1 // Copyright Abel Sinkovics (abel@sinkovics.hu) 2015.
2 // Distributed under the Boost Software License, Version 1.0.
3 // (See accompanying file LICENSE_1_0.txt or copy at
4 // http://www.boost.org/LICENSE_1_0.txt)
5
6 #include <boost/metaparse/string.hpp>
7 #include <boost/metaparse/sequence_apply.hpp>
8 #include <boost/metaparse/last_of.hpp>
9 #include <boost/metaparse/int_.hpp>
10 #include <boost/metaparse/token.hpp>
11 #include <boost/metaparse/lit_c.hpp>
12 #include <boost/metaparse/one_of.hpp>
13 #include <boost/metaparse/empty.hpp>
14 #include <boost/metaparse/entire_input.hpp>
15 #include <boost/metaparse/build_parser.hpp>
16
17 #include <boost/rational.hpp>
18
19 #include <boost/config.hpp>
20
21 #include <boost/mpl/int.hpp>
22
23 #include <iostream>
24
25 using boost::metaparse::sequence_apply2;
26 using boost::metaparse::last_of;
27 using boost::metaparse::int_;
28 using boost::metaparse::token;
29 using boost::metaparse::lit_c;
30 using boost::metaparse::one_of;
31 using boost::metaparse::empty;
32 using boost::metaparse::entire_input;
33 using boost::metaparse::build_parser;
34
35 template <class Num, class Denom>
36 struct rational
37 {
38 typedef rational type;
39
runrational40 static boost::rational<int> run()
41 {
42 return boost::rational<int>(Num::type::value, Denom::type::value);
43 }
44 };
45
46 typedef
47 sequence_apply2<
48 rational,
49
50 token<int_>,
51 one_of<
52 last_of<lit_c<'/'>, token<int_> >,
53 empty<boost::mpl::int_<1> >
54 >
55 >
56 rational_grammar;
57
58 typedef build_parser<entire_input<rational_grammar> > rational_parser;
59
60 #ifdef RATIONAL
61 # error RATIONAL already defined
62 #endif
63 #define RATIONAL(s) \
64 (::rational_parser::apply<BOOST_METAPARSE_STRING(s)>::type::run())
65
66 #if BOOST_METAPARSE_STD < 2011
67
main()68 int main()
69 {
70 std::cout << "Please use a compiler that supports constexpr" << std::endl;
71 }
72
73 #else
74
main()75 int main()
76 {
77 const boost::rational<int> r1 = RATIONAL("1/3");
78 const boost::rational<int> r2 = RATIONAL("4/4");
79 const boost::rational<int> r3 = RATIONAL("1");
80 const boost::rational<int> r4 = RATIONAL("13/11");
81
82 // Uncommenting the following line generates a compilation error. On a
83 // number of platforms the error report contains the following (or something
84 // similar):
85 // x__________________PARSING_FAILED__________________x<1, 3, digit_expected>
86 // where 1, 3 is the location of the error inside the string literal.
87 // const boost::rational<int> r5 = RATIONAL("7/");
88
89 std::cout
90 << r1 << std::endl
91 << r2 << std::endl
92 << r3 << std::endl
93 << r4 << std::endl;
94 }
95
96 #endif
97
98