transform/detail/when.hpp

0001 #if !defined(BOOST_PROTO_DONT_USE_PREPROCESSED_FILES)
0002
0003     #include <boost/proto/transform/detail/preprocessed/when.hpp>
0004
0005 #elif !defined(BOOST_PP_IS_ITERATING)
0006
0007     #if defined(__WAVE__) && defined(BOOST_PROTO_CREATE_PREPROCESSED_FILES)
0008         #pragma wave option(preserve: 2, line: 0, output: "preprocessed/when.hpp")
0009     #endif
0010
0011     ///////////////////////////////////////////////////////////////////////////////
0012     /// \file when.hpp
0013     /// Definition of when transform.
0014     //
0015     //  Copyright 2008 Eric Niebler. Distributed under the Boost
0016     //  Software License, Version 1.0. (See accompanying file
0017     //  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
0018
0019     #if defined(__WAVE__) && defined(BOOST_PROTO_CREATE_PREPROCESSED_FILES)
0020         #pragma wave option(preserve: 1)
0021     #endif
0022
0023     #define BOOST_PP_ITERATION_PARAMS_1                                                             \
0024         (3, (0, BOOST_PROTO_MAX_ARITY, <boost/proto/transform/detail/when.hpp>))
0025     #include BOOST_PP_ITERATE()
0026
0027     #if defined(__WAVE__) && defined(BOOST_PROTO_CREATE_PREPROCESSED_FILES)
0028         #pragma wave option(output: null)
0029     #endif
0030
0031 #else
0032
0033     #define N BOOST_PP_ITERATION()
0034
0035     /// \brief A grammar element and a PrimitiveTransform that associates
0036     /// a transform with the grammar.
0037     ///
0038     /// Use <tt>when\<\></tt> to override a grammar's default transform
0039     /// with a custom transform. It is for used when composing larger
0040     /// transforms by associating smaller transforms with individual
0041     /// rules in your grammar, as in the following transform which
0042     /// counts the number of terminals in an expression.
0043     ///
0044     /// \code
0045     /// // Count the terminals in an expression tree.
0046     /// // Must be invoked with initial state == mpl::int_<0>().
0047     /// struct CountLeaves
0048     ///   : or_<
0049     ///         when<terminal<_>, mpl::next<_state>()>
0050     ///       , otherwise<fold<_, _state, CountLeaves> >
0051     ///     >
0052     /// {};
0053     /// \endcode
0054     ///
0055     /// The <tt>when\<G, R(A0,A1,...)\></tt> form accepts either a
0056     /// CallableTransform or an ObjectTransform as its second parameter.
0057     /// <tt>when\<\></tt> uses <tt>is_callable\<R\>::value</tt> to
0058     /// distinguish between the two, and uses <tt>call\<\></tt> to
0059     /// evaluate CallableTransforms and <tt>make\<\></tt> to evaluate
0060     /// ObjectTransforms.
0061     template<typename Grammar, typename R BOOST_PP_ENUM_TRAILING_PARAMS(N, typename A)>
0062     struct when<Grammar, R(BOOST_PP_ENUM_PARAMS(N, A))>
0063       : detail::when_impl<Grammar, R, R(BOOST_PP_ENUM_PARAMS(N, A))>
0064     {};
0065
0066     #if N > 0
0067     /// \brief A grammar element and a PrimitiveTransform that associates
0068     /// a transform with the grammar.
0069     ///
0070     /// Use <tt>when\<\></tt> to override a grammar's default transform
0071     /// with a custom transform. It is for used when composing larger
0072     /// transforms by associating smaller transforms with individual
0073     /// rules in your grammar, as in the following transform which
0074     /// counts the number of terminals in an expression.
0075     ///
0076     /// \code
0077     /// // Count the terminals in an expression tree.
0078     /// // Must be invoked with initial state == mpl::int_<0>().
0079     /// struct CountLeaves
0080     ///   : or_<
0081     ///         when<terminal<_>, mpl::next<_state>()>
0082     ///       , otherwise<fold<_, _state, CountLeaves> >
0083     ///     >
0084     /// {};
0085     /// \endcode
0086     ///
0087     /// The <tt>when\<G, R(A0,A1,...)\></tt> form accepts either a
0088     /// CallableTransform or an ObjectTransform as its second parameter.
0089     /// <tt>when\<\></tt> uses <tt>is_callable\<R\>::value</tt> to
0090     /// distinguish between the two, and uses <tt>call\<\></tt> to
0091     /// evaluate CallableTransforms and <tt>make\<\></tt> to evaluate
0092     /// ObjectTransforms.
0093     template<typename Grammar, typename R BOOST_PP_ENUM_TRAILING_PARAMS(N, typename A)>
0094     struct when<Grammar, R(BOOST_PP_ENUM_PARAMS(N, A)...)>
0095       : detail::when_impl<Grammar, R, R(BOOST_PP_ENUM_PARAMS(N, A)...)>
0096     {};
0097     #endif
0098
0099     #undef N
0100
0101 #endif