| #ifndef BOOST_PP_IS_ITERATING |
| /////////////////////////////////////////////////////////////////////////////// |
| /// \file when.hpp |
| /// Definition of when transform. |
| // |
| // Copyright 2008 Eric Niebler. Distributed under the Boost |
| // Software License, Version 1.0. (See accompanying file |
| // LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) |
| |
| #ifndef BOOST_PROTO_TRANSFORM_WHEN_HPP_EAN_10_29_2007 |
| #define BOOST_PROTO_TRANSFORM_WHEN_HPP_EAN_10_29_2007 |
| |
| #include <boost/proto/detail/prefix.hpp> |
| #include <boost/preprocessor/cat.hpp> |
| #include <boost/preprocessor/repetition/enum_params.hpp> |
| #include <boost/preprocessor/repetition/enum_trailing_params.hpp> |
| #include <boost/preprocessor/iteration/iterate.hpp> |
| #include <boost/mpl/if.hpp> |
| #include <boost/proto/proto_fwd.hpp> |
| #include <boost/proto/traits.hpp> |
| #include <boost/proto/transform/call.hpp> |
| #include <boost/proto/transform/make.hpp> |
| #include <boost/proto/transform/impl.hpp> |
| #include <boost/proto/detail/suffix.hpp> |
| |
| namespace boost { namespace proto |
| { |
| /// \brief A grammar element and a PrimitiveTransform that associates |
| /// a transform with the grammar. |
| /// |
| /// Use <tt>when\<\></tt> to override a grammar's default transform |
| /// with a custom transform. It is for used when composing larger |
| /// transforms by associating smaller transforms with individual |
| /// rules in your grammar, as in the following transform which |
| /// counts the number of terminals in an expression. |
| /// |
| /// \code |
| /// // Count the terminals in an expression tree. |
| /// // Must be invoked with initial state == mpl::int_<0>(). |
| /// struct CountLeaves |
| /// : or_< |
| /// when<terminal<_>, mpl::next<_state>()> |
| /// , otherwise<fold<_, _state, CountLeaves> > |
| /// > |
| /// {}; |
| /// \endcode |
| /// |
| /// In <tt>when\<G, T\></tt>, when \c T is a class type it is a |
| /// PrimitiveTransform and the following equivalencies hold: |
| /// |
| /// <tt>boost::result_of\<when\<G,T\>(E,S,V)\>::::type</tt> is the same as |
| /// <tt>boost::result_of\<T(E,S,V)\>::::type</tt>. |
| /// |
| /// <tt>when\<G,T\>()(e,s,v)</tt> is the same as |
| /// <tt>T()(e,s,v)</tt>. |
| template<typename Grammar, typename PrimitiveTransform BOOST_PROTO_WHEN_BUILDING_DOCS(= Grammar)> |
| struct when |
| : PrimitiveTransform |
| { |
| typedef typename Grammar::proto_base_expr proto_base_expr; |
| }; |
| |
| /// \brief A specialization that treats function pointer Transforms as |
| /// if they were function type Transforms. |
| /// |
| /// This specialization requires that \c Fun is actually a function type. |
| /// |
| /// This specialization is required for nested transforms such as |
| /// <tt>when\<G, T0(T1(_))\></tt>. In C++, functions that are used as |
| /// parameters to other functions automatically decay to funtion |
| /// pointer types. In other words, the type <tt>T0(T1(_))</tt> is |
| /// indistinguishable from <tt>T0(T1(*)(_))</tt>. This specialization |
| /// is required to handle these nested function pointer type transforms |
| /// properly. |
| template<typename Grammar, typename Fun> |
| struct when<Grammar, Fun *> |
| : when<Grammar, Fun> |
| {}; |
| |
| /// \brief Syntactic sugar for <tt>when\<_, Fun\></tt>, for use |
| /// in grammars to handle all the cases not yet handled. |
| /// |
| /// Use <tt>otherwise\<T\></tt> in your grammars as a synonym for |
| /// <tt>when\<_, T\></tt> as in the following transform which |
| /// counts the number of terminals in an expression. |
| /// |
| /// \code |
| /// // Count the terminals in an expression tree. |
| /// // Must be invoked with initial state == mpl::int_<0>(). |
| /// struct CountLeaves |
| /// : or_< |
| /// when<terminal<_>, mpl::next<_state>()> |
| /// , otherwise<fold<_, _state, CountLeaves> > |
| /// > |
| /// {}; |
| /// \endcode |
| template<typename Fun> |
| struct otherwise |
| : when<_, Fun> |
| {}; |
| |
| #define BOOST_PP_ITERATION_PARAMS_1 (3, (0, BOOST_PROTO_MAX_ARITY, <boost/proto/transform/when.hpp>)) |
| #include BOOST_PP_ITERATE() |
| |
| }} // namespace boost::proto |
| |
| #endif |
| |
| #else |
| |
| #define N BOOST_PP_ITERATION() |
| |
| /// \brief A grammar element and a PrimitiveTransform that associates |
| /// a transform with the grammar. |
| /// |
| /// Use <tt>when\<\></tt> to override a grammar's default transform |
| /// with a custom transform. It is for used when composing larger |
| /// transforms by associating smaller transforms with individual |
| /// rules in your grammar, as in the following transform which |
| /// counts the number of terminals in an expression. |
| /// |
| /// \code |
| /// // Count the terminals in an expression tree. |
| /// // Must be invoked with initial state == mpl::int_<0>(). |
| /// struct CountLeaves |
| /// : or_< |
| /// when<terminal<_>, mpl::next<_state>()> |
| /// , otherwise<fold<_, _state, CountLeaves> > |
| /// > |
| /// {}; |
| /// \endcode |
| /// |
| /// The <tt>when\<G, R(A0,A1,...)\></tt> form accepts either a |
| /// CallableTransform or an ObjectTransform as its second parameter. |
| /// <tt>when\<\></tt> uses <tt>is_callable\<R\>::::value</tt> to |
| /// distinguish between the two, and uses <tt>call\<\></tt> to |
| /// evaluate CallableTransforms and <tt>make\<\></tt> to evaluate |
| /// ObjectTransforms. |
| template<typename Grammar, typename R BOOST_PP_ENUM_TRAILING_PARAMS(N, typename A)> |
| struct when<Grammar, R(BOOST_PP_ENUM_PARAMS(N, A))> |
| : transform<when<Grammar, R(BOOST_PP_ENUM_PARAMS(N, A))> > |
| { |
| typedef typename Grammar::proto_base_expr proto_base_expr; |
| |
| // Note: do not evaluate is_callable<R> in this scope. |
| // R may be an incomplete type at this point. |
| |
| template<typename Expr, typename State, typename Data> |
| struct impl : transform_impl<Expr, State, Data> |
| { |
| typedef call<R(BOOST_PP_ENUM_PARAMS(N, A))> call_; |
| typedef make<R(BOOST_PP_ENUM_PARAMS(N, A))> make_; |
| |
| typedef |
| typename mpl::if_c< |
| // OK to evaluate is_callable<R> here. |
| // R should be compete by now. |
| is_callable<R>::value |
| , call_ // "R" is a function to call |
| , make_ // "R" is an object to construct |
| >::type |
| which; |
| |
| typedef typename which::template impl<Expr, State, Data>::result_type result_type; |
| |
| /// Evaluate <tt>R(A0,A1,...)</tt> as a transform either with |
| /// <tt>call\<\></tt> or with <tt>make\<\></tt> depending on |
| /// whether <tt>is_callable\<R\>::::value</tt> is \c true or |
| /// \c false. |
| /// |
| /// \param e The current expression |
| /// \param s The current state |
| /// \param d An arbitrary data |
| /// \pre <tt>matches\<Expr, Grammar\>::::value</tt> is \c true |
| /// \return <tt>which()(e, s, d)</tt> |
| result_type operator ()( |
| typename impl::expr_param e |
| , typename impl::state_param s |
| , typename impl::data_param d |
| ) const |
| { |
| return typename which::template impl<Expr, State, Data>()(e, s, d); |
| } |
| }; |
| }; |
| |
| #undef N |
| |
| #endif |