Hi Thomas, Thomas S. Dye <t...@tsdye.com> writes: > Aloha all, > > Aaron Ecay <aarone...@gmail.com> writes: > >> Hi Nicolas, >> >> 2015ko urriak 29an, Nicolas Goaziou-ek idatzi zuen: >>> >>> Andreas Leha <andreas.l...@med.uni-goettingen.de> writes: >>> >>>> Generally, I think that caching is a sensitive area. And if we think >>>> that it is unpredictable and advise people to stay off of it, we are >>>> better off removing it than offering it in this state. At least until >>>> it behaves (more) predictable. >>> >>> Is it necessarily broken? >> >> If this means “can it ever work?” then I think the answer is “yes it >> can”. But I think the current implementation is broken and likely to >> remain so for the foreseeable future. The issues are: >> >> 1. :cache only works for code which is a pure function of its header args >> 2. When combined with :session, the environment that the code is evaluated >> in is not created anew each time it is run. This makes it much easier >> to leak references to (e.g.) variables defined in other blocks >> 3. The proper notion of purity is not easily defined when the code does >> things like modifying the emacs environment, touching the filesystem, >> or accessing the language’s RNG. >> 4. We (org devs) don’t actually understand how the semantics of cache >> interacts with other babel features. See: >> <http://mid.gmane.org/86fvqqc8jb....@somewhere.org>. >> >> 1-3 are likely to be extremely confusing for users, especially less >> technically sophisticated ones (what’s a “pure function” anyway)? The >> inability to give a clear introductory explanation of the feature in >> combination with 4 indicating we don’t actually understand it ourselves >> makes me feel like we should not be advertising, let alone recommending, >> it. >> >> The only other literate programming environment that I know of that >> implements such a feature is knitr (for R). They address these issues >> by providing (optional) free-variable analysis to construct a dependency >> graph between code blocks. There is also some handling of RNG seed >> values. The documentation <http://yihui.name/knitr/demo/cache/> is much >> more comprehensive, including a prominent statement about the dangers of >> side effect-ful code and a nuanced discussion of several issues, >> including the RNG. >> >> Aaron >> >> PS I’ve looked through my old notes on the interaction of cache with >> babel export. I can’t reproduce any of my old test cases, so maybe that >> bug has been fixed as a side effect of some other change. > > FWIW, I think relying on cache to speed up export is the wrong > approach. Having all code run during each export is, to me, a feature > that makes a document "live." I'm willing to be patient during export > to get this feature. > > If speed is important and a live document isn't desired, then one > solution is to rename the results and refer to this name in the > document, rather than to the name of the code block that produced the > results. I do this manually, which is OK, but I've often wanted > something like :persist-as my-result so I can be certain to have a good > link from the results back to the code that produced them.
There we go again. Another advice not to use the :cache. > > That said, points 2 and 4 seem to me serious issues that users must > understand if they choose to use :cache. So, at the least, the > documentation needs revision. > Just to add (maybe that belongs to point 4 anyway): And the caching should work predictably -- even during export. Regards, Andreas