add first exercise of lecture 8

1 files changed, 20 insertions, 0 deletions

diff --git a/lec08/Party.hs b/lec08/Party.hs
new file mode 100644
index 0000000..4ac241b
--- /dev/null
+++ b/lec08/Party.hs
@@ -0,0 +1,20 @@
+module Party where
+
+import Employee
+
+-- Exercise 1
+
+glCons :: Employee -> GuestList -> GuestList
+glCons e { empFun = ef } (GL es cf) = GL (e:es) (cf + ef)
+
+-- mappend (a.k.a. (<>)) has been moved to Semigroup
+instance Semigroup GuestList where
+  (<>) (GL es1 f1) (GL es2 f2) = GL (es1 ++ es2) (f1 + f2)
+
+instance Monoid GuestList where
+  mempty = GL [] 0
+
+moreFun :: GuestList -> GuestList -> GuestList
+moreFun gl1@(GL _ f1) gl2@(GL _ f2)
+  | f1 >= f2  = gl1
+  | otherwise = gl2