How to pass &rest arguments to another function in emacs lisp?

Question

I have a convinience defun in my init.el to do some logging

(defvar log4me::loglevel 5
  "Global loglevel.")

(defun log4me (level logmsg)
  "Log message."
  (interactive)
  (when (>= level log4elisp::loglevel)
    (message logmsg))))

It kind of works but somehow i frequently do

  (log4me somelevel (format "mymessage with %d" 1))

So i found the emacs lisp &rest parameters which i thought i might use like this:

(defun log4me (level logmsg &rest formatparams)
  "Log message."
  (interactive)
  (when (<= level log4elisp::loglevel)
    (message (format logmsg formatparams))))

(log4me 3 "Hello %ust!" 1)

which resuslts into "Format specifier doesn't match argument type" error since formatparams is actually (1) and not 1.

Is there a nice way to include format parameters into the log4elisp defun and make them arrive in the format function call as "normal" parameters (not a single list)?

@Rainer Joswig Thanks! I had the feeling that all i needed was a pointer to the right point in the documentation. apply worked well. Do you like to provide a short answer so that i can accept it? — Matthias
– Matthias, Commented Nov 1, 2014 at 18:25

sds · Accepted Answer · 2014-11-03 04:14:32Z

10

What you need is apply:

(defun log4me (level logmsg &rest formatparams)
  "Log message."
  (interactive)
  (when (<= level log4elisp::loglevel)
    (apply #'message logmsg formatparams)))

answered Nov 3, 2014 at 4:14

sds

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Comments

nomad · Accepted Answer · 2020-09-27 10:10:55Z

0

apply is perfect for functions, but is invalid for function-objects like macros. The following solution is applicable for both functions and macros.

(defun log4me (level logmsg &rest formatparams)
  "Log message."
  (interactive)
  (when (<= level log4elisp::loglevel)
    (eval (append '(message logmsg) formatparams))))

answered Sep 27, 2020 at 10:10

nomad

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