3_b_7: Add solution

2 files changed, 33 insertions, 1 deletions

diff --git a/README.md b/README.md
index 0d39a74..181cba9 100644
--- a/README.md
+++ b/README.md
@@ -59,7 +59,7 @@ more visible in the list the first exercise of a group is in bold italics.
 | 3_b_4          | yes    |      | |
 | 3_b_5          | yes    |      | |
 | 3_b_6          | yes    | 70   | |
-| 3_b_7          |        |      | |
+| 3_b_7          | yes    |      | |
 | 3_b_8          |        |      | |
 | 3_b_9          |        |      | |
 | 3_b_10         |        |      | |
diff --git a/ch03/3_b_7.hs b/ch03/3_b_7.hs
new file mode 100644
index 0000000..51f7849
--- /dev/null
+++ b/ch03/3_b_7.hs
@@ -0,0 +1,32 @@
+-- Define a function that joins a list of lists together using a separator value.
+--
+--     -- file: ch03/Intersperse.hs
+--     intersperse :: a -> [[a]] -> [a]
+--
+-- The separator should appear between elements of the list, but should not
+-- follow the last element. Your function should behave as follows.
+--
+--     ghci> :load Intersperse
+--     [1 of 1] Compiling Main             ( Intersperse.hs, interpreted )
+--     Ok, modules loaded: Main.
+--     ghci> intersperse ',' []
+--     ""
+--     ghci> intersperse ',' ["foo"]
+--     "foo"
+--     ghci> intersperse ',' ["foo","bar","baz","quux"]
+--     "foo,bar,baz,quux"
+
+myIntersperse :: a -> [[a]] -> [a]
+myIntersperse _ [] = []
+myIntersperse _ (x:[]) = x
+myIntersperse s (x:xs) = x ++ s:(myIntersperse s xs)
+
+-- ghci> :l 3_b_7.hs
+-- [1 of 1] Compiling Main             ( 3_b_7.hs, interpreted )
+-- Ok, one module loaded.
+-- ghci> myIntersperse ',' []
+-- ""
+-- ghci> myIntersperse ',' ["foo"]
+-- "foo"
+-- ghci> myIntersperse ',' ["foo","bar","baz","quux"]
+-- "foo,bar,baz,quux"