code: public static ExprBoolean toExprBoolean(Expression expr, Position start, Position end) {
  	if (expr instanceof Literal) {
  	    Boolean b = ((Literal) expr).getBoolean(null);
  	    if (b != null) {
  		return expr.getFactory().createLitBoolean(!b.booleanValue(), start, end);
  	    }
  	}
  	return new OpNegate(expr, start, end);
      }
docs: Create a String expression from a Expression
  
  @param left
  @param right
  
  @return String expression
  @throws TemplateException