Max Adjacent Product

let next memory current =
  let currentWinner = 
    match memory with
      | None, None ->              None
      | Some v, None ->            Some v
      | None, Some v ->            Some (v*current)
      | Some winning, Some last -> Some (max winning (current * last))

  currentWinner, Some current

let adjacentElementsProduct = fst << Array.fold next (None, None)