[Freeciv-Dev] Re: XML (OT)

[Petr Baudis <pasky@xxxxxxxxxxx>]

Originally to: David B. Smith


Dear diary, on Fri, Dec 07, 2001 at 
06:28:52PM CET, I got a letter, where
Andrew Sutton <ansutton@xxxxxxx> told me, 
that...
> On Friday 07 December 2001 11:00 am, Petr 
Baudis wrote:
> > They say something about impossibility of 
parsing C or perl syntax by yacc.
> > Well, dunno about yacc but it's then 
really funny that both perl and gcc
> > use bison, isn't it? And, honestly, even 
when writing IMHO relatively
> > complex grammar using bison, I never got 
into those problems.
> 
> having worked extensively with compilers in 
the last month or two, i can say
> *without* doubt that there are just some 
grammars that yacc/bison are
> incapable of parsing. it has to do with the 
algorithm used to for descent.
> yacc/bison generates bottum-up LALR(1) 
parser - it's just insufficient for
> sufficiently complex grammars. don't forget 
that you can manipulate a grammar
> specification to help resolve shift/reduce, 
reduce/reduce and other various
> ambiguities or infite recursion issues. you 
can also approximate some aspects
> of the grammar thru code. so they're 
probably right. it may be impossible to
> parse the C and perl syntaxes as specified, 
but for lack of a better tool,
> they make up for the shortcomings with more 
complex grammar implementations
> (like a fixed token lookahead).
Erm, another question, will we make some 
complex grammar for our config file?
;)

> > > both cases have their weak points. xml 
isn't very expressive and it's not
> > > really mean to be. writing your own 
parser will provide a more
> > > specialized language but is going to be 
a pain in the ass - regardless of
> > > how easy it is or how much experience 
anybody has.
> >
> > I don't think so :).
> 
> alot of it is going to have to deal with 
specification of the grammar itself.
> it's not easy to write the perfect grammar 
first time out, because you're
> going to miss something. then, going back 
and adding might prove to be
> somewhat difficult and its possible that 
you could break all the existing
> scripts/files by changing a rule to 
accomodate your addition.
Then your change will be rejected/reverted 
later ;).

-- 

                                Petr "Pasky" Baudis

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