extensible/JSON

aesonのFromJSON/ToJSONインスタンスがあらかじめ定義されているため、そのままJSONと相互変換できる。

Main.hs

code: (hs)

{- stack script

--resolver nightly-2018-05-09

--package extensible

--package aeson

--package bytestring

{-# LANGUAGE DataKinds #-}

{-# LANGUAGE TypeOperators #-}

module Main where

import Data.Extensible

import Data.Aeson (eitherDecode)

import qualified Data.ByteString.Lazy as BL (readFile)

import System.Environment (getArgs)

type Config = Record

'[ "name" >: String

, "age" >: Int

]

main :: IO ()

main = do

path <- getArgs

content <- BL.readFile path

case eitherDecode content of

Left e -> putStrLn e

Right json -> print (json :: Config)

config.json

code:_

{

"name": "guchi",

"age": 0

}

実行結果

code:_

$ ./Main.hs config.json

name @= "guchi" <: age @= 0 <: nil