First time I'm hearing about `named-let` and tail call optimisation in Emacs, thanks for sharing!

A clarification: Tail call optimisation in Emacs is not tied specifically to `named-let`, but it is tied to `cl-labels` (which `named-let` uses internally). Normal functions declared using `defun` don't currently support tail call optimisation.

(The tail call optimisation was only added to `cl-labels` recently, in Emacs 28.1: https://github.com/emacs-mirror/emacs/commit/29c7f8c915c3889...)