her.esy.fun/src/posts/0010-Haskell-Now/shell.nix

   { nixpkgs ? import (fetchTarball https://github.com/NixOS/nixpkgs/archive/19.09.tar.gz) {} }:
   let
     inherit (nixpkgs) pkgs;
     inherit (pkgs) haskellPackages;

     haskellDeps = ps: with ps; [
       base
       protolude
       containers
     ];

     ghc = haskellPackages.ghcWithPackages haskellDeps;

     nixPackages = [
       ghc
       pkgs.gdb
       haskellPackages.cabal-install
     ];
   in
   pkgs.stdenv.mkDerivation {
     name = "env";
     buildInputs = nixPackages;
     shellHook = ''
        export PS1="\n\[[hs:\033[1;32m\]\W\[\033[0m\]]> "
     '';
   }