What you have sounds good to me. IMO minimum viable product would be an island
grammar (meaning you can have any characters outside a ${} expression) and
inside would support an attribute name. Next steps could be nested expressions
and/or support for functions, added piecemeal as the contributor sees fit. I
wasn't involved in the early development of the EL grammar, so maybe someone
who was has some thoughts on a natural evolution.
Regards,
Matt
> On May 4, 2017, at 11:00 AM, Andrew Christianson
> <[email protected]> wrote:
>
> My bad, what does the sketch of the plan *look like*?
>
> -Andy
> ________________________________________
> From: Andrew Christianson
> Sent: Thursday, May 4, 2017 10:59:07 AM
> To: [email protected]
> Subject: Re: MiNiFi C++ Expression Language
>
> What does the sketch of the plan to do the separate implementation? Write a
> flex/bison grammar, hook it into the cmake build, and start using it? Any
> constraints on features or syntax that this separate implementation must
> support?
>
> -Andy
> ________________________________________
> From: Matt Burgess <[email protected]>
> Sent: Thursday, May 4, 2017 9:37:34 AM
> To: [email protected]
> Subject: Re: MiNiFi C++ Expression Language
>
> No plans that I know of. In the meantime, EL support for MiNiFi is kind of
> held hostage, so maybe the separate implementation is more viable in the
> nearer term. If/When the ANTLR4 upgrade happens, we could replace whatever
> exists by then with the cross-platform ANTLR target generation, and test the
> whole kit and caboodle.
>
> Anyone out there familiar with the aforementioned tools (or willing to
> hand-roll one)? What do you think about this "EL bootstrapping" approach?
>
> Thanks,
> Matt
>
>> On May 4, 2017, at 9:22 AM, Andrew Christianson
>> <[email protected]> wrote:
>>
>> Got it. So the crux of the problem is porting from v3 to v4, plus the added
>> uncertainty of the C++ v4 target.
>>
>> I'm assuming that NiFi wants to eventually get onto v4 anyway. If that's the
>> case, then porting to v4 is probably the ticket. Are there any concrete
>> plans to do so in the NiFi mother project yet?
>>
>> -Andy
>> ________________________________________
>> From: Matt Burgess <[email protected]>
>> Sent: Thursday, May 4, 2017 9:18:00 AM
>> To: [email protected]
>> Subject: Re: MiNiFi C++ Expression Language
>>
>> Correct, the current NiFi EL grammar is ANTLR3.
>>
>>
>>> On May 4, 2017, at 9:12 AM, Andrew Christianson
>>> <[email protected]> wrote:
>>>
>>> Do I understand correctly that NiFi is currently using ANTLRv3?
>>> ________________________________________
>>> From: Matt Burgess <[email protected]>
>>> Sent: Thursday, May 4, 2017 9:05:35 AM
>>> To: [email protected]
>>> Subject: Re: MiNiFi C++ Expression Language
>>>
>>> I haven't used Flex/Bison since a trivial example in college, so I'm not
>>> sure about the LOE for getting that set up, maybe there's a Maven-built
>>> project out there that we could look at for inspiration, but that seems
>>> unlikely :)
>>>
>>> An ANTLR4 refactor (assuming the C++ target is in good shape) would give us
>>> NiFi/MiNiFi EL compatibility (and full-featured EL support in MiNiFi C++),
>>> but we'd have to accept the risks of introducing bugs, regressions, etc. as
>>> a result of the refactor. Basically we'd just need to test the heck out of
>>> it on all platforms, which isn't a bad thing but adds to the LOE for the
>>> ANTLR4 upgrade, versus a smaller testing "surface" for incremental
>>> development of a C/C++ based grammar.
>>>
>>>
>>> On May 4, 2017, at 8:51 AM, Andrew Christianson
>>> <[email protected]> wrote:
>>>
>>>>> I tried a quick ANTLR4 upgrade myself, it's indeed a big job to refactor
>>>>> the existing grammar. Since the source and target for MiNiFi C++ is,
>>>>> well, C++, an alternative could be to use lex/yacc (Flex/Bison) [1],
>>>>> Lemon [2], Ragel [3], etc. The downside is maintaining two grammars, but
>>>>> we are doing that with all the MiNiFi components already. The upside is
>>>>> being able to support EL incrementally as the grammar is developed. What
>>>>> do you think?
>>>>
>>>> This seems like a pragmatic approach. What's the level-of-effort required
>>>> to do the initial grammar port and set up the build tooling? Less than
>>>> refactoring for ANTLR4? I'm not as familiar with the EL grammar situation.
>>>>
>>>> -Andy
>>>> ________________________________________
>>>> From: Matt Burgess <[email protected]>
>>>> Sent: Thursday, May 4, 2017 8:46:20 AM
>>>> To: [email protected]
>>>> Subject: Re: MiNiFi C++ Expression Language
>>>>
>>>> I tried a quick ANTLR4 upgrade myself, it's indeed a big job to refactor
>>>> the existing grammar. Since the source and target for MiNiFi C++ is, well,
>>>> C++, an alternative could be to use lex/yacc (Flex/Bison) [1], Lemon [2],
>>>> Ragel [3], etc. The downside is maintaining two grammars, but we are doing
>>>> that with all the MiNiFi components already. The upside is being able to
>>>> support EL incrementally as the grammar is developed. What do you think?
>>>>
>>>> Regards,
>>>> Matt
>>>>
>>>> [1] http://dinosaur.compilertools.net/
>>>> [2] http://www.hwaci.com/sw/lemon/
>>>> [3] http://www.colm.net/open-source/ragel/
>>>>
>>>>
>>>>
>>>> Sent from my iPhone
>>>>> On May 4, 2017, at 8:13 AM, Marc P. <[email protected]> wrote:
>>>>>
>>>>> Andrew,
>>>>> I am not aware of it being actively worked [1]. This would require using
>>>>> ANTLR4, but I don't believe C++ support is well tested [2]. Someone can
>>>>> correct me if I'm wrong, but there would have to be changes to both sides.
>>>>> I attempted a quick straw man with grammars, but didn't take it very far
>>>>> after making initial changes to the grammar. It generated code, but I'm
>>>>> uncertain of cross platform compatibility with the expression language. If
>>>>> that's not expected or required that will remove some limitations as a
>>>>> result of moving to ANTLR4.
>>>>>
>>>>> [1] https://issues.apache.org/jira/browse/MINIFI-140
>>>>> [2]
>>>>> http://www.soft-gems.net/index.php/tools/49-the-antlr4-c-target-is-here
>>>>>
>>>>> On Thu, May 4, 2017 at 8:07 AM, Andrew Christianson <
>>>>> [email protected]> wrote:
>>>>>
>>>>>> All,
>>>>>>
>>>>>> I see that we do not have support for the expression language yet in
>>>>>> MiNiFi C++. Is anyone actively working on this, and if so, is there an
>>>>>> ETA?
>>>>>> If no one is working on it, is there a general plan for how it should be
>>>>>> implemented? I think I recall seeing references to ANTLR
