libs/spirit/classic/example/fundamental/phoenix_calc.cpp
/*=============================================================================
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)
=============================================================================*/
////////////////////////////////////////////////////////////////////////////
//
// Full calculator example demonstrating Phoenix
// This is discussed in the "Closures" chapter in the Spirit User's Guide.
//
// [ JDG 6/29/2002 ]
//
////////////////////////////////////////////////////////////////////////////
#include <boost/spirit/include/classic_core.hpp>
#include <boost/spirit/include/classic_attribute.hpp>
#include <iostream>
#include <string>
////////////////////////////////////////////////////////////////////////////
using namespace std;
using namespace BOOST_SPIRIT_CLASSIC_NS;
using namespace phoenix;
////////////////////////////////////////////////////////////////////////////
//
// Our calculator grammar using phoenix to do the semantics
//
// 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 calc_closure : BOOST_SPIRIT_CLASSIC_NS::closure<calc_closure, double>
{
member1 val;
};
struct calculator : public grammar<calculator, calc_closure::context_t>
{
template <typename ScannerT>
struct definition
{
definition(calculator const& self)
{
top = expression[self.val = arg1];
expression
= term[expression.val = arg1]
>> *( ('+' >> term[expression.val += arg1])
| ('-' >> term[expression.val -= arg1])
)
;
term
= factor[term.val = arg1]
>> *( ('*' >> factor[term.val *= arg1])
| ('/' >> factor[term.val /= arg1])
)
;
factor
= ureal_p[factor.val = arg1]
| '(' >> expression[factor.val = arg1] >> ')'
| ('-' >> factor[factor.val = -arg1])
| ('+' >> factor[factor.val = arg1])
;
}
typedef rule<ScannerT, calc_closure::context_t> rule_t;
rule_t expression, term, factor;
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;
}