🚀 go-pugleaf

>I don't agree at all that "Prolog supports polymorphism and data
>abstraction better than many languages." In this respect, it's no better
>than Fortran.

Maybe so, maybe not. The confusion surrounding diff-structures often comes 
from misunderstandings about the semantics of LP. In order to use such beasts
as diff-lists one should:

1) avoid using unification for anything but argument transfer of terms
   with a "user-defined" "type".
2) define a (possibly unlogical) predicate 'diff_equal(X,Y)' for the
representations used.
3) Keep in mind that Prolog unification knows of no equality theory but the 
simplest one, that of the Herbrand universe. 

or
4) Possibly use Harald Soendergaards tools, when available.

Prolog gives nice possibilities to define "datatypes", i.e. user
defined representations with their own equality theory, in a much
cleaner way than FORTRAN, where you would have to define a function
procedure like BOOLEAN EQUAL(X,Y) where X and Y should be coded names
for diff-structures (how this is done without pointers and structures
cannot be considered elegant by any standard...).


--
(Alf) Thomas Sjoeland
SICS, PO Box 1263, S-164 28 KISTA, SWEDEN
Tel: +46 8 752 15 42  Fax: +46 8 751 72 30  Tel home: +46 8 80 44 08
Internet: thomas@sics.se (or the older alf@sics.se)
......