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- [#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]
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