Re: [Caml-list] Comparison of functional values

Re: [Caml-list] Comparison of functional values

[Arturo Borquez]

On Tue, 06 March 2001, Olivier Andrieu wrote:

> 
> 
> Hello list, 
> 
> I wanted to build a Set of functional value. But generic equality
> can't be used for functional values (raises an exception ...). It is
> therefore difficult to build a Set of such values because the Set.Make
> functor requires a comparison function and Pervasives.compare relies
> on (=).
> 
> Is there a way around this ? I thought I could use physical equality
> (wich is OK wrt functional values) but there's no such thing as
> `physical inequality'.
> 
> -- 
> Olivier Andrieu
> -------------------
> To unsubscribe, mail caml-list-request@inria.fr.  Archives: http://caml.inria.fr

Hi Olivier:
Perhaps this help

let a = fun f x -> x = x;;
let b = fun f x -> x = x;;
(a == b) = true;;
-: bool = false
not (a == b) = true;;
-: bool = true

Regards
Arturo Borquez


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Re: [Caml-list] Comparison of functional values

[Xavier Leroy]

> What I meant actually, was a «physical compare». I found out that 
> this (crude) C function works :
> 
> value phys_comp(value a, value b)
> {
>  if(a<b)
>    return Val_int(-1) ;
>  else if(a>b)
>    return Val_int(+1) ;
>  else 
>    return Val_int(0);
> }

No, it does not:  the GC can copy heap blocks and change the relative
ordering of their memory addresses.  You really need to pair your
functions with unique identifying integers.

- Xavier Leroy
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Re: [Caml-list] Comparison of functional values

[Olivier Andrieu]

 Alan Schmitt [Wednesday 7 March 2001] :
 > As stated in http://caml.inria.fr/ocaml/htmlman/manual031.html, != is
 > the negation of ==.

Salut Alan !

I known. But to use the Set functor, you need a `compare' function of
type ('a -> 'a -> int) whereas != and == have type ('a -> bool). 
So != does not seem very helpful here.

What I meant actually, was a «physical compare». I found out that 
this (crude) C function works :

value phys_comp(value a, value b)
{
 if(a<b)
   return Val_int(-1) ;
 else if(a>b)
   return Val_int(+1) ;
 else 
   return Val_int(0);
}

Olivier
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Re: [Caml-list] Comparison of functional values

[Alan Schmitt]

>Is there a way around this ? I thought I could use physical equality
>(wich is OK wrt functional values) but there's no such thing as
>`physical inequality'.
>

As stated in http://caml.inria.fr/ocaml/htmlman/manual031.html, != is
the negation of ==.

Alan Schmitt

--
The hacker: someone who figured things out and made something cool happen.
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[Caml-list] Comparison of functional values

[Olivier Andrieu]

Hello list, 

I wanted to build a Set of functional value. But generic equality
can't be used for functional values (raises an exception ...). It is
therefore difficult to build a Set of such values because the Set.Make
functor requires a comparison function and Pervasives.compare relies
on (=).

Is there a way around this ? I thought I could use physical equality
(wich is OK wrt functional values) but there's no such thing as
`physical inequality'.

-- 
Olivier Andrieu
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