qi/auxiliary/eps.hpp

0001 /*=============================================================================
0002     Copyright (c) 2001-2011 Joel de Guzman
0003
0004     Distributed under the Boost Software License, Version 1.0. (See accompanying
0005     file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
0006 ==============================================================================*/
0007 #if !defined(BOOST_SPIRIT_EPS_MARCH_23_2007_0454PM)
0008 #define BOOST_SPIRIT_EPS_MARCH_23_2007_0454PM
0009
0010 #if defined(_MSC_VER)
0011 #pragma once
0012 #endif
0013
0014 #include <boost/spirit/home/qi/domain.hpp>
0015 #include <boost/spirit/home/qi/skip_over.hpp>
0016 #include <boost/spirit/home/qi/meta_compiler.hpp>
0017 #include <boost/spirit/home/support/unused.hpp>
0018 #include <boost/spirit/home/support/info.hpp>
0019 #include <boost/spirit/home/support/common_terminals.hpp>
0020 #include <boost/fusion/include/at.hpp>
0021 #include <boost/type_traits/is_convertible.hpp>
0022
0023 namespace boost { namespace spirit
0024 {
0025     ///////////////////////////////////////////////////////////////////////////
0026     // Enablers
0027     ///////////////////////////////////////////////////////////////////////////
0028     template <>
0029     struct use_terminal<qi::domain, tag::eps>       // enables eps
0030       : mpl::true_ {};
0031
0032     template <typename A0>
0033     struct use_terminal<qi::domain
0034       , terminal_ex<tag::eps, fusion::vector1<A0> > // enables eps(bool-condition)
0035     > : is_convertible<A0, bool> {};
0036
0037     template <>                                     // enables eps(f)
0038     struct use_lazy_terminal<
0039         qi::domain, tag::eps, 1 /*arity*/
0040     > : mpl::true_ {};
0041 }}
0042
0043 namespace boost { namespace spirit { namespace qi
0044 {
0045 #ifndef BOOST_SPIRIT_NO_PREDEFINED_TERMINALS
0046     using spirit::eps;
0047 #endif
0048     using spirit::eps_type;
0049
0050     struct eps_parser : primitive_parser<eps_parser>
0051     {
0052         template <typename Context, typename Iterator>
0053         struct attribute
0054         {
0055             typedef unused_type type;
0056         };
0057
0058         template <typename Iterator, typename Context
0059           , typename Skipper, typename Attribute>
0060         bool parse(Iterator& first, Iterator const& last
0061           , Context& /*context*/, Skipper const& skipper
0062           , Attribute& /*attr*/) const
0063         {
0064             qi::skip_over(first, last, skipper);
0065             return true;
0066         }
0067
0068         template <typename Context>
0069         info what(Context& /*context*/) const
0070         {
0071             return info("eps");
0072         }
0073     };
0074
0075     struct semantic_predicate : primitive_parser<semantic_predicate>
0076     {
0077         template <typename Context, typename Iterator>
0078         struct attribute
0079         {
0080             typedef unused_type type;
0081         };
0082
0083         semantic_predicate(bool predicate_)
0084           : predicate(predicate_) {}
0085
0086         template <typename Iterator, typename Context
0087           , typename Skipper, typename Attribute>
0088         bool parse(Iterator& first, Iterator const& last
0089           , Context& /*context*/, Skipper const& skipper
0090           , Attribute& /*attr*/) const
0091         {
0092             qi::skip_over(first, last, skipper);
0093             return predicate;
0094         }
0095
0096         template <typename Context>
0097         info what(Context& /*context*/) const
0098         {
0099             return info("semantic-predicate");
0100         }
0101
0102         bool predicate;
0103     };
0104
0105     ///////////////////////////////////////////////////////////////////////////
0106     // Parser generators: make_xxx function (objects)
0107     ///////////////////////////////////////////////////////////////////////////
0108     template <typename Modifiers>
0109     struct make_primitive<tag::eps, Modifiers>
0110     {
0111         typedef eps_parser result_type;
0112         result_type operator()(unused_type, unused_type) const
0113         {
0114             return result_type();
0115         }
0116     };
0117
0118     template <typename Modifiers, typename A0>
0119     struct make_primitive<
0120         terminal_ex<tag::eps, fusion::vector1<A0> >
0121       , Modifiers>
0122     {
0123         typedef semantic_predicate result_type;
0124         template <typename Terminal>
0125         result_type operator()(Terminal const& term, unused_type) const
0126         {
0127             return result_type(fusion::at_c<0>(term.args) ? true : false);
0128         }
0129     };
0130 }}}
0131
0132 #endif