/Src/Dependencies/Boost/boost/proto/transform/when.hpp
http://hadesmem.googlecode.com/ · C++ Header · 197 lines · 64 code · 14 blank · 119 comment · 0 complexity · 2c0da20fa74cfe596d94065577e1410c MD5 · raw file
- ///////////////////////////////////////////////////////////////////////////////
- /// \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/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/at.hpp>
- #include <boost/mpl/if.hpp>
- #include <boost/mpl/map.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>
- 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,d)</tt> is the same as
- /// <tt>T()(e,s,d)</tt>.
- template<typename Grammar, typename PrimitiveTransform /*= Grammar*/>
- struct when
- : PrimitiveTransform
- {
- typedef Grammar first;
- typedef PrimitiveTransform second;
- typedef typename Grammar::proto_grammar proto_grammar;
- };
- /// \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>
- {};
- /// \brief This specialization uses the Data parameter as a collection
- /// of transforms that can be indexed by the specified rule.
- ///
- /// Use <tt>when\<T, external_transform\></tt> in your code when you would like
- /// to define a grammar once and use it to evaluate expressions with
- /// many different sets of transforms. The transforms are found by
- /// using the Data parameter as a map from rules to transforms.
- ///
- /// See \c action_map for an example.
- template<typename Grammar>
- struct when<Grammar, external_transform>
- : proto::transform<when<Grammar, external_transform> >
- {
- typedef Grammar first;
- typedef external_transform second;
- typedef typename Grammar::proto_grammar proto_grammar;
- template<typename Expr, typename State, typename Data>
- struct impl
- : Data::template when<Grammar>::template impl<Expr, State, Data>
- {};
- template<typename Expr, typename State, typename Data>
- struct impl<Expr, State, Data &>
- : Data::template when<Grammar>::template impl<Expr, State, Data &>
- {};
- };
- /// \brief For defining a map of Rule/Transform pairs for use with
- /// <tt>when\<T, external_transform\></tt> to make transforms external to the grammar
- ///
- /// The following code defines a grammar with a couple of external transforms.
- /// It also defines an action_map that maps from rules to transforms. It then
- /// passes that transforms map at the Data parameter to the grammar. In this way,
- /// the behavior of the grammar can be modified post-hoc by passing a different
- /// action_map.
- ///
- /// \code
- /// struct int_terminal
- /// : proto::terminal<int>
- /// {};
- ///
- /// struct char_terminal
- /// : proto::terminal<char>
- /// {};
- ///
- /// struct my_grammar
- /// : proto::or_<
- /// proto::when< int_terminal, proto::external_transform >
- /// , proto::when< char_terminal, proto::external_transform >
- /// , proto::when<
- /// proto::plus< my_grammar, my_grammar >
- /// , proto::fold< _, int(), my_grammar >
- /// >
- /// >
- /// {};
- ///
- /// struct my_transforms
- /// : proto::external_transforms<
- /// proto::when<int_terminal, print(proto::_value)>
- /// , proto::when<char_terminal, print(proto::_value)>
- /// >
- /// {};
- ///
- /// proto::literal<int> i(1);
- /// proto::literal<char> c('a');
- /// my_transforms trx;
- ///
- /// // Evaluate "i+c" using my_grammar with the specified transforms:
- /// my_grammar()(i + c, 0, trx);
- /// \endcode
- template<BOOST_PP_ENUM_PARAMS_WITH_A_DEFAULT(BOOST_MPL_LIMIT_MAP_SIZE, typename T, mpl::na)>
- struct external_transforms
- {
- typedef mpl::map<BOOST_PP_ENUM_PARAMS(BOOST_MPL_LIMIT_MAP_SIZE, T)> map_type;
- template<typename Rule>
- struct when
- : proto::when<_, typename mpl::at<map_type, Rule>::type>
- {};
- };
- // Other specializations of proto::when are generated by the preprocessor...
- #include <boost/proto/transform/detail/when.hpp>
- /// INTERNAL ONLY
- ///
- template<typename Grammar, typename Transform>
- struct is_callable<when<Grammar, Transform> >
- : mpl::true_
- {};
- }} // namespace boost::proto
- #endif