Change expression in body of elisp function with advice

Question

How do you match a specific expression in the body on elisp function when adding advice? Specifically, in the following example, I would like to advise the function to use find-file-noselect in place of find-file, ie. the line (find-file path) would be in effect (find-file-noselect path).

(defun tst-fun (path line column)
  (find-file path)
  (goto-char (point-min))
  (forward-line (1- line))
  (forward-char column))

;; not sure how to structure this
(defadvice tst-fun (around noselect activate)
  (find-file-noselect (ad-get-arg 0))
  ad-do-it)

I would rather have it as ad-add-function, but am trying to just get this working first.

Advice is run before, after, or instead of the advised function, but it doesn't modify how the original function itself works. — Barmar, Oct 27 '16 at 22:34
@Barmar so, there is no way to do something like set `ad-do-it` to `(cdr ad-do-it)`? — Rorschach, Oct 27 '16 at 22:36
That will call `tst-fun`, and then return the `cdr` of whatever it returns. — Barmar, Oct 27 '16 at 23:08

score 3 · Accepted Answer · edited Oct 28 '16 at 14:02

3

You could temporarily redefine find-file as find-file-noselect in the advice.

(require 'cl)
(defadvice tst-fun (around noselect activate)
  (flet ((find-file (&rest args)
           (apply 'find-file-noselect args)))
    ad-do-it))

edited Oct 28 '16 at 14:02

Stefan

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answered Oct 27 '16 at 22:40

Barmar

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I'm pretty sure there's no way to do that. Some other Lisp dialects had `:INSIDE` advice, where you could advise `find-file` only inside `tst-fun`, but Elisp doesn't have this. – Barmar Oct 27 '16 at 23:07
2

In "modern" Elisp, this would look like: `(require 'cl-lib) (advice-add 'tst-fun :around (lambda (orig &rest args) (cl-letf (((symbol-function 'find-file) #'find-file-noselect)) (apply orig args))`. – Stefan Oct 28 '16 at 14:05

Change expression in body of elisp function with advice

1 Answers1