I have a question about exercise 2.2 in LPN!.
In particular, it appears to be the case
that GProlog returns different results than does SWI-Prolog on question
5 in exercise 2.2.
I acknowledge this to be a very low-importance issue.
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 don't understand why GProlog
stops when it hits the rule "magic(X):- wizard(X)." Any pointers 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(housde_elf).
2. wizard(harry).
3. magic(wizard).
4. magic('McGonagall').
5. magic(Hermoine).