--- "Adam D. Lopresto" <[EMAIL PROTECTED]> wrote:
> I propose that since the empty pattern is no longer legal (and
> about time), we use "|" in patterns to indicate alternation without
> preference, and "||" to indicate "try the first, then the second,
> etc".
Hmm....
A neat idea, but can you elaborate on when it would matter?
> So
> "cat dog fox" ~~ /( fox | dog | cat )/;
> might match any of the three, and in fact is quite likely to match
> cat (since scanning the string could be a very long process), but
> "cat dog fox" ~~ /( fox || dog || cat )/;
> would be guaranteed to first try fox, then if that fails backtrack
> and try dog, and if that fails backtract to try cat. The choice of
> symbols parallels the junction and short-circuiting or operators,
> and in most cases when an alternation is specified, the programmer
> has no preference among the alternatives (indeed, in most cases only
> would could match anyway), so it seems silly to force the engine to
> prefer the first one.
I thought the requirement to prefer the first was largely an
optimization, so that it could bail when it had a match without
continuing to search. ("Wouldn't you know, it was in the *last* place I
looked for it!")
Are you proposing a more DFA-ish behavior, maybe?
Some programs actually embad a DFA for a quick "does it match?" as
*well* as an NFA for pulling out backreferences once the DFA finds a
hit, but I doubt anybody is planning to embed a pre-matching DFA in
Perl (if so, somebody please tell me now).
> I'm imagining that in the first example, the implementation would
> probably build an FSA and process each letter as it comes, while the
> second would rely on backtracking.
Sounds like DFA/NFA to me....
> What think you all?
Dunno. Would swell the footprint some, but might have some merit.
DFA's are generally faster, I believe, but P5's NFA is optimized to a
beautiful degree. Might be possible just by tuning the engine some
more, but then the codebase is still swelling....
Dan? Parrot's pure NFA, right?
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