Use the source's constructor order: left subtree, root value, right subtree.
data Tree a = Tree (Tree a) a (Tree a) | Empty

foldTree :: (b -> a -> b -> b) -> b -> Tree a -> b
foldTree node empty Empty = empty
foldTree node empty (Tree l x r) =
  node (foldTree node empty l) x (foldTree node empty r)

unfoldTree :: (s -> Maybe (s,a,s)) -> s -> Tree a
unfoldTree next seed = case next seed of
  Nothing -> Empty
  Just (ls,x,rs) ->
    Tree (unfoldTree next ls) x (unfoldTree next rs)
A tree fold replaces the two constructors by an algebra on already folded children. A tree unfold expands a seed either into the empty tree or into a root value and two new seeds. The definitions themselves work on arbitrary binary trees; preserving the binary search tree ordering requires the supplied algebra or seed expansion to respect its bounds.

Ancestors (12)

  1. a
  2. 4
  3. Functional programming, design and analysis of algorithms
  4. 2023
  5. Past exam of the year 1 of the computer science course of the University of Oxford
  6. Year 1 of the computer science course of the University of Oxford
  7. Computer science course of the University of Oxford
  8. Undergraduate course of the University of Oxford
  9. Course of the University of Oxford
  10. University of Oxford
  11. List of universities
  12. Home

View article source

Discussion (0)

New discussion

There are no discussions about this article yet.

Articles by others on the same topic (0)

There are currently no matching articles.
See all articles in the same topic Create my own version