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Postings from February 2009
On Sun, Feb 22, 2009 at 11:11:04PM +0000, Zefram wrote:
> demerphq wrote:
> > I guess we could bifurcate all
> >the regops, but that gets messy.
>
> I think only the iteration regops need this bifurcation.
> In /(?>(?:...)*)/, the "*" can be told at parse time that it's in a
> no-backtracking context, and it can compile to a regop that doesn't
> make backtracking records and throws away the internal backtracking
> records of the (?:...) at the end of each iteration. Whatever's inside
> the (?:...) doesn't need to be compiled any differently from usual.
> Although, in fact, in this case one can impute a (?>...) around it,
> and so pass the non-backtracking context inwards.
>
> There are more complicated cases. Generally, in /(?>(?:...){N,M})/, the
> (?:...) needs to keep its backtracking records for the first N iterations.
> After N iterations are complete, we know that we'll never backtrack
> through there, so all those backtracking records can be discarded, and
> each subsequent iteration's backtracking records can be discarded at
> the end of the iteration.
Note that if the inner (?:...) isn't too complex, then currenty only a
single backtracking record is pushed on the stack, and the counter within
that record is updated for each iteration.
--
"Strange women lying in ponds distributing swords is no basis for a system
of government. Supreme executive power derives from a mandate from the
masses, not from some farcical aquatic ceremony."
-- Dennis, "Monty Python and the Holy Grail"
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