[Boost-users] [Proto] loosing expression wrappers in transforms

Subject: [Boost-users] [Proto] loosing expression wrappers in transforms
From: Robert Valkenburg (rj.valkenburg_at_[hidden])
Date: 2010-04-30 00:44:26

Hi,

I have a grammar, domain and an extended expression  i.e.

 struct ga_domain  :  proto::domain<proto::generator<ga_expr>, ga_grammar>
{};

template<typename Expr>
struct ga_expr : boost::proto::extends<Expr, ga_expr<Expr>, ga_domain>
{
     //  ....
};

When the expression is  transformed some instances of the ga_expr<>  wrapper
get removed.  For example

// some function that expects a ga_expr<Expr> as 2nd arg
void evaluate_expr(Res& res, const ga_expr<Expr>& expr)
{
   //  ....
}

// some function which transforms the expression and calls  evaluate_expr()
template <class Res, class Expr>
void evaluate(Res& res, const ga_expr<Expr>& expr)
{
        BOOST_MPL_ASSERT((proto::matches< ga_expr<Expr>, ga_grammar>));
         evaluate_expr(res, ET::transform_expression()(expr) );
}

With the (do nothing)  transform

    struct  transform_expression : proto::nary_expr<proto::_,
proto::vararg<transform_expression> > {};

I get the following messages (using gcc 4.4.1,  boost 1.42)

In function ‘void clifford::evaluate(Res&, const clifford::ga_expr<Expr>&)
[with Res =
clifford::element<clifford::basis::basis<clifford::cga3::basis::rotator_basis_list,
mpl_::integral_c<unsigned int, 105u> >, clifford::cga3::cga3,
clifford::default_tags>, Expr =
boost::proto::exprns_::expr<clifford::tag::reverse_,
boost::proto::argsns_::list1<clifford::ga_expr<boost::proto::exprns_::expr<boost::proto::tag::terminal,
boost::proto::argsns_::term<const
clifford::element<clifford::basis::basis<boost::mpl::vector10_c<short int,
3, 5, 6, 9, 10, 12, 17, 18, 20, 24>, mpl_::integral_c<unsigned int,
18224744u> >, clifford::cga3::cga3, clifford::default_tags>&>, 0l> > >,
1l>]’:

error: no matching function for call to
‘evaluate_expr(clifford::element<clifford::basis::basis<clifford::cga3::basis::rotator_basis_list,
mpl_::integral_c<unsigned int, 105u> >, clifford::cga3::cga3,
clifford::default_tags>&,
boost::proto::exprns_::expr<clifford::tag::reverse_,
boost::proto::argsns_::list1<const
clifford::ga_expr<boost::proto::exprns_::expr<boost::proto::tag::terminal,
boost::proto::argsns_::term<const
clifford::element<clifford::basis::basis<boost::mpl::vector10_c<short int,
3, 5, 6, 9, 10, 12, 17, 18, 20, 24>, mpl_::integral_c<unsigned int,
18224744u> >, clifford::cga3::cga3, clifford::default_tags>&>, 0l> >&>,
1l>&)’

So the clifford::ga_expr<> wrapper got removed from the unary  reverse
operator and i'm not sure what i'm supposed to add to make it stay.

thanks