Module `Stdune.List`

include module type of struct include ListLabels end

List operations.

Some functions are flagged as not tail-recursive. A tail-recursive function uses constant stack space, while a non-tail-recursive function uses stack space proportional to the length of its list argument, which can be a problem with very long lists. When the function takes several list arguments, an approximate formula giving stack usage (in some unspecified constant unit) is shown in parentheses.

The above considerations can usually be ignored if your lists are not longer than about 10000 elements.

This module is intended to be used through StdLabels which replaces Array, Bytes, List and String with their labeled counterparts.

For example:

   open StdLabels

   let seq len = List.init ~f:(function i -> i) ~len

val length : 'a list -> int

Return the length (number of elements) of the given list.

val hd : 'a list -> 'a

Return the first element of the given list.

raises Failure
if the list is empty.

val compare_lengths : 'a list -> 'b list -> int

Compare the lengths of two lists. compare_lengths l1 l2 is equivalent to compare (length l1) (length l2), except that the computation stops after itering on the shortest list.

since 4.05.0

val compare_length_with : 'a list -> len:int -> int

Compare the length of a list to an integer. compare_length_with l n is equivalent to compare (length l) n, except that the computation stops after at most n iterations on the list.

since 4.05.0

val tl : 'a list -> 'a list

Return the given list without its first element.

raises Failure
if the list is empty.

val nth_opt : 'a list -> int -> 'a option

Return the n-th element of the given list. The first element (head of the list) is at position 0. Return None if the list is too short.

raises Invalid_argument
if n is negative.

since 4.05

val rev : 'a list -> 'a list

List reversal.

val append : 'a list -> 'a list -> 'a list

Catenate two lists. Same function as the infix operator @. Not tail-recursive (length of the first argument). The @ operator is not tail-recursive either.

val rev_append : 'a list -> 'a list -> 'a list

List.rev_append l1 l2 reverses l1 and concatenates it with l2. This is equivalent to (List.rev l1) @ l2, but rev_append is tail-recursive and more efficient.

val concat : 'a list list -> 'a list

Concatenate a list of lists. The elements of the argument are all concatenated together (in the same order) to give the result. Not tail-recursive (length of the argument + length of the longest sub-list).

val flatten : 'a list list -> 'a list

Same as concat. Not tail-recursive (length of the argument + length of the longest sub-list).

Iterators

val iter : f:('a -> unit) -> 'a list -> unit

List.iter f [a1; ...; an] applies function f in turn to a1; ...; an. It is equivalent to begin f a1; f a2; ...; f an; () end.

val iteri : f:(int -> 'a -> unit) -> 'a list -> unit

Same as List.iter, but the function is applied to the index of the element as first argument (counting from 0), and the element itself as second argument.

since 4.00.0

val map : f:('a -> 'b) -> 'a list -> 'b list

List.map f [a1; ...; an] applies function f to a1, ..., an, and builds the list [f a1; ...; f an] with the results returned by f. Not tail-recursive.

val mapi : f:(int -> 'a -> 'b) -> 'a list -> 'b list

Same as List.map, but the function is applied to the index of the element as first argument (counting from 0), and the element itself as second argument.

since 4.00.0

val rev_map : f:('a -> 'b) -> 'a list -> 'b list

List.rev_map f l gives the same result as List.rev (List.map f l), but is tail-recursive and more efficient.

val fold_left_map : 
  f:('a -> 'b -> 'a * 'c) ->
  init:'a ->
  'b list ->
  'a * 'c list

fold_left_map is a combination of fold_left and map hat threads an accumulator through calls to f

since 4.11.0

val fold_left : f:('a -> 'b -> 'a) -> init:'a -> 'b list -> 'a

List.fold_left f a [b1; ...; bn] is f (... (f (f a b1) b2) ...) bn.

val fold_right : f:('a -> 'b -> 'b) -> 'a list -> init:'b -> 'b

List.fold_right f [a1; ...; an] b is f a1 (f a2 (... (f an b) ...)). Not tail-recursive.

Iterators on two lists

val iter2 : f:('a -> 'b -> unit) -> 'a list -> 'b list -> unit

List.iter2 f [a1; ...; an] [b1; ...; bn] calls in turn f a1 b1; ...; f an bn.

raises Invalid_argument
if the two lists are determined to have different lengths.

val map2 : f:('a -> 'b -> 'c) -> 'a list -> 'b list -> 'c list

List.map2 f [a1; ...; an] [b1; ...; bn] is [f a1 b1; ...; f an bn].

raises Invalid_argument
if the two lists are determined to have different lengths. Not tail-recursive.

val rev_map2 : f:('a -> 'b -> 'c) -> 'a list -> 'b list -> 'c list

List.rev_map2 f l1 l2 gives the same result as List.rev (List.map2 f l1 l2), but is tail-recursive and more efficient.

val fold_left2 : 
  f:('a -> 'b -> 'c -> 'a) ->
  init:'a ->
  'b list ->
  'c list ->
  'a

List.fold_left2 f a [b1; ...; bn] [c1; ...; cn] is f (... (f (f a b1 c1) b2 c2) ...) bn cn.

raises Invalid_argument
if the two lists are determined to have different lengths.

val fold_right2 : 
  f:('a -> 'b -> 'c -> 'c) ->
  'a list ->
  'b list ->
  init:'c ->
  'c

List.fold_right2 f [a1; ...; an] [b1; ...; bn] c is f a1 b1 (f a2 b2 (... (f an bn c) ...)).

raises Invalid_argument
if the two lists are determined to have different lengths. Not tail-recursive.

List scanning

val for_all : f:('a -> bool) -> 'a list -> bool

for_all p [a1; ...; an] checks if all elements of the list satisfy the predicate p. That is, it returns (p a1) && (p a2) && ... && (p an).

val exists : f:('a -> bool) -> 'a list -> bool

exists p [a1; ...; an] checks if at least one element of the list satisfies the predicate p. That is, it returns (p a1) || (p a2) || ... || (p an).

val exists2 : f:('a -> 'b -> bool) -> 'a list -> 'b list -> bool

Same as List.exists, but for a two-argument predicate.

raises Invalid_argument
if the two lists are determined to have different lengths.

val mem : 'a -> set:'a list -> bool

mem a l is true if and only if a is equal to an element of l.

val memq : 'a -> set:'a list -> bool

Same as List.mem, but uses physical equality instead of structural equality to compare list elements.

List searching

val find_opt : f:('a -> bool) -> 'a list -> 'a option

find p l returns the first element of the list l that satisfies the predicate p. Returns None if there is no value that satisfies p in the list l.

since 4.05

val filter : f:('a -> bool) -> 'a list -> 'a list

filter p l returns all the elements of the list l that satisfy the predicate p. The order of the elements in the input list is preserved.

val find_all : f:('a -> bool) -> 'a list -> 'a list

find_all is another name for List.filter.

val partition : f:('a -> bool) -> 'a list -> 'a list * 'a list

partition p l returns a pair of lists (l1, l2), where l1 is the list of all the elements of l that satisfy the predicate p, and l2 is the list of all the elements of l that do not satisfy p. The order of the elements in the input list is preserved.

Association lists

val assoc_opt : 'a -> ('a * 'b) list -> 'b option

assoc_opt a l returns the value associated with key a in the list of pairs l. That is, assoc a [ ...; (a,b); ...] = b if (a,b) is the leftmost binding of a in list l. Returns None if there is no value associated with a in the list l.

since 4.05

val assq : 'a -> ('a * 'b) list -> 'b

Same as List.assoc, but uses physical equality instead of structural equality to compare keys.

val assq_opt : 'a -> ('a * 'b) list -> 'b option

Same as List.assoc_opt, but uses physical equality instead of structural equality to compare keys.

since 4.05.0

val mem_assoc : 'a -> map:('a * 'b) list -> bool

Same as List.assoc, but simply return true if a binding exists, and false if no bindings exist for the given key.

val mem_assq : 'a -> map:('a * 'b) list -> bool

Same as List.mem_assoc, but uses physical equality instead of structural equality to compare keys.

val remove_assoc : 'a -> ('a * 'b) list -> ('a * 'b) list

remove_assoc a l returns the list of pairs l without the first pair with key a, if any. Not tail-recursive.

val remove_assq : 'a -> ('a * 'b) list -> ('a * 'b) list

Same as List.remove_assoc, but uses physical equality instead of structural equality to compare keys. Not tail-recursive.

Lists of pairs

val split : ('a * 'b) list -> 'a list * 'b list

Transform a list of pairs into a pair of lists: split [(a1,b1); ...; (an,bn)] is ([a1; ...; an], [b1; ...; bn]). Not tail-recursive.

val combine : 'a list -> 'b list -> ('a * 'b) list

Transform a pair of lists into a list of pairs: combine [a1; ...; an] [b1; ...; bn] is [(a1,b1); ...; (an,bn)].

raises Invalid_argument
if the two lists have different lengths. Not tail-recursive.

Sorting

val fast_sort : cmp:('a -> 'a -> int) -> 'a list -> 'a list

Same as List.sort or List.stable_sort, whichever is faster on typical input.

val merge : cmp:('a -> 'a -> int) -> 'a list -> 'a list -> 'a list

Merge two lists: Assuming that l1 and l2 are sorted according to the comparison function cmp, merge cmp l1 l2 will return a sorted list containing all the elements of l1 and l2. If several elements compare equal, the elements of l1 will be before the elements of l2. Not tail-recursive (sum of the lengths of the arguments).

Iterators

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

Iterate on the list

since 4.07

val of_seq : 'a Seq.t -> 'a list

Create a list from the iterator

since 4.07

type 'a t = 'a list

val is_empty : _ t -> bool

val is_non_empty : _ t -> bool

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

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

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

val concat_map : 'a t -> f:('a -> 'b t) -> 'b t

val partition_map : 'a t -> f:('a -> ('b, 'c) Either.t) -> 'b t * 'c t

val rev_map_append : 'a t -> 'b t -> f:('a -> 'b) -> 'b t

val rev_partition_map : 'a t -> f:('a -> ('b, 'c) Either.t) -> 'b t * 'c t

type ('a, 'b) skip_or_either =

| Skip
| Left of 'a
| Right of 'b

val filter_partition_map : 
  'a t ->
  f:('a -> ('b, 'c) skip_or_either) ->
  'b t * 'c t

val rev_filter_partition_map : 
  'a t ->
  f:('a -> ('b, 'c) skip_or_either) ->
  'b t * 'c t

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

val findi : 'a t -> f:('a -> bool) -> ('a * int) option

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

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

val last : 'a t -> 'a option

val destruct_last : 'a t -> ('a list * 'a) option

val sort : 'a t -> compare:('a -> 'a -> Ordering.t) -> 'a t

val stable_sort : 'a t -> compare:('a -> 'a -> Ordering.t) -> 'a t

val sort_uniq : 'a t -> compare:('a -> 'a -> Ordering.t) -> 'a t

val compare : 'a t -> 'a t -> compare:('a -> 'a -> Ordering.t) -> Ordering.t

val assoc : ('a * 'b) t -> 'a -> 'b option

val singleton : 'a -> 'a t

val nth : 'a t -> int -> 'a option

val physically_equal : 'a t -> 'a t -> bool

val init : int -> f:(int -> 'a) -> 'a list

val hd_opt : 'a t -> 'a option

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

val hash : ('a -> int) -> 'a list -> int

val cons : 'a -> 'a t -> 'a t

val fold_map : 'a list -> init:'b -> f:('b -> 'a -> 'b * 'c) -> 'b * 'c list

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

val for_all2 : 
  'a list ->
  'b list ->
  f:('a -> 'b -> bool) ->
  (bool, [ `Length_mismatch ]) result

val reduce : 'a list -> f:('a -> 'a -> 'a) -> 'a option

val min : 'a list -> f:('a -> 'a -> Ordering.t) -> 'a option

val max : 'a list -> f:('a -> 'a -> Ordering.t) -> 'a option

Install

Dune Dependency

Authors

Maintainers

Sources

doc/lsp.stdune/Stdune/List/index.html

Module `Stdune.List`

Iterators

Iterators on two lists

List scanning

List searching

Association lists

Lists of pairs

Sorting

Iterators

package lsp

Install

Dune Dependency

Authors

Maintainers

Sources

doc/lsp.stdune/Stdune/List/index.html

Module Stdune.List

Iterators

Iterators on two lists

List scanning

List searching

Association lists

Lists of pairs

Sorting

Iterators

Module `Stdune.List`