AnkiSettings customizes the behavior of this algorithm. Refer to this section of the Anki manual for more details. It may be created with the createSettings function and its values may be changed form default by piping to the following functions:

New Cards

• setNewSteps : List Int -> AnkiSettings -> AnkiSettings -- Anki default: [1, 10] Sets the interval steps (in minutes) that a card must go through while in the learning process. Answering Again or Hard will return a card to step 0. Answering Easy will instantly graduate a card. Answering Good will advance the card 1 step. If this list is empty, cards will instantly graduate the first time they are reviewed, regardless of the Answer. Note that an interval must be at least 1 minute long; any value less than 1 minute will result in an interval of 1 minute.

• setGraduatingInterval : Int -> AnkiSettings -> AnkiSettings -- Anki default: 1 Sets the initial interval (in days) a card will be scheduled for upon graduating from the learning phase. If newSteps is empty, all new cards will be scheduled for this interval when first encountered, regardless of answer. Note that this interval will not be fuzzed, per Anki's source. Values less than 1 will result in 1 being used.

• setEasyInterval : Int -> AnkiSettings -> AnkiSettings -- Anki default: 4 Sets the initial interval (in days) a card will be scheduled for upon instantly graduating from the learning phase with an answer of Easy. This value is not used if newSteps is empty. Note that this interval will not be fuzzed, per Anki's source. Values less than 1 will result in 1 being used.`

• setStartingEase : Float -> AnkiSettings -> AnkiSettings -- Anki default: 2.5 Sets the initial ease that a card graduating from learning will have. Values less than 1.3 are ignored and result in 1.3 being used instead (as that is the minimum ease a card may have).

Reviews

• setEasyBonus : Float -> AnkiSettings -> AnkiSettings -- Anki default 1.3 Sets the multiplier for the next interval of a card that was answered Easy (i.e. additional interval length over merely answering Good. Values less than 1.0 are ignored.

• setIntervalModifier : Float -> AnkiSettings -> AnkiSettings -- Anki default 1.0 Set the multiplier for all intervals, e.g. setting it to 0.8 will result in all review intervals being 80% as long as they would normally be. This multiplier may be used to increase/decrease retention at the cost of increasing/decreasing study time, respectively. Values less than or equal to zero are ignored.

• setMaximumInterval : Int -> AnkiSettings -> AnkiSettings -- Anki default: 36500 Set the upper limit on the time the algorithm will schedule a card for (in days). Small values may be used to cap time between seeing a card (to increase retention). Values less than 1 are ignored. Note that, due to the limitations of integers, an absolute maximum interval of 1491308 days (4085 years) exists. Since you almost certainly won't be alive in 4000 years to study a card, this shouldn't be a problem.

• setHardInterval : Float -> AnkiSettings -> AnkiSettings -- Anki default: 1.2 Set the multiplier applied to the previous interval when Hard is answered to a card. Note that intervals are forced to be at least 1 day longer than the previous one (before fuzzing). As such, values <= 1 will have no effect. Additionally, values of hardInterval that would result in a longer interval than that from answering Good (i.e. that are larger than the ease of the card) are ignored, with ease being used instead. As such, it is probably good practice to keep this value <= 1.3, as that is the lower limit on ease.

Lapses

• lapseSteps : List Int -> AnkiSettings -> AnkiSettings -- Anki default: [10] Set the interval steps (in minutes) that a card must go through while relearning after a lapse. Answering Again or Hard will return a card to step 0. Answering Easy will instantly graduate a card back to review. Answering Good will advance the card 1 step. If this list is empty, cards will instantly graduate the first time they are reviewed, regardless of the Answer.
• lapseNewInterval : Float -> AnkiSettings -> AnkiSettings -- Anki default: 0.0 Set a multiplier for the pre-lapse interval to determine the new interval after graduating a card back from re-learning. Values less than 0.0 are ignored Note that this interval is not fuzzed, per Anki's source.
• lapseMinimumInterval : Int -> AnkiSettings -> AnkiSettings -- Anki default: 1 Set a minimum bound on the previous option, with lapsed cards getting a new interval of at least this value. Answers less than 1 are ignored.
• leechThreshold : Int -> AnkiSettings -> AnkiSettings -- Anki default: 8 Set the number of lapses before a card is considered a "leech." getDueCardIndices will return the leech status of each card in the deck. Additionally, getLeeches will return all leeches in a deck (regardless of due status). Setting this value to less than or equal to 0 turns off leeches entirely.

createSettings creates an AnkiSettings with the same default settings as the Anki program itself. It may be piped into the following functions to update from default:

• setNewSteps
• setGraduatingInterval
• setEasyInterval
• setStartingEase
• setEasyBonus
• setIntervalModifier
• setMaximumInterval
• setHardInterval
• setLapseSteps
• setLapseNewInterval
• setLapseMinimumInterval
• setLeechThreshold

An example follows:

createSettings
    |> setNewSteps [ 1, 2, 3 ]
    |> setLapseSteps [ 4, 5, 6 ]
    |> setLeechThreshold 0

setNewSteps sets the the interval steps (in minutes) that a card must go through while in the learning process. Answering Again or Hard will return a card to step 0. Answering Easy will instantly graduate a card. Answering Good will advance the card 1 step. If this list is empty, cards will instantly graduate the first time they are reviewed, regardless of the Answer. Note that an interval must be at least 1 minute long; any value less than 1 minute will result in an interval of 1 minute.

setGraduatingInterval sets the initial interval (in days) a card will be scheduled for upon graduating from the learning phase. If newSteps is empty, all new cards will be scheduled for this interval when first encountered, regardless of answer. Note that this interval will not be fuzzed, per Anki's source. Values less than 1 will result in 1 being used.

setEasyInterval sets the initial interval (in days) a card will be scheduled for upon instantly graduating from the learning phase with an answer of Easy. This value is not used if newSteps is empty. Note that this interval will not be fuzzed, per Anki's source. Values less than 1 will result in 1 being used.

setStartingEase sets the initial ease that a card graduating from learning will have. Values less than 1.3 are ignored and result in 1.3 being used instead (as that is the minimum ease a card may have).

setEasyBonus sets the multiplier for the next interval of a card that was answered Easy (i.e. additional interval length over merely answering Good. Values less than 1.0 are ignored.

setIntervalModifier sets the multiplier for all intervals, e.g. setting it to 0.8 will result in all review intervals being 80% as long as they would normally be. This multiplier may be used to increase/decrease retention at the cost of increasing/decreasing study time, respectively. Values less than or equal to zero are ignored.

setMaximumInterval sets the upper limit on the time the algorithm will schedule a card for (in days). Small values may be used to cap time between seeing a card (to increase retention). Values less than 1 are ignored. Note that, due to the limitations of integers, an absolute maximum interval of 1491308 days (4085 years) exists. Since you almost certainly won't be alive in 4000 years to study a card, this shouldn't be a problem.

setHardInterval sets the multiplier applied to the previous interval when Hard is answered to a card. Note that intervals are forced to be at least 1 day longer than the previous one. As such, values <= 1 will have no effect. Additionally, values of hardInterval that would result in a longer interval than that from answering Good (i.e. that are larger than the ease of the card) are ignored, with ease being used instead. As such, it is probably good practice to keep this value <= 1.3, as that is the lower limit on ease.

setLapseSteps sets the interval steps (in minutes) that a card must go through while relearning after a lapse. Answering Again or Hard will return a card to step 0. Answering Easy will instantly graduate a card back to review. Answering Good will advance the card 1 step. If this list is empty, cards will instantly graduate the first time they are reviewed, regardless of the Answer.

setLapseNewInterval sets a multiplier for the pre-lapse interval to determine the new interval after graduating a card back from re-learning. Values less than 0.0 are ignored Note that this interval is not fuzzed, per Anki's source.

setLapseMinimumInterval sets a minimum bound on the previous option, with lapsed cards getting a new interval of at least this value. Answers less than 1 are ignored.

setLeechThreshold sets the number of lapses before a card is considered a "leech." getDueCardIndices will return the leech status of each card in the deck. Additionally, getLeeches will return all leeches in a deck (regardless of due status). Setting this value to less than or equal to 0 turns off leeches entirely.

A Card represents a single question or unit of knowledge the user will review. In general terms, each would represent a single flashcard. Card is defined as an extensible record; as such, whatever necessary custom fields for a use case may simply be included in the record, e.g.:

type alias MyFlashcard =
    Card { prompt : String, answer : String }

A Card contains only the information necessary for scheduling and nothing else; all other information should be added as in the above example.

A Deck represents a list of cards to be studied (this might be called a "collection" in other software). It is a record with field cards, an Array of Card and field settings of AnkiSettings. Maintaining the state of a Deck may be handled by the user of the module or by this module itself. In general, it is probably best not to add a massive quantity of new (unstudied) cards to a deck at once.

SRSData contains all data necessary for the Anki system and may be created with the newSRSData function. It may additionally be saved/loaded using the Json encoder/decoder in this package

newSRSData creates a new SRSData for inclusion in a Card.

encoderSRSData provides a Json encoder for encoding SRSData from a Card.

decoderSRSData provides a Json decoder for decoding SRSData for a Card.

encoderAnkiSettings provides a Json encoder for encoding AnkiSettings from a Deck.

decoderAnkiSettings provides a Json decoder for decoding AnkiSettings for a Deck.

The Answer type represents how accurate/certain a user's response was to a card and must be passed to answerCard whenever a Card is reviewed. This package uses the same names as Anki, as presented below:

• Again -- An incorrect response.

• Hard -- A correct response that was challenging to produce. Should not be presented as an option when answering cards in the Learning queue. In the Learning queue, Hard is merely a synonym for Again.

• Good -- A correct response of appropriate difficulty.

• Easy -- A correct response that was excessively easy to produce (will increase ease and interval faster)

answerCardInDeck functions analogously to answerCard but handles maintenance of the Deck, which is typically what one would desire. When a card is presented to the user and answered, answerCardInDeck should be called with the current time (in the Time.Posix format returned by the now task of the core Time module), an Answer, the index of the card in the Deck, and the Deck itself. It returns the updated Deck. Use this function if you simply want to store a Deck and not worry about updating it manually (which is most likely what you want). Otherwise, use answerCard to handle updating the Deck manually. Handling the presentation of a card is the responsibility of the implementing program, as various behaviors might be desirable in different cases. Note that if an invalid (out of bounds) index is passed, the Deck is returned unaltered.

When a card is presented to the user and answered, answerCard should be called with the current time (in the Time.Posix format returned by the now task of the core Time module) and an Answer. It returns the updated card, which should replace the card in the Deck. Use this function if you want to handle updating the Deck manually; otherwise, use answerCardInDeck. Handling the presentation of a card is the responsibility of the implementing program, as various behaviors might be desirable in different cases.

getDueCardIndices takes the current time (in the Time.Posix format returned by the now task of the core Time module) and a Deck and returns the indices of the subset of the Deck that is due for review, as well as whether or not they are leeches (as List (Int, Bool)). The returned indices will be sorted in the following order:

1. Lapsed cards overdue for review
   1. Cards more overdue (by proportion of interval)
   2. Cards less overdue (by proportion of interval)
2. Review cards overdue for review
   1. Cards more overdue (by proportion of interval)
   2. Cards less overdue (by proportion of interval)
3. Learning cards overdue for review
   1. Cards more overdue (by proportion of interval)
   2. Cards less overdue (by proportion of interval)
4. Any new cards in the deck (never having been studied before).

getDueCardIndices will show cards up to 20 minutes early, as per Anki.

getLeeches takes a Deck and returns the indices of the subset of the Deck that are leeches (as List Int). The returned indices will be sorted in the following order:

1. Cards with more lapses

2. Cards with fewer lapses