use strict;

sub build_scale
{
    # The parameter is the key of the scale
    # as in "what key is a bicycle in? B flat"

    my $key = shift;
    my @notes = ('C', 'C#/Db', 'D', 'D#/Eb', 'E', 'F', 'F#/Gb',
                 'G', 'G#/Ab', 'A', 'A#/Bb', 'B');
    my @intervals = (0, 2, 4, 5, 7, 9, 11, 12);

    # Create a scale based on the intervals in a major scale
    my @scale = map {$notes[($key + $intervals[$_]) % 12]} (0..7);
    return @scale;
}

sub blues_in
{
    my $key = shift;
    my @scale = build_scale($key);

    #my @blues = qw( 1 1 1 1 4 4 1 1 5 4 1 1);
    my @blues  = qw( 0 0 0 0 3 3 0 0 4 4 0 0);

    print "Blues in $scale[0]:",
     join (" ", map {$scale[$_]} @blues),"\n";
}

sub chord_progression
{

    my @scale = build_scale( shift);
    # Create triads.  Increment each note within the scale.
    # All notes in the chord progression fall within the
    # major scale.
    my ($root, $third, $fifth) = (0, 2, 4);
    my @name = ('Maj', 'min', 'min', 'Maj', 'Maj', 'min', 'Dim', 'Maj'
+);
    for (0..7) {
        printf "%6s %3s: %6s, %6s, %6s\n",
        $scale[$root], $name[$_], $scale[$root],
        $scale[$third], $scale[$fifth];
        $root++;
        $third++;
        $fifth++;
        $root %= 7;
        $third %= 7;
        $fifth %= 7;
    }
    print "\n";
}


# Call the subroutine for each note in the scale
for (0..11)
{
#    chord_progression($_);
    blues_in($_);
}
[download]