Remove space from declaration of UDLs, because apparently it matters?!

Fixes #216.

README.md

@@ -57,7 +57,7 @@ Master status:
 
 [![Windows MSVC](https://github.com/tzlaine/parser/actions/workflows/windows.yml/badge.svg?branch=master)](https://github.com/tzlaine/parser/actions/workflows/windows.yml)
 
-[![macos-12 - Clang 14](https://github.com/tzlaine/parser/actions/workflows/macos-12.yml/badge.svg?branch=master)](https://github.com/tzlaine/parser/actions/workflows/macos-12.yml)
+[![macos-13 - Clang 14](https://github.com/tzlaine/parser/actions/workflows/macos-13.yml/badge.svg?branch=master)](https://github.com/tzlaine/parser/actions/workflows/macos-13.yml)
 
 Develop status:
 
@@ -67,6 +67,6 @@ Develop status:
 
 [![Windows MSVC](https://github.com/tzlaine/parser/actions/workflows/windows.yml/badge.svg?branch=develop)](https://github.com/tzlaine/parser/actions/workflows/windows.yml)
 
-[![macos-12 - Clang 14](https://github.com/tzlaine/parser/actions/workflows/macos-12.yml/badge.svg?branch=develop)](https://github.com/tzlaine/parser/actions/workflows/macos-12.yml)
+[![macos-13 - Clang 14](https://github.com/tzlaine/parser/actions/workflows/macos-13.yml/badge.svg?branch=develop)](https://github.com/tzlaine/parser/actions/workflows/macos-13.yml)
 
 [![License](https://img.shields.io/badge/license-boost-brightgreen.svg)](LICENSE_1_0.txt)

doc/parser.qbk

@@ -110,6 +110,7 @@
 
 
 [def _std_str_             `std::string`]
+[def _std_strs_            `std::string`s]
 [def _std_vec_char_        `std::vector<char>`]
 [def _std_vec_char32_      `std::vector<char32_t>`]
 
@@ -201,6 +202,7 @@
 [def _merge_               [globalref boost::parser::merge `merge[]`]]
 [def _sep_                 [globalref boost::parser::separate `separate[]`]]
 [def _transform_           [globalref boost::parser::transform `transform(f)[]`]]
+[def _delimiter_           [globalref boost::parser::delimiter `delimiter(p)[]`]]
 
 [def _omit_np_             [globalref boost::parser::omit `omit`]]
 [def _raw_np_              [globalref boost::parser::raw `raw`]]
@@ -211,11 +213,13 @@
 [def _merge_np_            [globalref boost::parser::merge `merge`]]
 [def _sep_np_              [globalref boost::parser::separate `separate`]]
 [def _transform_np_        [globalref boost::parser::transform `transform`]]
+[def _delimiter_np_        [globalref boost::parser::delimiter `delimiter`]]
 
 [def _blank_               [globalref boost::parser::blank `blank`]]
 [def _control_             [globalref boost::parser::control `control`]]
 [def _digit_               [globalref boost::parser::digit `digit`]]
 [def _punct_               [globalref boost::parser::punct `punct`]]
+[def _symb_                [globalref boost::parser::symb `symb`]]
 [def _hex_digit_           [globalref boost::parser::hex_digit `hex_digit`]]
 [def _lower_               [globalref boost::parser::lower `lower`]]
 [def _upper_               [globalref boost::parser::upper `upper`]]
@@ -239,6 +243,7 @@
 [def _more_about_rules_    [link boost_parser.tutorial.more_about_rules More About Rules]]
 [def _unicode_             [link boost_parser.tutorial.unicode_support Unicode Support]]
 [def _concepts_            [link boost_parser.concepts Concepts]]
+[def _seq_parser_example_  [link boost_parser.tutorial.attribute_generation.a_sequence_parser_attribute_example A sequence parser attribute example]]
 [def _ex_json_             [link boost_parser.extended_examples.parsing_json Parsing JSON]]
 [def _ex_cb_json_          [link boost_parser.extended_examples.parsing_json_with_callbacks Parsing JSON With Callbacks]]
 [def _rationale_           [link boost_parser.rationale Rationale]]

doc/tables.qbk

@@ -132,6 +132,11 @@ the input they match unless otherwise stated in the table below.]
      [ The code point type in Unicode parsing, or `char` in non-Unicode parsing.  See the entry for _ch_. ]
      []]
 
+    [[ `_symb_` ]
+     [ Matches a single symbol code point. ]
+     [ The code point type in Unicode parsing, or `char` in non-Unicode parsing.  See the entry for _ch_. ]
+     []]
+
     [[ `_hex_digit_` ]
      [ Matches a single hexidecimal digit code point. ]
      [ The code point type in Unicode parsing, or `char` in non-Unicode parsing.  See the entry for _ch_. ]
@@ -385,10 +390,10 @@ consume the input they match unless otherwise stated in the table below.]
     [[`*p`] [ Parses using `p` repeatedly until `p` no longer matches; always matches. ] [`std::string` if `_ATTR_np_(p)` is `char` or `char32_t`, otherwise `std::vector<_ATTR_np_(p)>`] [ Matching _e_ an unlimited number of times creates an infinite loop, which is undefined behavior in C++.  _Parser_ will assert in debug mode when it encounters `*_e_` (this applies to unconditional _e_ only). ]]
     [[`+p`] [ Parses using `p` repeatedly until `p` no longer matches; matches iff `p` matches at least once. ] [`std::string` if `_ATTR_np_(p)` is `char` or `char32_t`, otherwise `std::vector<_ATTR_np_(p)>`] [ Matching _e_ an unlimited number of times creates an infinite loop, which is undefined behavior in C++.  _Parser_ will assert in debug mode when it encounters `+_e_` (this applies to unconditional _e_ only). ]]
     [[`-p`] [ Equivalent to `p | _e_`. ] [`std::optional<_ATTR_np_(p)>`] []]
-    [[`p1 >> p2`] [ Matches iff `p1` matches and then `p2` matches. ] [`_bp_tup_<_ATTR_np_(p1), _ATTR_np_(p2)>` (See note.)] [ `>>` is associative; `p1 >> p2 >> p3`, `(p1 >> p2) >> p3`, and `p1 >> (p2 >> p3)` are all equivalent.  This attribute type only applies to the case where `p1` and `p2` both generate attributes; see _attr_gen_ for the full rules. ]]
+    [[`p1 >> p2`] [ Matches iff `p1` matches and then `p2` matches. ] [`_bp_tup_<_ATTR_np_(p1), _ATTR_np_(p2)>` (See note.)] [ `>>` is associative; `p1 >> p2 >> p3`, `(p1 >> p2) >> p3`, and `p1 >> (p2 >> p3)` are all equivalent.  This attribute type only applies to the case where `p1` and `p2` both generate attributes; see _attr_gen_ for the full rules.  Differs in precedence from `operator>`. ]]
     [[`p >> c`] [ Equivalent to `p >> lit(c)`. ] [`_ATTR_np_(p)`] []]
     [[`p >> r`] [ Equivalent to `p >> lit(r)`. ] [`_ATTR_np_(p)`] []]
-    [[`p1 > p2`] [ Matches iff `p1` matches and then `p2` matches.  No back-tracking is allowed after `p1` matches; if `p1` matches but then `p2` does not, the top-level parse fails. ] [`_bp_tup_<_ATTR_np_(p1), _ATTR_np_(p2)>` (See note.)] [ `>` is associative; `p1 > p2 > p3`, `(p1 > p2) > p3`, and `p1 > (p2 > p3)` are all equivalent.  This attribute type only applies to the case where `p1` and `p2` both generate attributes; see _attr_gen_ for the full rules. ]]
+    [[`p1 > p2`] [ Matches iff `p1` matches and then `p2` matches.  No back-tracking is allowed after `p1` matches; if `p1` matches but then `p2` does not, the top-level parse fails. ] [`_bp_tup_<_ATTR_np_(p1), _ATTR_np_(p2)>` (See note.)] [ `>` is associative; `p1 > p2 > p3`, `(p1 > p2) > p3`, and `p1 > (p2 > p3)` are all equivalent.  This attribute type only applies to the case where `p1` and `p2` both generate attributes; see _attr_gen_ for the full rules.  Differs in precedence from `operator>>`. ]]
     [[`p > c`] [ Equivalent to `p > lit(c)`. ] [`_ATTR_np_(p)`] []]
     [[`p > r`] [ Equivalent to `p > lit(r)`. ] [`_ATTR_np_(p)`] []]
     [[`p1 | p2`] [ Matches iff either `p1` matches or `p2` matches. ] [`std::variant<_ATTR_np_(p1), _ATTR_np_(p2)>` (See note.)] [ `|` is associative; `p1 | p2 | p3`, `(p1 | p2) | p3`, and `p1 | (p2 | p3)` are all equivalent.  This attribute type only applies to the case where `p1` and `p2` both generate attributes, and where the attribute types are different; see _attr_gen_ for the full rules. ]]
@@ -424,6 +429,15 @@ because, for any parser `p`, `_e_ | p` is equivalent to _e_, since _e_ always
 matches.  This is not true for _e_ parameterized with a condition.  For any
 condition `cond`, `_e_(cond)` is allowed to appear anywhere within an
 alternative parser.
+
+[important The C++ operators `>` and `>>` have different precedences.  This
+will sometimes come up in warnings from your compiler.  No matter how you do
+or do not parenthesize chains of parsers separated by `>` and `>>`, the
+resulting expression evaluates the same.  Feel free to add parentheses if your
+compiler complains.  More broadly, keep the C++ operator precedence rules in
+mind when writing your parsers _emdash_ the simplest thing to write may not
+have your intended semantics. ]
+
 ]
 
 [template table_attribute_generation

doc/tutorial.qbk

@@ -65,7 +65,7 @@ subparsers does.
 
 Finally, there is a /permutation parser/; it is created using `operator||`,
 as in `p1 || p2 || p3`.  A permutation parser tries to match all of its
-subparsers to the input, in any order.  So the parser `p1 || p2 || p3` is equivalent to `(p1 >> p2 >> p3) | (p1 >> p3 >> p2) | (p2 >> p1 >> p3) | (p2 >> p3 >> p1) | (p3 >> p1 >> p2) | (p3 >> p2 >> p1)`.  Hopefully its terseness is self-explanatory.  It matches the
+subparsers to the input, in any order.  So the parser `p1 || p2 || p3` is equivalent to `(p1 >> p2 >> p3) | (p1 >> p3 >> p2) | (p2 >> p1 >> p3) | (p2 >> p3 >> p1) | (p3 >> p1 >> p2) | (p3 >> p2 >> p1)`.  Hopefully the advantage of its terseness is self-explanatory.  It matches the
 input iff all of its subparsers do, regardless of the order they match in.
 
 _Parser_ parsers each have an /attribute/ associated with them, or explicitly
@@ -836,6 +836,14 @@ escaped quote character, since those always work.
 
 [quoted_string_example_5]
 
+Additionally, with each of the forms shown above, you can optionally provide a
+parser as a final argument, to will be used to parse each character inside the
+quotes.  You have to provide an actual full parser here; you cannot provide a
+character or string literal.  If you do not provide a character parser, _ch_
+is used.
+
+[quoted_string_example_6]
+
 [endsect]
 
 [section Parsing In Detail]
@@ -1442,6 +1450,24 @@ _merge_ and _sep_ create a copy of the given _seq_p_.
 
 _transform_ creates a _xfm_p_.
 
+[heading _delimiter_]
+
+The _delimiter_np_ directive enables the use of a delimiter within a
+permutation parser.  It *only* applies to permutation parsers, just as _merge_
+and _sep_ only apply to sequence parsers.  Consider this permutation parser.
+
+    constexpr auto parser = bp::int_ || bp::string("foo") || bp::char_('g');
+
+This will match all of: an integer, `"foo"`, and `'g'`, in any order (for
+example, `"foo g 42"`).  If you also want for those three elements to be
+delimited by commas, you could write this parser instead.
+
+    constexpr auto delimited_parser =
+        bp::delimiter(bp::lit(','))[bp::int_ || bp::string("foo") || bp::char_('g')];
+
+`delimited_parser` will parse the same elements as `parser`, but will also
+require commas between the elements (as in `"foo, g, 42"`).
+
 [endsect]
 
 [section Combining Operations]
@@ -1590,6 +1616,71 @@ attribute becomes `T`.
     [container_concept]
 ]
 
+[heading A sequence parser attribute example]
+
+Note that the application of `OP` is done in the style of a left-fold, and
+is therefore greedy.  This can lead to some non-obvious results.  For example,
+consider this program.  Thanks to Duncan Paterson for this very nice example!
+
+    #include <boost/parser/parser.hpp>
+    #include <print>
+
+    namespace bp = boost::parser;
+    int main() {
+      const auto id_set_action = [](auto &ctx) {
+        const auto& [left, right] = _attr(ctx);
+        std::println("{} = {}", left, right);
+      };
+
+      const auto id_parser = bp::char_('a', 'z') > *bp::char_('a', 'z');
+
+      const auto id_set = (id_parser >> '=' >> id_parser)[id_set_action];
+      bp::parse("left=right", id_set);
+      return 0;
+    }
+
+Perhaps surprisingly, this program prints `leftr = ight`!  Why is this?  This
+happens because `id_parser` seems to impose structure, but does not.  `id_set`
+is exactly equivalent to this (comments added to clarify which parts are which
+below).
+
+    const auto id_set = (
+      /*A*/ bp::char_('a', 'z') > /*B*/ *bp::char_('a', 'z') >>
+      /*C*/ '=' >>
+      /*D*/ bp::char_('a', 'z') > /*E*/ *bp::char_('a', 'z')
+    )[id_set_action];
+
+As _Parser_ applies `OP` to this sequence parser, the individual steps are:
+`A` and `B` get merged into a single _std_str_; `C` is ignored, since it
+produces no attribute; and `D` gets merged into the _std_str_ formed earlier
+by `A` and `B`; finally, we have `E`. `E` does not combine with `D`, as `D`
+was already consumed.  `E` also does not combine with the _std_str_ we formed
+from `A`, `B`, and `D`, since we don't combine adjacent containers.  In the
+end, we have a 2-tuple of _std_strs_, in which the first element contains all
+the characters parsed by `A`, `B`, and `D`, and in which the second element
+contains all the characters parsed by `E`.
+
+That's clearly not what we wanted here, though.  How do we get a top-level
+parser that would print `left = right`?  We use a _r_.  The parser used inside
+a _r_ can never combine with any parser(s) outside the _r_.  Instances of a
+rule are inherently separate from all parsers with which they are used,
+whether those parsers are _rs_ or non-_r_ parsers.  So, consider a _r_
+equivalent to the previous `id_parser` above.
+
+    namespace bp = boost::parser;
+    bp::rule<struct id_parser_tag, std::string> id_parser = "identifier";
+    auto const id_parser_def = bp::char_('a', 'z') > *bp::char_('a', 'z');
+    BOOST_PARSER_DEFINE_RULES(id_parser);
+
+Later, we can use it just as we used the previous non-rule version.
+
+    const auto id_set = (id_parser >> '=' >> id_parser)[id_set_action];
+
+This produces the results you might expect, since only the `bp::char_('a',
+'z') > *bp::char_('a', 'z')` parser inside the `id_parser` _r_ is ever
+eligible for combining via `OP`.
+
+
 [heading Alternative parser attribute rules]
 
 The rules for alternative parsers are much simpler.  For an alternative parer
@@ -2211,6 +2302,8 @@ common use cases for _rs_.  Use a _r_ if you want to:
 * fix the attribute type produced by a parser to something other than the
   default;
 
+* control the attributes generated by adjacent sequence parsers;
+
 * create a parser that produces useful diagnostic text;
 
 * create a recursive rule (more on this below);
@@ -2351,6 +2444,10 @@ action if:
 
 The notion of "compatible" is defined in _p_api_.
 
+[heading Controlling the attributes generated]
+
+See the _seq_parser_example_ in the _attr_gen_ section for details.
+
 [heading Creating a parser for better diagnostics]
 
 Each _r_ has associated diagnostic text that _Parser_ can use for failures of

include/boost/parser/config.hpp

@@ -73,6 +73,12 @@
 
 #endif
 
+// Follows logic in boost/config/detail/select_compiler_config.hpp.
+#if defined(__clang__) && !defined(__ibmxl__) && !defined(__CODEGEARC__)
+#elif defined(__GNUC__) && !defined(__ibmxl__)
+#define BOOST_PARSER_GCC
+#endif
+
 #if defined(__cpp_lib_constexpr_algorithms)
 #    define BOOST_PARSER_ALGO_CONSTEXPR constexpr
 #else

include/boost/parser/detail/printing.hpp

@@ -73,10 +73,10 @@ namespace boost { namespace parser { namespace detail {
         std::ostream & os,
         int components = 0);
 
-    template<typename Context, typename ParserTuple>
+    template<typename Context, typename ParserTuple, typename DelimiterParser>
     void print_parser(
         Context const & context,
-        perm_parser<ParserTuple> const & parser,
+        perm_parser<ParserTuple, DelimiterParser> const & parser,
         std::ostream & os,
         int components = 0);
 
@@ -245,6 +245,13 @@ namespace boost { namespace parser { namespace detail {
         std::ostream & os,
         int components = 0);
 
+    template<typename Context>
+    void print_parser(
+        Context const & context,
+        char_set_parser<symb_chars> const & parser,
+        std::ostream & os,
+        int components = 0);
+
     template<typename Context>
     void print_parser(
         Context const & context,
@@ -280,10 +287,14 @@ namespace boost { namespace parser { namespace detail {
         std::ostream & os,
         int components = 0);
 
-    template<typename Context, typename Quotes, typename Escapes>
+    template<
+        typename Context,
+        typename Quotes,
+        typename Escapes,
+        typename CharParser>
     void print_parser(
         Context const & context,
-        quoted_string_parser<Quotes, Escapes> const & parser,
+        quoted_string_parser<Quotes, Escapes, CharParser> const & parser,
         std::ostream & os,
         int components = 0);
 

include/boost/parser/detail/printing_impl.hpp

@@ -63,8 +63,9 @@ namespace boost { namespace parser { namespace detail {
     struct n_aray_parser<or_parser<ParserTuple>> : std::true_type
     {};
 
-    template<typename ParserTuple>
-    struct n_aray_parser<perm_parser<ParserTuple>> : std::true_type
+    template<typename ParserTuple, typename DelimiterParser>
+    struct n_aray_parser<perm_parser<ParserTuple, DelimiterParser>>
+        : std::true_type
     {};
 
     template<
@@ -206,15 +207,23 @@ namespace boost { namespace parser { namespace detail {
             context, parser, os, components, " | ...", " | ");
     }
 
-    template<typename Context, typename ParserTuple>
+    template<typename Context, typename ParserTuple, typename DelimiterParser>
     void print_parser(
         Context const & context,
-        perm_parser<ParserTuple> const & parser,
+        perm_parser<ParserTuple, DelimiterParser> const & parser,
         std::ostream & os,
         int components)
     {
+        if constexpr (!is_nope_v<DelimiterParser>) {
+            os << "delimiter(";
+            detail::print_parser(
+                context, parser.delimiter_parser_, os, components);
+            os << ")[";
+        }
         detail::print_or_like_parser(
             context, parser, os, components, " || ...", " || ");
+        if constexpr (!is_nope_v<DelimiterParser>)
+            os << "]";
     }
 
     template<
@@ -627,6 +636,16 @@ namespace boost { namespace parser { namespace detail {
         os << "punct";
     }
 
+    template<typename Context>
+    void print_parser(
+        Context const & context,
+        char_set_parser<symb_chars> const & parser,
+        std::ostream & os,
+        int components)
+    {
+        os << "symb";
+    }
+
     template<typename Context>
     void print_parser(
         Context const & context,
@@ -695,10 +714,14 @@ namespace boost { namespace parser { namespace detail {
         os << "\"";
     }
 
-    template<typename Context, typename Quotes, typename Escapes>
+    template<
+        typename Context,
+        typename Quotes,
+        typename Escapes,
+        typename CharParser>
     void print_parser(
         Context const & context,
-        quoted_string_parser<Quotes, Escapes> const & parser,
+        quoted_string_parser<Quotes, Escapes, CharParser> const & parser,
         std::ostream & os,
         int components)
     {

include/boost/parser/detail/stl_interfaces/view_adaptor.hpp

@@ -24,8 +24,9 @@
 #define BOOST_PARSER_USE_CPP23_STD_RANGE_ADAPTOR_CLOSURE 0
 #endif
 
-#if !BOOST_PARSER_USE_CPP23_STD_RANGE_ADAPTOR_CLOSURE &&               \
-    BOOST_PARSER_DETAIL_STL_INTERFACES_USE_CONCEPTS && defined(__GNUC__) && 12 <= __GNUC__
+#if !BOOST_PARSER_USE_CPP23_STD_RANGE_ADAPTOR_CLOSURE &&                       \
+    BOOST_PARSER_DETAIL_STL_INTERFACES_USE_CONCEPTS &&                         \
+    defined(BOOST_PARSER_GCC) && 12 <= __GNUC__
 #define BOOST_PARSER_USE_LIBSTDCPP_GCC12_RANGE_ADAPTOR_CLOSURE 1
 #else
 #define BOOST_PARSER_USE_LIBSTDCPP_GCC12_RANGE_ADAPTOR_CLOSURE 0

include/boost/parser/detail/text/detail/all_t.hpp

@@ -42,7 +42,8 @@ namespace boost::parser::detail::text::detail {
     template<typename R>
     constexpr bool view =
 #if BOOST_PARSER_DETAIL_TEXT_USE_CONCEPTS ||                                   \
-    (defined(__cpp_lib_concepts) && (!defined(__GNUC__) || 12 <= __GNUC__))
+    (defined(__cpp_lib_concepts) &&                                            \
+     (!defined(BOOST_PARSER_GCC) || 12 <= __GNUC__))
         std::ranges::view<R>
 #else
         range_<R> && !container_<R> &&

include/boost/parser/parser.hpp

@@ -1015,8 +1015,8 @@ namespace boost { namespace parser {
         template<typename T>
         struct is_perm_p : std::false_type
         {};
-        template<typename T>
-        struct is_perm_p<perm_parser<T>> : std::true_type
+        template<typename T, typename DelimiterParser>
+        struct is_perm_p<perm_parser<T, DelimiterParser>> : std::true_type
         {};
 
         template<typename T>
@@ -3413,10 +3413,14 @@ namespace boost { namespace parser {
         ParserTuple parsers_;
     };
 
-    template<typename ParserTuple>
+    template<typename ParserTuple, typename DelimiterParser>
     struct perm_parser
     {
         constexpr perm_parser(ParserTuple parsers) : parsers_(parsers) {}
+        constexpr perm_parser(
+            ParserTuple parsers, DelimiterParser delimiter_parser) :
+            parsers_(parsers), delimiter_parser_(delimiter_parser)
+        {}
 
 #ifndef BOOST_PARSER_DOXYGEN
 
@@ -3643,7 +3647,19 @@ namespace boost { namespace parser {
             };
             // Use one of the previously-unused parsers to parse one
             // alternative.
+            bool first_iteration = true;
             auto parsed_one = [&](auto) {
+                if constexpr (!detail::is_nope_v<DelimiterParser>) {
+                    if (!first_iteration) {
+                        detail::skip(first, last, skip, flags);
+                        bool local_success = true;
+                        delimiter_parser_.call(
+                            first, last, context, skip, flags, local_success);
+                        if (!local_success)
+                            return false;
+                    }
+                    first_iteration = false;
+                }
                 return (
                     parse_into(
                         Is,
@@ -3667,6 +3683,7 @@ namespace boost { namespace parser {
 #endif
 
         ParserTuple parsers_;
+        DelimiterParser delimiter_parser_;
     };
 
     namespace detail {
@@ -5605,7 +5622,7 @@ namespace boost { namespace parser {
                 return rhs.parser_.prepend(*this);
             } else {
                 return parser::parser_interface{
-                    perm_parser<tuple<parser_type, ParserType2>>{
+                    perm_parser<tuple<parser_type, ParserType2>, detail::nope>{
                         tuple<parser_type, ParserType2>{parser_, rhs.parser_}}};
             }
         }
@@ -6120,23 +6137,23 @@ namespace boost { namespace parser {
         }
     }
 
-    template<typename ParserTuple>
+    template<typename ParserTuple, typename DelimiterParser>
     template<typename Parser>
-    constexpr auto perm_parser<ParserTuple>::prepend(
+    constexpr auto perm_parser<ParserTuple, DelimiterParser>::prepend(
         parser_interface<Parser> parser) const noexcept
     {
         // If you're seeing this as a compile- or run-time failure, you've
         // tried to put an eps parser in a permutation-parser, such as "eps ||
         // int_".
         BOOST_PARSER_ASSERT(!detail::is_eps_p<Parser>{});
-        return parser_interface{perm_parser<decltype(detail::hl::prepend(
-            parsers_, parser.parser_))>{
-            detail::hl::prepend(parsers_, parser.parser_)}};
+        return parser_interface{perm_parser<
+            decltype(detail::hl::prepend(parsers_, parser.parser_)),
+            detail::nope>{detail::hl::prepend(parsers_, parser.parser_)}};
     }
 
-    template<typename ParserTuple>
+    template<typename ParserTuple, typename DelimiterParser>
     template<typename Parser>
-    constexpr auto perm_parser<ParserTuple>::append(
+    constexpr auto perm_parser<ParserTuple, DelimiterParser>::append(
         parser_interface<Parser> parser) const noexcept
     {
         // If you're seeing this as a compile- or run-time failure, you've
@@ -6144,13 +6161,14 @@ namespace boost { namespace parser {
         // || eps".
         BOOST_PARSER_ASSERT(!detail::is_eps_p<Parser>{});
         if constexpr (detail::is_perm_p<Parser>{}) {
-            return parser_interface{perm_parser<decltype(detail::hl::concat(
-                parsers_, parser.parser_.parsers_))>{
+            return parser_interface{perm_parser<
+                decltype(detail::hl::concat(parsers_, parser.parser_.parsers_)),
+                detail::nope>{
                 detail::hl::concat(parsers_, parser.parser_.parsers_)}};
         } else {
-            return parser_interface{perm_parser<decltype(detail::hl::append(
-                parsers_, parser.parser_))>{
-                detail::hl::append(parsers_, parser.parser_)}};
+            return parser_interface{perm_parser<
+                decltype(detail::hl::append(parsers_, parser.parser_)),
+                detail::nope>{detail::hl::append(parsers_, parser.parser_)}};
         }
     }
 
@@ -6305,6 +6323,36 @@ namespace boost { namespace parser {
         return repeat_directive<MinType, MaxType>{min_, max_};
     }
 
+    /** A directive that represents a `perm_parser`, where the items parsed
+        are delimited by `DelimiterParser`,
+        (e.g. `delimiter(delimter_parser)[some_perm_parser]`).  This directive
+        only applies to `perm_parser`s. */
+    template<typename DelimiterParser>
+    struct delimiter_directive
+    {
+        template<typename ParserTuple, typename DelimiterParser2>
+        constexpr auto operator[](
+            parser_interface<perm_parser<ParserTuple, DelimiterParser2>> rhs)
+            const noexcept
+        {
+            using parser_type = perm_parser<ParserTuple, DelimiterParser>;
+            return parser_interface{
+                parser_type{rhs.parser_.parsers_, delimiter_parser_}};
+        }
+
+        DelimiterParser delimiter_parser_;
+    };
+
+    /** Returns a `delimiter_directive` whose `operator[]` returns a
+        `perm_parser`, where the items parsed are delimited by
+        `delimiter_parser`. */
+    template<typename DelimiterParser>
+    constexpr delimiter_directive<DelimiterParser>
+    delimiter(parser_interface<DelimiterParser> delimiter_parser) noexcept
+    {
+        return delimiter_directive<DelimiterParser>{delimiter_parser.parser_};
+    }
+
     /** Represents a skip parser as a directive.  When used without a skip
         parser, e.g. `skip[parser_in_which_to_do_skipping]`, the skipper for
         the entire parse is used.  When given another parser, e.g.
@@ -7252,7 +7300,7 @@ namespace boost { namespace parser {
         return parser_interface{string_parser(str)};
     }
 
-    template<typename Quotes, typename Escapes>
+    template<typename Quotes, typename Escapes, typename CharParser>
     struct quoted_string_parser
     {
         constexpr quoted_string_parser() : chs_(), ch_('"') {}
@@ -7265,7 +7313,11 @@ namespace boost { namespace parser {
             typename Enable =
                 std::enable_if_t<detail::is_parsable_range_like_v<R>>>
 #endif
-        constexpr quoted_string_parser(R && r) : chs_((R &&) r), ch_(0)
+        constexpr quoted_string_parser(
+            R && r,
+            parser_interface<CharParser> char_p =
+                parser_interface{CharParser()}) :
+            chs_((R &&)r), char_p_(char_p), ch_(0)
         {
             BOOST_PARSER_DEBUG_ASSERT(r.begin() != r.end());
         }
@@ -7278,16 +7330,29 @@ namespace boost { namespace parser {
             typename Enable =
                 std::enable_if_t<detail::is_parsable_range_like_v<R>>>
 #endif
-        constexpr quoted_string_parser(R && r, Escapes escapes) :
-            chs_((R &&) r), escapes_(escapes), ch_(0)
+        constexpr quoted_string_parser(
+            R && r,
+            Escapes escapes,
+            parser_interface<CharParser> char_p =
+                parser_interface{CharParser()}) :
+            chs_((R &&)r), escapes_(escapes), char_p_(char_p), ch_(0)
         {
             BOOST_PARSER_DEBUG_ASSERT(r.begin() != r.end());
         }
 
-        constexpr quoted_string_parser(char32_t cp) : chs_(), ch_(cp) {}
+        constexpr quoted_string_parser(
+            char32_t cp,
+            parser_interface<CharParser> char_p =
+                parser_interface{CharParser()}) :
+            chs_(), char_p_(char_p), ch_(cp)
+        {}
 
-        constexpr quoted_string_parser(char32_t cp, Escapes escapes) :
-            chs_(), escapes_(escapes), ch_(cp)
+        constexpr quoted_string_parser(
+            char32_t cp,
+            Escapes escapes,
+            parser_interface<CharParser> char_p =
+                parser_interface{CharParser()}) :
+            chs_(), escapes_(escapes), char_p_(char_p), ch_(cp)
         {}
 
         template<
@@ -7376,11 +7441,11 @@ namespace boost { namespace parser {
             auto make_parser = [&]() {
                 if constexpr (detail::is_nope_v<Escapes>) {
                     return *((lit('\\') >> back_delim) |
-                             (char_ - back_delim))[append] > ch;
+                             (char_p_ - back_delim))[append] > ch;
                 } else {
                     return *((lit('\\') >> back_delim)[append] |
                              (lit('\\') >> parser_interface(escapes_))[append] |
-                             (char_ - back_delim)[append]) > ch;
+                             (char_p_ - back_delim)[append]) > ch;
                 }
             };
 
@@ -7402,15 +7467,17 @@ namespace boost { namespace parser {
         /** Returns a `parser_interface` containing a `quoted_string_parser`
             that uses `x` as its quotation marks. */
 #if BOOST_PARSER_USE_CONCEPTS
-        template<typename T>
+        template<typename T, typename Parser = char_parser<detail::nope>>
             requires(!parsable_range_like<T>)
 #else
         template<
             typename T,
+            typename Parser = char_parser<detail::nope>,
             typename Enable =
                 std::enable_if_t<!detail::is_parsable_range_like_v<T>>>
 #endif
-        constexpr auto operator()(T x) const noexcept
+        constexpr auto
+        operator()(T x, parser_interface<Parser> char_p = char_) const noexcept
         {
             if constexpr (!detail::is_nope_v<Quotes>) {
                 BOOST_PARSER_ASSERT(
@@ -7419,7 +7486,9 @@ namespace boost { namespace parser {
                      "quoted_string, like 'quoted_string('\"')('\\'')'.  Quit "
                      "it!'"));
             }
-            return parser_interface(quoted_string_parser(std::move(x)));
+            return parser_interface(
+                quoted_string_parser<detail::nope, detail::nope, Parser>(
+                    std::move(x), char_p));
         }
 
         /** Returns a `parser_interface` containing a `quoted_string_parser`
@@ -7430,14 +7499,18 @@ namespace boost { namespace parser {
             character begin matched is directly compared to the elements of
             `r`. */
 #if BOOST_PARSER_USE_CONCEPTS
-        template<parsable_range_like R>
+        template<
+            parsable_range_like R,
+            typename Parser = char_parser<detail::nope>>
 #else
         template<
             typename R,
+            typename Parser = char_parser<detail::nope>,
             typename Enable =
                 std::enable_if_t<detail::is_parsable_range_like_v<R>>>
 #endif
-        constexpr auto operator()(R && r) const noexcept
+        constexpr auto operator()(
+            R && r, parser_interface<Parser> char_p = char_) const noexcept
         {
             BOOST_PARSER_ASSERT(((
                 !std::is_rvalue_reference_v<R &&> ||
@@ -7453,10 +7526,14 @@ namespace boost { namespace parser {
                      "'quoted_string(char-range)(char-range)'.  Quit it!'"));
             }
             return parser_interface(
-                quoted_string_parser<decltype(BOOST_PARSER_SUBRANGE(
-                    detail::make_view_begin(r), detail::make_view_end(r)))>(
+                quoted_string_parser<
+                    decltype(BOOST_PARSER_SUBRANGE(
+                        detail::make_view_begin(r), detail::make_view_end(r))),
+                    detail::nope,
+                    Parser>(
                     BOOST_PARSER_SUBRANGE(
-                        detail::make_view_begin(r), detail::make_view_end(r))));
+                        detail::make_view_begin(r), detail::make_view_end(r)),
+                    char_p));
         }
 
         /** Returns a `parser_interface` containing a `quoted_string_parser`
@@ -7465,16 +7542,23 @@ namespace boost { namespace parser {
             sequence, and what character(s) each escape sequence represents.
             Note that `"\\"` and `"\ch"` are always valid escape sequences. */
 #if BOOST_PARSER_USE_CONCEPTS
-        template<typename T, typename U>
+        template<
+            typename T,
+            typename U,
+            typename Parser = char_parser<detail::nope>>
             requires(!parsable_range_like<T>)
 #else
         template<
             typename T,
             typename U,
+            typename Parser = char_parser<detail::nope>,
             typename Enable =
                 std::enable_if_t<!detail::is_parsable_range_like_v<T>>>
 #endif
-        auto operator()(T x, symbols<U> const & escapes) const noexcept
+        auto operator()(
+            T x,
+            symbols<U> const & escapes,
+            parser_interface<Parser> char_p = char_) const noexcept
         {
             if constexpr (!detail::is_nope_v<Quotes>) {
                 BOOST_PARSER_ASSERT(
@@ -7484,8 +7568,9 @@ namespace boost { namespace parser {
                      "it!'"));
             }
             auto symbols = symbol_parser(escapes.parser_);
-            auto parser = quoted_string_parser<detail::nope, decltype(symbols)>(
-                char32_t(x), symbols);
+            auto parser =
+                quoted_string_parser<detail::nope, decltype(symbols), Parser>(
+                    char32_t(x), symbols, char_p);
             return parser_interface(parser);
         }
 
@@ -7500,15 +7585,22 @@ namespace boost { namespace parser {
             escape sequence represents.  Note that `"\\"` and `"\ch"` are
             always valid escape sequences. */
 #if BOOST_PARSER_USE_CONCEPTS
-        template<parsable_range_like R, typename T>
+        template<
+            parsable_range_like R,
+            typename T,
+            typename Parser = char_parser<detail::nope>>
 #else
         template<
             typename R,
             typename T,
+            typename Parser = char_parser<detail::nope>,
             typename Enable =
                 std::enable_if_t<detail::is_parsable_range_like_v<R>>>
 #endif
-        auto operator()(R && r, symbols<T> const & escapes) const noexcept
+        auto operator()(
+            R && r,
+            symbols<T> const & escapes,
+            parser_interface<Parser> char_p = char_) const noexcept
         {
             BOOST_PARSER_ASSERT(((
                 !std::is_rvalue_reference_v<R &&> ||
@@ -7526,14 +7618,16 @@ namespace boost { namespace parser {
             auto symbols = symbol_parser(escapes.parser_);
             auto quotes = BOOST_PARSER_SUBRANGE(
                 detail::make_view_begin(r), detail::make_view_end(r));
-            auto parser =
-                quoted_string_parser<decltype(quotes), decltype(symbols)>(
-                    quotes, symbols);
+            auto parser = quoted_string_parser<
+                decltype(quotes),
+                decltype(symbols),
+                Parser>(quotes, symbols, char_p);
             return parser_interface(parser);
         }
 
         Quotes chs_;
         Escapes escapes_;
+        parser_interface<CharParser> char_p_;
         char32_t ch_;
     };
 
@@ -7717,12 +7811,18 @@ namespace boost { namespace parser {
         control;
 
     /** The punctuation character parser.  Matches the full set of Unicode
-        punctuation clases (specifically, "Pc", "Pd", "Pe", "Pf", "Pi", "Ps",
+        punctuation classes (specifically, "Pc", "Pd", "Pe", "Pf", "Pi", "Ps",
         and "Po"). */
     inline BOOST_PARSER_ALGO_CONSTEXPR
         parser_interface<char_set_parser<detail::punct_chars>>
             punct;
 
+    /** The symbol character parser.  Matches the full set of Unicode
+        symbol classes (specifically, "Sc", "Sk", "Sm", and "So"). */
+    inline BOOST_PARSER_ALGO_CONSTEXPR
+        parser_interface<char_set_parser<detail::symb_chars>>
+            symb;
+
     /** The lower case character parser.  Matches the full set of Unicode
         lower case code points (class "Ll"). */
     inline BOOST_PARSER_ALGO_CONSTEXPR
@@ -9443,9 +9543,6 @@ namespace boost { namespace parser {
         template<typename... Args>
         constexpr void static_assert_merge_attributes(tuple<Args...> parsers)
         {
-            // This code chokes older GCCs.  I can't figure out why, and this
-            // is an optional check, so I'm disabling it for those GCCs.
-#if !defined(__GNUC__) || 13 <= __GNUC__
             using context_t = parse_context<
                 false,
                 false,
@@ -9492,7 +9589,7 @@ namespace boost { namespace parser {
                         "type as one of the others.");
                     if constexpr (!std::is_same_v<t, first_t>) {
                         [[maybe_unused]] detail::print_type<tuple<Args...>>
-                            tuple_types;
+                            tuple_types(parsers);
                         [[maybe_unused]] detail::print_type<all_types>
                             attribute_types;
                         [[maybe_unused]] detail::print_type<first_t> first_type;
@@ -9500,7 +9597,6 @@ namespace boost { namespace parser {
                     }
                 }
             });
-#endif
         }
     }
 }}

include/boost/parser/parser_fwd.hpp

@@ -143,6 +143,8 @@ namespace boost { namespace parser {
 
         struct punct_chars
         {};
+        struct symb_chars
+        {};
         struct lower_case_chars
         {};
         struct upper_case_chars
@@ -207,7 +209,7 @@ namespace boost { namespace parser {
         `ParserTuple`, not the order of the parsers' matches.  It is an error
         to specialize `perm_parser` with a `ParserTuple` template parameter
         that includes an `eps_parser`. */
-    template<typename ParserTuple>
+    template<typename ParserTuple, typename DelimiterParser>
     struct perm_parser;
 
     /** Applies each parser in `ParserTuple`, in order.  The parse succeeds
@@ -380,7 +382,10 @@ namespace boost { namespace parser {
 
     /** Matches a string delimited by quotation marks; produces a
         `std::string` attribute. */
-    template<typename Quotes = detail::nope, typename Escapes = detail::nope>
+    template<
+        typename Quotes = detail::nope,
+        typename Escapes = detail::nope,
+        typename CharParser = char_parser<detail::nope>>
     struct quoted_string_parser;
 
     /** Matches an end-of-line (`NewlinesOnly == true`), whitespace

include/boost/parser/transform_replace.hpp

@@ -4,7 +4,8 @@
 #include <boost/parser/replace.hpp>
 
 #if (!defined(_MSC_VER) || BOOST_PARSER_USE_CONCEPTS) &&                       \
-    (!defined(__GNUC__) || 12 <= __GNUC__ || !BOOST_PARSER_USE_CONCEPTS)
+    (!defined(BOOST_PARSER_GCC) || 12 <= __GNUC__ ||                           \
+     !BOOST_PARSER_USE_CONCEPTS)
 
 
 namespace boost::parser {

include/boost/parser/tuple.hpp

@@ -128,7 +128,7 @@ namespace boost { namespace parser {
         /** A literal that can be used to concisely name `parser::llong`
             integral constants. */
         template<char... chars>
-        constexpr auto operator"" _c()
+        constexpr auto operator""_c()
         {
             constexpr long long n =
                 detail::parse_llong<sizeof...(chars)>({chars...});
@@ -185,14 +185,10 @@ namespace boost { namespace parser {
             template<typename T>
             operator T() const && noexcept
             {
-#if defined(__GNUC__) && __GNUC__ < 13
                 // Yuck.
                 std::remove_reference_t<T> * ptr = nullptr;
                 ptr += 1; // warning mitigation
                 return *ptr;
-#else
-                return std::declval<T>();
-#endif
             }
         };
 

test/github_issues.cpp

@@ -237,6 +237,27 @@ void github_issue_125()
     }
 }
 
+void github_issue_209()
+{
+    namespace bp = boost::parser;
+
+    BOOST_TEST(std::is_sorted(
+        std::begin(bp::detail::char_set<detail::punct_chars>::chars),
+        std::end(bp::detail::char_set<detail::punct_chars>::chars)));
+
+    BOOST_TEST(std::is_sorted(
+        std::begin(bp::detail::char_set<detail::symb_chars>::chars),
+        std::end(bp::detail::char_set<detail::symb_chars>::chars)));
+
+    BOOST_TEST(std::is_sorted(
+        std::begin(bp::detail::char_set<detail::lower_case_chars>::chars),
+        std::end(bp::detail::char_set<detail::lower_case_chars>::chars)));
+
+    BOOST_TEST(std::is_sorted(
+        std::begin(bp::detail::char_set<detail::upper_case_chars>::chars),
+        std::end(bp::detail::char_set<detail::upper_case_chars>::chars)));
+}
+
 
 int main()
 {
@@ -246,5 +267,6 @@ int main()
     github_issue_78();
     github_issue_90();
     github_issue_125();
+    github_issue_209();
     return boost::report_errors();
 }

test/parser.cpp

@@ -2753,6 +2753,16 @@ int main()
         BOOST_TEST(result == std::vector<uint32_t>({0x21, 0xfda}));
     }
 
+    // symb_
+    {
+        auto parser = +symb;
+
+        std::u32string str = U"$^\u20AC!\u2194\u220F\U0001D7C6b\u2280\U0001FACE\U0001039F";
+        std::vector<uint32_t> result;
+        BOOST_TEST(parse(str, parser, char_ - symb, result));
+        BOOST_TEST(result == std::vector<uint32_t>({U'$', U'^', 0x20AC, 0x2194, 0x220F, 0x2280, 0x1FACE}));
+    }
+
     // lower_
     {
         auto parser = +lower;

test/parser_perm.cpp

@@ -88,5 +88,66 @@ int main()
         }
     }
 
-return boost::report_errors();
+    {
+        using namespace bp::literals;
+        constexpr auto parser =
+            bp::delimiter(','_l)[bp::int_ || bp::string("foo") || bp::char_('g')];
+
+        {
+            auto result = bp::parse("42 foo g", parser, bp::ws);
+            BOOST_TEST(!result);
+            result = bp::parse("42, foo ,g", parser, bp::ws);
+            BOOST_TEST(result);
+            BOOST_TEST(
+                *result ==
+                (bp::tuple<int, std::string, double>(42, "foo"s, 'g')));
+        }
+        {
+            auto result = bp::parse(",42, g, foo", parser, bp::ws);
+            BOOST_TEST(!result);
+            result = bp::parse("42, g , foo", parser, bp::ws);
+            BOOST_TEST(result);
+            BOOST_TEST(
+                *result ==
+                (bp::tuple<int, std::string, double>(42, "foo"s, 'g')));
+        }
+        {
+            auto result = bp::parse("foo, 42, g,", parser, bp::ws);
+            BOOST_TEST(!result);
+            result = bp::parse("foo, 42, g", parser, bp::ws);
+            BOOST_TEST(result);
+            BOOST_TEST(
+                *result ==
+                (bp::tuple<int, std::string, double>(42, "foo"s, 'g')));
+        }
+        {
+            auto result = bp::parse("foo g 42", parser, bp::ws);
+            BOOST_TEST(!result);
+            result = bp::parse("foo, g, 42", parser, bp::ws);
+            BOOST_TEST(result);
+            BOOST_TEST(
+                *result ==
+                (bp::tuple<int, std::string, double>(42, "foo"s, 'g')));
+        }
+        {
+            auto result = bp::parse("g foo 42", parser, bp::ws);
+            BOOST_TEST(!result);
+            result = bp::parse("g ,foo ,42", parser, bp::ws);
+            BOOST_TEST(result);
+            BOOST_TEST(
+                *result ==
+                (bp::tuple<int, std::string, double>(42, "foo"s, 'g')));
+        }
+        {
+            auto result = bp::parse("g 42 foo", parser, bp::ws);
+            BOOST_TEST(!result);
+            result = bp::parse("g , 42 , foo", parser, bp::ws);
+            BOOST_TEST(result);
+            BOOST_TEST(
+                *result ==
+                (bp::tuple<int, std::string, double>(42, "foo"s, 'g')));
+        }
+    }
+
+    return boost::report_errors();
 }

test/parser_quoted_string.cpp

@@ -49,7 +49,7 @@ int main()
     }
 }
 
-// different_char
+// different_quote
 {
     constexpr auto parser = bp::quoted_string('\'');
 
@@ -75,9 +75,18 @@ int main()
         BOOST_TEST(result);
         BOOST_TEST(*result == "'foo'");
     }
+
+    {
+        constexpr auto parser = bp::quoted_string('\'', bp::char_("g\t"));
+
+        auto result = bp::parse(R"('\'ggg\'')", parser, bp::ws);
+        BOOST_TEST(result);
+        BOOST_TEST(*result == "'ggg'");
+        BOOST_TEST(!bp::parse(R"('\'fff\'')", parser, bp::ws));
+    }
 }
 
-// different_char_with_escapes
+// different_quote_with_escapes
 {
     {
         auto parser = bp::quoted_string('\'', cu_escapes);
@@ -119,6 +128,58 @@ int main()
     }
 }
 
+// different_quote_with_escapes_and_char_p
+{
+    {
+        auto parser = bp::quoted_string('\'', cu_escapes, bp::char_("g\t"));
+
+        {
+            auto result = bp::parse("", parser, bp::ws);
+            BOOST_TEST(!result);
+        }
+
+        {
+            auto result = bp::parse("'ggg'", parser, bp::ws);
+            BOOST_TEST(result);
+        }
+
+        {
+            auto result = bp::parse("'fff'", parser, bp::ws);
+            BOOST_TEST(!result);
+        }
+
+        {
+            auto result = bp::parse(R"('ggg\t')", parser, bp::ws);
+            BOOST_TEST(result);
+            BOOST_TEST(*result == "ggg\t");
+        }
+
+        {
+            auto result = bp::parse(R"('ggg\g')", parser, bp::ws);
+            BOOST_TEST(!result);
+        }
+    }
+    {
+        auto parser = bp::quoted_string('\'', cp_escapes);
+
+        {
+            auto result = bp::parse("", parser, bp::ws);
+            BOOST_TEST(!result);
+        }
+
+        {
+            auto result = bp::parse(R"('\tggg')", parser, bp::ws);
+            BOOST_TEST(result);
+            BOOST_TEST(*result == "\tggg");
+        }
+
+        {
+            auto result = bp::parse(R"('g\ggg')", parser, bp::ws);
+            BOOST_TEST(!result);
+        }
+    }
+}
+
 // char_set
 {
     constexpr auto parser = bp::quoted_string("'\"");
@@ -171,6 +232,15 @@ int main()
         // character.
         BOOST_TEST(!bp::parse(R"("\'foo")", parser, bp::ws));
     }
+
+    {
+        constexpr auto parser = bp::quoted_string("'\"", bp::char_("g"));
+
+        auto result = bp::parse(R"('\'ggg\'')", parser, bp::ws);
+        BOOST_TEST(result);
+        BOOST_TEST(*result == "'ggg'");
+        BOOST_TEST(!bp::parse(R"('\'fff\'')", parser, bp::ws));
+    }
 }
 
 // char_set_with_escapes
@@ -233,6 +303,15 @@ int main()
             BOOST_TEST(!result);
         }
     }
+
+    {
+        auto parser = bp::quoted_string("'\"", cu_escapes, bp::char_("g"));
+
+        auto result = bp::parse(R"('\'ggg\'')", parser, bp::ws);
+        BOOST_TEST(result);
+        BOOST_TEST(*result == "'ggg'");
+        BOOST_TEST(!bp::parse(R"('\'fff\'')", parser, bp::ws));
+    }
 }
 
 // doc_examples
@@ -279,6 +358,16 @@ int main()
     assert(result5);
     std::cout << *result5 << "\n"; // Prints (with a CRLF newline): some text
     //]
+
+    //[ quoted_string_example_6
+    auto result6 = bp::parse(
+        "'some text'", bp::quoted_string("'\"", bp::char_('g')), bp::ws);
+    assert(!result6);
+    result6 =
+        bp::parse("'gggg'", bp::quoted_string("'\"", bp::char_('g')), bp::ws);
+    assert(result6);
+    std::cout << *result6 << "\n"; // Prints: gggg
+    //]
 }
 
 return boost::report_errors();