/Prelude-v21.1.0/List/default.dhall

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Unpack an Optional containing a List, defaulting to an empty list when the Optional is None

Examples

default Bool (None (List Bool)) ≡ ([] : List Bool)
default Bool (Some [ True ]) ≡ [ True ]

Source

{-|
Unpack an `Optional` containing a `List`, defaulting to an empty list when the
`Optional` is `None`
-}
let default
: ∀(a : Type) → Optional (List a) → List a
= λ(a : Type) →
λ(o : Optional (List a)) →
merge { Some = λ(l : List a) → l, None = [] : List a } o

let example0 = assert : default Bool (None (List Bool)) ≡ ([] : List Bool)

let example1 = assert : default Bool (Some [ True ]) ≡ [ True ]

in default