Chalktalk and Sketch Interface Experiments (with a little bit of Computer Science)

Note: This post is assumes a little bit (byte) of familiarity with computer science — specifically the binary search tree data structure.

As an undergraduate I collaborated with another student (now graduated) to prototype a few computer science-related sketches in Chalktalk. The binary search tree (BST) was our first target, so we made the following sketch:

There are many operations to implement, and my question was how to activate, for example, visualizations for the various traversals (breadth first search, and pre-, in-, and post-order).

What I didn’t want was to introduce buttons or sliders that would clutter the interface or use mouse swipes that didn’t make sense.

Instead, I tried creating a sort of visual mnemomic for the traversals. I often find it easier to remember something if I can draw it or trace it in the air:

Glyphs are already recognized as sketches in Chalktalk, so what if I reused the recognition functionality so I could draw glyphs atop the tree to be recognized as commands? I made the following patterns:

The red squiggles / arrows mimmick the visitation order of nodes during a recursive procedure — something like the following, which runs an pre-order recursive traversal rooted at the provided node (see the in-line comments on lines beginning with //):

void BST_traversal_preorder(BST_Node* root)
{
    // back-track up the tree if there is no child node
    if (root == NULL) {
        return;
    }
    
    // print the current node first (arrow starts at the root)
    printf("%s\n", root->value); 
    // visit the left sub-tree first (arrow passes through the left child)
    BST_traversal_preorder(root->left);
    // visit the right sub-tree (arrow ends at the right child)
    BST_traversal_preorder(root->right);
}

For breadth-first search, a zig-zag represents the layer-by-layer sequence through the tree:

 

Here is a video showing the “glyph commands” for the tree traversals:

 

I’d like to look into these sorts of visual mnemonics more to see what effects they may have on one’s learning ability.

Also, I think it makes sense for strokes to be recognized as not only sketches, but also as other entities (such as sketch-specific commands or sub-worlds within the Chalktalk environment) depending on the context. That idea seems to be worth exploring further.