All,

I have a files of exercises written in latex that I'd like to parse. I am new to this so be kind.

The exercise occurs between

\begin{exer}
\end{exer}
[download]

pairs. Inside this pair are pairs:

\begin{exertext}...\end{exertext} delimiting the problem statement.

\begin{soln}...\end{soln} delimiting the problem solution

\begin{answer}...\end{answer} delimiting a backanswer that goes in the back of the textbook.

Finally, there are sporadic directions that are included betwen \begin{instructions}...\end{instructions} pairs. A short example:

\begin{instructions} In Exercises~\ref{2.nformst}  and~\ref{2.nformend
+} ,
given the function $\phi$, place the ordinary differential equation
$\phi(t,y,y')=0$ in normal form.
\end{instructions}

\begin{exer}
\begin{exertext}
\label{2.nformst} $\phi(x,y,z)=x^2z+(1+x)y$
\end{exertext}
\begin{soln}
$\phi(t,y,y') = t^2y'+(1+t)y = 0$ must be solved for $y'$.  We get
$$y'= -\frac{(1+t)y}{t^2}.$$
\end{soln}
\begin{answer}$y'= -\dfrac{(1+t)y}{t^2}.$\end{answer}
\end{exer}

\begin{exer}
\begin{exertext}
\label{2.nformend} $\phi(x,y,z)=xz-2y-x^2$
 \end{exertext}
\begin{soln}
 $\phi(t,y,y')=ty'-2y-t^2$ must be solved for $y'$. We get
  $$y'=\frac{2y+t^2}{t}.$$
 \end{soln}
\end{exer}

\begin{instructions}
In Exercises~\ref{2.1st}--\ref{exer2.1.6}, show that the given
solution is a general
solution of the differential equation. Use a computer or calculator to
sketch the solutions for the given values of the
arbitrary constant. Experiment with different intervals for $t$ until 
+you
have a plot that shows what you consider to be the most important
behavior of the family.
\end{instructions}

\begin{exer}
\begin{exertext}
\label{2.1st} $y'=-ty$, $y(t)=Ce^{-(1/2)\,t^2}$, $C=-3,-2,\ldots,3$
\end{exertext}
\begin{soln}
$y(t)' = -Cte^{-(1/2)\,t^2}$ and $-ty(t) = -tCe^{-(1/2)\,t^2}$, so
$y'=-ty$. \par
\exfig{ex2.1ans01}
\end{soln}
\begin{answer}\exfig{ex2.1ans01}\end{answer}
\end{exer}
[download]

Is there a module on CPAN which I can use to parse this document. My goal is to put all the exercise problem statements (delimited by \begin{exertext}...\end{exertext}) in a file, all the solutions in a second file, all the backanswers in a third file, etc.

Thanks.