% grammar.sty
%
% A package for writing grammars.
%
% Usage:
%
% Each grammar fragment lives in a Grammar environment:
%
%   \begin{Grammar}
%     ... rules ...
%   \end{Grammar}
%
% The Grammar environment can have an optional argument, which is used in
% HTML generation.
% Each rule is a collection of productions with the same lhs:
%
%   \begin{Rules}{nonterm}
%     ... right-hand sides ...
%   \end{Rules}
%
% where "nonterm" is the lhs nonterminal.  A right-hand side is
% formatted with the \RHS{} command.  The following commands may
% be used inside a \RHS{} command:
%
%   \GRP{item}		-- (item)
%   \OPT{item}		-- item?
%   \OPTGRP{item}	-- same as \OPT{\GRP{item}}
%   \LIST{item}		-- item*
%   \LISTGRP{item}	-- same as \LIST{\GRP{item}}
%   \LISTONE{item}	-- item+
%   \LISTONEGRP{item}	-- same as \LISTONE{\GRP{item}}
%
% To support lexical definitions, we also have the form
%   \begin{OneOfRule}{nonterm}
%     ... items ...
%   \end{OneOfRule}
%
% where "nonterm" is the lhs nonterminal.  The items are formatted with
% the \ITEM{item} command.
%
% This package also defines the following font commands:
%
%   \kw{item}		-- for keywords (default is bold \tt)
%   \nt{item}		-- for nonterminals (default is \it)
%   \term{item}		-- for terminal symbols (default is \it)
%   \sym{item}		-- for literal symbols (default is bold \tt)
%

\RequirePackage{ifthen}
\RequirePackage{amstext}

\makeatletter

\newboolean{G@firstrule}
\newcommand{\G@sepsymb}{
  \ifthenelse{\boolean{G@firstrule}}{$::=$}{$\mid$}}
\newcommand{\G@RHS}[2][]{
  \G@sepsymb{} & {#2} & {#1} \\
  \setboolean{G@firstrule}{false}%
}
\newcommand{\G@CONT}[1]{
  & \hspace*{1em} {#1} & \\
}
\newcommand{\G@ITEM}[1]{%
  \mbox{%
    \ifthenelse{\boolean{G@firstrule}}{$::=$}{$\mid$} #1}
  \setboolean{G@firstrule}{false}%
}

%
% font commands
\newcommand{\kw}[1]{\texttt{\bfseries{}#1}}
\newcommand{\nt}[1]{\textit{#1}}
\newcommand{\term}[1]{\textit{#1}}
\newcommand{\sym}[1]{\kw{#1}}

\newenvironment{Grammar}[1][]{%
  \begin{list}{}{
    \setlength{\leftmargin}{4em}%
    \setlength{\itemindent}{2em}%
    \setlength{\itemsep}{0em}%
    \setlength{\parsep}{0em}%
  }
  \newcommand{\GRP}[1]{$(\text{##1})$}%
  \newcommand{\OPT}[1]{$\text{\protect{##1}}^{\textit{opt}}$}%
  \newcommand{\OPTGRP}[1]{$(\text{##1})^{\textit{opt}}$}%
  \newcommand{\LIST}[1]{$\text{\protect{##1}}^{*}$}%
  \newcommand{\LISTGRP}[1]{$(\text{##1})^{*}$}%
  \newcommand{\LISTONE}[1]{$\text{\protect{##1}}^{+}$}%
  \newcommand{\LISTONEGRP}[1]{$(\text{##1})^{+}$}%
  \newenvironment{Rules}[1]{%
    \begin{samepage}%
    \setboolean{G@firstrule}{true}%
    \newcommand{\RHS}{\G@RHS}%
    \newcommand{\CONT}{\G@CONT}%
    \item[\nt{##1}]\mbox{}\\
    \begin{tabular}{clr}%
  }{%
    \end{tabular}%
    \end{samepage}\pagebreak[2]%
  }
  \newenvironment{OneOfRule}[1]{%
    \begin{samepage}%
    \setboolean{G@firstrule}{true}%
    \newcommand{\ITEM}{\G@ITEM}%
    \item[\nt{##1}]\mbox{}\\
  }{%
    \end{samepage}\pagebreak[2]%
  }
}{%
  \end{list}
}

\makeatother