On 05/29/2012 10:33 PM, Bart Janssens wrote: > On Tue, May 29, 2012 at 8:21 PM, Eric Niebler <e...@boostpro.com> 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. > > Just thinking out loud, could something like this work and be made recursive: > > boost::proto::when > < > proto::multiplies< <grammar for anything except double>, > proto::terminal<double> >, > proto::functional::make_multiplies(proto::_right, proto::_left) >>
This does not work since it does not propagate the double terminals up in the tree. Something like ( arg1 * ( arg1 * ( arg1 * 1.0 ) ) ) is transformed to ( arg1 * ( arg1 * ( 1.0 * arg1 ) ) ). _______________________________________________ proto mailing list proto@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/proto
