On Jul 21, 2008, at 11:03 AM, Jim Weirich wrote:

> (I would also not oppose a change that "extends" the definition of  
> dup to include returning self for immutable objects.

Heh, this thought just came to me.  We can explain :dup on nil (and  
other immutables) as implementing a copy on write strategy to  
duplication.  And since these objects are immutable, we have optimized  
away all the overhead of actually tracking "copy on write"

-- 
-- Jim Weirich
-- jim.weirich / gmail.com