Greater than operator in prolog

Question

I am working on SWI Prolog. I have some facts in my database. I am unable to figure out how to use 'greater than' operator(>) when constructing a new rule.

I have some facts of the form

student(john,3.2,cs).
student(mike,3.9,cs).

showing that john is a student, has a 3.2 cgpa, and belongs to CS department, similarly for mike.

Now i want to add a rule to my database

deanlist(X) which will return true if X's cgpa is greater than 3.8

According to my knowledge, i can add this rule as follows

deanlist(X):-
   X's cgpa is greater than 3.8

if i go with brute force approach, i can enlist all possibilites of cgpa greater than 3.8 using OR operator. Like i can add rule like

deanlist(X):-
   student(X,3.81,cs)
 ; student(X,3.82,cs)
 ; student(X,3.82,cs)
 .......so on to
   student(X,4.0,cs).

But i don't want to go that way because it becomes hard coded and should be avoided.

I have explore the following links

http://boklm.eu/prolog/page_10.html#101

http://www.swi-prolog.org/pldoc/man?section=operators

But i could not figure out how to use greater than operator in my case.

Please tell me how to use greater than operator in this case. Thanks

alykhank alykhank · Accepted Answer · 2016-04-30T06:43:19

You will need to use another statement for the GPA comparison after matching it to a new variable:

deanlist(X) :- student(X, Y, cs), Y > 3.8.

Then, deanlist(X). will return:

X = mike

Greater than operator in prolog

1 Answers