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 9This 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 20The same as [link foldl `foldl`], but once `P` rejects the input, 21`foldl_reject_incomplete` checks if `P` consumes any characters before rejecting 22the input. If so, `foldl_reject_incomplete` rejects the input with the same 23error 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 27Here 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 42For 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 47is 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 93
