Implement terminals

src/Dodge/Tree/Polymorphic.hs

@@ -9,6 +9,8 @@ the nodes in the trunk are [a,b] (note that d is not the first child of b).
  -}
 module Dodge.Tree.Polymorphic
     ( applyToRoot
+    , applyToSubtree
+    , applyToSubforest
     , treeFromPost
     , treeFromTrunk
     , splitTrunk
@@ -56,6 +58,22 @@ applyToNode (i:is) f (Node x xs) = Node x (ys ++ [applyToNode is f z] ++ zs)
   where
     (ys, z:zs) = splitAt i xs
 
+{- | Applies a function to a specific subtree determined by a list of indices.
+Unsafe (partial function).  -}
+applyToSubtree :: [Int] -> (Tree a -> Tree a) -> Tree a -> Tree a
+applyToSubtree [] f t = f t
+applyToSubtree (i:is) f (Node x xs) = Node x (ys ++ [applyToSubtree is f z] ++ zs)
+  where
+    (ys, z:zs) = splitAt i xs
+
+{- | Applies a function to a specific subforest determined by a list of indices.
+Unsafe (partial function).  -}
+applyToSubforest :: [Int] -> ([Tree a] -> [Tree a]) -> Tree a -> Tree a
+applyToSubforest [] f (Node p cs) = Node p (f cs)
+applyToSubforest (i:is) f (Node x xs) = Node x (ys ++ [applyToSubforest is f z] ++ zs)
+  where
+    (ys, z:zs) = splitAt i xs
+
 -- do not delete: find use for
 --{- |
 --Applies a function to the first node along a trunk that satisfies a given property.