Hello,

I'm writing Yet Another Guitar Chord Finder(tm), and as such I want to be able to map easily between note names and their positions in the chromatic scale. I want to be able to find that A is the first note on the chromatic, and that the second note on that scale is A#. My first instinct was to use a hash, but that only gets me one direction. I can always build a second "backwards" hash:

my %position_of = (
  'A'  => 1,
  'A#' => 2,
  # ...
);

my %note_at = ();
for my $note (keys %position_of) {
  $note_at{$position_of{$note}} = $note;
}
[download]

but I don't really like the idea of having two hashes that express basically the same thing. (Semantically, I know, the hashes don't, but the data are bijective, and I should be able to do it with one structure, dammit!)

Two hashes probably isn't a bad WTDI, but is there a better way?

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