Just another update

Task/Queue-Definition/00DESCRIPTION

@@ -1,6 +1,7 @@
 {{Data structure}}
 [[File:Fifo.gif|frame|right|Illustration of FIFO behavior]]
-Implement a FIFO queue. Elements are added at one side and popped from the other in the order of insertion.
+Implement a FIFO queue.
+Elements are added at one side and popped from the other in the order of insertion.
 
 Operations:
 * push (aka ''enqueue'') - add element

Task/Queue-Definition/Bracmat/queue-definition.bracmat

@@ -0,0 +1,10 @@
+  ( queue
+  =   (list=)
+      (enqueue=.(.!arg) !(its.list):?(its.list))
+      ( dequeue
+      =   x
+        .   !(its.list):?(its.list) (.?x)
+          & !x
+      )
+      (empty=.!(its.list):)
+  )

Task/Queue-Definition/Clojure/queue-definition.clj

@@ -5,10 +5,8 @@
   (swap! q conj x))
 
 (defn dequeue [q]
-  (if (seq @q)
-    (let [x (first @q)]
-      (swap! q subvec 1)
-      x)
+  (if-let [[f & r] (seq @q)]
+    (do (reset! q r) f)
     (throw (IllegalStateException. "Can't pop an empty queue."))))
 
 (defn queue-empty? [q]

Task/Queue-Definition/CoffeeScript/queue-definition.coffee

@@ -0,0 +1,38 @@
+# Implement a fifo as an array of arrays, to
+# greatly amortize dequeue costs, at some expense of
+# memory overhead and insertion time.  The speedup
+# depends on the underlying JS implementation, but
+# it's significant on node.js.
+Fifo = ->
+  max_chunk = 512
+  arr = [] # array of arrays
+  count = 0
+
+  self =
+    enqueue: (elem) ->
+      if count == 0 or arr[arr.length-1].length >= max_chunk
+        arr.push []
+      count += 1
+      arr[arr.length-1].push elem
+    dequeue: (elem) ->
+      throw Error("queue is empty") if count == 0
+      val = arr[0].shift()
+      count -= 1
+      if arr[0].length == 0
+        arr.shift()
+      val
+    is_empty: (elem) ->
+      count == 0
+
+# test
+do ->
+  max = 5000000
+  q = Fifo()
+  for i in [1..max]
+    q.enqueue
+      number: i
+
+  console.log q.dequeue()
+  while !q.is_empty()
+    v = q.dequeue()
+  console.log v

Task/Queue-Definition/UNIX-Shell/queue-definition-1.sh

@@ -0,0 +1,25 @@
+queue_push() {
+    typeset -n q=$1
+    shift
+    q+=("$@")
+}
+
+queue_pop() {
+    if queue_empty $1; then
+        print -u2 "queue $1 is empty"
+        return 1
+    fi
+    typeset -n q=$1
+    print "${q[0]}"     # emit the value of the popped element
+    q=( "${q[@]:1}" )   # and remove the first element from the queue
+}
+
+queue_empty() {
+    typeset -n q=$1
+    (( ${#q[@]} == 0 ))
+}
+
+queue_peek() {
+    typeset -n q=$1
+    print "${q[0]}"
+}

Task/Queue-Definition/UNIX-Shell/queue-definition-2.sh

@@ -0,0 +1,14 @@
+# any valid variable name can be used as a queue without initialization
+
+queue_empty foo && echo foo is empty || echo foo is not empty
+
+queue_push foo bar
+queue_push foo baz
+queue_push foo "element with spaces"
+
+queue_empty foo && echo foo is empty || echo foo is not empty
+
+print "peek: $(queue_peek foo)"; queue_pop foo
+print "peek: $(queue_peek foo)"; queue_pop foo
+print "peek: $(queue_peek foo)"; queue_pop foo
+print "peek: $(queue_peek foo)"; queue_pop foo