On 5/30/2012 4:33 AM, Joel Falcou wrote: > On 05/29/2012 08:21 PM, Eric Niebler wrote: >> On 5/29/2012 1:44 AM, Karsten Ahnert wrote: >>> I have an arithmetic expression template where multiplication is >>> commutative. Is there an easy way to order a chain of multiplications >>> such that terminals with values (like proto::terminal< double >) appear >>> at the beginning? For example that >>> >>> arg1 * arg1 * 1.5 * arg1 >>> >>> will be transformed to >>> >>> 1.5 * arg1 * arg1 * arg1 >>> >>> ? >>> >>> I can imagine some complicated algorithms swapping expressions and child >>> expressions but I wonder if there is a simpler way. >> There is no clever built-in Proto algorithm for commutative >> transformations like this, I'm afraid. I was going to suggest flattening >> to a fusion vector and using fusion sort, but I see there is no fusion >> sort! :-( Nevertheless, that seems like a promising direction to me. >> Once you have the sorted vector, you should(?) be able to use >> fusion::fold to build the correct proto tree from it. >> > > Won't having a way to build it properly from the get go be a better > solution ? > > This basically require the feature we spoke about earlier so that > building a X * Y > node check which from X or Y is a double and put it in the proper place ? > > Then when doing X * Expr, check if there is a double at child<0> of expr > and restructure the whole tree at generation time ?
That's not a bad suggestion. You can do this today with a custom generator. -- Eric Niebler BoostPro Computing http://www.boostpro.com _______________________________________________ proto mailing list proto@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/proto
