collection type function (exercise on day 1 of Clojure)
unless macro (exercise on day 2 of Clojure)
lazy fibonacci implementation (exercise on day 2 of Clojure)
protocal and defrecord type definition (exercise on day 2 of Clojure)
account transfers (exercise on day 3 of Clojure)
sleeping barber (exercise on day 3 of Clojure)