Playing "Racket Gin Rummy in ClojureScript" with Clojure

01 Jun 2012

In 2010 I built my first real Clojure application. It was a tool to execute semantic specifications of modeling languages and was part of my master thesis. Before I decided to use Clojure for this tool I built a little program to test the waters. This program was GinBot.

Whilst dabbling with functional programming languages I tried PLT Scheme (now PLT Racket). As part of the DrScheme editor came a couple of example games. My favorite is the Gin Rummy card game. The object of this game is to make a hand of 10 cards, consisting of a set of four cards and two sets of three cards. Players take turns and can choose to pick the top card of the discard pile or a face down card from the deck. For more information see the rules for Gin Rummy in the Racket documentation.

GinBot is a robot in software form that plays the Gin Rummy game against the computer opponent, using the strategy of the opponent, which is part of the available source in DrScheme.

GinBot playing Gin Rummy against a computer opponent by using screenshots and moving the mouse pointer

The Java robot

In order to autonomously let GinBot execute its strategy it needs to be able to see the cards on the table and be able to move cards around. Both of these are supported by the java.awt.Robot class. The aptly named createScreenCapture() does just that, and the other methods can move the mouse and execute mouse button presses and releases.

The final missing piece is to recognize the rank and face of a card from a screenshot. GinBot does this by first finding the borders of a playing card and then looking in the upper left corner for the rank number or character and suit symbol. A bit of experimentation showed that sampling a couple of pixels was sufficient to differentiate all the different cards. The experiment setup for this can be found in card.clj.

Gin Rummy in ClojureScript

To try out ClojureScript I ported the Scheme version to a webpage. (See Racket Gin Rummy in ClojureScript). The code for the opponent strategy in the ClojureScript version is verbatim copy of the version from the GinBot in Clojure. The latest version of GinBot plays against the ClojureScript version rather than the original Scheme version.

As an evaluation of the Clojure language the GinBot program was a great success. The strategy algorithm benefited greatly from the datastructures and sequence abstraction in Clojure for readability over the Scheme version. The Java interop also made Clojure a more convenient Java than Java.

From starting with Clojure to EuroClojure

Since I began using Clojure with the GinBot project, I have enjoyed working with Clojure. This includes starting as a freelance Clojure programmer. A particular highlight was the first EuroClojure conference in London in May 2012. During dinner we were joined by Rich Hickey and got to talk about Clojure with its creator.

Cheers to many more years enjoying Clojure.