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

Subject: Re: [Boost-users] [proto] need explanation in implementing distributive law
From: Mauro Bianco (mbianco_at_[hidden])
Date: 2010-10-05 08:43:52

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)) ]
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> > > >
{};

Regards,
Mauro.

On 22.03.2010 22:11, Andrew Durward wrote:
> As a follow-up, the attached code seems to compile and yield the expected
> result.
>
> andrew
>
>
>
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