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Re: [O] Tangle with conditional statement
From: |
Fabrice Niessen |
Subject: |
Re: [O] Tangle with conditional statement |
Date: |
Sat, 24 Aug 2013 16:04:28 +0200 |
User-agent: |
Gnus/5.130006 (Ma Gnus v0.6) Emacs/24.3.50 (windows-nt) |
Hello Andreas,
> First time poster to this mailing list.
> I was hoping i could get some pointers to a question I have not yet found a
> solution or example of.
>
> I use orgmode and tangled elisp src blocks to initiate emacs. I also use
> el-get to install packages, however sometimes these packages fail for
> various reasons and I would like to skip them so that the hall emacs
> initailisation doesn't brake. However for important packages i have them
> hardcoded in my init files so that the settings I have doesn't complain.
> But as I use org-mode to tangle this I can just flip the :tangle to "no" to
> to not tangle a specific section.
>
> my question: Is it possible to have a conditional statement for a tangled
> block so that only if a package is installed or a directory exist does the
> block tangle? Meaning that I wouldn't need to hard code all the el-get
> fetches in my init file.
> Is this a good idea? or should I work in conditions in the emacs src blocks
> instead?
> I realize now when I'm typing it out that it might come with some other
> issues like first time running it I would have to reinitialize emacs after
> package installs to get my settings but after that I guess it would be fine.
Instead of trying to put the "look if package is present" constraint on
Babel's side (and have a configuration file which you cannot exchange), I'd do
it on the Emacs (Lisp) side, as I did in my configuration file [1] with a
"try-require" function:
--8<---------------cut here---------------start------------->8---
(defvar leuven--missing-packages nil
"List of packages that `try-require' or `locate-library' can't find.")
;; require a feature/library if available; if not, fail silently
(defun try-require (feature)
"Attempt to load a library or module. Return true if the
library given as argument is successfully loaded. If not, instead
of an error, just add the package to a list of missing packages."
(let (time-start)
(condition-case err
;; protected form
(progn
(when leuven-load-verbose
(message "(info) Checking for `%s'..." feature))
(if (stringp feature)
(load-library feature)
(setq time-start (float-time))
(require feature))
t)
;; error handler
(file-error ;; condition
(progn
(when leuven-load-verbose
(message "(info) Checking for `%s'... missing" feature))
(add-to-list 'leuven--missing-packages feature 'append))
nil))))
--8<---------------cut here---------------end--------------->8---
Best regards,
Fabrice
[1] https://github.com/fniessen/emacs-leuven/blob/master/emacs-leuven.el
--
Fabrice Niessen
Leuven, Belgium