What is Expressiveness in a Computer Language

Pascal Costanza pc at p-cos.net
Fri Jun 16 05:47:09 EDT 2006

Torben Ægidius Mogensen wrote:
> Raffael Cavallaro <raffaelcavallaro at pas-d'espam-s'il-vous-plait-mac.com> writes:
>> On 2006-06-14 16:36:52 -0400, Pascal Bourguignon <pjb at informatimago.com> said:
>>> In lisp, all lists are homogenous: lists of T.
>> CL-USER 123 > (loop for elt in (list #\c 1 2.0d0 (/ 2 3)) collect
>> (type-of elt))
>> i.e., "heterogenous" in the common lisp sense: having different
>> dynamic types, not in the H-M sense in which all lisp values are of
>> the single union type T.
> What's the difference?  Dynamically types values _are_ all members of
> a single tagged union type.

Yes, but that's mostly a meaningless statement in a dynamically typed 
language. In a dynamically typed language, you typically don't care 
about the static types.

> The main difference is that the tages
> aren't always visible and that there are only a fixed, predefined
> number of them.

Depending on the language, the number of "tags" is not fixed.


3rd European Lisp Workshop
July 3 - Nantes, France - co-located with ECOOP 2006

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