Having skimmed the PicoLisp interpreter a long time ago, I remember it being like Emacs Lisp in that common performance-critical functions like mapcar were impl

Having skimmed the PicoLisp interpreter a long time ago, I remember it being like Emacs Lisp in that common performance-critical functions like mapcar were implemented in C. It seems like a very pragmatic way to get the performance you need without getting into byte codes or machine language. And since you are still interpreting the s-exprs directly, debugging and introspection remain easy.