chord_catalogue.clj

(ns music.chord-catalogue
  (:use [overtone.live] [overtone.inst.piano] 
        [clojure.math.combinatorics :only [combinations]]))

(declare gen-chords)
(declare play-chord-seq)

; The Chord Catalogue - Tom Johnson
(def chord-catalogue
  (mapcat (partial gen-chords 4) (range 2 14)))
(play-chord-seq chord-catalogue 300)


(defn binomial [n k]
  (let [rprod (fn [a b] (reduce * (range a (inc b))))]
    (/ (rprod (- n k -1) n) (rprod 1 k))))

(defn split-i [l i]
  (map (fn [[s e]]
         (subvec (vec l) s e))
       (partition 2 1 (reductions + (cons 0 i)))))

(defn gen-chords [octave n]
  (let [intervals (reduce #(%2 %1) (combinations (range 13) n)
                          (for [i (range n)] (partial sort-by #(nth % i))))
        chords (map #(map (partial octave-note octave) %) intervals)
        pause-posns (drop-while #(< % 1) (for [i (range 13)] (binomial i (dec n))))]
    (mapcat #(if (sequential? %) % [%])
            (interleave (split-i chords pause-posns) (repeat :pause)))))

(defn play-chord-seq [sequence delay]
  (doseq [[i chord] (map vector (range) sequence)]
    (if (not= chord :pause)
      (after-delay (* i delay) 
                   #(doseq [note chord] 
                      (piano note :vel 70 :decay 0 :release 0 :sustain 0))))))