Re: [dev] Lexers and parsers

From: Maurício <>
Date: Thu, 20 Aug 2009 15:23:56 -0300

I'm not actually facing a very specific problem. (Well, I am,
but it's easy to solve without a parser.) I just have seen many
situations where such parser could be usefull. I'll try some

(1) You have a programming language you want to write a compiler
for. You write a grammar for it. To test if this grammar actually
works, you can run 1GB of code in that language throw that parser,
and it will do or output something (maybe call printf) at specific

(2) You want to parser a natural language and test if a grammar
works well. I don't know how parsing of natural languages is done,

(3) You have lot of data that some program outputs and you want to
read that output, but it has no clear structure. You could test
a few grammars until you see you can extract information that is
easier to deal with.

One thing that is not clear to me is what would be an action to do
when a match is found. I imagine a formated output could be okay,
since that can be made into program calls if necessary.


> 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.

>> 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.
>> (...)
>> 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.
Received on Thu Aug 20 2009 - 18:23:56 UTC

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