Popularity
8.8
Stable
Activity
0.0
Stable
50
8
16

Monthly Downloads: 42
Programming language: Haskell
License: BSD 3-clause "New" or "Revised" License
Tags: Data Structures     Records     Bookkeeper    
Latest version: v0.2.5

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README

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 ()