Re: [Caml-list] Use Arg module to read keyword followed by unspecified number of arguments

[Richard Jones <rich@annexia.org>]

On Tue, May 23, 2006 at 12:17:18PM -0500, mulhern wrote:
> Hi!
> 
> I expect to be reading something like this:
> 
> -pred-files <arg1> <arg2> ... <argn> -key2 <arg> -extra-files <arg1>
> <arg2> ... <argn> -key4

Have you thought about _not_ using the Arg module?  A loop with
pattern matching is often good enough, or in this case two nested
loops:

let pred_files = ref []
let key2 = ref ""
let extra_files = ref []
let key4 = ref ""

let rec read_args = function
  | "-pred-files" :: args ->
      let args, rest = read_to_next_switch args in
      pred_files := args;
      read_args rest
  | "-key2" :: arg :: rest ->
      key2 := arg;
      read_args rest
  | "-extra-files" :: args ->
      let args, rest = read_to_next_switch args in
      extra_files := args;
      read_args rest
  | "-key4" :: arg :: rest ->
      key4 := arg;
      read_args rest
  | [] -> ()
  | arg :: _ ->
      prerr_endline (arg ^ ": unknown parameter");
      exit 2

and read_to_next_switch = function
  | (switch :: _) as rest when String.length switch > 0 && switch.[0] = '-' ->
      [], rest
  | arg :: rest ->
      let args, rest = read_to_next_switch rest in
      arg :: args, rest
  | [] ->
      [], []
  ;;

read_args (List.tl (Array.to_list Sys.argv)) ;;

print_endline ("pred-files = " ^ String.concat ", " !pred_files) ;;
print_endline ("key2 = " ^ !key2) ;;
print_endline ("extra-files = " ^ String.concat ", " !extra_files) ;;
print_endline ("key4 = " ^ !key4) ;;

----------------------------------------------------------------------
$ ./parse -pred-files arg1 arg2 arg3 -key2 key2 -extra-files arg1 arg2 -key4 key4
pred-files = arg1, arg2, arg3
key2 = key2
extra-files = arg1, arg2
key4 = key4

Rich.

-- 
Richard Jones, CTO Merjis Ltd.
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