In a quickie learning project a few months ago, I needed to deal with a "compass rose" of eight directions, and I also needed to know which points on the compass were adjacent, either for turning clockwise (deosil), or counter-clockwise (widdershins). I could have hand-constructed a pair of boringly static hash tables associating $deosil{north} = "northeast", and the opposite, $widder{northeast} = "north".

Instead, I thought I'd be creative. I defined an array of points around the compass in one direction, and then derived both hashes from it. I didn't intend for this to be a serious idiom with great advantages. One benefit is that it would be very easy to expand or redefine the compass points without risk of accidentally defining the hashes incorrectly or inconsistently is gone.

my %Deosil = ();
my %Widder = ();

do
{
    my @c = qw(north northeast east southeast
               south southwest west northwest);
    my @d = ($c[$#c], @c, $c[0]);

    %Deosil = (@d, @c);
    %Widder = reverse %Deosil;
};

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In reply to Deosil and Widdershins by halley

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