[consteval]

Nominal type systems are pretty much better across the board IMO. Much safer and much less to keep in your head. Modern langs like Rust or F# have very complete and nice to use type systems.

But yeah unfortunately not sure if JS is an appropriate target for these type systems. Nim does it, but I'm not sure how safe it is.

[adamscybot]

One language that comes to mind is ReasonML. It doesn't have runtime checking. It's structural and compile time, but the guarantees are supposedly cast iron. https://reasonml-old.github.io/guide/language/type#design-de...

    type thing = 
      | String(string)
      | Bool(bool);

    let arr: list(thing) = [];

    let add = (item: thing, dst: list(thing)): list(thing) => {
      switch (item) {
      | String(s) => dst @ [String(s)] 
      | Bool(b) => dst @ [Bool(b)]    
      };
    };

    let newList = add(String("asd"), arr);

This doesn't work, since the dst array has to be one that can contain both string and bool in the first place.