ideas on Sweave

[yihui]

It is simply horrible, if not impossible, to extend the standard Sweave function in base R, because it is poorly modularized in design and hard-coded in many places. Existing packages:

• brew is fairly light-weighted, and I like its simple style as well as its PHP-like nature (use <% %> instead of <<>>= @ and the awkward \Sexpr{})
• pgfSweave features beauty, which is extremely important to me; tikzDevice is an awesome package
• cacheSweave features cache, of course, and it is important to large-scale computation
• decumar is great in design; we no longer need to "ruin" the LaTeX document by weird illegal home-made nonsense pseudo-LaTeX code, since it puts literate programming code in LaTeX comments

What is my ideal Sweave package?

• we should be able to specify the pattern of R code to execute by ourselves; why? because literate programming with R should not be restricted to a particular type of output like LaTeX, HTML, or any other files; I want to borrow the design of decumar to put Sweave-related stuff in comments, but each language has its own definition of comments (may begin with % or <!--, ...); for example, <!-- first-chunk, source=abc.R, noecho, figure, width=5, height=4 --> is used in an HTML page to refer to a code chunk in an R script abc.R which looks like ## <label>:first-chunk
• beside putting R code in the main file (probably as comments), we can also put R code in an R script and use a label to reference a code chunk in the main file, which brings us huge convenience that we can run the R code whenever we want (imagine how difficult it is to run R code in LyX/Sweave without compiling the whole document!!), and this makes Stangle a useless invention (code is separated with the main file, so no need to export code again)
• issues that may be difficult
  • parse options, especially for plots
  • recursive weaving, e.g. parse files under \input{}
• misc issues
  • output should not be mangled with the leading prompts like > and + by default; that is too bad for other people trying to copy and run your code
  • should be able to freely specify the styles to be applied to the input code and output (instead of hard-coded Schunk, Sinput, ...); this can be convenient for HTML output since it gives us the flexibility to use CSS
  • should not expect the users to print() grid-based graphics; make it natural that they just feel like they typed the commands in R (qplot() alone should produce the plot; why expect me to print(qplot()) in Sweave?); I believe this is one of the ideas in evaluate
  • how about a package name knit?

Finally, I need time and I wish other Sweave users may find the above ideas useful and like to contribute.

[yihui]

most of above features have been finished; the rest of work is to write some default hooks, then long live the knit engine!