Fix new game resize bug

src/Dodge/Layout/Tree/Either.hs

@@ -3,6 +3,7 @@ Combining and composing trees with 'Either' nodes.
 -}
 module Dodge.Layout.Tree.Either
     ( expandTreeBy
+    , appendEitherTree
     , connectRoom
     , deadRoom
     ) where
@@ -20,6 +21,16 @@ expandTreeBy f (Node x xs) = appendAndRemove $ f x
     appendAndRemove (Node (Left y)  ys) = Node y (map appendAndRemove ys)
     appendAndRemove (Node (Right y) _ ) = Node y (map (expandTreeBy f) xs)
 
+-- | Appends a second either forest at the 'Right' elements of a first either
+-- tree.
+-- Makes such 'Right' elements into 'Left's.
+appendEitherTree 
+    :: Tree (Either a a)    -- ^ The first tree
+    -> [Tree (Either a a)]    -- ^ The forest to append
+    -> Tree (Either a a)
+appendEitherTree (Node (Left x) ts) ts'  = Node (Left x) $ map (flip appendEitherTree ts') ts
+appendEitherTree (Node (Right x) ts) ts' = Node (Left x) ts'
+
 removeEither (Left y)  = y
 removeEither (Right y) = y