Supplying examples with CPAN modules

One of the optional metrics used by CPANTS is whether the module has examples. I think it checks if there is an eg/ directory but actually having an eg/ directory with examples does not give the users much.

Most of the people install the modules using CPAN.pm or the native package management tool. Neither of those install the examples. Very few download the source and unzip it so they won't see the examples.

OK, I admit. I always have trouble locating examples even when the documentation of the module tells me to look at them.

So what other options are there?

POD in the sample script

If there is POD in the example files then search.cpan.org will display them, but of course it will display the POD and not the code.

Generate a module and install it

In Win32::GuiTest there is a make_eg.pl script that is executed when the distribution is generated. It takes all the files from the eg/ directory and creates a module called Win32::GuiTest::Examples putting the examples in the POD section. This means the actual examples can be easily read on search.cpan.org and once the module is installed they can be easily found by typing


  perldoc Win32::GuiTest::Examples

Install the examples

In Padre and in [dist:Padre::Plugin::Parrot] we instruct CPAN.pm to install the examples in the share directory. Actually we have a share/ directory and the examples are within that directory in share/examples. Then in Makefile.PL we have instruction to install the share directory. (In the case of Module::Install it is a call to install_share.)

Once the module is installed the examples are also installed and they can be found with the following call:


  $dir = File::Spec->catdir(
		File::ShareDir::dist_dir('Padre-Plugin-Parrot'),
		'examples');

That is


  File::ShareDir::dist_dir('Padre-Plugin-Parrot')

returns the path to the share directory of the package.

In Padre then we can create menu items to Open Example that will open the regular Open File window just it will position it in the directory of the examples supplied by Padre. Similarily the Parrot Plugin has (or I think will have in the next release) a menu item for the same thing.

Of course it is not restricted to people using Padre as anyone could use the above code.

run examples embedded in modules

There are a number of modules on CPAN with some way to run the examples embedded in modules. for example if you look at the SDL::Tutorial package of SDL_Perl, you know, the newly (and rightly) hyped module that will help you burn all your free time by writing games in Perl... there you will find simple instructions on how to run the sample script:


  perl -MSDL::Tutorial -e 1


Auto-extract examples

There are a number of modules on CPAN with some form of auto-extract examples I just can't find them. The idea there is that the sample script is embedded in a module and running


  perl -MModule::Name -e1

will create a file example.pl that will hold the example script. Actually I think the SDL examples meant to do this as well but if I remember correctly they don't extract anything, just run the example.

Conclusion

As we can see there are several ways to include examples in a CPAN distribution with varying levels of ease of use. Actually we could even combine all the solutions and make sure people have several easy ways to see running examples of the modules on CPAN.

These could also help a lot with module evaluation and learning.

Published on 2009-10-23 by Gabor Szabo
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