Flake for using Haskell in nix develop

.ghci

:def hoogle \x -> return $ ":!hoogle --count=15 \"" ++ x ++ "\""
:def doc \x -> return $ ":!hoogle --info \"" ++ x ++ "\""
:set -Wall
:set -fno-warn-type-defaults -ferror-spans -freverse-errors -fprint-expanded-synonyms
:set prompt "\ESC[0;32m%s\n\ESC[m[ghci]\ESC[38;5;172mλ \ESC[m"
:set prompt-cont " \ESC[38;5;172m> \ESC[m"

flake.nix

{
  description = "Simple haskell nix flake";

  nixConfig.bash-prompt = "[nix]\\e\[38;5;172mλ \\e\[m";

  inputs = {
    nixpkgs.url = "nixpkgs/nixos-21.05";

    flake-utils = {
      url = "github:numtide/flake-utils";
      inputs.nixpkgs.follows = "nixpkgs";
    };
  };

  outputs = { flake-utils, nixpkgs, self }:
    flake-utils.lib.eachDefaultSystem (system:
      let
        config = {};
        overlays = [];
        pkgs = import nixpkgs { inherit config overlays system; };
      in rec {
        devShell = pkgs.haskellPackages.shellFor {
          packages = p: [
          ];

          buildInputs = with pkgs.haskellPackages; [
            cabal-install

            # Helpful tools for `nix develop` shells
            #
            #ghcid                   # https://github.com/ndmitchell/ghcid
            #haskell-language-server # https://github.com/haskell/haskell-language-server
            #hlint                   # https://github.com/ndmitchell/hlint
            #ormolu                  # https://github.com/tweag/ormolu
          ];

          withHoogle = true;
        };
      }
    );
}