[pstricks] How do you do if then?

[David Arnold]

All,

This produces a 2 by 4 arrow of boxes. I'd like the first row to have  
four boxes, but the second row to stop at three boxes. This shoud use  
some sort of if then statement, I would imagine, to limit the second  
row to three boxes. How do you use if then in pstricks to get what I  
want?

\documentclass{article}

\usepackage{pstricks}
\usepackage{pstricks-add}
\include{pst-func}

\def\Box{\psframebox{\rule{3mm}{0pt}\rule{0pt}{3mm}}}

\begin{document}

\begin{pspicture}(1,0.5)(4,2.5)
\multido{\iA=1+1}{4}{%
   \multido{\iB=1+1}{2}{%
     \rput(\iA,\iB){\rnode{p\iA\iB}{\Box}}}}
\ncbox[linearc=0.35,nodesep=0.2,linecolor=blue]{p11}{p31}
\ncbox[linearc=0.35,nodesep=0.2,linecolor=blue]{p12}{p32}
\end{pspicture}

\end{document}

Thanks.

David.