Representation of First-In, First-Out(FIFO) data structure.

Returns empty queue.

head empty == Nothing

Create queue from list. The newest element comes head of the queue.

[ "H" -- The Last-In element is "H"
, "e"
, "l"
, "l"
, "o"
]
    |> fromListLIFO
    |> head
--> Just "H"

Create queue from list. The oldest element of the list comes head of the queue.

[]
    |> (::) "H" -- The First-In element is "H"
    |> (::) "e"
    |> (::) "l"
    |> (::) "l"
    |> (::) "o"
    |> fromListFIFO
    |> head
--> Just "H"

Returns True if the argument has no element.

empty
    |> enqueue "a"
    |> isEmpty
--> False


empty
    |> enqueue "a"
    |> dequeue
    |> isEmpty
--> True

Returns the oldest element injected in the queue wrapped in Maybe.

empty
    |> head
--> Nothing


empty
    |> enqueue "e"
    |> enqueue "l"
    |> enqueue "m"
    |> head
--> Just "e"

Returns the newest element if exists, wrapped in Maybe. Worst-case time complexity of this operation is O(log N).

empty
    |> enqueue 100
    |> enqueue 200
    |> rear
--> Just 200


empty
    |> enqueue 100
    |> dequeue
    |> rear
--> Nothing

Returns how many elements is contained in the queue. The time complexity is O(log N).

empty
    |> length
--> 0


empty
    |> enqueue 1
    |> enqueue 2
    |> enqueue 3
    |> dequeue
    |> length
--> 2

Inject a new element into the rear side of the queue.

empty
    |> enqueue 100
    |> enqueue 200
    |> head
--> Just 100

Returns queue without the oldest element of the given queue.

empty
    |> enqueue "e"
    |> enqueue "l"
    |> enqueue "m"
    |> enqueue "i"
    |> enqueue "s"
    |> enqueue "h"
    |> dequeue
    |> head
--> Just "l"

Convert a queue to List. The Last-In element in the queue will become the head of the returned list.

empty
    |> enqueue 100
    |> enqueue 200
    |> enqueue 300 -- The Last-In element is 300
    |> toListLIFO
--> [300,200,100]

Convert a queue to List. The First-In element in the queue will become the head of the returned list.

empty
    |> enqueue 100 -- The First-In element is 100
    |> enqueue 200
    |> enqueue 300
    |> toListFIFO
--> [100,200,300]