HList.size()の実装が悪い？

永遠にコンパイルが終わらない.kt

sealed class HList {
    class Body<out A, out B : HList>(val head: A, val rest: B) : HList() {

    }

    object Tail : HList()
    
    companion object {
        fun <E1> of(e1: E1) = Body(e1, Tail)
        
        fun <E1, E2> of(e1: E1, e2: E2) = Body(e1, Body(e2, Tail))
        
        
    }
}

fun HList.size(): Int {
    return size(0)
}

private tailrec fun HList.size(acc: Int = 0): Int {
    return when (this) {
        is HList.Body<*, *> -> this.size(acc + 1)
        HList.Tail -> acc
    }
}