LISP-FSRS

Implementation of the FSRS algorithm in Common Lisp and auto-transpiled to Emacs Lisp.

Usage

Common Lisp

CL-USER> (ql:quickload :lisp-fsrs)      ; Ensure you have cloned this repository into the `local-projects' directory under your Quicklisp installation root.
To load "lisp-fsrs":
  Load 1 ASDF system:
    lisp-fsrs
; Loading "lisp-fsrs"
(:LISP-FSRS)
CL-USER> (defparameter *parameters* (coerce '(0.2172 1.1771 3.2602 16.1507 7.0114 0.57 2.0966 0.0069 1.5261 0.112 1.0178 1.849 0.1133 0.3127 2.2934 0.2191 3.0004 0.7536 0.3332 0.1437 0.2) 'fsrs:parameters))
*PARAMETERS*
CL-USER> (defparameter *scheduler* (fsrs:make-scheduler :parameters *parameters*))
*SCHEDULER*
CL-USER> (defparameter *card* (fsrs:make-card))
*CARD*
CL-USER> *card*
#S(LISP-FSRS:CARD
   :CARD-ID 0
   :STATE :LEARNING
   :STEP 0
   :STABILITY NIL
   :DIFFICULTY NIL
   :DUE @2025-06-08T13:39:42.230941+08:00
   :LAST-REVIEW NIL)
CL-USER> (setf *card* (fsrs:scheduler-review-card *scheduler* *card* :good))
#S(LISP-FSRS:CARD
   :CARD-ID 0
   :STATE :LEARNING
   :STEP 1
   :STABILITY 3.2602
   :DIFFICULTY 4.884632
   :DUE @2025-06-08T13:49:49.476969+08:00
   :LAST-REVIEW @2025-06-08T13:39:49.476969+08:00)
CL-USER> (setf *card* (fsrs:scheduler-review-card *scheduler* *card* :good))
#S(LISP-FSRS:CARD
   :CARD-ID 0
   :STATE :REVIEW
   :STEP NIL
   :STABILITY 3.5362437
   :DIFFICULTY 4.8680573
   :DUE @2025-06-12T13:39:50.242969+08:00
   :LAST-REVIEW @2025-06-08T13:39:50.242969+08:00)

To generate the fsrs package for Emacs after changing the code, ensure you are running the current Lisp session using sly in Emacs, then:

CL-USER> (ql:quickload :lisp-fsrs/emacs)
To load "lisp-fsrs/emacs":
  Load 1 ASDF system:
    lisp-fsrs/emacs
; Loading "lisp-fsrs/emacs"
[package lisp-fsrs.emacs]..
(:LISP-FSRS/EMACS)
CL-USER> (fsrs.emacs:translate-system)
NIL

Emacs Lisp

ELISP> (package-vc-install "https://github.com/open-spaced-repetition/lisp-fsrs.git")
t
ELISP> (setq fsrs-parameters [0.2172 1.1771 3.2602 16.1507 7.0114 0.57 2.0966 0.0069 1.5261 0.112 1.0178 1.849 0.1133 0.3127 2.2934 0.2191 3.0004 0.7536 0.3332 0.1437 0.2])
[0.2172 1.1771 3.2602 16.1507 7.0114 0.57 2.0966 0.0069 1.5261 0.112
        1.0178 1.849 0.1133 0.3127 2.2934 0.2191 3.0004 0.7536 0.3332
        0.1437 0.2]

ELISP> (setq fsrs-scheduler (fsrs-make-scheduler))
#s(fsrs-scheduler :parameters
                  [0.2172 1.1771 3.2602 16.1507 7.0114 0.57 2.0966
                          0.0069 1.5261 0.112 1.0178 1.849 0.1133
                          0.3127 2.2934 0.2191 3.0004 0.7536 0.3332
                          0.1437 0.2]
                  :desired-retention 0.9 :learning-steps
                  ((1 :minute) (10 :minute)) :relearning-steps
                  ((10 :minute)) :maximum-interval (36500 :day)
                  :enable-fuzzing-p t)

ELISP> (setq fsrs-card (fsrs-make-card))
#s(fsrs-card :card-id 0 :state :learning :step 0 :stability nil
             :difficulty nil :due "2025-06-08T05:38:50Z" :last-review
             nil)

ELISP> (setq fsrs-card (cl-nth-value 0 (fsrs-scheduler-review-card fsrs-scheduler fsrs-card :good)))
#s(fsrs-card :card-id 0 :state :learning :step 1 :stability 3.2602
             :difficulty 4.884631634813845 :due "2025-06-08T05:48:52Z"
             :last-review "2025-06-08T05:38:52Z")

ELISP> (setq fsrs-card (cl-nth-value 0 (fsrs-scheduler-review-card fsrs-scheduler fsrs-card :good)))
#s(fsrs-card :card-id 0 :state :review :step nil :stability
             3.536243655619573 :difficulty 4.868056502338024 :due
             "2025-06-10T05:38:53Z" :last-review
             "2025-06-08T05:38:53Z")