tabu and tabularx compatibility - for htlatex, tex4ht and migration between tabu and tabularx

Question

Is it possible to renew the tabularx environment so that it will take the tabularx style parameters? Or the other way around?

\begin{tabularx}{\textwidth}{ ... }
% ...
\end{tabularx}

\begin{tabu} to \linewidth { ... }
% ...
\end{tabu}

something like:

\renewenvironment{tabularx}{\begin{tabu} to #1 ...}{\end{tabu}}

or

\renewenvironment{tabu}{\begin{tabularx}{#1} ...}{\end{tabularx}}

This would help me to find out if the tabularx package can be used for tex4ht and the tabu package for pdflatex. I'm aware that tabu seems to be more powerful, but it appears from a first look that most of the tabu parameters could be definded so they will be ignored when producing html tables.

Answer 1

If you want to change \begin{tabu} to <dimen> into \begin{tabularx}{<dimen}, while keeping normal tabu environments you can do

\documentclass{article}
\usepackage{tabularx,tabu}

\makeatletter
\let\originaltabu\tabu
\def\tabu#1#{%
  \setbox\z@=\hbox#1{}%
  \ifdim\wd\z@=\z@
    \expandafter\@firstoftwo
  \else
    \expandafter\@secondoftwo
  \fi
  {\originaltabu}%
  {\let\endtabu\endtabularx\tabularx{\wd\z@}}%
}
\makeatother

\begin{document}

\begin{tabu}{|c|c|c|}
aa & bbbb & ccc \\
1 & 0 & 2
\end{tabu}

\bigskip

\begin{tabu} to 8cm{|X|X|X|}
aa & bbbb & ccc \\
1 & 0 & 2
\end{tabu}

\end{document}

I asked the author of tabu to avoid the syntax to <dimen>, he didn't want to accept the advice. However the trick of absorbing all the tokens up to the first brace allows us to use (abuse, perhaps) the fact that \hbox accepts such a syntax.

So the first tabu executes \setbox0=\hbox{} (\z@ is inner for zero as number or length) and the width of the box is zero. Thus the “true” part is followed and \originaltabu is executed.

The second tabu, instead, does \setbox0=\hbox to 8cm{} and the box becomes 8cm wide, so the “false” part is followed, leading to a (local) redefinition of \endtabu to \endtabularx and executing \tabularx{8cm}, after which the column specifiers are absorbed.

I added vertical rules just for better showing the result, not because I recommend their usage (I don't, actually).

Answer 2

I don't understand why but this seems to work:

  \let\tabuo\tabu
  \let\endtabuo\endtabu
  \renewenvironment{tabu}[2]{\tabuo to #1 {#2}}{\endtabuo}

Would it be safer to use \LetLtxMacro instead of \let ?

And how would it work the other way around (i.e. to define a tabu environment that maps to tabularx syntax)?

Edit: Maybe I also solved it the other way around but only for the case when it's separated by one space and the to is really always there.

\def\tabu #1  to  #2#3{\tabularx{#2}{#3}}
\let\endtabu\endtabularx

or

\def\tabu #1#2  #3#4{\tabularx{#3}{#4}}
\let\endtabu\endtabularx

Can someone tell me what is the magic behind the double spaces after \def in TeX please?