HN does not use markdown code block formatting so this is hard to read. Formatting code blocks is simple, two blank spaces before any line to make it a code block and no need for extra newlines (unlike between paragraphs):

  double deposit(double amount)
    in (amount > 0, "Deposit amount must be positive")
    out (result; result == balance)
  {
    balance += amount;
    return balance;
  }