FSRS for Rust

This crate contains a Rust API for training FSRS parameters, and for using them to schedule cards.

The Free Spaced Repetition Scheduler (FSRS) is a modern spaced repetition algorithm. It is based on the DSR model proposed by Piotr Wozniak, the creator of SuperMemo.

FSRS-rs is a Rust implementation of FSRS. It is designed to be used in Anki, a popular spaced repetition software. Anki 23.10 has already integrated FSRS as an alternative scheduler.

For more information about the algorithm, please refer to the wiki page of FSRS.

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Quickstart

Read this for an explanation of how to determine the optimal retention for your use case.

// Pick whichever percentage is to your liking (see above)
let optimal_retention = 0.75;
// Use default parameters/weights for the scheduler
let fsrs = FSRS::new(Some(&[]))?;

// Create a completely new card
let day1_states = fsrs.next_states(None, optimal_retention, 0)?;

// Rate as `hard` on the first day
let day1 = day1_states.hard;
dbg!(&day1); // scheduled as `in 4 days`

// Now we review the card 2 days later
let day3_states = fsrs.next_states(Some(day1.memory), optimal_retention, 2)?;

// Rate as `good` this time
let day3 = day3_states.good;
dbg!(day3);

Online development

You can use https://idx.google.com/import.

Local development

add

#!/bin/sh
cargo fmt
cargo clippy -- -D warnings
git add .

to .git/hooks/pre-commit, then chmod +x .git/hooks/pre-commit

Bindings

• c https://github.com/open-spaced-repetition/fsrs-rs-c
• python https://github.com/open-spaced-repetition/fsrs-rs-python
• nodejs https://github.com/open-spaced-repetition/fsrs-rs-nodejs
• dart https://github.com/open-spaced-repetition/fsrs-rs-dart
• php https://github.com/open-spaced-repetition/fsrs-rs-php

Q&A

• What is the difference between fsrs-rs and rs-fsrs

  If you only want to schedule cards, use [lang]-fsrs or the bindings.

  If you need to optimize, use this crate or its bindings.

• Why use two crates instead of one?

  Calculating the weights involves tensor operations so the data types are different (Tensor vs Vec/Slice). If we were to use one crate, this would mean using cfg to change the variable type, which would be tedious. Because of this, instead we publish two separate crates.

  Another reason is, it would be hard to port to other languages while using Tensors.

• What about the name?

  Before this crate was made, go-fsrs and other libraries already existed, so the name rs-fsrs was chosen.

  Then we wanted to port the torch version to Rust so that everyone could optimize on their own devices (tch-rs uses libtorch which is too heavy). Since the algorithm is called fsrs, we add an -rs on the end.