anchor.diff:        name = "devEnv";
         paths = [
           libmikey
  -        # myHaskellEnv
           myPython3Env
           cabal2nix
   
  
positive.code:     # $ nix-build "<nixpkgs>" -A example-pkg-hello
      example-pkg-hello = callPackage ~/.dotfiles/nix/pkgs/example-pkg-hello {};
  
  
      # ----------------
      # Haskell packages
      # ----------------
      #
      # Overrides to the nix Haskell package set.
      haskellPackages = super.haskellPackages.override {
        overrides = self: super: with haskell.lib; {
          # ----------------------------------
          # -- A little note to future self --
          # ----------------------------------
          #
          # Haskell packages will commonly fail with dependency or test
          # failures. Two functions help out here: `doJailbreak` and
          # `dontCheck`. `doJailbreak` essentially says, ignore all
          # dependency version constraints and try to compile
          # anyway. `dontCheck` does not run tests (of course it still
          # fails if compilation fails).
          #
          # If that doesn't work, and the package itself must be fixed,
          # the steps are:
          #
          # 1. Fork the package, download locally.
          # 2. Use cabal2nix --shell to generate a shell.nix file.
          # 3. nix-shell shell.nix. Try to get compiling again using just
          #    `cabal build`.
          # 4. Push up PR with fix.
          # 5. Meanwhile let's override the `src` in the original derivation.
          #    Use `nix-prefetch-git` to get the necessary info, e.g.:
          #
          #    $ nix-prefetch-git https://github.com/mjhoy/psc-package.git 039a42ba780a4f8e342e578177f584d13a6288a7
          #
          #    Now use the output from this in an override:
          #    psc-package = super.psc-package.overrideAttrs (oldAttrs: { src = fetchgit { ... } })
  
          # https://github.com/NixOS/nixpkgs/pull/57587
          hakyll = haskell.lib.markUnbroken super.hakyll;
        };
      };
  
      nodejsEnv = with pkgs; buildEnv {
        name = "nodeEnv";
        paths = [
  
negative.code:       ];
      };
  
      myPython3Env = python3.withPackages (p: with p; [
        virtualenv
        pip
  