Hi I am working on a PROLOG family tree question, and this is what I have so far:
/*1. Write Prolog clauses to express the following three relationships,
* given the parent/2 relationship: grandparent/2, sibling/2, cousin/2.*/
% clauses
parent(jill, amy).
parent(jill, tim).
parent(jill, john).
parent(amy, grace).
parent(amy, anna).
parent(tim, sam).
parent(tim, joel).
parent(tim, ben).
% rules
grandparent(X,Y) :-
parent(Z,Y),
parent(X,Z).
sibling(X, Y) :-
parent(Z, X),
parent(Z, Y).
cousin(X,Y) :-
parent(P, X),
parent(S, Y),
sibling(P, S).
When I put:
?- sibling(X, tim).
the output gives:
X = amy
but both john and amy are tim's sibling. The same problem happens with:
?- cousin(ben, X).
which gives:
X = grace
when both grace and anna are ben's cousins.
What changes do I need to make in order for the code to output all of tim's siblings and ben's cousins?
Thanks. :)
First of all, you've got a little bug over there.
You should correct the sibling rule - just a small hint here, try to use the rule as so
sibling(grace,grace)
and back to your issue, after you're getting first response click the ; or any of these ; n r space TAB keys, as the result you see is the first correct response. If you want to see the next correct result you need to use one of the keys above.
You can also try to use findall predicate to see all the results in the list
?- findall(X, cousin(grace, X),Z).
Z = [sam, joel, ben].
Related
I have this prolog file:
daughter(anna, vera).
daughter(vera, oleg).
daughter(olga, pavel).
daughter(olga, alla).
daughter(alla, lidia).
man(oleg).
man(victor).
man(pavel).
not(P) :- (call(P) -> fail ; true).
woman(X) :- not(man(X)).
?- woman(X). always returns false. ?- man(X). returns all three male entries though.
I also tried woman(X) :- \+man(X). but certain syntax is not the problem it seems.
If I try to check a certain person it works: ?- woman(anna). returns true.
I'm quite new to prolog and can't even suggest what is wrong here.
UPD. I want all people who are not men to be classified as men. The question is - why can't I do woman(X) and get all non-men?
?- woman(anna).
true.
?- woman(X).
false.
?- man(X).
X = oleg ;
X = victor ;
X = pavel.
UPD2. Solution
The problem was caused by floundering as was pointed out in the comments. I needed woman(X) rule to implement this rule: mothers_names(X, Y) :- not(man(X)), daughter(Y,X).
In a nutshell, inverting the query works: mothers_names(X, Y) :- daughter(Y,X), not(man(X)). because first predicate makes X in not(man(X)) limited to several values.
How to create such logic in GNU Prolog? How to define not_a_parent() predicate?
parent(john,chris).
parent(mary,chris).
not_a_parent(X) :- \+ parent(X,Y).
The interesting answer to the similar question is What is the logical 'not' in Prolog?. But I do not see how to implement it here.
This worked for me:
parent(john,chris).
parent(mary,chris).
parent(mary,suzanne).
parent(suzanne,jane).
parent(suzanne,peter).
parent(peter,rose).
parent(jerry,rose).
parent(jane,carl).
not_a_parent(NonParents) :- setof(Z,Y^parent(Y,Z),SetOfChildren),
findNonParents(SetOfChildren, NonParents, []),!.
findNonParents([],A,A).
findNonParents([H|SetOfChildren], NonParents, A):-
not(call(parent(H,_))),
findNonParents(SetOfChildren,NonParents,[H|A]).
findNonParents([_|SetOfChildren], NonParents, A):-
findNonParents(SetOfChildren,NonParents,A).
Result for querying not_a_parent(NonParents) is:
?- not_a_parent(NonParents).
NonParents = [rose, chris, carl].
You need to enumerate all the persons somehow. For example
not_a_parent(X) :- ( X = john ; X = mary ; X = chris ), \+ parent(X,_).
In any real program you would probably have some simple way to get all persons, and then you can do
not_a_parent(X) :- person(X), \+ parent(X,_).
You need to get all the instances of parent/2 such that X never unifies parent(X,_). findall(Template, Goal, Instances) executes the Goal until it fails and populate the list Instances with the terms that unify the Template. That way, if the list Instances is empty then parent(X,_) does not exist.
So your predicate would be like:
not_a_parent(X):- findall(_, parent(X,_) , []).
I'm new to Prolog. Is it possible to "declare" a list as a fact in Prolog, and then access it easily? I'm working on a family-tree type problem. To start, I would like to declare a bunch of males as belonging to a list of males. I then would like to be able to query if a particular person is a male. Here is the code I've written so far:
% ------------------------------------------------------------------------- %
% Facts:
males([john, joseph, aaron, peter, paul, mark, ben, adam, daniel]).
% ------------------------------------------------------------------------- %
% Rules:
% Member of a List
member(X, [X|_]).
member(X, [_|T]) :- member(X, T).
male(X) :- member(X, males).
However, my output is not as expected:
21 ?- male(john).
false.
I know my member() rules are working, since I can produce the following result:
23 ?- member(john, [peter, paul, john]).
true
Can anyone point me in the right direction? Thank you in advance.
The usual proper way to do this in Prolog would be to declare your list as a table of facts:
male(john).
male(joseph).
% etc
If you do it like this, you have already defined your male/1 and can query it either like this:
?- male(joseph).
true.
Or like this:
?- male(M).
M = john ;
M = joseph ;
% etc
You can start with Prolog by reading through the first chapter of "Learn Prolog Now!". Its first example is exactly the same as your problem.
I'm not an expert in prolog but I know a solution to this (could be not the only one)
male(X) :- males(Y), member(X, Y)
The way I understand it is that predicates doesn't return variables, they assign values to the parameters given, so Y now have been assigned the array of males and now you can look for X in Y
Let's say there is a simple database of people in Prolog
person(john).
person(mary).
person(john).
person(susan).
I need to match the entires exactly once:
john-mary, john-john, john-susan, mary-john, mary-susan, john-susan
I tried coming up with something like this:
match:- person(X),!,person(Y), write(X),write(-), write(Y),nl.
run:- person(X), match(X), fail.
But it's matching many times, and matches a person to him/herself, which shouldn't be.
Basically, what I need is to iterate over all Xs and make Prolog to look strictly "below" for Ys.
A quick solution would be to number your people:
person(1, john).
person(2, mary).
person(3, john).
person(4, susan).
Then you could match people like this:
match(X-Y) :-
person(I, X), person(J, Y), I < J.
Since you have two john entries, I'm not sure any other solution is going to work. Normally you could fake an ordering using #>/2 but that would require your atoms to be unique, and since they aren't, it would prevent the john-john solution.
Edit: Since we're willing to use findall/3 to materialize the database of people, we can treat this as a list problem and find a functional solution. Let's get all the combinations in a list:
combinations([X|Rest], X, Y) :- member(Y, Rest).
combinations([_|Rest], X, Y) :- combinations(Rest, X, Y).
With this predicate in hand, we can find the solution:
combined_folks(People) :-
findall(P, person(P), Persons),
findall(X-Y, combinations(Persons, X, Y), People).
?- combined_folks(X).
X = [john-mary, john-john, john-susan, mary-john, mary-susan, john-susan].
That actually turned out to be pretty clean!
person(john).
person(mary).
person(john).
person(susan).
match :- findall(P,person(P),People), match_all(People).
match_all([_]) :- !.
match_all([P|People]) :- match_2(P,People), match_all(People).
match_2(_,[]) :- !.
match_2(P1,[P2|People]) :- format('~a-~a~n',[P1,P2]), match_2(P1,People).
?- match.
% facts
mother(john, dana).
father(john, david).
mother(chelsea, dana).
father(chelsea, david).
mother(jared, dana).
father(jared, david).
% queries
father(X,Y) :- father(X,Y), write(Y).
mother(X,Y) :- mother(X,Y), write(Y).
parent(X,Y) :- father(X,Y);mother(X,Y).
sibling(X,Y) :- parent(X,Z), parent(Y,Z), write(Y).
I am having trouble getting these queries to work. when I type in the father command, it will tell me yes or no correctly, but won't do the write command (same with mother). "parent" doesn't work at all for me (therefor sibling doesn't either). Also, if I type in sibling(X,Y). I need to get all siblings...for example, sibling(john, chelsea). I need to output all the possible siblings (jared as well). Let me know where I am going wrong, I really don't see an issue with my logic here. Thanks!
Basically you can remove your mother and father predicates that are not facts. They are infinite loops. Since parent use them and sibling use parent, all your predicates are infinite loops.
To see what happens, you can do that :
?- trace, father(john, X).
and observe how prolog handles the query. You'll soon observe than to resolve father, he needs to solve father, and that to solve father, he needs to solve father, and that it never stops...
When the two problematic are removed, I obtain a correct behaviour :
?- father(john, X).
X = david.
?- parent(john, X).
X = david ;
X = dana.
?- sibling(john, X).
john
X = john ;
chelsea
X = chelsea ;
jared
X = jared ;
john
X = john ;
chelsea
X = chelsea ;
jared
X = jared.
Now, to make your sibling predicate better, you could say that someone is not its own sibling and that if you have one common parent it's enough (it will remove the duplicates) :
sibling(X,Y) :- father(Y,Z), father(X, Z), X =\= Y.