🚀 go-pugleaf

In article <7240@skye.ed.ac.uk> ken@aiai.ed.ac.uk (Ken Johnson) writes:

   Path: nmsu.edu!lynx!umn.edu!umeecs!caen!uunet!mcsun!uknet!edcastle!aiai!ken
   From: ken@aiai.ed.ac.uk (Ken Johnson)
   Newsgroups: comp.lang.prolog
   Keywords: singleton
   Date: 18 Aug 92 17:16:03 GMT
   References: <1992Aug17.172126.19111@watson.ibm.com> <5100@sersun1.essex.ac.uk>
   Followup-To: comp.lang.prolog
   Organization: Bugs-R-Us
   Lines: 30

   In article <5100@sersun1.essex.ac.uk> palmm@essex.ac.uk (Palmer M J)
   writes:

   #  Some systems (e.g.  Qunitus Prolog) allow you to use the form _VarName. 
   #  This is still an anonymous variable but with a name.  You might like to
   #  try this. 

   Forgive my pedantry, but (in Edinburgh Prolog) ocurrences of variables
   with the same name are equal to each other, even if the name begins with
   _.  So _A and _B, etc., are not anonymous variables.  The point is that
   the singleton variable check is not applied to such variable names. 


this isn't pedantry, it is error.  each occurence of _ *is* an
anonymous variable.  it is true that _A is *not* anonymous.

for example:

Quintus Prolog Release 3.1.1 (Sun-4, SunOS 4.1)
Copyright (C) 1990, Quintus Corporation.  All rights reserved.
2100 Geng Road, Palo Alto, California U.S.A. (415) 813-3800

| ?- [user].
| diff(_,_).
| diff2(_A,_A).
| 
% user compiled in module user, 0.033 sec 188 bytes

yes
| ?- diff(2,3).

yes
| ?- diff2(2,3).

no
| ?-