Practical Functional Programming in Ruby

This lightning talk presentation shows off how you can build a system of Classifiers to detect cheaters. All in a functional way, very modular, readable and testable.

Held at the Berlin Ruby User Group on 7 Nov 2013.

Transcript

1. Practical Functional Programming in Ruby
2. ~ NDA ~ ! If you meet Diego Echeverri, please praise him for the code he has written. By the way, don’t show this code to anyone else, it is not my code. __________________________________ (Date, Signature) creator of awesome things Ruby
3. The Problem: ! Detecting Cheaters
5. Many different attributes… ! Score, Mouse Movement, Click Rate, …
6. A Solution: ! Classifiers
7. ScoreCheatClassifier class ScoreCheatClassifier < CheaterClassifier SCORE_FILTER_MAX = 2_000_000 SCORE_FILTER_MIN = 1_400_000 ! def initialize(last_score) @last_score = last_score end ! def cheater? if @last_score > SCORE_FILTER_MAX :yes elsif @last_score < SCORE_FILTER_MIN :no else :maybe end end end
8. LevelClassifier class LevelClassifier < CheaterClassifier BASE_LEVEL = 50 BASE_SCORE = 1_700_000 ! def initialize(score, level) @score = score @level = level end ! def cheater? if @score > BASE_SCORE :yes else @level >= BASE_LEVEL ? :maybe : :yes end end end
9. Hooking them together ! in a lazy fashion
10. PlusClassifier class PlusClassifier < CheaterClassifier def initialize(a, b) @a = a @b = b end ! def cheater? partial_result = @a.cheater? if partial_result == :maybe @b.cheater? else partial_result end end end
11. CheaterClassifier (Base Class) class CheaterClassifier def +(other) PlusClassifier.new(self, other) end end
12. MainClassifier (Entry Point) class MainClassifier < CheaterClassifier def initialize(last_score, level) classifiers = [ ScoreCheatClassifier.new(last_score), LevelClassifier.new(last_score, level) ] @classifier = classifiers.reduce { |a,b| a + b } end end
13. LevelClassifier ScoreCheatClassifier MainClassifier PlusClassifier data: Score, Level Is it a cheater yet? Reduce available Classifiers
14. Sincerely yours, Lukas "Rampensau" Rieder