; week-07.lisp: linear automata for music

; apply an arbitrary function to three numbers

(defun apply-rule-to-triple (rule triple)
  (funcall rule triple))

; different kinds of arbitrary functions you might apply....

(defun average-rule (triple)
  (/ (+ (nth 0 triple)
	(nth 1 triple)
	(nth 2 triple))
     3.0))

(defun modulo-rule (triple)
  (mod (+ (nth 0 triple)
	  (nth 1 triple)
	  (nth 2 triple)) 1.0))

(defun add-subtract-rule (triple)
  (- (+ (nth 0 triple)
	(nth 1 triple))
     (nth 2 triple)))

; get three numbers from an arbitrary-length list

(defun first-three (input-list counter)
  (if (>= counter 3)
      nil
      (cons (car input-list)
	    (first-three (cdr input-list) (+ counter 1)))))

; produce one generation of a linear automaton

(defun la-generation (rule input-list)
  (if (< (length input-list) 3)
      input-list
      (cons (apply-rule-to-triple rule (first-three input-list 0))
	    (la-generation rule (cdr input-list)))))

; recursively produce many generations of a linear automaton

(defun la-generations (rule input-list generations)
  (if (<= generations 0)
      nil
      (let ((next-generation (la-generation rule input-list)))
	(cons next-generation 
	      (la-generations rule next-generation (- generations 1))))))

; produce a list of random values

(defun random-list (list-length lower-bound upper-bound)
  (if (<= list-length 0)
      nil
      (cons (+ (random (- upper-bound lower-bound)) lower-bound)
	    (random-list (- list-length 1) lower-bound upper-bound))))

; (la-generations #'average-rule (random-list 20 30 100) 10)

; render automaton output as a sequence of MIDI chords

(defun la-render (start-time input-list)
  (if (null input-list)
      nil
      (append (make-chord start-time (car input-list))
	    (la-render (+ start-time 0.5) (cdr input-list)))))

; produce one MIDI chord from a list of numbers between 0.0 and 1.0

(defun make-chord (start-time input-list)
  (if (null input-list)
      nil
      (cons (new midi 
	      :time start-time
	      :keynum (round (+ (* (car input-list) 88) 21))
	      :duration (+ (random 0.4) 0.1)
	      :amplitude (+ (random 0.6) 0.2))
	    (make-chord start-time (cdr input-list)))))

#| test examples
(events (la-render 0 (la-generations #'average-rule 
				     (random-list 10 0.0 1.0) 30)) 
	"test.mid")

(events (la-render 0 (la-generations #'modulo-rule 
				     (random-list 10 0.0 1.0) 30)) 
	"test.mid")

(events (la-render 0 (la-generations #'add-subtract-rule 
				     (random-list 10 0.0 1.0) 30)) 
	"test.mid")
|#