mob
   player
       var
          level = 1
          exp = 0
          max_exp = 1000

       proc
           level_up_check()
               while(exp >= max_exp)
                    level++
                    exp -= max_exp
                    max_exp += max_exp
                    src << "you are now level [level]!"
       verb
           gain_exp()
               exp += 100
               level_up_check()