ceph/src/boost/libs/metaparse/doc/foldl1.qbk

   1 [#foldl1]
   2 [section foldl1]
   3
   4 [h1 Synopsis]
   5
   6   template <class P, class State, class ForwardOp>
   7   struct foldl1;
   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 `foldl1` applies `P` on the input string repeatedly as long as `P` accepts the
  21 input. The result of parsing is equivalent to
  22 `boost::mpl::fold<Sequence, State, ForwardOp>`, where `Sequence` is the sequence
  23 of the results of the applications of `P`.
  24
  25 When `P` rejects the input for the first time, `foldl1` rejects it as well. At
  26 least one successful application of `P` is required for `foldl1` to accept the
  27 input.
  28
  29 [h1 Header]
  30
  31   #include <boost/metaparse/foldl1.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   foldl1<p, t, f>
  39
  40   last_of<look_ahead<p>, foldl<p, t, f>>
  41
  42 [h1 Example]
  43
  44   #include <boost/metaparse/foldl1.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 = foldl1<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