[Lio]

I think they've missed a trick there, they could have used `|` like low-type does.

e.g.

  def greet(name: String | "Hello"): String

I know it's all subjective but I think that reads better and it's valid ruby.

To be honest low-type with a static analysis tool would be my favourite syntax for this.

https://github.com/low-rb/low_type