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;;; gnosis-algorithm.el --- Spaced Repetition Algorithm for Gnosis -*- lexical-binding: t; -*-
;; Copyright (C) 2023-2024 Thanos Apollo
;; Author: Thanos Apollo <[email protected]>
;; Keywords: extensions
;; URL: https://git.thanosapollo.org/gnosis
;; Version: 0.0.1
;; Package-Requires: ((emacs "29.1"))
;; This program is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.
;; This program is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
;; GNU General Public License for more details.
;; You should have received a copy of the GNU General Public License
;; along with this program. If not, see <https://www.gnu.org/licenses/>.
;;; Commentary:
;; Handles date calculation as well as ef & interval calculations.
;; Gnosis implements a highly customizable algorithm, inspired by SM-2.
;; Gnosis algorithm does not use user's subjective rating of a note to
;; determine the next review interval, but instead uses the user's
;; success or failure in recalling the answer of a note.
;; Each gnosis note has an ef (easiness factor), which is a list of 3
;; values. The last value is the total ef for a note, which will be
;; used to determine the next interval upon a successful answer recall,
;; the second value is the ef-decrease value, this value will be
;; subtracted from the the total ef upon failure to recall the answer of
;; a note, the first value is the ef increase, will be added to the
;; total ef upon a successful recall.
;; Each gnosis deck has a gnosis-algorithm-ef-threshold, it's an
;; integer value that refers to the consecutive success or failures to
;; recall an answer. Upon reaching the threshold, gnosis-algorithm-ef-decrease
;; or gnosis-algorithm-ef-increase will be applied to the ef-increase or
;; ef-decrease of note.
;;; Code:
(require 'cl-lib)
(require 'calendar)
(defcustom gnosis-algorithm-interval '(1 3)
"Gnosis initial interval for initial successful reviews.
First item: First interval,
Second item: Second interval."
:group 'gnosis
:type '(list integer))
(defcustom gnosis-algorithm-ef '(0.35 0.30 1.3)
"Gnosis easiness factor.
First item : Increase value
Second item: Decrease value
Third item : Total ef"
:group 'gnosis
:type '(list float))
(defcustom gnosis-algorithm-ff 0.5
"Gnosis forgetting factor.
Used to calcuate new interval for failed questions.
NOTE: This value should be less than 1.0."
:group 'gnosis
:type 'float)
(defcustom gnosis-algorithm-ef-increase 0.1
"Value to increase ef increase value with.
Increase ef-increase value by this amount for every
`gnosis-algorithm-ef-threshold' number of successful reviews."
:group 'gnosis
:type 'float)
(defcustom gnosis-algorithm-ef-decrease 0.2
"Value to decrease ef decrease value with.
Decrease ef decrease value by this amount for every
`gnosis-algorithm-ef-threshold' number of failed reviews."
:group 'gnosis
:type 'float)
(defcustom gnosis-algorithm-ef-threshold 3
"Threshold for updating ef increase/decrease values.
Refers to the number of consecutive successful or failed reviews."
:group 'gnosis
:type 'integer)
(defun gnosis-algorithm-replace-at-index (index new-item list)
"Replace item at INDEX with NEW-ITEM in LIST."
(cl-loop for item in list
for i from 0
collect (if (= i index) new-item item)))
(defun gnosis-algorithm-round-items (list)
"Round all items in LIST to 2 decimal places."
(cl-loop for item in list
collect (/ (round (* item 100)) 100.0)))
(defun gnosis-algorithm-date (&optional offset)
"Return the current date in a list (year month day).
Optional integer OFFSET is a number of days from the current date."
(let* ((now (decode-time))
(now (list (decoded-time-month now)
(decoded-time-day now)
(decoded-time-year now))))
(let ((date (if (zerop (or offset 0))
now
(calendar-gregorian-from-absolute
(+ offset (calendar-absolute-from-gregorian now))))))
(list (nth 2 date) (nth 0 date) (nth 1 date)))))
(defun gnosis-algorithm-date-diff (date)
"Find the difference between the current date and the given DATE.
DATE format must be given as (year month day)."
(let ((given-date (encode-time 0 0 0 (caddr date) (cadr date) (car date))))
(- (time-to-days (current-time))
(time-to-days given-date))))
(cl-defun gnosis-algorithm-next-ef (&key ef success increase decrease threshold
c-successes c-failures)
"Return the new EF, (increase-value decrease-value total-value)
Calculate the new e-factor given existing EF and SUCCESS, either t or nil.
Next EF is calculated as follows:
Upon a successful review, increase total ef value (nth 2) by
ef-increase value (nth 0).
Upon a failed review, decrease total ef by ef-decrease value (nth 1).
For every THRESHOLD of C-SUCCESSES (consecutive successful reviews)
reviews, increase ef-increase by INCREASE.
For every THRESHOLD of C-FAILURES reviews, decrease ef-decrease value
by DECREASE."
(cl-assert (listp ef) nil "Assertion failed: ef must be a list")
(cl-assert (booleanp success) nil "Assertion failed: success must be a boolean value")
(cl-assert (numberp increase) nil "Assertion failed: increase must be a number")
(cl-assert (numberp decrease) nil "Assertion failed: decrease must be a number")
(cl-assert (numberp threshold) nil "Assertion failed: threshold must be a number")
(let ((threshold-p (= (% (max 1 (if success c-successes c-failures)) threshold) 0))
(new-ef (if success (gnosis-algorithm-replace-at-index 2 (+ (nth 2 ef) (nth 0 ef)) ef)
(gnosis-algorithm-replace-at-index 2 (max 1.3 (- (nth 2 ef) (nth 1 ef))) ef))))
(cond ((and success threshold-p)
(setf new-ef (gnosis-algorithm-replace-at-index 0 (+ (nth 0 ef) increase) new-ef)))
((and (not success) threshold-p
(setf new-ef (gnosis-algorithm-replace-at-index 1 (+ (nth 1 ef) decrease) new-ef)))))
(gnosis-algorithm-round-items new-ef)))
(cl-defun gnosis-algorithm-next-interval (&key last-interval ef success successful-reviews
failure-factor initial-interval)
"Calculate next interval.
LAST-INTERVAL: number of days since last review
EF: Easiness factor
SUCCESS: t if review was successful, nil otherwise
SUCCESSFUL-REVIEWS: number of successful reviews
FAILURE-FACTOR: factor to multiply last interval by if review was unsuccessful
INITIAL-INTERVAL: list of initial intervals for initial successful
reviews. Will be used to determine the next interval for the first 2
successful reviews."
(cl-assert (< gnosis-algorithm-ff 1) "Value of `gnosis-algorithm-ff' must be lower than 1")
;; This should only occur in testing env or when the user has made breaking changes.
(cl-assert (> (nth 2 ef) 1) "Total ef value must be above 1")
(let* ((ef (nth 2 gnosis-algorithm-ef))
(interval (cond ((and (= successful-reviews 0) success)
(car initial-interval))
((and (= successful-reviews 1) success)
(cadr initial-interval))
(t (if success
(* ef last-interval)
(* failure-factor last-interval))))))
(gnosis-algorithm-date (round interval))))
(provide 'gnosis-algorithm)
;;; gnosis-algorithm.el ends here
|
