Tweaks

src/TreeHelp.hs

@@ -27,6 +27,7 @@ module TreeHelp (
     safeUpdateSingleNode,
     numTraversable,
     treeAttachDeep,
+    subtree,
 ) where
 
 import Control.Lens
@@ -49,12 +50,7 @@ treePost xs = treeFromPost (init xs) (last xs)
 {- | Creates a tree with one trunk branch,
 input as a list, that ends in another tree.
 -}
-treeFromTrunk ::
-    -- | The trunk
-    [a] ->
-    -- | The end of the tree
-    Tree a ->
-    Tree a
+treeFromTrunk :: [a] -> Tree a -> Tree a
 treeFromTrunk = flip $ foldr f
   where
     f x t = Node x [t]
@@ -72,6 +68,12 @@ applyToSubtree :: [Int] -> (Tree a -> Tree a) -> Tree a -> Tree a
 applyToSubtree [] f t = f t
 applyToSubtree (i : is) f (Node x xs) = Node x (xs & ix i %~ applyToSubtree is f)
 
+-- the following is probably better, but hasn't been checked
+subtree :: (Applicative g,Foldable f) => f Int -> (Tree b -> g (Tree b)) -> Tree b -> g (Tree b)
+subtree = foldr f id
+  where
+    f i g = (branches . ix i) . g
+
 {- | Applies a function to a specific subforest determined by a list of indices.
 Partial.
 -}