Global CLI flag in OCaml Core.Command - ocaml

Question

I am currently creating a CLI application in OCaml and using Core.Command, the CLI parser included in core (v0.10), to parse the command line.
I want to have a global flag that can be used for any subcommand (like the --paginate or --git-dir flags in git for example).
For instance, I want a -debug flag so that the two following commands are valid
my-cli -debug hello world
my-cli -debug goodbye world
However, I could not find a way to do this with the Core.Command API.
Here is a simplified version what I currently have.
open Core
let initialize_logger debug =
Logs.set_reporter (Logs_fmt.reporter ());
let log_level = if debug then Logs.Debug else Logs.Info in
Logs.set_level (Some log_level)
let some_func_with_logging () =
Logs.debug (fun m -> m "the flag debug was passed!")
let hello name =
some_func_with_logging ();
Printf.printf "Hello %s!\n" name
let goodbye name =
some_func_with_logging ();
Printf.printf "Goodbye %s!\n" name
let hello_command =
let open Command.Let_syntax in
Command.basic
~summary:"says hello"
[%map_open
let name = anon ("name" %: string)
and debug = flag "debug" no_arg ~doc:"debug" in
fun () ->
initialize_logger debug;
hello name
]
let goodbye_command =
let open Command.Let_syntax in
Command.basic
~summary:"says goodbye"
[%map_open
let name = anon ("name" %: string)
and debug = flag "debug" no_arg ~doc:"debug" in
fun () ->
initialize_logger debug;
goodbye name
]
let main_command =
Command.group ~summary:"a cool CLI tool"
[ ("hello", hello_command);
("goodbye", goodbye_command);
]
let () = Command.run main_command
There are two main issues here:
the debug flag as well as the call to initialize_logger is duplicated in every subcommand
the debug flag needs to be passed after the subcommand when invoking the command: my-cli hello world -debug instead of my-cli -debug hello world
Is there a clean way to handle this with Core.Command API?