empty type

empty type

[Fernando Alegre]

Hi,

I think this is a bug, but I'm not sure. I mistakenly defined type e using
Haskell notation, and it was accepted. However, it shadowed the unit type.
Can someone confirm whether this should be acceptable or not?

Thanks.

        Objective Caml version 3.09.2

# type e = ();;
type e = ()
# type t = A of e | B of unit;;
type t = A of e | B of unit
# A();;
- : t = A ()
# B();;
This expression has type e but is here used with type unit


Fernando

Re: [Caml-list] empty type

[skaller]

On Mon, 2007-02-19 at 08:47 -0500, Fernando Alegre wrote:
> Hi,
> 
> I think this is a bug, but I'm not sure. I mistakenly defined type e using
> Haskell notation, and it was accepted. However, it shadowed the unit type.
> Can someone confirm whether this should be acceptable or not?
> 
> Thanks.
> 
>         Objective Caml version 3.09.2
> 
> # type e = ();;

What? That sure looks like a bug. () is a value of type unit ..
it isn't a type.

-- 
John Skaller <skaller at users dot sf dot net>
Felix, successor to C++: http://felix.sf.net

RE : [Caml-list] empty type

[Mathias Kende]

>What? That sure looks like a bug. () is a value of type unit ..
>it isn't a type.

It's not a type, but just a valid name for a constructor that can be
redefined if necessary (although one surely does not want to do so).

Mathias Kende

Re: RE : [Caml-list] empty type

[Andrej Bauer]

Mathias Kende wrote:
> It's not a type, but just a valid name for a constructor that can be
> redefined if necessary (although one surely does not want to do so).

Way cool:

# type t = () of int * int ;;
type t = () of int * int
# () (3, 4) ;;
- : t = () (3, 4)

Andrej

Re: RE : [Caml-list] empty type

[Fernando Alegre]

How about this:

# type t = () of int;;
type t = () of int
# begin end;;
The constructor () expects 1 argument(s),
but is here applied to 0 argument(s)

Fernando

On Mon, Feb 19, 2007 at 05:03:58PM +0100, Andrej Bauer wrote:
> Mathias Kende wrote:
> >It's not a type, but just a valid name for a constructor that can be
> >redefined if necessary (although one surely does not want to do so).
> 
> Way cool:
> 
> # type t = () of int * int ;;
> type t = () of int * int
> # () (3, 4) ;;
> - : t = () (3, 4)
> 
> Andrej
> 
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Re: RE : [Caml-list] empty type

[Bruno De Fraine]

On 19 Feb 2007, at 17:03, Andrej Bauer wrote:

> Mathias Kende wrote:
>> It's not a type, but just a valid name for a constructor that can be
>> redefined if necessary (although one surely does not want to do so).
>
> Way cool:
>
> # type t = () of int * int ;;
> type t = () of int * int
> # () (3, 4) ;;
> - : t = () (3, 4)

If you redefine :: you get an infix constructor:

# type expr = Num of int | :: of expr * expr ;;
type expr = Num of int | :: of expr * expr
# Num 1 :: Num 2 :: Num 3 ;;
- : expr = :: (Num 1, :: (Num 2, Num 3))
# :: (Num 2, Num 3) ;;
Syntax error
# let a :: b = Num 1 :: Num 2 :: Num 3 ;;
Warning P: this pattern-matching is not exhaustive.
Here is an example of a value that is not matched:
Num _
val a : expr = Num 1
val b : expr = :: (Num 2, Num 3)

Bruno

-- 
Bruno De Fraine
Vrije Universiteit Brussel
Faculty of Applied Sciences, INFO - SSEL
Room 4K208, Pleinlaan 2, B-1050 Brussels
tel: +32 (0)2 629 29 75
fax: +32 (0)2 629 28 70
e-mail: Bruno.De.Fraine@vub.ac.be

Re: [Caml-list] empty type

[Richard Jones]

On Mon, Feb 19, 2007 at 08:47:38AM -0500, Fernando Alegre wrote:
> 
> Hi,
> 
> I think this is a bug, but I'm not sure. I mistakenly defined type e using
> Haskell notation, and it was accepted. However, it shadowed the unit type.
> Can someone confirm whether this should be acceptable or not?

It tripped us up before:

http://caml.inria.fr/pub/ml-archives/caml-list/2005/06/e1a4be2ebe9ced1cbdc06979a7e8ae17.en.html

Rich.

-- 
Richard Jones
Red Hat UK Limited