Outside of the nix language I have zero functional programming experience, nor had I ever taken a theoretical math class back in my days as a student. While the manual has this notation to explain functions the manual also has examples to explain every function. My eyes glazed right over this notation as there was never any need to understand it.
I have been using NixOS as my daily driver since around 17.03 - 17.09 and never once had the inclination or need to run a trivial google search and find out how to read that.
