Kotlin Design Patterns Visitor domain model

VisitorDomainModel.kt

abstract class Expression

class DoubleExpression(private val value: Double) : Expression()

class AdditionExpression(
    private val left: Expression,
    private val right: Expression
) : Expression()

fun main() {
    // 1+(2+3)
    AdditionExpression(
        left = DoubleExpression(1.0),
        right = AdditionExpression(
            left = DoubleExpression(2.0),
            right = DoubleExpression(3.0)
        )
    )
}