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

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Retrieve the first element of the list

Examples

head Natural [ 0, 1, 2 ] ≡ Some 0
head Natural ([] : List Natural) ≡ None Natural

Source

--| Retrieve the first element of the list
let head
: ∀(a : Type) → List a → Optional a
= List/head

let example0 = assert : head Natural [ 0, 1, 2 ] ≡ Some 0

let example1 = assert : head Natural ([] : List Natural) ≡ None Natural

in head