package batteries

some x returns Some x.

• since 2.2.0

may f (Some x) calls f x and may f None does nothing.

map f (Some x) returns Some (f x) and map f None returns None.

bind (Some x) f returns f x and bind None f returns None.

@example "Our functions return option types. Compose them to propagate None."

let pick_long case =
  try
    Some (List.find (fun data -> List.length data > 1000) case)
  with Not_found -> None
let last_null data = List.rindex_of 0 data
let interesting_positions dataset =
  List.filter_map
    (fun case -> Option.bind last_null (pick_long case))
    dataset

apply None x returns x and apply (Some f) x returns f x

filter f None returns None, filter f (Some x) returns Some x if f x is true, and None otherwise.

default x (Some v) returns v and default x None returns x.

Like default, with the arguments reversed. None |? 10 returns 10, while Some "foo" |? "bar" returns "foo".

Note This operator does not short circuit like ( || ) and ( && ). Both arguments will be evaluated.

• since 2.0

Like default, but the default value is passed as a thunk that is only computed if needed.

• since 2.1

map_default f x (Some v) returns f v and map_default f x None returns x.

Like map_default, but the default value is passed as a thunk that is only computed if needed.

• since 2.1

is_none None returns true otherwise it returns false.

is_some (Some x) returns true otherwise it returns false.

get (Some x) returns x.

• raises Invalid_argument

  on get None.

get_exn (Some x) e returns x and get_exn None e raises e.

Compare two options, possibly using custom comparators for the value. None is always assumed to be less than Some _. The parameter cmp defaults to Pervasives.compare.

Test for equality between option types, possibly using a custom equality predicate. The parameter eq defaults to Pervasives.(=).

• since 1.4.0

enum (Some x) returns the singleton x, while enum None returns the empty enumeration.

of_enum e consumes the first element of e, if it exists, and returns Some e. If e is empty, return None.

This module provides everything needed to write and execute computations in the Option monad.

Comparison between optional values

• since 2.2.0

Operations on options, with labels.