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NNTP-Posting-Date: Sun, 11 Aug 2024 18:56:25 +0000
From: steve g <sgonedes1977@gmail.com>
Newsgroups: gnu.emacs.help
Subject: Re: TCO with named-let via macros
References: <m11q42e6zz.fsf@void.com> <8734oi5ksx.fsf@axel-reichert.de> <m1ttgxhkp3.fsf@void.com> <87ed6wjffl.fsf@gmail.com> <87y154m645.fsf@axel-reichert.de>
Date: Sun, 11 Aug 2024 14:56:19 -0400
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Axel Reichert <mail@axel-reichert.de> writes:

> steve g <sgonedes1977@gmail.com> writes:
>
< > check the elisp manual. it shows how to implement true tail recursion
< > in emacs.
< >
< > (defun elisp-sum (args)
< >   (elisp-sum-aux args 0))
< >
< > (defun elisp-sum-aux (args res)
< >   (if (null args)
< >       res
< >       (elisp-sum-aux (cdr args) (+ (car args) res))))
< >
< > you can byte compile it. very simple.
>

> ... and then easily find out that it will enter the debugger for large
> ARGS, say
>
>   (defun elisp-sum (number-sequence 1 10000000))


I was thinking more of the concept; no more than that.

(elisp-sum (number-sequence 1 107)).. there is a limit to list length; that is
usually time.


> But with
>
> (defmacro defun-tco (name args body)
>   "Wraps a 'named-let' around BODY to have a TCO of function NAME with ARGS."
>   (declare (indent defun))
>   (let ((bindings (gensym)))
>     (setq bindings (mapcar #'(lambda (arg) (list arg arg)) args))
>     `(defun ,name ,args
>        (named-let ,name ,bindings
>          ,body))))
>


yes, yes; lambda bindings will certainly work better. even in common
lisp there is a limit to the length of &rest arguments and can take some
time to process large lists; sometimes crashing the stack.

If you are interested in non-deterministic software then screamer is
fairly cool.

> and
>
> (defun-tco elisp-sum-aux (args res)
>   (if (null args)
>       res
>     (elisp-sum-aux (cdr args) (+ (car args) res))))
>
> a



>   (defun elisp-sum (number-sequence 1 10000000))
>
> will do.

this is probably the best option - just mentioning that recursion does
work fairly well in emacs lisp...


>
> Best regards

same


> Axel