77 lines
2.0 KiB
Plaintext
77 lines
2.0 KiB
Plaintext
[#foldl1]
|
|
[section foldl1]
|
|
|
|
[h1 Synopsis]
|
|
|
|
template <class P, class State, class ForwardOp>
|
|
struct foldl1;
|
|
|
|
This is a [link parser_combinator parser combinator].
|
|
|
|
[table Arguments
|
|
[[Name] [Type]]
|
|
[[`P`] [[link parser parser]]]
|
|
[[`State`] [[link metaprogramming_value template metaprogramming value]]]
|
|
[[`ForwardOp`] [[link metafunction_class template metafunction class] taking two arguments]]
|
|
]
|
|
|
|
[h1 Description]
|
|
|
|
`foldl1` applies `P` on the input string repeatedly as long as `P` accepts the
|
|
input. The result of parsing is equivalent to
|
|
`boost::mpl::fold<Sequence, State, ForwardOp>`, where `Sequence` is the sequence
|
|
of the results of the applications of `P`.
|
|
|
|
When `P` rejects the input for the first time, `foldl1` rejects it as well. At
|
|
least one successful application of `P` is required for `foldl1` to accept the
|
|
input.
|
|
|
|
[h1 Header]
|
|
|
|
#include <boost/metaparse/foldl1.hpp>
|
|
|
|
[h1 Expression semantics]
|
|
|
|
For any `p` parser, `t` class, `f` metafunction class taking two arguments the
|
|
following are equivalent:
|
|
|
|
foldl1<p, t, f>
|
|
|
|
last_of<look_ahead<p>, foldl<p, t, f>>
|
|
|
|
[h1 Example]
|
|
|
|
#include <boost/metaparse/foldl1.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>
|
|
|
|
using namespace boost::metaparse;
|
|
|
|
using int_token = token<int_>;
|
|
using sum_op =
|
|
boost::mpl::lambda<boost::mpl::plus<boost::mpl::_1, boost::mpl::_2>>::type;
|
|
|
|
using ints = foldl1<int_token, boost::mpl::int_<0>, sum_op>;
|
|
|
|
static_assert(
|
|
get_result<
|
|
ints::apply<BOOST_METAPARSE_STRING("11 13 3 21"), start>
|
|
>::type::value == 48,
|
|
"ints should sum the numbers"
|
|
);
|
|
|
|
static_assert(
|
|
is_error<ints::apply<BOOST_METAPARSE_STRING(""), start>>::type::value,
|
|
"when no numbers are provided, it should be an error"
|
|
);
|
|
|
|
[endsect]
|
|
|