Add distinction between an empty node and a leaf to allow truncating the output right after a node

src/Stream.hs

@@ -16,6 +16,7 @@ instance Functor Stream where
     Stream $ (\(a, stream) -> (f a, fmap f stream)) <$> pairs
 
 instance Tree Stream where
+  getStructure (Stream []) = Leaf
   getStructure (Stream pairs) =
     Node $ (\(s, stream) -> (s, getStructure stream)) <$> pairs
 

src/Tree.hs

@@ -3,7 +3,7 @@ module Tree (
     , Structure(..)
   ) where
 
-data Structure = Node [(String, Structure)]
+data Structure = Leaf | Node [(String, Structure)]
 
 class Functor a => Tree a where
   getStructure :: a String -> Structure
@@ -12,7 +12,8 @@ class Functor a => Tree a where
   draw = unlines . getLines . getStructure . fmap show
 
 getLines :: Structure -> [String]
-getLines (Node []) = ["╼"]
+getLines Leaf = ["╼"]
+getLines (Node []) = [""]
 getLines (Node [(s, structure)]) = showBlock '─' (s, structure)
 getLines (Node ((s, structure):pairs)) = concat $
   showBlock '┬' (s, structure) : showBlocks pairs