From: Goswin von Brederlow <goswin-v-b@web.de>
To: "David Allsopp" <dra-news@metastack.com>
Cc: "'Jon Harrop'" <jon@ffconsultancy.com>, <caml-list@yquem.inria.fr>
Subject: Re: [Caml-list] Constructors are not functions
Date: Thu, 08 Oct 2009 14:37:07 +0200 [thread overview]
Message-ID: <87ljjmxdsc.fsf@frosties.localdomain> (raw)
In-Reply-To: <005501ca468d$dc9b51a0$95d1f4e0$@metastack.com> (David Allsopp's message of "Tue, 6 Oct 2009 15:04:02 +0100")
"David Allsopp" <dra-news@metastack.com> writes:
> Jon Harrop wrote:
>> David Allsopp wrote:
>> > I think it would be possible to simulate the SML behaviour in OCaml
>> > using camlp4 (if you assume that for [type foo = Bar of int] that future
>> > unbound references to [bar] are interpreted as [fun x -> bar x] instead of an
>> > error)
>>
>> Only if you turned multi-argument type constructors into single-
>> argument ones
>> taking a tuple, i.e. type definitions like:
>>
>> type t = Bar of int * int
>>
>> must become:
>>
>> type t = Bar of (int * int)
>
> That's not the case at all - there'd be no reason not to interpret [bar] as [fun x y -> Bar(x, y)] for [Bar of int * int]. What would be hairy in camlp4 would be having to read .cmi files to deal with types defined outside your source file, but that's still not impossible...
>
>
> David
Then what about
type t1 = Bar of int * int
type t2 = Foo of (int * int)
If you treat constructors as functions taking one argument then
t1: int * int -> t1
t2: int * int -> t2
But:
# let x = (1,2);;
val x : int * int = (1, 2)
# Foo(x);;
- : t2 = Foo (1, 2)
# Bar(x);;
Error: The constructor Bar expects 2 argument(s),
but is here applied to 1 argument(s)
As functions "Bar" would have to deconstruct the tuple while "Foo"
uses it directly. And I would rather have curried constructors as in
"Bar 1 : int -> t1".
The difference between t1 and t2 gets lost. I actually hate that you
can write "Bar(1,2)" and "Foo(1,2)" Same problem there. It is unclear
if you pass 2 arguments or a tuple.
This should really be
t1: int -> int -> t1
t2: int * int -> t2
fun x y -> Bar x y
fun (x,y) -> Foo (x,y)
MfG
Goswin
next prev parent reply other threads:[~2009-10-08 12:42 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-10-06 12:01 Chantal KELLER
2009-10-06 12:19 ` [Caml-list] " Philippe Wang
2009-10-06 12:38 ` Jon Harrop
2009-10-06 13:38 ` Richard Jones
2009-10-10 11:49 ` blue storm
2009-10-06 12:45 ` David Allsopp
2009-10-06 12:46 ` David Allsopp
2009-10-06 13:14 ` Jim Farrand
2009-10-06 13:51 ` Michel Mauny
2009-10-06 13:15 ` Jon Harrop
2009-10-06 14:04 ` David Allsopp
2009-10-06 14:51 ` Jon Harrop
2009-10-06 15:24 ` Richard Jones
2009-10-06 16:31 ` Jacques Garrigue
2009-10-08 12:37 ` Goswin von Brederlow [this message]
2009-10-09 6:29 ` David Allsopp
2009-10-10 6:16 ` Goswin von Brederlow
2009-10-06 13:18 ` Gerd Stolpmann
2009-10-06 15:50 ` Jérémie Dimino
2009-10-06 21:55 ` blue storm
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