In this talk from RubyFringe, Reginald Braithwaite talks about his experiments with rewriting Ruby in Ruby.
Among his projects is the Rewrite gem, which brings hygienic macros to Ruby (using ParseTree to get the Ruby AST for Ruby code at runtime). He shows the origins of these ideas in languages as Scheme, LISP or Haskell, and how this approach could be used to write more expressive code without having to abuse concepts such as Open Classes.
Reginald has recently starting blogging about similar topics in a blog set up as a Github repository.