tables
Adapted from the question:
Inside a tabular environment (non-math context), how to have only 1 curly bracket (e.g. only the left one) spanning multiple lines of text, please?
\documentclass[12pt]{article}
\usepackage[a4paper]{geometry}
\begin{document}
I don't want the right curly bracket,
$\left\{
\begin{tabular}{c}
list item 1 \\
list item 2 \\
list item 3
\end{tabular}
\right\}$
only the left one please.
\end{document}
The problem is that the \begin{...} and \end{...} pair commands automatically create a "group" so that, in effect, the & and \\ are "out of scope" for the tabular, while inside the "production" environment they just show up at a place where the compiler is not expecting them.
A second problem with your definitions is that, even if they would work, they would be adding an extra \\ at the end of the tabular, adding an unwanted space at the end. Perhaps some more appropriate definitions would be
\documentclass[a4paper,10pt]{article}
\newcommand{\production}[1]{#1 ::= &}
\newenvironment{grammar}{\tabular{p{3cm}l}}{\endtabular}
\begin{document}
\begin{grammar}
\production{XmlStartTag} ... \\
\production{XmlOtherTag} ... \\
\production{XmlEndTag} ...
\end{grammar}
\end{document}
Note no \\ at the end of the last production. Also in the definition of the grammar you don't need to repeat the work of \begin/\end, and you can instead directly use \tabular and \endtabular.
You are mis-using the l column which is designed for single-line entries. In the tabular you should use a p column to allow line breaking to the specified width. In its simplest use longtable markup is identical to tabular just change the environment name and it allows page breaking. The following document shows you a tabular using p and the equivalent longtable.
\documentclass{article}
\setlength\textheight{15\baselineskip}
\usepackage{longtable}
\begin{document}
\begin{tabular}{ll}
$X\sim\mathsf{N}(\mu,\,{\sigma}^{2})$& the random variable $X$
has normal (Gaussian) distribution\\ & with mean $\mu$ and variance ${\sigma}^{2}$\\
\end{tabular}
\begin{tabular}{lp{6cm}}
$X\sim\mathsf{N}(\mu,\,{\sigma}^{2})$& the random variable $X$
has normal (Gaussian) distribution with mean $\mu$ and variance ${\sigma}^{2}$
\end{tabular}
\begin{longtable}{lp{6cm}}
$X\sim\mathsf{N}(\mu,\,{\sigma}^{2})$& the random variable $X$
has normal (Gaussian) distribution with mean $\mu$ and variance ${\sigma}^{2}$\\
$X\sim\mathsf{N}(\mu,\,{\sigma}^{2})$& the random variable $X$
has normal (Gaussian) distribution with mean $\mu$ and variance ${\sigma}^{2}$\\
$X\sim\mathsf{N}(\mu,\,{\sigma}^{2})$& the random variable $X$
has normal (Gaussian) distribution with mean $\mu$ and variance ${\sigma}^{2}$\\
$X\sim\mathsf{N}(\mu,\,{\sigma}^{2})$& the random variable $X$
has normal (Gaussian) distribution with mean $\mu$ and variance ${\sigma}^{2}$\\
$X\sim\mathsf{N}(\mu,\,{\sigma}^{2})$& the random variable $X$
has normal (Gaussian) distribution with mean $\mu$ and variance ${\sigma}^{2}$\\
$X\sim\mathsf{N}(\mu,\,{\sigma}^{2})$& the random variable $X$
has normal (Gaussian) distribution with mean $\mu$ and variance ${\sigma}^{2}$\\
$X\sim\mathsf{N}(\mu,\,{\sigma}^{2})$& the random variable $X$
has normal (Gaussian) distribution with mean $\mu$ and variance ${\sigma}^{2}$\\
\end{longtable}
\end{document}
Best Answer
Just change
\right\}to\right.. (The "." immediately after\rightstands for "nothing here".)