3_b_6: Add solution

2 files changed, 26 insertions, 1 deletions

diff --git a/README.md b/README.md
index 9218b56..0d39a74 100644
--- a/README.md
+++ b/README.md
@@ -58,7 +58,7 @@ more visible in the list the first exercise of a group is in bold italics.
 | 3_b_3          | yes    |      | |
 | 3_b_4          | yes    |      | |
 | 3_b_5          | yes    |      | |
-| 3_b_6          |        | 70   | |
+| 3_b_6          | yes    | 70   | |
 | 3_b_7          |        |      | |
 | 3_b_8          |        |      | |
 | 3_b_9          |        |      | |
diff --git a/ch03/3_b_6.hs b/ch03/3_b_6.hs
new file mode 100644
index 0000000..74d46ac
--- /dev/null
+++ b/ch03/3_b_6.hs
@@ -0,0 +1,25 @@
+-- Create a function that sorts a list of lists based on the length of each
+-- sublist. (You may want to look at the sortBy function from the Data.List
+-- module.)
+
+import Data.List
+
+myCompare :: [a] -> [a] -> Ordering
+myCompare a b = if len_a < len_b
+                then LT
+                else if len_a == len_b
+                     then EQ
+                     else GT
+  where len_a = length a
+        len_b = length b
+
+mySort :: [[a]] -> [[a]]
+mySort xs = Data.List.sortBy myCompare xs
+
+-- ghci> :l 3_b_6.hs
+-- [1 of 1] Compiling Main             ( 3_b_6.hs, interpreted )
+-- Ok, one module loaded.
+-- ghci> mySort []
+-- []
+-- ghci> mySort [[2, 3], [7, 8, 9, 10], [1], [], [4, 5, 6]]
+-- [[],[1],[2,3],[4,5,6],[7,8,9,10]]