Here is a MIDI::Simple version:

use MIDI::Simple;
my %chords = (
    major   => [0, 4, 7, 12],
    minor   => [0, 3, 7, 12],
    major7  => [0, 4, 7, 11],
    minor7  => [0, 3, 7, 10],
    minor75 => [0, 3, 6, 10],
    dim     => [0, 3, 6, 9],
    dom7    => [0, 4, 7, 10],
    major9  => [0, 4, 7, 11, 14],
    minor9  => [0, 3, 7, 10, 14],
);

sub chord {
# chord(NOTE, CHORD);
# NOTE is the base note of the chord (numeric or name)
# CHORD is a reference to the chord array
# uses MIDI::Simple's interval procedure
# returns a list of notes (numeric or name) based on the format of NOT
+E
  my ($note, $chord) = @_;
  return interval $chord, $note;
}

my $note = 'Cs5'; # C sharp, 5th octave (D flat)
my @CsMajor5 = chord2($note, $chords{major});
print "C sharp major chord, 5th octave: @CsMajor5\n";
# displays: C sharp major chord, 5th octave: Df5 F5 Af5 Df6
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