| University of Toronto - Fall 2002 | Department of Computer Science |
November 24: People still seem to be having difficulty
setting up things for question 1. Here is a fully working example: samplefamily.P, sample.P, sample.in, sample.out.
November 23: Despite this being contrary to the
specifications, it's ok if your solution for delete only
returns one answer for the query ?- delete(X,[a,a,b,b],L).
November 22: I remember this issue frustrating me last
time I worked with XSB, and it's frustrating me again. So :-
[basics]. loads basics.P, but only makes it available
to the interactive prompt, and not to the predicates in the file where
it's located. You actually have to use import for all this
to work:
:- import append/3 from basics.
will make append available to predicates within the file where it's
located (but not to the interactive prompt--go figure). If you need to
import more than one predicate (you won't need to in this assignment, but
you might in the project), you can provide a comma-separated list of them.
The /3 indicates the arity of the predicate you're importing,
3 in the case of append since it takes 3 arguments.
November 20: For question 5 (a) (even), you
may not use length or mod.
November 19: Well, I should have tested the
instructions below before posting them... A student pointed out that,
despite having [ps4family]. at the beginning of
ps4q1.P, the relations defined there are not available. The
error I made is: when you pipe a test suite into Prolog, it treats
everything as a query. So in a .in file,
[ps4family]. is interpreted as the query ?-
[ps4family]. and the file is loaded as a side-effect of executing
the query. However, in a fact base file, everything is treated as facts
and rules. Now, what's a query? It's actually a Horn Clause without a
head. So to load another file from within a .P file, you
must write :- [ps4family]., a Horn Clause without a head, and
then it will get executed. So that's the line you need at the beginning
of your ps4q1.P file.
November 16: Small typo in ps4family.P:
it should have read married, not maried. It is
now fixed. Please continue using the correct spelling provided in the
handout.
November 13: For question 1, you should assume that
male, female, and parent are
defined as we defined them in class, providing family information. Of
course, assume married is defined. You should also assume
that sibling is defined as follows:
sibling(X,Y) :- parent(P,X), parent(P,Y), \+(X=Y).
Please download the file ps4family.P, which contains the
definition for sibling, and load it at the beginning of your
ps4q1.P file, by placing the command
[ps4family]. at the beginning. You may modify
ps4family.P as much as you want to add more family data and
test your code, but do not add new predicates and do not change the
definition of sibling. Any helper predicates you need should
of course be placed in ps4q1.P with the rest of your code.
If you need any further predicates we saw in class or tutorial, you will
have to include them in your ps4q1.P file.
Also, for question 1 only, don't worry if your solutions
produce duplicate answers. (You can't avoid it without using the cut,
which we haven't discussed yet, and which you are not allowed to use for
this assignment.)