What is Expressiveness in a Computer Language

[Rob Thorpe]

Chris Smith wrote:
> Torben Ægidius Mogensen <torbenm at app-3.diku.dk> wrote:
> > That's not really the difference between static and dynamic typing.
> > Static typing means that there exist a typing at compile-time that
> > guarantess against run-time type violations.  Dynamic typing means
> > that such violations are detected at run-time.  This is orthogonal to
> > strong versus weak typing, which is about whether such violations are
> > detected at all.  The archetypal weakly typed language is machine code
> > -- you can happily load a floating point value from memory, add it to
> > a string pointer and jump to the resulting value.  ML and Scheme are
> > both strongly typed, but one is statically typed and the other
> > dynamically typed.
>
> Knowing that it'll cause a lot of strenuous objection, I'll nevertheless
> interject my plea not to abuse the word "type" with a phrase like
> "dynamically typed".  If anyone considers "untyped" to be perjorative,
> as some people apparently do, then I'll note that another common term is
> "type-free," which is marketing-approved but doesn't carry the
> misleading connotations of "dynamically typed."  We are quickly losing
> any rational meaning whatsoever to the word "type," and that's quite a
> shame.

I don't think dynamic typing is that nebulous.  I remember this being
discussed elsewhere some time ago, I'll post the same reply I did then
..


A language is statically typed if a variable has a property - called
it's type - attached to it, and given it's type it can only represent
values defined by a certain class.

A language is latently typed if a value has a property - called it's
type - attached to it, and given it's type it can only represent values
defined by a certain class.

Some people use dynamic typing as a word for latent typing, others use
it to mean something slightly different.  But for most purposes the
definition above works for dynamic typing also.

Untyped and type-free mean something else: they mean no type checking
is done.