Wsrtjtyk

I'm writing a custom command that uses minipages to display its contents:

newcommand{example}[1]{noindentbegin{minipage}{linewidth}#1end{minipage}}

The spacing around this command should be similar to that of the align environment: abovedisplayskip above, and belowdisplayskip after, so I add parvspace{…} before and after:

newcommand{example}[1]{%

  parvspace{abovedisplayskip}

  noindentbegin{minipage}{linewidth}#1end{minipage}

  paraddvspace{belowdisplayskip}}

This isn't perfect, though: it adds an extra parskip before and after the contents, even if there are no blank lines around the command:

AAA % too much space (extra parskip) after this

example{lipsum[1]}

BBB % too much space (extra parskip) before that

I can remove the first one by changing the definition to this:

newcommand{example}[1]{%

  ifvmodeelseparvspace{-parskip}fivspace{abovedisplayskip}

  noindentbegin{minipage}{linewidth}#1end{minipage}

  paraddvspace{belowdisplayskip}}

But what's the equivalent fix for the bottom of the command? If I use a negative space the parskip will always be suppressed. Ideally, I'd like text immediately following the command to not be indented, just like with [].

Here's a minimal example:

documentclass{minimal}



usepackage{lipsum}

setlength{parskip}{50pt}



newcommand{example}[1]{%

  ifvmodeelseparvspace{-parskip}fivspace{abovedisplayskip}

  noindentbegin{minipage}{linewidth}#1end{minipage}

  paraddvspace{belowdisplayskip}}



begin{document}



% There should be small spaces after AAA and before BBB

AAA

example{lipsum[1]}

BBB



% There should be a large space after AAA and a small one before BBB

% And BBB shouldn't be indented

AAA



example{lipsum[1]}

BBB



% There should be a small space after AAA and a large one before BBB

AAA

example{lipsum[1]}



BBB

end{document} 

The standard way to do this would be to define your environment as a trivlist, almost all latex display environments (verbatim, center, quote,..) are defined as trivlists (special one-item version of list) exactly for this reason.

The trivlist code detects whether there is a paragraph break before the list and if so has paragraph spacing before and after, but if there is no paragraph break before the list then the internal par after the list is hidden and paragraph indentation of the following text is suppressed.

begin{center}end{center} for example is defined by

defcenter{trivlist centeringitemrelax}

defendcenter{endtrivlist}

Here is a possible solution.
I'm defining the macro tentativepar which inserts par and sets both parskip and parindent to 0pt.
It moreover temporarily redefines par and everypar (which is inserted at the start of every paragraph) to reset the original values (and themselves).

The net effect is that tentativepar will insert a paragraph break without any skip or indentation unless it is followed by another par.

Here is an example:

documentclass{article}



setlength{parskip}{50pt}



%% vv We need to store a couple of values

newskipsavedparskip

newskipsavedparindent

newtokssavedeverypar



makeatletter

newcommand*tentativepar{%

  par

  savedparskipparskip         %% <- store original parskip

  savedparindentparindent     %% <- store original parindent

  expandaftersavedeveryparexpandafter{theeverypar}

  %% ^^ store original everypar

  parskip0pt                   %% <- set parskip to 0pt

  parindent0pt                 %% <- set parindent to 0pt

  %% vv restore everything that was saved after the first par

  defpar{%

    @restorepar                  %% <- restore original par

    expandaftereveryparexpandafter{thesavedeverypar}%

    parskipsavedparskip         %% <- reset parskip

    parindentsavedparindent     %% <- reset parindent

    par                          %% still insert a paragraph break

  }%

  %% vv or at the stat of the next paragraph

  expandaftereveryparexpandafter{%

    thesavedeverypar

    @restorepar                  %% <- restore original par

    expandaftereveryparexpandafter{thesavedeverypar}%

    parskipsavedparskip         %% <- reset parskip

    parindentsavedparindent     %% <- reset parindent

  }

}

makeatother



newcommand{example}[1]{%

  ifvmodeelsetentativeparfi

  vspace{abovedisplayskip}

  noindentbegin{minipage}{.5linewidth}#1end{minipage}%

  vspace{belowdisplayskip}

  tentativepar

}



begin{document}



AAA

example{There should be small spaces after AAA and before BBB}

BBB



AAA



example{There should be a large space after AAA and a small one before BBB. And BBB shouldn't be indented.}

BBB



AAA

example{There should be a small space after AAA and a large one before BBB}



BBB



CCC



end{document}