PaymentModeling.fsx

type CheckNumber = CheckNumber of int

type CardNumber = CardNumber of int

type CardType =
    | Visa
    | Mastercard

type CreditCard = {
    CardType : CardType
    CardNumber : CardNumber
}

type PaymentMethod =
    | Cash
    | Check of CheckNumber
    | Card of CreditCard

type PaymentAmount = PaymentAmount of decimal

type Currency =
    | EUR
    | CHF
    | USD

type Priority =
    | High
    | Medium
    | Low

type Payment = {
    Amount : PaymentAmount
    Currency : Currency
    Method : PaymentMethod
    Priority : Priority option
}

let printPaymentMethod payment =
    match payment.Method with
    | Cash -> printfn "Cash"
    | Check checkNumber -> printfn "Check %A" checkNumber
    | Card card ->
        match card.CardType with
        | Visa -> printfn "Visa"
        | Mastercard -> printfn "Mastercard"
    payment    

let handlePayment payment =
    match payment.Priority with
    | Some priority when priority = High -> printfn "Express payment"
    | Some _ -> printfn "Normal payment"
    | None -> printfn "No priority"
    payment

let payment = {
    Amount = PaymentAmount 5.50m
    Currency = EUR
    Method = Card { CardType = Visa; CardNumber = (CardNumber 13371234); }
    Priority = Some High
}

payment |> printPaymentMethod |> handlePayment