What is Expressiveness in a Computer Language

[Rob Thorpe]

Vesa Karvonen wrote:
> In comp.lang.functional Anton van Straaten <anton at appsolutions.com> wrote:
> > Let me add another complex subtlety, then: the above description misses
> > an important point, which is that *automated* type checking is not the
> > whole story.  I.e. that compile time/runtime distinction is a kind of
> > red herring.
>
> I agree.  I think that instead of "statically typed" we should say
> "typed" and instead of "(dynamically|latently) typed" we should say
> "untyped".
>
> > In a statically-checked language, people tend to confuse automated
> > static checking with the existence of types, because they're thinking in
> > a strictly formal sense: they're restricting their world view to what
> > they see "within" the language.
>
> That is not unreasonable.  You see, you can't have types unless you
> have a type system.  Types without a type system are like answers
> without questions - it just doesn't make any sense.
>
> > Then they look at programs in a dynamically-checked language, and see
> > checks happening at runtime, and they assume that this means that the
> > program is "untyped".
>
> Not in my experience.  Either a *language* specifies a type system or
> not.  There is little room for confusion.  Well, at least unless you
> equate "typing" with being "well-defined" or "safe" and go to great
> lengths to convince yourself that your program has "latent types" even
> without specifying a type system.

The question is: What do you mean by "type system"?
Scheme and Lisp both define how types work in their specifications
clearly, others may do too, I don't know.
Of-course you may not consider that as a type system if you mean "type
system" to mean a static type system.

> > It's certainly close enough to say that the *language* is untyped.
>
> Indeed.  Either a language has a type system and is typed or has no
> type system and is untyped.  I see very little room for confusion
> here.  In my experience, the people who confuse these things are
> people from the dynamic/latent camp who wish to see types everywhere
> because they confuse typing with safety or having well-defined
> semantics.

No.  It's because the things that we call latent types we use for the
same purpose that programmers of static typed languages use static
types for.

Statically typed programmers ensure that the value of some expression
is of some type by having the compiler check it.  Programmers of
latently typed languages check, if they think it's important, by asking
what the type of the result is.

The objection here is that advocates of statically typed language seem
to be claiming the "type" as their own word, and asking that others use
their definitions of typing, which are really specific to their
subjects of interest. This doesn't help advocates of static languages/
latently typed languages, or anyone else.  It doesn't help because
no-one else is likely to change their use of terms, there's no reason
why they would.  All that may happen is that users of statically typed
languages change the words they use.  This would confuse me, for one. I
would much rather understand what ML programmers, for example, are
saying and that's hard enough as it is.

There's also my other objection, if you consider latently typed
languages untyped, then what is assembly?