Proto for Boost mailing list page: [proto] Externalizing grammar pattern matching

Subject: [proto] Externalizing grammar pattern matching
From: Joel Falcou (joel.falcou_at_[hidden])
Date: 2010-11-23 10:19:48

Here is some classical pattern matching using proto::or_

https://gist.github.com/711891

This is pretty canonical I guess (unless my proto-fu is rusting).
As stated in the comments, my main concern is that adding new 
pattern->value rules need to edit or_<>. Also classical.

For a long time it didn't bothered me until I needed to ship some code
doing this AND wanting to be extended by random contributors to add new 
patterns.

I brainstormed and conjured something like:

https://gist.github.com/711895

(hold your horses on the crappiness of my MPL, it's a quick'n'dirty demo 
code trying to get around the fact that mpl::pair, for whatever silly 
reason, IS NOT a MPL RandomAccessSequence :| )

So it's slightly better. Now I dont have to touch the or_<>, just the
mpl::vector. Close but no cigare.

After some other hours, I found a way to make a MPL map look-a-like 
where the insertion is external:

https://gist.github.com/711906

Alas, i can't find a way to put a decent mpl::iterator over this so both 
puzzles pieces fits.

So, question is: is there a way to have an extensible list of 
when<pattern,rule> that can be extended "from the outside", something
like a proto::switch_ but with patterns instead of tag ?

My daydream being something akin to :

https://gist.github.com/711914

So, now, I'll be grateful if you can answer this by some "you moron, use 
X" :D