tree-traversals (hackage): The tree-traversals package defines in-order, pre-order, post-order, level-order, and reversed level-order traversals for tree-like types:  The package also provides newtype wrappers for the various traversals so they may be used with traverse, i.e.  To implement the various orders, the tree-traversals package provides the Control.Applicative.Phases.Phases applicative transformer for organizing effects into distinct phases.  Instances of Data.Traversable.TreeLike.TreeLike are provided for rose trees (Data.Tree.Tree), binary trees (Data.BinaryTree.BinaryTree), forests (Data.Traversable.TreeLike.Forest), and algebraic combinations of trees (Data.Functor.Compose.Compose outerTree innerTree, Data.Functor.Product fstTree sndTree, Data.Functor.Sum leftTree rightTree).
Keywords: data|library