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Jason is a fully-fledged interpreter for an extended version of AgentSpeak, a BDI agent-oriented logic programming language.

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package jason.functions;

import jason.JasonException;
import jason.asSemantics.DefaultArithFunction;
import jason.asSemantics.TransitionSystem;
import jason.asSemantics.Unifier;
import jason.asSyntax.LogicalFormula;
import jason.asSyntax.Term;

import java.util.Iterator;

/**
  Function: .count(B): counts the number of occurrences of a particular belief
  (pattern) in the agent's belief base, as the internal action .count.

  
Example:


   .count(a(2,_)): returns the number of beliefs
  that unify with a(2,_).

  

  @see jason.stdlib.count internal action version

  @author Jomi
*/
public class Count extends DefaultArithFunction  {

    public String getName() {
        return ".count";
    }

    @Override
    public double evaluate(TransitionSystem ts, Term[] args) throws Exception {
        if (ts == null) {
            throw new JasonException("The TransitionSystem parameter of the function '.count' cannot be null.");
        }
        LogicalFormula logExpr = (LogicalFormula)args[0];
        int n = 0;
        Iterator iu = logExpr.logicalConsequence(ts.getAg(), new Unifier());
        while (iu.hasNext()) {
            iu.next();
            n++;
        }
        return n;
    }

    @Override
    public boolean checkArity(int a) {
        return a == 1;
    }

    @Override
    public boolean allowUngroundTerms() {
        return true;
    }

}