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The advantage of the monadic approach is that it's easy to abstract over, because it's just an ordinary type in the language. So e.g. in scala I can call the same "sequence" method on a List[Option[Int]] as I do on a List[Future[Int]] or a List[ErrorMessage \/ Int]].

Unions seem like more of a language-level feature, so I'm not sure you could abstract over them in the same way.

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I totally agree. Ridding yourself of nils via the Maybe monad offers incredible abstraction potential, but would feel out of place in Crystal's Rubyishness without deeper thought into bringing other monads into play too.

Nonetheless, I am thrilled that we are seeing more and more languages that don't have implicit nullability on any type.

I re-read my initial comment and can see some ambiguity in my phrasing "Maybe being monadic ...". That wasn't me saying "maybe it is true that being monadic..." but rather "the fact that Maybe is monadic..."

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