# Musical note frequencies in the 12 equal temperament system

let frequency_A4: Frequency = 440 Hz  # the A above middle C, A4

fn note_frequency(n: Scalar) -> Frequency = frequency_A4 * 2^(n / 12)

print(note_frequency(12))  # one octave higher up (A5), 880 Hz
print(note_frequency(7))   # E4
print(note_frequency(-3))  # C4
assert_eq(note_frequency(12), 2 * frequency_A4)
assert_eq(note_frequency(7),  659.255 Hz, 1 mHz)
assert_eq(note_frequency(-3), 369.994 Hz, 1 mHz)