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foldr_reject_incomplete1

Synopsis

template <class P, class State, class BackwardOp>
struct foldr_reject_incomplete1;

This is a parser combinator.

Table 28. Arguments

Name

Type

P

parser

State

template metaprogramming value

BackwardOp

template metafunction class taking two arguments


Description

The same as foldr1, but once P rejects the input, foldr_reject_incomplete1 checks if P consumes any characters before rejecting the input. If so, foldr_reject_incomplete1 rejects the input with the same error message this last application of P returned. Otherwise foldr_reject_incomplete1 accepts the input and gives the same result as foldr1.

Header

#include <boost/metaparse/foldr_reject_incomplete1.hpp>

Expression semantics

For any p parser, t class, f metafunction class taking two arguments, s compile-time string and pos source position

foldr_reject_incomplete1<p, t, f>::apply<s, pos>

is equivalent to

first_of<foldr1<p, t, f>, fail_at_first_char_expected<p> >::apply<s, pos>

Example

#include <boost/metaparse/foldr_reject_incomplete1.hpp>
#include <boost/metaparse/lit_c.hpp>
#include <boost/metaparse/last_of.hpp>
#include <boost/metaparse/token.hpp>
#include <boost/metaparse/int_.hpp>
#include <boost/metaparse/string.hpp>
#include <boost/metaparse/start.hpp>
#include <boost/metaparse/get_result.hpp>
#include <boost/metaparse/is_error.hpp>

#include <boost/mpl/lambda.hpp>
#include <boost/mpl/plus.hpp>
#include <boost/mpl/int.hpp>

using namespace boost::metaparse;

using int_token = token<int_>;
using plus_token = token<lit_c<'+'>>;
using plus_int = last_of<plus_token, int_token>;
using sum_op =
  boost::mpl::lambda<boost::mpl::plus<boost::mpl::_1, boost::mpl::_2>>::type;

using ints = foldr_reject_incomplete1<plus_int, boost::mpl::int_<11>, sum_op>;

static_assert(
  get_result<
    ints::apply<BOOST_METAPARSE_STRING("+ 13 + 3 + 21"), start>
  >::type::value == 48,
  "ints should sum the numbers"
);

static_assert(
  is_error<
    ints::apply<BOOST_METAPARSE_STRING("+ 13 + 3 +"), start>
  >::type::value,
  "when the last number is missing, it should be an error"
);

static_assert(
  is_error<ints::apply<BOOST_METAPARSE_STRING(""), start>>::type::value,
  "when no numbers are provided, it should be an error"
);

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