[Tex/LaTex] Defining a new environment extending a verbatim environment

environmentsmacrosverbatim

Why is it not possible to define a new environment that extends a verbatim environment?
Consider, e.g.:

\documentclass{article}
\newenvironment{myverbatim}{\tiny\begin{verbatim}}{\end{verbatim}}
\begin{document}
\begin{myverbatim}
  test
\end{myverbatim}
\end{document}

Compiling with pdflatex gives the error:

Runaway argument?
^^M  test^^M\end{myverbatim}^^M\end{document}^^M^^M
! File ended while scanning use of \@xverbatim.
<inserted text> 
                \par

(A motivation for this question can be found here: "Format a verbatim paragraph". From which it should be clear that I cannot use the listings or fancyvrb packages)

It would be nice with a basic and perhaps more detailed explanation (for this particular case and the reason for the error message) than what is given in, for instance, this discussion: "Why doesn’t verbatim work within…", and if there could be workarounds for simple cases like the one in this example..

Edit1:

Based on the answers so far, I feel that I need to be more precise about my case: I am trying to get the following code to work somehow (Confer with "Format a verbatim paragraph" for more details)

\documentclass{article}
\makeatletter
\begingroup
  \catcode`|=0
  \catcode`[=1
  \catcode`]=2
  \catcode`\{=12
  \catcode`\}=12
  \catcode`\\=12
  |gdef|myvr@xverbatim#1\end{myverbA}[#1|end[myverbA]]
|endgroup
\newenvironment{myverbA}{%
  \let\@xverbatim=\myvr@xverbatim
  \verbatim
}{%
}
\makeatother
\newenvironment{myverbB}{\tiny\begin{myverbA}}{\end{myverbA}}
\begin{document}
\begin{myverbB}
  test
\end{myverbB}
\end{document}

Edit2:

Based on egreg's answer, I tried the following:

\documentclass{article}
\usepackage{etoolbox}
\makeatletter
\begingroup
  \catcode`|=0
  \catcode`[=1
  \catcode`]=2
  \catcode`\{=12
  \catcode`\}=12
  \catcode`\\=12
  |gdef|myvr@xverbatim#1\end{myverbA}[#1|end[myverbA]]
|endgroup
\newenvironment{myverbA}{%
  \let\@xverbatim=\myvr@xverbatim
  \verbatim
}{%
}
\newenvironment{myverbB}
  {\preto\verbatim@font{\tiny}
   \myverbA}
  {\endmyverbA}
\makeatother
\begin{document}
\begin{myverbB}
  test
\end{myverbB}
\end{document}

which produces the error:

Runaway argument?
^^M  test^^M\end{myverbB}^^M\end{document}^^M^^M
! File ended while scanning use of \@xverbatim.
<inserted text> 
                \par

Best Answer

The main problem with using your definition of myverbatim can be defined in terms of a combination of scope and macro replacement. That is, something that starts with

\begin{<some-env>}

is expected to end with

\end{<some-env>}

If it doesn't, there's a problem, since the scope is not clearly defined. In your case, you start it with

\begin{myverbatim}

which is internally replaced with (removing the font change to \tiny for now)

\begin{verbatim}

Now, since you're in the verbatim environment (that is, a successful call was made to \begin{verbatim}), LaTeX starts gobbling up contents and printing them as-is until it arrives at a single line of code that resembles

\end{verbatim}

That's just how the verbatim environment works. It it looking for the stopping point. However, this never happens since the replacement of \end{myverbatim} (in your code) to \end{verbatim} (as per your definition) never occurs within the verbatim environment; verbatim doesn't perform the replacement of macros with their definitions. As such, TeX just keeps on scanning, producing what is considered a "Runaway argument" error.

Taking the above into account, a broad view on the replacement leaves your MWE to resemble (I've added a comment):

\documentclass{article}
\newenvironment{myverbatim}{\tiny\begin{verbatim}}{\end{verbatim}}
\begin{document}
\tiny\begin{verbatim}% Replacement text for \begin{myverbatim}
  test
\end{myverbatim}% No replacement since you're in the verbatim environment
\end{document}

Clearly the above doesn't start and end with the same environment.

If you want to have more flexibility with verbatim, use the verbatim package which allows you to do the following:

enter image description here

\documentclass{article}
\usepackage{verbatim}% http://ctan.org/pkg/verbatim
\newenvironment{myverbatim}%
  {\endgraf\tiny\verbatim}%
  {\endverbatim}
\begin{document}
Some text before.
\begin{myverbatim}
test
test
\end{myverbatim}
Some text after.
\end{document}

The verbatim package is a means to obtain your desired solution, just like fancyvrb and listings would be. Of course, a more rudimentary implementation (specific to your case) would be to merely change the font used by verbatim - stored in the macro \verbatim@font:

\makeatletter
\renewcommand{\verbatim@font}{\tiny\ttfamily}
\makeatother

Sure you can just precede the verbatim environment with \tiny and it will work just as well, but \verbatim@font is called within the verbatim environment, and therefore is constrained to only function there, not outside of it.

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