karma/auxiliary/eps.hpp

0001 //  Copyright (c) 2001-2011 Hartmut Kaiser
0002 //
0003 //  Distributed under the Boost Software License, Version 1.0. (See accompanying
0004 //  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
0005
0006 #if !defined(BOOST_SPIRIT_KARMA_EPS_APRIL_21_2007_0246PM)
0007 #define BOOST_SPIRIT_KARMA_EPS_APRIL_21_2007_0246PM
0008
0009 #if defined(_MSC_VER)
0010 #pragma once
0011 #endif
0012
0013 #include <boost/spirit/home/support/common_terminals.hpp>
0014 #include <boost/spirit/home/support/info.hpp>
0015 #include <boost/spirit/home/karma/domain.hpp>
0016 #include <boost/spirit/home/karma/meta_compiler.hpp>
0017 #include <boost/spirit/home/karma/delimit_out.hpp>
0018 #include <boost/spirit/home/support/unused.hpp>
0019 #include <boost/fusion/include/at.hpp>
0020
0021 namespace boost { namespace spirit
0022 {
0023     ///////////////////////////////////////////////////////////////////////////
0024     // Enablers
0025     ///////////////////////////////////////////////////////////////////////////
0026
0027     // enables eps
0028     template <>
0029     struct use_terminal<karma::domain, tag::eps>
0030       : mpl::true_ {};
0031
0032     // enables eps(bool-condition)
0033     template <typename A0>
0034     struct use_terminal<karma::domain
0035         , terminal_ex<tag::eps, fusion::vector1<A0> > >
0036       : is_convertible<A0, bool> {};
0037
0038     // enables lazy eps(f)
0039     template <>
0040     struct use_lazy_terminal<karma::domain, tag::eps, 1>
0041       : mpl::true_ {};
0042
0043 }}
0044
0045 ///////////////////////////////////////////////////////////////////////////////
0046 namespace boost { namespace spirit { namespace karma
0047 {
0048 #ifndef BOOST_SPIRIT_NO_PREDEFINED_TERMINALS
0049     using boost::spirit::eps;
0050 #endif
0051     using boost::spirit::eps_type;
0052
0053     struct eps_generator : primitive_generator<eps_generator>
0054     {
0055         template <typename Context, typename Unused>
0056         struct attribute
0057         {
0058             typedef unused_type type;
0059         };
0060
0061         template <
0062             typename OutputIterator, typename Context, typename Delimiter
0063           , typename Attribute>
0064         static bool generate(OutputIterator& sink, Context&, Delimiter const& d
0065           , Attribute const& /*attr*/)
0066         {
0067             return karma::delimit_out(sink, d); // always do post-delimiting
0068         }
0069
0070         template <typename Context>
0071         info what(Context const& /*context*/) const
0072         {
0073             return info("eps");
0074         }
0075     };
0076
0077     struct semantic_predicate : primitive_generator<semantic_predicate>
0078     {
0079         template <typename Context, typename Unused>
0080         struct attribute
0081         {
0082             typedef unused_type type;
0083         };
0084
0085         semantic_predicate(bool predicate)
0086           : predicate_(predicate)
0087         {}
0088
0089         template <
0090             typename OutputIterator, typename Context, typename Delimiter
0091           , typename Attribute>
0092         bool generate(OutputIterator& sink, Context&, Delimiter const& d
0093           , Attribute const& /*attr*/) const
0094         {
0095             // only do post-delimiting when predicate is true
0096             return predicate_ && karma::delimit_out(sink, d);
0097         }
0098
0099         template <typename Context>
0100         info what(Context const& /*context*/) const
0101         {
0102             return info("semantic-predicate");
0103         }
0104
0105         bool predicate_;
0106     };
0107
0108     ///////////////////////////////////////////////////////////////////////////
0109     // Generator generators: make_xxx function (objects)
0110     ///////////////////////////////////////////////////////////////////////////
0111     template <typename Modifiers>
0112     struct make_primitive<tag::eps, Modifiers>
0113     {
0114         typedef eps_generator result_type;
0115         result_type operator()(unused_type, unused_type) const
0116         {
0117             return result_type();
0118         }
0119     };
0120
0121     template <typename Modifiers, typename A0>
0122     struct make_primitive<
0123         terminal_ex<tag::eps, fusion::vector1<A0> >
0124       , Modifiers>
0125     {
0126         typedef semantic_predicate result_type;
0127
0128         template <typename Terminal>
0129         result_type operator()(Terminal const& term, unused_type) const
0130         {
0131             return result_type(fusion::at_c<0>(term.args));
0132         }
0133     };
0134
0135 }}}
0136
0137 #endif