https://github.com/fosskers/microlens-aeson

Lenses and Traversals for Aeson, based on Microlens.
https://github.com/fosskers/microlens-aeson

aeson haskell lens

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Lenses and Traversals for Aeson, based on Microlens.

• Host: GitHub
• URL: https://github.com/fosskers/microlens-aeson
• Owner: fosskers
• License: mit
• Created: 2017-04-27T22:40:57.000Z (over 7 years ago)
• Default Branch: master
• Last Pushed: 2024-06-05T05:21:05.000Z (7 months ago)
• Last Synced: 2024-11-08T19:50:30.117Z (2 months ago)
• Topics: aeson, haskell, lens
• Language: Haskell
• Homepage:
• Size: 3.32 MB
• Stars: 14
• Watchers: 3
• Forks: 6
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • Changelog: CHANGELOG.md
  • License: LICENSE
  • Authors: AUTHORS.md

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README

        
microlens-aeson

===============

![](https://github.com/fosskers/microlens-aeson/workflows/Tests/badge.svg)

[![Hackage](https://img.shields.io/hackage/v/microlens-aeson.svg?style=flat)](https://hackage.haskell.org/package/microlens-aeson)

[![Stackage Nightly](http://stackage.org/package/microlens-aeson/badge/nightly)](http://stackage.org/nightly/package/microlens-aeson)

[![Stackage LTS](http://stackage.org/package/microlens-aeson/badge/lts)](http://stackage.org/lts/package/microlens-aeson)

`microlens-aeson` provides Traversals for the

[Aeson](http://hackage.haskell.org/package/aeson) library's `Value` type,

while obeying the `Traversal` laws.

`microlens-aeson` is derived from `lens-aeson`, but is based upon `microlens`

to reduce the amount of dependencies involved.

Here is the dependency graph for `lens-aeson`:

![lens-aeson dependencies](lens-aeson.png)

And that for `microlens-aeson`:

![microlens-aeson dependencies](microlens-aeson.png)

Usage

-----

`microlens-aeson` provides Traversals into both lazy and strict variants

of all the text types. Here are some examples:

```haskell

{-# LANGUAGE OverloadedStrings #-}

import Data.Aeson

import Data.Text (Text)

import Lens.Micro

import Lens.Micro.Aeson

--------------------------

-- Manipulating primatives

--------------------------

-- | Optionally getting one value

a :: Maybe Int

a = ("37" :: Text) ^? _Integer  -- Just 37

-- | Setting one value within encoded JSON

b :: Text

b = ("true" :: Text) & _Bool .~ False  -- "false"

----------------------

-- Manipulating arrays

----------------------

-- | Get all values as an Aeson type.

c :: [Value]

c = ("[1, 2, 3]" :: Text) ^.. values  -- [Number 1.0, Number 2.0, Number 3.0]

-- | Get all values cast to some simpler number type.

d :: [Double]

d = ("[1, 2, 3]" :: Text) ^.. values . _Double  -- [1.0, 2.0, 3.0]

-- | Access a specific index, and set a `Value` directly.

e :: Text

e = "[1,2,3]" & nth 1 .~ Number 20  -- "[1,20,3]"

-----------------------

-- Manipulating objects

-----------------------

-- | Access all values of the key/value pairs.

f :: Text

f = "{\"a\":4,\"b\":7}" & members . _Number %~ (*10)  -- "{\"a\":40,\"b\":70}"

-- | Access via a given key.

g :: Maybe Value

g = ("{\"a\": 100, \"b\": 200}" :: Text) ^? key "a"  -- Just (Number 100.0)

-----------------------------------

-- Aeson `Value`s from encoded JSON

-----------------------------------

h :: Maybe Value

h = ("{\"a\":4,\"b\":7}" :: Text) ^? _Value

-- Just (Object (fromList [("a",Number 4.0),("b",Number 7.0)]))

```

See the Haddock documentation for a full API specification.

Migration from Data.Aeson.Lens

------------------------------

The functions provided here are Traversals, not Prisms, therefore

creation of encoded JSON from Haskell types like:

```haskell

>>> _Bool # True :: String

"true"

```

is no longer possible. Otherwise, if your use cases are strictly like

those listed in the Usage section above, then you need only to switch

the import from `Data.Aeson.Lens` to `Lens.Micro.Aeson`.