Re: [Caml-list] OCaml wishlist

["Yaron Minsky" <yminsky@cs.cornell.edu>]

Here's a simple way of approximating what you want.  It's ugly, but camlp4
could be used for providing the appropriate syntactic sugar, I imagine.

exception Return

let rval = ref None in
try


with
  Return ->
     match !rval with





> On Tue, Oct 21, 2003 at 01:28:13PM -0400, William Lovas wrote:
>> What you want is a return *statement*, but such a beast is incompatible
>> with O'Caml, since O'Caml is an expression-oriented language.  I don't
>> see
>> an easy way of making a `return' expression that behaves the way you
>> want
>> it to.
>
> Perhaps there's a misunderstanding here. I don't want to change the
> expression-oriented nature of the language. The 'return' would and
> must return the same type as the rest of the code.
>
>> Better, though, in my opinion, would be to adapt your
>> mental syntax to fit the functional style than to adapt the functional
>> language to cater to your imperative style.
>
> I'm really looking for help on this! My working theory at the moment
> though is that writing UIs involves writing essentially imperative
> code. One small example from some real code:
>
>   let quit _ =
>     if !test_id = 0 then (
>       GMain.Main.quit (); false
>     ) else (
>       let icon = GMisc.image () in
>       icon#set_stock `DIALOG_QUESTION;
>       icon#set_icon_size `DIALOG;
>       let buttons = [ "Quit"; "Cancel" ] in
>       let ans = GToolbox.question_box ~title:"Quit" ~icon ~buttons
>           ("Are you sure you want to quit? This may lose any\n" ^
>            "results from this assessment.") in
>       if ans = 1 then (
>         GMain.Main.quit (); false       (* User requested quit. *)
>        )
>       else
>         true                            (* Don't close the window. *)
>      )
>   in
>
>   window#connect#destroy ~callback:GMain.quit;
>   window#event#connect#delete ~callback:quit;
>   quit_item#connect#activate ~callback:(fun () -> quit (); ());
>
> I think there's definitely a case for being able to write:
>
>   if !test_id = 0 then (	(* Not in a test - can quit immediately. *)
>     GMain.Main.quit ();
>     return false
>   );
>
>   (* .. rest of code ... *)
>
> But perhaps, as you say, I'm missing the functional solution to this.
>
> (I can dig around and find some more examples like this if it would help).
>
> Rich.
>
> --
> Richard Jones. http://www.annexia.org/ http://freshmeat.net/users/rwmj
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