Got a ten now. I think i'm getting the hang of thngs now :)

objsets/src/main/scala/objsets/TweetSet.scala

@@ -34,14 +34,16 @@ class Tweet(val user: String, val text: String, val retweets: Int) {
  */
 abstract class TweetSet {
 
+  def isEmpty: Boolean 
+
   /**
    * This method takes a predicate and returns a subset of all the elements
    * in the original set for which the predicate is true.
    *
    * Question: Can we implment this method here, or should it remain abstract
    * and be implemented in the subclasses?
    */
-    def filter(p: Tweet => Boolean): TweetSet = filterAcc(p, new Empty)
+    def filter(p: Tweet => Boolean): TweetSet = filterAcc(p,new Empty)
 
   /**
    * This is a helper method for `filter` that propagetes the accumulated tweets.
@@ -54,7 +56,7 @@ abstract class TweetSet {
    * Question: Should we implment this method here, or should it remain abstract
    * and be implemented in the subclasses?
    */
-    def union(that: TweetSet): TweetSet
+    def union(that: TweetSet): TweetSet 
 
   /**
    * Returns the tweet from this set which has the greatest retweet count.
@@ -65,7 +67,7 @@ abstract class TweetSet {
    * Question: Should we implment this method here, or should it remain abstract
    * and be implemented in the subclasses?
    */
-    def mostRetweeted: Tweet 
+    def mostRetweeted: Tweet
 
   /**
    * Returns a list containing all tweets of this set, sorted by retweet count
@@ -76,9 +78,7 @@ abstract class TweetSet {
    * Question: Should we implment this method here, or should it remain abstract
    * and be implemented in the subclasses?
    */
-    def descendingByRetweet: TweetList
-
-    def empty:Boolean
+    def descendingByRetweet: TweetList 
 
   /**
    * The following methods are already implemented
@@ -109,15 +109,12 @@ abstract class TweetSet {
 }
 
 class Empty extends TweetSet {
-
-  def descendingByRetweet: TweetList= Nil
-
-  def empty= true
-
-  def filterAcc(p: Tweet => Boolean, acc: TweetSet): TweetSet = acc //same as returning empty
-
+    def filterAcc(p: Tweet => Boolean, acc: TweetSet): TweetSet = acc
+    def isEmpty: Boolean = true
+
     def union(that: TweetSet): TweetSet = that
-    def mostRetweeted = throw new java.util.NoSuchElementException
+    def mostRetweeted: Tweet = throw new java.util.NoSuchElementException("No Tweets here")
+    def descendingByRetweet: TweetList = Nil
 
   /**
    * The following methods are already implemented
@@ -133,31 +130,33 @@ class Empty extends TweetSet {
 }
 
 class NonEmpty(elem: Tweet, left: TweetSet, right: TweetSet) extends TweetSet {
+
+  def filterAcc(p: Tweet => Boolean, acc: TweetSet): TweetSet = {
+    if(p(elem)) left.filterAcc(p,right.filterAcc(p,acc.incl(elem)))
+    else left.filterAcc(p,right.filterAcc(p,acc))
+  }
 
-    def descendingByRetweet: TweetList= new Cons(mostRetweeted, remove(mostRetweeted).descendingByRetweet)
-    def empty=false
-    def mostRetweeted = {
-      lazy val leftMost = left.mostRetweeted
-  		lazy val rightMost = right.mostRetweeted
+  def union(that: TweetSet): TweetSet = {
+    filterAcc(tw => true,that)
+  }
 
-  		if( !left.empty && leftMost.retweets > elem.retweets )
-  			if( !right.empty && rightMost.retweets > leftMost.retweets )
-  				rightMost
-  			else
-  				leftMost
-  		else if( !right.empty && rightMost.retweets > elem.retweets )
-  			rightMost
-  		else
-  			elem
+  def isEmpty: Boolean = false  
+  def mostRetweeted: Tweet = {
+    lazy val leftMost= left.mostRetweeted
+    lazy val rightMost= right.mostRetweeted
+    if(!left.isEmpty && leftMost.retweets > elem.retweets){
+      if(!right.isEmpty && rightMost.retweets > leftMost.retweets)
+        rightMost
+      else
+        leftMost  
     }
+    else if(!right.isEmpty && rightMost.retweets > elem.retweets)
+      rightMost
+    else
+      elem
+  }  
+  def descendingByRetweet: TweetList = new Cons(mostRetweeted,remove(mostRetweeted).descendingByRetweet) 
 
-    def filterAcc(p: Tweet => Boolean, acc: TweetSet): TweetSet = {
-       if(p(elem)) left.filterAcc(p, right.filterAcc(p, acc.incl(elem)))
-       else left.filterAcc(p, right.filterAcc(p, acc))
-    }
-
-    def union(that: TweetSet): TweetSet= ((left union right) union that) incl elem
-
   /**
    * The following methods are already implemented
    */
@@ -213,6 +212,7 @@ object GoogleVsApple {
 
   lazy val googleTweets: TweetSet = ???
   lazy val appleTweets: TweetSet = ???
+
   /**
    * A list of all tweets mentioning a keyword from either apple or google,
    * sorted by the number of retweets.