package containers

  1. Overview
  2. Docs

Helpers for the standard Seq type

See oseq for a richer API.

  • since 3.0
type 'a iter = ('a -> unit) -> unit
type 'a gen = unit -> 'a option
type 'a equal = 'a -> 'a -> bool
type 'a ord = 'a -> 'a -> int
type 'a printer = Stdlib.Format.formatter -> 'a -> unit

Basics

include module type of Stdlib.Seq
type !'a t = unit -> 'a node
and !'a node = 'a Stdlib__Seq.node =
  1. | Nil
  2. | Cons of 'a * 'a t
val find_index : ('a -> bool) -> 'a t -> int option
val find_mapi : (int -> 'a -> 'b option) -> 'a t -> 'b option
exception Forced_twice
val once : 'a t -> 'a t
val transpose : 'a t t -> 'a t t
val partition_map : ('a -> ('b, 'c) Stdlib.Either.t) -> 'a t -> 'b t * 'c t
val partition : ('a -> bool) -> 'a t -> 'a t * 'a t
val of_dispenser : (unit -> 'a option) -> 'a t
val to_dispenser : 'a t -> unit -> 'a option
val ints : int -> int t
val nil : 'a t
val empty : 'a t
val cons : 'a -> 'a t -> 'a t
val singleton : 'a -> 'a t
val init : int -> (int -> 'a) -> 'a t

init n f corresponds to the sequence f 0; f 1; ...; f (n-1).

  • raises Invalid_argument

    if n is negative.

  • since 3.10
val repeat : ?n:int -> 'a -> 'a t

repeat ~n x repeats x n times then stops. If n is omitted, then x is repeated forever.

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

forever f corresponds to the infinite sequence containing all the f ().

  • since 3.10
val cycle : 'a t -> 'a t

Cycle through the iterator infinitely. The iterator shouldn't be empty.

val iterate : ('a -> 'a) -> 'a -> 'a t

iterate f a corresponds to the infinite sequence containing a, f a, f (f a), ...]

  • since 3.10
val unfold : ('b -> ('a * 'b) option) -> 'b -> 'a t

unfold f acc calls f acc and:

  • if f acc = Some (x, acc'), yield x, continue with unfold f acc'.
  • if f acc = None, stops.
val is_empty : 'a t -> bool

is_empty xs checks in the sequence xs is empty

val head : 'a t -> 'a option

Head of the list.

val head_exn : 'a t -> 'a

Unsafe version of head.

  • raises Not_found

    if the list is empty.

val tail : 'a t -> 'a t option

Tail of the list.

val tail_exn : 'a t -> 'a t

Unsafe version of tail.

  • raises Not_found

    if the list is empty.

val uncons : 'a t -> ('a * 'a t) option

uncons xs return None if xs is empty other

  • since 3.10
val equal : 'a equal -> 'a t equal

Equality step by step. Eager.

val compare : 'a ord -> 'a t ord

Lexicographic comparison. Eager.

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

Fold on values.

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

Alias for fold

val foldi : ('a -> int -> 'b -> 'a) -> 'a -> 'b t -> 'a

fold_lefti f init xs applies f acc i x where acc is the result of the previous computation or init for the first one, i is the index in the sequence (starts at 0) and x is the element of the sequence.

  • since 3.10
val fold_lefti : ('a -> int -> 'b -> 'a) -> 'a -> 'b t -> 'a

Alias of foldi.

  • since 3.10
val iter : ('a -> unit) -> 'a t -> unit
val iteri : (int -> 'a -> unit) -> 'a t -> unit

Iterate with index (starts at 0).

val length : _ t -> int

Number of elements in the list. Will not terminate if the list if infinite: use (for instance) take to make the list finite if necessary.

val take : int -> 'a t -> 'a t
val take_while : ('a -> bool) -> 'a t -> 'a t
val drop : int -> 'a t -> 'a t
val drop_while : ('a -> bool) -> 'a t -> 'a t
val map : ('a -> 'b) -> 'a t -> 'b t
val mapi : (int -> 'a -> 'b) -> 'a t -> 'b t

Map with index (starts at 0).

val fmap : ('a -> 'b option) -> 'a t -> 'b t
val filter : ('a -> bool) -> 'a t -> 'a t
val append : 'a t -> 'a t -> 'a t
val product_with : ('a -> 'b -> 'c) -> 'a t -> 'b t -> 'c t

Fair product of two (possibly infinite) lists into a new list. Lazy. The first parameter is used to combine each pair of elements.

val map_product : ('a -> 'b -> 'c) -> 'a t -> 'b t -> 'c t

Alias of product_with.

  • since 3.10
val product : 'a t -> 'b t -> ('a * 'b) t

Specialization of product_with producing tuples.

val group : 'a equal -> 'a t -> 'a t t

group eq l groups together consecutive elements that satisfy eq. Lazy. For instance group (=) [1;1;1;2;2;3;3;1] yields [1;1;1]; [2;2]; [3;3]; [1].

val uniq : 'a equal -> 'a t -> 'a t

uniq eq l returns l but removes consecutive duplicates. Lazy. In other words, if several values that are equal follow one another, only the first of them is kept.

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

for_all p [a1; ...; an] checks if all elements of the sequence satisfy the predicate p. That is, it returns (p a1) && ... && (p an) for a non-empty list and true if the sequence is empty. It consumes the sequence until it finds an element not satisfying the predicate.

  • since 3.3
val exists : ('a -> bool) -> 'a t -> bool

exists p [a1; ...; an] checks if at least one element of the sequence satisfies the predicate p. That is, it returns (p a1) || ... || (p an) for a non-empty sequence and false if the list is empty. It consumes the sequence until it finds an element satisfying the predicate.

  • since 3.3
val find : ('a -> bool) -> 'a t -> 'a option

find p [a1; ...; an] return Some ai for the first ai satisfying the predicate p and return None otherwise.

  • since 3.10
val find_map : ('a -> 'b option) -> 'a t -> 'b option

find f [a1; ...; an] return Some (f ai) for the first ai such that f ai = Some _ and return None otherwise.

  • since 3.10
val scan : ('a -> 'b -> 'a) -> 'a -> 'b t -> 'a t

scan f init xs is the sequence containing the intermediate result of fold f init xs.

  • since 3.10
val flat_map : ('a -> 'b t) -> 'a t -> 'b t
val concat_map : ('a -> 'b t) -> 'a t -> 'b t

Alias of flat_map

  • since 3.10
val filter_map : ('a -> 'b option) -> 'a t -> 'b t
val flatten : 'a t t -> 'a t
val concat : 'a t t -> 'a t

Alias of flatten.

  • since 3.10
val range : int -> int -> int t
val (--) : int -> int -> int t

a -- b is the range of integers containing a and b (therefore, never empty).

val (--^) : int -> int -> int t

a -- b is the integer range from a to b, where b is excluded.

Operations on two Collections

val fold2 : ('acc -> 'a -> 'b -> 'acc) -> 'acc -> 'a t -> 'b t -> 'acc

Fold on two collections at once. Stop as soon as one of them ends.

val fold_left2 : ('acc -> 'a -> 'b -> 'acc) -> 'acc -> 'a t -> 'b t -> 'acc

Alias for fold2.

  • since 3.10
val map2 : ('a -> 'b -> 'c) -> 'a t -> 'b t -> 'c t

Map on two collections at once. Stop as soon as one of the arguments is exhausted.

val iter2 : ('a -> 'b -> unit) -> 'a t -> 'b t -> unit

Iterate on two collections at once. Stop as soon as one of them ends.

val for_all2 : ('a -> 'b -> bool) -> 'a t -> 'b t -> bool
val exists2 : ('a -> 'b -> bool) -> 'a t -> 'b t -> bool
val merge : 'a ord -> 'a t -> 'a t -> 'a t

Merge two sorted iterators into a sorted iterator.

val sorted_merge : 'a ord -> 'a t -> 'a t -> 'a t

Alias of merge.

  • since 3.10
val zip : 'a t -> 'b t -> ('a * 'b) t

Combine elements pairwise. Stop as soon as one of the lists stops.

val unzip : ('a * 'b) t -> 'a t * 'b t

Split each tuple in the list.

val split : ('a * 'b) t -> 'a t * 'b t

Alias of unzip.

  • since 3.10
val zip_i : 'a t -> (int * 'a) t

zip_i seq zips the index of each element with the element itself.

  • since 3.8

Misc

val sort : cmp:'a ord -> 'a t -> 'a t

Eager sort. Require the iterator to be finite. O(n ln(n)) time and space.

val sort_uniq : cmp:'a ord -> 'a t -> 'a t

Eager sort that removes duplicate values. Require the iterator to be finite. O(n ln(n)) time and space.

val memoize : 'a t -> 'a t

Avoid recomputations by caching intermediate results.

Fair Combinations

val interleave : 'a t -> 'a t -> 'a t

Fair interleaving of both streams.

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

Fair version of flat_map.

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

Fair version of (<*>).

Implementations

val return : 'a -> 'a t
val pure : 'a -> 'a t
val (>>=) : 'a t -> ('a -> 'b t) -> 'b t
val (>|=) : 'a t -> ('a -> 'b) -> 'b t
val (<*>) : ('a -> 'b) t -> 'a t -> 'b t
val (>>-) : 'a t -> ('a -> 'b t) -> 'b t

Infix version of fair_flat_map.

val (<.>) : ('a -> 'b) t -> 'a t -> 'b t

Infix version of fair_app.

Infix operators

module Infix : sig ... end
module type MONAD = sig ... end
module Traverse (M : MONAD) : sig ... end

Conversions

val of_list : 'a list -> 'a t
val to_list : 'a t -> 'a list

Gather all values into a list.

val of_array : 'a array -> 'a t

Iterate on the array.

val to_array : 'a t -> 'a array

Convert into array.

val to_rev_list : 'a t -> 'a list

Convert to a list, in reverse order. More efficient than to_list.

val to_iter : 'a t -> 'a iter
val to_gen : 'a t -> 'a gen
val of_gen : 'a gen -> 'a t

of_gen g consumes the generator and caches intermediate results.

val of_string : string -> char t

Iterate on characters.

  • since 3.7

IO

val pp : ?pp_start:unit printer -> ?pp_stop:unit printer -> ?pp_sep:unit printer -> 'a printer -> 'a t printer

pp ~pp_start ~pp_stop ~pp_sep pp_item ppf s formats the sequence s on ppf. Each element is formatted with pp_item, pp_start is called at the beginning, pp_stop is called at the end, pp_sep is called between each elements. By defaults pp_start and pp_stop does nothing and pp_sep defaults to (fun out -> Format.fprintf out ",@ ").