in reply to Re (chip): Re3: Technical Interview
in thread Technical Interview

Don't feel bad if you didn't know that; I actually caught TheDamian in the same mistake at TPC5.
Well, it's certainly true: chip did indeed catch me out at TPC5. And in front of 400-500 people!

Though in fairness, my mistake occurred in SelfGOL: quite possibly the most complex 1000 bytes of Perl ever written.

But it wasn'tbecause I was unaware of the @_-sharing nature of &foo. In fact, the code in question deliberately abused that feature. I messed up because I (carelessly) relied on the behaviour once to often within the same block.

Nevertheless, I was very grateful to chip. His correction encoraged me to make SelfGOL even more diabolical. As indeed has this thread.

>;-)

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Re (chip): Re5: Technical Interview
by chip (Curate) on Jan 01, 2002 at 00:27 UTC
    Damian is right about SelfGol; it is excruciatingly diabolical. It evidences a skill in Perl compression and obfuscation far beyond my own. My work with Perl has mostly been under the hood, so to speak. Knowing your car can help you be a good driver, but it won't turn you into Evel Knievel. Damian's coding stunts left his TPC5 audience, myself included, in awe.

    But more basic forces were also at work that day. As every teacher learns, nothing quite motivates a roomful of students to cleverness like the thrill of catching the teacher in a mistake.

    Come to think of it, Damian mentioned early in that very presentation that he had recently enjoyed catching Jeffrey Friedl--regex guru nonpareil--in a regex error. Did Damian's own anecdote plant a seed in my mind, which then bore fruit when I noticed his error? Who can know....

        -- Chip Salzenberg, Free-Floating Agent of Chaos

[reply]
      Come to think of it, Damian mentioned early in that very presentation that he had recently enjoyed catching Jeffrey Friedl--regex guru nonpareil--in a regex error.
      Actually, it was the younger regex Jedi, our very own japhy, whom I caught out.
      As every teacher learns, nothing quite motivates a roomful of students to cleverness like the thrill of catching the teacher in a mistake.
      So true. In fact, it was precisely by manipulating that basic human desire (i.e. to see the mighty stumble ;-) that I caught out someone as highly clueful as japhy. I deliberately made it look like I'd made a mistake, when in fact I was demonstrating an inconsistency in a rarely-used behaviour.

      Specifically, I showed some code equivalent to the following: 

          $var =~ s?pattern?string?;

      [download]
      and asked what was unusual about the substitution.

      Most regex adepts will reply:

      The use of ? as the delimiter causes the regex to match at most once between calls to reset (as described in the perlop manpage).

      But the real answer is:

      The use of ? as the delimiter doesn't cause the regex to match at most once between calls to reset. That behaviour only applies to matches, not substitutions.
      I have to confess that I much prefer this proxied variation on chip's "humble the guru" motivational technique, rather than the version in which the presenter himself is the one who gets humbled! ;-)
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