Hello!
https://hexdocs.pm/commanded/aggregates.html

# state mutators

  def apply(%BankAccount{} = state, %MoneyWithdrawn{balance: balance}),
    do: %BankAccount{state | balance: balance}

  def apply(%BankAccount{} = state, %AccountOverdrawn{}),
    do: %BankAccount{state | state: :overdrawn}

  # private helpers

  defp withdraw_money(%BankAccount{account_number: account_number, balance: balance}, amount) do
    %MoneyWithdrawn{
      account_number: account_number,
      amount: amount,
      balance: balance - amount
    }
  end

I am going through commanded guides and this thing is sooooo curious!
What is the point to store new balance in event? Logically, state mutator should calculate new balance from amount in MoneyWithdrawn event?
Thanks