ceph/src/boost/libs/metaparse/doc/foldl_reject_incomplete_start_with_parser.qbk

   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