Why is my macro not expanded inside of \special{…}?

Question

I am writing my first LaTeX/TeX macro and not going anywhere with it. Could you please tell me what I am doing wrong in the code below.

I have the following definitions.

\def\defcolor#1#2{%
   \expandafter\def\csname #1\endcsname{#2}}

\def\colortext#1#2{%
   \special{ts: text fillcolor \csname#1\endcsname}{#2}%
}

I use them in my LaTeX file as follows:

\defcolor{red}{1.0,0.0,0.0}

Now when I use \red I see 1.0,0.0,0.0 in the text. Which is what I am expecting and happy to see! The problem is the \colortext command. When I call the \colortext command like the following

\colortext{red}{sometext}

I see the following output in my .dvi file

ts: text fillcolor \red

Instead of what I want

ts: text fillcolor 1.0,0.0,0.0

The \red macro is not getting expanded inside the replacement text of the \colortext macro. How do I fix this problem?

Answer 1

First make sure that \red is defined before you use \colortext, because \csname UndefinedMacro\endcsname will expand only so far till \UndefinedMacro, not further.

You could add a test for this:

\makeatletter
\def\colortext#1#2{%
   \@ifundefined{#1}
      {\PackageError{yourpackage}{Color '#1' not defined yet!}{}}
      {\special{ts: text fillcolor \csname#1\endcsname}{#2}}%
}
\makeatother

If this isn't the problem expand it manually:

\makeatletter
\def\colortext#1#2{%
   \@ifundefined{#1}
      {\PackageError{yourpackage}{Color '#1' not defined yet!}{}}
      {{\edef\@tempa{\noexpand\special{ts: text fillcolor \csname#1\endcsname}}\@tempa{#2}}%
}
\makeatother

You can then debug it by adding \show\@tempa after its definition.

Note the second { } to keep \@tempa local. I assume here that \special doesn't mind the group

Answer 2

try it this way

\documentclass{article}

\makeatletter
\def\defcolor#1#2{\@namedef{#1}{#2}}%
\def\colortext#1#2{\special{ts: text fillcolor \@nameuse{#1}}{#2}}
\makeatother
\begin{document}

\defcolor{red}{1.0,0.0,0.0}

\colortext{red}{sometext}

\end{document}