Apologies in advance for:
Asking what might not be a relevant question in this list.
Asking a flatly novice question.
Relative to the online instructional material in `Learn Prolog Now!`,
exercise 2.2
It appears to be the case that GProlog returns different results than does
SWI-Prolog on question 5 in exercise 2.2.
Text of the exercise is at the bottom of this message.
SWI-Prolog 7.2.2 returns:
?- magic(Hermoine).
Hermoine = dobby ;
Hermoine = hermoine ;
Hermoine = 'McGonagall' ;
Hermoine = rita_skeeter .
GProlog 1.4.4 returns
?- magic(Hermoine).
Hermoine = dobby ? ;
uncaught exception: error(existence_error(procedure,wizard/1),magic/1)
I understand SWI-Prolog's results, but can't understand why GProlog stops
when it hits the rule "magic(X):- wizard(X)."
Any pointers or cautions away from posting such questions in this list are
terrifically appreciated!
Text of the exercise follows:
Exercise 2.2
We are working with the following knowledge base:
%%%%%%%%%%%%%%%%%%%%%%%%%
house_elf(dobby).
witch(hermoine).
witch('McGonagall').
witch(rita_skeeter).
magic(X):- house_elf(X).
magic(X):- wizard(X).
magic(X):- witch(X).
Which of the following queries are satisfied?...
1. magic(house_elf).
2. wizard(harry).
3. magic(wizard).
4. magic('McGonagall').
5. magic(Hermoine).
%%%%%%%%%%%%%%%%%%%%%%%%%
Best wishes,
_don
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