package ppxlib

  1. Overview
  2. Docs
package ppxlib
Legend:
Library
Module
Module type
Parameter
Class
Class type
include module type of struct include StdLabels.List end
type 'a t = 'a list =
  1. | []
  2. | :: of 'a * 'a list

An alias for the type of lists.

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.

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. Raise Failure "hd" 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 cons : 'a -> 'a list -> 'a list

cons x xs is x :: xs

  • since 4.05.0
val tl : 'a list -> 'a list

Return the given list without its first element. Raise Failure "tl" if the list is empty.

val nth : 'a list -> int -> 'a

Return the n-th element of the given list. The first element (head of the list) is at position 0. Raise Failure "nth" if the list is too short. Raise Invalid_argument "List.nth" if n is negative.

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. Raise Invalid_argument "List.nth" if n is negative.

  • since 4.05
val rev : 'a list -> 'a list

List reversal.

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 flatten : 'a list list -> 'a list

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

Iterators

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

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

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

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

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 for_all2 : f:('a -> 'b -> bool) -> 'a list -> 'b list -> bool

Same as List.for_all, but for a two-argument predicate. Raise Invalid_argument if the two lists are determined to have different lengths.

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

Same as List.exists, but for a two-argument predicate. Raise 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 : f:('a -> bool) -> 'a list -> 'a

find p l returns the first element of the list l that satisfies the predicate p. Raise Not_found if there is no value that satisfies p in the list l.

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

assoc 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. Raise Not_found if there is no value associated with a in the list l.

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.

Lists of pairs

Sorting

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

Sort a list in increasing order according to a comparison function. The comparison function must return 0 if its arguments compare as equal, a positive integer if the first is greater, and a negative integer if the first is smaller (see Array.sort for a complete specification). For example, Stdlib.compare is a suitable comparison function. The resulting list is sorted in increasing order. List.sort is guaranteed to run in constant heap space (in addition to the size of the result list) and logarithmic stack space.

The current implementation uses Merge Sort. It runs in constant heap space and logarithmic stack space.

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

Same as List.sort, but the sorting algorithm is guaranteed to be stable (i.e. elements that compare equal are kept in their original order) .

The current implementation uses Merge Sort. It runs in constant heap space and logarithmic stack space.

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 sort_uniq : cmp:('a -> 'a -> int) -> 'a list -> 'a list

Same as List.sort, but also remove duplicates.

  • since 4.03.0

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
include sig ... end
val merge : [> `not_tail_recursive ]
val remove_assoc : [> `not_tail_recursive ]
val remove_assq : [> `not_tail_recursive ]
val rev_mapi : 'a t -> f:(int -> 'a -> 'b) -> 'b t
val fold_right2 : 'a list -> 'b list -> init:'c -> f:('a -> 'b -> 'c -> 'c) -> 'c
val map : 'a list -> f:('a -> 'b) -> 'b list
val mapi : 'a t -> f:(int -> 'a -> 'b) -> 'b list
val fold_right : 'a list -> init:'b -> f:('a -> 'b -> 'b) -> 'b
val append : 'a list -> 'a list -> 'a list
val concat : 'a list list -> 'a t
val rev_combine : 'a list -> 'b list -> ('a * 'b) t
val combine : 'a list -> 'b list -> ('a * 'b) list
val split : ('a * 'b) list -> 'a t * 'b t
val map2 : 'a list -> 'b list -> f:('a -> 'b -> 'c) -> 'c list
val partition_map : ('a -> ('b, 'c) Either.t) -> 'a t -> 'b list * 'c list
val init : len:int -> f:(int -> 'a) -> 'a list
val is_empty : 'a t -> bool
val rev_filter_opt : 'a option list -> 'a t
val filter_opt : 'a option list -> 'a list
val filter_map : 'a list -> f:('a -> 'b option) -> 'b t
val concat_map : 'a list -> f:('a -> 'b list) -> 'b t
val find_map : 'a t -> f:('a -> 'b option) -> 'b option
val find_map_exn : 'a t -> f:('a -> 'b option) -> 'b
val last : 'a t -> 'a option
val split_while : 'a t -> f:('a -> bool) -> 'a list * 'a t
val find_a_dup : 'elt t -> compare:('elt -> 'elt -> int) -> 'elt option
val assoc_opt : 'a -> ('a * 'b) list -> 'b option
val iter : 'a list -> f:('a -> unit) -> unit
OCaml

Innovation. Community. Security.

GitHub Discord Twitter Peertube RSS
About
Changelog Releases Industrial Users Academic Users Why OCaml
Ecosystem
Packages Community Events OCaml Planet Jobs
Resources
Install OCaml Get Started Platform Tools Language Manual Standard Library API Books Exercises Papers OCaml Playground Logo
Policies
Carbon Footprint Governance Privacy Code of Conduct