Question7

Question7.cpp

/* example question implementation in spirit:

7. Construct an attribute grammar for the language L so that:
@    has value  2 
*@*  has value  4  - surrounding an expression with two stars squares its value 
(@)  has value  3  - putting brackets around an expressions adds 1 to the value
((@))    has value         4
(*(@)*)   has value  10
  ((*((@))*))     has value 18 
(((*(*(@)*)*))) has value 103
*/




#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix_core.hpp>
#include <boost/spirit/include/phoenix_operator.hpp>
#include <iostream>
#include <string>

namespace client
{
    namespace qi = boost::spirit::qi;
    namespace ascii = boost::spirit::ascii;
    namespace phoenix = boost::phoenix;
    
    using qi::_1;
    using ascii::space;
    
    template <typename Iterator>
    struct parse_grammar : qi::grammar<Iterator, unsigned()>
    {
        parse_grammar() : parse_grammar::base_type(start)
        {
            using qi::eps;
            using qi::lit;
            using qi::_val;
            using qi::_1;
            using ascii::char_;
            
            start = lit('@') >> qi::attr(2)
                 | lit('*') >> start >> lit('*') [_val *= _val]
                 | lit('(') >> start >> lit(')') [_val += 1];
        }
        
        qi::rule<Iterator, unsigned()> start;
    
    };
}

int main()
{
    using namespace client;
    
    parse_grammar<std::string::const_iterator> parser;
    
    std::string str;
    unsigned result;
    
    while (std::getline(std::cin, str))
    {
        if (str.empty() || str[0] == 'q' || str[0] == 'Q')
            break;
            
        auto iter = str.cbegin();
        auto end = str.cend();
        
        bool r = parse(iter, end, parser, result);
        
        if (r && iter == end)
        {
            std::cout << "---- success" << std::endl;
            std::cout << "result = " << result << std::endl;
            std::cout << "---- " << std::endl;
        }
        else
        {
            std::string rest(iter, end);
            std::cout << "---- failure" << std::endl;
            std::cout << " stopped at: \": " << rest << "\"" << std::endl;
            std::cout << "----" << std::endl;
        }
    }
    
    std::cout << "end." << std::endl;
    return 0;
}