Chunk dependency checking

[cameronbracken]

Like the weave package

[halpo]

cacheSweave recently added this feature as well. https://github.com/rdpeng/cachesweave/commit/194037747cac7eaedd2e80186eebc82350d059b9#L1L219 I would love to see this in pgfSweave.

[yihui]

maybe I'm asking a stupid question, but I don't understand why we ever need this dependency feature since lazy loading is already used, which means objects are never really loaded unless they are really going to be used, so what extra benefits does this feature give us?

[halpo]

Consider the case I'm dealing with. Chuck 1 generates simulation data. Chuck 2 describes that data. I run it get some results and find that I need to modify one of the parameters. I update chuck 1 and re run. with caching turned on nothing changed in chunk 2 so it does not get updated and those results now reflect the old simulation and not the new simulation. Turning on dependencies allows you to say update this chunk if anything that it depends on changes.

[yihui]

Got it. Thanks a lot!