Result monad for dart

result.dart

class Result<Success, Error extends Exception> {
  final Success? successIfAny;
  final Error? errorIfAny;

  const Result.success(this.successIfAny) : errorIfAny = null;
  const Result.error(this.errorIfAny) : successIfAny = null;
  
  Result<Success, Error> onSuccess(Function(Success) handler) {
    if (successIfAny == null) return this;
    handler(successIfAny as Success);
    return this;
  }

  Result<Success, Error> onError(Function(Error) handler) {
    if (errorIfAny == null) return this;
    handler(errorIfAny as Error);
    return this;
  }
}