15 messages in org.perl.perl5-portersRe: Pattern matching in SNOBOL4 (long...| From | Sent On | Attachments |
|---|---|---|
| Mark-Jason Dominus | Apr 15, 1998 10:23 pm | |
| Ilya Zakharevich | Apr 15, 1998 11:34 pm | |
| Moore, Paul | Apr 16, 1998 2:16 am | |
| Moore, Paul | Apr 16, 1998 2:49 am | |
| Chaim Frenkel | Apr 16, 1998 6:50 am | |
| Mark-Jason Dominus | Apr 16, 1998 7:20 am | |
| Ilya Zakharevich | Apr 16, 1998 9:53 am | |
| Ilya Zakharevich | Apr 16, 1998 10:08 am | |
| Larry Wall | Apr 16, 1998 10:41 am | |
| Chaim Frenkel | Apr 16, 1998 11:03 am | |
| Ton Hospel | Apr 16, 1998 3:18 pm | |
| kst...@chapin.edu | Apr 16, 1998 4:41 pm | |
| Peter Prymmer | Apr 16, 1998 4:55 pm | |
| Ton Hospel | Apr 17, 1998 1:39 pm | |
| Ton Hospel | Apr 17, 1998 2:20 pm |
| Subject: | Re: Pattern matching in SNOBOL4 (long, digression) | |
|---|---|---|
| From: | Ilya Zakharevich (il...@math.ohio-state.edu) | |
| Date: | Apr 16, 1998 9:53:55 am | |
| List: | org.perl.perl5-porters | |
Moore, Paul writes:
If you know Emacs syntax tables, you know that this is mostly useless, since you need to know quoting/commenting/escaping rules too. But Perl can do BAL *now*.
I agree with your point on quoting etc (in principle). But for simplified cases (80-20 stuff where 80% of the cases are good enough) BAL can be helpful.
Can you explain how to do BAL inside an arbitrary RE? I can't think where to start, even.
See ./t/op/pat.t, find the longest and urgliest multiline pattern. OK, OK:
sub matchit { m/ ( \( (?{ $c = 1 }) # Initialize (?: (?(?{ $c == 0 }) # PREVIOUS iteration was OK, stop the loop (?! ) # Fail: will unwind one iteration back ) (?: [^()]+ # Match a big chunk (?= [()] ) # Do not try to match subchunks | \( (?{ ++$c }) | \) (?{ --$c }) ) )+ # This may not match with different subblocks ) (?(?{ $c != 0 }) (?! ) # Fail ) # Otherwise the chunk 1 may succeed with $c>0 /xg; }
As above, agreed, and great. Can you show how, please? And is it possible to package the code up as a named, reusable chunk?
Put it into $matched_parens (you may need to change () to (?:) to make it relocatable).
I wanted to add (?. ) code for generic relocatable stuff (whatever is inside (?. ) will use separate numeration of parens and \17), but that moment the endless discussion on hierarchical matches looked like it may produce something more general and simple. Unfortunately, now I do not remember the results of this discussion.
*(EXPR) for match-time expression evaluation
??? What does it do?
Named, reusable chunks of code, is my picture of the important point.
You can put any RE into $expr now. This may need some "relocatable support", of course, if they use \17.
POS(N) jump to position N
??? What does it do?
POS(N) is a zero-width assertion that we are currently at position N in the string. You could maybe do that with (?{...}) except for the fact that that cannot fail. Could (?{...}) be extended so that the code could return a succeed/fail indicator?
See documentation for (?(cond)blah|foo) and (?!), and the example above.
Ilya