let {

  makeDrv = name: progName: derivation {
    inherit name progName;
    system = "@system@";
    builder = "@shell@";
    shell = "@shell@";
    args = ["-e" "-x" ./user-envs.builder.sh];
  };

  body = [
    (makeDrv "foo-1.0" "foo")
    (makeDrv "foo-2.0pre1" "foo")
    (makeDrv "bar-0.1" "bar")
    (makeDrv "foo-2.0" "foo")
    (makeDrv "bar-0.1.1" "bar")
  ];
  
}