[Rd] Off-topic: Pretty-printing R (or S) code with GNU a2ps

[Kurt Hornik]

	[Manually approved by MM -- because it contains binary attachment ]

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>>>>> Dirk Eddelbuettel writes:

> GNU a2ps is a fairly versatile text-to-anything processor.  It is
> useful for typsetting source code from a wide variety of programming
> languages.  As R (ie S) wasn't supported yet, I quickly cobbled a
> style sheet for the S language together. Stylesheets are documented in
> the texinfo docs for a2ps, and examples can be found in
> /usr/share/a2ps/sheets (on Debian at least, others distros or unices
> probably have similar locations). IIRC a2ps exists for NT but might
> require Cygwin. I typeset on Linux and only print on NT :)

> Well, as I still don't really know what I'm doing with R, I would
> appreciate comments / feedback / input from anyone could spend a
> moment or two on this.  To activate the stylesheet, simple patch

>       /usr/share/a2ps/sheets/sheets.map

> as per the short diff below which declares that the stylesheet s.ssh
> shall be used for filenames matching /*.[RS]/.  The sheet itself is
> attached, just place it in the same directory, ie
> /usr/share/a2ps/sheets/.

> Usage then simply becomes
>       a2ps -Pdisplay foo.R
> or
>       a2ps foo.R -o foo.ps; gv foo.ps
> in case the "display" device isn't defined.

Thanks for bringing this up.  We have locally used style sheets S.ssh
for S code and Rd.ssh for Rd documentation format, both written by T
Hothorn.  I attach these files below.

> A few points / questions:

>  * content:  a2ps uses tricks to use TeX symbols. It works well to typset
>    <- with \leftarrow (uncomment that in s.ssh to see) but I couldn't tell
>    it to parse
>       a<-2
>    it only finds <- with whitespace, eg
>       a <- 2

Torsten gets this right by using a different alphabet, I think.

>    What could be done about <<- ?  Is there a matching TeX symbol?

Dunno.

>  * more content: Is the list of keywords really that short? I couldn't find
>    much else...

R-lang says:

	The following identifiers have a special meaning and should not
	be used for object names

	     if else repeat while function for in next break
	     TRUE FALSE NULL NA Inf NaN
	     ... ..1 ..2 etc.

so I think this is the list of keywords to use.

(Yes switch() is not in there ...)

>  * scope:  Are other file extensions in use? Are there conventions for S or
>    Splus files?  Any clever way to make a2ps understand the files in 
>    $R_HOME/library/$PACKAGE/R  are also R?  Could file(1) be taught what 
>    an R file is?

I think assuming that extensions `.R' and `.Rd' for R code and doc
source files are pretty safe.  The package installer will also allow for
code extensions `.r', `.S', `.s', and `.q', but I think only the last of
these may be specific enough to make it into the extension list.

No R magic in general.  ESS think .R/.r are safe for auto-mode-alist and
.S/.s need enforcing.  [One could try checking for Emacs-style mode
magic but I think that would be a bad idea.]

>  * editorial: shall this be the s.ssh or r.ssh or rs.ssh?

I think we want S.ssh, as this is a style sheet for code written in the
S language.

Best,
-k


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