What is Expressiveness in a Computer Language

[David Hopwood]

David Hopwood wrote:
> Anton van Straaten wrote:
> 
>>I'm suggesting that if a language classifies and tags values in a way
>>that supports the programmer in static reasoning about the behavior of
>>terms, that calling it "untyped" does not capture the entire picture,
>>even if it's technically accurate in a restricted sense (i.e. in the
>>sense that terms don't have static types that are known within the
>>language).
>>
>>Let me come at this from another direction: what do you call the
>>classifications into number, string, vector etc. that a language like
>>Scheme does?  And when someone writes a program which includes the
>>following lines, how would you characterize the contents of the comment:
>>
>>; third : integer -> integer
>>(define (third n) (quotient n 3))
> 
> I would call it an informal type annotation. But the very fact that
> it has to be expressed as a comment, and is not checked,

What I meant to say here is "and is not used in any way by the language
implementation,"

> means that
> the *language* is not typed (even though Scheme is dynamically tagged,
> and even though dynamic tagging provides *partial* support for a
> programming style that uses this kind of informal annotation).

-- 
David Hopwood <david.nospam.hopwood at blueyonder.co.uk>