Re: 'a versus ('a)

If you have several type parameters you need to write ('a, 'b, 'c) for
example. 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.

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).

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
>
>
>
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> Posted by: Manfred Lotz <[email protected]>
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