Lists of Lists

Lists can be inserted as elements in larger lists. We can easily create ad hoc structures as needed:

We can also build any classic computer science data structure out of lists of lists, by defining constructors (blocks to make an example of the structure), selectors (blocks to pull out a piece of the structure), and mutators (blocks to change the contents of the structure) as needed. Here we create binary trees with selectors that check for input of the correct data type; only one selector is shown but the ones for left and right children are analogous.