From: Ramakrishnan Muthukrishnan <ram@rkrishnan.org>
Date: Wed, 24 Dec 2014 16:43:41 +0000 (+0530)
Subject: hw7: exercise 2, part 1
X-Git-Url: https://git.rkrishnan.org/?p=yorgey.git;a=commitdiff_plain;h=45444928a772dd1542f16a2813423c1b9562724e

hw7: exercise 2, part 1
---

diff --git a/hw7/JoinList.hs b/hw7/JoinList.hs
index 4edc744..6ef51a8 100644
--- a/hw7/JoinList.hs
+++ b/hw7/JoinList.hs
@@ -2,7 +2,7 @@
 module JoinList where
 
 import Data.Monoid
-
+import Sized
 
 data JoinList m a = Empty
                   | Single m a
@@ -20,3 +20,13 @@ Empty +++ x = x
 x +++ Empty = x
 alst1 +++ alst2 = Append ((tag alst1) `mappend` (tag alst2)) alst1 alst2
 
+-- exercise 2
+-- 1. index
+indexJ :: (Sized b, Monoid b) =>
+          Int -> JoinList b a -> Maybe a
+indexJ _ Empty = Nothing
+indexJ n _ | n < 0 = Nothing
+indexJ _ (Single _ a) = Just a
+indexJ n (Append _ l r) | n < (getSize (size (tag l))) = indexJ n l
+                        | otherwise = indexJ (n - getSize (size (tag l))) r
+