With my simple lens implementation i can perform the usual modify, set, get and delete operations:

```js
// Lens type

const Lens = f => ({runLens: f, [Symbol.toStringTag]: "Lens"});

const objLens = map => k =>
  Lens(f => o =>
    map(x => Object.assign({}, o, {[k]: x})) (f(o[k]))); // object lens

// Id type

const Id = x => ({runId: x, [Symbol.toStringTag]: "Id"});
const idMap = f => tx => Id(f(tx.runId)); // functor

// Const type

const Const = x => ({runConst: x, [Symbol.toStringTag]: "Const"});
const constMap = f => tx => Const(tx.runConst); // functor

// auxiliary function

const _const = x => y => x;

// MAIN

const o = {foo: "abc", bar: 123};

const get = objLens(constMap) ("foo").runLens(x => Const(x)) (o),
  set = objLens(idMap) ("bat").runLens(_const(Id(true))) (o),
  mod = objLens(idMap) ("foo").runLens(s => Id(s.toUpperCase())) (o),
  del = objLens(idMap) ("foo").runLens(_const(Id(null))) (o); //*

console.log("get", get.runConst);
console.log("set", set.runId);
console.log("mod", mod.runId);
console.log("del", del.runId);
```

However, `delete` is unsatisfying as I want to delete the whole property rather than merely replacing the value with nothing.

How can I achieve this?

\*Please note that i usually would have used a proper `Option` type to indicate no values.