use compare instead of guards

Author: MatthijsBlom

source_md/making-our-own-types-and-typeclasses.md

@@ -1139,10 +1139,11 @@ singleton x = Node x EmptyTree EmptyTree
 
 treeInsert :: (Ord a) => a -> Tree a -> Tree a
 treeInsert x EmptyTree = singleton x
-treeInsert x (Node a left right)
-    | x == a = Node x left right
-    | x < a  = Node a (treeInsert x left) right
-    | x > a  = Node a left (treeInsert x right)
+treeInsert x (Node a left right) =
+  case x `compare` a of
+    LT -> Node a (treeInsert x left) right
+    EQ -> Node x left right
+    GT -> Node a left (treeInsert x right)
 ```
 
 The `singleton` function is just a shortcut for making a node that has something and then two empty subtrees.
@@ -1168,11 +1169,12 @@ If it's bigger, check to see if it's in the right subtree.
 
 ```{.haskell:hs}
 treeElem :: (Ord a) => a -> Tree a -> Bool
-treeElem x EmptyTree = False
-treeElem x (Node a left right)
-    | x == a = True
-    | x < a  = treeElem x left
-    | x > a  = treeElem x right
+treeElem _ EmptyTree = False
+treeElem x (Node a left right) =
+  case x `compare` a of
+    LT -> treeElem x left
+    EQ -> True
+    GT -> treeElem x right
 ```
 
 All we had to do was write up the previous paragraph in code.