Define a polymorphic Tree data type, where a Tree is either a Node with a left subtree, a value, and a right subtree; or it is a Leaf with just a value.

(a) Three polymorphic functions -- inOrder, preOrder, and postOrder -- to traverse the tree in-order, pre-order, and post-order. Each function takes a tree and returns a list with the contents of the tree when traversed in that order.

(b) A polymorphic function, search, which takes two arguments a Tree and a key and returns a boolean result based on whether the key is found in the tree.

(c) A polymorphic function, replace, which takes three arguments a Tree t, a value before, and a value after and returns a variant of t with ALL instances of before replaced with the value after.