Front page | perl.perl5.porters |
Postings from September 2011
On Mon, 26 Sep 2011, Father Chrysostomos via RT wrote:
> *at the current starting position*
>
> (*THEN) acts like (*COMMIT) in the example given above.
Aha.
Since we are quoting "man perlre", here's another bit of confusion:
"(?PARNO)" "(?-PARNO)" "(?+PARNO)" "(?R)" "(?0)"
Similar to "(??{ code })" except it does not involve
compiling any code, instead it treats the contents of a
capture buffer as an independent pattern that must match at
the current position.
Consider this pattern (ignore white space):
^.*? (?1) c (?(DEFINE) (a(*THEN)b) )
When I read "an independent pattern", it suggests to me that the effect
of (*THEN) is confined to that independent pattern. However, experiment
with Perl shows that I am wrong here as well. The pattern as it stands
does not match "aabc", but if |(*F) is added after b, it does.
As it happens, PCRE processes recursions/subroutines differently to
Perl, or perhaps I should say that the other way round, since PCRE had
them first. :-) So another difference probably doesn't matter much.
However, I'm still thinking about this whole issue with regard to PCRE
implementation. It tries to resolve where (*THEN) should back up to at
compile time, but looking at the example above, it seems to me that it
can only be done dynamically, at run time.
Regards,
Philip
--
Philip Hazel
Thread Previous
|
Thread Next