implement takeJ from second exercise of lecture 7

1 files changed, 12 insertions, 0 deletions

diff --git a/lec07/JoinList.hs b/lec07/JoinList.hs
index 5c1165e..ccfa838 100644
--- a/lec07/JoinList.hs
+++ b/lec07/JoinList.hs
@@ -43,3 +43,15 @@ dropJ n jl@(Append m jl1 jl2)
       where
         s1 = getSize $ size $ tag jl1
         m' = getSize $ size m
+
+takeJ :: (Sized b, Monoid b) => Int -> JoinList b a -> JoinList b a
+takeJ _ Empty = Empty
+takeJ n _ | n <= 0 = Empty
+takeJ n jl@(Single _ _) = jl
+takeJ n jl@(Append m jl1 jl2)
+      | n >= m' = jl
+      | n < s1 = takeJ n jl1
+      | n >= s1 = jl1 +++ takeJ (n - s1) jl2
+      where
+        s1 = getSize $ size $ tag jl1
+        m' = getSize $ size m