7. Recursion II: Lazy Sequences

Activity 7.01: Historical, Player-Centric Elo

Solution:

1. Set up your project, which should be based on the code written for the last exercises in this chapter.
2. The solution follows the pattern established with take-matches. Let's start with the parameters. We need to define separate behaviors for matches played by the "focus player" and matches played between other players. The first thing we need is, of course, a way to identify the player, so we'll add a player-slug argument. This wasn't necessary in take-matches because there we treated all the matches the same, regardless of who played in them.

   In take-matches, we had a limit argument to control how deeply we walked the tree. In this case, we need two different parameters, which we will call focus-depth and opponent-depth. Together, that gives us the following parameters for our new focus-history function:

   (defn focus-history [tree player-slug focus-depth opponent...