| /*============================================================================= |
| 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_, |
| (char, sign) |
| (client::ast::operand, operand_) |
| ) |
| |
| BOOST_FUSION_ADAPT_STRUCT( |
| client::ast::operation, |
| (char, operator_) |
| (client::ast::operand, operand_) |
| ) |
| |
| BOOST_FUSION_ADAPT_STRUCT( |
| client::ast::program, |
| (client::ast::operand, first) |
| (std::list<client::ast::operation>, 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"); |
| |
| BOOST_SPIRIT_DEFINE( |
| expression = |
| term |
| >> *( (char_('+') >> term) |
| | (char_('-') >> term) |
| ) |
| , |
| |
| term = |
| factor |
| >> *( (char_('*') >> factor) |
| | (char_('/') >> factor) |
| ) |
| , |
| |
| factor = |
| uint_ |
| | '(' >> expression >> ')' |
| | (char_('-') >> factor) |
| | (char_('+') >> 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; |
| } |