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 9This 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 20The 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` 22consumes any characters before rejecting the input. If so, 23`foldl_reject_incomplete_start_with_parser` rejects the input with the same 24error message this last application of `P` returned. Otherwise 25`foldl_reject_incomplete_start_with_parser` accepts the input and gives the same 26result as [link foldl_start_with_parser `foldl_start_with_parser`]. 27 28Here is a diagram showing how `foldl_reject_incomplete_start_with_parser` works 29by 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 38Further details can be found in the 39[link introducing-foldl_reject_incomplete_start_with_parser Introducing foldl_reject_incomplete_start_with_parser] 40section 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 48For 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 53is 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] 101 102
