Anonymous records and overloaded labels

Latest on Hackage:0.2.5

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BSD3 licensed by Julian K. Arni
Maintained by

Bookkeeper Build Status

Bookkeeper is a new Haskell library that uses the new OverloadedLabels feature of GHC 8 to provide a new take on datatypes and records:

{-# LANGUAGE DataKinds #-}
{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE OverloadedLabels #-}
import Bookkeeper

jane :: Book '[ "name" :=> String, "age" :=> Int ]
jane = emptyBook
     & #name =: "Jane"
     & #age =: 30

-- >>> jane
-- Book {age = 30, name = "Jane"}
-- >>> jane ?: #name
-- "Jane"

It bears some similarities to Nikita Volkov’s record library, but requires no Template Haskell.

Accesing a field that does not exist is a type error, made nicer with GHCs new custom type errors:

 -- >>> jane ?: #address
--   • The provided Book does not contain the field "address"
--     Book type:
--     '["age" ':-> Int, "name" ':-> String]

The order in which fields are inserted or appear in types does not matter. That is, in:

-- type A = Book '[ "field1" :=> Int,  "field2" :=> Bool]
-- type B = Book '[ "field2" :=> Bool, "field1" :=> Int ]

Types A and B are the same.

You can set, modify, or get fields. See the haddocks for more information.

main :: IO ()
main = return ()



  • Added ‘rlens’ and lens ‘IsLabel’ instance.


  • Implement ‘fromRecord’ for converting values from record.

  • Add ‘Data.Default’ instance

  • Add ‘Gettable’, ‘Settable’, ‘Modifiable’ type synonyms.

  • Added Eq instance
  • Added Show instance
  • Changed the implementation of ‘set’ and ‘modify’. It no longer needs ‘ChooseFirst’ to be in scope, and the class constraints changed.
  • Removed ‘ChooseFirst’.

  • Initial release
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