Queue/Usage: Difference between revisions

=={{header|Clojure}}==

The "pop" function implies mutating the input, but since Clojure data structures are immutable we use a mutable reference to an immutable data structure; in this case an <tt>atom</tt> holding a vector:

<lang clojure>

(defn make-queue []

(atom []))

(defn push-queue [q x]

(swap! q conj x))

(defn pop-queue [q]

(if (pos? (count @q))

(let [x (first @q)]

(swap! q subvec 1)

x)))

</lang>

Alternately, one could use a <tt>ref</tt> if coordination between multiple threads was required:

<lang clojure>

(defn make-queue []

(ref []))

(defn push-queue [q x]

(alter q conj x))

(defn pop-queue [q]

(if (pos? (count @q))

(let [x (first @q)]

(alter q subvec 1)

x)))

</lang>

The <tt>push-queue </tt> and <tt>pop-queue </tt> functions would need to be called from within a <tt>dosync</tt> transaction.