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/*=============================================================================
Copyright (c) 2001-2014 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)
=============================================================================*/
///////////////////////////////////////////////////////////////////////////////
//
// A Calculator example demonstrating generation of AST. The AST,
// once created, is traversed, 1) To print its contents and
// 2) To evaluate the result.
//
// [ JDG April 28, 2008 ] For BoostCon 2008
// [ JDG February 18, 2011 ] Pure attributes. No semantic actions.
// [ JDG January 9, 2013 ] Spirit X3
//
///////////////////////////////////////////////////////////////////////////////
#if defined(_MSC_VER)
# pragma warning(disable: 4345)
#endif
#include <boost/config/warning_disable.hpp>
#include <boost/spirit/home/x3.hpp>
#include <boost/spirit/home/x3/support/ast/variant.hpp>
#include <boost/fusion/include/adapt_struct.hpp>
#include <iostream>
#include <string>
#include <list>
#include <numeric>
namespace x3 = boost::spirit::x3;
namespace client { namespace ast
{
///////////////////////////////////////////////////////////////////////////
// The AST
///////////////////////////////////////////////////////////////////////////
struct nil {};
struct signed_;
struct program;
struct operand : x3::variant<
nil
, unsigned int
, x3::forward_ast<signed_>
, x3::forward_ast<program>
>
{
using base_type::base_type;
using base_type::operator=;
};
struct signed_
{
char sign;
operand operand_;
};
struct operation
{
char operator_;
operand operand_;
};
struct program
{
operand first;
std::list<operation> rest;
};
}}
BOOST_FUSION_ADAPT_STRUCT(client::ast::signed_,
sign, operand_
)
BOOST_FUSION_ADAPT_STRUCT(client::ast::operation,
operator_, operand_
)
BOOST_FUSION_ADAPT_STRUCT(client::ast::program,
first, rest
)
namespace client { namespace ast
{
///////////////////////////////////////////////////////////////////////////
// The AST Printer
///////////////////////////////////////////////////////////////////////////
struct printer
{
typedef void result_type;
void operator()(nil) const {}
void operator()(unsigned int n) const { std::cout << n; }
void operator()(operation const& x) const
{
boost::apply_visitor(*this, x.operand_);
switch (x.operator_)
{
case '+': std::cout << " add"; break;
case '-': std::cout << " subt"; break;
case '*': std::cout << " mult"; break;
case '/': std::cout << " div"; break;
}
}
void operator()(signed_ const& x) const
{
boost::apply_visitor(*this, x.operand_);
switch (x.sign)
{
case '-': std::cout << " neg"; break;
case '+': std::cout << " pos"; break;
}
}
void operator()(program const& x) const
{
boost::apply_visitor(*this, x.first);
for (operation const& oper: x.rest)
{
std::cout << ' ';
(*this)(oper);
}
}
};
///////////////////////////////////////////////////////////////////////////
// The AST evaluator
///////////////////////////////////////////////////////////////////////////
struct eval
{
typedef int result_type;
int operator()(nil) const { BOOST_ASSERT(0); return 0; }
int operator()(unsigned int n) const { return n; }
int operator()(int lhs, operation const& x) const
{
int rhs = boost::apply_visitor(*this, x.operand_);
switch (x.operator_)
{
case '+': return lhs + rhs;
case '-': return lhs - rhs;
case '*': return lhs * rhs;
case '/': return lhs / rhs;
}
BOOST_ASSERT(0);
return 0;
}
int operator()(signed_ const& x) const
{
int rhs = boost::apply_visitor(*this, x.operand_);
switch (x.sign)
{
case '-': return -rhs;
case '+': return +rhs;
}
BOOST_ASSERT(0);
return 0;
}
int operator()(program const& x) const
{
return std::accumulate(
x.rest.begin(), x.rest.end()
, boost::apply_visitor(*this, x.first)
, *this);
}
};
}}
namespace client
{
///////////////////////////////////////////////////////////////////////////////
// The calculator grammar
///////////////////////////////////////////////////////////////////////////////
namespace calculator_grammar
{
using x3::uint_;
using x3::char_;
x3::rule<class expression, ast::program> const expression("expression");
x3::rule<class term, ast::program> const term("term");
x3::rule<class factor, ast::operand> const factor("factor");
auto const expression_def =
term
>> *( (char_('+') >> term)
| (char_('-') >> term)
)
;
auto const term_def =
factor
>> *( (char_('*') >> factor)
| (char_('/') >> factor)
)
;
auto const factor_def =
uint_
| '(' >> expression >> ')'
| (char_('-') >> factor)
| (char_('+') >> factor)
;
BOOST_SPIRIT_DEFINE(expression, term, factor);
auto calculator = expression;
}
using calculator_grammar::calculator;
}
///////////////////////////////////////////////////////////////////////////////
// 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::ast::program ast_program;
typedef client::ast::printer ast_print;
typedef client::ast::eval ast_eval;
std::string str;
while (std::getline(std::cin, str))
{
if (str.empty() || str[0] == 'q' || str[0] == 'Q')
break;
auto& calc = client::calculator; // Our grammar
ast_program program; // Our program (AST)
ast_print print; // Prints the program
ast_eval eval; // Evaluates the program
iterator_type iter = str.begin();
iterator_type end = str.end();
boost::spirit::x3::ascii::space_type space;
bool r = phrase_parse(iter, end, calc, space, program);
if (r && iter == end)
{
std::cout << "-------------------------\n";
std::cout << "Parsing succeeded\n";
print(program);
std::cout << "\nResult: " << eval(program) << std::endl;
std::cout << "-------------------------\n";
}
else
{
std::string rest(iter, end);
std::cout << "-------------------------\n";
std::cout << "Parsing failed\n";
std::cout << "stopped at: \"" << rest << "\"\n";
std::cout << "-------------------------\n";
}
}
std::cout << "Bye... :-) \n\n";
return 0;
}
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