Re: [Boost-users] [proto] need explanation in implementing distributive law

5 Oct 2010


      On 10/5/2010 5:43 AM, Mauro Bianco wrote:
...
Hi all,
It is probably already been discovered by everyone at this point, but
the code proposed by Andrew does not to work properly to apply
distributivity more than once in an expression [works for a*(b+c) but
not for a*(b+c*(d+c)) ]
Funny, I never saw the original message. Perhaps it's stuck in a
moderation queue or lost in the ether(net).
...
Here a modified version that seems to work recursively.
How does it look?
...
,
struct distr :
  proto::or_<
    proto::when<
      proto::multiplies< proto::_, proto::plus< proto::_, proto::_ > >,
      proto::call<distr( // THIS IS TO RECURSE
        proto::_make_plus(
          proto::_make_multiplies(
            proto::_left,
            proto::_left( proto::_right )
          ),
          proto::_make_multiplies(
            proto::_left,
            proto::_right( proto::_right )
          )
        )
      )
    >
  proto::otherwise<proto::nary_expr<proto::_, proto::vararg<distr> > > >
{};
Yes, this looks reasonable.

-- 
Eric Niebler
BoostPro Computing
http://www.boostpro.com