Subject: Re: [Boost-users] [Proto] implementing an computer algebra system with proto
From: Eric Niebler (eric_at_[hidden])
Date: 2009-02-09 18:33:08
Kim Kuen Tang wrote:
> Hi Dave and Eric,
>
> i have written an grammar to do some transformations on an expression
> and would like to know your opinions.
>
> If the grammar matches the pattern var_+a, then it should transform the
> tree to var_=(0-a)/1.
> So the resulting callable transform would be :
>
> proto::when<
> //var_+a
> proto::plus<proto::terminal<placeholder>,
> proto::terminal<proto::_> >
> ,proto::_make_assign(
> proto::_left
> ,proto::_make_divides(proto::_make_minus(Zero
> ,proto::_right),One )
> )
>
> How should one implement the two macros Zero and One.
Try this:
// default-constructs an int
struct Zero
: proto::make<int>
{};
// initializes and int with a default-constructed mpl::int_<1>
// object (which is convertible to an int with value of 1).
struct One
: proto::make<int(mpl::int_<1>())>
{};
HTH,
-- Eric Niebler BoostPro Computing http://www.boostpro.com