Module:Yesno

return function( arg, default )

   arg = type( arg ) == 'string' and mw.ustring.lower( arg ) or arg

   if arg == nil then
       return nil
   end

   if
       arg == true or
       arg == 'yes' or
       arg == 'y' or
       arg == 'true' or
       tonumber( arg ) ==  1
   then
       return true
   end

   if
       arg == false or
       arg == 'no' or
       arg == 'n' or
       arg == 'false' or
       tonumber( arg ) == 0
   then
       return false
   end

   return default

end