Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

This is an old version of boost. Click here for the latest version's documentation home page.

libs/spirit/example/fundamental/roman_numerals.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)
=============================================================================*/
///////////////////////////////////////////////////////////////////////////////
//
//  A Roman Numerals Parser (demonstrating the symbol table). This is 
//  discussed in the "Symbols" chapter in the Spirit User's Guide.
//
//  [ JDG 8/22/2002 ]
//
///////////////////////////////////////////////////////////////////////////////
#include <boost/spirit/core.hpp>
#include <boost/spirit/symbols/symbols.hpp>
#include <iostream>
#include <string>

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

///////////////////////////////////////////////////////////////////////////////
//
//  Parse roman hundreds (100..900) numerals using the symbol table.
//  Notice that the data associated with each slot is passed
//  to attached semantic actions.
//
///////////////////////////////////////////////////////////////////////////////
struct hundreds : symbols<unsigned>
{
    hundreds()
    {
        add
            ("C"    , 100)
            ("CC"   , 200)
            ("CCC"  , 300)
            ("CD"   , 400)
            ("D"    , 500)
            ("DC"   , 600)
            ("DCC"  , 700)
            ("DCCC" , 800)
            ("CM"   , 900)
        ;
    }

} hundreds_p;

///////////////////////////////////////////////////////////////////////////////
//
//  Parse roman tens (10..90) numerals using the symbol table.
//
///////////////////////////////////////////////////////////////////////////////
struct tens : symbols<unsigned>
{
    tens()
    {
        add
            ("X"    , 10)
            ("XX"   , 20)
            ("XXX"  , 30)
            ("XL"   , 40)
            ("L"    , 50)
            ("LX"   , 60)
            ("LXX"  , 70)
            ("LXXX" , 80)
            ("XC"   , 90)
        ;
    }

} tens_p;

///////////////////////////////////////////////////////////////////////////////
//
//  Parse roman ones (1..9) numerals using the symbol table.
//
///////////////////////////////////////////////////////////////////////////////
struct ones : symbols<unsigned>
{
    ones()
    {
        add
            ("I"    , 1)
            ("II"   , 2)
            ("III"  , 3)
            ("IV"   , 4)
            ("V"    , 5)
            ("VI"   , 6)
            ("VII"  , 7)
            ("VIII" , 8)
            ("IX"   , 9)
        ;
    }

} ones_p;

///////////////////////////////////////////////////////////////////////////////
//
//  Semantic actions
//
///////////////////////////////////////////////////////////////////////////////
struct add_1000
{
    add_1000(unsigned& r_) : r(r_) {}
    void operator()(char) const { r += 1000; }
    unsigned& r;
};

struct add_roman
{
    add_roman(unsigned& r_) : r(r_) {}
    void operator()(unsigned n) const { r += n; }
    unsigned& r;
};

///////////////////////////////////////////////////////////////////////////////
//
//  roman (numerals) grammar
//
///////////////////////////////////////////////////////////////////////////////
struct roman : public grammar<roman>
{
    template <typename ScannerT>
    struct definition
    {
        definition(roman const& self)
        {
            first
                =   +ch_p('M')  [add_1000(self.r)]
                ||  hundreds_p  [add_roman(self.r)]
                ||  tens_p      [add_roman(self.r)]
                ||  ones_p      [add_roman(self.r)];

            //  Note the use of the || operator. The expression
            //  a || b reads match a or b and in sequence. Try
            //  defining the roman numerals grammar in YACC or
            //  PCCTS. Spirit rules! :-)
        }

        rule<ScannerT> first;
        rule<ScannerT> const&
        start() const { return first; }
    };

    roman(unsigned& r_) : r(r_) {}
    unsigned& r;
};

///////////////////////////////////////////////////////////////////////////////
//
//  Main driver code
//
///////////////////////////////////////////////////////////////////////////////
int
main()
{
    cout << "/////////////////////////////////////////////////////////\n\n";
    cout << "\t\tRoman Numerals Parser\n\n";
    cout << "/////////////////////////////////////////////////////////\n\n";
    cout << "Type a Roman Numeral ...or [q or Q] to quit\n\n";

    //  Start grammar definition

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

        unsigned n = 0;
        roman roman_p(n);
        if (parse(str.c_str(), roman_p).full)
        {
            cout << "parsing succeeded\n";
            cout << "result = " << n << "\n\n";
        }
        else
        {
            cout << "parsing failed\n\n";
        }
    }

    cout << "Bye... :-) \n\n";

    return 0;
}