Re: [Libguestfs] [PATCH 2/2] OCaml tools: add output selection for --machine-readable

On Tue, Aug 21, 2018 at 05:44:30PM +0200, Pino Toscano wrote: > +let machine_readable_printf fs = > + let get_machine_readable_channel () = > + let open_machine_readable_channel () = > + match !machine_readable_output with > + | NoOutput -> > + (* Trying to use machine_readable_printf when --machine-readable was > + * not enabled, and thus machine_readable () returns false. > + *) > + failwith "internal error: machine_readable_printf used with no --machine-readable" I wonder if there's a way to avoid this error at compile time. Replace the ‘machine_readable ()’ function that returns boolean with one which returns an optional printf function. Then caller code would do: match machine_readable () with | None -> () (* ie. not --machine-readable *) | Some pr -> pr "stuff\n"; exit 0

Of course the devil will be in the details as to whether this actually works with our existing callers.

> + fprintf (get_machine_readable_channel ()) fs I'm surprised this works and you didn't need to use ksprintf.

> (* No elements and machine-readable mode? Print some facts. *) > if elements = [] && machine_readable () then ( > - printf "virt-dib\n"; > + machine_readable_printf "virt-dib\n"; > let formats_list = Output_format.list_formats () in > - List.iter (printf "output:%s\n") formats_list; > + List.iter (machine_readable_printf "output:%s\n") formats_list; > exit 0 > ); So this caller would become: match machine_readable (), elements = [] with | None, _ -> () | Some pr, [] -> (* existing code, replacing printf with pr *)

| Some _, _ -> (* this is a new case giving an error when the user uses --machine-readable + a list of elements, which I believe is not caught in the current code *) error (f_"--machine-readable cannot be used with elements on the command line")