readString method
Implementation
String readString() {
  if (peek() == "\"" || peek() == "'") {
    return readQuotedString();
  } else
    return readUnquotedString();
}
String readString() {
  if (peek() == "\"" || peek() == "'") {
    return readQuotedString();
  } else
    return readUnquotedString();
}