[Caml-list] Warning 28.

[Caml-list] Warning 28.

[Ivan Gotovchits]

After switching to a newer version of Ocaml I've started to receive
some interesting warnings on my old codebase. And there is one warning
that I do not understand. I have the following patter matching:

    ...
    | Ref n -> ...
    ...

where Ref is:

type t =
  ...
  | Ref of int

Compiler issues me a warning:

«Warning 28: wildcard pattern given as argument to a constant constructor»

Sorry, but if I understand this wording correctly, then I do not see
anything criminal in issuing a wildcard pattern to a constant
constructor. What is wrong?
-- 
         (__) 
         (oo) 
   /------\/ 
  / |    ||   
 *  /\---/\ 
    ~~   ~~   
...."Have you mooed today?"...

Re: [Caml-list] Warning 28.

[Virgile Prevosto]

Hello Ivan,

2013/6/5 Ivan Gotovchits <ivg@ieee.org>:
>     | Ref n -> ...
>     ...
>
> where Ref is:
>
> type t =
>   ...
>   | Ref of int
>
> Compiler issues me a warning:
>
> «Warning 28: wildcard pattern given as argument to a constant constructor»
>
> Sorry, but if I understand this wording correctly, then I do not see
> anything criminal in issuing a wildcard pattern to a constant
> constructor. What is wrong?

OCaml is not complaining about your Ref constructor, but another one
that does not have any argument, but is nevertheless given a wildcard
pattern in the matching, as e.g. None in
the following code:

# let f default = function
  | Some n -> n
  | None _ -> default;;
Warning 28: wildcard pattern given as argument to a constant constructor

The 'None _'  is suspicious at best. Tolerating such kind of pattern
reportedly eases generation of OCaml code, and that's why it is a
warning and not a plain error.

Best regards,
--
E tutto per oggi, a la prossima volta
Virgile

Re: [Caml-list] Warning 28.

[Ivan Gotovchits]

Virgile Prevosto <virgile.prevosto@m4x.org> writes:


> OCaml is not complaining about your Ref constructor, but another one
> that does not have any argument, but is nevertheless given a wildcard
> pattern in the matching, as e.g. None in
> the following code:
>
> # let f default = function
>   | Some n -> n
>   | None _ -> default;;
> Warning 28: wildcard pattern given as argument to a constant constructor
>

Indeed, right above there was a true constant constructor with a
wildcard, though, for some reason, compiler was wrong in his estimation
of the error position, that confused me.

Thanks!

Re: [Caml-list] Warning 28.

[Alain Frisch]

On 06/05/2013 09:04 AM, Ivan Gotovchits wrote:
> for some reason, compiler was wrong in his estimation
> of the error position, that confused me.

Could you produce a simple reproduction case and submit it to the 
bugtracker?

-- Alain