emacs/elisp: What is the hash (pound, number sign, octothorp) symbol used for?

Question

What does this do?

(add-hook \'compilation-mode-hook #\'my-setup-compile-mode)

...and is it different than

(add-hook \'com         


        

Answer 1

I found this question while searching for what the hash meant in something I found while hacking mode-line-format:

#("-%-" 0 3
  (help-echo "Display as tooltip when mouse hovers or with display-local-help."))

which is a format used for text properties in strings where:

• "-%-", text to be propertized: one dash and a %-construct that results in "dashes sufficient to fill the remainder of the mode line", resulting in the famous Emacs ------.
• 0, the first character upon which the text properties apply.
• 3, the last character upon which the text properties apply, i.e. the entire "-%-".
• (help-echo "..."), a property and a string as its argument.

This can be created with the propertize function:

(propertize "Hover over me!" 'help-echo '"congratulations!")

would be the same as #("Hover over me!" 0 14 (help-echo "Congratulations!")):

If you're using font lock mode, using the buffer-substring command might produce something like this:

(buffer-substring 1 28) ; First 27 characters in the current buffer
 ⇒ #(";; This buffer is for notes"
     0 3
     (fontified t face font-lock-comment-delimiter-face)
     3 27
     (fontified t face font-lock-comment-face))

So you could create something like: