[texhax] A macro programming question

[Paul Isambert]

Le 12/09/2011 08:05, Vafa Khalighi a écrit :
> > I am trying to figure out how I can make longtable typeset RTL tabulars but
I
started with something much simpler to understand what I should do. The
bigtabular package is defined as:
> >
> > %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
> > \newskip\Tabularleftskip  \Tabularleftskip\@flushglue
> > \newskip\Tabularrightskip \Tabularrightskip\@flushglue
> > \newbox\Tabularbox
> > \newcount\Tabularcount
> > \newcount\Tabularcolumns
> > \def\@Tabclassz{\global\advance\Tabularcount\@ne\@tabclassz}
> > \let\@latexclassiii\@classiii
> > \def\@Tabclassiii{\global\advance\Tabularcount\@ne\@latexclassiii}
> > \def\@Tabularcr{{\ifnum0=`}\fi\@ifstar{\@xTabularcr}{\@xTabularcr}}
> > \def\@xTabularcr{\@ifnextchar[{\@argTabularcr}{\ifnum0=`{\fi}\cr
> >   \noalign{\pagebreak[1]}}}
> >
> > \def\@argTabularcr[#1]{\ifnum0=`{\fi}\ifdim #1>\z@
> >    \unskip\@xargarraycr{#1}\else \@yargarraycr{#1}\fi
> >  \noalign{\pagebreak[1]}}
> > \let\@latexhline\hline
> > \let\@latextabarray\@tabarray
> > \def\@tabarray{\let\hline\@latexhline\@latextabarray}
> > \def\Tabularhline{\multispan{\Tabularcolumns}{\unskip\leaders\hrule
> >     height\arrayrulewidth\hfill}\cr
> >   \noalign{\vskip-\arrayrulewidth\pagebreak[2]}%
> >   \multispan{\Tabularcolumns}{\unskip\leaders\hrule
> >     height\arrayrulewidth\hfill}\cr}
> >
> > \def\Tabular#1{\trivlist\item[]\noindent
> >   \setbox\Tabularbox\vbox\bgroup
> >     \let\@acol\@tabacol
> >     \let\@classz\@Tabclassz
> >     \let\@classiii\@Tabclassiii
> >     \let\@classiv\@tabclassiv
> >     \let\\\@Tabularcr
> >     \setbox\@arstrutbox=\hbox{\vrule
> >         height\arraystretch \ht\strutbox
> >         depth\arraystretch  \dp\strutbox
> >         width\z@}%
> >     \global\Tabularcount\z@
> >     \@mkpream{#1}%
> >     \Tabularcolumns\Tabularcount
> >     \let\hline\Tabularhline
> >     \let\@classiii\@latexclassiii
> >     \tabskip\Tabularleftskip
> >     \edef\@preamble{\halign to\linewidth\bgroup
> >       \tabskip\z@ \@arstrut \@preamble
> >       \tabskip\Tabularrightskip \cr}%
> >     \let\@starpbox\@@startpbox
> >     \let\@endpbox\@@endpbox
> >     \let\@sharp##\let\protect\relax
> >     \lineskip\z@\baselineskip\z@
> >     \@preamble}
> >
> > \def\endTabular{\crcr\egroup\egroup\unvbox\Tabularbox\endtrivlist}
> > %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
> >
> > To make it typeset tabular right to left, I thought of changing \Tabular and
\endTabular as follow:
> >
> > \def\Tabular#1{\trivlist\item[]\noindent
> >   \setbox\Tabularbox\vbox\bgroup
> >     \let\@acol\@tabacol
> >     \let\@classz\@Tabclassz
> >     \let\@classiii\@Tabclassiii
> >     \let\@classiv\@tabclassiv
> >     \let\\\@Tabularcr
> >     \setbox\@arstrutbox=\hbox{\vrule
> >         height\arraystretch \ht\strutbox
> >         depth\arraystretch  \dp\strutbox
> >         width\z@}%
> >     \global\Tabularcount\z@
> >     \@mkpream{#1}%
> >     \Tabularcolumns\Tabularcount
> >     \let\hline\Tabularhline
> >     \let\@classiii\@latexclassiii
> >     \tabskip\Tabularleftskip
> >     \edef\@preamble{\halign to\linewidth\bgroup
> >       \tabskip\z@ \@arstrut \@preamble
> >       \tabskip\Tabularrightskip \cr}%
> >     \let\@starpbox\@@startpbox
> >     \let\@endpbox\@@endpbox
> >     \let\@sharp##\let\protect\relax
> >     \lineskip\z@\baselineskip\z@
> >    \hbox\bgroup\beginR\vbox\bgroup \@preamble}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% This is my first change
> >
> >
\def\endTabular{\crcr\egroup\egroup\endR\egroup\egroup\unvbox\Tabularbox\endtrivlist}
> > %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
> >
> > but it no longer works (tabular appears on one page and no pagebreak
happens).
What should I do to fix this?


When \Tabularbox is unboxed, it normally releases the horizontal boxes making up
the lines of the tabular; in your case, it releases the first hbox you've added,
in which the lines of the tabular are still taken as a whole (hence no
possibility to break).

I don't know much about RTL typesetting, but to me the solution is simply to add
\beginR just after

    \setbox\Tabularbox\vbox\bgroup

and \endR between the two \egroup's in the original \endTabular.

Best,
Paul