This is a dynamically typed language, it has nothing in its static type system to distinguish between definitely-assigned values and optionally-assigned values.

This is a dynamically typed language, it has nothing in its static type system to distinguish between definitely-assigned values and optionally-assigned values. That is, there's no way to tell the compiler that a variable or function parameter or return value is a T vs a Maybe<T> or Either<T,U>. At best it could perform definite assignment analysis on variable declarations, but it can't go very far. In particular, it would do nothing for function return values. As a result, the best it could give you is runtime errors when you e.g. access the value of a dynamic Maybe without checking for presence first. Without static analysis, this isn't hugely useful.