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?
>
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