From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Fabrice Niessen" Subject: Re: Tangle with conditional statement Date: Sat, 24 Aug 2013 16:04:28 +0200 Message-ID: <867gfbjic3.fsf@somewhere.org> References: Mime-Version: 1.0 Content-Type: text/plain Return-path: List-Id: "General discussions about Org-mode." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: emacs-orgmode-bounces+geo-emacs-orgmode=m.gmane.org-mXXj517/zsQ@public.gmane.org Sender: emacs-orgmode-bounces+geo-emacs-orgmode=m.gmane.org-mXXj517/zsQ@public.gmane.org To: emacs-orgmode-mXXj517/zsQ@public.gmane.org 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