var [const] D=Dictionary;	// short cut
// blank symbol and terminating state(s) are Void
var Lt=-1, Sy=0, Rt=1;  // Left, Stay, Right

fcn printTape(tape,pos){
   tape.keys.apply("toInt").sort()
      .pump(String,'wrap(i){ ((pos==i) and "(%s)" or " %s ").fmt(tape[i]) })
      .println();
}
fcn turing(state,[D]tape,[Int]pos,[D]rules,verbose=True,n=0){
   if(not state){
      print("%d steps. Length %d. Tape: ".fmt(n,tape.len()));
      printTape(tape,Void);
      return(tape);
   }
   r:=rules[state][tape[pos] = tape.find(pos)];
   if(verbose) printTape(tape,pos);
   tape[pos]=r[0];
   return(self.fcn(r[2],tape,pos+r[1],rules,verbose,n+1));
}