[lmm]

> And (compile-time) macros are one thing, but what happens when you need metaprogramming at runtime (for example dynamic code generation)?

I'd agree that stage polymorphism is rarely used or appreciated in languages that don't have it (though I see no reason it should be incompatible with typing; as far as I can see your example is much the same as e.g. Scala's LMS; as with macros of course it's substantially more cumbersome to do this in a language with much more syntax than lisp[1]). I'm not sure that it qualifies as a "blub paradox" since to my mind it's a performance optimization rather than something that fundamentally changes language expressiveness - having AST-like datastructures that are gradually transformed/interpreted at runtime is very much a standard technique in ML-family languages, wider adoption of stage polymorphism would mostly lead to programming the same way and having it run faster, I think.

[1] I'm not convinced that it would be impossible to make a language with ML-style types but a very lightweight syntax that made metaprogramming easier. Personally even looking at e.g. Haskell I find myself wishing for a more visible syntax more often than I'm wishing for better interpreter tower performance, shrug.