Helper : reads a list of tokens / sample : T_STRING ',' T_STRING ...
```ebnf
list ::= separator? ( item separator )* item
```
function(item, separator, preserveFirstSeparator) {
    const result = [];

    if (this.token == separator) {
      if (preserveFirstSeparator) result.push(null);
      this.next();
    }

    if (typeof item === "function") {
      do {
        result.push(item.apply(this, []));
        if (this.token != separator) {
          break;
        }
      } while (this.next().token != this.EOF);
    } else {
      if (this.expect(item)) {
        result.push(this.text());
      } else {
        return [];
      }
      while (this.next().token != this.EOF) {
        if (this.token != separator) break;
        // trim current separator & check item
        if (this.next().token != item) break;
        result.push(this.text());
      }
    }
    return result;
  }