[antlr-interest] Re: Local lookahead depth
Oliver Zeigermann
oliver at zeigermann.de
Sun Nov 9 21:48:44 PST 2003
John D. Mitchell wrote:
>>>>>>"Oliver" == Oliver Zeigermann <oliver at zeigermann.de> writes:
>>>>>>
>>>>>>>lgcraymer wrote:
>
> [...]
>
>
>>>Also, as to actions in lookahead code: this is something that Ter
>>>supported in PCCTS under the name "guarded predicates" or some such. I
>>>don't know that it saw much use, and I suspect that usage indicates a
>>>too early incorporation of semantic information into the
>>>translator--tree transformation helps avoid that.
>
>
>>1.) You might really increase the set of parseable languages using this
>>technique
>
>
>>>From a theoretical standpoint? Nope, I can't see how you've increased the
> power at all.
>
>>>From a "what's easiest/most-efficient to do with tool/framework/etc. XYZ"?
> Okay.
I have to admit I really do not recall my example of a language that can
not be parsed without it, but can with it. Maybe I am mistaken, but have
to think about it and will deliver it as soon as I have got it :)
But have a look at what I posted in reply to Loring.
>
>
>>2.) Sometimes using tree transformation is too expensive
>
>
> No personal offense intended but... Many people keep saying things like
> that and I really don't believe that they understand the problem that they
> are nominally trying to solve (let alone understanding the actual problem
> that may need to be solved).
Not offending in any way :)
> For example, if very high speed is so important then what the hell are you
> doing using any "language" that needs such complexity to lex, parse,
> understand, and act upon to solve the problem? I.e., why aren't you using
> a purpose specific, fixed, highly normalized language that's extremely easy
> to robustly deal with rapidly?
Again, have a look at the example I posted to Loring.
Oliver
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