Noon van der Silk

Autosave Mathematica files for undo purposes

Anyone who has used Mathematica¹ for more than 5 minutes probably knows that the undo functionality will leave you feeling pretty sad. You can very quickly find yourself having deleted something that you wanted to keep, and having Control-Z completely ignore your requests to go back in time.

I was complaining about this on Google+ a while back when I realised that there is a very easy solution - Autosave copies of your Mathematica files somehow, and then rollback to a different version if you want one!

“Brilliant”, I thought, I’ll just write a Mathematica plugin to do this! Ah, but infact it turns out I can be even lazier than that, and get this functionality entirely outside of Mathematica, and I can use Haskell and git in the process (you aren’t really having fun until you use Haskell to solve a minor inconvenience.)

So I happened to have the following programs installed, which are used to monitor a folder for file changes and to run actions upon file changes,

• Commando
• Conscript

So step (1) is to install these. Step (2) is to install git (or some other source control system, it doesn’t matter which).

Step (3) is to now edit all your Mathematica files in some special directory; I’ve chosen ~/mathematica_working. So I’ve turned this into a git repository with git init, and then I have the following two scripts in the folder:

# start.sh
commando -c echo | grep --line-buffered '.nb' | conscript ./autosave.sh

# start.sh
git add . && git commit -m "Auto-save."

and every time I start working on some Mathematica files, I run ./start. This begins tracking changes.

Now, every time I save a document in Mathematica, this setup auto-commits it. The output in this terminal looks something like this, depending on what you change:

[master eded096] Auto-save.
 1 file changed, 1 insertion(+), 1 deletion(-)

So now I have a nice history of changes to Mathematica files. If I accidentally delete a big chunk of code, or just want to see what I used to have, I can use all the machinery that the source-control system makes available to me! And because the Mathematica files are in a plaintext format, it’s not impossible to review the diffs meaningfully! (It’s not exactly amazingly-pleasant though.)