Introduction to Recursion. Write a program to enhance the program of relationships including recursive rules. [Relationships such as ancestors, descendants, predecessors etc.]

Introduction to recursion in prolog:

The recursion in any language is a function that can call itself until the goal has been succeed. In Prolog, recursion appears when a predicate contains a goal that refers to itself.

As we have seen in the earlier chapters when a rule is called Prolog create a new query with new variables. So, it makes no difference whether a rule calls another rule or calls itself.

In Prolog and in any language, a recursive definition always has at least two parts. A first fact that acts like a stopping condition and a rule that call itself simplified. At each level the first fact is checked. If the fact is true then the recursion ends. If not, then recursion continues.

A recursive rule must never call itself with the same arguments! If that happens then the program will never end.

A Prolog program including Recursion:

parent(john,tom). parent(john,bob). parent(john,sue). parent(mary,bob). parent(mary,sue). parent(tom,mercy). parent(bob,clue). parent(bob,ray). parent(sue,clue). parent(sue,ray).

parent(sou,vedik). parent(vedik,harsh). parent(harsh,ved). parent(ved,milan). parent(milan,vishal). parent(vishal,chakki).

male(john). male(tom). male(ray). male(bob). female(mary). female(mercy). female(sue). female(clue).

grandp(X,Y):-

parent(X,A),parent(A,Y).

brother(X,Y):-

parent(A,Y),parent(A,X),male(X).

sister(X,Y):-

parent(A,Y)parent(A,X),female(X).

uncle(X,Y):-

parent(A,X),brother(Y,A).

aunty(X,Y):-

parent(A,X),sister(Y,A).

cousins(X,Y):-

uncle(X,A),parent(A,Y), Y\=X.

ansc(X,Y):-

parent(X,Y).

ansc(X,Y):-

ansc(A,Y),parent(X,A).

Input:

parent(X,tom). parent(X,mercy). parent(X,harsh). parent(X,ved). male(mary). ansc(X,chakki).

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