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1 | [#foldr1] |
2 | [section foldr1] | |
3 | ||
4 | [h1 Synopsis] | |
5 | ||
6 | template <class P, class State, class BackwardOp> | |
7 | struct foldr1; | |
8 | ||
9 | This is a [link parser_combinator parser combinator]. | |
10 | ||
11 | [table Arguments | |
12 | [[Name] [Type]] | |
13 | [[`P`] [[link parser parser]]] | |
14 | [[`State`] [[link metaprogramming_value template metaprogramming value]]] | |
15 | [[`BackwardOp`] [[link metafunction_class template metafunction class] taking two arguments]] | |
16 | ] | |
17 | ||
18 | [h1 Description] | |
19 | ||
20 | `foldr1` applies `P` on the input string repeatedly as long as `P` accepts the | |
21 | input. The result of parsing is equivalent to | |
22 | `boost::reverse_fold<Sequence, State, BackwardOp>`, where `Sequence` is the | |
23 | sequence of the results of the applications of `P`. | |
24 | ||
25 | When `P` rejects the input for the first time, `foldr1` rejects it as well. At | |
26 | least one successful application of `P` is required for `foldr1` to accept the | |
27 | input. | |
28 | ||
29 | [h1 Header] | |
30 | ||
31 | #include <boost/metaparse/foldr1.hpp> | |
32 | ||
33 | [h1 Expression semantics] | |
34 | ||
35 | For any `p` parser, `t` class, `f` metafunction class taking two arguments the | |
36 | following are equivalent: | |
37 | ||
38 | foldr1<p, t, f> | |
39 | ||
40 | last_of<look_ahead<p>, foldr<p, t, f>> | |
41 | ||
42 | [h1 Example] | |
43 | ||
44 | #include <boost/metaparse/foldr1.hpp> | |
45 | #include <boost/metaparse/token.hpp> | |
46 | #include <boost/metaparse/int_.hpp> | |
47 | #include <boost/metaparse/string.hpp> | |
48 | #include <boost/metaparse/start.hpp> | |
49 | #include <boost/metaparse/get_result.hpp> | |
50 | #include <boost/metaparse/is_error.hpp> | |
51 | ||
52 | #include <boost/mpl/lambda.hpp> | |
53 | #include <boost/mpl/plus.hpp> | |
54 | ||
55 | using namespace boost::metaparse; | |
56 | ||
57 | using int_token = token<int_>; | |
58 | using sum_op = | |
59 | boost::mpl::lambda<boost::mpl::plus<boost::mpl::_1, boost::mpl::_2>>::type; | |
60 | ||
61 | using ints = foldr1<int_token, boost::mpl::int_<0>, sum_op>; | |
62 | ||
63 | static_assert( | |
64 | get_result< | |
65 | ints::apply<BOOST_METAPARSE_STRING("11 13 3 21"), start> | |
66 | >::type::value == 48, | |
67 | "ints should sum the numbers" | |
68 | ); | |
69 | ||
70 | static_assert( | |
71 | is_error<ints::apply<BOOST_METAPARSE_STRING(""), start>>::type::value, | |
72 | "when no numbers are provided, it should be an error" | |
73 | ); | |
74 | ||
75 | [endsect] | |
76 |