add fifth exercise of lecture 6

1 files changed, 12 insertions, 0 deletions

diff --git a/lec06/Fibonacci.hs b/lec06/Fibonacci.hs
index 9993169..bc9e366 100644
--- a/lec06/Fibonacci.hs
+++ b/lec06/Fibonacci.hs
@@ -34,3 +34,15 @@ streamMap f (Cons a as) = Cons (f a) (streamMap f as)
 streamFromSeed :: (a -> a) -> a -> Stream a
 streamFromSeed f s = Cons s (streamFromSeed f (f s))
 
+-- Exercise 5
+
+nats :: Stream Integer
+nats = streamFromSeed (+1) 0
+
+-- The number of times an integer can be evenly divided by 2.
+evenDiv2 :: Integer -> Integer
+evenDiv2 n = toInteger $ length $ takeWhile even $ iterate (`quot` 2) n
+
+ruler :: Stream Integer
+ruler = streamMap evenDiv2 $ streamFromSeed (+1) 1
+