Let's stop parser Hell

Dmitry Olshansky dmitry.olsh at gmail.com
Sat Jul 7 13:29:24 PDT 2012


On 08-Jul-12 00:19, Roman D. Boiko wrote:
> On Saturday, 7 July 2012 at 20:09:56 UTC, Andrei Alexandrescu wrote:
>> On 7/7/12 3:17 PM, Dmitry Olshansky wrote:
>>> I'll have to point out that the whole point about integrated lexing is
>>> moot. It's more of liability then benefit. At very least it's just
>>> implementation curiosity not advantage.
>>
>> Interesting. I'll have to ask for more details on why.
>>
>> Andrei
>
> +1. Personally I associate PEG with a parser that includes a
> __distributed__ lexer inside,


Well put yet it's still lexer. And most horribly it's not optimized to 
DFAs most of the time last time I've checked papers.

  which gives the advantage of having to
> check less alternatives at each step (that's similar to deterministic
> parsing). If lexer is separate, it seems to be more difficult to scan
> for only a subset of possible tokens.
>
And given the backtracking nature of PEGs you'll do your distributed 
thing many times over or ... spend a lot of RAM to remember not to redo 
it. I recall lexing takes even more then parsing itself.

-- 
Dmitry Olshansky




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