Records and deep access

Before we dive into lenses, let’s review Haskell’s built-in support for data access and its shortcomings.

Haskell’s built-in support for data access is the named fields of record types that we first saw in Chapter 2, Algebraic Data Types. Here is a small example of this:

data Employee = MkEmployee { firstName :: String
                           , lastName  :: String
                           , salary    :: Int
                           }

This Employee type has one data constructor, MkEmployee, with three...