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# DA.Optional
> Reference documentation for Daml module DA.Optional.
Daml module
DA.Optional
The Optional type encapsulates an optional value. A value of type
## Functions
### `fromSome`
`fromSome` : [`Optional`](/appdev/reference/daml-standard-library/prelude#type-da-internal-prelude-optional-37153) `a` -> `a`
The `fromSome` function extracts the element out of a `Some` and
throws an error if its argument is `None`.
Note that in most cases you should prefer using `fromSomeNote`
to get a better error on failures.
### `fromSomeNote`
`fromSomeNote` : [`Text`](/appdev/reference/daml-standard-library/prelude#type-ghc-types-text-51952) -> [`Optional`](/appdev/reference/daml-standard-library/prelude#type-da-internal-prelude-optional-37153) `a` -> `a`
Like `fromSome` but with a custom error message.
### `catOptionals`
`catOptionals` : \[[`Optional`](/appdev/reference/daml-standard-library/prelude#type-da-internal-prelude-optional-37153) `a`] -> \[`a`]
The `catOptionals` function takes a list of `Optionals` and returns a
list of all the `Some` values.
### `listToOptional`
`listToOptional` : \[`a`] -> [`Optional`](/appdev/reference/daml-standard-library/prelude#type-da-internal-prelude-optional-37153) `a`
The `listToOptional` function returns `None` on an empty list or
`Some` a where a is the first element of the list.
### `optionalToList`
`optionalToList` : [`Optional`](/appdev/reference/daml-standard-library/prelude#type-da-internal-prelude-optional-37153) `a` -> \[`a`]
The `optionalToList` function returns an empty list when given
`None` or a singleton list when not given `None`.
### `fromOptional`
`fromOptional` : `a` -> [`Optional`](/appdev/reference/daml-standard-library/prelude#type-da-internal-prelude-optional-37153) `a` -> `a`
The `fromOptional` function takes a default value and a `Optional`
value. If the `Optional` is `None`, it returns the default values
otherwise, it returns the value contained in the `Optional`.
### `isSome`
`isSome` : [`Optional`](/appdev/reference/daml-standard-library/prelude#type-da-internal-prelude-optional-37153) `a` -> [`Bool`](/appdev/reference/daml-standard-library/prelude#type-ghc-types-bool-66265)
The `isSome` function returns `True` iff its argument is of the
form `Some _`.
### `isNone`
`isNone` : [`Optional`](/appdev/reference/daml-standard-library/prelude#type-da-internal-prelude-optional-37153) `a` -> [`Bool`](/appdev/reference/daml-standard-library/prelude#type-ghc-types-bool-66265)
The `isNone` function returns `True` iff its argument is
`None`.
### `mapOptional`
`mapOptional` : (`a` -> [`Optional`](/appdev/reference/daml-standard-library/prelude#type-da-internal-prelude-optional-37153) `b`) -> \[`a`] -> \[`b`]
The `mapOptional` function is a version of `map` which can throw out
elements. In particular, the functional argument returns something
of type `Optional b`. If this is `None`, no element is added on to
the result list. If it is `Some b`, then `b` is included in the
result list.
### `whenSome`
`whenSome` : [`Applicative`](/appdev/reference/daml-standard-library/prelude#class-da-internal-prelude-applicative-9257) `m` => [`Optional`](/appdev/reference/daml-standard-library/prelude#type-da-internal-prelude-optional-37153) `a` -> (`a` -> `m` ()) -> `m` ()
Perform some operation on `Some`, given the field inside the
`Some`.
### `whenSome_`
`whenSome_` : [`Applicative`](/appdev/reference/daml-standard-library/prelude#class-da-internal-prelude-applicative-9257) `m` => [`Optional`](/appdev/reference/daml-standard-library/prelude#type-da-internal-prelude-optional-37153) `a` -> (`a` -> `m` `b`) -> `m` ()
Perform some operation on `Some` and discard its result,
given the field inside the `Some`.
### `whenNone`
`whenNone` : [`Applicative`](/appdev/reference/daml-standard-library/prelude#class-da-internal-prelude-applicative-9257) `m` => [`Optional`](/appdev/reference/daml-standard-library/prelude#type-da-internal-prelude-optional-37153) `a` -> `m` `a` -> `m` `a`
Perform some operation on `None`.
Otherwise returns content of `Some` pured to Applicative.
### `whenNone_`
`whenNone_` : [`Applicative`](/appdev/reference/daml-standard-library/prelude#class-da-internal-prelude-applicative-9257) `m` => [`Optional`](/appdev/reference/daml-standard-library/prelude#type-da-internal-prelude-optional-37153) `a` -> `m` `b` -> `m` ()
Perform some operation on `None`. Do nothing for `Some`.
Convenient for discarding `Some` content.
### `findOptional`
`findOptional` : (`a` -> [`Optional`](/appdev/reference/daml-standard-library/prelude#type-da-internal-prelude-optional-37153) `b`) -> \[`a`] -> [`Optional`](/appdev/reference/daml-standard-library/prelude#type-da-internal-prelude-optional-37153) `b`
The `findOptional` returns the value of the predicate at the first
element where it returns `Some`. `findOptional` is similar to `find` but it
allows you to return a value from the predicate. This is useful both as a more
type safe version if the predicate corresponds to a pattern match
and for performance to avoid duplicating work performed in the predicate.
## History