Re: Design/structure X3 parser more like Qi parser

On 12/20/2016 03:02 AM, Sandro Pirkwieser wrote:
[snip]
 >> Hence, Sandro, could you provide some use-case for this feature?
 >

 > The main topic (aside the more recent performance
 > analysis) was the question to "better" (at least in my
 > view) encapsulate an X3 parser than with namespaces,
 > i.e. more in the style of a Qi parser. There a larger,
 > more complex parser can be built by incorporating several
 > smaller ones as class members, yet retaining a nice
 > encapsulation. Something that does not seem possible with
 > X3.

 > An alternative, using parsers defined in functions (as for
 > make_csv_parser), is not always an option though, as such
 > parsers cannot be recursive (rule A is defined via rule B
 > and vice versa).

 > Your prototype allows using BOOST_SPIRIT_DEFINE inside a
 > struct, hence would definitely come closer to the Qi like
 > encapsulation.

Hi, Sandro.

The code:

https://github.com/cppljevans/spirit/blob/get_rhs/workbench/x3/csv_parser/x3_crtp.hpp

implements the csv_parser pretty much as encapsulated as the
qi versiion at:

https://github.com/cppljevans/spirit/blob/get_rhs/workbench/x3/csv_parser/qi.hpp

Unfortunately, the runtime suffers the same slowdown as the
x3 version.  The timings here:

https://github.com/cppljevans/spirit/blob/get_rhs/workbench/x3/csv_parser/means.out

where produced by:

   make -k USE_MACRO_INCLUDE=1 means

Those timings, and looking at the code, indicates the
slowdown is due to the attribute transforms done by:

https://github.com/cppljevans/spirit/blob/get_rhs/include/boost/spirit/home/x3/nonterminal/detail/rule.hpp#L310

That's because, as shown here:

https://github.com/cppljevans/spirit/blob/get_rhs/workbench/x3/csv_parser/means.out#L5

and here:

https://github.com/cppljevans/spirit/blob/get_rhs/workbench/x3/csv_parser/means.out#L7

the time is *less* than the time for the qi method here:

https://github.com/cppljevans/spirit/blob/get_rhs/workbench/x3/csv_parser/means.out#L1

OTOH, the lines where XRULE0 occurs (meaning the attribute
transform is done within the rule_definition::parse
function), the times are more than the qi method.

 > I haven't tried it yet, but is it also possible to use
 > parameters, like the field separator fort the CSV parser?
 > As it can't be given at the time of construction, as for
 > make_csv_parser(), one could probably use x3::with<>.

This is done here:

https://github.com/cppljevans/spirit/blob/get_rhs/workbench/x3/csv_parser/x3_crtp.hpp#L28

 > Best regards,
 > Sandro
 >
HTH.

-regards,
Larry



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