bank_in_fsharp.fs

module Bank    
    
    // Model
    
    type Amount = decimal
    
    type Balance = {
        CurrentAmount: Amount
    }   
    
    type ActiveAccount = {
        AccountNumber: string;
        Balance: Balance
    }

    type Events =
        | LargeAmountOfCashWithdrawnEvent of ActiveAccount * Amount
        | CashWithdrawnEvent of ActiveAccount * Amount


    // Behavour

    let WithdrawalCash(account, amount) = transaction { 
        
        ensure ( account.IsStillOpen 
            && account.Balance.CurrentAmount - amount < 0.0m
        )
        
        let newBalance = account.Balance.CurrentAmount - amount

        if (newBalance > 100.0m) then
            yield LargeAmountOfCashWithdrawnEvent(account, newBalance)

        yield CashWithdrawnEvent(account, newBalance)
    }