Lacking Natural Simplicity

Random musings on books, code, and tabletop games.

defadvice lets you improve existing functions!

I used defadvice in emacs lisp and it made the world so much better!

Specifically, I use the function smart-unicode-hyphen from xmlunicode.el 1 when entering text that is to be typeset. The first time you hit hyphen it inserts a hyphen. The second time you hit hyphen it changes it to an em dash. The third time you hit hyphen it changes it to an en dash. If you hit it again it changes it back to a hyphen. Unfortunately, I’ve never found a monospaced font that has em dashes and en dashes that are distinguishable from hyphens visually. (Not to mention the minus character, which is also important to enter correctly for typesetting.) So it is hard to tell what character you have just inserted, especially since you have to remember which comes after which in the sequence.

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Specifically, I have a very small minor mode that makes hyphens, double and single quotes, and periods smart, so they insert the proper Unicode characters in the right situations.

But I have a function tkb-describe-character that looks up the character under the cursor (or before, if you specified a prefix interactively or a value when called non-interactively) that looks up the character in the variable unicode-character-list (which is defined in unichars.el) and contains the character values and unicode names for the characters.

So, I wrote a defadvice function that runs (tkb-describe-character t) after smart-unicode-hyphen runs, so it looks at the character just before it and describes it, so I know what it is!

It works wonderfully!

That's the thing about defadvice: it lets you customize functions to better adapt them to how you need to work. Another way emacs lets you customize it to better suit your needs.

I got my copies of xmlunicode.el (copyright 2003 by Norman Walsh) and unichars.el (unattributed) off the Internet long ago. It looks like you can get xmlunicode.el from his xmlunicode github repository, and it looks like the replacement for unichars.el is xmlunicode-character-list.el.

Here's my code:

;; look at https://github.com/ndw/xmlunicode for xmlunicode.el and a way
;; to make something like unichars.el.  xmlunicode.el provides the
;; "smart-unicode-*" functions.
(load-library "xmlunicode")
(load-library "unichars")

(defun tkb-describe-character (before)
  "Describe the character after point (before if a prefix was specified)
if it is a unicode character."
  (interactive "P")
  (let* ((char (if before (char-before) (char-after)))
         (info (assoc (encode-char char 'ucs) unicode-character-list))
         (info (cons (format "#x%X" (car info)) info)))
    (message "%S" info)))
(tkb-keys ((kbd "C-c k d") #'tkb-describe-character))

(define-minor-mode tkb-smart-unicode-mode
  "Toggle smart unicode punctuation" nil " ♻⚔☣☥☸◉⅙✽☮" ; "✘▧▧⚅☑☢☹☺♠♥♦♣♨"
  '(("\"" . unicode-smart-double-quote)
    ("'"  . unicode-smart-single-quote)
    ("-"  . unicode-smart-hyphen)
    ("."  . unicode-smart-period)))

(defadvice unicode-smart-hyphen (after tkb-after-unicode-smart-hyphen last
                                       activate compile)
  (tkb-describe-character t))

Here's a gist, and the raw gist if you want to download it directly.

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