1/*=============================================================================
2 Copyright (c) 2001-2014 Joel de Guzman
3
4 Distributed under the Boost Software License, Version 1.0. (See accompanying
5 file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
6=============================================================================*/
7///////////////////////////////////////////////////////////////////////////////
8//
9// A Calculator example demonstrating generation of AST. The AST,
10// once created, is traversed, 1) To print its contents and
11// 2) To evaluate the result.
12//
13// [ JDG April 28, 2008 ] For BoostCon 2008
14// [ JDG February 18, 2011 ] Pure attributes. No semantic actions.
15// [ JDG January 9, 2013 ] Spirit X3
16//
17///////////////////////////////////////////////////////////////////////////////
18
19#include <boost/spirit/home/x3.hpp>
20#include <boost/spirit/home/x3/support/ast/variant.hpp>
21#include <boost/fusion/include/adapt_struct.hpp>
22
23#include <iostream>
24#include <string>
25#include <list>
26#include <numeric>
27
28namespace x3 = boost::spirit::x3;
29
30namespace client { namespace ast
31{
32 ///////////////////////////////////////////////////////////////////////////
33 // The AST
34 ///////////////////////////////////////////////////////////////////////////
35 struct nil {};
36 struct signed_;
37 struct program;
38
39 struct operand : x3::variant<
40 nil
41 , unsigned int
42 , x3::forward_ast<signed_>
43 , x3::forward_ast<program>
44 >
45 {
46 using base_type::base_type;
47 using base_type::operator=;
48 };
49
50 struct signed_
51 {
52 char sign;
53 operand operand_;
54 };
55
56 struct operation
57 {
58 char operator_;
59 operand operand_;
60 };
61
62 struct program
63 {
64 operand first;
65 std::list<operation> rest;
66 };
67}}
68
69BOOST_FUSION_ADAPT_STRUCT(client::ast::signed_,
70 sign, operand_
71)
72
73BOOST_FUSION_ADAPT_STRUCT(client::ast::operation,
74 operator_, operand_
75)
76
77BOOST_FUSION_ADAPT_STRUCT(client::ast::program,
78 first, rest
79)
80
81namespace client { namespace ast
82{
83 ///////////////////////////////////////////////////////////////////////////
84 // The AST Printer
85 ///////////////////////////////////////////////////////////////////////////
86 struct printer
87 {
88 typedef void result_type;
89
90 void operator()(nil) const {}
91 void operator()(unsigned int n) const { std::cout << n; }
92
93 void operator()(operation const& x) const
94 {
95 boost::apply_visitor(visitor: *this, visitable: x.operand_);
96 switch (x.operator_)
97 {
98 case '+': std::cout << " add"; break;
99 case '-': std::cout << " subt"; break;
100 case '*': std::cout << " mult"; break;
101 case '/': std::cout << " div"; break;
102 }
103 }
104
105 void operator()(signed_ const& x) const
106 {
107 boost::apply_visitor(visitor: *this, visitable: x.operand_);
108 switch (x.sign)
109 {
110 case '-': std::cout << " neg"; break;
111 case '+': std::cout << " pos"; break;
112 }
113 }
114
115 void operator()(program const& x) const
116 {
117 boost::apply_visitor(visitor: *this, visitable: x.first);
118 for (operation const& oper: x.rest)
119 {
120 std::cout << ' ';
121 (*this)(oper);
122 }
123 }
124 };
125
126 ///////////////////////////////////////////////////////////////////////////
127 // The AST evaluator
128 ///////////////////////////////////////////////////////////////////////////
129 struct eval
130 {
131 typedef int result_type;
132
133 int operator()(nil) const { BOOST_ASSERT(0); return 0; }
134 int operator()(unsigned int n) const { return n; }
135
136 int operator()(int lhs, operation const& x) const
137 {
138 int rhs = boost::apply_visitor(visitor: *this, visitable: x.operand_);
139 switch (x.operator_)
140 {
141 case '+': return lhs + rhs;
142 case '-': return lhs - rhs;
143 case '*': return lhs * rhs;
144 case '/': return lhs / rhs;
145 }
146 BOOST_ASSERT(0);
147 return 0;
148 }
149
150 int operator()(signed_ const& x) const
151 {
152 int rhs = boost::apply_visitor(visitor: *this, visitable: x.operand_);
153 switch (x.sign)
154 {
155 case '-': return -rhs;
156 case '+': return +rhs;
157 }
158 BOOST_ASSERT(0);
159 return 0;
160 }
161
162 int operator()(program const& x) const
163 {
164 return std::accumulate(
165 first: x.rest.begin(), last: x.rest.end()
166 , init: boost::apply_visitor(visitor: *this, visitable: x.first)
167 , binary_op: *this);
168 }
169 };
170}}
171
172namespace client
173{
174 ///////////////////////////////////////////////////////////////////////////////
175 // The calculator grammar
176 ///////////////////////////////////////////////////////////////////////////////
177 namespace calculator_grammar
178 {
179 using x3::uint_;
180 using x3::char_;
181
182 x3::rule<class expression, ast::program> const expression("expression");
183 x3::rule<class term, ast::program> const term("term");
184 x3::rule<class factor, ast::operand> const factor("factor");
185
186 auto const expression_def =
187 term
188 >> *( (char_('+') >> term)
189 | (char_('-') >> term)
190 )
191 ;
192
193 auto const term_def =
194 factor
195 >> *( (char_('*') >> factor)
196 | (char_('/') >> factor)
197 )
198 ;
199
200 auto const factor_def =
201 uint_
202 | '(' >> expression >> ')'
203 | (char_('-') >> factor)
204 | (char_('+') >> factor)
205 ;
206
207 BOOST_SPIRIT_DEFINE(
208 expression
209 , term
210 , factor
211 );
212
213 auto calculator = expression;
214 }
215
216 using calculator_grammar::calculator;
217
218}
219
220///////////////////////////////////////////////////////////////////////////////
221// Main program
222///////////////////////////////////////////////////////////////////////////////
223int
224main()
225{
226 std::cout << "/////////////////////////////////////////////////////////\n\n";
227 std::cout << "Expression parser...\n\n";
228 std::cout << "/////////////////////////////////////////////////////////\n\n";
229 std::cout << "Type an expression...or [q or Q] to quit\n\n";
230
231 typedef std::string::const_iterator iterator_type;
232 typedef client::ast::program ast_program;
233 typedef client::ast::printer ast_print;
234 typedef client::ast::eval ast_eval;
235
236 std::string str;
237 while (std::getline(is&: std::cin, str&: str))
238 {
239 if (str.empty() || str[0] == 'q' || str[0] == 'Q')
240 break;
241
242 auto& calc = client::calculator; // Our grammar
243 ast_program program; // Our program (AST)
244 ast_print print; // Prints the program
245 ast_eval eval; // Evaluates the program
246
247 iterator_type iter = str.begin();
248 iterator_type end = str.end();
249 boost::spirit::x3::ascii::space_type space;
250 bool r = phrase_parse(first&: iter, last: end, p: calc, s: space, attr&: program);
251
252 if (r && iter == end)
253 {
254 std::cout << "-------------------------\n";
255 std::cout << "Parsing succeeded\n";
256 print(program);
257 std::cout << "\nResult: " << eval(program) << std::endl;
258 std::cout << "-------------------------\n";
259 }
260 else
261 {
262 std::string rest(iter, end);
263 std::cout << "-------------------------\n";
264 std::cout << "Parsing failed\n";
265 std::cout << "stopped at: \"" << rest << "\"\n";
266 std::cout << "-------------------------\n";
267 }
268 }
269
270 std::cout << "Bye... :-) \n\n";
271 return 0;
272}
273

source code of boost/libs/spirit/example/x3/calc/calc4.cpp