data-default-generics

A class for types with a default value

Monthly Downloads: 8

Programming language: Haskell

License: BSD 3-clause "New" or "Revised" License

Tags: Data    

Latest version: v0.5.1

README

data-default-generics

A class for types with a default value.

This is a fork of the package originally developed by Lukas Mai, data-default, with the following additions:

• Regrouped everything in a single module
• Added several instances, namely Either, Text, ByteString, etc
• Added Generics support by Jonathan Fischoff, with some additional support for recursive datatypes by me, with the precious help of José Pedro Magalhães

It should be usable as a drop-in replacement.

Usage

Supose you've got a structure:

data TestRec = TestRec
  { bool    :: Bool
  , txt     :: T.Text
  , bs      :: BSL.ByteString
  , lst     :: [CInt]
  , ut      :: UTCTime
  } deriving (Eq,Show)

And you want to quickly define a default value for it, in a way that does not require code changes if the structure later gets altered. Modify the previous to:

{-# LANGUAGE DeriveGeneric       #-} 

(...)
import Data.Default.Generics
import GHC.Generics
(...)

data TestRec = TestRec
  { bool    :: Bool
  , txt     :: T.Text
  , bs      :: BSL.ByteString
  , lst     :: [CInt]
  , ut      :: UTCTime
  } deriving (Eq,Show, Generic)

instance Default TestRec 

And then you can use the default value for this structure as def, as long as you import Data.Default.Generics.

Bugs

Issues and pull requests are most welcome. Any additional instance for data types from the Haskell Platform will be considered.