tokenReader.js

class TokenReader {
  constructor(tokens) {
    this.tokens = tokens;
    this.pos = 0;
  }
  read() {
    if (this.pos < this.tokens.length) {
      return this.tokens[this.pos++];
    }
    return null;
  }
  peek() {
    if (this.pos < this.tokens.length) {
      return this.tokens[this.pos];
    }
    return null;
  }
  unread() {
    if (this.pos > 0) {
      this.pos--;
    }
  }
}

module.exports = TokenReader;