Changes on equality between 3.06 and 3.08.3

Changes on equality between 3.06 and 3.08.3

[Olivier Michel]

Hi dear ocamlers,

I just noticed the following change in Ocaml between release 3.06 and 3.08.3, as far
as equality on records is concerned :


////////////////////////////////////////////////////////////////////////////////
//
//release 3.06
//

dellfp-3 7 > /ocaml
        Objective Caml version 3.06

# type toto = { b : int -> int; } ;;
type toto = { b : int -> int; }
# let a = { b = (fun x -> x) } ;;
val a : toto = {b = <fun>}
# a = a;;
- : bool = true


//
//release 3.08.3
//


dellfp-3 8 > ocaml
        Objective Caml version 3.08.3

# type toto = { b : int -> int; };;
type toto = { b : int -> int; }
# let a = { b = (fun x -> x) } ;;
val a : toto = {b = <fun>}
# a = a;;
Exception: Invalid_argument "equal: functional value".

////////////////////////////////////////////////////////////////////////////////

Is this supposed to be a bug, or a feature ? Will future releases of Ocaml follow
the new way of handling equality between records or the old one ?

Best regards,
Olivier.

--
Olivier MICHEL                       Email : michel@lami.univ-evry.fr
Universite d'Evry Val d'Essonne      http  : www.lami.univ-evry.fr/~michel
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91000 Evry - FRANCE

Re: [Caml-list] Changes on equality between 3.06 and 3.08.3

[Damien Doligez]

On Apr 28, 2005, at 12:02, Olivier Michel wrote:

> I just noticed the following change in Ocaml between release 3.06 and 
> 3.08.3, as far
> as equality on records is concerned :
>
> # type toto = { b : int -> int; };;
> type toto = { b : int -> int; }
> # let a = { b = (fun x -> x) } ;;
> val a : toto = {b = <fun>}
> # a = a;;
> Exception: Invalid_argument "equal: functional value".
>
>
> Is this supposed to be a bug, or a feature ? Will future releases of 
> Ocaml follow
> the new way of handling equality between records or the old one ?

New feature.  Carefully thought out.  Well documented.  Ultimately 
caused
by a strange wart of the IEEE floating-point standards.

You should use the "compare" function if you want the old behaviour.

-- Damien

Re: [Caml-list] Changes on equality between 3.06 and 3.08.3

[Alex Baretta]

Olivier Michel wrote:
> Hi dear ocamlers,
> 
> I just noticed the following change in Ocaml between release 3.06 and 3.08.3, as far
> as equality on records is concerned :
> ..
> # a = a;;
> Exception: Invalid_argument "equal: functional value".

Keep in mind that in 3.06 physical equality (==) implied structural 
equality (=). Now, (=) now longer checks for (==), so no functional 
value can be found to be structurally equal to any other functional 
value. The following line illustrates this point.

# (=) (=) (=);;
Exception: Invalid_argument "equal: functional value".

Actually, an interesting question related to this one is why the 
following line behaves as it does.

# (==) (==) (==);;
- : bool = false


Alex


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Re: [Caml-list] Changes on equality between 3.06 and 3.08.3

[Olivier Andrieu]

 > Alex Baretta [Thu, 28 Apr 2005]:
 > Actually, an interesting question related to this one is why the
 > following line behaves as it does.
 > 
 > # (==) (==) (==);;
 > - : bool = false

Probably because == is defined by an "external" in pervasives.ml, not
a regular function definition. So here, when you use (==), you're
building three closures.

-- 
   Olivier

Re: [Caml-list] Changes on equality between 3.06 and 3.08.3

[Marcin 'Qrczak' Kowalczyk]

Olivier Andrieu <andrieu@ijm.jussieu.fr> writes:

>  > # (==) (==) (==);;
>  > - : bool = false
>
> Probably because == is defined by an "external" in pervasives.ml,
> not a regular function definition. So here, when you use (==),
> you're building three closures.

Two. OCaml materializes function objects corresponding to external
functions each time they are used instead of once at the point of
their definition (presumably because it assumes that usually they are
not passed as first-class objects at all), but application of such
function doesn't need the function object but jumps straight to its
machine code.

-- 
   __("<         Marcin Kowalczyk
   \__/       qrczak@knm.org.pl
    ^^     http://qrnik.knm.org.pl/~qrczak/

Re: [Caml-list] Changes on equality between 3.06 and 3.08.3

[Jon Harrop]

On Thursday 28 April 2005 18:06, Olivier Andrieu wrote:
>  > Alex Baretta [Thu, 28 Apr 2005]:
>  > Actually, an interesting question related to this one is why the
>  > following line behaves as it does.
>  >
>  > # (==) (==) (==);;
>  > - : bool = false
>
> Probably because == is defined by an "external" in pervasives.ml, not
> a regular function definition. So here, when you use (==), you're
> building three closures.

# let f = (==) in (==) f f;;
- : bool = true

Interesting. I don't like it, but it's interesting. :-)

-- 
Dr Jon D Harrop, Flying Frog Consultancy Ltd.
Objective CAML for Scientists
http://www.ffconsultancy.com/products/ocaml_for_scientists