Comment by cubefox

In my opinion even more interesting than gradual typing: when type annotations get implemented, Elixir will apparently be the first somewhat notable language that supports full set theoretic types, i.e., not just unions and intersections but also complements ("negations").

This is interesting because TypeScript and Scala only support set theoretic union and intersection types, but {union, intersection} is not functionally complete, while {union, intersection, complement} is [1]. So Elixir will be able to express arbitrary set theoretic types while TypeScript can't. E.g. "A or (B and not C)" or "Either A or B".

1: https://en.wikipedia.org/wiki/Functional_completeness#Set_th...