Re: [Caml-list] Generic printer patch

["Gerd Stolpmann" <info@gerd-stolpmann.de>]

>>> 2) Could you imagine to generalize it to Format.formatter or to
>>> out_channel (without creating a string and concatenating)? Romain
>>> Bardou
>>> add in the mantis tracker (I can't give you the bugtracking number
>>> since
>>> mantis "is currently offline for maintenance") a feature wish for a new
>>> conversion specification that can print anything. Do you think you can
>>> fulfill is dream?
>
> Here is the feature request I proposed:
>
> http://caml.inria.fr/mantis/view.php?id=4956
>
> Here is the response by Pierre Weis:
>
> "This is a major feature wish that requires careful thinking and a lot
> of work!
>
> Furthermore, we would not have a completely satisfactory solution in the
> end (due to this <poly> catch all case that tend to propagate, as far as
> you use polymorphic functions). The correct solution to get this feature
> in its full glory is a major modification of the type system along the
> lines of G'Caml.

Well, G'Caml did not appear finally. But this explains why no generic
printer has been added so far: There was always the hope to get this
feature automatically by some generalization in the compiler. Same for
type-safe unmarshalling, and other features needing introspection.

On the one hand, these features are badly needed by users. On the other
hand, the language designers strive for an excellent solution, and not one
that will become obsolete sooner or later.

The situation is different today. We'll now have GADTs in the next
release, which work quite differently, and which are no replacement for a
separate introspection solution (like the one Alain suggests), but could
be a clever add-on. So, it has become more likely that the pragmatism wins
this time, because it makes the new playground GADTs more enjoyable (in
particular when the compiler supports the generation of "standard GADTs"
just representing the structure of a type).

Gerd

>
> In short, a natural feature wish in a strongly typed polymorphic
> language; we had it in mind for decades; unfortunately, we are not yet
> ready to offer it, even in the rather limited extent you proposed."
>
> In other words: what you did is awesome but I'm not sure that it will be
> added in the trunk :(
>
> Cheers,
>
> --
> Romain Bardou
>
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>
>


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