{-
Convert an `Optional` value into the equivalent `List`

Examples:

```
./toList Integer ([1] : Optional Integer) = [1] : List Integer

./toList Integer ([] : Optional Integer) = [] : List Integer
```
-}
let toList : ∀(a : Type) → Optional a → List a
    =   λ(a : Type)
    →   λ(o : Optional a)
    →   Optional/fold a o (List a) (λ(x : a) → [x] : List a) ([] : List a)

in  toList