grain.cs

public interface IBankAccountGrain : IGrainWithGuidKey
{
    Task Deposit(decimal amount);
    Task Withdraw(decimal amount);
    Task<decimal> Balance();
}

public class BankAccountGrain : JournaledGrain<BankAccountState>, IBankAccountGrain
{
    public Task Deposit(decimal amount)
    {
        RaiseEvent(new Deposited
        {
            Amount = amount
        });
        return ConfirmEvents();
    }

    public Task Withdraw(decimal amount)
    {
        RaiseEvent(new Withdrawn
        {
            Amount = amount
        });
        return ConfirmEvents();
    }

    public Task<decimal> Balance()
    {
        return Task.FromResult(State.Balance);
    }
}