{-
`listMax` returns the largest element of a `List` or `None Natural` if the
`List` is empty
-}
let max =
        ./max sha256:1f3b18da330223ab039fad11693da72c7e68d516f50502c73f41a89a097b62f7
      ? ./max

let Optional/map =
        ../Optional/map sha256:e7f44219250b89b094fbf9996e04b5daafc0902d864113420072ae60706ac73d
      ? ../Optional/map

let listMax
    : List Natural → Optional Natural
    =   λ(xs : List Natural)
      → Optional/map
          Natural
          Natural
          (λ(n : Natural) → List/fold Natural xs Natural max n)
          (List/head Natural xs)

let example0 = assert : listMax [ 1, 2 ] ≡ Some 2

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

let property0 = λ(n : Natural) → assert : listMax [ n ] ≡ Some n

in  listMax