Boost C++ Libraries

libs/spirit/classic/example/fundamental/ast_calc.cpp

/*=============================================================================
    Copyright (c) 2001-2003 Daniel Nuffer
    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)
=============================================================================*/
///////////////////////////////////////////////////////////////////////////////
//
//  Demonstrates the ASTs. This is discussed in the
//  "Trees" chapter in the Spirit User's Guide.
//
///////////////////////////////////////////////////////////////////////////////
#define BOOST_SPIRIT_DUMP_PARSETREE_AS_XML

#include <boost/spirit/include/classic_core.hpp>
#include <boost/spirit/include/classic_ast.hpp>
#include <boost/spirit/include/classic_tree_to_xml.hpp>
#include "tree_calc_grammar.hpp"

#include <iostream>
#include <stack>
#include <functional>
#include <string>
#include <cassert>

#if defined(BOOST_SPIRIT_DUMP_PARSETREE_AS_XML)
#include <map>
#endif

// This example shows how to use an AST.
////////////////////////////////////////////////////////////////////////////
using namespace std;
using namespace BOOST_SPIRIT_CLASSIC_NS;

typedef char const*         iterator_t;
typedef tree_match<iterator_t> parse_tree_match_t;
typedef parse_tree_match_t::tree_iterator iter_t;

////////////////////////////////////////////////////////////////////////////
long evaluate(parse_tree_match_t hit);
long eval_expression(iter_t const& i);

long evaluate(tree_parse_info<> info)
{
    return eval_expression(info.trees.begin());
}

long eval_expression(iter_t const& i)
{
    cout << "In eval_expression. i->value = " <<
        string(i->value.begin(), i->value.end()) <<
        " i->children.size() = " << i->children.size() << endl;

    if (i->value.id() == calculator::integerID)
    {
        assert(i->children.size() == 0);

        // extract integer (not always delimited by '\0')
        string integer(i->value.begin(), i->value.end());

        return strtol(integer.c_str(), 0, 10);
    }
    else if (i->value.id() == calculator::factorID)
    {
        // factor can only be unary minus
        assert(*i->value.begin() == '-');
        return - eval_expression(i->children.begin());
    }
    else if (i->value.id() == calculator::termID)
    {
        if (*i->value.begin() == '*')
        {
            assert(i->children.size() == 2);
            return eval_expression(i->children.begin()) *
                eval_expression(i->children.begin()+1);
        }
        else if (*i->value.begin() == '/')
        {
            assert(i->children.size() == 2);
            return eval_expression(i->children.begin()) /
                eval_expression(i->children.begin()+1);
        }
        else
            assert(0);
    }
    else if (i->value.id() == calculator::expressionID)
    {
        if (*i->value.begin() == '+')
        {
            assert(i->children.size() == 2);
            return eval_expression(i->children.begin()) +
                eval_expression(i->children.begin()+1);
        }
        else if (*i->value.begin() == '-')
        {
            assert(i->children.size() == 2);
            return eval_expression(i->children.begin()) -
                eval_expression(i->children.begin()+1);
        }
        else
            assert(0);
    }
    else
    {
        assert(0); // error
    }

    return 0;
}

////////////////////////////////////////////////////////////////////////////
int
main()
{
    // look in tree_calc_grammar for the definition of calculator
    calculator calc;

    cout << "/////////////////////////////////////////////////////////\n\n";
    cout << "\t\tThe simplest working calculator...\n\n";
    cout << "/////////////////////////////////////////////////////////\n\n";
    cout << "Type an expression...or [q or Q] to quit\n\n";

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

        tree_parse_info<> info = ast_parse(str.c_str(), calc);

        if (info.full)
        {
#if defined(BOOST_SPIRIT_DUMP_PARSETREE_AS_XML)
            // dump parse tree as XML
            std::map<parser_id, std::string> rule_names;
            rule_names[calculator::integerID] = "integer";
            rule_names[calculator::factorID] = "factor";
            rule_names[calculator::termID] = "term";
            rule_names[calculator::expressionID] = "expression";
            tree_to_xml(cout, info.trees, str.c_str(), rule_names);
#endif

            // print the result
            cout << "parsing succeeded\n";
            cout << "result = " << evaluate(info) << "\n\n";
        }
        else
        {
            cout << "parsing failed\n";
        }
    }

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