In a recent discussion, a friend told me 'she was glad I was glad', to which I (of course) immediately replied that 'I was glad she was glad I was glad'. One thing led to another (well, not that....) and voila:

#! /usr/bin/perl
use strict;
my $limit = $ARGV[0] || 10;

my $index = 0;
my $result = "I am glad.";
$result = ( "I am", "you are" )[ $index = not $index ] . 
   " glad " . $result foreach ( 1..$limit );

print $result, "\n";
[download]

This thing takes an integer from the command line and writes a (possibly ridiculously long) string saying 'I am glad you are glad I am glad...' eg.

c:/Data $ perl fn.pl 20
I am glad you are glad I am glad you are glad I am glad you are glad I
+ am glad you are glad I am glad you are glad I am glad you are glad I
+ am glad you are glad I am glad you are glad I am glad you are glad I
+ am glad you are glad I am glad.
[download]

The point here is the little list that toggles between 'I am' and 'you are'. The above snippet solves this nicely, but I find it noisy. Having read something about closures recently I then came up with the following:

#! /usr/bin/perl
use strict;
my $limit = $ARGV[0] || 10;

my $result = "jeg er glad.";
while( my $head = &swap ) {
    $result =  $head. " er glad " . $result;
}
print $result, "\n";

BEGIN {
    my @oss = qw( jeg du );
    my ( $index, $count );
    sub swap{
    ( $limit > $count++ ) ?
               return $oss[ $index = not $index ] : return;
    }
}
[download]

The code does the same (although the result is in norwegian), and I like this better as it results in only one word where I want the toggle. As a downside, the code's "framework" is extremely verbose.

How does one toggle between two values in a simple and elegant way? Not too long-winded? Not too obscure?

As a bonus question, why doesn't ...

$result =  $head. " er glad " . $result while( my $head = &swap );
[download]

... work under strict? It works with $head predeclared, but I'd rather not as one-liners are more neat. It seems to me that a statement like the above would define $head in the preceding line. Does a my statement inside a condition only apply to the following block? Not the logical "preceding block" to which the conditional is linked?

As a side note, I forgot why I named the variable $head. Now it makes sense, though, if only I knew why.

Cheers!