Re: [dev] Lexers and parsers

From: pancake <>
Date: Thu, 20 Aug 2009 17:40:20 +0200

Can you expose a practical example of this? Maybe taking use cases as
design roots we can catch a better idea of how to implement this or
how to solve the problem you are facing.


Maurício wrote:
> (2/2 - I believe these messages didn't went to
> the list. Sorry if they actually did.)
>>> (...) If you had such "shell yacc", how would you like it to be
>>> or behave?
>> (...) So the important thing is being able to whip something up
>> quickly; this isn't parser "specs" that's going to be carefully
>> developed and then used for a very long time.
> Sure. I want something that helps testing and can deal with
> complex input, or even input with unknown structure to which you
> want to check if one works, even if temporarily. Example: someone
> gives you some unorganized data and you just want to transform it
> into something you can deal with.
>> A general point: one of the most important things to think
>> about, particularly with parsers, is what would be most
>> effective in tracking down the inevitable problems when there's
>> a bug in the user input and/or mismatched input, particularly if
>> it happens in the middle of a pipe process: how are you going to
>> report which part of the input stream was wrong, particularly if
>> it doesn't exist on its own, in a way which is effective for a
>> human to track down the problem? (...)
> The exact answer will probably depend on the chosen grammar type
> and parsing algorithm. Allowing specified limits on match size or
> deepness of analysis we could get error logs to be readable.
> However, "errors" in these tools should not be errors in a strict
> sense. I do want to write a tool that you can use to check grammar
> hyphotesis on text, and that means that even if you don't get
> fatal errors you still want to know how well your grammar did with
> some input, and get meaninfull report on, say, how long a match
> had to be to solve ambiguity, how deep an analysis had to be to
> find a match, which false matches were more common etc, and you
> want this report to be good for automated analysis.
> Best,
> Maurício
Received on Thu Aug 20 2009 - 15:40:20 UTC

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