著者: ph10 日付: To: Zoltán Herczeg CC: pcre-dev@exim.org, ND 題目: Re: [pcre-dev] (*THEN) works differently in Perl
On Tue, 2 Jul 2019, Zoltán Herczeg wrote:
> Perhaps the misunderstanding comes from the fact that we are talking
> about the pattern and they talk about the matching process. So (*THEN)
> simply starts a backtrack, and when an alternation is encountered, it
> switches to the next alternative.
That is indeed what happens in the pcre2_match() interpreter.
> But this happens normally as well, so what is the exact purpose of
> this verb then?
Not quite. (*THEN) suppresses going back to a previous backtrack inside
the branch. In the Perl example
if COND matches, but FOO fails to match, it does not go back to
backtrack points inside COND (which it would do without (*THEN)), but
instead abandons the entire branch and jumps to try to match COND2. It's
a sort of branch-level (*COMMIT).
At a simple level I suppose it's also equivalent to
((?>COND) FOO | ...
but perhaps there are more complicated examples that can't be written
that way.
