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

   1 [#foldl_reject_incomplete]
   2 [section foldl_reject_incomplete]
   3
   4 [h1 Synopsis]
   5
   6   template <class P, class State, class ForwardOp>
   7   struct foldl_reject_incomplete;
   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   [[`ForwardOp`] [[link metafunction_class template metafunction class] taking two arguments]]
  16 ]
  17
  18 [h1 Description]
  19
  20 The same as [link foldl `foldl`], but once `P` rejects the input,
  21 `foldl_reject_incomplete` checks if `P` consumes any characters before rejecting
  22 the input. If so, `foldl_reject_incomplete` rejects the input with the same
  23 error message this last application of `P` returned. Otherwise
  24 `foldl_reject_incomplete` accepts the input and gives the same result as
  25 [link foldl `foldl`].
  26
  27 Here is a diagram showing how `foldl_reject_incomplete` works by example:
  28
  29   using int_token = token<int_>;
  30   using plus_token = token<lit_c<'+'>>;
  31   using plus_int = last_of<plus_token, int_token>;
  32   using sum_op = mpl::lambda<mpl::plus<mpl::_1, mpl::_2>>::type;
  33
  34 [$images/metaparse/foldl_reject_incomplete_diag1.png [width 70%]]
  35
  36 [h1 Header]
  37
  38   #include <boost/metaparse/foldl_reject_incomplete.hpp>
  39
  40 [h1 Expression semantics]
  41
  42 For any `p` parser, `t` class, `f` metafunction class taking two arguments,
  43 `s` compile-time string and `pos` source position
  44
  45   foldl_reject_incomplete<p, t, f>::apply<s, pos>
  46
  47 is equivalent to
  48
  49   first_of<foldl<p, t, f>, fail_at_first_char_expected<p> >::apply<s, pos>
  50
  51 [h1 Example]
  52
  53   #include <boost/metaparse/foldl_reject_incomplete.hpp>
  54   #include <boost/metaparse/lit_c.hpp>
  55   #include <boost/metaparse/last_of.hpp>
  56   #include <boost/metaparse/token.hpp>
  57   #include <boost/metaparse/int_.hpp>
  58   #include <boost/metaparse/string.hpp>
  59   #include <boost/metaparse/start.hpp>
  60   #include <boost/metaparse/get_result.hpp>
  61   #include <boost/metaparse/is_error.hpp>
  62
  63   #include <boost/mpl/lambda.hpp>
  64   #include <boost/mpl/plus.hpp>
  65   #include <boost/mpl/int.hpp>
  66
  67   using namespace boost::metaparse;
  68
  69   using int_token = token<int_>;
  70   using plus_token = token<lit_c<'+'>>;
  71   using plus_int = last_of<plus_token, int_token>;
  72   using sum_op =
  73     boost::mpl::lambda<boost::mpl::plus<boost::mpl::_1, boost::mpl::_2>>::type;
  74
  75   using ints = foldl_reject_incomplete<plus_int, boost::mpl::int_<11>, sum_op>;
  76
  77   static_assert(
  78     get_result<
  79       ints::apply<BOOST_METAPARSE_STRING("+ 13 + 3 + 21"), start>
  80     >::type::value == 48,
  81     "ints should sum the numbers"
  82   );
  83
  84   static_assert(
  85     is_error<
  86       ints::apply<BOOST_METAPARSE_STRING("+ 13 + 3 +"), start>
  87     >::type::value,
  88     "when the last number is missing, it should be an error"
  89   );
  90
  91 [endsect]
  92