Dart_either

Either monad for Dart language and Flutter framework. The library for error handling and railway oriented programming. Supports `Monad comprehensions` (both `sync` and `async` versions). Supports `async map` and `async flatMap` hiding the boilerplate of working with asynchronous computations `Future<Either<L, R>>`. Error handler library for type-safe and easy work with errors on Dart and Flutter. Either is an alternative to Nullable value and Exceptions.