No description, website, or topics provided.
Haskell CSS JavaScript
Clone or download
Fetching latest commit…
Cannot retrieve the latest commit at this time.
Permalink
Failed to load latest commit information.
bench
doctest
exec
src
test
.ghci
.gitignore
.travis.yml
CHANGELOG.md
LICENSE
README.md
Setup.hs
bookkeeper.cabal
package.yaml
stack.yaml

README.md

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 ()