1/*=============================================================================
2 Copyright (c) 2001-2011 Hartmut Kaiser
3 Copyright (c) 2001-2011 Joel de Guzman
4
5 Distributed under the Boost Software License, Version 1.0. (See accompanying
6 file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
7=============================================================================*/
8///////////////////////////////////////////////////////////////////////////////
9//
10// Plain calculator example demonstrating the grammar. The parser is a
11// syntax checker only and does not do any semantic evaluation.
12//
13// [ JDG May 10, 2002 ] spirit1
14// [ JDG March 4, 2007 ] spirit2
15// [ HK November 30, 2010 ] spirit2/utree
16//
17///////////////////////////////////////////////////////////////////////////////
18
19// This rather naive example demonstrates that you can pass an instance of a
20// utree as the attribute for almost any grammar. As the result the utree will
21// be filled with the parse tree as generated during the parsing. This is most
22// of the time not what's desired, but is usually a good first step in order to
23// prepare your grammar to generate a customized AST. See the calc_utree_ast
24// example for a modified version of this grammar filling the attribute with a
25// AST (abstract syntax tree) representing the math expression as matched from
26// the input.
27
28// #define BOOST_SPIRIT_DEBUG
29
30#include <boost/spirit/include/qi.hpp>
31#include <boost/spirit/include/support_utree.hpp>
32
33#include <iostream>
34#include <string>
35
36namespace client
37{
38 namespace qi = boost::spirit::qi;
39 namespace ascii = boost::spirit::ascii;
40 namespace spirit = boost::spirit;
41
42 ///////////////////////////////////////////////////////////////////////////////
43 // Our calculator grammar
44 ///////////////////////////////////////////////////////////////////////////////
45 template <typename Iterator>
46 struct calculator : qi::grammar<Iterator, ascii::space_type, spirit::utree()>
47 {
48 calculator() : calculator::base_type(expression)
49 {
50 using qi::uint_;
51 using qi::char_;
52
53 expression =
54 term
55 >> *( (char_('+') >> term)
56 | (char_('-') >> term)
57 )
58 ;
59
60 term =
61 factor
62 >> *( (char_('*') >> factor)
63 | (char_('/') >> factor)
64 )
65 ;
66
67 factor =
68 uint_
69 | '(' >> expression >> ')'
70 | (char_('-') >> factor)
71 | (char_('+') >> factor)
72 ;
73
74 BOOST_SPIRIT_DEBUG_NODE(expression);
75 BOOST_SPIRIT_DEBUG_NODE(term);
76 BOOST_SPIRIT_DEBUG_NODE(factor);
77 }
78
79 qi::rule<Iterator, ascii::space_type, spirit::utree()> expression;
80 qi::rule<Iterator, ascii::space_type, spirit::utree::list_type()> term;
81 qi::rule<Iterator, ascii::space_type, spirit::utree::list_type()> factor;
82 };
83}
84
85///////////////////////////////////////////////////////////////////////////////
86// Main program
87///////////////////////////////////////////////////////////////////////////////
88int main()
89{
90 std::cout << "/////////////////////////////////////////////////////////\n\n";
91 std::cout << "Expression parser...\n\n";
92 std::cout << "/////////////////////////////////////////////////////////\n\n";
93 std::cout << "Type an expression...or [q or Q] to quit\n\n";
94
95 using boost::spirit::ascii::space;
96 using boost::spirit::utree;
97 typedef std::string::const_iterator iterator_type;
98 typedef client::calculator<iterator_type> calculator;
99
100 calculator calc; // Our grammar
101
102 std::string str;
103 while (std::getline(is&: std::cin, str&: str))
104 {
105 if (str.empty() || str[0] == 'q' || str[0] == 'Q')
106 break;
107
108 std::string::const_iterator iter = str.begin();
109 std::string::const_iterator end = str.end();
110 utree ut;
111 bool r = phrase_parse(first&: iter, last: end, expr: calc, skipper: space, attr&: ut);
112
113 if (r && iter == end)
114 {
115 std::cout << "-------------------------\n";
116 std::cout << "Parsing succeeded: " << ut << "\n";
117 std::cout << "-------------------------\n";
118 }
119 else
120 {
121 std::string rest(iter, end);
122 std::cout << "-------------------------\n";
123 std::cout << "Parsing failed\n";
124 std::cout << "stopped at: \": " << rest << "\"\n";
125 std::cout << "-------------------------\n";
126 }
127 }
128
129 std::cout << "Bye... :-) \n\n";
130 return 0;
131}
132
133
134

source code of boost/libs/spirit/example/qi/calc_utree_naive.cpp