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- /*=============================================================================
- Copyright (c) 2001-2003 Hartmut Kaiser
- Copyright (c) 2002-2003 Joel de Guzman
- http://spirit.sourceforge.net/
- Use, modification and distribution is subject to 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)
- =============================================================================*/
- ///////////////////////////////////////////////////////////////////////////////
- //
- // This sample shows, how to use Phoenix for implementing a
- // simple (RPN style) calculator [ demonstrating phoenix ]
- //
- // [ HKaiser 2001 ]
- // [ JDG 6/29/2002 ]
- //
- ///////////////////////////////////////////////////////////////////////////////
- #include <boost/spirit/include/classic_core.hpp>
- #include <boost/spirit/include/classic_attribute.hpp>
- #include <boost/spirit/include/phoenix1_functions.hpp>
- #include <iostream>
- #include <string>
- ///////////////////////////////////////////////////////////////////////////////
- using namespace std;
- using namespace BOOST_SPIRIT_CLASSIC_NS;
- using namespace phoenix;
- ///////////////////////////////////////////////////////////////////////////////
- //
- // Our RPN calculator grammar using phoenix to do the semantics
- // The class 'RPNCalculator' implements a polish reverse notation
- // calculator which is equivalent to the following YACC description.
- //
- // exp:
- // NUM { $$ = $1; }
- // | exp exp '+' { $$ = $1 + $2; }
- // | exp exp '-' { $$ = $1 - $2; }
- // | exp exp '*' { $$ = $1 * $2; }
- // | exp exp '/' { $$ = $1 / $2; }
- // | exp exp '^' { $$ = pow ($1, $2); } /* Exponentiation */
- // | exp 'n' { $$ = -$1; } /* Unary minus */
- // ;
- //
- // The different notation results from the requirement of LL parsers not to
- // allow left recursion in their grammar (would lead to endless recursion).
- // Therefore the left recursion in the YACC script before is transformated
- // into iteration. To some, this is less intuitive, but once you get used
- // to it, it's very easy to follow.
- //
- // Note: The top rule propagates the expression result (value) upwards
- // to the calculator grammar self.val closure member which is
- // then visible outside the grammar (i.e. since self.val is the
- // member1 of the closure, it becomes the attribute passed by
- // the calculator to an attached semantic action. See the
- // driver code that uses the calculator below).
- //
- ///////////////////////////////////////////////////////////////////////////////
- struct pow_
- {
- template <typename X, typename Y>
- struct result { typedef X type; };
- template <typename X, typename Y>
- X operator()(X x, Y y) const
- {
- using namespace std;
- return pow(x, y);
- }
- };
- // Notice how power(x, y) is lazily implemented using Phoenix function.
- function<pow_> power;
- struct calc_closure : BOOST_SPIRIT_CLASSIC_NS::closure<calc_closure, double, double>
- {
- member1 x;
- member2 y;
- };
- struct calculator : public grammar<calculator, calc_closure::context_t>
- {
- template <typename ScannerT>
- struct definition {
- definition(calculator const& self)
- {
- top = expr [self.x = arg1];
- expr =
- real_p [expr.x = arg1]
- >> *(
- expr [expr.y = arg1]
- >> (
- ch_p('+') [expr.x += expr.y]
- | ch_p('-') [expr.x -= expr.y]
- | ch_p('*') [expr.x *= expr.y]
- | ch_p('/') [expr.x /= expr.y]
- | ch_p('^') [expr.x = power(expr.x, expr.y)]
- )
- | ch_p('n') [expr.x = -expr.x]
- )
- ;
- }
- typedef rule<ScannerT, calc_closure::context_t> rule_t;
- rule_t expr;
- rule<ScannerT> top;
- rule<ScannerT> const&
- start() const { return top; }
- };
- };
- ///////////////////////////////////////////////////////////////////////////////
- //
- // Main program
- //
- ///////////////////////////////////////////////////////////////////////////////
- int
- main()
- {
- cout << "/////////////////////////////////////////////////////////\n\n";
- cout << "\t\tExpression parser using Phoenix...\n\n";
- cout << "/////////////////////////////////////////////////////////\n\n";
- cout << "Type an expression...or [q or Q] to quit\n\n";
- calculator calc; // Our parser
- string str;
- while (getline(cin, str))
- {
- if (str.empty() || str[0] == 'q' || str[0] == 'Q')
- break;
- double n = 0;
- parse_info<> info = parse(str.c_str(), calc[var(n) = arg1], space_p);
- // calc[var(n) = arg1] invokes the calculator and extracts
- // the result of the computation. See calculator grammar
- // note above.
- if (info.full)
- {
- cout << "-------------------------\n";
- cout << "Parsing succeeded\n";
- cout << "result = " << n << endl;
- cout << "-------------------------\n";
- }
- else
- {
- cout << "-------------------------\n";
- cout << "Parsing failed\n";
- cout << "stopped at: \": " << info.stop << "\"\n";
- cout << "-------------------------\n";
- }
- }
- cout << "Bye... :-) \n\n";
- return 0;
- }
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