add first part of sixth exercise of lecture 6HEADmaster

1 files changed, 16 insertions, 0 deletions

diff --git a/lec06/Fibonacci.hs b/lec06/Fibonacci.hs
index bc9e366..375e5ef 100644
--- a/lec06/Fibonacci.hs
+++ b/lec06/Fibonacci.hs
@@ -1,3 +1,6 @@
+{-# OPTIONS_GHC -fno-warn-missing-methods #-}
+-- ^ option for exercise 6
+
 -- Exercise 1
 
 fib :: Integer -> Integer
@@ -46,3 +49,16 @@ evenDiv2 n = toInteger $ length $ takeWhile even $ iterate (`quot` 2) n
 ruler :: Stream Integer
 ruler = streamMap evenDiv2 $ streamFromSeed (+1) 1
 
+-- Exercise 6 (Optional)
+
+x :: Stream Integer
+x = Cons 0 $ Cons 1 $ streamRepeat 0
+
+instance Num (Stream Integer) where
+         fromInteger n = Cons n $ streamRepeat 0
+         negate s      = streamMap negate s
+         (+) s1 s2     = streamMap (\p -> fst p + snd p) $ zip s1 s2
+                       where zip (Cons a0 sa) (Cons b0 sb) = Cons (a0,b0) (zip sa sb)
+         (*) (Cons a0 sa) b@(Cons b0 sb) = Cons (a0*b0) $ (streamMap (*a0) sb + (sa*b))
+
+