https://github.com/fumieval/deriving-aeson

Scrap your hand-rolled aeson instances
https://github.com/fumieval/deriving-aeson

Last synced: about 1 year ago
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Scrap your hand-rolled aeson instances

• Host: GitHub
• URL: https://github.com/fumieval/deriving-aeson
• Owner: fumieval
• License: bsd-3-clause
• Created: 2020-02-26T07:29:42.000Z (over 6 years ago)
• Default Branch: master
• Last Pushed: 2024-11-23T02:29:14.000Z (over 1 year ago)
• Last Synced: 2025-03-29T14:06:46.927Z (about 1 year ago)
• Language: Haskell
• Homepage: http://hackage.haskell.org/package/deriving-aeson
• Size: 250 KB
• Stars: 112
• Watchers: 6
• Forks: 8
• Open Issues: 4
• Metadata Files:
  • Readme: README.md
  • Changelog: CHANGELOG.md
  • License: LICENSE

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README

          
deriving-aeson

====

[![Hackage](https://img.shields.io/hackage/v/deriving-aeson.svg)](https://hackage.haskell.org/package/deriving-aeson)

![Haskell CI](https://github.com/fumieval/deriving-aeson/workflows/Haskell%20CI/badge.svg)

[![Discord](https://img.shields.io/discord/664807830116892674?color=%237095ec&label=Discord&style=plastic)](https://discord.gg/DG93Tgs)

![logo](https://github.com/fumieval/deriving-aeson/blob/master/logo/logo.png?raw=true)

This package provides a newtype wrapper where you can customise

[aeson](https://hackage.haskell.org/package/aeson)'s generic methods using a

type-level interface, which synergises well with DerivingVia.

```haskell

{-# LANGUAGE DerivingVia, DataKinds, DeriveGeneric #-}

import Data.Aeson

import Deriving.Aeson

import qualified Data.ByteString.Lazy.Char8 as BL

data User = User

  { userId :: Int

  , userName :: String

  , userAPIToken :: Maybe String

  } deriving Generic

  deriving (FromJSON, ToJSON)

  via CustomJSON '[OmitNothingFields, FieldLabelModifier '[StripPrefix "user", CamelToSnake]] User

testData :: [User]

testData = [User 42 "Alice" Nothing, User 43 "Bob" (Just "xyz")]

main = BL.putStrLn $ encode testData

-- [{"name":"Alice","id":42},{"api_token":"xyz","name":"Bob","id":43}]

```

`Deriving.Aeson.Stock` contains some aliases for even less boilerplates.

* `Prefixed str` = `CustomJSON '[FieldLabelModifier (StripPrefix str)]`

* `PrefixedSnake str` = `CustomJSON '[FieldLabelModifier (StripPrefix str, CamelToSnake)]`

* `Suffixed str` = `CustomJSON '[FieldLabelModifier (StripSuffix str)]`

* `SuffixedSnake str` = `CustomJSON '[FieldLabelModifier (StripSuffix str, CamelToSnake)]`

* `Snake` = `CustomJSON '[FieldLabelModifier '[StripPrefix str, CamelToSnake]]`

* `Vanilla` = `CustomJSON '[]`

How it works

----

The wrapper type has a phantom type parameter `t`, a type-level builder of an [Option](http://hackage.haskell.org/package/aeson-1.4.6.0/docs/Data-Aeson.html#t:Options).

Type-level primitives are reduced to one `Option` by the `AesonOptions` class.

```haskell

newtype CustomJSON t a = CustomJSON { unCustomJSON :: a }

class AesonOptions xs where

  aesonOptions :: Options

instance AesonOptions xs => AesonOptions (OmitNothingFields ': xs) where

  aesonOptions = (aesonOptions @xs) { omitNothingFields = True }

...

```

You can use any (static) function for name modification by adding an instance of `StringModifier`.

```haskell

data ToLower

instance StringModifier ToLower where

  getStringModifier "" = ""

  getStringModifier (c : xs) = toLower c : xs

```

Previous studies

----

* [Type-driven safe derivation of ToJSON and FromJSON, using DerivingVia in GHC 8.6 and some type-level hacks](https://gist.github.com/konn/27c00f784dd883ec2b90eab8bc84a81d)

* [Strip prefices from JSON representation](https://gist.github.com/fumieval/5c89205d418d5f9cafac801afbe94969)