I've only had passing experience with Lisp but the macro facility seems 
incredibly powerful and useful, especially for defining mini-languages.  
Also functions are real first-class constructs in Lisp and not in Ruby, 
afaict.  I'm sure there's other stuff but those are the features I envy 
from Lisp.

Now, how much less readable than Ruby is Lisp? ;)

William James wrote:

>How much less powerful than Lisp is Ruby?
>  
>