<aside> 💡 Dr. Kiczales summarises the whole idea of this chapter pretty succinctly:

...the big summary of kind of what we've seen so far is, if you have arbitrary size information, then you need arbitrary size data. That requires a well formed self referential type comment. That leads to a natural recursion in the template. That leads a recursive call in the function. You should test the base case first, and you should always trust the natural recursion.

</aside>

What is “arbitrary-sized data”?

• So far, we’ve only touched on what’s known as fixed-size data — data which represents a known and fixed amount of information in advance.

• Here, we’ll explore the concept of arbitrary-sized data — data which represents information whose volume isn’t fixed.

  • Examples:
    • Names and information about students in a class
    • Clothes in your wardrobe
    • Names and information of your followers on Instagram (or any other social media platform for the matter)

• Arbitrary-sized data can be represented through compound data, and the simplest form of arbitrary-sized data comes in the form of lists.

Building lists from scratch

• Lists can be constructed in 2 ways:

  • using the list keyword
  • using the cons keyword

• Using list is simple enough - simply insert the keyword into parentheses and insert the components of the list thereafter.