Example of using DSL marker annotation

dsl_marker.kt

@DslMarker
annotation class ReceiptDsl

data class Amount(val total: Int, val tax: Float)
data class Receipt(val title: String, val date: String, val staffName: String, val amount: Amount)

@ReceiptDsl
class AmountBuilder {
    var total: Int = 0
    var tax: Float = .0f
    fun build() = Amount(total, tax)
}

@ReceiptDsl
class ReceiptBuilder {
    var title: String = ""
    var date: String = ""
    var staffName: String = ""
    private var amount: Amount? = null

    fun amount(λ: AmountBuilder.() -> Unit) = AmountBuilder().apply(λ).build()
    fun build() = Receipt(title, date, staffName, amount ?: amount{})
}

fun receipt(λ: ReceiptBuilder.() -> Unit) = ReceiptBuilder().apply(λ).build()

fun main(args: Array<String>) {

    val john = receipt {
        title = "Beef noodle"
        date = "2018/6/28"
        staffName = "John"

        amount {
            total = 990
            tax = 9.9F
        }
    }

    receipt {
        title = "Beef rice"
        date = "2018/6/28"
        staffName = "Mary"

        amount {
            total = 980
            tax = 9.9F
        }
    }

    println(john)
}