scaml translation of the example on page 217 of the book "ブロックチェーンアプリケーション開発の教科書"

metacoin.ml

open SCaml

type balances = (address, nat) map
type storage = balances

type parameter =
  | Activate
  | Send of {to_ : address; amount : nat}

let activate addr (balances : balances) =
  Map.update addr (Some (Nat 10000)) balances

let send sender receiver (amount:nat) (balances : balances)=
  match Map.get sender balances with
  | None -> failwith ""
  | Some (n : nat) ->
    begin match isnat (n -^ amount) with
      | None -> failwith ""
      | Some n' ->
      let receivers_balance = match Map.get receiver balances with
        | None -> Nat 0
        | Some m -> m
      in
      Map.update receiver (Some (receivers_balance +^ amount))
        (Map.update sender (Some n') balances)
    end

let main (p : parameter) (s : storage) : (operation list * storage) =
  match p with
  | Activate ->
    (([]: operation list), activate (Global.get_sender ()) s)
  | Send {to_; amount} ->
    (([]: operation list), send (Global.get_sender ()) to_ amount s)