3_b_4: Add solution

2 files changed, 16 insertions, 1 deletions

diff --git a/README.md b/README.md
index 0157c7f..4ffc8f3 100644
--- a/README.md
+++ b/README.md
@@ -56,7 +56,7 @@ more visible in the list the first exercise of a group is in bold italics.
 | **_3_b_1_**    | yes    | 69   | |
 | 3_b_2          | yes, in 3_b_1 |      | |
 | 3_b_3          | yes    |      | |
-| 3_b_4          |        |      | |
+| 3_b_4          | yes    |      | |
 | 3_b_5          |        |      | |
 | 3_b_6          |        | 70   | |
 | 3_b_7          |        |      | |
diff --git a/ch03/3_b_4.hs b/ch03/3_b_4.hs
new file mode 100644
index 0000000..a711085
--- /dev/null
+++ b/ch03/3_b_4.hs
@@ -0,0 +1,15 @@
+-- Turn a list into a palindrome, i.e. it should read the same both backwards
+-- and forwards. For example, given the list [1,2,3], your function should
+-- return [1,2,3,3,2,1].
+
+makePalindrome :: [a] -> [a]
+makePalindrome [] = []
+makePalindrome (x:xs) = [x] ++ (makePalindrome xs) ++ [x]
+
+-- ghci> :l 3_b_4.hs
+-- [1 of 1] Compiling Main             ( 3_b_4.hs, interpreted )
+-- Ok, one module loaded.
+-- ghci> makePalindrome []
+-- []
+-- ghci> makePalindrome [1, 2, 3]
+-- [1,2,3,3,2,1]