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From: Richard Smith <null@void.com>
Newsgroups: gnu.emacs.help
Subject: Re: TCO with named-let via macros
Date: Tue, 08 Apr 2025 10:26:56 +0100
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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))
>
> 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))))
>
> 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.
>
> Best regards
>
> Axel

Hi there - several months later...
Axel, Steve in particular with your responses.
I got a job as a welder - my first local job on moving here - and had a
"winter campaign".  Was exhausting getting back into it.
Strengthening-up my torso to do weld-runs quickly And accurately And
able to overcome perturbations like the "hose" from machine to MIG
gun/torch snagging and dragging while continuing welding at constant
rate.
Then mental tiredness of getting to grips with the various products and
what they needed.
Just had a chance to look through those posts again.
Thanks so much.
Best wishes, Rich S