Boost C++ Libraries

libs/spirit/example/fundamental/full_calc.cpp

/*=============================================================================
    Copyright (c) 2001-2003 Dan Nuffer
    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 using STL functors
//  This is discussed in the "Functional" chapter in the Spirit User's Guide.
//
//  Ported to Spirit v1.5 from v1.2/1.3 example by Dan Nuffer
//  [ JDG 9/18/2002 ]
//
////////////////////////////////////////////////////////////////////////////
#include <boost/spirit/core.hpp>
#include <iostream>
#include <stack>
#include <functional>
#include <string>

////////////////////////////////////////////////////////////////////////////
using namespace std;
using namespace boost::spirit;

////////////////////////////////////////////////////////////////////////////
//
//  Semantic actions
//
////////////////////////////////////////////////////////////////////////////
struct push_int
{
    push_int(stack<long>& eval_)
    : eval(eval_) {}

    void operator()(char const* str, char const* /*end*/) const
    {
        long n = strtol(str, 0, 10);
        eval.push(n);
        cout << "push\t" << long(n) << endl;
    }

    stack<long>& eval;
};

template <typename op>
struct do_op
{
    do_op(op const& the_op, stack<long>& eval_)
    : m_op(the_op), eval(eval_) {}

    void operator()(char const*, char const*) const
    {
        long rhs = eval.top();
        eval.pop();
        long lhs = eval.top();
        eval.pop();

        cout << "popped " << lhs << " and " << rhs << " from the stack. ";
        cout << "pushing " << m_op(lhs, rhs) << " onto the stack.\n";
        eval.push(m_op(lhs, rhs));
    }

    op m_op;
    stack<long>& eval;
};

template <class op>
do_op<op>
make_op(op const& the_op, stack<long>& eval)
{
    return do_op<op>(the_op, eval);
}

struct do_negate
{
    do_negate(stack<long>& eval_)
    : eval(eval_) {}

    void operator()(char const*, char const*) const
    {
        long lhs = eval.top();
        eval.pop();

        cout << "popped " << lhs << " from the stack. ";
        cout << "pushing " << -lhs << " onto the stack.\n";
        eval.push(-lhs);
    }

    stack<long>& eval;
};

////////////////////////////////////////////////////////////////////////////
//
//  Our calculator grammar
//
////////////////////////////////////////////////////////////////////////////
struct calculator : public grammar<calculator>
{
    calculator(stack<long>& eval_)
    : eval(eval_) {}

    template <typename ScannerT>
    struct definition
    {
        definition(calculator const& self)
        {
            integer =
                lexeme_d[ (+digit_p)[push_int(self.eval)] ]
                ;

            factor =
                    integer
                |   '(' >> expression >> ')'
                |   ('-' >> factor)[do_negate(self.eval)]
                |   ('+' >> factor)
                ;

            term =
                factor
                >> *(   ('*' >> factor)[make_op(multiplies<long>(), self.eval)]
                    |   ('/' >> factor)[make_op(divides<long>(), self.eval)]
                    )
                    ;

            expression =
                term
                >> *(  ('+' >> term)[make_op(plus<long>(), self.eval)]
                    |   ('-' >> term)[make_op(minus<long>(), self.eval)]
                    )
                    ;
        }

        rule<ScannerT> expression, term, factor, integer;
        rule<ScannerT> const&
        start() const { return expression; }
    };

    stack<long>& eval;
};

////////////////////////////////////////////////////////////////////////////
//
//  Main program
//
////////////////////////////////////////////////////////////////////////////
int
main()
{
    cout << "/////////////////////////////////////////////////////////\n\n";
    cout << "\t\tThe simplest working calculator...\n\n";
    cout << "/////////////////////////////////////////////////////////\n\n";
    cout << "Type an expression...or [q or Q] to quit\n\n";

    stack<long> eval;
    calculator  calc(eval); //  Our parser

    string str;
    while (getline(cin, str))
    {
        if (str.empty() || str[0] == 'q' || str[0] == 'Q')
            break;

        parse_info<> info = parse(str.c_str(), calc, space_p);

        if (info.full)
        {
            cout << "-------------------------\n";
            cout << "Parsing succeeded\n";
            cout << "-------------------------\n";
        }
        else
        {
            cout << "-------------------------\n";
            cout << "Parsing failed\n";
            cout << "stopped at: \": " << info.stop << "\"\n";
            cout << "-------------------------\n";
        }
    }

    cout << "Bye... :-) \n\n";
    return 0;
}