[kepler-dev] Re: zero-length arrays

[Shawn Bowers]

On Wed, 11 Aug 2004, Tobin Fricke wrote:

> On Wed, 11 Aug 2004, Bertram Ludaescher wrote:
> 
> > (e.g., [] for arrays (aka lists!?) and {a: 17, b:18} or so for
> 
> [] is the "matrix" data type.  We don't really have a "list"  data type.
> It would be sort of nice if we could have an abstract 'ArrayToken' with
> underlying Array, List, etc, implementations, a la Java.  Right now
> there's no way to append to an ArrayToken w/o copying the whole thing.

Isn't this last point just an implementation detail? Ultimately, a list is
the "abstract" data structure, and array is just a common programming
language implementation for a list-like structure.  The more general
construct is really "collection" for which bags (mult-sets), sets, and
lists are specific types of collections.  

Also, it isn't clear to me that an empty record is a useful structure,
whereas I definately see how an empty array (or more specifically an empty
list) is useful. 

To illustrate, most database management systems let you create a table
without any tuples (i.e., an empty set), but few permit a table without
any attributes (an empty record).

(Actually, I know SQL 92 doesn't permit this, including Access, but e.g.,
postgresql "extends" the standard and permits tables without columns ...
but anyway, hopefully that doesn't take away too much from the point --
these are just details ;-)

shawn


> 
> There could be a convention that {:} is the empty record, or something
> like that.  (Or is it a record with a null-valued null-key ?!)
> 
> tobin
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