Here is my string: "A1234567890A". Here is my regex:

m{
  A         # A
  (?:
    [^AB]*  # 0 or more non-A and non-B characters
    . B     # any character, then a B
  )*        # this combo, 0 or more times
  [^AB]*    # 0 or more non-A and non-B characters
  A         # an A
}x
[download]

Now, before you ask, this is related to a) unrolling the loop, and b) reversing a regex. But it's also a very isolated case of the regex engine being a ninny.

This what I personally think the regex engine should do:

BEFORE & AFTER       REGEX
<>  <A01234567890A>  A
<A>  <01234567890A>  [^AB]*
<A01234567890>  <A>  .
<A01234567890A>  <>  B       FAILED
<A0123456789>  <0A>  .
<A01234567890>  <A>  B       FAILED
[download]

At this point, Perl should NOT try to do:

<A012345678>  <90A>  .
<A0123456789>  <0A>  B       FAILED
[download]

since Perl should KNOW that '0' was matched by [^AB]*, so it can't POSSIBLY match B. Instead, Perl should realize it should give up, and continue:

<A01234567890>  <A>  [^AB]*
<A01234567890>  <A>  A
<A01234567890A>  <>          FINISHED
[download]

This is NOT the case. Perl zips ALL the way back to the first 0 in the string, trying to match .B until it is exhausted, and goes back to the '...890' having been matched by [^AB]*, and it goes to the [^AB]* outside the (?:...)*. This matches nothing, and then the 'A' matches.

My gripe is that Perl should know that if something COULD be matched by [^AB]*, then it CAN'T match 'B'.

$_="goto+F.print+chop;\n=yhpaj";F1:eval

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