struct
  let concat ~(run_with : Machine.t) bunch_of_files ~result_path =
    let open KEDSL in
    let program =
      Program.(
        exec ["mkdir"; "-p"; Filename.dirname result_path]
        && shf "cat %s > %s"
          (List.map bunch_of_files
             ~f:(fun o -> Filename.quote o#product#path)
           |> String.concat ~sep:" ") result_path
      ) in
    let name =
      sprintf "concat-all-%s" (Filename.basename result_path) in
    workflow_node
      (single_file result_path ~host:Machine.(as_host run_with))
      ~name
      ~edges:(
        on_failure_activate Remove.(file ~run_with result_path)
        :: List.map ~f:depends_on bunch_of_files)
      ~make:(Machine.run_stream_processor run_with ~name  program)

  let cat_folder ~host
      ~(run_program : Machine.Make_fun.t)
      ?(depends_on=[]) ~files_gzipped ~folder ~destination = 
    let deps = depends_on in
    let open KEDSL in
    let name = "cat-folder-" ^ Filename.quote folder in
    let edges =
      on_failure_activate (Remove.path_on_host ~host destination)
      :: List.map ~f:depends_on deps in
    if files_gzipped then (
      workflow_node (single_file destination ~host)
        ~edges ~name
        ~make:(
          run_program ~name
            Program.(
              shf "gunzip -c %s/* > %s" (Filename.quote folder)
                (Filename.quote destination)))
    ) else (
      workflow_node
        (single_file destination ~host)
        ~edges ~name
        ~make:(
          run_program ~name
            Program.(
              shf "cat %s/* > %s" (Filename.quote folder) (Filename.quote destination)))
    )

end