(defvar *out* (cl-out123:connect (cl-out123:make-output NIL :channels 1 :encoding :float)))

(defun square-wave (position length)
  (if (= 1 (floor (mod position length) (/ length 2)))
      1.0s0
      0.0s0))

(defun sawtooth-wave (position length)
  (coerce (/ (mod position length) length) 'single-float))

(defun sine-wave (position length)
  (sin (* (/ position length) (coerce pi 'single-float))))

(defmacro modincf (i mod &optional (delta 1))
  `(setf ,i (mod (+ ,i ,delta) ,mod)))

(defun play (wave-type frequency &key (buffer-size 1024))
  (cl-out123:start *out*)
  (unwind-protect
       (let* ((sample-rate (cl-out123:playback-format *out*))
              (sample-length (floor sample-rate frequency))
              (j 0))
         (cffi:with-foreign-object (buffer :float buffer-size)
           (loop (loop for i from 0 below buffer-size
                       do (setf (cffi:mem-aref buffer :float i)
                                (funcall wave-type j sample-length))
                          (modincf j sample-length))
                 (cl-out123:play-directly *out* buffer buffer-size))))
    (cl-out123:stop *out*)))