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

(ns music
  (:require [clojure.core.match :refer [match]]))

;; 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 {::tempo 120} note1] ;; note1 modified to have tempo 120
[:modify {::tempo 120
          ::instrument "Dope Organ"}
 [:= note1 note2]] ;; 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 {::tempo tempo} music])

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

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

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

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

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

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

(defn pitch 
  "Returns the pitch class and octave represented by the absolute pitch.
   In cases of enharmonic equivalence, returns the sharp rather than the flat."
  [abs-pitch]
  (let [scale [:C :C# :D :D# :E :F :F# :G :G# :A :A# :B]
        octave (quot abs-pitch 12)
        index (rem abs-pitch 12)]
    [(nth scale index) octave]))

(defn trans [n [pitch-class octave]]
  (pitch (+ (abs-pitch pitch-class octave) n)))

(defn line 
  "Combines musics via the sequential (:+) operator"
  [[m & ms :as musics]]
  (if (nil? (seq musics))
    (rest 0)
    [:+ m (line ms)]))

(defn chord 
  "Combines musics via the simultaneous (:=) operator"
  [[m & ms :as musics]]
  (if (nil? (seq musics))
    (rest 0)
    [:= m (line ms)]))

(defn max-pitch [[p & ps :as pitches]]
  (if (nil? (seq pitches))
    (pitch 0)
    (let [max-ps (max-pitch ps)]
      (if (> (abs-pitch p) (abs-pitch max-ps))
       p
       max-ps))))

(defn dur
  "Computes the duration of the music value"
  [music]
  (match music
         {:duration d} d
         [:+ m & ms] (+ (dur m) (dur (into [:+] ms)))
         [:+] 0
         [:= & ms] (apply max (map dur ms))
         [:=] 0
         [:modify {:tempo r} m] (/ (dur m) r)
         [:modify _ m] (dur m)))