Lens

Lenses are the simplest and most intuitive optics. They represent a unique focus that always exists.

You can create a lens by calling:

lens<Part, Whole>({
	getter,
	mapper,
	setter,
}: {
	getter: (whole: Whole) => Part
	mapper?: (mod: (p: Part) => Part, w: Whole) => Whole
	setter: (part: Part, whole: Whole) => Whole
})

getter function returns the value of the focus, setter updates it and optionally mapper applies a modifying function. When mapper is not provided, it is derived from getter and setter

Most of the time, however, you will be better off composing ready-made lenses than using this more generic optic.