~/env/vulkan.nix :
with import <nixpkgs> {};
clangStdenv.mkDerivation {
  name = "vulkan_env";
  buildInputs = [ clang_5 llvm_5 lldb_5 clang-tools cmake gnumake qtcreator
                  mesa_noglu vulkan-loader xorg.libxcb xorg.xcbutil xorg.libX11 xorg.libpciaccess
                  xorg.libXrandr xorg.libXpresent libxkbcommon xorg
                  libpng glm graphviz python2Full ];
}

» nix-shell ~/env/vulkan.nix  --show-trace
error: while evaluating the attribute ‘buildInputs’ of the derivation ‘vulkan_env’ at /nix/var/nix/profiles/per-user/root/channels/nixos/pkgs/stdenv/generic/make-derivation.nix:98:11:
cannot coerce a set to a string, at /nix/var/nix/profiles/per-user/root/channels/nixos/pkgs/stdenv/generic/make-derivation.nix:98:11