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clojure impl
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}</lang>
=={{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-fifo []
(atom []))
(defn push-fifo [f x]
(swap! f conj x))
(defn pop-fifo [f]
(if (pos? (count @f))
(let [x (first @f)]
(swap! f subvec 1)
x)))
</lang>
Alternately, one could use a <tt>ref</tt> if coordination between multiple threads was required:
<lang clojure>
(defn make-fifo []
(ref []))
(defn push-fifo [f x]
(alter f conj x))
(defn pop-fifo [f]
(if (pos? (count @f))
(let [x (first @f)]
(alter f subvec 1)
x)))
</lang>
The <tt>push-fifo</tt> and <tt>pop-fifo</tt> functions would need to be called from within a <tt>dosync</tt> transaction.
=={{header|Common Lisp}}==
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