Re: [Caml-list] strange typechecking result

[Matej Kosik <5764c029b688c1c0d24a2e97cd764f@gmail.com>]

On 22/02/13 18:33, Leo White wrote:
>>
>
> I think that by default recursive uses of a function are monomorphic.
> You can fix this with an explicit polymorphic annotation:
>
> let rec f1: 'a. 'a -> unit = fun _ -> ()
> and f2 r1 = f1 r1.l1
> and f3 r2 = f1 r2.l2;;
>
> Regards,
>
> Leo
>

Yuri, Leo, thanks.

Now I see that there is even simpler program, that demonstrates the problem:

   let rec f1 _ =
     ()

   and f2 (value:int) =
     f1 value

   and f3 (value:char) =
     f1 value

The typechecker rejects it for similar reasons.

   File "test.ml", line 8, characters 5-10:
   Error: This expression has type char but an expression
          was expected of type int.

That's quite strange.

I would like to ask:

- Where is that restriction explained?
   (I've searched Ocaml reference manual for "monomorphic" but nothing
    relevant seemed to come up)

- Where are things like:

      'a. 'a -> unit

   described?

   I've already seen it in some document, but now I fail
   to find it again.