Prolog: Variables

Variables in prolog starts with capital letter (or) underscore symbol.

Example

X, Parent, Person1 are variables.

relations.pl

male(krishna).
male(rama).
male(hari).

female(chamu).
female(sowmya).
female(sailaja).
female(sridevi).

parents(krishna, devi, lakshman).
parents(rama, devi, lakshman).
parents(hari, sudha, jangayya).
parents(chamu, lakshmi, narayana).
parents(sowmya, harini, ramakrishna).
parents(sailaja, nhargavi, narayana).
parents(sridevi, lakshmi, narayana).

brothers(Person1, Person2) :- male(Person1), male(Person2), parents(Person1, Mother, Father), parents(Person2, Mother, Father).

sisters(Person1, Person2) :- female(Person1), female(Person2), parents(Person1, Mother, Father), parents(Person2, Mother, Father).

In the above example, Person1, Person2, Mother and Father are variables.

Anonymous variable

Some times, you may need to use a variable, but name may not be used. In that case, you can use anonymous variable. Anonymous variable is defined using _ symbol.

For example,

relations.pl

male(krishna).
male(rama).
male(hari).

female(chamu).
female(sowmya).
female(sailaja).
female(sridevi).

parents(krishna, devi, lakshman).
parents(rama, devi, lakshman).
parents(hari, sudha, jangayya).
parents(chamu, lakshmi, narayana).
parents(sowmya, harini, ramakrishna).
parents(sailaja, nhargavi, narayana).
parents(sridevi, lakshmi, narayana).

brothers(Person1, Person2) :- male(Person1), male(Person2), parents(Person1, Mother, Father), parents(Person2, Mother, Father).

sisters(Person1, Person2) :- female(Person1), female(Person2), parents(Person1, Mother, Father), parents(Person2, Mother, Father).

If you want to check, is Krishna has any brothers? You can use below statement.

brothers(_, krishna).

_ is replaced with an occurrence of a distinct variable .

Previous                                                 Next                                                 Home