Place newline in backnaur package

Question

I'm using the backnaur package to write the BNF of a simple programming language I made. But now I have a fairly long definition and it gives an overflow. I tried adding newlines using \\ but this results in an odd alignment. I've also tried \newline but this doesn't do anything. I can't anything about newlines in the package documentation (http://ctan.sharelatex.com/tex-archive/macros/latex/contrib/backnaur/backnaur.pdf). This is my code:

\documentclass[dutch]{arabart}
\usepackage[T1]{fontenc}
\usepackage[latin9]{inputenc}
\usepackage{geometry}
\geometry{verbose,tmargin=2.5cm,bmargin=2.5cm,lmargin=2.5cm,rmargin=2.5cm}
\usepackage{amsmath}
\usepackage{amsthm}

\makeatletter
\numberwithin{equation}{section}
\numberwithin{figure}{section}

\usepackage{backnaur}

\makeatother

\usepackage{babel}
\begin{document}
\section{Syntax van de taal}
\begin{bnf*}
\bnfprod{function\_call\_void}{
    \bnfts{setLight} \bnfpn{expression} \bnfpn{light} \bnfpn{expression} \bnfpn{expression} \bnfpn{expression}
    \bnfor
    \bnfts{drive} \bnfpn{expression} \bnfpn{direction} \bnfpn{expression}
    \bnfor
    \bnfts{closeBot} \bnfpn{expression}
    \bnfor
    \bnfts{print} \bnfpn{expression}
    \bnfor
    \bnfts{printLn} \bnfpn{expression}
    \bnfor
    \bnfts{sleep} \bnfpn{expression}
}\\
\end{bnf*}
\end{document}

And this is an image showing my problem:

Answer 1

I don't think the package provides for line breaks; you can add them as follows.

\documentclass[draft,dutch]{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{babel}
\usepackage{geometry}
\geometry{tmargin=2.5cm,bmargin=2.5cm,lmargin=2.5cm,rmargin=2.5cm}
\usepackage{backnaur}

\newenvironment{bnfsplit}[1][0.7\textwidth]
 {\minipage[t]{#1}$}
 {$\endminipage}

\begin{document}
\section{Syntax van de taal}
\begin{bnf*}
\bnfprod{function\_call\_void}{
  \begin{bnfsplit}
  \bnfts{setLight} \bnfpn{expression} \bnfpn{light} 
    \bnfpn{expression} \bnfpn{expression} \bnfpn{expression}
  \\ \bnfor
    \bnfts{drive} \bnfpn{expression} \bnfpn{direction} \bnfpn{expression}
  \bnfor
    \bnfts{closeBot} \bnfpn{expression}
  \\ \bnfor
    \bnfts{print} \bnfpn{expression}
  \bnfor
    \bnfts{printLn} \bnfpn{expression}
    \bnfor
    \bnfts{sleep} \bnfpn{expression}
  \end{bnfsplit}
}\\
\end{bnf*}
\end{document}

The bnfsplit environment takes an optional argument, default 0.5\textwidth; adjust it manually with

\begin{bnfsplit}[0.7\textwidth]

or whatever.