tyro

tyro is a dependently typed JSON parsing library, that provides a quick way to create JSON parsers by deriving them from a type level description of the position of the value to be obtained. It provides some of the same functionality as Aeson lenses, but derives the parsers from types rather than doing a generic parse and applying prisms. This was mostly an experiment in dependent typing.

Examples

Type driven interface

{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE TypeOperators #-}

import Data.Tyro
import Data.Aeson (decode)
import qualified Data.ByteString.Lazy as B

json = "{\"key1\":[{\"key2\":41},{\"key2\":42}]}" :: B.ByteString

-- Extract [41, 42] inside the Tyro types
parsed = decode json :: Maybe ("key1" >%> List ("key2" >%> Extract Integer))

-- We can dispose of the types using unwrap
values :: Maybe [Integer]
values = fmap unwrap parsed

Value driven interface (experimental)

The value driven interface is still experimental, and in the process of being refined.

{-# LANGUAGE OverloadedStrings #-}
import Data.Tyro

json = "{\"key1\": {\"key2\" :  [41, 42]}}" :: B.ByteString

-- Extract [41, 42] inside the JSON
parsed = json %%> "key1" >%> "key2" >%> extract :: Maybe [Integer]