12 This is a [link lazy_metafunction lazy template metafunction] that supports
13 [link currying currying].
17 [[`C`] [[link boxed_value boxed] character value]]
22 Checks if `C` is a letter. Returns a boxed boolean value.
26 #include <boost/metaparse/util/is_letter.hpp>
28 [h1 Expression semantics]
30 The following expressions are equivalent:
32 is_letter<>::apply<boost::mpl::char_<'a'>>::type
35 is_letter<>::apply<boost::mpl::char_<'z'>>::type
38 is_letter<>::apply<boost::mpl::char_<'A'>>::type
41 is_letter<>::apply<boost::mpl::char_<'Z'>>::type
44 is_letter<>::apply<c>::type
49 #include <boost/metaparse/util/is_letter.hpp>
51 #include <type_traits>
53 using namespace boost::metaparse;
57 using type = std::integral_constant<char, 'A'>;
61 util::is_letter<std::integral_constant<char, 'A'>>::type::value,
62 "A should be a letter"
66 !util::is_letter<std::integral_constant<char, '0'>>::type::value,
67 "a number should not be a letter"
71 util::is_letter<>::type
72 ::apply<std::integral_constant<char, 'A'>>::type::value,
73 "it should support currying"
77 util::is_letter<returns_char>::type::value,
78 "it should support lazy evaluation"