Boost C++ Libraries

libs/spirit/example/x3/roman.cpp

/*=============================================================================
    Copyright (c) 2001-2015 Joel de Guzman
    Copyright (c) 2015 Ahmed Charles

    Distributed under 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 August 22, 2002 ] spirit1
//  [ JDG March 13, 2007 ]  spirit2
//  [ JDG May 13, 2015 ]    spirit X3
//
///////////////////////////////////////////////////////////////////////////////

#include <boost/spirit/home/x3.hpp>

#include <iostream>
#include <string>

namespace client
{
    namespace x3 = boost::spirit::x3;
    namespace ascii = boost::spirit::x3::ascii;

    ///////////////////////////////////////////////////////////////////////////////
    //  Parse roman hundreds (100..900) numerals using the symbol table.
    //  Notice that the data associated with each slot is the parser's attribute
    //  (which is passed to attached semantic actions).
    ///////////////////////////////////////////////////////////////////////////////
    struct hundreds_ : x3::symbols<unsigned>
    {
        hundreds_()
        {
            add
                ("C"    , 100)
                ("CC"   , 200)
                ("CCC"  , 300)
                ("CD"   , 400)
                ("D"    , 500)
                ("DC"   , 600)
                ("DCC"  , 700)
                ("DCCC" , 800)
                ("CM"   , 900)
            ;
        }

    } hundreds;

    ///////////////////////////////////////////////////////////////////////////////
    //  Parse roman tens (10..90) numerals using the symbol table.
    ///////////////////////////////////////////////////////////////////////////////
    struct tens_ : x3::symbols<unsigned>
    {
        tens_()
        {
            add
                ("X"    , 10)
                ("XX"   , 20)
                ("XXX"  , 30)
                ("XL"   , 40)
                ("L"    , 50)
                ("LX"   , 60)
                ("LXX"  , 70)
                ("LXXX" , 80)
                ("XC"   , 90)
            ;
        }

    } tens;

    ///////////////////////////////////////////////////////////////////////////////
    //  Parse roman ones (1..9) numerals using the symbol table.
    ///////////////////////////////////////////////////////////////////////////////
    struct ones_ : x3::symbols<unsigned>
    {
        ones_()
        {
            add
                ("I"    , 1)
                ("II"   , 2)
                ("III"  , 3)
                ("IV"   , 4)
                ("V"    , 5)
                ("VI"   , 6)
                ("VII"  , 7)
                ("VIII" , 8)
                ("IX"   , 9)
            ;
        }

    } ones;

    ///////////////////////////////////////////////////////////////////////////////
    //  roman (numerals) grammar
    //
    //      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! :-)
    ///////////////////////////////////////////////////////////////////////////////
    namespace parser
    {
        using x3::eps;
        using x3::lit;
        using x3::_val;
        using x3::_attr;
        using ascii::char_;

        auto set_zero = [](auto& ctx){ _val(ctx) = 0; };
        auto add1000 = [](auto& ctx){ _val(ctx) += 1000; };
        auto add = [](auto& ctx){ _val(ctx) += _attr(ctx); };

        x3::rule<class roman, unsigned> const roman = "roman";

        auto const roman_def =
            eps                 [set_zero]
            >>
            (
                -(+lit('M')     [add1000])
                >>  -hundreds   [add]
                >>  -tens       [add]
                >>  -ones       [add]
            )
        ;

        BOOST_SPIRIT_DEFINE(roman);
    }
}

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

    typedef std::string::const_iterator iterator_type;
    using client::parser::roman; // Our parser

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

        iterator_type iter = str.begin();
        iterator_type const end = str.end();
        bool r = parse(iter, end, roman, result);

        if (r && iter == end)
        {
            std::cout << "-------------------------\n";
            std::cout << "Parsing succeeded\n";
            std::cout << "result = " << result << std::endl;
            std::cout << "-------------------------\n";
        }
        else
        {
            std::string rest(iter, end);
            std::cout << "-------------------------\n";
            std::cout << "Parsing failed\n";
            std::cout << "stopped at: \": " << rest << "\"\n";
            std::cout << "-------------------------\n";
        }
    }

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