Update: It would be kind of the inside-out solution to this problem, you could get a function callback for every combination of values, but I think to get an actual iterator function using this method, similar to the iterator produced by my $iter = do { my $i; sub { $i++ } };, you'd need a co-routine. Unless tilly can wrangle it out of his code :-)

There does seem to be a Coroutine Module on CPAN, might be fun to look into :)

Update: Taking the initiative, I wrangled tilly's code myself (just couldn't wait for the book :)

use strict;
use warnings;

my $iterator = mk_iter(
  [1..2], ["a".."c"], [3..5]
);

while (my @arr = $iterator->()) {
 print "@arr\n";
}

sub mk_iter {
  my $range = shift;
  my $i = 0;
  my $end = @$range;
  my $iter = sub {
    return unless $i < $end;
    return $$range[$i++];
  };
  @_ ? ret_iter($iter, @_) : $iter;
}

sub ret_iter {
  my $iter = shift;
  my $range = shift;
  my $i = 0;
  my $end = @$range;
  my @arr;
  my $new_iter = sub {
    $i = 0 unless $i < $end;
    return unless $i or @arr = $iter->();
    return @arr, $$range[$i++];
  };
  @_ ? ret_iter($new_iter, @_) : $new_iter;
}

#####################################
# Update
# Here's a variation which is closer to what was
# Originally asked for, i.e. all combinations from
# 2-4 characters
use strict;
use warnings;

use strict;
use warnings;

my $iterator = make_iter(
 2,4,[qw(A C G N T)]
);

while (my @arr = $iterator->()) {
 print "@arr\n";
}

sub make_iter {
  my ($start, $end, $range) = @_;
  my $nxt_iter = sub { return };
  my $iter = sub {
    my @data;
    unless (@data = $nxt_iter->()) {
        return unless $start <= $end;
        $nxt_iter = mk_iter( ($range) x $start++);
        return $nxt_iter->();
    };
    @data;
  }
}
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