Ejemplo de tipos algebraicos en TypeScript

algebraicTypes.ts

enum DiscountKind {
    NoDiscount,
    Special,
    Resident,
    Family,
    Business
}

interface Discount {
    kind: DiscountKind;
    percentage: number;
}

type NoDiscount = Discount & { kind: DiscountKind.NoDiscount }
type SpecialResident = Discount & { kind: DiscountKind.Special }
type Resident = Discount & { kind: DiscountKind.Resident }
type Family = Discount & { kind: DiscountKind.Family }
type Business = Discount & { kind: DiscountKind.Business }
type SubsidyPlusBusiness = { business: Business, resident: Resident }


type SpanishSubsidy =
    | SpecialResident
    | Resident
    | Family

type FlightDiscount =
    | SpanishSubsidy
    | Business
    | SubsidyPlusBusiness
    | NoDiscount

function handleFlightDiscount(discount: FlightDiscount): number {
    if ('business' in discount) {
        return discount.business.percentage + discount.resident.percentage
    }
    switch (discount.kind) {
        case DiscountKind.NoDiscount: {
            return discount.percentage
        }
        case DiscountKind.Special: {
            return discount.percentage
        }
        case DiscountKind.Resident: {
            return discount.percentage
        }
        case DiscountKind.Family: {
            return discount.percentage
        }
        case DiscountKind.Business: {
            return discount.percentage
        }
    }
}

console.log(handleFlightDiscount({ kind: DiscountKind.NoDiscount, percentage: 12 }))
console.log(handleFlightDiscount({ kind: DiscountKind.Special, percentage: 12 }))
console.log(handleFlightDiscount({ kind: DiscountKind.Resident, percentage: 12 }))
console.log(handleFlightDiscount({ kind: DiscountKind.Family, percentage: 12 }))
console.log(handleFlightDiscount({ kind: DiscountKind.Business, percentage: 12 }))
console.log(handleFlightDiscount({ business: { kind: DiscountKind.Business, percentage: 12 }, resident: { kind: DiscountKind.Resident, percentage: 34} }))