How to use a macro as the point arguments of both pspicture and \psframe?

Question

I forgot the rule to use \expandafter such that \rect can be used as the point arguments of both psframe and pspicture.

\documentclass{standalone}

\usepackage{pstricks}

\def\rect{(-3,-3)(3,3)}

\begin{document}

\begin{pspicture}[showgrid=top]\rect
    \psframe[linecolor=red]\rect
\end{pspicture}

\end{document}

Could you review it once more?

Answer 1

PSTricks expects

\begin{pspicture}[<options>]

to be followed by explicit coordinates. Thus \rect must be expanded before TeX starts looking to \begin.

\newcommand{\expandcoord}[2]{%
  \expandafter\expandcoordaux\expandafter{#2}{#1}%
}
\newcommand\expandcoordaux[2]{#2#1}

Then you can say

\expandcoord{\begin{pspicture}[showgrid=top]}{\rect}
  \expandcoord{\psframe[linecolor=red]}{\rect}
\end{pspicture}

The main problem here is that \expandafter only jumps over one token, so an indirect way has to be taken. This, of course, will break auto-pst-pdf or similar packages.