@node Binary Search Tree
@section Binary Search Tree

A simple ``read only'' binary search tree.

@defun make-tree pred? lst
Constructs a new tree. @var{pred?} should be a procedure taking the
first element of @var{lst}, along with each element, and should return
a boolean value indicating if the specific element should go in the
left or right subtree. (left subtree is ``truthy'' values).

This operation is done recursively.
@end defun

@defun tree-node tree
Return the value of a tree node.
@end defun

@defun left-subtree tree
Return all ``truthy'' children of tree node.
@end defun

@defun right-subtree tree
Return all ``falsy children of tree node.
@end defun

@defun length-of-longest-branch tree
Get the depth of a tree.
@end defun

@defun tree-map proc tree
Apply proc onto the value of every node in tree, keeping the structure
of the tree.

@b{Note:} this can cause the tree to no longer be a binary search
tree, but simply a ``formless'' binary tree.
@end defun