spirit/example/karma/calc2_ast_vm.hpp

/*=============================================================================
    Copyright (c) 2001-2010 Joel de Guzman
    Copyright (c) 2001-2010 Hartmut Kaiser

    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 which gets dumped into
//  a human readable format afterwards.
//
//  [ JDG April 28, 2008 ]
//  [ HK April 28, 2008 ]
//
///////////////////////////////////////////////////////////////////////////////

#if !defined(SPIRIT_EXAMPLE_CALC2_AST_APR_30_2008_1011AM)
#define SPIRIT_EXAMPLE_CALC2_AST_APR_30_2008_1011AM

#include <boost/variant.hpp>
#include <boost/spirit/include/phoenix_operator.hpp>
#include <boost/spirit/include/phoenix_function.hpp>
#include <boost/spirit/include/phoenix_statement.hpp>
#include <boost/spirit/include/karma_domain.hpp>
#include <boost/spirit/include/support_attributes_fwd.hpp>

///////////////////////////////////////////////////////////////////////////////
//  Our AST
///////////////////////////////////////////////////////////////////////////////
struct binary_op;
struct unary_op;
struct nil {};

struct expression_ast
{
    typedef
        boost::variant<
            nil // can't happen!
          , int
          , boost::recursive_wrapper<binary_op>
          , boost::recursive_wrapper<unary_op>
        >
    type;

    // expose variant types 
    typedef type::types types;

    // expose variant functionality
    int which() const { return expr.which(); }

    // constructors
    expression_ast()
      : expr(nil()) {}

    expression_ast(unary_op const& expr)
      : expr(expr) {}

    expression_ast(binary_op const& expr)
      : expr(expr) {}

    expression_ast(unsigned int expr)
      : expr(expr) {}

    expression_ast(type const& expr)
      : expr(expr) {}

    expression_ast& operator+=(expression_ast const& rhs);
    expression_ast& operator-=(expression_ast const& rhs);
    expression_ast& operator*=(expression_ast const& rhs);
    expression_ast& operator/=(expression_ast const& rhs);

    type expr;
};

// expose variant functionality
namespace boost
{
    // this function has to live in namespace boost for ADL to correctly find it
    template <typename T>
    inline T get(expression_ast const& expr)
    {
        return boost::get<T>(expr.expr);
    }

    // the specialization below tells Spirit to handle expression_ast as if it 
    // where a 'real' variant
    namespace spirit { namespace traits
    {
        // the specialization below tells Spirit to handle expression_ast as 
        // if it where a 'real' variant (if used with Spirit.Karma)
        template <>
        struct not_is_variant<expression_ast, karma::domain>
          : mpl::false_ {};

        // the specialization of variant_which allows to generically extract
        // the current type stored in the given variant like type
        template <>
        struct variant_which<expression_ast>
        {
            static int call(expression_ast const& v)
            {
                return v.which();
            }
        };
    }}
}

enum byte_code
{
    op_neg = 1,     //  negate the top stack entry
    op_pos,         //  essentially a no-op (unary plus)
    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
};

///////////////////////////////////////////////////////////////////////////////
struct binary_op
{
    binary_op() {}
    
    binary_op(
        int op
      , expression_ast const& left
      , expression_ast const& right)
      : op(op), left(left), right(right) {}

    int op;
    expression_ast left;
    expression_ast right;
};

struct unary_op
{
    unary_op(
        int op
      , expression_ast const& right)
    : op(op), right(right) {}

    int op;
    expression_ast right;
};

inline expression_ast& expression_ast::operator+=(expression_ast const& rhs)
{
    expr = binary_op(op_add, expr, rhs);
    return *this;
}

inline expression_ast& expression_ast::operator-=(expression_ast const& rhs)
{
    expr = binary_op(op_sub, expr, rhs);
    return *this;
}

inline expression_ast& expression_ast::operator*=(expression_ast const& rhs)
{
    expr = binary_op(op_mul, expr, rhs);
    return *this;
}

inline expression_ast& expression_ast::operator/=(expression_ast const& rhs)
{
    expr = binary_op(op_div, expr, rhs);
    return *this;
}

// We should be using expression_ast::operator-. There's a bug
// in phoenix type deduction mechanism that prevents us from
// doing so. Phoenix will be switching to BOOST_TYPEOF. In the
// meantime, we will use a phoenix::function below:
template <char Op>
struct unary_expr
{
    template <typename T>
    struct result { typedef T type; };

    expression_ast operator()(expression_ast const& expr) const
    {
        return unary_op(Op, expr);
    }
};

boost::phoenix::function<unary_expr<op_pos> > pos;
boost::phoenix::function<unary_expr<op_neg> > neg;

#endif