Language, engine, and tooling for expressing, testing, and evaluating composable language rules on input strings.
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Makan Diarra and facebook-github-bot Extend support for Ramadan and Eid al-Fitr from 2029 to 2050
Summary: Extended Ramadan and Eid al-Fitr from 2029 to 2050 in computed.hs

Reviewed By: chinmay87

Differential Revision: D10304284

fbshipit-source-id: 5240046977632411bf067769499e6afbcda0af7b
Latest commit 4943798 Oct 12, 2018

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Duckling is a Haskell library that parses text into structured data.

"the first Tuesday of October"
=> {"value":"2017-10-03T00:00:00.000-07:00","grain":"day"}


A Haskell environment is required. We recommend using stack.

On macOS you'll need to install PCRE development headers. The easiest way to do that is with Homebrew:

brew install pcre

If that doesn't help, try running brew doctor and fix the issues it finds.


To compile and run the binary:

$ stack build
$ stack exec duckling-example-exe

The first time you run it, it will download all required packages.

This runs a basic HTTP server. Example request:

$ curl -XPOST --data 'locale=en_GB&text=tomorrow at eight'

See exe/ExampleMain.hs for an example on how to integrate Duckling in your project. If your backend doesn't run Haskell or if you don't want to spin your own Duckling server, you can directly use's built-in entities.

Supported dimensions

Duckling supports many languages, but most don't support all dimensions yet (we need your help!). Please look into this directory for language-specific support.

Dimension Example input Example value output
AmountOfMoney "42€" {"value":42,"type":"value","unit":"EUR"}
Distance "6 miles" {"value":6,"type":"value","unit":"mile"}
Duration "3 mins" {"value":3,"minute":3,"unit":"minute","normalized":{"value":180,"unit":"second"}}
Email "" {"value":""}
Numeral "eighty eight" {"value":88,"type":"value"}
Ordinal "33rd" {"value":33,"type":"value"}
PhoneNumber "+1 (650) 123-4567" {"value":"(+1) 6501234567"}
Quantity "3 cups of sugar" {"value":3,"type":"value","product":"sugar","unit":"cup"}
Temperature "80F" {"value":80,"type":"value","unit":"fahrenheit"}
Time "today at 9am" {"values":[{"value":"2016-12-14T09:00:00.000-08:00","grain":"hour","type":"value"}],"value":"2016-12-14T09:00:00.000-08:00","grain":"hour","type":"value"}
Url "" {"value":"","domain":""}
Volume "4 gallons" {"value":4,"type":"value","unit":"gallon"}

Custom dimensions are also supported.

Extending Duckling

To regenerate the classifiers and run the test suite:

$ stack build :duckling-regen-exe && stack exec duckling-regen-exe && stack test

It's important to regenerate the classifiers after updating the code and before running the test suite.

To extend Duckling's support for a dimension in a given language, typically 3 files need to be updated:

  • Duckling/<Dimension>/<Lang>/Rules.hs
  • Duckling/<Dimension>/<Lang>/Corpus.hs
  • Duckling/Dimensions/<Lang>.hs (if not already present in Duckling/Dimensions/Common.hs)

To add a new language:

To add a new locale:

Rules have a name, a pattern and a production. Patterns are used to perform character-level matching (regexes on input) and concept-level matching (predicates on tokens). Productions are arbitrary functions that take a list of tokens and return a new token.

The corpus (resp. negative corpus) is a list of examples that should (resp. shouldn't) parse. The reference time for the corpus is Tuesday Feb 12, 2013 at 4:30am.

Duckling.Debug provides a few debugging tools:

$ stack repl --no-load
> :l Duckling.Debug
> debug (makeLocale EN $ Just US) "in two minutes" [This Time]
in|within|after <duration> (in two minutes)
-- regex (in)
-- <integer> <unit-of-duration> (two minutes)
-- -- integer (0..19) (two)
-- -- -- regex (two)
-- -- minute (grain) (minutes)
-- -- -- regex (minutes)
[Entity {dim = "time", body = "in two minutes", value = RVal Time (TimeValue (SimpleValue (InstantValue {vValue = 2013-02-12 04:32:00 -0200, vGrain = Second})) [SimpleValue (InstantValue {vValue = 2013-02-12 04:32:00 -0200, vGrain = Second})] Nothing), start = 0, end = 14}]


Duckling is BSD-licensed. We also provide an additional patent grant.