Last week I wrote a small function in Perl that rotates and array to left.

The function takes the item from the front and appends it to the back.

# precondition: @list >= 1;
sub rotate_left_by_one {
    my $ar = shift;
    my $item = shift @$ar;
    push @$ar, $item;
    return;
}

After calling this function as many times as the length of the array, it leaves the items in the same order they started in. Every call to this function puts a different item in the first location. I use it to compare this item to the rest of the items.

You would use it like this:

while (1 .. @list) {
    # your code
    rotate_left_by_one(\@list);
}

This function works great when the code doesn’t depend on the order of the items in @list. The items in @list will be in a different order than what it started with for most of the iterations of the loop. This means that the code in the loop body needs to have the commutative property.