3_a_2: Add solution

2 files changed, 27 insertions, 2 deletions

diff --git a/README.md b/README.md
index ae090f7..22b09be 100644
--- a/README.md
+++ b/README.md
@@ -1,5 +1,5 @@
 # Real World Haskell solutions
-
+0;115;0c
 These are solutions to exercises from me reading the first edition of the [the
 Real World Haskell book](https://book.realworldhaskell.org/). I hope they will
 be helpful in your journey to the world of Haskell.
@@ -52,7 +52,7 @@ more visible in the list the first exercise of a group is in bold italics.
 | 2_b_2          | yes    |      | |
 | 2_b_3          | yes    |      | |
 | **_3_a_1_**    | yes    | 60   | 3. Defining types, streamlining functions |
-| 3_a_2          |        |      | |
+| 3_a_2          | yes    |      | |
 | **_3_b_1_**    |        | 69   | |
 | 3_b_2          |        |      | |
 | 3_b_3          |        |      | |
diff --git a/ch03/3_a_2.hs b/ch03/3_a_2.hs
new file mode 100644
index 0000000..42282e7
--- /dev/null
+++ b/ch03/3_a_2.hs
@@ -0,0 +1,25 @@
+-- Define a tree type that has only one constructor, like our Java
+-- example. Instead of the Empty constructor, use the Maybe type to refer to a
+-- node's children.
+
+-- The assignment doesn't explicitly specify whether it should be possible to
+-- create an empty tree at the root level, so this tree type doesn't support
+-- that.
+
+data Tree a = Node a (Maybe (Tree a)) (Maybe (Tree a))
+              deriving (Show)
+
+
+--          parent
+--            /\
+--           /  \
+-- left child   right child
+--                  /
+--                 /
+--            left child
+
+simpleTree = Node "parent" (Just (Node "left child" Nothing
+                                                    Nothing))
+                           (Just (Node "right child" (Just (Node "left child" Nothing
+                                                                              Nothing))
+                                                     Nothing))