List (ppxlib.Stdppx.List)

include module type of struct include StdLabels.List end

type 'a t = 'a list =

| []
| :: of 'a * 'a list

An alias for the type of lists.

val length : 'a list -> int

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

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 reaching the end of the shortest list.

since 4.05

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

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

since 4.05

val cons : 'a -> 'a list -> 'a list

cons x xs is x :: xs

since 4.05

val hd : 'a list -> 'a

Return the first element of the given list.

raises Failure
if the list is empty.

val tl : 'a list -> 'a list

Return the given list without its first element.

raises Failure
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.

raises Failure
if the list is too short.

raises Invalid_argument
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.

raises Invalid_argument
if n is negative.

since 4.05

val rev : 'a list -> 'a list

List reversal.

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

rev_append l1 l2 reverses l1 and concatenates it with l2. This is equivalent to (rev l1) @ l2.

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

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

Comparison

val equal : eq:('a -> 'a -> bool) -> 'a list -> 'a list -> bool

equal eq [a1; ...; an] [b1; ..; bm] holds when the two input lists have the same length, and for each pair of elements ai, bi at the same position we have eq ai bi.

Note: the eq function may be called even if the lists have different length. If you know your equality function is costly, you may want to check compare_lengths first.

since 4.12

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

compare cmp [a1; ...; an] [b1; ...; bm] performs a lexicographic comparison of the two input lists, using the same 'a -> 'a -> int interface as Stdlib.compare:

a1 :: l1 is smaller than a2 :: l2 (negative result) if a1 is smaller than a2, or if they are equal (0 result) and l1 is smaller than l2
the empty list [] is strictly smaller than non-empty lists

Note: the cmp function will be called even if the lists have different lengths.

since 4.12

Iterators

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

Same as 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

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

rev_map ~f l gives the same result as rev (map f l), but is more efficient.

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

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

since 4.11

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

fold_left ~f ~init [b1; ...; bn] is f (... (f (f init b1) b2) ...) bn.

Iterators on two lists

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

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

rev_map2 ~f l1 l2 gives the same result as rev (map2 f l1 l2), but is more efficient.

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

fold_left2 ~f ~init [a1; ...; an] [b1; ...; bn] is f (... (f (f init a1 b1) a2 b2) ...) an bn.

raises 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 ~f [a1; ...; an] checks if all elements of the list satisfy the predicate f. That is, it returns (f a1) && (f a2) && ... && (f an) for a non-empty list and true if the list is empty.

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

exists ~f [a1; ...; an] checks if at least one element of the list satisfies the predicate f. That is, it returns (f a1) || (f a2) || ... || (f an) for a non-empty list and false if the list is empty.

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

Same as for_all, but for a two-argument predicate.

raises 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 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 ~set is true if and only if a is equal to an element of set.

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

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

List searching

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

find ~f l returns the first element of the list l that satisfies the predicate f.

raises Not_found
if there is no value that satisfies f in the list l.

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

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

since 4.05

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

find_index ~f xs returns Some i, where i is the index of the first element of the list xs that satisfies f x, if there is such an element.

It returns None if there is no such element.

since 5.1

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

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

since 5.1

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

filter ~f l returns all the elements of the list l that satisfy the predicate f. 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 filter.

val filteri : f:(int -> 'a -> bool) -> 'a list -> 'a list

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

since 4.11

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

partition ~f l returns a pair of lists (l1, l2), where l1 is the list of all the elements of l that satisfy the predicate f, and l2 is the list of all the elements of l that do not satisfy f. 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.

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

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

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

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

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

since 4.05

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

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

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

Same as sort, but also remove duplicates.

since 4.03

Lists and Sequences

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

Iterate on the list.

since 4.07

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

Create a list from a sequence.

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:('d -> 'e -> 'f -> 'g) ->
  'h

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

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

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

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

val concat : 'a list list -> 'b t

val rev_combine : 'a list -> 'b list -> ('c * 'd) t

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

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

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

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

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

val is_empty : 'a t -> bool

val rev_filter_opt : 'a option list -> 'b t

val filter_opt : 'a option list -> 'b 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:('b -> 'c option) -> 'd option

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

val last : 'a t -> 'b option

val split_while : 'a t -> f:('a -> bool) -> 'a list * 'a t

val find_a_dup : 'elt t -> compare:('elt0 -> 'elt0 -> int) -> 'elt option

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

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