Grammar with numbered rules

Question

I'd like to represent a grammar where rules are numbered (for example, the following grammar: http://en.wikipedia.org/wiki/LR_parser#Additional_Example_1.2B1), in order to refer to those rules later in an action table. However, I don't find any way to do this properly. Ideally, the rules numbers would be right-aligned, like in a alignat environment.

Currently, I simply put the numbers directly in the grammar, and the output is not really readable.

My code:

\documentclass[11pt]{article}
\usepackage{syntax}

\begin{document}

\setlength{\grammarparsep}{20pt plus 1pt minus 1pt}
\setlength{\grammarindent}{12em}
\begin{grammar}
<E> ::= <E> \lit{*} <B>    (1)
    \alt <E> \lit{+} <B>   (2)
    \alt <B>               (3)

<B> ::= \lit{0}            (4)
    \alt \lit{1}           (5)
\end{grammar}

\end{document}

(note that the E and B were between 'less than' and 'greater than' symbols, I removed them from the listing because they seem to badly interact with stackexchange).

Answer 1

This should work for many cases; I'm no expert in these kinds of grammars.

I suggest you to define a new environment, patching the grammar environment to add line numbers.

\documentclass[11pt]{article}
\usepackage[pass,showframe]{geometry} % just to show the margins

\usepackage{syntax}

\usepackage{etoolbox} % for patching
\makeatletter
% define the main command on the model of the original one
% we add stepping the counter and typesetting the number
\def\gr@implnumbereditem<#1> #2 {%
  \stepcounter{grammarline}%
  \sbox\z@{\hskip\labelsep\grammarlabel{#1}{#2}}
  \strut\@@par%
  \vskip-\parskip%
  \vskip-\baselineskip%
  \hrule\@height\z@\@depth\z@\relax%
  \item[%
    \rlap{\hskip\dimexpr\linewidth+\grammarindent\relax %% add the number
          \llap{(\thegrammarline)}}%
    \unhbox\z@]%
  \catcode`\<\active%
}
% copy the grammar environment under a new name
\let\numberedgrammar\grammar
\let\endnumberedgrammar\endgrammar
% now patch the new environment
\pretocmd\numberedgrammar{\setcounter{grammarline}{0}}{}{}
\patchcmd\numberedgrammar
  {\gr@implitem}
  {\gr@implnumbereditem}
  {}{}
\patchcmd\numberedgrammar
  {\def\alt{\\\llap{\textbar\quad}}}
  {\let\alt\alt@num}
  {}{}

% the command for numbering the \alt lines
\def\alt@num{\\\relax
  \stepcounter{grammarline}%
  \rlap{\hskip\dimexpr\linewidth-\labelwidth+\grammarindent-\labelsep\relax
        \llap{(\thegrammarline)}}% add the number
  \llap{\textbar\quad}}

\newcounter{grammarline}
\makeatother

\begin{document}

\setlength{\grammarparsep}{20pt plus 1pt minus 1pt}
\setlength{\grammarindent}{5em}
Some text above
\begin{numberedgrammar}
<E> ::= <E> \lit{*} <B>
  \alt <E> \lit{+} <B>
  \alt <B>

<B> ::= \lit{0}
  \alt \lit{1}
\end{numberedgrammar}
Some text below
\begin{enumerate}
\item a
\begin{numberedgrammar}
<E> ::= <E> \lit{*} <B>
  \alt <E> \lit{+} <B>
  \alt <B>

<B> ::= \lit{0}
  \alt \lit{1}
\end{numberedgrammar}
\end{enumerate}
\end{document}