HList

HList.swift

protocol HList {
    associatedtype Head
    associatedtype Tail
}

struct HCons<H, T: HList>: HList {
    typealias Head = H
    typealias Tail = T

    let head: H
    let tail: T

    init(_ head: H, _ tail: T) {
        self.head = head
        self.tail = tail
    }
}

struct HNil: HList {
    typealias Head = Never
    typealias Tail = Never
}