util.set: Add set:empty() to discover if the set is the empty set

diff --git a/util/set.lua b/util/set.lua
index 892f1c9d3f70e14bc75a3d36df9ebdcd98531078..bb318adf5290a207d41c3c7f0a2144acf4dd2dcd 100644 (file)
--- a/util/set.lua
+++ b/util/set.lua
@@ -91,6 +91,10 @@ function new(list)
                end
        end
        
+       function set:empty()
+               return not next(items);
+       end
+       
        if list then
                set:add_list(list);
        end