Stack implementation in Clojure using Protocols and Records

I was trying to experiment with Clojure Protocols and Records recently, and came up with a toy example to clarify my understanding of their usage in the context of developing a simple Stack Abstract Data Type.

For an excellent tutorial on utilizing protocols and records in Clojure btw – check out Kotka.de – Memoize done right .


;; Stack example abstract data type using Clojure protocols and records
;; viksit at gmail dot com
;; 2010

(ns viksit.stack
  (:refer-clojure :exclude [pop]))

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

(defrecord Stack [coll]
  PStack
  (push [_ val]
	(swap! coll conj val))
  (pop [_]
       (let [ret (first @coll)]
	 (swap! coll rest)
	 ret))
  (top [_]
       (first @coll)))

;; Testing
stack> (def s (Stack. (atom '())))
#'stack/s
stack> (push s 10)
(10)
stack> (push s 20)
(20 10)
stack> (top s)
20
stack> s
#:stack.Stack{:coll #}
stack> (pop s)
20

More tutorial links on Protocols,

[1] http://blog.higher-order.net/2010/05/05/circuitbreaker-clojure-1-2/
[2] http://freegeek.in/blog/2010/05/clojure-protocols-datatypes-a-sneak-peek/
[3] http://groups.google.com/group/clojure/browse_thread/thread/b8620db0b7424712