At a quick glance, it seems to be missing some hook to resolve class hierarchies - which is needed when merging stacks with different types. Consider

    var foo = expr ? new Foo() : new Bar();

For such an expression, some superclass or superinterface for both Foo and Bar has to be chosen.

What I am curios about is, if the java classfile API[1] provides a good model that could work in Haskell as well - I always had the impression that it was heavily influenced by functional programming, for example it uses "lifting transforms"[2].

PS: Good work on the label resolving part - this model is also used by the Java Classfile API and before it, ASM.

[1]: https://docs.oracle.com/en/java/javase/26/docs/api/java.base... [2]: https://docs.oracle.com/en/java/javase/26/docs/api/java.base...