter '"..k.."' should be a number";
+		end
+	end
+
+	if mode == "incremental" then
+		if _VERSION == "Lua 5.4" then
+			collectgarbage(mode,
+				user.threshold or defaults.threshold,
+				user.speed or defaults.speed,
+				user.step_size or defaults.step_size
+			);
+		else
+			collectgarbage("setpause", user.threshold or defaults.threshold);
+			collectgarbage("setstepmul", user.speed or defaults.speed);
+		end
+	elseif mode == "generational" then
+		collectgarbage(mode,
+			user.minor_threshold or defaults.minor_threshold,
+			user.major_threshold or defaults.major_threshold
+		);
+	end	
+	return true;
+end
+
+return {
+	configure = configure;
+};