What is Expressiveness in a Computer Language

[Chris Smith]

Joachim Durchholz <jo at durchholz.org> wrote:
> > The immutability comes from the fact (perhaps implicit in these 
> > textbooks, or perhaps they are not really texts on formal type theory) 
> > that types are assigned to expressions,
> 
> That doesn't *define* what's a type or what isn't!
> 

I'm sorry if you don't like it, but that's all there is.  That's the 
point that's being missed here.  It's not as if there's this thing 
called a type, and then we can consider how it is used by formal type 
systems.  A type, in formal type theory, is ANY label that is assigned 
to expressions of a program for the purpose of making a formal type 
system work.  If you wish to claim a different use of the word and then 
try to define what is or is not a type, then be my guest.  However, 
formal type theory will still not adopt whatever restrictions you come 
up with, and will continue to use the word type as the field has been 
using the word for a good part of a century now.

The first step toward considering the similarities and differences 
between the different uses of "type" in dynamic type systems and formal 
type theory is to avoid confusing aspects of one field with the other.

-- 
Chris Smith - Lead Software Developer / Technical Trainer
MindIQ Corporation