class Cell {
  init(previous, next, data) {
    this.previous = previous;
    this.next = next;
    this.data = data;
  }
}

class Tape {
  init() {
    this.current = Cell(nil, nil, 0);
  }

  backward() {
    if (this.current.previous == nil) {
      this.current.previous = Cell(nil, this.current, 0);
    }

    this.current = this.current.previous;
  }

  forward() {
    if (this.current.next == nil) {
      this.current.next = Cell(this.current, nil, 0);
    }

    this.current = this.current.next;
  }

  increment() {
    this.current.data = this.current.data + 1;
  }

  decrement() {
    this.current.data = this.current.data - 1;
  }
}

class Interpreter {
  init(bfpath) {
    this.bfpath = bfpath;
  }

  run() {
    var tape = Tape();
    var instruction = read(this.bfpath);
    
    while (instruction != nil) {
      if (instruction == ">") {
        tape.forward();
      }

      if (instruction == "<") {
        tape.backward();
      }

      if (instruction == "+") {
        tape.increment();
      }

      if (instruction == "-") {
        tape.decrement();
      }

      if (instruction == ".") {
        asciiOut(tape.current.data);
      }

      if (instruction == ",") {
        tape.current.data = promptAscii("");
      }

      if (instruction == "[" and tape.current.data == 0) {
        instruction = read(this.bfpath);
        var bracketCount = 1;
        while (bracketCount > 0 and instruction != nil) {
          if (instruction == "[") { bracketCount = bracketCount + 1; }
          if (instruction == "]") { bracketCount = bracketCount - 1; }
          if (bracketCount > 0) { instruction = read(this.bfpath); }
        }
      }

      if (instruction == "]" and tape.current.data != 0) {
        instruction = read(this.bfpath, true);
        var bracketCount = 1;
        while (bracketCount > 0 and instruction != nil) {
          if (instruction == "]") { bracketCount = bracketCount + 1; }
          if (instruction == "[") { bracketCount = bracketCount - 1; }
          if (bracketCount > 0) { instruction = read(this.bfpath, true); }
        }
      }

      instruction = read(this.bfpath);
    }
  }
}

var bfScript = args(0);
var interpreter = Interpreter(bfScript);
interpreter.run();