[antlr-interest] Re: Local lookahead depth

[Oliver Zeigermann]

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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