diff --git a/posts/Cool_new_scratch_buffers.mdwn b/posts/Cool_new_scratch_buffers.mdwn new file mode 100644 index 0000000..db63cf4 --- /dev/null +++ b/posts/Cool_new_scratch_buffers.mdwn @@ -0,0 +1,75 @@ +I had a thought today: It would be nice if I could have more than one +scratch buffer, and even nicer if they could easily have different +major modes. + +So, I had this function in my emacs init file, `raise-scratch`: + +[[!format el """ +(defun raise-scratch () + "Show the *scratch* buffer." + (interactive) + (switch-to-buffer "*scratch*")) +"""]] + +Its nice, it allowed me to do exactly what I wanted to do, easily open +my scratch buffer. I bound this to `XF86HomePage`, which makes sense +to me, since emacs always starts in the `*scratch*` buffer. + +Today, though, it didn't seem to be quite enough. As I said, it would +be nice to have the ability to have multiple scratch buffers with +different major modes. This is handy for messing around with some +`sawfish-mode` code, or `python-mode`, for example. + +[[!format el """ +(defun raise-scratch (&optional mode) + "Show the *scratch* buffer. If called with a universal +argument, ask the user which mode to use. If MODE is not nil, +open a new buffer with the name *MODE-scratch* and load MODE as +its major mode." + (interactive (list (if current-prefix-arg + (read-string "Mode: ") + nil))) + (let* ((bname (if mode + (concat "*" mode "-scratch*") + "*scratch*")) + (buffer (get-buffer bname)) + (mode-sym (intern (concat mode "-mode")))) + + (unless buffer + (setq buffer (generate-new-buffer bname)) + (with-current-buffer buffer + (when (fboundp mode-sym) + (funcall mode-sym)))) + + (switch-to-buffer buffer))) +"""]] + +This is quite a bit bigger. It now takes an optional `mode` argument, +when it is called interactively it will check if the universal prefix +argument (`C-u`) was used and if so, asks for the value of `mode`. + +If mode has been specified it will create a new buffer with the name +`*MODE-scratch*`. It will then insert a file local property line +specifying the major mode to use and then switches to it. + +It's the first time I'm using a list with the `interactive` command, +it always seemed very alien to me, but it seems quite clear how it +works now. + +It was a challenge to figure out how I wanted to do this. My first +idea was to ask for a file extension and match that to +`auto-mode-alist`, but that has regexps for keys, so not easily +matched. Then there is the problem of figuring out how to load the +right major mode in another way, since adding such a file local +property line happens *after* the buffer has been loaded, and thus has +no effect on which major mode is chosen. + +Of course, this approach doesn't ensure the right major mode gets +chosen, but that's really up to whomever uses it. + +It makes me very happy to use such an extensible editor. + +**Update:** fixed my flawed code. + +[[!meta date="2012-08-02 00:27:00"]] +[[!tag emacs elisp coding]]