Padded two-column arrays

Question

I am using the following kind of 'padded array' many times:

\setlength{\fboxrule}{0pt}
\setlength{\fboxsep}{3pt}
\fbox{
\ensuremath{
\begin{array}{|l|l|}
\hline 
A & B\\ 
C & D\\
\vdots & \vdots \\
E & F\\
\hline 
\end{array}
}
} 

I'd like to be able to just write, e.g.,

\begin{DRS}
A & B\\ 
C & D\\
\vdots & \vdots \\
E & F\\
\end{DRS}

(or the same with a command instead of an environment), but I don't know a clean way to set this up. The problem is that fbox is a command, and array an environment, so I'm not sure of the right way to mix the two. I could possibly hack it together, e.g. using the environ package (which I just found by searching on this topic), but it would be nice to know the right way to do this.

Thanks!

Edit: this is the kind of image I'm producing (using nested DRSs):

Answer 1

If you need some padding, then ask explicitly for it:

\documentclass{article}

\newif\ifDRSmath
\newenvironment{DRS}
  {\relax\ifmmode\global\DRSmathtrue\else$\fi
   \kern3pt\begin{array}{|l|l|}
   \noalign{\kern3pt}
   \hline\mathstrut}
  {\hline
   \noalign{\kern3pt}
   \end{array}\kern3pt
   \ifDRSmath\global\DRSmathfalse\else$\fi}

\begin{document}
\begin{DRS}
    A & B\\ 
    C & D\\
    \vdots & \vdots \\
    E & F\\
\end{DRS}
\begin{DRS}
    A & B\\ 
    C & D\\
    \vdots & \vdots \\
    E & F\\
\end{DRS}

\end{document}

The conditional is needed for being able to use the environment both in text mode and in math mode. There will work in both modes: at the start we check for math mode, at the end only for \ifDRSmath and this trick will avoid issuing $ improperly.

Answer 2

You can use either a normal \newenvironment (as in the DRSX environment below), or the environ package (as in the DRS environment):

There is no need to use \fbox{} as a normal \hline will do the job.

Code:

\documentclass{article}
\usepackage{environ}

\NewEnviron{DRS}{%
    \setlength{\fboxrule}{0pt}
    \setlength{\fboxsep}{3pt}
    $\begin{array}{|l|l|}%
        \hline
        \BODY%
        \hline
    \end{array}$%
}

\newenvironment{DRSX}{%
    \setlength{\fboxrule}{0pt}
    \setlength{\fboxsep}{3pt}
    \begin{math}\begin{array}{|l|l|}%
        \hline
}{%
    \hline
    \end{array}\end{math}%
}


\begin{document}
\begin{DRS}
    A & B\\ 
    C & D\\
    \vdots & \vdots \\
    E & F\\
\end{DRS}
\begin{DRSX}
    A & B\\ 
    C & D\\
    \vdots & \vdots \\
    E & F\\
\end{DRSX}
\end{document}