🚀 go-pugleaf

Dave Chase writes:
>All this drivel about what language xyzzy can or can't do is pretty
>tiresome, since nobody is saying anything new.  The arguments are also
>pretty pointless, since most of the languages discussed (all but ML,
>Russell, and Quest), whether "statically" or "dynamically" typed, have
>pitifully inadequate type systems (Eiffel too -- nice touch, leaving
>that contravariance hole in there for procedure types), if they claim
>to have type systems at all.

Nothing new under the Sun, eh?

It may not be true for you, but I find that reviewing basic concepts
and assumptions is an extremely fruitful line of thought.  

>(2) does any "expert" out there care to explain how "data types are
>    values"?  (Hans Boehm is not allowed to answer this question)

"What operations are allowed on a datum" is representable as data.

The point is not that data types "are" values.  The point is that
viewing data types as values is a useful approach to problem solving.

Of course, "data type" means different things to different people.  To
some, it is the "word size" used to hold the bit patterns that
represent values.  To some, it is what kind of register holds these
values.  To some, it is a syntactic feature of a programming language.

If you are dealing with large data objects (much larger than the word
size of the machine you are working on), it becomes convenient to
"tag" these structures so that functions may reject values which are
outside their domain.  This is analogous to the sort of thing that you
need to do to insure that machine operations are doing meaningful
work, but it is also different.  

Disclaimer: this technique is not monopolized by any language, though
some languages specialize in certain forms of this technique.

Raul Rockwell