Module Stdlib.Queue

First-in first-out queues.

This module implements queues (FIFOs), with in-place modification.

Unsynchronized accesses

Unsynchronized accesses to a queue may lead to an invalid queue state. Thus, concurrent accesses to queues must be synchronized (for instance with a Mutex.t).

type !'a t

The type of queues containing elements of type 'a.

exception Empty

Raised when Queue.take or Queue.peek is applied to an empty queue.

val create : unit -> 'a t

Return a new queue, initially empty.

val add : 'a -> 'a t -> unit

add x q adds the element x at the end of the queue q.

val push : 'a -> 'a t -> unit

push is a synonym for add.

val take : 'a t -> 'a

take q removes and returns the first element in queue q, or raises Empty if the queue is empty.

val take_opt : 'a t -> 'a option

take_opt q removes and returns the first element in queue q, or returns None if the queue is empty.

  • since 4.08
val pop : 'a t -> 'a

pop is a synonym for take.

val peek : 'a t -> 'a

peek q returns the first element in queue q, without removing it from the queue, or raises Empty if the queue is empty.

val peek_opt : 'a t -> 'a option

peek_opt q returns the first element in queue q, without removing it from the queue, or returns None if the queue is empty.

  • since 4.08
val top : 'a t -> 'a

top is a synonym for peek.

val clear : 'a t -> unit

Discard all elements from a queue.

val copy : 'a t -> 'a t

Return a copy of the given queue.

val is_empty : 'a t -> bool

Return true if the given queue is empty, false otherwise.

val length : 'a t -> int

Return the number of elements in a queue.

val iter : ('a -> unit) -> 'a t -> unit

iter f q applies f in turn to all elements of q, from the least recently entered to the most recently entered. The queue itself is unchanged.

val fold : ('b -> 'a -> 'b) -> 'b -> 'a t -> 'b

fold f accu q is equivalent to List.fold_left f accu l, where l is the list of q's elements. The queue remains unchanged.

val transfer : 'a t -> 'a t -> unit

transfer q1 q2 adds all of q1's elements at the end of the queue q2, then clears q1. It is equivalent to the sequence iter (fun x -> add x q2) q1; clear q1, but runs in constant time.

Iterators

val to_seq : 'a t -> 'a Seq.t

Iterate on the queue, in front-to-back order. The behavior is not specified if the queue is modified during the iteration.

  • since 4.07
val add_seq : 'a t -> 'a Seq.t -> unit

Add the elements from a sequence to the end of the queue.

  • since 4.07
val of_seq : 'a Seq.t -> 'a t

Create a queue from a sequence.

  • since 4.07