69 lines
2.2 KiB
C++
69 lines
2.2 KiB
C++
/*=============================================================================
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Copyright (c) 2003 Vaclav Vesely
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http://spirit.sourceforge.net/
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Use, modification and distribution is subject to the Boost Software
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License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
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http://www.boost.org/LICENSE_1_0.txt)
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=============================================================================*/
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//
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// This example demonstrates the behaviour of epsilon_p when used as parser
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// generator.
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//
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// The "r" is the rule, which is passed as a subject to the epsilon_p parser
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// generator. The "r" is the rule with binded semantic actions. But epsilon_p
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// parser generator is intended for looking forward and we don't want to
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// invoke semantic actions of subject parser. Hence the epsilon_p uses
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// the no_actions policy.
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//
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// Because we want to use the "r" rule both in the epsilon_p and outside of it
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// we need the "r" to support two differant scanners, one with no_actions
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// action policy and one with the default action policy. To achieve this
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// we declare the "r" with the no_actions_scanner_list scanner type.
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//
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//-----------------------------------------------------------------------------
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#define BOOST_SPIRIT_RULE_SCANNERTYPE_LIMIT 2
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#include <boost/assert.hpp>
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#include <iostream>
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#include <boost/cstdlib.hpp>
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#include <boost/spirit/include/classic_core.hpp>
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#include <boost/spirit/include/phoenix1.hpp>
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using namespace std;
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using namespace boost;
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using namespace BOOST_SPIRIT_CLASSIC_NS;
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using namespace phoenix;
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//-----------------------------------------------------------------------------
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int main()
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{
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rule<
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// Support both the default phrase_scanner_t and the modified version
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// with no_actions action_policy
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no_actions_scanner_list<phrase_scanner_t>::type
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> r;
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int i(0);
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r = int_p[var(i) += arg1];
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parse_info<> info = parse(
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"1",
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// r rule is used twice but the semantic action is invoked only once
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epsilon_p(r) >> r,
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space_p
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);
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BOOST_ASSERT(info.full);
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// Check, that the semantic action was invoked only once
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BOOST_ASSERT(i == 1);
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return exit_success;
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}
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//-----------------------------------------------------------------------------
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