Re: [Boost-users] [OT] Interested in good (fast, robust) boost-based JSON API

1 Dec 2009

      On Tue, Dec 1, 2009 at 4:03 PM, Dominique Devienne <ddevienne@gmail.com> wrote:
...
On Tue, Dec 1, 2009 at 4:42 PM, OvermindDL1 <overminddl1@gmail.com> wrote:
...
On Tue, Dec 1, 2009 at 12:44 PM, Dominique Devienne <ddevienne@gmail.com> wrote:
...
Would you mind sharing the grammar and parser in
http://boost-spirit.com/repository/grammars/show_contents.php perhaps,
with a Boost like license?
I did post the old version (that worked on a much older Spirit trunk,
not the current release) on the Spirit list a long while ago.  I meant
to update it and give it a better interface and a karma output too
then give it to Spirit as an example, I just need to get motivated to
give the little amount of time that I have available, to it.  ;-)
I'm still interested in just the Spirit 2.1 grammar for JSON if you
don't mind, to implement just an event-based SAX-like parser for JSON.
I'd happily use a full reading and writing impl, but I'd be happy with
just the grammar for now.
...
(*hint* poke me to get it done, random emails, that helps a ton).
Consider yourself poked ;) Thanks, --DD
Ew... I really did make this back when I was still learning Spirit, I
can make it better now for sure...

Just to show you the simple grammar for JSON parsing though, I was
trying to follow the Spec *to*the*letter*, and this is what I came up
with (which I definitely need to redesign for the modern Spirit2.1).
As stated, this is for the old trunk Spirit so it might not compile
with the current version...

		struct JSON_grammar : qi::grammar<typename
StringType::const_iterator, Value(),
boost::spirit::ODL1_JSON_Char_Class::space_type>
		{
			JSON_grammar() : JSON_grammar::base_type(ValueRule)
			{
				using qi::on_error;
				using qi::fail;
				using qi::debug;
				using qi::lit;
				using qi::raw;
				using spirit::double_;
				using namespace boost::spirit::ODL1_JSON_Char_Class;

				ValueRule
					=(	lit("null")						[spirit::_val = null_const()]
					|	lit("false")					[spirit::_val = false_const()]
					|	lit("true")						[spirit::_val = true_const()]
					|	double_							[spirit::_val = spirit::_1]
					|	StringRule						[spirit::_val = spirit::_1]
					|	ArrayRule						[spirit::_val = spirit::_1]
					|	ObjectRule						[spirit::_val = spirit::_1]
					);

				StringRule
					=	char_('"')						[spirit::_val = ""]
					>>	*(
						(char_-(char_("\"\\")|cntrl))	[spirit::_val += spirit::_1]
						|(lit('\\')	>>
							(lit('b')					[spirit::_val += '\b']
							|lit('f')					[spirit::_val += '\f']
							|lit('n')					[spirit::_val += '\n']
							|lit('r')					[spirit::_val += '\r']
							|lit('t')					[spirit::_val += '\t']
							|	(	lit('u')
									>>	hex4			[spirit::_val += spirit::_1]
								)
							|char_						[spirit::_val += spirit::_1]
							)
						)
					)
					>>	'"'
					;

				ArrayRule
					%=	'['
					>>	ValueRule % ','
					>>	']'
					;

				ObjectRule
					%=	'{'
					>>	(StringRule >> ':' >> ValueRule) % ','
					>>	'}'
					;

				ValueRule.name("ValueRule");
				StringRule.name("StringRule");
				ArrayRule.name("ArrayRule");
				ObjectRule.name("ObjectRule");

				on_error<fail>
					(
					ValueRule
					, onerror()
					);

#ifdef ODL1_JSON_DEBUG
				debug(ValueRule);
				debug(StringRule);
				debug(ArrayRule);
				debug(ObjectRule);
#endif // ODL1_JSON_DEBUG
			}

			qi::rule<typename StringType::const_iterator, Value(),
boost::spirit::ODL1_JSON_Char_Class::space_type> ValueRule;
			qi::rule<typename StringType::const_iterator, StringType()> StringRule;
			qi::rule<typename StringType::const_iterator, ValueArray(),
boost::spirit::ODL1_JSON_Char_Class::space_type> ArrayRule;
			qi::rule<typename StringType::const_iterator, ValueObject(),
boost::spirit::ODL1_JSON_Char_Class::space_type> ObjectRule;
			qi::uint_parser<unsigned, 16, 4, 4> hex4;
		};

Yuck, that really is ugly...  That should show you how it works, but
yeah, wait until I can actually redesign it.  I do not have time right
this moment (keep poking me and I may have this odd hour here or
there), but should have some dedicated time late next week, just keep
on poking/emailing me.