Re: [Caml-list] Newbie comment on constructor syntax

[Romain Bardou <romain@cryptosense.com>]

On 10/11/2015 11:44, Alain Frisch wrote:
> On 10/11/2015 11:25, Romain Bardou wrote:
>> In the Mantis thread I proposed that #C or (C) would be the curried
>> version of constructor C.
>
> If we go in the direction of making n-ary constructors behave as
> constructor taking a tuple (at the expression level) then it seems
> confusing that #C would mean something different for:
>
>    type t = A of int * int
>
> and for:
>
>    type t = A of (int * int)
>
> Moreover, I'm not sure about the benefit:  how often do you need to
> partially apply a constructor?  And it's easy to define manually the
> helper function (let a x y = A (x, y)) if needed.  I don't think adding
> dedicated syntax is justified here.
>
> Andreas suggested that a non-constant unapplied constructor would be
> interpreted as a function (i.e. just A would be interpreted as (fun x ->
> A x)).  This would allow writing for instance "List.map Some l", and
> have the nice consequence that "Some e" becomes equivalent to "(Some)
> e".  The only drawback I can think of with this idea is less useful
> error locations when changing a constant constructor into a non-constant
> one.
>
> Alain
>

That #C would mean something different for the definitions is an issue 
with the syntax and the semantics of constructor definitions I believe, 
which is already rather confusing :)

That being said it's true that most of the time when I use a constructor 
as a function, the constructor has arity 1. In fact, most of the time it 
is Some.

Cheers,

-- 
Romain Bardou