--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/util/set.lua	Sun Mar 22 12:13:39 2009 +0000
@@ -0,0 +1,75 @@
+
+module "set"
+
+function new(list)
+	local items = {};
+	local set = { items = items };
+	
+	function set:add(set, item)
+		items[item] = true;
+	end
+	
+	function set:contains(set, item)
+		return items[item]
+	end
+	
+	function set:items(set)
+		return items;
+	end
+	
+	function set:remove(set, item)
+		items[item] = nil;
+	end
+	
+	function set:add_list(set, list)
+		for _, item in ipairs(list) do
+			items[item] = true;
+		end
+	end
+	
+	function set:include(set, otherset)
+		for item in pairs(otherset) do
+			items[item] = true;
+		end
+	end
+
+	function set:exclude(set, otherset)
+		for item in pairs(otherset) do
+			items[item] = nil;
+		end
+	end
+	
+	return set;
+end
+
+function union(set1, set2)
+	local set = new();
+	local items = set.items;
+	
+	for item in pairs(set1.items) do
+		items[item] = true;
+	end
+
+	for item in pairs(set2.items) do
+		items[item] = true;
+	end
+	
+	return set;
+end
+
+function difference(set1, set2)
+	local set = new();
+	local items = set.items;
+	
+	for item in pairs(set1.items) do
+		items[item] = true;
+	end
+
+	for item in pairs(set2.items) do
+		items[item] = nil;
+	end
+	
+	return set;
+end
+
+return _M;