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Re^3: Pascal-Sierpinski for golfers

by hbm (Hermit)
on Nov 30, 2011 at 17:39 UTC ( #940909=note: print w/ replies, xml ) Need Help??


in reply to Re^2: Pascal-Sierpinski for golfers
in thread Pascal-Sierpinski for golfers

I really appreciate two tricks:

  • s// /
    I understand this, and have used the empty expression before with m//, but never thought to try it with s///.
     
  • for($/)x16
    A slick way of getting the newline (vis-à-vis -l print until...)!
    Changing the loop to for($_)x16 is informative.
    And, since a bare print prints both $_ and $/, I found it rather unobvious which variable holds the strings.


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Re^4: Pascal-Sierpinski for golfers
by eyepopslikeamosquito (Canon) on Dec 01, 2011 at 03:16 UTC

    for($/)x16
    A slick way of getting the newline (vis--vis -l print until...)! Changing the loop to for($_)x16 is informative. And, since a bare print prints both $_ and $/, I found it rather unobvious which variable holds the strings.
    Actually, $/ is the input record separator, so a bare print does not print it. What's being printed is just the (localized) $_ inside the for loop. Of course, a bare print will print $\, aka the output record separator, often seen in golf, as in, for example, The golf course looks great, my swing feels good, I like my chances (Part I).

    The for($/)x16 loop aliases $/ and, despite the x16, only the single $/ value is (repeatedly) changed, as you will discover by printing it after the loop has terminated. Replacing "print" with "warn" like so:

    s/^|\d+/$&+$'||1/eg,warn("du='$_' ds='$/'\n"),s// /for($/)x16; warn("at end du='$_' ds='$/'\n");
    should clarify. BTW, this eccentric "for loop aliasing" trick is often seen in golf; see, for example, Drunk on golf: 99 Bottles of Beer in the "Bottle Golf Tip No 2" section (search for Cantor). Finally, the "for loop aliasing" trick is a specific example of Eugene van der Pijll's general golfing mantra, "Can't possibly work, let's try it anyway". :)

      Doh, I flubbed that ($/ vs. $\). I so often print$/,/expr/?this:that, I confused myself.

      And darn you - I had already read your lengthy linked topics, and perhaps all of their references, but I find them irresistable! This time through, I most enjoyed this gem:

      s///ge>>9?print:do$0

      The :do$0 is one *sick* loop. And the return value from s/// idea gave me the following "for 1 to 15" method:

      perl -le'$_=1;{print,s/(\d+) ?/+$1 $1/g,s/\S+/$&/eeg>16||redo}'

      A couple more tricks for me!

        Yes, I too find the "do$0" loop hilarious. A great write-up of its use in the 2002 Kolakoski game by good ol' Rick Klement can be found here and also in Mtv's book of golf (page 105). I believe Ton Hospel was the first person to use the eccentric "do$0" loop in a golf competition. And thanks for the "redo" tip; I'd forgotten about redo after all these years. :)

        Update: Just noticed another Rick Klement gem where he concludes with: Lesson to be learned: try something before you say "that can't work" ... which looks like an independent invention of Eugene van der Pijll's famous golfing aphorism: Can't possibly work, let's try it anyway. :)

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