Guess what is the print out?

pg has asked for the wisdom of the Perl Monks concerning the following question:

I just made this small piece of code to entertain my fellow monks. Guess what are the results from the last two lines (Tomorrow is a holiday, remembrance day, in Canada, so happy holiday, is it also a holiday in some other countries?):

my @a = ();
$a[0] = \@a;
my $expr = '$a[0]';
my $index;
for ($index = 0; $index < 1000; $index ++) {
    $expr = "\${$expr}[0]";
}
print $expr, "\n";
eval "print $expr";
[download]

Comment on Guess what is the print out? Download Code

Replies are listed 'Best First'.
Re: Guess what is the print out? by dws (Chancellor) on Nov 11, 2002 at 05:27 UTC
Since `$expr` starts out holding the string `'$a[0]'` (without quotes), each time through the loop adds `'${'` to the front, and `'}[0]'` to the back (without the quotes). I'm guessing that something like `${${${ .... ${$a[0]}[0]}[0] ... }[0]` is printed. I haven't a clue what the eval'd print prints, but I suspect it involves a lot of autovivification. (After running the snippet: D'oh)	[reply] [d/l] [select]
Re: Guess what is the print out? by diotalevi (Canon) on Nov 11, 2002 at 05:22 UTC
You'll be happier if you learn a perlier syntax for doing iterations ala `for (0 .. 999) { $expr = "\${$expr}[0]"; }`. It's at least prettier than your excessivly verbose usage of for() `__SIG__ use B; printf "You are here %08x\n", unpack "L!", unpack "P4", pack "L!", B::svref_2object(sub{})->OUTSIDE;` [download]	[reply] [d/l] [select]
Re: Guess what is the print out? by submersible_toaster (Chaplain) on Nov 11, 2002 at 05:17 UTC
Happy holiday ... struth - I thought australiens had it good down here in the 'Land of the Long-Weekend' but no such luck - It's an offical 'day' though , some call it Veteran's Day or Rememberance Day , I believe originally it was Armistice Day	[reply]