Ackermann function in Dhall

ackermann.dhall

-- Credit to: https://news.ycombinator.com/item?id=15186988

let iterate
    : (Natural → Natural) → Natural → Natural
    =   λ(f : Natural → Natural)
      → λ(n : Natural)
      → Natural/fold (n + 1) Natural f 1

let increment : Natural → Natural = λ(n : Natural) → n + 1

let ackermann
    : Natural → Natural → Natural
    = λ(m : Natural) → Natural/fold m (Natural → Natural) iterate increment

in  ackermann