for a different twist, try merlyn's range-based magical autoincrement.

#!/usr/bin/perl
use strict;
use warnings;
$|++;

my $alphaGen = sub { scalar glob "{A,B,C}{A,B,C}" };

print $_,$/ while $_ = $alphaGen->();
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i figure if this is homework, you'd never get away with submitting this answer -- but you (and others) might learn this sweet little trick.

~Particle *accelerates*