HLists and HMaps in typescript

h.ts

// HList
class HList { }
class HNil extends HList { 
    static readonly instance = new HNil();
    private constructor() { 
        super();
    } 
}

class HCons<Value, Next extends HList> extends HList {
    constructor(readonly value: Value, readonly next: Next) {      
        super()  
    }
}

function hcons<V, Next extends HList>(value: V, next: Next) { return new HCons<V, Next>(value, next); }
const hnil = HNil.instance;

// sample
var t = hcons(1, hcons("lol", hcons(true, hnil)));  // t: HCons<number, HCons<string, HCons<boolean, HNil>>>


// HMap
interface Pair<Key, Val> { 
    key: Key; 
    value: Val 
}
function hmap<K, V, N extends HList>(key: K, value: V, next: N): HCons<Pair<K,V>, N> { return hcons({key:key, value: value}, next); }

//sample 
var map = hmap<"a", number, HCons<Pair<"b", boolean>, HNil>>("a", 1, hmap<"b", boolean, HNil>("b", true, hnil));
// map: HCons<Pair<"a", number>, HCons<Pair<"b", boolean>, HNil>>