Increase parskip after first paragraph in environment

Question

I have an environment and I'd like to increase the \parskip between the first and second paragraphs in the environment, but only the first and second paragraphs.

I can achieve the effect manually with

\begin{myenv}
  First par

  \medskip
  Second par

  Third par
\end{myenv}

Is there a way to do this automatically?

Answer 1

Two choices, I won't tell which one I prefer. 😉

\documentclass{article}

\makeatletter
\newenvironment{jason}
 {\par\def\par{\@@par\medskip\let\par\@@par}}
 {\par}
\makeatother

\newenvironment{egreg}[1]
 {\par#1\par\medskip}
 {\par}

\begin{document}

\section{Jason}

This is Jason's idea:

\begin{jason}
First line

Second line

Third line
\end{jason}

\section{Egreg}

This is Egreg's idea:

\begin{egreg}{First line}
Second line

Third line
\end{egreg}

\end{document}

In the first realization, \par is redefined to end the paragraph (because \@@par is the primitive \par), issue a \medskip and then redefine itself to the primitive meaning.