Stack: Difference between revisions
→{{header|Clojure}}
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"Tests whether or not the stack is empty."
[] (= () (deref (:elements stack))))</lang>
We can make this a bit smaller and general by using defprotocol along with deftype. Here is a revised version using defprotocol. Note that in both of these examples, the flip function is unnecessary. You could accomplish the same thing using a lambda, but flip is much more general.
<lang lisp>(defn flip
"Flips a functions argument list."
[f] (fn [& args] (apply f (reverse args))))
(defprotocol StackOps
(push-stack [this x] "Pushes an item to the top of the stack.")
(pop-stack [this] "Pops an item from the top of the stack.")
(top-stack [this] "Shows what's on the top of the stack.")
(empty-stack? [this] "Tests whether or not the stack is empty."))
(deftype Stack [elements]
StackOps
(push-stack [x] (dosync (alter elements (flip cons) x)))
(pop-stack [] (let [fst (first (deref elements))]
(dosync (alter elements rest)) fst))
(top-stack [] (first (deref elements)))
(empty-stack? [] (= () (deref elements))))
(def stack (Stack (ref ())))</lang>
== {{header|Common Lisp}} ==
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