[Rd] problem with \eqn (PR#8322)

Hin-Tak Leung hin-tak.leung at cimr.cam.ac.uk
Wed Nov 23 11:11:25 CET 2005

Ross Boylan wrote:
> On Mon, 2005-11-21 at 10:27 +0000, Hin-Tak Leung wrote:
>>Kurt Hornik wrote:
>>>Definitely a problem in Rdconv.
>>>$ cat foo.Rd 
>>>  \eqn{{A}}{B}
>>>hornik at mithrandir:~/tmp$ R-d CMD Rdconv -t latex foo.Rd | grep eqn
>>>shows what is going on.
>>There is a "work-around" - putting extra spaces between the two braces:
>>$ cat foo.Rd
>>   \eqn{ {A} }{B}
>>$R CMD Rdconv -t latex foo.Rd
>>\eqn{ {A} }{B}
> Terrific!  I can confirm that works for me and, in a way, a work-around
> is better than a fix.  With the work-around, I can distribute the
> package without needing to require that people get some not-yet-release
> version of R that fixes the problem.  I do hope the problem gets fixed
> though :)
> By the way, I  couldn't see how the perl code excerpted earlier paid any
> attention to {}.  But perl is not my native tongue.
> Ross

Glad to hear - the extra space in the latex-eqn-processed part of
\eqn (versus the ascii part) possibly get skipped so there shouldn't
be visual difference if it works.

Regarding the perl code - "share/perl/R/Rdconv.pm" around line 400 - 
reproduced again here - the way I understand it, "\eqn{{a}}{b}" is first
transformed into something like
"\eqnbraces1brace2abrace2brace1brace1bbrace1", then called as
"get_arguments {'eqn', ..., 2}", which then tries to extract "a" and 
"b". $ID is defined elsewhere to be "brace1", etc. That's the idea.
The 4 regular expressions - the 1st, 2nd and the 4th probably should be
non-greedy (i.e. "??" instead of "?", and ".*?" instead of ".*"). But 
then, this is just my idea and I haven't tried very hard to figure out
what it is supposed and not supposed to do...

For those who wants to get to the bottom of it, I think inserting
something like this (this just append $text into a tmp file) would be 
useful, against the small snipplet that Kurt provided:
     open(JUNK, ">> /tmp/junk");
	print JUNK "outer/inner loop:", $text, "\n";


## Get the arguments of a command.
sub get_arguments {
     my ($command, $text, $nargs) = @_;
     ## Arguments of get_arguments:
     ##  1, command: next occurence of 'command' is searched
     ##  2, text:    'text' is the text containing the command
     ##  3, nargs:   the optional number of arguments to be extracted;
     ##              default 1
     my @retval;
     ## Returns a list with the id of the last closing bracket and the
     ## arguments.

     if($text =~ /\\($command)(\[[^\]]+\])?($ID)/){
         $id = $3;
         $text =~ /$id(.*)$id/s;
         $retval[1] = $1;
         my $k=2;
         while(($k<=$nargs) && ($text =~ /$id($ID)/)){
             $id = $1;
             $text =~ /$id\s*(.*)$id/s;
             $retval[$k++] = $1;
     $retval[0] = $id;


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