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From: Dmitry Bely <dmitry.bely@gmail.com>
To: Philippe Veber <philippe.veber@gmail.com>
Cc: Caml List <caml-list@inria.fr>
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Subject: Re: [Caml-list] Labelled parameter bug?

On Wed, Aug 24, 2011 at 7:01 PM, Philippe Veber
<philippe.veber@gmail.com> wrote:

>> The following fragment compiles without a warning but produces strange
>> results:
>>
>> let f ?(p1="p1") ~p2 p3 =
>>  Printf.printf "p1=%s, p2=%s, p3=%s\n" p1 p2 p3
>>
>> let _ =
>>  f "p2" "p3"; (* 1 *)
>>  let f2 = f "p2" in
>>  f2 "p3" (* 2 *)

(...)

> This first application also applies optional arguments situated before the
> anoymous argument, so it remains the second (labeled) argument only.
>
> There is indeed a special case where you can drop labels if you provide the
> exact number of arguments. This means that f "p2" "p3" is equivalent to f
> ~p2:"p2" "p3". This is written in the manual
> (http://caml.inria.fr/pub/docs/manual-ocaml/manual006.html) :
>
> "As an exception to the above parameter matching rules, if an application is
> total, labels may be omitted. In practice, most applications are total, so
> that labels can be omitted in applications. "
>
> So this is actually the intended behavior, AFAIU

Indeed. Thanks for the detailed explanation. But shouldn't the
compiler decide that the partial application skipping labeled
parameter is suspicious and generate a warning?

- Dmitry Bely