3_b_8: Add solution

2 files changed, 26 insertions, 1 deletions

diff --git a/README.md b/README.md
index 181cba9..e2dd4be 100644
--- a/README.md
+++ b/README.md
@@ -60,7 +60,7 @@ more visible in the list the first exercise of a group is in bold italics.
 | 3_b_5          | yes    |      | |
 | 3_b_6          | yes    | 70   | |
 | 3_b_7          | yes    |      | |
-| 3_b_8          |        |      | |
+| 3_b_8          | yes    |      | |
 | 3_b_9          |        |      | |
 | 3_b_10         |        |      | |
 | 3_b_11         |        |      | |
diff --git a/ch03/3_b_8.hs b/ch03/3_b_8.hs
new file mode 100644
index 0000000..a2f1939
--- /dev/null
+++ b/ch03/3_b_8.hs
@@ -0,0 +1,25 @@
+-- Using the binary tree type that we defined earlier in this chapter, write a
+-- function that will determine the height of the tree. The height is the
+-- largest number of hops from the root to an Empty. For example, the tree Empty
+-- has height zero; Node "x" Empty Empty has height one; Node "x" Empty (Node
+-- "y" Empty Empty) has height two; and so on.
+
+{-- From examples/examples/ch03/Tree.hs --}
+data Tree a = Node a (Tree a) (Tree a)
+            | Empty
+              deriving (Show)
+{-- End of code from examples --}
+
+treeHeight :: Tree a -> Int
+treeHeight Empty = 0
+treeHeight (Node _ l r) = 1 + max (treeHeight l) (treeHeight r)
+
+-- ghci> :l 3_b_8.hs
+-- [1 of 1] Compiling Main             ( 3_b_8.hs, interpreted )
+-- Ok, one module loaded.
+-- ghci> treeHeight Empty
+-- 0
+-- ghci> treeHeight (Node "x" Empty Empty)
+-- 1
+-- ghci> treeHeight (Node "x" Empty (Node "y" Empty Empty))
+-- 2