[Caml-list] strange compiler's tolerance

[Caml-list] strange compiler's tolerance

[Matej Kosik]

Hi,

Today I noticed a strange compiler's tolerance.
The compiler will not protest here:

   type foo = Bar | Baz

   ;;

   match Bar with
     | Bar _ -> ()
     | Baz -> ()

Why doesn't the compiler protest that I used wildcard after "Bar" constructor?
(It does protest if I put any other pattern except for the wildcard).

This slightly breaks the logic. Doesn't it?

Re: [Caml-list] strange compiler's tolerance

[Pippijn van Steenhoven]

[-- Attachment #1: Type: text/plain, Size: 133 bytes --]

Hi,

OCaml as of 4.00.1 does complain about this with a warning. Allowing it
is mostly useful (and used) in generated code.

Pippijn

[-- Attachment #2: Digital signature --]
[-- Type: application/pgp-signature, Size: 836 bytes --]

Re: [Caml-list] strange compiler's tolerance

[Gabriel Scherer]

[-- Attachment #1: Type: text/plain, Size: 1324 bytes --]

The pattern _ has been extended to accept any number of arguments. If you
think of it

  type foo = Foo of int * bool
  let f (Foo _) = ()

is already quite strange (replacing _ by a variable here doesn't work), but
extremely convenient (you don't want to have to remember the constructor's
arity just to ignore it). It was extended to 0-ary constructors for
consistency, but you can disable this allowance by marking warning 28
(ocamlc -warn-help) as an error.


On Thu, Oct 24, 2013 at 3:47 PM, Matej Kosik <
5764c029b688c1c0d24a2e97cd764f@gmail.com> wrote:

> Hi,
>
> Today I noticed a strange compiler's tolerance.
> The compiler will not protest here:
>
>   type foo = Bar | Baz
>
>   ;;
>
>   match Bar with
>     | Bar _ -> ()
>     | Baz -> ()
>
> Why doesn't the compiler protest that I used wildcard after "Bar"
> constructor?
> (It does protest if I put any other pattern except for the wildcard).
>
> This slightly breaks the logic. Doesn't it?
>
> --
> Caml-list mailing list.  Subscription management and archives:
> https://sympa.inria.fr/sympa/**arc/caml-list<https://sympa.inria.fr/sympa/arc/caml-list>
> Beginner's list: http://groups.yahoo.com/group/**ocaml_beginners<http://groups.yahoo.com/group/ocaml_beginners>
> Bug reports: http://caml.inria.fr/bin/caml-**bugs<http://caml.inria.fr/bin/caml-bugs>
>

[-- Attachment #2: Type: text/html, Size: 2032 bytes --]

Re: [Caml-list] strange compiler's tolerance

[Virgile Prevosto]

Hello,

2013/10/24 Matej Kosik <5764c029b688c1c0d24a2e97cd764f@gmail.com>:
> Hi,
>
> Today I noticed a strange compiler's tolerance.
> The compiler will not protest here:
>
>   type foo = Bar | Baz
>
>   ;;
>
>   match Bar with
>     | Bar _ -> ()
>     | Baz -> ()
>

It's not a bug, it's a "dubious feature". See
http://caml.inria.fr/mantis/view.php?id=5502 for more information. If
like me you indeed find that's it's more dubious than a feature,
warning 28
"Wildcard pattern given as argument to a constant constructor" is your
friend and is set by default.

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