nixpkgs/pkgs/build-support/fetchcvs/default.nix

# example tags:
# date="2007-20-10"; (get the last version before given date)
# tag="<tagname>" (get version by tag name)
# If you don't specify neither one date="NOW" will be used (get latest)

{stdenv, cvs, nix}: {url, module, tag ? null, date ? null, sha256}:

stdenv.mkDerivation {
  name = "cvs-export";
  builder = ./builder.sh;
  buildInputs = [cvs nix];
  inherit url module sha256 tag date;
}