Groups | Search | Server Info | Login | Register

Groups > gnu.emacs.help > #60993

Re: TCO with named-let via macros

Show all headers | View raw

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

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