Chris@16: ///////////////////////////////////////////////////////////////////////////////
Chris@16: /// \file when.hpp
Chris@16: /// Definition of when transform.
Chris@16: //
Chris@16: //  Copyright 2008 Eric Niebler. Distributed under the Boost
Chris@16: //  Software License, Version 1.0. (See accompanying file
Chris@16: //  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
Chris@16: 
Chris@16: #ifndef BOOST_PROTO_TRANSFORM_WHEN_HPP_EAN_10_29_2007
Chris@16: #define BOOST_PROTO_TRANSFORM_WHEN_HPP_EAN_10_29_2007
Chris@16: 
Chris@16: #include <boost/preprocessor/cat.hpp>
Chris@16: #include <boost/preprocessor/repetition/enum_params.hpp>
Chris@16: #include <boost/preprocessor/repetition/enum_trailing_params.hpp>
Chris@16: #include <boost/preprocessor/iteration/iterate.hpp>
Chris@16: #include <boost/mpl/at.hpp>
Chris@16: #include <boost/mpl/if.hpp>
Chris@16: #include <boost/mpl/map.hpp>
Chris@16: #include <boost/mpl/eval_if.hpp>
Chris@16: #include <boost/proto/proto_fwd.hpp>
Chris@16: #include <boost/proto/traits.hpp>
Chris@16: #include <boost/proto/transform/call.hpp>
Chris@16: #include <boost/proto/transform/make.hpp>
Chris@16: #include <boost/proto/transform/impl.hpp>
Chris@16: #include <boost/proto/transform/env.hpp>
Chris@16: 
Chris@101: #if defined(_MSC_VER)
Chris@16: # pragma warning(push)
Chris@16: # pragma warning(disable : 4714) // function 'xxx' marked as __forceinline not inlined
Chris@16: #endif
Chris@16: 
Chris@16: namespace boost { namespace proto
Chris@16: {
Chris@16:     namespace detail
Chris@16:     {
Chris@16:         template<typename Grammar, typename R, typename Fun>
Chris@16:         struct when_impl
Chris@16:           : transform<when<Grammar, Fun> >
Chris@16:         {
Chris@16:             typedef Grammar first;
Chris@16:             typedef Fun second;
Chris@16:             typedef typename Grammar::proto_grammar proto_grammar;
Chris@16: 
Chris@16:             // Note: do not evaluate is_callable<R> in this scope.
Chris@16:             // R may be an incomplete type at this point.
Chris@16: 
Chris@16:             template<typename Expr, typename State, typename Data>
Chris@16:             struct impl : transform_impl<Expr, State, Data>
Chris@16:             {
Chris@16:                 // OK to evaluate is_callable<R> here. R should be compete by now.
Chris@16:                 typedef
Chris@16:                     typename mpl::if_c<
Chris@16:                         is_callable<R>::value
Chris@16:                       , proto::call<Fun> // "R" is a function to call
Chris@16:                       , proto::make<Fun> // "R" is an object to construct
Chris@16:                     >::type
Chris@16:                 which;
Chris@16: 
Chris@16:                 typedef typename which::template impl<Expr, State, Data>::result_type result_type;
Chris@16: 
Chris@16:                 /// Evaluate <tt>R(A0,A1,...)</tt> as a transform either with
Chris@16:                 /// <tt>call\<\></tt> or with <tt>make\<\></tt> depending on
Chris@16:                 /// whether <tt>is_callable\<R\>::value</tt> is \c true or
Chris@16:                 /// \c false.
Chris@16:                 ///
Chris@16:                 /// \param e The current expression
Chris@16:                 /// \param s The current state
Chris@16:                 /// \param d An arbitrary data
Chris@16:                 /// \pre <tt>matches\<Expr, Grammar\>::value</tt> is \c true
Chris@16:                 /// \return <tt>which()(e, s, d)</tt>
Chris@16:                 BOOST_FORCEINLINE
Chris@16:                 result_type operator ()(
Chris@16:                     typename impl::expr_param   e
Chris@16:                   , typename impl::state_param  s
Chris@16:                   , typename impl::data_param   d
Chris@16:                 ) const
Chris@16:                 {
Chris@16:                     return typename which::template impl<Expr, State, Data>()(e, s, d);
Chris@16:                 }
Chris@16:             };
Chris@16:         };
Chris@16:     }
Chris@16: 
Chris@16:     /// \brief A grammar element and a PrimitiveTransform that associates
Chris@16:     /// a transform with the grammar.
Chris@16:     ///
Chris@16:     /// Use <tt>when\<\></tt> to override a grammar's default transform
Chris@16:     /// with a custom transform. It is for used when composing larger
Chris@16:     /// transforms by associating smaller transforms with individual
Chris@16:     /// rules in your grammar, as in the following transform which
Chris@16:     /// counts the number of terminals in an expression.
Chris@16:     ///
Chris@16:     /// \code
Chris@16:     /// // Count the terminals in an expression tree.
Chris@16:     /// // Must be invoked with initial state == mpl::int_<0>().
Chris@16:     /// struct CountLeaves
Chris@16:     ///   : or_<
Chris@16:     ///         when<terminal<_>, mpl::next<_state>()>
Chris@16:     ///       , otherwise<fold<_, _state, CountLeaves> >
Chris@16:     ///     >
Chris@16:     /// {};
Chris@16:     /// \endcode
Chris@16:     ///
Chris@16:     /// In <tt>when\<G, T\></tt>, when \c T is a class type it is a
Chris@16:     /// PrimitiveTransform and the following equivalencies hold:
Chris@16:     ///
Chris@16:     /// <tt>boost::result_of\<when\<G,T\>(E,S,V)\>::type</tt> is the same as
Chris@16:     /// <tt>boost::result_of\<T(E,S,V)\>::type</tt>.
Chris@16:     ///
Chris@16:     /// <tt>when\<G,T\>()(e,s,d)</tt> is the same as
Chris@16:     /// <tt>T()(e,s,d)</tt>.
Chris@16:     template<typename Grammar, typename PrimitiveTransform /*= Grammar*/>
Chris@16:     struct when
Chris@16:       : PrimitiveTransform
Chris@16:     {
Chris@16:         typedef Grammar first;
Chris@16:         typedef PrimitiveTransform second;
Chris@16:         typedef typename Grammar::proto_grammar proto_grammar;
Chris@16:     };
Chris@16: 
Chris@16:     /// \brief A specialization that treats function pointer Transforms as
Chris@16:     /// if they were function type Transforms.
Chris@16:     ///
Chris@16:     /// This specialization requires that \c Fun is actually a function type.
Chris@16:     ///
Chris@16:     /// This specialization is required for nested transforms such as
Chris@16:     /// <tt>when\<G, T0(T1(_))\></tt>. In C++, functions that are used as
Chris@16:     /// parameters to other functions automatically decay to funtion
Chris@16:     /// pointer types. In other words, the type <tt>T0(T1(_))</tt> is
Chris@16:     /// indistinguishable from <tt>T0(T1(*)(_))</tt>. This specialization
Chris@16:     /// is required to handle these nested function pointer type transforms
Chris@16:     /// properly.
Chris@16:     template<typename Grammar, typename Fun>
Chris@16:     struct when<Grammar, Fun *>
Chris@16:       : when<Grammar, Fun>
Chris@16:     {};
Chris@16: 
Chris@16:     /// \brief Syntactic sugar for <tt>when\<_, Fun\></tt>, for use
Chris@16:     /// in grammars to handle all the cases not yet handled.
Chris@16:     ///
Chris@16:     /// Use <tt>otherwise\<T\></tt> in your grammars as a synonym for
Chris@16:     /// <tt>when\<_, T\></tt> as in the following transform which
Chris@16:     /// counts the number of terminals in an expression.
Chris@16:     ///
Chris@16:     /// \code
Chris@16:     /// // Count the terminals in an expression tree.
Chris@16:     /// // Must be invoked with initial state == mpl::int_<0>().
Chris@16:     /// struct CountLeaves
Chris@16:     ///   : or_<
Chris@16:     ///         when<terminal<_>, mpl::next<_state>()>
Chris@16:     ///       , otherwise<fold<_, _state, CountLeaves> >
Chris@16:     ///     >
Chris@16:     /// {};
Chris@16:     /// \endcode
Chris@16:     template<typename Fun>
Chris@16:     struct otherwise
Chris@16:       : when<_, Fun>
Chris@16:     {};
Chris@16: 
Chris@16:     namespace envns_
Chris@16:     {
Chris@16:         // Define the transforms global
Chris@16:         BOOST_PROTO_DEFINE_ENV_VAR(transforms_type, transforms);
Chris@16:     }
Chris@16: 
Chris@16:     using envns_::transforms;
Chris@16: 
Chris@16:     /// \brief This specialization uses the Data parameter as a collection
Chris@16:     /// of transforms that can be indexed by the specified rule.
Chris@16:     ///
Chris@16:     /// Use <tt>when\<T, external_transform\></tt> in your code when you would like
Chris@16:     /// to define a grammar once and use it to evaluate expressions with
Chris@16:     /// many different sets of transforms. The transforms are found by
Chris@16:     /// using the Data parameter as a map from rules to transforms.
Chris@16:     ///
Chris@16:     /// See \c action_map for an example.
Chris@16:     template<typename Grammar>
Chris@16:     struct when<Grammar, external_transform>
Chris@16:       : proto::transform<when<Grammar, external_transform> >
Chris@16:     {
Chris@16:         typedef Grammar first;
Chris@16:         typedef external_transform second;
Chris@16:         typedef typename Grammar::proto_grammar proto_grammar;
Chris@16: 
Chris@16:         template<typename Expr, typename State, typename Data>
Chris@16:         struct impl
Chris@16:           : remove_reference<
Chris@16:                 typename mpl::eval_if_c<
Chris@16:                     proto::result_of::has_env_var<Data, transforms_type>::value
Chris@16:                   , proto::result_of::env_var<Data, transforms_type>
Chris@16:                   , proto::result_of::env_var<Data, data_type>
Chris@16:                 >::type
Chris@16:             >::type::template when<Grammar>::template impl<Expr, State, Data>
Chris@16:         {};
Chris@16:     };
Chris@16: 
Chris@16:     /// \brief For defining a map of Rule/Transform pairs for use with
Chris@16:     /// <tt>when\<T, external_transform\></tt> to make transforms external to the grammar
Chris@16:     ///
Chris@16:     /// The following code defines a grammar with a couple of external transforms.
Chris@16:     /// It also defines an action_map that maps from rules to transforms. It then
Chris@16:     /// passes that transforms map at the Data parameter to the grammar. In this way,
Chris@16:     /// the behavior of the grammar can be modified post-hoc by passing a different
Chris@16:     /// action_map.
Chris@16:     ///
Chris@16:     /// \code
Chris@16:     /// struct int_terminal
Chris@16:     ///   : proto::terminal<int>
Chris@16:     /// {};
Chris@16:     /// 
Chris@16:     /// struct char_terminal
Chris@16:     ///   : proto::terminal<char>
Chris@16:     /// {};
Chris@16:     /// 
Chris@16:     /// struct my_grammar
Chris@16:     ///   : proto::or_<
Chris@16:     ///         proto::when< int_terminal, proto::external_transform >
Chris@16:     ///       , proto::when< char_terminal, proto::external_transform >
Chris@16:     ///       , proto::when<
Chris@16:     ///             proto::plus< my_grammar, my_grammar >
Chris@16:     ///           , proto::fold< _, int(), my_grammar >
Chris@16:     ///         >
Chris@16:     ///     >
Chris@16:     /// {};
Chris@16:     /// 
Chris@16:     /// struct my_transforms
Chris@16:     ///   : proto::external_transforms<
Chris@16:     ///         proto::when<int_terminal, print(proto::_value)>
Chris@16:     ///       , proto::when<char_terminal, print(proto::_value)>
Chris@16:     ///     >
Chris@16:     /// {};
Chris@16:     ///
Chris@16:     /// proto::literal<int> i(1);
Chris@16:     /// proto::literal<char> c('a');
Chris@16:     /// my_transforms trx;
Chris@16:     ///
Chris@16:     /// // Evaluate "i+c" using my_grammar with the specified transforms:
Chris@16:     /// my_grammar()(i + c, 0, trx);
Chris@16:     /// \endcode
Chris@16:     template<BOOST_PP_ENUM_PARAMS_WITH_A_DEFAULT(BOOST_MPL_LIMIT_MAP_SIZE, typename T, mpl::na)>
Chris@16:     struct external_transforms
Chris@16:     {
Chris@16:         typedef mpl::map<BOOST_PP_ENUM_PARAMS(BOOST_MPL_LIMIT_MAP_SIZE, T)> map_type;
Chris@16: 
Chris@16:         template<typename Rule>
Chris@16:         struct when
Chris@16:           : proto::when<_, typename mpl::at<map_type, Rule>::type>
Chris@16:         {};
Chris@16:     };
Chris@16: 
Chris@16:     // Other specializations of proto::when are generated by the preprocessor...
Chris@16:     #include <boost/proto/transform/detail/when.hpp>
Chris@16: 
Chris@16:     /// INTERNAL ONLY
Chris@16:     ///
Chris@16:     template<typename Grammar, typename Transform>
Chris@16:     struct is_callable<when<Grammar, Transform> >
Chris@16:       : mpl::true_
Chris@16:     {};
Chris@16: 
Chris@16: }} // namespace boost::proto
Chris@16: 
Chris@101: #if defined(_MSC_VER)
Chris@16: # pragma warning(pop)
Chris@16: #endif
Chris@16: 
Chris@16: #endif