What is Expressiveness in a Computer Language

[Chris Smith]

Rob Thorpe <robert.thorpe at antenova.com> wrote:
> 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.

I'm assuming you mean "class" in the general sense, rather than in the 
sense of a specific construct of some subset of OO programming 
languages.

Now I define a class of values called "correct" values.  I define these 
to be those values for which my program will produce acceptable results.  
Clearly there is a defined class of such values: (1) they are 
immediately defined by the program's specification for those lines of 
code that produce output; (2) if they are defined for the values that 
result from any expression, then they are defined for the values that 
are used by that expression; and (3) for any value for which correctness 
is not defined by (1) or (2), we may define its "correct" values as the 
class of all possible values.  Now, by your definition, any language 
which provides checking of that property of correctness for values is 
latently typed.  Of course, there are no languages that assign this 
specific class of values; but ANY kind of correctness checking on values 
that a language does (if it's useful at all) is a subset of the perfect 
correctness checking system above.  Apparently, we should call all such 
systems "latent type systems".  Can you point out a language that is not 
latently typed?

I'm not trying to poke holes in your definition for fun.  I am proposing 
that there is no fundamental distinction between the kinds of problems 
that are "type problems" and those that are not.  Types are not a class 
of problems; they are a class of solutions.  Languages that solve 
problems in ways that don't assign types to variables are not typed 
languages, even if those same problems may have been originally solved 
by type systems.

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

Hence, they don't exist, and the definitions being used here are rather 
pointless.

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