val mem : 'a list->'a->equal:('a->'a-> bool)-> bool
Checks whether the provided element is there, using equal.
val length : 'a list-> int
val is_empty : 'a list-> bool
val iter : 'a list->f:('a-> unit)-> unit
val fold : 'a list->init:'accum->f:('accum->'a->'accum)->'accum
fold t ~init ~f returns f (... f (f (f init e1) e2) e3 ...) en, where e1..en are the elements of t
val fold_result :
'a list->init:'accum->f:('accum->'a->('accum, 'e)Base.Result.t)->('accum, 'e)Base.Result.t
fold_result t ~init ~f is a short-circuiting version of fold that runs in the Result monad. If f returns an Error _, that value is returned without any additional invocations of f.
val fold_until :
'a list->init:'accum->f:('accum->'a->('accum, 'final)Base.Container.Continue_or_stop.t)->finish:('accum->'final)->'final
fold_until t ~init ~f ~finish is a short-circuiting version of fold. If f returns Stop _ the computation ceases and results in that value. If f returns Continue _, the fold will proceed. If f never returns Stop _, the final result is computed by finish.
Example:
type maybe_negative =
| Found_negative of int
| All_nonnegative of { sum : int }
(** [first_neg_or_sum list] returns the first negative number in [list], if any,
otherwise returns the sum of the list. *)
let first_neg_or_sum =
List.fold_until ~init:0
~f:(fun sum x ->
if x < 0
then Stop (Found_negative x)
else Continue (sum + x))
~finish:(fun sum -> All_nonnegative { sum })
;;
let x = first_neg_or_sum [1; 2; 3; 4; 5]
val x : maybe_negative = All_nonnegative {sum = 15}
let y = first_neg_or_sum [1; 2; -3; 4; 5]
val y : maybe_negative = Found_negative -3
val exists : 'a list->f:('a-> bool)-> bool
Returns true if and only if there exists an element for which the provided function evaluates to true. This is a short-circuiting operation.
val for_all : 'a list->f:('a-> bool)-> bool
Returns true if and only if the provided function evaluates to true for all elements. This is a short-circuiting operation.
Returns the sum of f i for all i in the container.
val find : 'a list->f:('a-> bool)->'a option
Returns as an option the first element for which f evaluates to true.
val find_map : 'a list->f:('a->'b option)->'b option
Returns the first evaluation of f that returns Some, and returns None if there is no such element.
val to_list : 'a list->'a list
val to_array : 'a list->'a array
val min_elt : 'a list->compare:('a->'a-> int)->'a option
Returns a minimum (resp maximum) element from the collection using the provided compare function, or None if the collection is empty. In case of a tie, the first element encountered while traversing the collection is returned. The implementation uses fold so it has the same complexity as fold.
val max_elt : 'a list->compare:('a->'a-> int)->'a option
t >>= f returns a computation that sequences the computations represented by two monad elements. The resulting computation first does t to yield a value v, and then runs the computation returned by f v.
return v returns the (trivial) computation that returns v.
val join : 'a list list->'a list
join t is t >>= (fun t' -> t').
val ignore_m : 'a list->unit list
ignore_m t is map t ~f:(fun _ -> ()). ignore_m used to be called ignore, but we decided that was a bad name, because it shadowed the widely used Caml.ignore. Some monads still do let ignore = ignore_m for historical reasons.
val all : 'a list list->'a list list
val all_unit : unit list list->unit list
Like all, but ensures that every monadic value in the list produces a unit value, all of which are discarded rather than being collected into a list.
Or_unequal_lengths is used for functions that take multiple lists and that only make sense if all the lists have the same length, e.g., iter2, map3. Such functions check the list lengths prior to doing anything else, and return Unequal_lengths if not all the lists have the same length.
val of_list : 'a list->'a list
of_list is the identity function. It is useful so that the List module matches the same signature that other container modules do, namely:
val of_list : 'a List.t -> 'a t
val nth : 'a list->int ->'a option
val nth_exn : '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 if the list is too short or 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 to l2. This is equivalent to (List.rev l1) @ l2, but rev_append is more efficient.
val unordered_append : 'a list->'a list->'a list
unordered_append l1 l2 has the same elements as l1 @ l2, but in some unspecified order. Generally takes time proportional to length of first list, but is O(1) if either list is empty.
val rev_map : 'a list->f:('a->'b)->'b list
rev_map l ~f gives the same result as List.rev (ListLabels.map f l), but is more efficient.
val iter2_exn : 'a list->'b list->f:('a->'b-> unit)-> unit
iter2 [a1; ...; an] [b1; ...; bn] ~f calls in turn f a1 b1; ...; f an bn. The exn version will raise if the two lists have different lengths.
val fold2_exn : 'a list->'b list->init:'c->f:('c->'a->'b->'c)->'c
fold2 ~f ~init:a [b1; ...; bn] [c1; ...; cn] is f (... (f (f a b1 c1) b2 c2)
...) bn cn. The exn version will raise if the two lists have different lengths.
val fold2 :
'a list->'b list->init:'c->f:('c->'a->'b->'c)->'cOr_unequal_lengths.t
val for_alli : 'a list->f:(int ->'a-> bool)-> bool
Like List.for_all, but passes the index as an argument.
val for_all2_exn : 'a list->'b list->f:('a->'b-> bool)-> bool
Like List.for_all, but for a two-argument predicate. The exn version will raise if the two lists have different lengths.
filter l ~f 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 rev_filter : 'a list->f:('a-> bool)->'a list
Like filter, but reverses the order of the input list.
val filteri : 'a list->f:(int ->'a-> bool)->'a list
val partition_map :
'a list->f:('a->('b, 'c)Base__.Either0.t)->'b list * 'c list
partition_map t ~f partitions t according to f.
val partition3_map :
'a list->f:('a->[ `Fst of 'b| `Snd of 'c| `Trd of 'd ])->'b list * 'c list * 'd list
val partition_tf : 'a list->f:('a-> bool)->'a list * 'a list
partition_tf l ~f 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. The "tf" suffix is mnemonic to remind readers at a call that the result is (trues, falses).
val partition_result :
('ok, 'error)Base.Result.t list->'ok list * 'error list
partition_result l returns a pair of lists (l1, l2), where l1 is the list of all Ok elements in l and l2 is the list of all Error elements. The order of elements in the input list is preserved.
val split_n : 'a list->int ->'a list * 'a list
split_n [e1; ...; em] n is ([e1; ...; en], [en+1; ...; em]).
If n > m, ([e1; ...; em], []) is returned.
If n < 0, ([], [e1; ...; em]) is returned.
val sort : 'a list->compare:('a->'a-> int)->'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, Poly.compare is a suitable comparison function.
The current implementation uses Merge Sort. It runs in linear heap space and logarithmic stack space.
Presently, the sort is stable, meaning that two equal elements in the input will be in the same order in the output.
val stable_sort : 'a list->compare:('a->'a-> int)->'a list
Like sort, but guaranteed to be stable.
val merge : 'a list->'a list->compare:('a->'a-> int)->'a list
Merges two lists: assuming that l1 and l2 are sorted according to the comparison function compare, merge compare 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.
val hd : 'a list->'a option
val tl : 'a list->'a list option
val hd_exn : 'a list->'a
Returns the first element of the given list. Raises if the list is empty.
val tl_exn : 'a list->'a list
Returns the given list without its first element. Raises if the list is empty.
val findi : 'a list->f:(int ->'a-> bool)->(int * 'a) option
val findi_exn : 'a list->f:(int ->'a-> bool)-> int * 'a
Like find_exn, but passes the index as an argument.
val find_exn : 'a list->f:('a-> bool)->'a
find_exn t ~f returns the first element of t that satisfies f. It raises Caml.Not_found or Not_found_s if there is no such element.
val find_map_exn : 'a list->f:('a->'b option)->'b
Returns the first evaluation of f that returns Some. Raises Caml.Not_found or Not_found_s if f always returns None.
Like find_map and find_map_exn, but passes the index as an argument.
val find_mapi : 'a list->f:(int ->'a->'b option)->'b option
val find_mapi_exn : 'a list->f:(int ->'a->'b option)->'b
val append : 'a list->'a list->'a list
E.g., append [1; 2] [3; 4; 5] is [1; 2; 3; 4; 5]
val map : 'a list->f:('a->'b)->'b list
map f [a1; ...; an] applies function f to a1, a2, ..., an, in order, and builds the list [f a1; ...; f an] with the results returned by f.
folding_map is a version of map that threads an accumulator through calls to f.
val folding_map : 'a list->init:'b->f:('b->'a->'b * 'c)->'c list
val folding_mapi :
'a list->init:'b->f:(int ->'b->'a->'b * 'c)->'c list
fold_map is a combination of fold and map that threads an accumulator through calls to f.
val fold_map : 'a list->init:'b->f:('b->'a->'b * 'c)->'b * 'c list
val fold_mapi :
'a list->init:'b->f:(int ->'b->'a->'b * 'c)->'b * 'c list
val concat_map : 'a list->f:('a->'b list)->'b list
concat_map t ~f is concat (map t ~f), except that there is no guarantee about the order in which f is applied to the elements of t.
val concat_mapi : 'a list->f:(int ->'a->'b list)->'b list
concat_mapi t ~f is like concat_map, but passes the index as an argument
map2 [a1; ...; an] [b1; ...; bn] ~f is [f a1 b1; ...; f an bn]. The exn version will raise if the two lists have different lengths.
val map2_exn : 'a list->'b list->f:('a->'b->'c)->'c list
val rev_map3_exn :
'a list->'b list->'c list->f:('a->'b->'c->'d)->'d list
val rev_map3 :
'a list->'b list->'c list->f:('a->'b->'c->'d)->'d listOr_unequal_lengths.t
Analogous to map2.
val map3_exn :
'a list->'b list->'c list->f:('a->'b->'c->'d)->'d list
val map3 :
'a list->'b list->'c list->f:('a->'b->'c->'d)->'d listOr_unequal_lengths.t
val rev_map_append : 'a list->'b list->f:('a->'b)->'b list
rev_map_append l1 l2 ~f reverses l1 mapping f over each element, and appends the result to the front of l2.
val fold_right : 'a list->f:('a->'b->'b)->init:'b->'b
fold_right [a1; ...; an] ~f ~init:b is f a1 (f a2 (... (f an b) ...)).
val fold_left : 'a list->init:'b->f:('b->'a->'b)->'b
fold_left is the same as Container.S1.fold, and one should always use fold rather than fold_left, except in functors that are parameterized over a more general signature where this equivalence does not hold.
Transform a list of pairs into a pair of lists: unzip [(a1,b1); ...; (an,bn)] is ([a1; ...; an], [b1; ...; bn]).
val unzip : ('a * 'b) list->'a list * 'b list
val unzip3 : ('a * 'b * 'c) list->'a list * 'b list * 'c list
Transform a pair of lists into an (optional) list of pairs: zip [a1; ...; an] [b1;
...; bn] is [(a1,b1); ...; (an,bn)]. Returns Unequal_lengths if the two lists have different lengths.
mapi is just like map, but it also passes in the index of each element as the first argument to the mapped function. Tail-recursive.
val rev_mapi : 'a list->f:(int ->'a->'b)->'b list
val iteri : 'a list->f:(int ->'a-> unit)-> unit
iteri is just like iter, but it also passes in the index of each element as the first argument to the iter'd function. Tail-recursive.
val foldi : 'a list->init:'b->f:(int ->'b->'a->'b)->'b
foldi is just like fold, but it also passes in the index of each element as the first argument to the folded function. Tail-recursive.
val reduce_exn : 'a list->f:('a->'a->'a)->'a
reduce_exn [a1; ...; an] ~f is f (... (f (f a1 a2) a3) ...) an. It fails on the empty list. Tail recursive.
val reduce : 'a list->f:('a->'a->'a)->'a option
val reduce_balanced : 'a list->f:('a->'a->'a)->'a option
reduce_balanced returns the same value as reduce when f is associative, but differs in that the tree of nested applications of f has logarithmic depth.
This is useful when your 'a grows in size as you reduce it and f becomes more expensive with bigger inputs. For example, reduce_balanced ~f:(^) takes n*log(n) time, while reduce ~f:(^) takes quadratic time.
val reduce_balanced_exn : 'a list->f:('a->'a->'a)->'a
val group : 'a list->break:('a->'a-> bool)->'a list list
group l ~break returns a list of lists (i.e., groups) whose concatenation is equal to the original list. Each group is broken where break returns true on a pair of successive elements.
Example:
group ~break:(<>) ['M';'i';'s';'s';'i';'s';'s';'i';'p';'p';'i'] ->
[['M'];['i'];['s';'s'];['i'];['s';'s'];['i'];['p';'p'];['i']]
val groupi : 'a list->break:(int ->'a->'a-> bool)->'a list list
This is just like group, except that you get the index in the original list of the current element along with the two elements.
Example, group the chars of "Mississippi" into triples:
groupi ~break:(fun i _ _ -> i mod 3 = 0)
['M';'i';'s';'s';'i';'s';'s';'i';'p';'p';'i'] ->
[['M'; 'i'; 's']; ['s'; 'i'; 's']; ['s'; 'i'; 'p']; ['p'; 'i']]
val sort_and_group : 'a list->compare:('a->'a-> int)->'a list list
Group equal elements into the same buckets. Sorting is stable.
val chunks_of : 'a list->length:int ->'a list list
chunks_of l ~length returns a list of lists whose concatenation is equal to the original list. Every list has length elements, except for possibly the last list, which may have fewer. chunks_of raises if length <= 0.
val last : 'a list->'a option
The final element of a list. The _exn version raises on the empty list.
val last_exn : 'a list->'a
val is_prefix : 'a list->prefix:'a list->equal:('a->'a-> bool)-> bool
is_prefix xs ~prefix returns true if xs starts with prefix.
val is_suffix : 'a list->suffix:'a list->equal:('a->'a-> bool)-> bool
is_suffix xs ~suffix returns true if xs ends with suffix.
val find_consecutive_duplicate :
'a list->equal:('a->'a-> bool)->('a * 'a) option
find_consecutive_duplicate t ~equal returns the first pair of consecutive elements (a1, a2) in t such that equal a1 a2. They are returned in the same order as they appear in t. equal need not be an equivalence relation; it is simply used as a predicate on consecutive elements.
val remove_consecutive_duplicates :
?which_to_keep:[ `First | `Last ]->'a list->equal:('a->'a-> bool)->'a list
Returns the given list with consecutive duplicates removed. The relative order of the other elements is unaffected. The element kept from a run of duplicates is determined by which_to_keep.
val dedup_and_sort : 'a list->compare:('a->'a-> int)->'a list
Returns the given list with duplicates removed and in sorted order.
val find_a_dup : 'a list->compare:('a->'a-> int)->'a option
find_a_dup returns a duplicate from the list (with no guarantees about which duplicate you get), or None if there are no dups.
val contains_dup : 'a list->compare:('a->'a-> int)-> bool
Returns true if there are any two elements in the list which are the same. O(n log n) time complexity.
val find_all_dups : 'a list->compare:('a->'a-> int)->'a list
find_all_dups returns a list of all elements that occur more than once, with no guarantees about order. O(n log n) time complexity.
val all_equal : 'a list->equal:('a->'a-> bool)->'a option
all_equal returns a single element of the list that is equal to all other elements, or None if no such element exists.
val count : 'a list->f:('a-> bool)-> int
count l ~f is the number of elements in l that satisfy the predicate f.
val counti : 'a list->f:(int ->'a-> bool)-> int
val range :
?stride:int ->?start:[ `inclusive | `exclusive ]->?stop:[ `inclusive | `exclusive ]->int ->int ->int list
range ?stride ?start ?stop start_i stop_i is the list of integers from start_i to stop_i, stepping by stride. If stride < 0 then we need start_i > stop_i for the result to be nonempty (or start_i = stop_i in the case where both bounds are inclusive).
val range' :
compare:('a->'a-> int)->stride:('a->'a)->?start:[ `inclusive | `exclusive ]->?stop:[ `inclusive | `exclusive ]->'a->'a->'a list
range' is analogous to range for general start/stop/stride types. range' raises if stride x returns x or if the direction that stride x moves x changes from one call to the next.
val init : int ->f:(int ->'a)->'a list
init n ~f is [(f 0); (f 1); ...; (f (n-1))]. It is an error if n < 0. init applies f to values in decreasing order; starting with n - 1, and ending with 0. This is the opposite order to Array.init.
val rev_filter_map : 'a list->f:('a->'b option)->'b list
rev_filter_map l ~f is the reversed sublist of l containing only elements for which f returns Some e.
val rev_filter_mapi : 'a list->f:(int ->'a->'b option)->'b list
rev_filter_mapi is just like rev_filter_map, but it also passes in the index of each element as the first argument to the mapped function. Tail-recursive.
val filter_map : 'a list->f:('a->'b option)->'b list
filter_map l ~f is the sublist of l containing only elements for which f returns Some e.
val filter_mapi : 'a list->f:(int ->'a->'b option)->'b list
filter_mapi is just like filter_map, but it also passes in the index of each element as the first argument to the mapped function. Tail-recursive.
val filter_opt : 'a option list->'a list
filter_opt l is the sublist of l containing only elements which are Some e. In other words, filter_opt l = filter_map ~f:Fn.id l.
val sub : 'a list->pos:int ->len:int ->'a list
sub pos len l is the len-element sublist of l, starting at pos.
val take : 'a list->int ->'a list
take l n returns the first n elements of l, or all of l if n > length l. take l n = fst (split_n l n).
val drop : 'a list->int ->'a list
drop l n returns l without the first n elements, or the empty list if n >
length l. drop l n is equivalent to snd (split_n l n).
val take_while : 'a list->f:('a-> bool)->'a list
take_while l ~f returns the longest prefix of l for which f is true.
val drop_while : 'a list->f:('a-> bool)->'a list
drop_while l ~f drops the longest prefix of l for which f is true.
val split_while : 'a list->f:('a-> bool)->'a list * 'a list
drop_last l drops the last element of l, returning None if l is empty.
val drop_last_exn : 'a list->'a list
val concat : 'a list list->'a list
Concatenates a list of lists. The elements of the argument are all concatenated together (in the same order) to give the result. Tail recursive over outer and inner lists.
val concat_no_order : 'a list list->'a list
Like concat, but faster and without preserving any ordering (i.e., for lists that are essentially viewed as multi-sets).
val cons : 'a->'a list->'a list
val cartesian_product : 'a list->'b list->('a * 'b) list
Returns a list with all possible pairs -- if the input lists have length len1 and len2, the resulting list will have length len1 * len2.
transpose m transposes the rows and columns of the matrix m, considered as either a row of column lists or (dually) a column of row lists.
Example:
transpose [[1;2;3];[4;5;6]] = [[1;4];[2;5];[3;6]]
On non-empty rectangular matrices, transpose is an involution (i.e., transpose
(transpose m) = m). Transpose returns None when called on lists of lists with non-uniform lengths.
val transpose_exn : 'a list list->'a list list
transpose_exn transposes the rows and columns of its argument, throwing an exception if the list is not rectangular.
val intersperse : 'a list->sep:'a->'a list
intersperse xs ~sep places sep between adjacent elements of xs. For example, intersperse [1;2;3] ~sep:0 = [1;0;2;0;3].
stable_dedup Same as dedup but maintains the order of the list and doesn't allow compare function to be specified (otherwise, the implementation in terms of Set.t would hide a heavyweight functor instantiation at each call).
This function is deprecated because it uses polymorphic comparison under the hood without being obvious to the caller.
deprecated [since 2021-08] Use [Set.stable_dedup_list] or [stable_dedup_staged] instead.
stable_dedup_staged is the same as dedup_and_sort but maintains the order of the list. This function is staged because it instantiates a functor when compare is passed.
See also Set.stable_dedup_list, which is the underlying implementation of this function and lets you avoid the functor instantiation when you already have such a module on hand.
exn_if_dup ~compare ?context t ~to_sexp raises if t contains a duplicate. It will specifically raise a Duplicate_found exception and use context as its second argument. O(n log n) time complexity.
slice t start stop returns a new list including elements t.(start) through t.(stop-1), normalized Python-style with the exception that stop = 0 is treated as stop = length t.
zip_with_remainder xs ys zips as many elements as possible of xs and ys together and also returns the un-zipped remainder of the longer input, if the inputs have different lengths.
If xs and ys have the same length, zip_with_remainder xs ys returns the same thing as (zip_exn xs ys, None)