Nathaniel Gray wrote:
> On Tue, Jun 17, 2008 at 4:20 AM, Jeremy Yallop <jeremy.yallop@ed.ac.uk> wrote:
>> I'm pleased to announce a new release of `patterns', an OCaml
>> framework for writing extensions to pattern matching using Camlp4.
> 
> Ooh, very interesting!  Have you looked at "active patterns" in F#?
> They look really useful and I've been wanting to code them up in
> camlp4 for a while now but haven't had the time.  It sounds like your
> framework could make that much easier.

Yes, one of the reason for writing the framework was to be able to 
implement F#-like active patterns.  I think it should be reasonably 
straightforward to do -- in fact, I'd expect design considerations to 
take up more time than actual implementation work (although I say that 
from the perspective of being already familiar with the "patterns" 
framework, of course).  If I remember rightly, there's a note at the end 
of the ICFP07 active patterns paper about using polymorphic variants to 
add active patterns in OCaml, which seems like it might be a good 
starting point.

You might also be interested in the "views" feature of Martin Jambon's 
"Micmatch", which is along the same lines as active patterns:

      http://martin.jambon.free.fr/micmatch-manual.html#htoc10

Jeremy.