Programming Clojure, 2nd Edition

Scoring a Clojurebreaker Game

As a Clojure programmer, one question you will often ask is, “Where do I need state to solve this problem?” Or, better yet, “How much of this problem can I solve without using any state?”

With Clojurebreaker (and with many other games), the game logic itself is a pure function. It takes a secret and a guess and returns a score. Identifying this fact early gives us two related advantages:

• The score function will be trivial to write and test in isolation.
• We can comfortably proceed to implement score without even thinking about how the rest of the system will work.

Scoring itself divides into two parts: tallying the exact matches and tallying the matches that are out of order. Each of these parts can be its own ...