What is Expressiveness in a Computer Language

[Marshall]

Matthias Blume wrote:
> "Marshall" <marshall.spight at gmail.com> writes:
>
> > Torben Ægidius Mogensen wrote:
> >>
> >> That's not true.  ML has variables in the mathematical sense of
> >> variables -- symbols that can be associated with different values at
> >> different times.  What it doesn't have is mutable variables (though it
> >> can get the effect of those by having variables be immutable
> >> references to mutable memory locations).
> >
> > While we're on the topic of terminology, here's a pet peeve of
> > mine: "immutable variable."
> >
> > immutable = can't change
> > vary-able = can change
> >
> > Clearly a contradiction in terms.
>
> No, it is not a contradiction.  See the mathematical usage of the word
> "variable".

I am not saying that this kind of terminology isn't common; what
I'm saying is that it isn't good. And I think I gave a pretty clear
and solid definition of the two words, and those definitions are
decidedly contradictory.


> Immutable variables can stand for different values at
> different times, even without mutation involved, usually because they
> are bound by some construct such as lambda.

Well, that's a good point actually. Parameters are variable
no matter how you look at it. I was speaking more in terms
of locals.


> > If you have a named value that cannot be updated, it makes
> > no sense to call it "variable" since it isn't *able* to *vary.*
>
> Mutation is not the only way for an expression to evaluate to
> different values over time.

I suppose the difficulty arises from the difference
between the connotation of "mutate" in a PLT context, which is
support for destructive assignment, and the meaning of the word
in the larger context.

Anyway, I don't see how your sentence above contradicts
my sentence. We do not use the term "update" to describe
the process of binding values to parameters upon function
invocation. (Am I wrong?)


Marshall