\documentclass[12pt]{article}
\usepackage[margin=1in]{geometry}
\usepackage{mathptmx,amsmath}
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%--- Define a new language for tex
\weaveOpts{newlang = TeX:tex}

%--- Formatting for TeX
\TeXweaveOpts{prompt="", results=tex,
  beforeout="\fbox{\begin{minipage}{\linewidth}",
  afterout="\end{minipage}}"}

%--- Formatting for tex
\texweaveOpts{prompt="", results=tex,
  codefmt="fontsize=\footnotesize",
  beforecode="\par\noindent\begin{minipage}[t]{.48\linewidth}",
  aftercode="\end{minipage}\hfill",
  beforeout="\begin{minipage}[t]{.48\linewidth}",
  afterout="\end{minipage}"}

\begin{document}
\section*{\LaTeX{} test}
If you want to make a handout showing how to do stuff in \LaTeX{},
it's pretty easy to do.  This is one instance where it is convenient to define a new ``language'' so that we have a choice of two formats.

\subsection*{Stacked format}
If we use the \texttt{TeX} language, we get a stacked format
\begin{TeXcode}
To solve the equation $ax^2 + bx + c=0$, use
\begin{equation}\label{qe}
  x = \frac{-b \pm \sqrt{b^2 - 4ac}} {2a}
\end{equation}
Equation~(\ref{qe}) is called the \emph{quadratic formula}.
\end{TeXcode}

\subsection*{Side-by-side format}
If we use the \texttt{tex} language, we get a side-by-side display:
\begin{texcode}
To solve the equation 
$ax^2 + bx + c=0$, use
\begin{equation}\label{qe}
  x = \frac{-b \pm \sqrt{b^2 - 4ac}} {2a}
\end{equation}
Equation~(\ref{qe}) is called 
the \emph{quadratic formula}.
\end{texcode}


\end{document}