source: downloads/boost_1_33_1/libs/spirit/example/intermediate/parameters.cpp @ 12

/*=============================================================================
    Copyright (c) 2001-2003 Hartmut Kaiser
    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)
=============================================================================*/
///////////////////////////////////////////////////////////////////////////////
// This sample show the usage of parser parameters.
//
// Parser parameters are used to pass some values from the outer parsing scope
// to the next inner scope. They can be imagined as the opposite to the return
// value paradigm, which returns some value from the inner to the next outer
// scope. See the "Closures" chapter in the User's Guide.

#include <string>
#include <iostream>
#include <cassert>

#if defined(_MSC_VER) /*&& !defined(__COMO__)*/
#pragma warning(disable: 4244)
#pragma warning(disable: 4355)
#endif // defined(_MSC_VER) && !defined(__COMO__)

#include <boost/spirit/core.hpp>
#include <boost/spirit/symbols/symbols.hpp>

#include <boost/spirit/phoenix/tuples.hpp>
#include <boost/spirit/phoenix/tuple_helpers.hpp>
#include <boost/spirit/phoenix/primitives.hpp>
#include <boost/spirit/attribute/closure.hpp>

///////////////////////////////////////////////////////////////////////////////
// used namespaces
using namespace boost::spirit;
using namespace phoenix;
using namespace std;

///////////////////////////////////////////////////////////////////////////////
// Helper class for encapsulation of the type for the parsed variable names
class declaration_type
{
public:
    enum vartype {
        vartype_unknown = 0,        // unknown variable type
        vartype_int = 1,            // 'int'
        vartype_real = 2            // 'real'
    };

    declaration_type() : type(vartype_unknown)
    {
    }
    template <typename ItT>
    declaration_type(ItT const &first, ItT const &last)
    {
        init(string(first, last-first-1));
    }
    declaration_type(declaration_type const &type_) : type(type_.type)
    {
    }
    declaration_type(string const &type_) : type(vartype_unknown)
    {
        init(type_);
    }

// access to the variable type
    operator vartype const &() const { return type; }
    operator string ()
    {
        switch(type) {
        default:
        case vartype_unknown:   break;
        case vartype_int:       return string("int");
        case vartype_real:      return string("real");
        }
        return string ("unknown");
    }

    void swap(declaration_type &s) { std::swap(type, s.type); }

protected:
    void init (string const &type_)
    {
        if (type_ == "int")
            type = vartype_int;
        else if (type_ == "real")
            type = vartype_real;
        else
            type = vartype_unknown;
    }

private:
    vartype type;
};

///////////////////////////////////////////////////////////////////////////////
//
//  used closure type
//
///////////////////////////////////////////////////////////////////////////////
struct var_decl_closure : boost::spirit::closure<var_decl_closure, declaration_type>
{
    member1 val;
};

///////////////////////////////////////////////////////////////////////////////
//
//  symbols_with_data
//
//      Helper class for inserting an item with data into a symbol table
//
///////////////////////////////////////////////////////////////////////////////
template <typename T, typename InitT>
class symbols_with_data
{
public:
    typedef
        symbol_inserter<T, boost::spirit::impl::tst<T, char> >
        symbol_inserter_t;

    symbols_with_data(symbol_inserter_t const &add_, InitT const &data_) :
        add(add_), data(as_actor<InitT>::convert(data_))
    {
    }

    template <typename IteratorT>
    symbol_inserter_t const &
    operator()(IteratorT const &first_, IteratorT const &last) const
    {
        IteratorT first = first_;
        return add(first, last, data());
    }

private:
    symbol_inserter_t const &add;
    typename as_actor<InitT>::type data;
};

template <typename T, typename CharT, typename InitT>
inline
symbols_with_data<T, InitT>
symbols_gen(symbol_inserter<T, boost::spirit::impl::tst<T, CharT> > const &add_,
    InitT const &data_)
{
    return symbols_with_data<T, InitT>(add_, data_);
}

///////////////////////////////////////////////////////////////////////////////
// The var_decl_list grammar parses variable declaration list

struct var_decl_list :
    public grammar<var_decl_list, var_decl_closure::context_t>
{
    template <typename ScannerT>
    struct definition
    {
        definition(var_decl_list const &self)
        {
        // pass variable type returned from 'type' to list closure member 0
            decl = type[self.val = arg1] >> +space_p >> list(self.val);

        // m0 to access arg 0 of list --> passing variable type down to ident
            list = ident(list.val) >> *(',' >> ident(list.val));

        // store identifier and type into the symbol table
            ident = (*alnum_p)[symbols_gen(symtab.add, ident.val)];

        // the type of the decl is returned in type's closure member 0
            type =
                    str_p("int")[type.val = construct_<string>(arg1, arg2)]
                |   str_p("real")[type.val = construct_<string>(arg1, arg2)]
                ;

            BOOST_SPIRIT_DEBUG_RULE(decl);
            BOOST_SPIRIT_DEBUG_RULE(list);
            BOOST_SPIRIT_DEBUG_RULE(ident);
            BOOST_SPIRIT_DEBUG_RULE(type);
        }

        rule<ScannerT> const&
        start() const { return decl; }

    private:
        typedef rule<ScannerT, var_decl_closure::context_t> rule_t;
        rule_t type;
        rule_t list;
        rule_t ident;
        symbols<declaration_type> symtab;

        rule<ScannerT> decl;        // start rule
    };
};

///////////////////////////////////////////////////////////////////////////////
// main entry point
int main()
{
var_decl_list decl;
declaration_type type;
char const *pbegin = "int  var1";

    if (parse (pbegin, decl[assign(type)]).full) {
        cout << endl
             << "Parsed variable declarations successfully!" << endl
             << "Detected type: " << declaration_type::vartype(type)
             << " (" << string(type) << ")"
             << endl;
    } else {
        cout << endl
             << "Parsing the input stream failed!"
             << endl;
    }
    return 0;
}