Simple calculation inside \def command

Question

I would like to define a command that does some simple calculation, like this:

\def\rectangle(#1,#2)(#3,#4)#5{
   \psframe(#1,#2)(#3,#4)
   \rput((#1+#3)/2,(#2+#4)/2){#5}
}
%
\rectangle(1,1)(49,49){X}

The goal is to draw a rectangle, then write some text in the center of the rectangle.

Apparently, what I did doesn't work.

What is the correct way to do it?

Answer 1

Here is an example using \newcommand instead of \def. The coordinate calculation is performed at the postscript level level (\rput(! x y)), consider the reverse polish notation:

\documentclass{article}
\usepackage{pstricks}

\newcommand{\rectangle}[5]{
   \psframe(#1,#2)(#3,#4)
   \rput(!  #3 #1 add 2 div   #4 #2 add 2 div){#5}
}

% #3 #1 sub 2 div #1 add => (#3 - #1) / 2 + #1 => x
% #4 #2 sub 2 div #2 add => (#4 - #2) / 2 + #2 => y

\begin{document}

\begin{figure}
   \begin{pspicture}(4,4)
      \rectangle{1}{1}{4}{4}{center}
   \end{pspicture}
\end{figure}

\end{document}

If you want to keep the syntax

\rectangle(a,b)(c,d){text}

here's how you can do with xparse:

\documentclass{article}

\usepackage{xparse}
\usepackage{pstricks}

\NewDocumentCommand{\rectangle}{
  >{\SplitArgument{1}{,}} r() % argument of type (<x>,<y>), will be passed as {<x>}{<y>}
  >{\SplitArgument{1}{,}} r() % ditto
  m                           % argument in braces
}{%
  \dorectangle#1#2{#3}%
}

% same as before, just changed the name    
\NewDocumentCommand{\dorectangle}{ m m m m m }{% 
  \psframe(#1,#2)(#3,#4)%
  \rput(!  #3 #1 add 2 div   #4 #2 add 2 div){#5}%
}

\begin{document}

\begin{pspicture}(4,4)
\rectangle(1,1)(4,4){center}
\end{pspicture}

\end{document}

And here is a solution using \def:

\documentclass{article}
\usepackage{pstricks}

\def\rectangle(#1,#2)(#3,#4)#5{
   \psframe(#1,#2)(#3,#4)
   \rput(!  #3 #1 add 2 div   #4 #2 add 2 div){#5}
}

\begin{document}

\begin{figure}
  \begin{pspicture}(4,4)
    \rectangle(1,1)(4,4){center}
  \end{pspicture}
\end{figure}

\end{document}

Answer 2

I'm not sure if this is what you want, but it does achieve your goal.

In Plain TeX:

\long\def\Boxit#1#2{\vbox{\hrule\hbox{\vrule\vbox spread#1pt{\vfil
                     \hbox spread#1pt{\hfil#2\hfil}\vfil}\vrule}\hrule}}
\def\Boxedtext#1#2#3{\Boxit{0}{\vbox to #1{\hsize=#2\vfill\hbox to\hsize{\hfill#3\hfill}\vfill}}}                               

\Boxedtext{1in}{1.5in}{Hi there!}
\bye