package base

ascending is identical to compare. descending x y = ascending y x. These are intended to be mnemonic when used like List.sort ~compare:ascending and List.sort ~cmp:descending, since they cause the list to be sorted in ascending or descending order, respectively.

between t ~low ~high means low <= t <= high

clamp_exn t ~min ~max returns t', the closest value to t such that between t' ~low:min ~high:max is true.

Raises if not (min <= max).

E.g., append (of_list [a; b]) (of_list [c; d; e]) is of_list [a; b; c; d; e]

Concatenates a nested container. The elements of the inner containers are concatenated together in order to give the result.

map f (of_list [a1; ...; an]) applies f to a1, a2, ..., an, in order, and builds a result equivalent to of_list [f a1; ...; f an].

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

filter_map t ~f applies f to every x in t. The result contains every y for which f x returns Some y.

concat_map t ~f is equivalent to concat (map t ~f).

partition_tf t ~f returns a pair t1, t2, where t1 is all elements of t that satisfy f, and t2 is all elements of t that do not satisfy f. The "tf" suffix is mnemonic to remind readers that the result is (trues, falses).

partition_map t ~f partitions t according to f.

Checks whether the provided element is there, using equality on elts.

iter must allow exceptions raised in f to escape, terminating the iteration cleanly. The same holds for all functions below taking an f.

fold t ~init ~f returns f (... f (f (f init e1) e2) e3 ...) en, where e1..en are the elements of 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.

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

Returns true if and only if there exists an element for which the provided function evaluates to true. This is a short-circuiting operation.

Returns true if and only if the provided function evaluates to true for all elements. This is a short-circuiting operation.