Hi. I'm brand new to Prolog and am having trouble understanding some
of the results I get from the gprolog interpreter. For instance, the
following simple program is meant to yield 'true' for both c(foo) and
c(bar):
a(foo).
a(bar).
b(foo).
c(X) :- a(X) ; b(X).
But in fact I get this:
| ?- c(foo).
true ? ;
yes
| ?- c(bar).
true ? ;
no
Could someone humor me and tell me why I am prompted for another
result after 'true' (and why the 'yes' after the first result and the
'no' after the second). I get the same behavior if I use:
c(X) :- a(X).
c(X) :- b(X).
Also, I've had to define my own negation operator because if I try to
compile something like:
d(X) :- not a(X).
...I get an error:
/[...]/test.pl:29 error: syntax error: . or operator expected after
expression (char:13)
1 error(s)
compilation failed
I've read most of TFM as well as a Prolog tutorial, but I don't see
why this shouldn't work. Btw. this is gprolog 1.2.16 on i386 Linux.
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