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- ///////////////////////////////////////////////////////////////////////////////
- // lookahead_matcher.hpp
- //
- // 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_XPRESSIVE_DETAIL_CORE_MATCHER_LOOKAHEAD_MATCHER_HPP_EAN_10_04_2005
- #define BOOST_XPRESSIVE_DETAIL_CORE_MATCHER_LOOKAHEAD_MATCHER_HPP_EAN_10_04_2005
- // MS compatible compilers support #pragma once
- #if defined(_MSC_VER)
- # pragma once
- #endif
- #include <boost/assert.hpp>
- #include <boost/mpl/bool.hpp>
- #include <boost/xpressive/detail/detail_fwd.hpp>
- #include <boost/xpressive/detail/core/quant_style.hpp>
- #include <boost/xpressive/detail/core/state.hpp>
- #include <boost/xpressive/detail/utility/save_restore.hpp>
- #include <boost/xpressive/detail/utility/ignore_unused.hpp>
- namespace boost { namespace xpressive { namespace detail
- {
- ///////////////////////////////////////////////////////////////////////////////
- // lookahead_matcher
- // Xpr can be either a static_xpression, or a shared_matchable
- //
- template<typename Xpr>
- struct lookahead_matcher
- : quant_style<quant_none, 0, Xpr::pure>
- {
- lookahead_matcher(Xpr const &xpr, bool no, bool pure = Xpr::pure)
- : xpr_(xpr)
- , not_(no)
- , pure_(pure)
- {
- }
- void inverse()
- {
- this->not_ = !this->not_;
- }
- template<typename BidiIter, typename Next>
- bool match(match_state<BidiIter> &state, Next const &next) const
- {
- return Xpr::pure || this->pure_
- ? this->match_(state, next, mpl::true_())
- : this->match_(state, next, mpl::false_());
- }
- template<typename BidiIter, typename Next>
- bool match_(match_state<BidiIter> &state, Next const &next, mpl::true_) const
- {
- BidiIter const tmp = state.cur_;
- if(this->not_)
- {
- // negative look-ahead assertions do not trigger partial matches.
- save_restore<bool> partial_match(state.found_partial_match_);
- detail::ignore_unused(partial_match);
- if(this->xpr_.match(state))
- {
- state.cur_ = tmp;
- return false;
- }
- else if(next.match(state))
- {
- return true;
- }
- }
- else
- {
- if(!this->xpr_.match(state))
- {
- return false;
- }
- state.cur_ = tmp;
- if(next.match(state))
- {
- return true;
- }
- }
- BOOST_ASSERT(state.cur_ == tmp);
- return false;
- }
- template<typename BidiIter, typename Next>
- bool match_(match_state<BidiIter> &state, Next const &next, mpl::false_) const
- {
- BidiIter const tmp = state.cur_;
- // matching xpr could produce side-effects, save state
- memento<BidiIter> mem = save_sub_matches(state);
- if(this->not_)
- {
- // negative look-ahead assertions do not trigger partial matches.
- save_restore<bool> partial_match(state.found_partial_match_);
- detail::ignore_unused(partial_match);
- if(this->xpr_.match(state))
- {
- restore_action_queue(mem, state);
- restore_sub_matches(mem, state);
- state.cur_ = tmp;
- return false;
- }
- restore_action_queue(mem, state);
- if(next.match(state))
- {
- reclaim_sub_matches(mem, state, true);
- return true;
- }
- reclaim_sub_matches(mem, state, false);
- }
- else
- {
- if(!this->xpr_.match(state))
- {
- restore_action_queue(mem, state);
- reclaim_sub_matches(mem, state, false);
- return false;
- }
- state.cur_ = tmp;
- restore_action_queue(mem, state);
- if(next.match(state))
- {
- reclaim_sub_matches(mem, state, true);
- return true;
- }
- restore_sub_matches(mem, state);
- }
- BOOST_ASSERT(state.cur_ == tmp);
- return false;
- }
- Xpr xpr_;
- bool not_;
- bool pure_; // false if matching xpr_ could modify the sub-matches
- };
- }}}
- #endif
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