A good point that Lisp encapsulates a lot of the extensibility I describe, but I think there's two missing parts: a strong type system and a clear story for FFI. With Haskell (or Rust or Scala or OCaml or ...) you could take advantage of static type guarantees, both for productivity as well as for generating more efficient code. That isn't to say you can't type check Lisp code, but that you could get it for free with a statically typed language. For FFI, if your eDSL is going to be generating CUDA code or whatever, then you need a clear way to translate values between the two sides. This is easy for a language like Rust and is doable for languages like Haskell, but I don't know if anything like that has been tried for Lisp.