type String {
  str value;

  void printStr();
  void printLine();
  Integer strToInt();
  Float strToFloat();
  Integer strLen();
  String substr(int, int);
  Character charAt(int);
}

class StrBox() : String impl String {
  init str value;

  void printStr() { printStr(value); }
  
  void printLine() { printLine(value); }

  Integer strToInt() { return new IntBox(value = strToInt(value)); }

  Float strToFloat() { return new FloatBox(value = strToFloat(value)); }

  Integer strLen() { return new IntBox(value = strLen(value)); }

  String substr(int start, int end) {
    return new StrBox(value = substr(value, start, end));
  }

  Character charAt(int i) {
    return new CharBox(value = charAt(value, i));
  }

  export String : value, printStr, printLine, strToInt, strToFloat, strLen,
                  substr, charAt;
}