My simple multi-package Haskell project template

I’m a new beginner to Haskell and I want to do Haskell development on NixOS. After some learning and researching, I finally settled on the existing Haskell infrastructure in Nixpkgs. So I managed to make this flake template that helps develop, package, and deliver a Haskell software. I hope this can help you get started on a new Haskell project more conveniently and provide a reference for others who are new to Nix or Haskell. Although many techniques used in this template are trivial to you, I...