[Libguestfs] Re: factorization would be nice

[Richard W.M. Jones]

On Wed, Aug 12, 2009 at 10:07:16AM +0200, Jim Meyering wrote:
> Hi Rich,
> 
> I've changed part of generator.ml to look like this:
> 
>       (match snd style with
>        | [] -> ()
>        | args ->
>            pr "  memset (&args, 0, sizeof args);\n";
>            pr "\n";
>            pr "  if (!xdr_guestfs_%s_args (xdr_in, &args)) {\n" name;
>            pr "    reply_with_error (\"%%s: daemon failed to decode procedure arguments\", \"%s\");\n" name;
>            pr "    return;\n";
>            pr "  }\n";
>            List.iter (
>              function
>              | Pathname n ->
>                  pr "  char *%s = args.%s;\n" n n;
>                  pr "  ABS_PATH (%s, goto done);\n" n;
>              | Device n ->
>                  pr "  char *%s = args.%s;\n" n n;
>                  pr "  RESOLVE_DEVICE (%s, goto done);" n;
> 	     | Dev_or_Path n ->
>                  pr "  char *%s = args.%s;\n" n n;
>                  pr "  REQUIRE_ROOT_OR_RESOLVE_DEVICE (%s, goto done);" n;
>              | String n -> pr "  char *%s = args.%s;\n" n n
>              | OptString n -> pr "  %s = args.%s ? *args.%s : NULL;\n" n n n
>              | StringList n ->
>                  pr "  %s = realloc (args.%s.%s_val,\n" n n n;
>                  pr "                sizeof (char *) * (args.%s.%s_len+1));\n" n n;
>                  pr "  if (%s == NULL) {\n" n;
>                  pr "    reply_with_perror (\"realloc\");\n";
>                  pr "    goto done;\n";
>                  pr "  }\n";
>                  pr "  %s[args.%s.%s_len] = NULL;\n" n n n;
>                  pr "  args.%s.%s_val = %s;\n" n n n;
>              | Bool n -> pr "  %s = args.%s;\n" n n
>              | Int n -> pr "  %s = args.%s;\n" n n
>              | FileIn _ | FileOut _ -> ()
>            ) args;
>            pr "\n"
>       );
> 
> Note the 4-x repeated statement:
> 
>                  pr "  char *%s = args.%s;\n" n n;
> 
> What's the best way to avoid that?

Just created a nested function:

  let pr_args n =
    pr "  char *%s = args.%s;\n" n n
  in

  (* ... *)
  pr_args n

You can create functions anywhere, at any level of nesting, even
inside expressions, and nested functions are common and a Good Thing.

Rich.

-- 
Richard Jones, Emerging Technologies, Red Hat  http://et.redhat.com/~rjones
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