Result<T, E> class sealed

Result of an operation that can either succeed with T or fail with E.

Use Ok for successful values and Err for failures. Chain validation or conversion steps with andThen, and recover failures with orElse.

Result<int, String> parseCount(String text) {
  final value = int.tryParse(text);
  return value == null ? const Err('invalid count') : Ok(value);
}

Result<int, String> requirePositive(int value) {
  return value > 0 ? Ok(value) : const Err('count must be positive');
}

final count = parseCount('42').andThen(requirePositive);