Diff

--- a/util/set.lua	Tue Apr 21 21:11:12 2009 +0100
+++ b/util/set.lua	Wed Apr 22 20:14:11 2009 +0100
@@ -1,10 +1,60 @@
-local ipairs, pairs = 
-      ipairs, pairs;
+local ipairs, pairs, setmetatable, next, tostring = 
+      ipairs, pairs, setmetatable, next, tostring;
+local t_concat = table.concat;
 
 module "set"
 
+local set_mt = {};
+function set_mt.__call(set, _, k)
+	return next(set._items, k);
+end
+function set_mt.__add(set1, set2)
+	return _M.union(set1, set2);
+end
+function set_mt.__sub(set1, set2)
+	return _M.difference(set1, set2);
+end
+function set_mt.__div(set, func)
+	local new_set, new_items = _M.new();
+	local items, new_items = set._items, new_set._items;
+	for item in pairs(items) do
+		if func(item) then
+			new_items[item] = true;
+		end
+	end
+	return new_set;
+end
+function set_mt.__eq(set1, set2)
+	local set1, set2 = set1._items, set2._items;
+	for item in pairs(set1) do
+		if not set2[item] then
+			return false;
+		end
+	end
+	
+	for item in pairs(set2) do
+		if not set1[item] then
+			return false;
+		end
+	end
+	
+	return true;
+end
+function set_mt.__tostring(set)
+	local s, items = { }, set._items;
+	for item in pairs(items) do
+		s[#s+1] = tostring(item);
+	end
+	return t_concat(s, ", ");
+end
+
+local items_mt = {};
+function items_mt.__call(items, _, k)
+	return next(items, k);
+end
+
 function new(list)
-	local items = {};
+	local items = setmetatable({}, items_mt);
 	local set = { _items = items };
 	
 	function set:add(item)
@@ -41,11 +91,15 @@
 		end
 	end
 	
+	function set:empty()
+		return not next(items);
+	end
+	
 	if list then
 		set:add_list(list);
 	end
 	
-	return set;
+	return setmetatable(set, set_mt);
 end
 
 function union(set1, set2)
@@ -87,4 +141,8 @@
 	return set;
 end
 
+function xor(set1, set2)
+	return union(set1, set2) - intersection(set1, set2);
+end
+
 return _M;