(or emacs irrelevant)

Making Elisp regex look nicer

11 Jan 2015

This is just a small improvement to make e.g. \\( show up in regular expressions without the escape chars, but instead fontified with font-lock-keyword-face. It doesn't affect the underlying code at all, just makes it look nicer. For the \\| I chose ∨ - the logical or character.

The code

(defun fontify-glyph (item glyph)
  `((,item
     (0 font-lock-keyword-face t)
     (0 (prog1
            (compose-region (match-beginning 0)
                            (match-end 0)
                            ,glyph) nil)))))

(font-lock-add-keywords 'emacs-lisp-mode
                        (fontify-glyph "\\\\\\\\|" "∨"))
(font-lock-add-keywords 'emacs-lisp-mode
                        (fontify-glyph "\\\\\\\\(" "("))
(font-lock-add-keywords 'emacs-lisp-mode
                        (fontify-glyph "\\\\\\\\)" ")"))

How it looks like

At first, I wanted to just inline a picture, but then I thought that htmlize-buffer would be able to handle it. It didn't, so I just edited a small snippet by hand:

(or (string-match "^([^\n%|]*?)|(([^\n]*)?$" str)
    (string-match "^([^\n%|]*?)(%[^\n]*)?$" str))

It's really satisfying to see those escape chars vanish as I type in a capture group in the regex, especially with the help of lispy-mode. Here are some relevant tests for the regex support:

(should (string= (lispy-with "\"a regex \\\\|\"" "(")
                 "\"a regex \\\\(|\\\\)\""))
(should (string= (lispy-with "\"\\\\(|foo\\\\)\"" "\C-?")
                 "\"|foo\""))
(should (string= (lispy-with "\"\\\\(foo\\\\)|\"" "\C-?")
                 "\"foo|\""))
(should (string= (lispy-with "\"|\\\\(foo\\\\)\"" "\C-d")
                 "\"|foo\""))
(should (string= (lispy-with "\"\\\\(foo|\\\\)\"" "\C-d")
                 "\"foo|\""))