containers

A modular, clean and powerful extension of the OCaml standard library
IN THIS PACKAGE
Module CCList
type 'a iter = ( 'a -> unit ) -> unit

Fast internal iterator.

  • since 2.8
type 'a gen = unit -> 'a option
type 'a printer = Format.formatter -> 'a -> unit
type 'a random_gen = Random.State.t -> 'a
val length : 'a list -> int

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

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

cons x xs is x :: xs

  • since 4.03.0 (4.05.0 in ListLabels)
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 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, 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).

Comparison

Iterators

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

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

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

val concat_map : ( 'a -> 'b list ) -> 'a list -> 'b list

concat_map f l gives the same result as concat (map f l). Tail-recursive.

  • since 4.10.0
val fold_left_map : ( 'a -> 'b -> 'a * 'c ) -> 'a -> 'b list -> 'a * 'c list

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

  • since 4.11.0
val fold_left : ( 'a -> 'b -> 'a ) -> 'a -> 'b list -> 'a

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

Iterators on two lists

val iter2 : ( '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 map2 : ( 'a -> 'b -> 'c ) -> 'a list -> 'b list -> 'c 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 : ( '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 tail-recursive and more efficient.

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

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.

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

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

  • raises Invalid_argument

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

List scanning

val for_all : ( '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 : ( '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 : ( '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 : ( '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 memq : 'a -> 'a list -> bool

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

List searching

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

find_all is another name for filter.

val filteri : ( 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 4.11.0
val partition : ( '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 assq : 'a -> ('a * 'b) list -> 'b

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

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

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

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

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

Lists of pairs

Sorting

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

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

val merge : ( '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).

Lists and Sequences

type +'a t = 'a list
val empty : 'a t

empty is [].

val is_empty : _ t -> bool

is_empty l returns true iff l = [].

  • since 0.11
val map : ( 'a -> 'b ) -> 'a t -> 'b t

map f [a0; a1; …; an] applies function f in turn to a0; a1; …; an. Safe version of List.map.

val append : 'a t -> 'a t -> 'a t

append l1 l2 returns the list that is the concatenation of l1 and l2. Safe version of List.append.

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

cons_maybe (Some x) l is x :: l. cons_maybe None l is l.

  • since 0.13
val cons' : 'a t -> 'a -> 'a t

cons' l x is the same as x :: l. This is convenient for fold functions such as List.fold_left or Array.fold_left.

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

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 l is preserved. Safe version of List.filter.

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

fold_right f [a1; …; an] b is f a1 (f a2 ( … (f an b) … )). Safe version of List.fold_right.

val fold_while : ( 'a -> 'b -> 'a * [ `Stop | `Continue ] ) -> 'a -> 'b t -> 'a

fold_while f init l folds until a stop condition via ('a, `Stop) is indicated by the accumulator.

  • since 0.8
val fold_map : ( 'acc -> 'a -> 'acc * 'b ) -> 'acc -> 'a list -> 'acc * 'b list

fold_map f init l is a fold_left-like function, but it also maps the list to another list.

  • since 0.14
val fold_map_i : ( 'acc -> int -> 'a -> 'acc * 'b ) -> 'acc -> 'a list -> 'acc * 'b list

fold_map_i f init l is a foldi-like function, but it also maps the list to another list.

  • since 2.8
val fold_on_map : f:( 'a -> 'b ) -> reduce:( 'acc -> 'b -> 'acc ) -> 'acc -> 'a list -> 'acc

fold_on_map ~f ~reduce init l combines map f and fold_left reduce init in one operation.

  • since 2.8
val scan_left : ( 'acc -> 'a -> 'acc ) -> 'acc -> 'a list -> 'acc list

scan_left f init l returns the list [init; f init x0; f (f init x0) x1; …] where x0, x1, etc. are the elements of l.

  • since 1.2, but only
  • since 2.2 with labels
val reduce : ( 'a -> 'a -> 'a ) -> 'a list -> 'a option

reduce f (hd::tl) returns Some (fold_left f hd tl). If l is empty, then None is returned.

  • since 3.2
val reduce_exn : ( 'a -> 'a -> 'a ) -> 'a list -> 'a

reduce_exn is the unsafe version of reduce.

  • raises Invalid_argument

    if the given list is empty.

  • since 3.2
val fold_map2 : ( 'acc -> 'a -> 'b -> 'acc * 'c ) -> 'acc -> 'a list -> 'b list -> 'acc * 'c list

fold_map2 f init l1 l2 is to fold_map what List.map2 is to List.map.

  • raises Invalid_argument

    if the lists do not have the same length.

  • since 0.16
val fold_filter_map : ( 'acc -> 'a -> 'acc * 'b option ) -> 'acc -> 'a list -> 'acc * 'b list

fold_filter_map f init l is a fold_left-like function, but also generates a list of output in a way similar to filter_map.

  • since 0.17
val fold_filter_map_i : ( 'acc -> int -> 'a -> 'acc * 'b option ) -> 'acc -> 'a list -> 'acc * 'b list

fold_filter_map_i f init l is a foldi-like function, but also generates a list of output in a way similar to filter_map.

  • since 2.8
val fold_flat_map : ( 'acc -> 'a -> 'acc * 'b list ) -> 'acc -> 'a list -> 'acc * 'b list

fold_flat_map f init l is a fold_left-like function, but it also maps the list to a list of lists that is then flatten'd.

  • since 0.14
val fold_flat_map_i : ( 'acc -> int -> 'a -> 'acc * 'b list ) -> 'acc -> 'a list -> 'acc * 'b list

fold_flat_map_i f init l is a fold_left-like function, but it also maps the list to a list of lists that is then flatten'd.

  • since 2.8
val count : ( 'a -> bool ) -> 'a list -> int

count p l counts how many elements of l satisfy predicate p.

  • since 1.5, but only
  • since 2.2 with labels
val count_true_false : ( 'a -> bool ) -> 'a list -> int * int

count_true_false p l returns a pair (int1,int2) where int1 is the number of elements in l that satisfy the predicate p, and int2 the number of elements that do not satisfy p.

  • since 2.4
val init : int -> ( int -> 'a ) -> 'a t

init len f is f 0; f 1; …; f (len-1).

  • raises Invalid_argument

    if len < 0.

  • since 0.6
val combine : 'a list -> 'b list -> ('a * 'b) list

combine [a1; …; an] [b1; …; bn] is [(a1,b1); …; (an,bn)]. Transform two lists into a list of pairs. Like List.combine but tail-recursive.

  • raises Invalid_argument

    if the lists have distinct lengths.

  • since 1.2, but only
  • since 2.2 with labels
val combine_gen : 'a list -> 'b list -> ('a * 'b) gen

combine_gen l1 l2 transforms two lists into a gen of pairs. Lazy version of combine. Unlike combine, it does not fail if the lists have different lengths; instead, the output has as many pairs as the smallest input list.

  • since 1.2, but only
  • since 2.2 with labels
val combine_shortest : 'a list -> 'b list -> ('a * 'b) list

combine_shortest [a1; …; am] [b1; …; bn] is [(a1,b1); …; (am,bm)] if m <= n. Like combine but stops at the shortest list rather than raising.

  • since 3.1
val split : ('a * 'b) t -> 'a t * 'b t

split [(a1,b1); …; (an,bn)] is ([a1; …; an], [b1; …; bn]). Transform a list of pairs into a pair of lists. A tail-recursive version of List.split.

  • since 1.2, but only
  • since 2.2 with labels
val compare : ( 'a -> 'a -> int ) -> 'a t -> 'a t -> int

compare cmp l1 l2 compares the two lists l1 and l2 using the given comparison function cmp.

val compare_lengths : 'a t -> 'b t -> int

compare_lengths l1 l2 compare the lengths of the two lists l1 and l2. Equivalent to compare (length l1) (length l2) but more efficient.

  • since 1.5, but only
  • since 2.2 with labels
val compare_length_with : 'a t -> int -> int

compare_length_with l x compares the length of the list l to an integer x. Equivalent to compare (length l) x but more efficient.

  • since 1.5, but only
  • since 2.2 with labels
val equal : ( 'a -> 'a -> bool ) -> 'a t -> 'a t -> bool

equal p l1 l2 returns true if l1 and l2 are equal.

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

flat_map f l maps and flattens at the same time (safe). Evaluation order is not guaranteed.

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

flat_map_i f l maps with index and flattens at the same time (safe). Evaluation order is not guaranteed.

  • since 2.8
val flatten : 'a t t -> 'a t

flatten [l1]; [l2]; … concatenates a list of lists. Safe version of List.flatten.

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

product comb l1 l2 computes the cartesian product of the two lists, with the given combinator comb.

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

fold_product f init l1 l2 applies the function f with the accumulator init on all the pair of elements of l1 and l2. Fold on the cartesian product.

val cartesian_product : 'a t t -> 'a t t

cartesian_product [[l1]; [l2]; …; [ln]] produces the cartesian product of this list of lists, by returning all the ways of picking one element per sublist. NOTE the order of the returned list is unspecified. For example:

# cartesian_product [[1;2];[3];[4;5;6]] |> sort =
[[1;3;4];[1;3;5];[1;3;6];[2;3;4];[2;3;5];[2;3;6]];;
# cartesian_product [[1;2];[];[4;5;6]] = [];;
# cartesian_product [[1;2];[3];[4];[5];[6]] |> sort =
[[1;3;4;5;6];[2;3;4;5;6]];;

invariant: cartesian_product l = map_product id l.

  • since 1.2, but only
  • since 2.2 with labels
val map_product_l : ( 'a -> 'b list ) -> 'a list -> 'b list list

map_product_l f l maps each element of l to a list of objects of type 'b using f. We obtain [l1; l2; …; ln] where length l=n and li : 'b list. Then, it returns all the ways of picking exactly one element per li.

  • since 1.2, but only
  • since 2.2 with labels
val diagonal : 'a t -> ('a * 'a) t

diagonal l returns all pairs of distinct positions of the list l, that is the list of List.nth i l, List.nth j l if i < j.

val partition_map_either : ( 'a -> ( 'b, 'c ) CCEither.t ) -> 'a list -> 'b list * 'c list

partition_map_either f l maps f on l and gather results in lists:

  • if f x = Left y, adds y to the first list.
  • if f x = Right z, adds z to the second list.
  • since 3.3
val partition_filter_map : ( 'a -> [< `Left of 'b | `Right of 'c | `Drop ] ) -> 'a list -> 'b list * 'c list

partition_filter_map f l maps f on l and gather results in lists:

  • if f x = `Left y, adds y to the first list.
  • if f x = `Right z, adds z to the second list.
  • if f x = `Drop, ignores x.
  • since 3.3
val partition_map : ( 'a -> [< `Left of 'b | `Right of 'c | `Drop ] ) -> 'a list -> 'b list * 'c list
  • deprecated

    use partition_filter_map instead

  • since 0.11
val group_by : ?hash:( 'a -> int ) -> ?eq:( 'a -> 'a -> bool ) -> 'a t -> 'a list t

group_by ?hash ?eq l groups equal elements, regardless of their order of appearance. precondition: for any x and y, if eq x y then hash x=hash y must hold.

  • since 2.3
val join : join_row:( 'a -> 'b -> 'c option ) -> 'a t -> 'b t -> 'c t

join ~join_row a b combines every element of a with every element of b using join_row. If join_row returns None, then the two elements do not combine. Assume that b allows for multiple iterations.

  • since 2.3
val join_by : ?eq:( 'key -> 'key -> bool ) -> ?hash:( 'key -> int ) -> ( 'a -> 'key ) -> ( 'b -> 'key ) -> merge:( 'key -> 'a -> 'b -> 'c option ) -> 'a t -> 'b t -> 'c t

join_by ?eq ?hash key1 key2 ~merge la lb is a binary operation that takes two sequences a and b, projects their elements resp. with key1 and key2, and combine values (x,y) from (a,b) with the same key using merge. If merge returns None, the combination of values is discarded. precondition: for any x and y, if eq x y then hash x=hash y must hold.

  • since 2.3
val join_all_by : ?eq:( 'key -> 'key -> bool ) -> ?hash:( 'key -> int ) -> ( 'a -> 'key ) -> ( 'b -> 'key ) -> merge:( 'key -> 'a list -> 'b list -> 'c option ) -> 'a t -> 'b t -> 'c t

join_all_by ?eq ?hash key1 key2 ~merge la lb is a binary operation that takes two sequences a and b, projects their elements resp. with key1 and key2, and, for each key k occurring in at least one of them:

  • compute the list l1 of elements of a that map to k
  • compute the list l2 of elements of b that map to k
  • call merge k l1 l2. If merge returns None, the combination of values is discarded, otherwise it returns Some c and c is inserted in the result.
  • since 2.3
val group_join_by : ?eq:( 'a -> 'a -> bool ) -> ?hash:( 'a -> int ) -> ( 'b -> 'a ) -> 'a t -> 'b t -> ('a * 'b list) t

group_join_by ?eq ?hash key la lb associates to every element x of the first sequence, all the elements y of the second sequence such that eq x (key y). Elements of the first sequences without corresponding values in the second one are mapped to [] precondition: for any x and y, if eq x y then hash x=hash y must hold.

  • since 2.3
val sublists_of_len : ?last:( 'a list -> 'a list option ) -> ?offset:int -> int -> 'a list -> 'a list list

sublists_of_len ?last ?offset n l returns sub-lists of l that have length n. By default, these sub-lists are non overlapping: sublists_of_len 2 [1;2;3;4;5;6] returns [1;2]; [3;4]; [5;6].

Examples:

  • sublists_of_len 2 [1;2;3;4;5;6] = [[1;2]; [3;4]; [5;6]].
  • sublists_of_len 2 ~offset:3 [1;2;3;4;5;6] = [1;2];[4;5].
  • sublists_of_len 3 ~last:CCOption.return [1;2;3;4] = [1;2;3];[4].
  • sublists_of_len 2 [1;2;3;4;5] = [[1;2]; [3;4]].
  • parameter offset

    the number of elements skipped between two consecutive sub-lists. By default it is n. If offset < n, the sub-lists will overlap; if offset > n, some elements will not appear at all.

  • parameter last

    if provided and the last group of elements g is such that length g < n, last g is called. If last g = Some g', g' is appended; otherwise g is dropped. If last = CCOption.return, it will simply keep the last group. By default, last = fun _ -> None, i.e. the last group is dropped if shorter than n.

  • raises Invalid_argument

    if offset <= 0 or n <= 0. See CCList.sublists_of_len for more details.

  • since 1.0, but only
  • since 1.5 with labels
val chunks : int -> 'a list -> 'a list list

chunks n l returns consecutives chunks of size at most n from l. Each item of l will occur in exactly one chunk. Only the last chunk might be of length smaller than n. Invariant: (chunks n l |> List.flatten) = l.

  • since 3.2
val intersperse : 'a -> 'a list -> 'a list

intersperse x l inserts the element x between adjacent elements of the list l.

  • since 2.1, but only
  • since 2.2 with labels
val interleave : 'a list -> 'a list -> 'a list

interleave [x1…xn] [y1…ym] is [x1;y1;x2;y2;…] and finishes with the suffix of the longest list.

  • since 2.1, but only
  • since 2.2 with labels
val pure : 'a -> 'a t

pure x is return x.

val mguard : bool -> unit t

mguard c is pure () if c is true, [] otherwise. This is useful to define a list by comprehension, e.g.:

# let square_even xs =
      let* x = xs in
      let* () = mguard (x mod 2 = 0) in
      return @@ x * x;;
val square_even : int list -> int list = <fun>
# square_even [1;2;4;3;5;2];;
- : int list = [4; 16; 4]
  • since 3.1
val return : 'a -> 'a t

return x is x.

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

take n l takes the n first elements of the list l, drop the rest.

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

drop n l drops the n first elements of the list l, keep the rest.

val hd_tl : 'a t -> 'a * 'a t

hd_tl (x :: l) returns hd, l.

  • raises Failure

    if the list is empty.

  • since 0.16
val take_drop : int -> 'a t -> 'a t * 'a t

take_drop n l returns l1, l2 such that l1 @ l2 = l and length l1 = min (length l) n.

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

take_while f l returns the longest prefix of l for which f is true.

  • since 0.13
val drop_while : ( 'a -> bool ) -> 'a t -> 'a t

drop_while f l drops the longest prefix of l for which f is true.

  • since 0.13
val take_drop_while : ( 'a -> bool ) -> 'a t -> 'a t * 'a t

take_drop_while p l = take_while p l, drop_while p l.

  • since 1.2, but only
  • since 2.2 with labels
val last : int -> 'a t -> 'a t

last n l takes the last n elements of l (or less if l doesn't have that many elements).

val head_opt : 'a t -> 'a option

head_opt l returns Some x (the first element of the list l) or None if the list l is empty.

  • since 0.20
val tail_opt : 'a t -> 'a t option

tail_opt l returns Some l' (the given list l without its first element) or None if the list l is empty.

  • since 2.0
val last_opt : 'a t -> 'a option

last_opt l returns Some x (the last element of l) or None if the list l is empty.

  • since 0.20
val find_pred : ( 'a -> bool ) -> 'a t -> 'a option

find_pred p l finds the first element of l that satisfies p, or returns None if no element satisfies p.

  • since 0.11
val find_opt : ( 'a -> bool ) -> 'a t -> 'a option

find_opt p l is the safe version of find.

  • since 1.5, but only
  • since 2.2 with labels
val find_pred_exn : ( 'a -> bool ) -> 'a t -> 'a

find_pred_exn p l is the unsafe version of find_pred.

  • raises Not_found

    if no such element is found.

  • since 0.11
val find_map : ( 'a -> 'b option ) -> 'a t -> 'b option

find_map f l traverses l, applying f to each element. If for some element x, f x = Some y, then Some y is returned. Otherwise the call returns None.

  • since 0.11
val find_mapi : ( int -> 'a -> 'b option ) -> 'a t -> 'b option

find_mapi f l is like find_map, but also pass the index to the predicate function.

  • since 0.11
val find_idx : ( 'a -> bool ) -> 'a t -> (int * 'a) option

find_idx p x returns Some (i,x) where x is the i-th element of l, and p x holds. Otherwise returns None.

val remove : eq:( 'a -> 'a -> bool ) -> key:'a -> 'a t -> 'a t

remove ~eq ~key l removes every instance of key from l. Tail-recursive.

  • parameter eq

    equality function.

  • since 0.11
val filter_map : ( 'a -> 'b option ) -> 'a t -> 'b t

filter_map f l is the sublist of l containing only elements for which f returns Some e. Map and remove elements at the same time.

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

keep_some l retains only elements of the form Some x. Like filter_map CCFun.id.

  • since 1.3, but only
  • since 2.2 with labels
val keep_ok : ( 'a, _ ) result t -> 'a t

keep_ok l retains only elements of the form Ok x.

  • since 1.3, but only
  • since 2.2 with labels
val all_some : 'a option t -> 'a t option

all_some l returns Some l' if all elements of l are of the form Some x, or None otherwise.

  • since 1.3, but only
  • since 2.2 with labels
val all_ok : ( 'a, 'err ) result t -> ( 'a t, 'err ) result

all_ok l returns Ok l' if all elements of l are of the form Ok x, or Error e otherwise (with the first error met).

  • since 1.3, but only
  • since 2.2 with labels
val sorted_mem : cmp:( 'a -> 'a -> int ) -> 'a -> 'a list -> bool

sorted_mem ~cmp x l and mem x l give the same result for any sorted list l, but potentially more efficiently.

  • since 3.5
val sorted_merge : cmp:( 'a -> 'a -> int ) -> 'a list -> 'a list -> 'a list

sorted_merge ~cmp l1 l2 merges elements from both sorted list using the given comparison function cmp.

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

sorted_diff ~cmp l1 l2 returns the elements in l1 that are not in l2. Both lists are assumed to be sorted with respect to cmp and duplicate elements in the input lists are treated individually; for example, sorted_diff ~cmp [1;1;1;2;2;3] [1;2;2] would be [1;1;3]. It is the left inverse of sorted_merge; that is, sorted_diff ~cmp (sorted_merge ~cmp l1 l2) l2 is always equal to l1 for sorted lists l1 and l2.

  • since 3.5
val sort_uniq : cmp:( 'a -> 'a -> int ) -> 'a list -> 'a list

sort_uniq ~cmp l sorts the list l using the given comparison function cmp and remove duplicate elements.

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

sorted_merge_uniq ~cmp l1 l2 merges the sorted lists l1 and l2 and removes duplicates.

  • since 0.10
val sorted_diff_uniq : cmp:( 'a -> 'a -> int ) -> 'a list -> 'a list -> 'a list

sorted_diff_uniq ~cmp l1 l2 collects the elements in l1 that are not in l2 and then remove duplicates. Both lists are assumed to be sorted with respect to cmp and duplicate elements in the input lists are treated individually; for example, sorted_diff_uniq ~cmp [1;1;1;2;2] [1;2;2;2] would be [1]. sorted_diff_uniq ~cmp l1 l2 and uniq_succ ~eq (sorted_diff ~cmp l1 l2) always give the same result for sorted l1 and l2 and compatible cmp and eq.

  • since 3.5
val is_sorted : cmp:( 'a -> 'a -> int ) -> 'a list -> bool

is_sorted ~cmp l returns true iff l is sorted (according to given order).

  • parameter cmp

    the comparison function.

  • since 0.17
val sorted_insert : cmp:( 'a -> 'a -> int ) -> ?uniq:bool -> 'a -> 'a list -> 'a list

sorted_insert ~cmp ?uniq x l inserts x into l such that, if l was sorted, then sorted_insert x l is sorted too.

  • parameter uniq

    if true and x is already in sorted position in l, then x is not duplicated. Default false (x will be inserted in any case).

  • since 0.17
val sorted_remove : cmp:( 'a -> 'a -> int ) -> ?all:bool -> 'a -> 'a list -> 'a list

sorted_remove ~cmp x l removes x from a sorted list l such that the return value is sorted too. By default, it is the left inverse of sorted_insert; that is, sorted_remove ~cmp x (sorted_insert ~cmp x l) is equal to l for any sorted list l.

  • parameter all

    if true then all occurrences of x will be removed. Otherwise, only the first x will be removed (if any). Default false (only the first will be removed).

  • since 3.5
val uniq_succ : eq:( 'a -> 'a -> bool ) -> 'a list -> 'a list

uniq_succ ~eq l removes duplicate elements that occur one next to the other. Examples: uniq_succ ~eq:(=) [1;2;1] = [1;2;1]. uniq_succ ~eq:(=) [1;1;2] = [1;2].

  • since 0.10
val group_succ : eq:( 'a -> 'a -> bool ) -> 'a list -> 'a list list

group_succ ~eq l groups together consecutive elements that are equal according to eq.

  • since 0.11

Indices

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

mapi f l is like map, but the function f is applied to the index of the element as first argument (counting from 0), and the element itself as second argument.

val iteri : ( int -> 'a -> unit ) -> 'a t -> unit

iteri f l is like iter, but the function f is applied to the index of the element as first argument (counting from 0), and the element itself as second argument.

val iteri2 : ( int -> 'a -> 'b -> unit ) -> 'a t -> 'b t -> unit

iteri2 f l1 l2 applies f to the two lists l1 and l2 simultaneously. The integer passed to f indicates the index of element.

  • raises Invalid_argument

    when lists do not have the same length.

  • since 2.0, but only
  • since 2.2 with labels
val foldi : ( 'b -> int -> 'a -> 'b ) -> 'b -> 'a t -> 'b

foldi f init l is like fold but it also passes in the index of each element, from 0 to length l - 1 as additional argument to the folded function f. Tail-recursive.

val foldi2 : ( 'c -> int -> 'a -> 'b -> 'c ) -> 'c -> 'a t -> 'b t -> 'c

foldi2 f init l1 l2 folds on the two lists l1 and l2, with index of each element passed to the function f. Computes f(… (f init i_0 l1_0 l2_0) …) i_n l1_n l2_n .

  • raises Invalid_argument

    when lists do not have the same length.

  • since 2.0, but only
  • since 2.2 with labels
val get_at_idx : int -> 'a t -> 'a option

get_at_idx i l returns Some i-th element of the given list l or None if the list l is too short. If the index is negative, it will get element starting from the end of the list l.

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

nth_opt l n returns Some n-th element of l. Safe version of nth.

  • raises Invalid_argument

    if the int is negative.

  • since 1.5, but only
  • since 2.2 with labels
val get_at_idx_exn : int -> 'a t -> 'a

get_at_idx_exn i l gets the i-th element of l, or

  • raises Not_found

    if the index is invalid. The first element has index 0. If the index is negative, it will get element starting from the end of the list.

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

set_at_idx i x l replaces the i-th element with x (removes the old one), or does nothing if index is too high. If the index is negative, it will set element starting from the end of the list.

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

insert_at_idx i x l inserts x at i-th position, between the two existing elements. If the index is too high, append at the end of the list. If the index is negative, it will insert element starting from the end of the list.

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

remove_at_idx i l removes element at given index i. Does nothing if the index is too high. If the index is negative, it will remove element starting from the end of the list.

Set Operators

Those operations maintain the invariant that the list does not contain duplicates (if it already satisfies it).

val add_nodup : eq:( 'a -> 'a -> bool ) -> 'a -> 'a t -> 'a t

add_nodup ~eq x set adds x to set if it was not already present. Linear time.

  • since 0.11
val remove_one : eq:( 'a -> 'a -> bool ) -> 'a -> 'a t -> 'a t

remove_one ~eq x set removes one occurrence of x from set. Linear time.

  • since 0.11
val mem : ?eq:( 'a -> 'a -> bool ) -> 'a -> 'a t -> bool

mem ?eq x l is true iff x is equal to an element of l. A comparator function eq can be provided. Linear time.

val subset : eq:( 'a -> 'a -> bool ) -> 'a t -> 'a t -> bool

subset ~eq l1 l2 tests if all elements of the list l1 are contained in the list l2 by applying eq.

val uniq : eq:( 'a -> 'a -> bool ) -> 'a t -> 'a t

uniq ~eq l removes duplicates in l w.r.t the equality predicate eq. Complexity is quadratic in the length of the list, but the order of elements is preserved. If you wish for a faster de-duplication but do not care about the order, use sort_uniq.

val union : eq:( 'a -> 'a -> bool ) -> 'a t -> 'a t -> 'a t

union ~eq l1 l2 is the union of the lists l1 and l2 w.r.t. the equality predicate eq. Complexity is product of length of inputs.

val inter : eq:( 'a -> 'a -> bool ) -> 'a t -> 'a t -> 'a t

inter ~eq l1 l2 is the intersection of the lists l1 and l2 w.r.t. the equality predicate eq. Complexity is product of length of inputs.

Other Constructors

val range_by : step:int -> int -> int -> int t

range_by ~step i j iterates on integers from i to j included, where the difference between successive elements is step. Use a negative step for a decreasing list.

  • raises Invalid_argument

    if step=0.

  • since 0.18
val range : int -> int -> int t

range i j iterates on integers from i to j included. It works both for decreasing and increasing ranges.

val range' : int -> int -> int t

range' i j is like range but the second bound j is excluded. For instance range' 0 5 = [0;1;2;3;4].

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

replicate n x replicates the given element x n times.

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

repeat n l concatenates the list l with itself n times.

Association Lists

module Assoc : sig ... end
val assoc : eq:( 'a -> 'a -> bool ) -> 'a -> ('a * 'b) t -> 'b

assoc ~eq k alist returns the value v associated with key k in alist. Like Assoc.get_exn.

  • since 2.0
val assoc_opt : eq:( 'a -> 'a -> bool ) -> 'a -> ('a * 'b) t -> 'b option

assoc_opt ~eq k alist returns Some v if the given key k is present into alist, or None if not present. Like Assoc.get.

  • since 1.5, but only
  • since 2.0 with labels
val assq_opt : 'a -> ('a * 'b) t -> 'b option

assq_opt k alist returns Some v if the given key k is present into alist. Like Assoc.assoc_opt but use physical equality instead of structural equality to compare keys. Safe version of assq.

  • since 1.5, but only
  • since 2.0 with labels
val mem_assoc : ?eq:( 'a -> 'a -> bool ) -> 'a -> ('a * _) t -> bool

mem_assoc ?eq k alist returns true iff k is a key in alist. Like Assoc.mem.

  • since 2.0
val remove_assoc : eq:( 'a -> 'a -> bool ) -> 'a -> ('a * 'b) t -> ('a * 'b) t

remove_assoc ~eq k alist returns the alist without the first pair with key k, if any. Like Assoc.remove.

  • since 2.0

References on Lists

  • since 0.3.3
module Ref : sig ... end
module type MONAD = sig ... end
module Traverse (M : MONAD) : sig ... end

Conversions

val random : 'a random_gen -> 'a t random_gen
val random_non_empty : 'a random_gen -> 'a t random_gen
val random_len : int -> 'a random_gen -> 'a t random_gen
val random_choose : 'a t -> 'a random_gen

random_choose l randomly chooses an element in the list l.

  • raises Not_found

    if the list is empty.

val random_sequence : 'a random_gen t -> 'a t random_gen
val to_string : ?start:string -> ?stop:string -> ?sep:string -> ( 'a -> string ) -> 'a t -> string

to_string ?start ?stop ?sep item_to_string l prints l to a string using sep as a separator between elements of l.

  • since 2.7
val to_iter : 'a t -> 'a iter

to_iter l returns a iter of the elements of the list l.

  • since 2.8
val to_seq : 'a t -> 'a Seq.t

to_seq l returns a Seq.t of the elements of the list l. Renamed from to_std_seq since 3.0.

  • since 3.0
val of_iter : 'a iter -> 'a t

of_iter iter builds a list from a given iter. In the result, elements appear in the same order as they did in the source iter.

  • since 2.8
val of_seq_rev : 'a Seq.t -> 'a t

of_seq_rev seq builds a list from a given Seq.t, in reverse order. Renamed from to_std_seq_rev since 3.0.

  • since 3.0
val of_seq : 'a Seq.t -> 'a t

of_seq seq builds a list from a given Seq.t. In the result, elements appear in the same order as they did in the source Seq.t. Renamed from of_std_seq since 3.0.

  • since 3.0
val to_gen : 'a t -> 'a gen

to_gen l returns a gen of the elements of the list l.

val of_gen : 'a gen -> 'a t

of_gen gen builds a list from a given gen. In the result, elements appear in the same order as they did in the source gen.

Infix Operators

It is convenient to open CCList.Infix to access the infix operators without cluttering the scope too much.

  • since 0.16
module Infix : sig ... end
include module type of Infix
val (>|=) : 'a t -> ( 'a -> 'b ) -> 'b t

l >|= f is the infix version of map with reversed arguments.

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

l1 @ l2 concatenates two lists l1 and l2. As append.

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

funs <*> l is product (fun f x -> f x) funs l.

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

f <$> l is like map.

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

l >>= f is flat_map f l.

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

i -- j is the infix alias for range. Bounds included.

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

i --^ j is the infix alias for range'. Second bound j excluded.

  • since 0.17
val let+ : 'a t -> ( 'a -> 'b ) -> 'b t
val and+ : 'a t -> 'b t -> ('a * 'b) t
val let* : 'a t -> ( 'a -> 'b t ) -> 'b t
val and* : 'a t -> 'b t -> ('a * 'b) t
val and& : 'a list -> 'b list -> ('a * 'b) list

(and&) is combine_shortest. It allows to perform a synchronized product between two lists, stopping gently at the shortest. Usable both with let+ and let*.

# let f xs ys zs =
    let+ x = xs
    and& y = ys
    and& z = zs in
    x + y + z;;
val f : int list -> int list -> int list -> int list = <fun>
# f [1;2] [5;6;7] [10;10];;
- : int list = [16; 18]
  • since 3.1

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 ppf l prints the contents of a list.