developPackage.nix

# https://www.srid.ca/1948201.html

let
  pkgs = import <nixpkgs> { };
  compilerVersion = "ghc865"; 
  compiler = pkgs.haskell.packages."${compilerVersion}";
in
  compiler.developPackage {
    root = ./.;
    source-overrides = {
      named = builtins.fetchTarball 
        "https://github.com/monadfix/named/archive/e684a00.tar.gz";
    };
    modifier = drv:
      pkgs.haskell.lib.addBuildTools drv (with pkgs.haskellPackages;
        [ cabal-install
          ghcid
        ]);
  }

simple.nix

# https://www.srid.ca/1948201.html

let 
  pkgs = import <nixpkgs> { };
in 
  pkgs.haskellPackages.developPackage {
    root = ./.;
    modifier = drv:
      pkgs.haskell.lib.addBuildTools drv (with pkgs.haskellPackages;
        [ cabal-install
          ghcid
        ]);
  }