Module Base.Queue

A queue implemented with an array.

The implementation will grow the array as necessary. The array will never automatically be shrunk, but the size can be interrogated and set with capacity and set_capacity.

Iteration functions (iter, fold, map, concat_map, filter, filter_map, filter_inplace, and some functions from Container.S1) will raise if the queue is modified during iteration.

Also see Linked_queue, which has different performance characteristics.

module type S = sig ... end
type 'a t
val compare : ('a -> 'a -> int) -> 'a t -> 'a t -> int
include S with type 'a t := 'a t
include Sexpable.S1 with type 'a t := 'a t
val t_of_sexp : (Sexplib0.Sexp.t -> 'a) -> Sexplib0.Sexp.t -> 'a t
val sexp_of_t : ('a -> Sexplib0.Sexp.t) -> 'a t -> Sexplib0.Sexp.t
include Indexed_container.S1 with type 'a t := 'a t
include Container.S1 with type 'a t := 'a t
val mem : 'a t -> 'a -> equal:('a -> 'a -> bool) -> bool

Checks whether the provided element is there, using equal.

val length : 'a t -> int
val is_empty : 'a t -> bool
val iter : 'a t -> f:('a -> unit) -> unit
val fold : 'a t -> init:'accum -> f:('accum -> 'a -> 'accum) -> 'accum

fold t ~init ~f returns f (... f (f (f init e1) e2) e3 ...) en, where e1..en are the elements of t

val fold_result : 'a t -> init:'accum -> f:('accum -> 'a -> ('accum, 'e) Result.t) -> ('accum, 'e) Result.t

fold_result t ~init ~f is a short-circuiting version of fold that runs in the Result monad. If f returns an Error _, that value is returned without any additional invocations of f.

val fold_until : 'a t -> init:'accum -> f:('accum -> 'a -> ('accum, 'final) Base__Container_intf.Export.Continue_or_stop.t) -> finish:('accum -> 'final) -> 'final

fold_until t ~init ~f ~finish is a short-circuiting version of fold. If f returns Stop _ the computation ceases and results in that value. If f returns Continue _, the fold will proceed. If f never returns Stop _, the final result is computed by finish.

Example:

type maybe_negative =
  | Found_negative of int
  | All_nonnegative of { sum : int }

(** [first_neg_or_sum list] returns the first negative number in [list], if any,
    otherwise returns the sum of the list. *)
let first_neg_or_sum =
  List.fold_until ~init:0
    ~f:(fun sum x ->
      if x < 0
      then Stop (Found_negative x)
      else Continue (sum + x))
    ~finish:(fun sum -> All_nonnegative { sum })
;;

let x = first_neg_or_sum [1; 2; 3; 4; 5]
val x : maybe_negative = All_nonnegative {sum = 15}

let y = first_neg_or_sum [1; 2; -3; 4; 5]
val y : maybe_negative = Found_negative -3
val exists : 'a t -> f:('a -> bool) -> bool

Returns true if and only if there exists an element for which the provided function evaluates to true. This is a short-circuiting operation.

val for_all : 'a t -> f:('a -> bool) -> bool

Returns true if and only if the provided function evaluates to true for all elements. This is a short-circuiting operation.

val count : 'a t -> f:('a -> bool) -> int

Returns the number of elements for which the provided function evaluates to true.

val sum : (module Base__Container_intf.Summable with type t = 'sum) -> 'a t -> f:('a -> 'sum) -> 'sum

Returns the sum of f i for all i in the container.

val find : 'a t -> f:('a -> bool) -> 'a option

Returns as an option the first element for which f evaluates to true.

val find_map : 'a t -> f:('a -> 'b option) -> 'b option

Returns the first evaluation of f that returns Some, and returns None if there is no such element.

val to_list : 'a t -> 'a list
val to_array : 'a t -> 'a array
val min_elt : 'a t -> compare:('a -> 'a -> int) -> 'a option

Returns a minimum (resp maximum) element from the collection using the provided compare function, or None if the collection is empty. In case of a tie, the first element encountered while traversing the collection is returned. The implementation uses fold so it has the same complexity as fold.

val max_elt : 'a t -> compare:('a -> 'a -> int) -> 'a option

These are all like their equivalents in Container except that an index starting at 0 is added as the first argument to f.

val foldi : 'a t -> init:_ -> f:(int -> _ -> 'a -> _) -> _
val iteri : 'a t -> f:(int -> 'a -> unit) -> unit
val existsi : 'a t -> f:(int -> 'a -> bool) -> bool
val for_alli : 'a t -> f:(int -> 'a -> bool) -> bool
val counti : 'a t -> f:(int -> 'a -> bool) -> int
val findi : 'a t -> f:(int -> 'a -> bool) -> (int * 'a) option
val find_mapi : 'a t -> f:(int -> 'a -> 'b option) -> 'b option
val singleton : 'a -> 'a t

singleton a returns a queue with one element.

val of_list : 'a list -> 'a t

of_list list returns a queue t with the elements of list in the same order as the elements of list (i.e. the first element of t is the first element of the list).

val of_array : 'a array -> 'a t
val init : int -> f:(int -> 'a) -> 'a t

init n ~f is equivalent to of_list (List.init n ~f).

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

enqueue t a adds a to the end of t.

val enqueue_all : 'a t -> 'a list -> unit

enqueue_all t list adds all elements in list to t in order of list.

val dequeue : 'a t -> 'a option

dequeue t removes and returns the front element of t, if any.

val dequeue_exn : 'a t -> 'a
val peek : 'a t -> 'a option

peek t returns but does not remove the front element of t, if any.

val peek_exn : 'a t -> 'a
val clear : _ t -> unit

clear t discards all elements from t.

val copy : 'a t -> 'a t

copy t returns a copy of t.

val map : 'a t -> f:('a -> 'b) -> 'b t
val mapi : 'a t -> f:(int -> 'a -> 'b) -> 'b t
val concat_map : 'a t -> f:('a -> 'b list) -> 'b t

Creates a new queue with elements equal to List.concat_map ~f (to_list t).

val concat_mapi : 'a t -> f:(int -> 'a -> 'b list) -> 'b t
val filter_map : 'a t -> f:('a -> 'b option) -> 'b t

filter_map creates a new queue with elements equal to List.filter_map ~f (to_list t).

val filter_mapi : 'a t -> f:(int -> 'a -> 'b option) -> 'b t
val filter : 'a t -> f:('a -> bool) -> 'a t

filter is like filter_map, except with List.filter.

val filteri : 'a t -> f:(int -> 'a -> bool) -> 'a t
val filter_inplace : 'a t -> f:('a -> bool) -> unit

filter_inplace t ~f removes all elements of t that don't satisfy f. If f raises, t is unchanged. This is inplace in that it modifies t; however, it uses space linear in the final length of t.

val filteri_inplace : 'a t -> f:(int -> 'a -> bool) -> unit
include Equal.S1 with type 'a t := 'a t
val equal : 'a Equal.equal -> 'a t Equal.equal
include Invariant.S1 with type 'a t := 'a t
val invariant : ('a -> unit) -> 'a t -> unit
val create : ?capacity:int -> unit -> _ t

Create an empty queue.

val last : 'a t -> 'a option

last t returns the most recently enqueued element in t, if any.

val last_exn : 'a t -> 'a
val blit_transfer : src:'a t -> dst:'a t -> ?len:int -> unit -> unit

Transfers up to len elements from the front of src to the end of dst, removing them from src. It is an error if len < 0.

Aside from a call to set_capacity dst if needed, runs in O(len) time

val get : 'a t -> int -> 'a

get t i returns the i'th element in t, where the 0'th element is at the front of t and the length t - 1 element is at the back.

val set : 'a t -> int -> 'a -> unit
val capacity : _ t -> int

Returns the current length of the backing array.

val set_capacity : _ t -> int -> unit

set_capacity t c sets the capacity of t's backing array to at least max c (length t). If t's capacity changes, then this involves allocating a new backing array and copying the queue elements over. set_capacity may decrease the capacity of t, if c < capacity t.