Another thing I'd like to experiment in language design is a typesystem based on Cantor's set theory.
Basically, a type is a logic predicate that is granted to always stay true during the data lifetime.
Such approach meld the difference between structural type system, nominative type system and (value-)dependent type system.
If you have two types, Integer and Even, you can pass an Integer to a function than takes an Even only if you have checked if such integer is even.
And, obviously, you can always use an Even value when you need an Integer.
Imagine a `head` function that only apply to NonEmptyList, that is a List whose length is greater than 0, and so on.
Why Cantor set theory?
Because people learn it at primary school and well... I'm naive... just like #Dijkstra. 😉
