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From: Marco Kuhlmann <marco.kuhlmann@gmx.net>
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Subject: BNF grammar
Date: Tue, 16 Oct 2001 15:27:35 +0200 (MEST)
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    Hi all!

I would like to define an environment "bnfgrammar" to typeset
grammars in BNF format. What I thought is that you could type

    \startbnfgrammar
      t \BNFis x\in X           \BNFcomment{(variable)}
        \BNFor f(t_1,\dots,t_n) \BNFcomment{(function term)}
    \stopbnfgrammar

and get a properly formatted grammar:

    t ::= x\in X                (variable)
       |  f(t_1,\dots,t_n)      (function term)

My first try was to use a self-defined tabulate environment:

\definetabulate
  [bnfgrammar]
  [|lm|cm|lm|]

\setuptabulate
  [bnfgrammar]
  [inner=\@bnfgrammarsetup]

\def\@bnfgrammarsetup{%
  \def\BNFdf{\NC}
  \def\BNFis{\NC \mathrel{:=} \NC}
  \def\BNFor{\NC \NR \NC \NC \mathrel{|} \NC}}

This got me quite far, as I can now type:

  \startbnfgrammar
    \BNFdf t
    \BNFis x\in X
    \BNFor f(t_1,\dots,t_n)
  \stopbnfgrammar

However, the following problems remain:

1. Pagebreaks should not be allowed in the grammar. (Is there an
   equivalent to the samepage environment for LaTeX?)

2. I would like to get rid of the \BNFdf command. Unfortunately,
   I was not able to write something like

   \def\startbnfgrammar{%
     \start@bnfgrammar \NC}

   with @bnfgrammar being bnfgrammar from above. I guess this has
   to do with that the tabulation scans in everything until the
   next \stoptabulate command and gets confused.

3. How should I implement the \BNFcomment command? I want the
   comment to be placed in a \hbox of a given width, which then
   should be aligned on the right text margin. Normally, I would
   just use \hfill to flush that box to the right, but this does
   not work with tabulate, as all the widths are calculated on
   demand.

Does anyone has a neat solution to this problem? Is there
something better than tabulate for this purpose?

    Cheers,
    Marco

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