Evaluation

EvalByPolymorphism.kt

sealed class MathExpression {
    abstract fun eval(): Int
}

data class Addition(val left: MathExpression, val right: MathExpression) : MathExpression() {
    override fun eval(): Int = left.eval() + right.eval()
}

data class Subtraction(val left: MathExpression, val right: MathExpression) : MathExpression() {
    override fun eval(): Int = left.eval() - right.eval()
}

data class Number(val value: Int) : MathExpression() {
    override fun eval(): Int = value
}