CODEWITHSUNDEEP
emacselisp
Jisang Yoo
Jisang Yoo

Reputation: 3745

how to update evaluation result comments of Emacs Lisp forms easilly

Say I have this code which shows usage examples of mapcar

(mapcar #'1+ (list 10 20 30)) ; ⇒ (11 21 31)

(mapcar (lambda (it)
          (* 2 it))
        (list 0 1 2 3))
;; ⇒ (0 2 4 6)

(require cl-lib)
(cl-mapcar #'+
           '(1 2 3)
           '(10 20 30))
;; ⇒ (11 22 33)

I may be keeping that code somewhere written so that I can use it on a tutorial or so that whenever I forget how mapcar works, I can quickly read the code.

Now suppose I want to update some of the examples in the code. For example, I may change (list 0 1 2 3) in the second example to some other list. Right after I change the example, the corresponding result comment is then outdated. The result comment need to be updated as well. So I evaluate the form, copy the result, and replace the old result in the comment with new result. Is there a package I can use to help me do that all easily and less tediously? This is a different problem than problems that the litable or ielm package solve because this is simply about updating existing example code.

Right now what I use is:

(defun my-insert-eval-last-sexp ()
  (interactive)
  (let ((beg (point)))
    (let ((current-prefix-arg '(4)))
      (call-interactively 'eval-last-sexp))
    (goto-char beg)
    (if (looking-back ")")
        (insert " ; "))
    (insert "⇒ ")
    (move-end-of-line 1)))

which still isn't enough because it simply adds the result comment rather than updating an old one, and has a bug of odd stuff getting inserted when the form evaluates to a number:

(+ 1 2)
;; ⇒ 3 (#o3, #x3)

Upvotes: 4

Views: 241

Answers (2)

Andreas Röhler
Andreas Röhler

Reputation: 4804

Respective thing your function does is implemented in org-mode, i.e. org-babel.

See in Info, Org Mode, 14 Working with source code

Upvotes: 2

Drew
Drew

Reputation: 30701

Well, I'm not sure I want to encourage this kind of thing ;-), but this will get you a little closer to what you are trying to do, IIUC:

 (defun my-insert-eval-last-sexp ()
   (interactive)
   (let ((this-command  'eval-print-last-sexp))
     (save-excursion (eval-last-sexp-1 t)))
   (when (looking-back ")") (insert " ; "))
   (insert "⇒ ")
   (move-end-of-line 1))

  1. You don't need to save point and then explicitly go back to it --- use save-excursion.

  2. You don't need to bind the prefix arg and call the command interactively. Just call it (or its helper function) directly, passing the arg you want.

  3. You need to tweak the behavior to prevent it from thinking this is the second occurrence of the command, which is what causes it to print the octal etc. number info. The let binding does that (but is an ugly little hack).

Upvotes: 2

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