# Module Parameters

### 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 t-bgcolor.

It starts, surprisingly enough, with a line saying

\startmodule[bgcolor]


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

\unprotect


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

\setupmodule[color=red]


Our strategy will be to define a variable \BColor for the background color which will be set by the module; for this, we will use the processaction mechanism .

So we define a macro \BColor and define it:

\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}]


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

\setupbackgrounds[page][background=color,backgroundcolor=\BColor]


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

\protect
\stopmodule
\endinput


A simple test document will look like this:

\setupcolors[state=start]
\usemodule[bgcolor][color=blue]

\starttext

Hello world!

\stoptext


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 \getmoduleparameter{color}.

-- Thomas 18:28, 26 April 2006 (CEST) --