Homework: Statement and Recursion II

1. Using recursion, complete the body of the following static method.

   /**
    * Refactors the given {@code Statement} so that every IF_ELSE statement
    * with a negated condition (NEXT_IS_NOT_EMPTY, NEXT_IS_NOT_ENEMY,
    * NEXT_IS_NOT_FRIEND, NEXT_IS_NOT_WALL) is replaced by an equivalent
    * IF_ELSE with the opposite condition and the "then" and "else" BLOCKs
    * switched. Every other statement is left unmodified.
    * 
    * @param s
    *            the {@code Statement}
    * @updates s
    * @ensures <pre>
    * s = [#s refactored so that IF_ELSE statements with "not"
    *   conditions are simplified so the "not" is removed]
    * </pre>
    */
   public static void simplifyIfElse(Statement s) {
       switch (s.kind()) {
           case BLOCK: {
   
               // TODO - fill in case
   
               break;
           }
           case IF: {
   
               // TODO - fill in case
   
               break;
           }
           case IF_ELSE: {
   
               // TODO - fill in case
   
               break;
           }
           case WHILE: {
   
               // TODO - fill in case
   
               break;
           }
           case CALL: {
               // nothing to do here...can you explain why?
               break;
           }
           default: {
               // this will never happen...can you explain why?
               break;
           }
       }
   }