Fakerjs.Data.Undefinable

data Undefinable t0

A undefinable type. This type constructor is intended to be used for interoperating with JavaScript functions which accept or return undefined values.

The runtime representation of Undefinable T is the same as that of T, except that it may also be undefined. For example, the JavaScript values undefined, [], and [1,2,3] may all be given the type Undefinable (Array Int). Similarly, the JavaScript values [], [undefined], and [1,2,undefined,3] may all be given the type Array (Undefinable Int).

There is one pitfall with Undefinable, which is that values of the type Undefinable T will not function as you might expect if the type T happens to itself permit undefined as a valid runtime representation.

In particular, values of the type Undefinable (Undefinable T) will ‘collapse’, in the sense that the PureScript expressions notUndefined undefined and undefined will both leave you with a value whose runtime representation is just undefined. Therefore it is important to avoid using Undefinable T in situations where T itself can take undefined as a runtime representation. If in doubt, use Maybe instead.

Undefinable does not permit lawful Functor, Applicative, or Monad instances as a result of this pitfall, which is why these instances are not provided.

Instances

• (Show a) => Show (Undefinable a)
• (Eq a) => Eq (Undefinable a)
• Eq1 Undefinable
• (Ord a) => Ord (Undefinable a)
• Ord1 Undefinable

undefined :: forall a. Undefinable a

The undefined value.

notUndefined :: forall a. a -> Undefinable a

Wrap a non-undefined value.

toMaybe :: forall a. Undefinable a -> Maybe a

Represent undefined using Maybe a as Nothing. Note that this function can violate parametricity, as it inspects the runtime representation of its argument (see the warning about the pitfall of Undefinable above).

toUndefinable :: forall a. Maybe a -> Undefinable a

Takes Nothing to undefined, and Just a to a.