Suppress indentation after environment in LaTeX

Question

I'm trying to create a new environment in my LaTeX document where indentation in the next paragraph following the environment is suppressed.

I have been told (TeXbook and LaTeX source) that by setting \everypar to {\setbox0\lastbox}, the TeX typesetter will execute this at the beginning of the next paragraph and thus remove the indentation:

\everypar{\setbox0\lastbox}

So this is what I do, but to no effect (following paragraph is still indented):

\newenvironment{example}
  {\begin{list}
     {}
     {\setlength\leftmargin{2em}}}
  {\end{list}\everypar{\setbox0\lastbox}}

I have studied LaTeX's internals as well as I could manage. It seems that the \end routine says \endgroup and \par at some point, which may be the reason LaTeX ignores my \everypar setting. \global doesn't help either. I know about \noindent but want to do this automatically.

Example document fragment:

This is paragraph text. This is paragraph text, too.

\begin{example}
  \item This is the first item in the list.
  \item This is the second item in the list.
\end{example}

This is more paragraph text. I don't want this indented, please.

Internal routines and switches of interest seem to be \@endpetrue, \@endparenv and others. Thanks for your help.

Answer 1

You should not mess with the \everypar token list, unless you know exactly what you are doing. Use

\setlength{\parindent}{0pt}

to get rid of indenting in the whole document.

Answer 2

Can't you avoid this by not having a blank line between your environment and the next line?

This is paragraph text. This is paragraph text, too.

\begin{example}
  \item This is the first item in the list.
  \item This is the second item in the list.
\end{example}
% (No blank line)
This is more paragraph text. I don't want this indented, please.

Answer 3

I couldn't get anything to work without redefining \end, but I'm certainly no expert.

The following is quite hacky, but worked in my limited testing. Of course this will interfere with nested environments (you should be able to redefine \begin to restore the old \end if you have problems).

\newenvironment{example}{%
  \bgroup
  \let\oldend=\end
  \def\end##1{\oldend{##1}\csname @afterindentfalse\endcsname
                          \csname @afterheading\endcsname}
  \begin{list}{}
    {\setlength\leftmargin{2em}}
  }{%
  \end{list}
  \egroup
}

Answer 4

Include \@afterindentfalse\@afterheading at the end of your definition.