spirit/example/x3/calc/calc4.cpp

/*=============================================================================
    Copyright (c) 2001-2014 Joel de Guzman

    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 Calculator example demonstrating generation of AST. The AST,
//  once created, is traversed, 1) To print its contents and
//  2) To evaluate the result.
//
//  [ JDG April 28, 2008 ]      For BoostCon 2008
//  [ JDG February 18, 2011 ]   Pure attributes. No semantic actions.
//  [ JDG January 9, 2013 ]     Spirit X3
//
///////////////////////////////////////////////////////////////////////////////

#include <boost/spirit/home/x3.hpp>
#include <boost/spirit/home/x3/support/ast/variant.hpp>
#include <boost/fusion/include/adapt_struct.hpp>

#include <iostream>
#include <string>
#include <list>
#include <numeric>

namespace x3 = boost::spirit::x3;

namespace client { namespace ast
{
    ///////////////////////////////////////////////////////////////////////////
    //  The AST
    ///////////////////////////////////////////////////////////////////////////
    struct nil {};
    struct signed_;
    struct program;

    struct operand : x3::variant<
            nil
          , unsigned int
          , x3::forward_ast<signed_>
          , x3::forward_ast<program>
        >
    {
        using base_type::base_type;
        using base_type::operator=;
    };

    struct signed_
    {
        char sign;
        operand operand_;
    };

    struct operation
    {
        char operator_;
        operand operand_;
    };

    struct program
    {
        operand first;
        std::list<operation> rest;
    };
}}

BOOST_FUSION_ADAPT_STRUCT(client::ast::signed_,
    sign, operand_
)

BOOST_FUSION_ADAPT_STRUCT(client::ast::operation,
    operator_, operand_
)

BOOST_FUSION_ADAPT_STRUCT(client::ast::program,
    first, rest
)

namespace client { namespace ast
{
    ///////////////////////////////////////////////////////////////////////////
    //  The AST Printer
    ///////////////////////////////////////////////////////////////////////////
    struct printer
    {
        typedef void result_type;

        void operator()(nil) const {}
        void operator()(unsigned int n) const { std::cout << n; }

        void operator()(operation const& x) const
        {
            boost::apply_visitor(*this, x.operand_);
            switch (x.operator_)
            {
                case '+': std::cout << " add"; break;
                case '-': std::cout << " subt"; break;
                case '*': std::cout << " mult"; break;
                case '/': std::cout << " div"; break;
            }
        }

        void operator()(signed_ const& x) const
        {
            boost::apply_visitor(*this, x.operand_);
            switch (x.sign)
            {
                case '-': std::cout << " neg"; break;
                case '+': std::cout << " pos"; break;
            }
        }

        void operator()(program const& x) const
        {
            boost::apply_visitor(*this, x.first);
            for (operation const& oper: x.rest)
            {
                std::cout << ' ';
                (*this)(oper);
            }
        }
    };

    ///////////////////////////////////////////////////////////////////////////
    //  The AST evaluator
    ///////////////////////////////////////////////////////////////////////////
    struct eval
    {
        typedef int result_type;

        int operator()(nil) const { BOOST_ASSERT(0); return 0; }
        int operator()(unsigned int n) const { return n; }

        int operator()(int lhs, operation const& x) const
        {
            int rhs = boost::apply_visitor(*this, x.operand_);
            switch (x.operator_)
            {
                case '+': return lhs + rhs;
                case '-': return lhs - rhs;
                case '*': return lhs * rhs;
                case '/': return lhs / rhs;
            }
            BOOST_ASSERT(0);
            return 0;
        }

        int operator()(signed_ const& x) const
        {
            int rhs = boost::apply_visitor(*this, x.operand_);
            switch (x.sign)
            {
                case '-': return -rhs;
                case '+': return +rhs;
            }
            BOOST_ASSERT(0);
            return 0;
        }

        int operator()(program const& x) const
        {
            return std::accumulate(
                x.rest.begin(), x.rest.end()
              , boost::apply_visitor(*this, x.first)
              , *this);
        }
    };
}}

namespace client
{
    ///////////////////////////////////////////////////////////////////////////////
    //  The calculator grammar
    ///////////////////////////////////////////////////////////////////////////////
    namespace calculator_grammar
    {
        using x3::uint_;
        using x3::char_;

        x3::rule<class expression, ast::program> const expression("expression");
        x3::rule<class term, ast::program> const term("term");
        x3::rule<class factor, ast::operand> const factor("factor");

        auto const expression_def =
            term
            >> *(   (char_('+') >> term)
                |   (char_('-') >> term)
                )
            ;

        auto const term_def =
            factor
            >> *(   (char_('*') >> factor)
                |   (char_('/') >> factor)
                )
            ;

        auto const factor_def =
                uint_
            |   '(' >> expression >> ')'
            |   (char_('-') >> factor)
            |   (char_('+') >> factor)
            ;

        BOOST_SPIRIT_DEFINE(
            expression
          , term
          , factor
        );

        auto calculator = expression;
    }

    using calculator_grammar::calculator;

}

///////////////////////////////////////////////////////////////////////////////
//  Main program
///////////////////////////////////////////////////////////////////////////////
int
main()
{
    std::cout << "/////////////////////////////////////////////////////////\n\n";
    std::cout << "Expression parser...\n\n";
    std::cout << "/////////////////////////////////////////////////////////\n\n";
    std::cout << "Type an expression...or [q or Q] to quit\n\n";

    typedef std::string::const_iterator iterator_type;
    typedef client::ast::program ast_program;
    typedef client::ast::printer ast_print;
    typedef client::ast::eval ast_eval;

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

        auto& calc = client::calculator;    // Our grammar
        ast_program program;                // Our program (AST)
        ast_print print;                    // Prints the program
        ast_eval eval;                      // Evaluates the program

        iterator_type iter = str.begin();
        iterator_type end = str.end();
        boost::spirit::x3::ascii::space_type space;
        bool r = phrase_parse(iter, end, calc, space, program);

        if (r && iter == end)
        {
            std::cout << "-------------------------\n";
            std::cout << "Parsing succeeded\n";
            print(program);
            std::cout << "\nResult: " << eval(program) << 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;
}