(R-ints.info)Use of TeX dialects

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11 Use of TeX dialects
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Various dialects of TeX are used for different purposes in R. The policy
is that manuals be written in 'texinfo', and for convenience the main
and Windows FAQs are also.  This has the advantage that is is easy to
produce HTML and plain text versions as well as typeset manuals.

   LaTeX is not used directly, but rather as an intermediate format for
typeset help documents and for vignettes.

   Care needs to be taken about the assumptions made about the R user's
system: it may not have either 'texinfo' or a TeX system installed.  We
have attempted to abstract out the cross-platform differences, and
almost all the setting of typeset documents is done by
'tools::texi2dvi'.  This is used for offline printing of help documents,
preparing vignettes and for package manuals via 'R CMD Rd2pdf'.  It is
not currently used for the R manuals created in directory 'doc/manual'.

   'tools::texi2dvi' makes use of a system command 'texi2dvi' where
available.  On a Unix-alike this is usually part of 'texinfo', whereas
on Windows if it exists at all it would be an executable, part of
MiKTeX. If none is available, the R code runs a sequence of
'(pdf)latex', 'bibtex' and 'makeindex' commands.

   This process has been rather vulnerable to the versions of the
external software used: particular issues have been 'texi2dvi' and
'texinfo.tex' updates, mismatches between the two(1), versions of the
LaTeX package 'hyperref' and quirks in index production.  The licenses
used for LaTeX and latterly 'texinfo' prohibit us from including 'known
good' versions in the R distribution.

   On a Unix-alike 'configure' looks for the executables for TeX and
friends and if found records the absolute paths in the system 'Renviron'
file.  This used to record 'false' if no command was found, but it
nowadays records the name for looking up on the path at run time.  The
latter can be important for binary distributions: one does not want to
be tied to, for example, TeX Live 2007.

   ---------- Footnotes ----------

   (1) Linux distributions tend to unbundle 'texinfo.tex' from
'texinfo'.