/* iGASM Example */
  /* "Towers of Hanoi". */
  
  FUNCTIONS
      agent : Number;
      goal  : Number -> Number;
      st    : String -> Stack;
      fromPole, toPole, auxPole : Number -> String;
  
  INITIAL
      goal(1) := 7;
      fromPole(1) := "left";
      toPole(1)   := "right";
      auxPole(1)  := "middle";
      agent   := 1;
      st("right")   := emptyStack;
      st("middle")  := emptyStack;
      st("left")    := stPush(stPush(stPush(stPush(stPush(stPush(stPush(emptyStack,
                                        7), 6), 5), 4), 3), 2), 1);
                                        
  RULES
      IF goal(agent) = 0 THEN
          agent := agent - 1;
      ELSEIF goal(agent) != stTop(st(fromPole(agent))) THEN
          agent := agent + 1;
          goal(agent+1) := goal(agent) - 1;
          fromPole(agent+1) := fromPole(agent);
          toPole(agent+1)   := auxPole(agent);
          auxPole(agent+1)  := toPole(agent);
      ELSE
          st(fromPole(agent)) := stPop( st(fromPole(agent)));
          st(toPole(agent))   := stPush( st(toPole(agent)), goal(agent) );
          goal(agent) := goal(agent) - 1;
          fromPole(agent) := auxPole(agent);
          auxPole(agent)  := fromPole(agent);
        writeln := frompole(agent)+" -> "+toPole(agent);
      ENDIF
          
  FINAL
      goal(agent) = undef;