stack.clj

(defprotocol PStack
  "A stack protocol"
  (push [this val] "Push element in")
  (pop* [this] "Pop element from stack")
  (top [this] "Get top element from stack"))

(defrecord FStack [coll]
  PStack
  (push [_ val]
    "Return the stack with the new element inserted"
    (FStack. (conj coll val)))
  (pop* [_]
    "Return the stack without the top element"
    (FStack. (rest coll)))
  (top [_]
    "Return the top value of the stack"
    (first coll)))