| /*============================================================================= |
| 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; |
| } |
| |
| |