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[Caml-list] Constructors as functions and tuples in constructors
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Date: -- (:)
From: Nicolas Cannasse <warplayer@f...>
Subject: Re: [Caml-list] Constructors as functions and tuples in constructors
> Gentlemen!
>
> There are two features, which might it be useful to support in the
> language w/out modifying it much. And they both are about greater
> generality of the language.
>
> First, it would be nice to have constructors as functions like below:
>
> List. map Some [17]

This is only syntaxic sugar. First class constructors are easy to add to the
language, that's just a matter of will from the INRIA team to choose to add
it or not ( meaning : since they didn't put the feature in the language yet,
they might have good reasons to do so. ).

> Second, it would also be nice not to have "the concept of constructor
> arity", and treat the code below as correct:
>
> type t = A of int * int
> let _ =
>   match A (17, 0) with
>     A z -> match z with (x, y) -> ()
>
> Does anybody know, whether this is possible? Or, if not, what are the
> prohibiting reasons?

This is possible :
type t = A of (int * int)

Notice the difference :
- in the first case, you alloc a block with tag "A" of size 2
- in the second, you alloc a block with tag "A" of size 1 containing a tuple
(a block of size 2 with tag 0 containing the two ints). There is then one
more indirection in your integers access but the tuple can be returned
directly without any added allocation.

Nicolas Cannasse

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