What is Expressiveness in a Computer Language

[Matthias Blume]

"Rob Thorpe" <robert.thorpe at antenova.com> writes:

> 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.

By this definition, all languages are statically typed (by making that
"certain class" the set of all values).  Moreover, this "definition",
when read the way you probably wanted it to be read, requires some
considerable stretch to accommodate existing static type systems such
as F_\omega.

Perhaps better: A language is statically typed if its definition
includes (or ever better: is based on) a static type system, i.e., a
static semantics with typing judgments derivable by typing rules.
Usually typing judgmets associate program phrases ("expressions") with
types given a typing environment.

> 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.

This "definition" makes little sense.  Any given value can obviously
only represent one value: itself.  "Dynamic types" are nothing more
than sets of values, often given by computable predicates.

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

Look up "untyped lambda calculus".