contract SpendContract =
  function withdraw : (int) => int

contract SpendTest =

  function spend(to, amount) =
    let total = Contract.balance
    Chain.spend(to, amount)
    total - amount

  function withdraw(amount) : int =
    spend(Call.caller, amount)

  function withdraw_from(account, amount) =
    account.withdraw(amount)
    withdraw(amount)

  function spend_from(from, to, amount) =
    from.withdraw(amount)
    Chain.spend(to, amount)
    Chain.balance(to)

  function get_balance() = Contract.balance
  function get_balance_of(a) = Chain.balance(a)