What is a type error?

[Marshall]

Andreas Rossberg wrote:
> Marshall wrote:
> >
> > After all, what are the alternatives? Purely-functional
> > languages remove themselves from a large class of
> > problems that I consider important: data management.
>
> Maybe, but I have yet to see how second-class variables are really more
> adequate in dealing with it.
>
> And note that even with second-class state you can still have aliasing
> issues - you just need mutable arrays and pass around indices. Keys in
> databases are a more general form of the same problem.

So for array a, you would claim that "a[5]" is an alias for
(a part of) "a"? That seems to stretch the idea of aliasing
to me. With these two expressions, it is obvious enough
what is going on; with two arbitrary pointers, it is not.

It seems to me the source of the problem is the opacity
of pointers, but perhaps I am missing something.


> > I have explored the OO path to its bitter end and am
> > convinced it is not the way. So what is left? Uniqueness
> > types and logic programming, I suppose. I enjoy logic
> > programming but it doesn't seem quite right. But notice:
> > no pointers there!  And it doesn't seem to suffer from the
> > lack.
>
> Uh, aliasing all over the place! Actually, I think that logic
> programming, usually based on deep unification, brings by far the worst
> incarnation of aliasing issues to the table.

Hmmm. Can you elaborate just a bit?


Marshall