[Haskell-beginners] How to nest arbitrary things

[Imants Cekusins]

> how to write an "unpack" function

is this what Lenses are all about?

https://www.fpcomplete.com/school/to-infinity-and-beyond/pick-of-the-week/a-little-lens-starter-
tutorial

I stumbled across Lenses only recently so can not write a working example yet.

if Lenses are relevant to this topic, could someone kindly post an
appropriate (Truck Parcel Can) datatype and an "unpack" with Lenses
example?