/Prelude-v23.0.0/Optional/concat.dhall

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Flatten two Optional layers into a single Optional layer

Examples

concat Natural (Some (Some 1)) ≡ Some 1
concat Natural (Some (None Natural)) ≡ None Natural
concat Natural (None (Optional Natural)) ≡ None Natural

Source

--| Flatten two `Optional` layers into a single `Optional` layer
let concat
: ∀(a : Type) → Optional (Optional a) → Optional a
= λ(a : Type) →
λ(x : Optional (Optional a)) →
merge { Some = λ(y : Optional a) → y, None = None a } x

let example0 = assert : concat Natural (Some (Some 1)) ≡ Some 1

let example1 = assert : concat Natural (Some (None Natural)) ≡ None Natural

let example2 = assert : concat Natural (None (Optional Natural)) ≡ None Natural

in concat