Groups | Search | Server Info | Login | Register

Groups > gnu.emacs.help > #60996

Re: TCO with named-let via macros

Show all headers | View raw

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

Back to gnu.emacs.help | Previous | Next — Previous in thread | Next in thread | Find similar

Thread

thanks - calculate pi fn. in elisp Richard Smith <null@void.com> - 2024-07-09 19:48 +0100
  TCO with named-let via macros (was: thanks - calculate pi fn. in elisp) Axel Reichert <mail@axel-reichert.de> - 2024-07-09 23:15 +0200
    Re: TCO with named-let via macros Richard Smith <null@void.com> - 2024-07-10 06:28 +0100
      Re: TCO with named-let via macros steve g <sgonedes1977@gmail.com> - 2024-08-10 15:56 -0400
        Re: TCO with named-let via macros Richard Smith <null@void.com> - 2024-08-10 22:28 +0100
    Re: TCO with named-let via macros Richard Smith <null@void.com> - 2024-07-10 06:36 +0100
      Re: TCO with named-let via macros steve g <sgonedes1977@gmail.com> - 2024-08-10 16:22 -0400
        Re: TCO with named-let via macros Axel Reichert <mail@axel-reichert.de> - 2024-08-10 23:15 +0200
          Re: TCO with named-let via macros steve g <sgonedes1977@gmail.com> - 2024-08-11 14:56 -0400
          Re: TCO with named-let via macros Richard Smith <null@void.com> - 2025-04-08 10:26 +0100
    Re: TCO with named-let via macros Richard Smith <null@void.com> - 2024-07-10 06:59 +0100
    Re: TCO with named-let via macros Richard Smith <null@void.com> - 2024-07-10 09:18 +0100
      Re: TCO with named-let via macros steve g <sgonedes1977@gmail.com> - 2024-08-10 16:26 -0400
        Re: TCO with named-let via macros Richard Smith <null@void.com> - 2024-08-10 22:51 +0100

csiph-web