core.clj

(ns overtone-chrismas.core
  (:use [overtone.live]))

(defn foo [freq]
  (pan2 (sin-osc freq)))

; ドレミの周波数を定義
(def doremi {:none 0
             :do  261.6
             :re  293.6
             :mi  329.6
             :fa  349.2
             :so  392
             :ra  440
             :si  493.8
             :do2 523.3
             :re2 587})

(defn key-on [note]
  (demo 0.3 (foo (note doremi))))

(defn play-notes [notes]
  (dorun (map #(do (key-on %) (Thread/sleep 300))
              notes)))

;ジングルベル
(defn play-jingle-bells []
  (play-notes
   [:do :ra :so :fa :do :none
    :do :ra :so :fa :re :none
    :re :si :ra :so :mi :none
    :do2 :do2 :si :so :ra :none

    :do :ra :so :fa :do :none
    :do :ra :so :fa :re :none
    :re :si :ra :so :do2 :do2 :do2 :do2
    :re2 :do2 :si :ra :so :none

    :do2 :none
    :ra :ra :ra :none :ra :ra :ra :none
    :ra :do2 :fa :so :ra :none
    :si :si :si :si :si :ra :ra :ra
    :ra :so :so :ra :so :none

    :do2 :none
    :ra :ra :ra :none :ra :ra :ra :none
    :ra :do2 :fa :so :ra :none
    :si :si :si :si :si :ra :ra :ra
    :do2 :do2 :si :so :fa
    ])
)

project.clj

(defproject overtone-chrismas "1.0.0-SNAPSHOT"
  :description "FIXME: write description"
  :dependencies [[org.clojure/clojure "1.3.0"]
                 [overtone "0.5.0"]])

Excellent work :-)

If you're interested, I've fixed up a few things here: https://gist.github.com/1457193