FoldingTrees

FoldingTrees implements a dynamic tree structure in which some nodes may be "folded," i.e., marked to avoid descent among that node's children. It also supports interactive text menus based on folding trees.

For example, after saying using FoldingTrees, a "table of contents" like

I. Introduction
  A. Some background
    1. Stuff you should have learned in high school
    2. Stuff even Einstein didn't know
  B. Defining the problem
II. How to solve it

could be created like this:

root = Node("")
chap1 = Node("Introduction", root)
chap1A = Node("Some background", chap1)
chap1A1 = Node("Stuff you should have learned in high school", chap1A)
chap1A2 = Node("Stuff even Einstein didn't know", chap1A)
chap1B = Node("Defining the problem", chap1)
chap2 = Node("How to solve it", root)

You don't have to create them in this exact order, the only constraint is that you create the parents before the children. In general you create a node as Node(data, parent), where data can be any type. The root node is the only one that you create without a parent, i.e., root = Node(data), and the type of data used to create root is enforced for all leaves of the tree. You can specify the type with root = Node{T}(data) if necessary. There is no explicit limit on the number of children that a node may have.

Using the AbstractTrees package, the tree above displays as

julia> print_tree(root)

├─   Introduction
│  ├─   Some background
│  │  ├─   Stuff you should have learned in high school
│  │  └─   Stuff even Einstein didn't know
│  └─   Defining the problem
└─   How to solve it

Now let's fold the section named "Some background":

julia> fold!(chap1A)
true

julia> print_tree(root)

├─   Introduction
│  ├─ + Some background
│  └─   Defining the problem
└─   How to solve it

You can use unfold! to reverse the folding and toggle! to switch folding.

There are a few utilities that you can learn about by reading their docstrings:

• isroot: determine whether a node is the root node
• count_open_leaves: count the number of nodes in the tree above the first fold on all branches
• next, prev: efficient ordered visitation of open nodes (depth-first)
• nodes: access nodes, rather than their data, during iteration (example: foreach(unfold!, nodes(root)))

On suitable Julia versions (ones for which isdefined(REPL.TerminalMenus, :ConfiguredMenu) is true, a.k.a. 1.6.0-DEV.201 or higher), you can use such trees to create interactive menus via TerminalMenus.

Suppose root is the same Node we created above, in the original unfolded state. Then

julia> using REPL.TerminalMenus

julia> menu = TreeMenu(root)

julia> choice = request(menu; cursor=2)

 >    Introduction
       Some background
        Stuff you should have learned in high school
        Stuff even Einstein didn't know
       Defining the problem
      How to solve it

The initial blank line is due to our root, which displays as an empty string; we set the initial "cursor position," indicated visually by >, to skip over that item. You can use the up/down arrow keys to navigate over different items in the menu. Choose an item by hitting Enter, toggle folding at the cursor position by hitting the space bar:

julia> choice = request(menu; cursor=2)

      Introduction
 > +   Some background
       Defining the problem
      How to solve it

One can create very large menus with thousands of options, in which case the menu scrolls with the arrow keys and PgUp/PgDn. As described in the TerminalMenus documentation, you can customize aspects of the menu's appearance, such as the number of items visible simultaneously and the characters used to indicate scrolling and the cursor position. TreeMenu includes optional keyword arguments pagesize, dynamic, maxsize, and keypress to control various aspects of the interactive menu. See the docstring for TreeMenu for more information.

For Node objects where data is not an AbstractString, you will most likely want to specialize FoldingTrees.writeoption for your type. See ?FoldingTrees.writeoption for details.