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

[Alain Frisch <alain.frisch@lexifi.com>]

On 09/11/2015 19:08, Gabriel Scherer wrote:
> If we gave a functional semantic to the unapplied constructor, then I
> think that good taste would mandate for the application of this
> function and the application of the constructor to be equivalent. This
> means that by choosing a tuple-taking function, we commit to the
> tuple-application syntax (that nobody likes), and that choosing a
> currified function creates an unpleasant inconsistency in the
> language.
>
> I don't know whether we could ever manage to transition to a currified
> syntax for constructors, but right now it is at least conceivable
> because the application syntax is just a concrete syntax choice, it
> does not affect typing. Turning unapplied constructor into a function
> (tuplified or currified) makes it a typing property, observable at
> specification boundaries: we cannot change it.

Making it easier to switch in the distant future to currified 
constructors does not seem a strong argument against improving the 
language now (especially reducing bad surprises for beginners).

The tuple-like syntax is not very much liked, but this is partly caused 
by the fact that arguments cannot be manipulated as real tuples.  With 
the proposed change, this argument goes away.

Moreover, *if* we ever wanted to switch to currified constructors, this 
would not be a purely syntactic rewriting anyway, even with the current 
language.  One would need to have access to constructor declarations to 
drive the rewriting process.  If you one allows oneself to get such 
information out of the type checker, doing the rewriting even in 
presence of the currently suggested changes would be possible as well 
(with extra wrapping/unwrapping).


Alain


>
> On Mon, Nov 9, 2015 at 6:33 PM, Alain Frisch <alain.frisch@lexifi.com> wrote:
>> On 09/11/2015 11:35, Andreas Rossberg wrote:
>>>
>>> Yes please, I would appreciate such sugar.
>>
>>
>> I've now submitted a cleaner implementation, working on both expressions and
>> patterns:
>>
>> https://github.com/ocaml/ocaml/pull/284
>>
>>> Even more I would appreciate
>>> generalising that to allowing constructors to be used as first-class
>>> expressions (i.e., unapplied "C" -> "fun (x1,...,xN) -> C (x1,...,xN)"
>>> when C is a constructor with arity > 0). I had to write some AST mapping
>>> code recently that would have vastly benefited from that.
>>
>>
>> This is not covered (and now, it could simply be "fun x -> C x" :-)).  I
>> don't see anything clever to be done on patterns for "unapplied
>> constructors", though.
>>
>>
>> Alain
>>
>>
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