effekt VS cooltt

I like it. Modern languages that distinguish between pure and impure programs like Flix, Koka, and Effekt do so on the type level instead of syntactically. This has three advantages:

The problem with checked exceptions been identified and solved. The same problem and solution applies to effect handlers. Effekt is a language with lexical effect handlers which doesn't have this problem. Consider the following program in Effekt:

Yes, for you this is the right decision. But for us going to CPS makes everything significantly easier and in cases where you do use control effects significantly faster. For our language Effekt we are exploring different tradeoffs in different backends.

This pattern they observe is nicely captured by effect handlers. These examples are written in Effekt.

This is beyond my level of expertise. But effect tracking? There are some cool languages out there that do that consistently! Search for "algebraic effects". My favorite is Koka. Effekt also seems to be a popular choice.

https://effekt-lang.org/ A research language with effect handlers and lightweight effect polymorphism

Examples are languages like Koka, Effekt, Links, or Unison. These languages come with a type-and-effect system: a function's type not only tell you which values the function accepts and which values it returns, but also which effects it has. This is relevant to your question, because throwing an exception is one such effect.

It seems that with Effekt we are pursuing the same goal, but coming from the opposite direction, perhaps one day we will meet in the middle :). We start from a purely functional language and carefully add effects like mutation.

- https://effekt-lang.org/

If you're looking for stuff pushing the boundaries of PL research, Agda (especially Cubical Agda) might be cool to look at. It's got lots of cutting edge stuff in it, pushing the boundaries of what is currently possible with dependent type theory. It's not the only language out there with cubical features (see also: cooltt), but it's probably one of the more fleshed-out implementations in terms of being practically useful. The 1Lab makes heavy use of it. There's also Introduction to Univalent Foundations of Mathematics with Agda that might be interesting to look at too!