Re: 'a versus ('a)

(* phantom type: http://camltastic.blogspot.com/2008/05/phantom-types.html *)
type _ foo = Foo

(* GADT: http://caml.inria.fr/pub/docs/manual-ocaml-4.03/extn.html#sec238 *)
type _ tag =
  | TInt : int tag
  | TFloat : float tag

On Mon, May 30, 2016 at 4:54 PM, Manfred Lotz [email protected]
[ocaml_beginners] <[email protected]> wrote:
> Thanks for your answer.
>
> On Mon, 30 May 2016 14:51:40 -0400
> "Gabriel Scherer [email protected] [ocaml_beginners]"
> <[email protected]> wrote:
>
>> If you have several type parameters you need to write ('a, 'b, 'c) for
>> example.
>
> Yes.
>
>> For a single parameter, both are perfectly equivalent, so you
>> can use the one you like best. I think just 'a is more common; I don't
>> remember seeing ('a) in the wild, although it could make sense for
>> consistency or if in a temporary state if you had two parameters and
>> are currently editing the code to try it with only one.
>>
>
> Good. For me 'a without parenthesis looks more natural.
>
>> You can also not give a name to the parameter by using _ in this
>> position. This is sometimes used with some advanced features/patterns:
>> when defining a phantom type (where the parameter is not used at all),
>> or when using a GADT (where the parameter value will be set by each
>> constructor separately).
>>
>
> Hm, I have to admit that in order to understand this better I would
> need an example.
>
>
>> On Mon, May 30, 2016 at 2:32 PM, Manfred Lotz [email protected]
>> [ocaml_beginners] <[email protected]> wrote:
>> > I have seen both 'a and ('a) in type definitions like this:
>> >
>> > type 'a tree = Leaf of 'a | Node of 'a tree * 'a tree;;
>> >
>> > type ('a) tree = Leaf of 'a | Node of 'a tree * 'a tree;;
>> >
>> > It seems they are equivalent.
>> >
>> > Is there a reason why I would write ('a) instead of just 'a? Or is
>> > is just a matter of taste?
>> >
>> > --
>> > Manfred
>> >
>> >
>> >
>> >
>> > ------------------------------------
>> > Posted by: Manfred Lotz <[email protected]>
>> > ------------------------------------
>> >
>> > Archives up to December 31, 2011 are also downloadable at
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>> > of the very official ocaml list (the seniors' one) can be found at
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>> >
>> > Yahoo Groups Links
>> >
>> >
>> >
>
>
>
> ------------------------------------
> Posted by: Manfred Lotz <[email protected]>
> ------------------------------------
>
> Archives up to December 31, 2011 are also downloadable at http://www.connettivo.net/cntprojects/ocaml_beginners
> The archives of the very official ocaml list (the seniors' one) can be found at http://caml.inria.fr
> Attachments are banned and you're asked to be polite, avoid flames etc.
> ------------------------------------
>
> Yahoo Groups Links
>
>
>