Ch6 Ex2

Author: wangwangwar

Ch6/src/Lib.hs

@@ -2,7 +2,8 @@ module Lib
     ( knapsack01,
     example,
     fib,
-    fibs1
+    fibs1,
+    fibs2
     ) where
 
 import Data.Array
@@ -35,3 +36,12 @@ fibInner n a b = fibInner (n - 1) b (a + b)
 -- The infinite list of all Fibonacci numbers
 fibs1 :: [Integer]
 fibs1 = map fib [1..] 
+
+-- Exercise 2
+
+-- More efficient implementation for fibs
+fibs2 :: [Integer]
+fibs2 = fibs2Inner 1 1
+
+fibs2Inner :: Integer -> Integer -> [Integer]
+fibs2Inner a b = a: (fibs2Inner b (a + b))

Ch6/test/Spec.hs

@@ -7,7 +7,8 @@ tests = TestList
     "fib 0" ~: fib 0 ~?= 0,
     "fib 1" ~: fib 1 ~?= 1,
     "fib 7" ~: fib 7 ~?= 13,
-    "take 5 fibs1" ~: take 5 fibs1 ~?= [1, 1, 2, 3, 5]
+    "take 5 fibs1" ~: take 5 fibs1 ~?= [1, 1, 2, 3, 5],
+    "take 5 fibs2" ~: take 5 fibs2 ~?= [1, 1, 2, 3, 5]
     ]
 
 main = do