CODEWITHSUNDEEP
prolog
user949814
user949814

Reputation:

GNUProlog only returns one of the values for a query

% facts
mother(john, dana).
father(john, david).
mother(chelsea, dana).
father(chelsea, david).
mother(jared, dana).
father(jared, david).
% queries
parent(X,Y) :- father(X,Y);mother(X,Y).

When I type in "parent(john, X).", I get X = dana, but not X== david. However, on my previous question, the person who responded to me seems to get both parents. Is this a limitation of gprolog or am I still doing something wrong?

Upvotes: 1

Views: 2678

Answers (2)

user502187
user502187

Reputation:

In the interactive top-level query answering loop you get a next solution by typing the semicolon ";".

Your example works fine in GNU Prolog:

GNU Prolog 1.4.0
By Daniel Diaz
Copyright (C) 1999-2011 Daniel Diaz
| ?- [user].
compiling user for byte code...
mother(john, dana).
father(john, david).
parent(X,Y) :- father(X,Y);mother(X,Y).

user compiled, 4 lines read - 725 bytes written, 33109 ms

(2 ms) yes
| ?- parent(john,X).

X = david ? ;

X = dana

yes

Bye

Upvotes: 2

gusbro
gusbro

Reputation: 22585

To get all the results you have to press the semicolon key ;, once for each solution.

If you want to get all the results as a list, you can try

?- findall(X, parent(john, X), L).

L = [david,dana]

Upvotes: 4

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