lib/lexer.js
function() {
    while (this.input) {
      var prev = this.input;
      this.advance();
      if (this.input && prev === this.input) {
        throw new Error(`no lexers registered for: "${this.input.substr(0, 10)}"`);
      }
    }
  }
function() {
    while (this.input) {
      var prev = this.input;
      this.advance();
      if (this.input && prev === this.input) {
        throw new Error(`no lexers registered for: "${this.input.substr(0, 10)}"`);
      }
    }
  }
Get the next AST token