Re: Line lexer...

[S'orlok Reaves <sorlok_reaves@xxxxxxxxx>]

I once made a binary file parser with SableCC, similar
to what you're describing. I had to use a custom Lexer
to read "X bytes" dynamically (although, I think
SableCC4 might be able to get around this.) 

My opinion was that I didn't gain any real benefit
from using SableCC. (Note: This is the ONLY parser
project that I regretted using SableCC for.) In the
scenario you described, I'd hand-write a recursive
descent parser. But if there's a chance you'll be
switching formats (you mention XML) then stick to
SableCC --you'll be able to recycle your front-end.

Any other thoughts/experiences?
-->Seth
By the way, the standard approach when using a custom
lexer is NOT to change the lexer class, but to
override it.





--- Javier Abdul Cordoba Gandara
<cordobaj@xxxxxxxxxxxxxxxxxxxx> wrote:

> 
> 	Hi all. I've been using SableCC for quite some time
> now. Now I'm facing a project where I need to
> process lines of data that represent transactions in
> very fixed formats (spaces are showed only for
> simplicity):
> 
> FI 0001a 0104abcde 0209123456789 0302aa SE 0002ab 
> 
> 	where FI(RST), SE(COND) are headers of so called
> segments, and fields are marked as 00-01, 00 is the
> 'id' of the field and 01 is the lenght of the
> segment, a is the data. So it follows that in
> 0209123456789, 02 is the 'id', 09 is the length and
> 123456789 the data, etc.
> 
> 	Next, I have that segments represent
> data/operations and there are some constraints on
> how they can be structured, the same applies to
> fields (that have real names, numbers are just
> codes).
> 
> 	We have processors from plain C to annotated Java
> with fancy filters and so on, but all are hard coded
> monsters that you'll hate to meet. I want something
> simpler and higher level, ¿would you recommend me to
> implement a scanner for the line oriented thing? I
> started to change Lexer class to an interface, etc.
> you know the story, but I also want to evaluate
> speed and memory issues (millions of transactions
> you know). Then I stopped and wanted to know your
> opinion.
> 
> 	Maybe next step is XML migration but thats why I
> want to get a real parser involved :) Or maybe this
> is overkill for such a dumb format and I must settle
> for good old C. 
> 
> 	Thank you and good luck with SableCC 4 I really
> want to play with it >.<
> 
> 
> Javier Abdul Córdoba Gándara
> Buró de Crédito
> Sistemas - Desarrollo
> Tel. 54494900 Ext. 5935
> 
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