Topher Cyll has written an outstanding article for Ruby Code & Style[0].

"If It's Not Nailed Down, Steal It: Pattern Matching, S-Expressions, and 
Domain Specific Languages in Ruby."

Summary:
There's a whole world of language features that we sometimes miss out on 
as Rubyists, such as pattern matching, S-expressions, and external 
domain-specific languages. But the good news is that we can have them, 
too, as long as we're not afraid to steal a few things first.


Take a gander, post some comments, and keep having fun with Ruby.

A big thanks to Topher, and thanks also to the RC&S advisory board and 
editors for helping get this out.

About RC&S:

Ruby Code & Style is the premiere online zine by and for the Ruby 
community.   We're always on the lookout for quality articles geared 
towards Ruby developers (and we're now able to pay the writers).   If 
you have an idea you think you may want to write about, please drop me a 
line: ruby.code.and.style AT gmail DOT com


[0] http://www.artima.com/rubycs/articles/patterns_sexp_dsls.html

James Britt
Editor-in-Chief, Ruby Code & Style