Spaced Repetition ¶ ↑

Ruby gem that implements the SM-2 algorithm of SuperMemo. See www.supermemo.com/english/ol/sm2.htm for more details.

The plan is to add more algorithms in the future, e.g. Mnemosyne.

gem install tworgy-spaced-repetition

The gem provides a mixin which should be added to a class that represents something you want to remember, e.g. a flash card class. The mixin adds several methods (described below) to calculate the date when the next repetition should occur.

Importantly, the mixin depends on several methods existing on the hosting class. The mixin should throw an exception if it cannot find the appropriate methods.

class FlashCardExample 
  attr_accessor :easiness_factor, :number_repetitions, :quality_of_last_recall, :next_repetition     

  include SuperMemo::SM2
end

Create an instance of the object as per usual

fc = FlashCardExample.new

Reset the data to begin with

fc.reset_spaced_repetition_data
fc.easiness_factor => 2.5  
fc.number_repetitions => 0  
fc.quality_of_last_recall => nil  
fc.next_repetition => Date.today

Calculate the next interval/date (Note: SM2 expects a number between 0-5)

fc.process_recall_result(4)

fc.repetition_interval => 1 (day)
fc.next_repetition => tomorrow (Date.today + 1 day)

Currently this gem only includes the SM-2 version of the SuperMemo algorithm. Although more recent versions of the SuperMemo algorithm exist, some popular open source and commercial alternatives to SuperMemo (such as Mnemosyne) base their algorithms on the SM-2 algorithm, as they judge it a superior algorithm to the more recent iterations. The author of Mnemosyne (the leading open source alternative) makes the point that there is a conflict of interest underlying commercial products like SuperMemo, in that companies have a vested interest in claiming the newer algorithms are better regardless of whether they actually are.