Are there any Ruby modules that allow documentation to act as source 
code? I was thinking of the problem of how souce code sometimes diverge 
from its documentation. So maybe there could be a way to specify the 
interface: the number of arguments and their types in the documentation, 
and possibly pre- and post-conditions, and then the documentation would 
be turned into code at runtime. I guess this would be implemented 
something like Perl's source filters[1]. Possibly some constants and 
such could be defined this way as well, version numbers, etc.

I'm not sure if this is a good idea or not; I haven't completely thought 
it through. It seems like I've read about this being done before in some 
other langage, but a brief search hasn't turned up anything.

Any thoughts?

Randy.

1. <http://perldoc.com/perl5.8.4/pod/perlfilter.html>