clojure-school-of-music/src/music.clj

(ns music)

;; an octave is an int, e.g. 4
;; a pitch class is a keyword from :Abb to G##
;; a pitch is a [pitch class, octave] vector, e.g. [:C 4] is middle C
;; a duration is a rational number, e.g. 1/8
;; a note has a duration, optionally a pitch, and optionally any other necessary keys (e.g. loudness)
;; {:duration 1/8 :pitch [:A# 3]} is a note. {:duration 1/4} is a note (really, a rest)

;; [:= noteA noteB] represents noteA played simultaneously with noteB
;; [:+ noteA noteB] represents noteA played followed by noteB

;; [:modify noteA control] annotates noteA with the control map
;; control maps have keys like ::tempo, ::transpose, ::instrument, ::phrase, ::player, ::keysig

;; primitives
(def note1 {:duration 1/4, :pitch [:Eb 4]})
(def note2 {:duration 1/4, :pitch [:G 4]})
(def note3 {:duration 1/8, :pitch [:F 4]})
(def rest1 {:duration 1/8})

[:= note1 note2] ;; note1 simultaneous with note2
[:+ note1 note3] ;; note1 followed by note3
[:+ [:= note1 note2] note3] ;; note1 simultaneous with note2, followed by note3
[:modify note1 {::tempo 120}] ;; note1 modified to have tempo 120
[:modify [:= note1 note2] {::tempo 120 ::instrument "Dope Organ"}] ;; note1 simultaneous with note2 modified with tempo and instrument

;; can be nested to arbitrary complexity
(def song
  [:= [:+ {:duration 1/4, :pitch [:D 3]}
          {:duration 1/4, :pitch [:E 3]}
          {:duration 1/4, :pitch [:F 3]}]
      [:+ {:duration 1/4, :pitch [:F 3]}
          {:duration 1/4, :pitch [:G 3]}
          {:duration 1/4, :pitch [:A 3]}]])

(defn note [duration pitch]
  {:duration duration, :pitch pitch})

(defn rest [duration]
  {:duration duration})

(defn tempo [tempo music]
  [:modify music {::tempo tempo}])

(defn transpose [abs-pitch music]
  [:modify music {::transpose abs-pitch}])

(defn instrument [instrument music]
  [:modify music {::instrument instrument}])

(defn phrase [phrase-attributes music]
  [:modify music {::phrase phrase-attributes}])

(defn player [player-name music]
  [:modify music {::player player-name}])

(defn keysig [pitch-class mode music]
  [:modify music {::keysig [pitch-class mode]}])

(defn pc-to-int [pitch-class]
  (case pitch-class
    :Cbb -2 :Cb -1 :C 0 :C# 1 :C## 2
    :Dbb 0 :Db 1 :D 2 :D# 3 :D## 4
    :Ebb 2 :Eb 3 :E 4 :E# 5 :E## 6
    :Fbb 3 :Fb 4 :F 5 :F# 6 :F## 7
    :Gbb 5 :Gb 6 :G 7 :G# 8 :G## 9
    :Abb 7 :Ab 8 :A 9 :A# 10 :A## 11
    :Bbb 9 :Bb 10 :B 11 :B# 12 :B## 13))

(defn abs-pitch [pitch-class octave]
  "Returns the absolute pitch of a pitch class at an octave"
  (+ (* 12 octave) (pc-to-int pitch-class)))

;; TODO
(defn pitch [abs-pitch]
  "Returns the pitch class and octave represented by the absolute pitch.
   In cases of enharmonic equivalence, returns the sharp rather than the flat."
  ())

;; TODO exercise 2.1 (ii-V-I function)
;; this will involve being able to answer, "what pitch is n semitones above this one?"

(def ii-V-I
  (let [Dm [:= (note 1 [:D 4])
               (note 1 [:F 4])
               (note 1 [:A 4])]
        Gmaj [:= (note 1 [:G 4])
                 (note 1 [:B 4])
                 (note 1 [:D 5])]
        Cmaj [:= (note 2 [:C 4])
                 (note 2 [:E 4])
                 (note 2 [:G 4])]]
    [:+ Dm Gmaj Cmaj]))