Here's another way to install Sparrow 2.1.3 (the current version) on NixOS:
```
environment.systemPackages [
...
# Install Sparrow 2.1.3
(pkgs.callPackage (pkgs.fetchurl {
url = "https://gist.githubusercontent.com/emmanuelrosa/a6f3c5ca3977d933064129ae723cfac2/raw/896c10bbfbf1f650e54626229c74d294b829f680/sparrow.nix";;
hash = "sha256-F7l9h7HPniXXm7dHL4IWmzzhMBHTcrYwieKnaxAyj+w=";
}) {})
];
```
The example above installs from a Gist I just created: https://gist.github.com/emmanuelrosa/a6f3c5ca3977d933064129ae723cfac2
It's the same code in the Nixpkgs PR (https://github.com/NixOS/nixpkgs/pull/380755) except packaged into a single file.