[REBOL] Re: Sameness - a pragmatic approach.
From: lmecir:mbox:vol:cz at: 11-Feb-2003 16:33
Hi Gabriele,
...
> It is just a matter of definitions. I could simply start by
> enumerating the types that are mutable and the ones that are
> immutable, then enumerate the functions that cause a mutation in a
> mutable value, and then saying that values of the immutable types
> are never the same, and two values of a mutable type are the same
> when they are equal before and after an arbitrary mutation of one
> of them.
>
> Regards,
> Gabriele.
That sounds legal. But the definition of mutability seems more complicated than the sameness
to me.
Let's take Rebol errors as an example. Originally I thought, that they were immutable.
So I could have put them on the list of immutable datatypes. Later I found out, that
I was wrong and I corrected myself. I was able to do so, because I had a definition of
mutability. In the case of your definition I would never have a chance to find out that
I was wrong, because I simply couldn't have been. This doesn't look like a pragmatic
approach.
Rebol dates may serve as another example. Set-paths originally didn't work for dates
as we all remember. According to my definition they were immutable. Interestingly enough,
the situation hasn't changed after the set-path introduction, i.e. the definition showed
a good stability. Isn't that a good property?
Ciao
-L
