[Rd] embed Sweave driver in .Rnw file

[Romain Francois]

Hello,

Sweave lets you use alternative drivers through the driver argument, and 
several packages take advantage of that and define custom Sweave driver 
for various purposes. Most of them are listed on the Reproducible 
Research CTV: 
(http://cran.r-project.org/web/views/ReproducibleResearch.html)

The next natural step is for package developpers to take advantage of 
this in their vignettes. In Rcpp we work around the way package building 
works and we do:
- let R build a dummy vignette
- then use the inst/doc/Makefile to replace it with a vignette that is 
processed by the driver from the highlight package (giving syntax 
highlighting).

I played with Sweave so that it would be able to create the driver from 
some text included in the text of the .Rnw file:

$ svn diff
Index: src/library/utils/R/Sweave.R
===================================================================
--- src/library/utils/R/Sweave.R	(revision 53846)
+++ src/library/utils/R/Sweave.R	(working copy)
@@ -20,6 +20,16 @@
  # We don't need srclines for code, but we do need it for text, and 
it's easiest
  # to just keep it for everything.

+SweaveGetDriver <- function(file){
+    txt <- readLines(file)
+    line <- grep( "\\SweaveDriver", txt, value = TRUE )
+    if( length(line) ){
+        txt <- sub( "^.*\\SweaveDriver[{](.*)[}]", "\\1", line[1L] )
+        driver <- try( eval( parse( text = txt ) ), silent = TRUE )
+        if( !inherits( driver, "try-error") ) driver
+    }
+}
+
  Sweave <- function(file, driver=RweaveLatex(),
                     syntax=getOption("SweaveSyntax"), ...)
  {
@@ -28,7 +38,9 @@
      else if(is.function(driver))
          driver <- driver()

-
+    drv <- SweaveGetDriver(file)
+    if( !is.null(drv) ) driver <- drv
+
      if(is.null(syntax))
          syntax <- SweaveGetSyntax(file)
      if(is.character(syntax))



This allows one to write something like this in their file:

%\SweaveDriver{ { require(highlight); HighlightWeaveLatex() } }

So that when calling :

 > Sweave( "somefile.Rnw" )

the highlight driver is used instead of the default driver.

Could something like that be added to Sweave ?

Romain

-- 
Romain Francois
Professional R Enthusiast
+33(0) 6 28 91 30 30
http://romainfrancois.blog.free.fr
|- http://bit.ly/fT2rZM : highlight 0.2-5
|- http://bit.ly/gpCSpH : Evolution of Rcpp code size
`- http://bit.ly/hovakS : RcppGSL initial release