A friend and I wanted to learn ClojureScript and core.async. ClojureScript lets you write JavaScript with a Clojure-like syntax. Core.async is supposed to be a fancy new way to handle asynchronous programming. Tic Tac Toe seemed like a simple-enough yet complex-enough task to get familiar with both. First I wrote the game in vanilla ClojureScript then I rewrote it using core.async to see how much fancier it really was.
Well, the pure ClojureScript version and the core.async version weighed in at about the same number of lines of code. Maybe it's because I come from JavaScript background, but I found the non-async version easier to read. It models the code I've written for normal JavaScript programs more closely. However, when I look at the core.async version, I notice that all game state is contained within the game loop. It's also nice that all the events are passed through channels, which are only read from in the game loop as well.
I would say the biggest change is that the core.async version doesn't require any quasi-global variables for tracking game state. In the normal version I had 3 variables for storing state:
(def player (atom ttt/X))
(def board-data (atom nil))
(def board-dom (atom nil))
While in the core.async version, the only quasi-global variable is the channel that passes click events. The rest of the state stays within the game loop. The real version of the loop can be seen on github, but this is a pseudo-code version.
(defn game-loop [first-player]
(go
(loop [board empty-board player first-player]
(let [event (<! click-channel)]
new-board (view-to-data dom)
next-player (if (= player X) O X)]
(if (win? board)
(recur (create) first-player))
(if (full? board)
(recur (create) first-player))
(recur new-board next-player)))))