Smart constructor lens function. Used to easily construct a Lens

name :: Lens Person String
name = lens _name $ \p n -> p { _name = n }

Lens that operates on itself

update AddOne = do
  this += 1

A Lens is a generalized getter and setter.

Lenses allow both the retrieval of values from fields in a record and the assignment of values to fields in a record. The power of a Lens comes from its ability to be composed with other lenses.

In the context of building applications with miso, the model is often a deeply nested product type. This makes it highly conducive to Lens operations (as defined below).