boost_1_45_0/libs/spirit/example/qi/calc5.cpp

/*=============================================================================
    Copyright (c) 2001-2010 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)
=============================================================================*/
///////////////////////////////////////////////////////////////////////////////
//
//  Yet another calculator example! This time, we will compile to a simple
//  virtual machine. This is actually one of the very first Spirit example
//  circa 2000. Now, it's ported to Spirit2.
//
//  [ JDG Sometime 2000 ]       pre-boost
//  [ JDG September 18, 2002 ]  spirit1
//  [ JDG April 8, 2007 ]       spirit2
//
///////////////////////////////////////////////////////////////////////////////

#include <boost/config/warning_disable.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix_core.hpp>
#include <boost/spirit/include/phoenix_container.hpp>
#include <boost/spirit/include/phoenix_statement.hpp>
#include <boost/spirit/include/phoenix_object.hpp>
#include <boost/spirit/include/phoenix_operator.hpp>

#include <iostream>
#include <string>
#include <vector>

namespace client
{
    namespace qi = boost::spirit::qi;
    namespace phoenix = boost::phoenix;
    namespace ascii = boost::spirit::ascii;

    ///////////////////////////////////////////////////////////////////////////
    //  The Virtual Machine
    ///////////////////////////////////////////////////////////////////////////
    enum byte_code
    {
        op_neg,     //  negate the top stack entry
        op_add,     //  add top two stack entries
        op_sub,     //  subtract top two stack entries
        op_mul,     //  multiply top two stack entries
        op_div,     //  divide top two stack entries
        op_int,     //  push constant integer into the stack
    };

    class vmachine
    {
    public:

        vmachine(unsigned stackSize = 4096)
          : stack(stackSize)
          , stack_ptr(stack.begin())
        {
        }

        int top() const { return stack_ptr[-1]; };
        void execute(std::vector<int> const& code);

    private:

        std::vector<int> stack;
        std::vector<int>::iterator stack_ptr;
    };

    void vmachine::execute(std::vector<int> const& code)
    {
        std::vector<int>::const_iterator pc = code.begin();
        stack_ptr = stack.begin();

        while (pc != code.end())
        {
            switch (*pc++)
            {
                case op_neg:
                    stack_ptr[-1] = -stack_ptr[-1];
                    break;

                case op_add:
                    --stack_ptr;
                    stack_ptr[-1] += stack_ptr[0];
                    break;

                case op_sub:
                    --stack_ptr;
                    stack_ptr[-1] -= stack_ptr[0];
                    break;

                case op_mul:
                    --stack_ptr;
                    stack_ptr[-1] *= stack_ptr[0];
                    break;

                case op_div:
                    --stack_ptr;
                    stack_ptr[-1] /= stack_ptr[0];
                    break;

                case op_int:
                    *stack_ptr++ = *pc++;
                    break;
            }
        }
    }

    ///////////////////////////////////////////////////////////////////////////
    //  Our calculator grammar and compiler
    ///////////////////////////////////////////////////////////////////////////
    template <typename Iterator>
    struct calculator : qi::grammar<Iterator, ascii::space_type>
    {
        calculator(std::vector<int>& code)
          : calculator::base_type(expression)
          , code(code)
        {
            using namespace qi::labels;
            using qi::uint_;
            using qi::on_error;
            using qi::fail;

            using phoenix::val;
            using phoenix::ref;
            using phoenix::push_back;
            using phoenix::construct;

            expression =
                term
                >> *(   ('+' > term             [push_back(ref(code), op_add)])
                    |   ('-' > term             [push_back(ref(code), op_sub)])
                    )
                ;

            term =
                factor
                >> *(   ('*' > factor           [push_back(ref(code), op_mul)])
                    |   ('/' > factor           [push_back(ref(code), op_div)])
                    )
                ;

            factor =
                uint_                           [
                                                    push_back(ref(code), op_int),
                                                    push_back(ref(code), _1)
                                                ]
                |   '(' > expression > ')'
                |   ('-' > factor               [push_back(ref(code), op_neg)])
                |   ('+' > factor)
                ;

            expression.name("expression");
            term.name("term");
            factor.name("factor");

            on_error<fail>
            (
                expression
              , std::cout
                    << val("Error! Expecting ")
                    << _4                               // what failed?
                    << val(" here: \"")
                    << construct<std::string>(_3, _2)   // iterators to error-pos, end
                    << val("\"")
                    << std::endl
            );
        }

        qi::rule<Iterator, ascii::space_type> expression, term, factor;
        std::vector<int>& code;
    };

    template <typename Grammar>
    bool compile(Grammar const& calc, std::string const& expr)
    {
        std::string::const_iterator iter = expr.begin();
        std::string::const_iterator end = expr.end();
        bool r = phrase_parse(iter, end, calc, ascii::space);

        if (r && iter == end)
        {
            std::cout << "-------------------------\n";
            std::cout << "Parsing succeeded\n";
            std::cout << "-------------------------\n";
            return true;
        }
        else
        {
            std::cout << "-------------------------\n";
            std::cout << "Parsing failed\n";
            std::cout << "-------------------------\n";
            return false;
        }
    }
}

///////////////////////////////////////////////////////////////////////////////
//  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::calculator<iterator_type> calculator;

    client::vmachine mach;          //  Our virtual machine
    std::vector<int> code;          //  Our VM code
    calculator calc(code);          //  Our grammar

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

        code.clear();
        if (client::compile(calc, str))
        {
            mach.execute(code);
            std::cout << "\n\nresult = " << mach.top() << std::endl;
            std::cout << "-------------------------\n\n";
        }
    }

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