let
  lib = import <nixpkgs/lib>;
  # >>=/bind for lists
  # listBind :: [a] -> (a -> [b]) -> [b]
  listBind = lib.flip lib.concatMap;
  dms = ["foo" "bar" "baz"];
  vms = ["1" "2" "3"];
in 
  listBind dms (dm:
    listBind vms (vm:
      lib.singleton (dm + vm)
    )
  )