Clojure Protocols & expression problem

[Don]

bearophile wrote:
> A short video about Clojure 1.2 Protocols, created to solve the expression problem (that D doesn't solve well yet), they are like fake multimetods because they are like single dispatch :-) (So they need just a virtual table, that the JavaVM can optimize well):
> 
> http://vimeo.com/11236603
> 
> By the way, you can see an example of the expression problem here, this is D code that solves one case of it:
> http://codepad.org/RPw6Kxu6
> 
> This is the same in Python with the multimethod (module inlined at the top), it's similar to CLisp CLOS solution:
> http://codepad.org/tWsYomoZ
> 
> Bye,
> bearophile

Has anyone tried to solve the expression problem by using opDispatch?