In article <izpvvgcn5a.fsf@mocha.CS.Princeton.EDU>,
Matthias Blume <firstname.lastname@example.org> wrote:
>In article <E9AxB1.7nA@ecf.toronto.edu> email@example.com (Patrick Doyle)
> In article <izhggvrukk.fsf@mocha.CS.Princeton.EDU>,
> Matthias Blume <firstname.lastname@example.org> wrote:
> > - Things that _actually_ look the same in each and every
> > respect_are_ the same. Things that we can distinguish between
> > do _not_ look the same (by definition -- this is what we mean by
> > being able to distinguish).
> I wouldn't necessarily agree. The difficulty lies in mutable objects. If
> I have two mutable objects, alike in every way, and I change one, then the
> other doesn't change. [ ... ]
>Sorry, you are right, but you missed my point. If there is an
>operation (here: modify one object and observe the change -- or
>rather: non-change -- in the other), that lets you distinguish between
>the two things, then they don't look the same (and never did). It's a
>matter of what one means by "they look the same".
Sounds a bit Orwellian to me. :-)
>And moreover, if the language has both mutable _and_ immutable things,
>then it should support the concept of identity for the former and not
>for the latter. Since that was what started the thread: ML is such a
>language, and it gets this issue exactly right.
Interesting. I must look into that language.