//File: Negation.java
//Name: Trai Pham
//Date: 02/16/2020
//Course: CSE 8B
/**
Not sure what Negation does
*/
public class Negation extends BooleanExpression{
  public Negation(BooleanExpression someVar){
    this.a = someVar;
  }
  public Value evaluate(){
    if(!(this.a instanceof BooleanExpression)){
      return null;
    }
    if(this.a == null){
      return null;
    }
    // BooleanValue var = this.a.boolEvaluate();
//use both evaluate, boolEvaluate, typecasting, and instanceof
//convert Value to BooleanValue
    Value test = this.a.evaluate();
    BooleanValue try01 = (BooleanValue) test;
//apply negation to variable of value
    Value negate = new BooleanValue(!(try01.boolEvaluate()));
    return negate;
  }
}