bug fix in moreFun and solution to exercise 3

diff --git a/hw8/Party.hs b/hw8/Party.hs
index 2a5cf79425d156d7020190bb000715cf8eb78733..d303b01f3296c99d6ea4933b020437cb0c5c2e42 100644 (file)
--- a/hw8/Party.hs
+++ b/hw8/Party.hs
@@ -17,8 +17,8 @@ instance Monoid GuestList where
 
 -- moreFun
 moreFun :: GuestList -> GuestList -> GuestList
-moreFun g1@(GL _ f1) g2@(GL _ f2) | f1 > f2 = g1
-                                  | otherwise = g2
+moreFun g1 g2 | g1 > g2 = g1
+              | otherwise = g2
 
 -- treeFold :: (Tree a -> b -> b) -> b -> Tree a -> b
 -- treeFold combine e= treeDestructor e f
@@ -39,3 +39,15 @@ treeFold f e (Node v []) = f e v
 treeFold f e (Node v ts) = let b = foldr (\t acc -> treeFold f acc t) e ts
                            in
                              f b v
+-- exercise 3
+-- nextLevel
+-- if the big boss comes, no question, his reportee managers are not
+-- coming. So, we just take the send list from each pair and concat them.
+-- if the big boss is not coming, then we pick the list from the pair that
+-- has most fun and concat them all.
+nextLevel :: Employee -> [(GuestList, GuestList)] -> (GuestList, GuestList)
+nextLevel e lst =
+    let withBoss = glCons e $ mconcat $ map snd lst
+        withoutBoss = mconcat $ map (uncurry moreFun) lst
+    in
+      (withBoss, withoutBoss)