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1 | [#foldl_reject_incomplete_start_with_parser] |
2 | [section foldl_reject_incomplete_start_with_parser] | |
3 | ||
4 | [h1 Synopsis] | |
5 | ||
6 | template <class P, class StateP, class ForwardOp> | |
7 | struct foldl_reject_incomplete_start_with_parser; | |
8 | ||
9 | This is a [link parser_combinator parser combinator]. | |
10 | ||
11 | [table Arguments | |
12 | [[Name] [Type]] | |
13 | [[`P`] [[link parser parser]]] | |
14 | [[`StateP`] [[link parser parser]]] | |
15 | [[`ForwardOp`] [[link metafunction_class template metafunction class] taking two arguments]] | |
16 | ] | |
17 | ||
18 | [h1 Description] | |
19 | ||
20 | The same as [link foldl_start_with_parser `foldl_start_with_parser`], but once | |
21 | `P` rejects the input, `foldl_reject_incomplete_start_with_parser` checks if `P` | |
22 | consumes any characters before rejecting the input. If so, | |
23 | `foldl_reject_incomplete_start_with_parser` rejects the input with the same | |
24 | error message this last application of `P` returned. Otherwise | |
25 | `foldl_reject_incomplete_start_with_parser` accepts the input and gives the same | |
26 | result as [link foldl_start_with_parser `foldl_start_with_parser`]. | |
27 | ||
28 | Here is a diagram showing how `foldl_reject_incomplete_start_with_parser` works | |
29 | by example: | |
30 | ||
31 | using int_token = token<int_>; | |
32 | using plus_token = token<lit_c<'+'>>; | |
33 | using plus_int = last_of<plus_token, int_token>; | |
34 | using sum_op = mpl::lambda<mpl::plus<mpl::_1, mpl::_2>>::type; | |
35 | ||
36 | [$images/metaparse/foldl_reject_incomplete_start_with_parser_diag1.png [width 70%]] | |
37 | ||
38 | Further details can be found in the | |
39 | [link introducing-foldl_reject_incomplete_start_with_parser Introducing foldl_reject_incomplete_start_with_parser] | |
40 | section of the [link manual User Manual]. | |
41 | ||
42 | [h1 Header] | |
43 | ||
44 | #include <boost/metaparse/foldl_reject_incomplete_start_with_parser.hpp> | |
45 | ||
46 | [h1 Expression semantics] | |
47 | ||
48 | For any `p` parser, `pt` class, `f` metafunction class taking two arguments, | |
49 | `s` compile-time string and `pos` source position | |
50 | ||
51 | foldl_reject_incomplete_start_with_parser<p, pt, f>::apply<s, pos> | |
52 | ||
53 | is equivalent to | |
54 | ||
55 | first_of< | |
56 | foldl_start_with_parser<p, pt, f>, | |
57 | fail_at_first_char_expected<p> | |
58 | >::apply<s, pos> | |
59 | ||
60 | [h1 Example] | |
61 | ||
62 | #include <boost/metaparse/foldl_reject_incomplete_start_with_parser.hpp> | |
63 | #include <boost/metaparse/lit_c.hpp> | |
64 | #include <boost/metaparse/last_of.hpp> | |
65 | #include <boost/metaparse/token.hpp> | |
66 | #include <boost/metaparse/int_.hpp> | |
67 | #include <boost/metaparse/string.hpp> | |
68 | #include <boost/metaparse/start.hpp> | |
69 | #include <boost/metaparse/get_result.hpp> | |
70 | #include <boost/metaparse/is_error.hpp> | |
71 | ||
72 | #include <boost/mpl/lambda.hpp> | |
73 | #include <boost/mpl/plus.hpp> | |
74 | ||
75 | using namespace boost::metaparse; | |
76 | ||
77 | using int_token = token<int_>; | |
78 | using plus_token = token<lit_c<'+'>>; | |
79 | using plus_int = last_of<plus_token, int_token>; | |
80 | using sum_op = | |
81 | boost::mpl::lambda<boost::mpl::plus<boost::mpl::_1, boost::mpl::_2>>::type; | |
82 | ||
83 | using ints = | |
84 | foldl_reject_incomplete_start_with_parser<plus_int, int_token, sum_op>; | |
85 | ||
86 | static_assert( | |
87 | get_result< | |
88 | ints::apply<BOOST_METAPARSE_STRING("11 + 13 + 3 + 21"), start> | |
89 | >::type::value == 48, | |
90 | "ints should sum the numbers" | |
91 | ); | |
92 | ||
93 | static_assert( | |
94 | is_error< | |
95 | ints::apply<BOOST_METAPARSE_STRING("11 + 13 + 3 +"), start> | |
96 | >::type::value, | |
97 | "when the last number is missing, it should be an error" | |
98 | ); | |
99 | ||
100 | [endsect] | |
101 |