pkgs:
let
  inherit (builtins)
    map elem;

  inherit (pkgs) stdenv;
in
pkg: inst:
stdenv.mkDerivation {
  # I don't like using `name' instead of `pname' and `version', but
  # regrettably not all packages use `pname' and `version' yet, so for the
  # sake of consistency, we treat all packages as if they didn't use `pname'
  # and `version'.
  name = pkg.name + "-shim";
  nativeBuildInputs = [pkg];
  dontUnpack = true;
  buildPhase = ''
if [ -d ${pkg}/bin ]; then
    mkdir -p "$out/bin"
    for exe in $(ls "${pkg}/bin/"); do
        cat >"$out/bin/$exe" <<EOF
#!/bin/sh

term=urxvt
which \$term >/dev/null 2>&1 || term=xterm

if [ "\$DISPLAY" ]; then
    \$term -e nix shell '${inst}' --command '$exe' \$*
else
    nix shell '${inst}' --command '$exe' \$*
fi
EOF
        chmod +x "$out/bin/$exe"
    done
fi

for dir in "share/applications" "share/icons"; do
    if [ -d "${pkg}/$dir" ]; then
        mkdir -p "$out/$dir"
        cp -a "${pkg}/$dir/"* "$out/$dir"
    fi
done
'';
}