Implement a correct isSubsequenceOf function

Closes #4

Author: dwayne

ch11/AsPatterns.hs

@@ -3,10 +3,11 @@ module AsPatterns where
 import Data.Char (toUpper)
 
 isSubsequenceOf :: Eq a => [a] -> [a] -> Bool
-isSubsequenceOf [] _ = True
-isSubsequenceOf _ [] = False
-isSubsequenceOf s@(x:xs) (y:ys) =
-  (x == y && isSubsequenceOf xs ys) || isSubsequenceOf s ys
+isSubsequenceOf s t = go s t
+  where
+    go [] _ = True
+    go _ [] = False
+    go (a:as) (b:bs) = (a == b && go as bs) || go s bs
 
 capitalizeWords :: String -> [(String, String)]
 capitalizeWords = go . words