1 files changed, 37 insertions, 0 deletions
diff --git a/ex69.hs b/ex69.hs
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index 0000000..04596be
--- /dev/null
+++ b/ex69.hs
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+
+-- compute length of list
+
+
+listlen :: [a] -> Int
+listlen2 :: [a] -> Int -> Int
+
+listlen ( x:xs )    = listlen2 xs 1
+listlen2 ( x:xs ) n = listlen2 xs (n + 1)
+listlen2 [] n       = n
+
+myReverse (x:xs)  = myReverse xs ++ [x]
+myReverse []      = []
+
+makePalin x       = x ++ myReverse x
+
+isPalin a         = a == myReverse a
+
+
+
+-- in python: ",".join(["abc", "def"])
+join :: String -> [String] -> String
+
+join sep (x:xs)  | xs /= [] = x ++ sep ++ join sep xs
+join sep [x]       = x
+
+
+-- a tree
+
+data Tree a = Node a (Tree a) (Tree a)
+            | Empty
+              deriving Show
+
+--height :: Tree -> Int
+
+height (Node _ left right)   =  max ((height left) + 1) ((height right) + 1)
+height Empty = 0