Stdlib.Queue
First-in first-out queues.
This module implements queues (FIFOs), with in-place modification.
Warning This module is not thread-safe: each Queue.t
value must be protected from concurrent access (e.g. with a Mutex.t
). Failure to do so can lead to a crash.
Raised when Queue.take
or Queue.peek
is applied to an empty queue.
let create: unit => t('a);
Return a new queue, initially empty.
let add: 'a => t('a) => unit;
add x q
adds the element x
at the end of the queue q
.
let push: 'a => t('a) => unit;
push
is a synonym for add
.
let take: t('a) => 'a;
take q
removes and returns the first element in queue q
, or raises Empty
if the queue is empty.
let take_opt: t('a) => option('a);
take_opt q
removes and returns the first element in queue q
, or returns None
if the queue is empty.
let pop: t('a) => 'a;
pop
is a synonym for take
.
let peek: t('a) => 'a;
peek q
returns the first element in queue q
, without removing it from the queue, or raises Empty
if the queue is empty.
let peek_opt: t('a) => option('a);
peek_opt q
returns the first element in queue q
, without removing it from the queue, or returns None
if the queue is empty.
let top: t('a) => 'a;
top
is a synonym for peek
.
let clear: t('a) => unit;
Discard all elements from a queue.
let is_empty: t('a) => bool;
Return true
if the given queue is empty, false
otherwise.
let length: t('a) => int;
Return the number of elements in a queue.
let iter: ('a => unit) => t('a) => 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.
let fold: ('b => 'a => 'b) => 'b => t('a) => '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.
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.
Iterate on the queue, in front-to-back order. The behavior is not specified if the queue is modified during the iteration.