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===Module parameters===

As of April 2006, ConTeXt provides a new mechanism for defining parameters
when calling a module. This is interesting for all those who consider
writing their own modules. It allows you to set variables in the call and
use them '''within''' the module's code; this was possible, but much less
convenient before. Here's a brief sample explaining how this mechanism
works. It consists of a test module and an example file; they are dull (I
admit) but instructive (I hope). Most of what I write here I've learnt from Taco, so all praise is due to him.

Our module will allow users to set the background color for a document. So
we call it <tt>t-bgcolor</tt>.

It starts, surprisingly enough, with a line saying

<pre>
\startmodule[bgcolor]
</pre>

Since we need to use some internal parameters, we have to "unprotect" the
contents of the module:

<pre>
\unprotect
</pre>

The next step is to set up the module with default parameters:

<pre>
\setupmodule[color=red]
</pre>

Our strategy will be to define a variable <tt>\BColor</tt> for the background color which
will be set by the module; for this, we will use the
[[Commands_with_KeyVal_arguments|processaction]] mechanism .

So we define a macro <tt>\BColor</tt> and define it:

<pre>
\processaction[\currentmoduleparameter{color}]
[blue=> \def\BColor{blue},
red=> \def\BColor{red},
yellow=> \def\BColor{yellow},
\v!unknown=> \def\BColor{white},
\v!default=> \def\BColor{red}]
</pre>

We then use this variable to define the background of our document:

<pre>
\setupbackgrounds[page][background=color,backgroundcolor=\BColor]
</pre>

And that's it! We now just have to finish the module with these lines:

<pre>
\protect
\stopmodule
\endinput
</pre>

A simple test document will look like this:

<pre>
\setupcolors[state=start]
\usemodule[bgcolor][color=blue]

\starttext

Hello world!

\stoptext
</pre>

This is just meant as a first example; of course, there are many more possibilities to use this mechanism. If you want to use the parameters directly in your code, you can use the form <tt>\getmoduleparameter{color}</tt>.

-- [[User:Thomas|Thomas]] 18:28, 26 April 2006 (CEST) --
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