Lens.Aeson

Lens-Aeson-test.cabal

-- Initial Lens-Aeson-test.cabal generated by cabal init.  For further
-- documentation, see http://haskell.org/cabal/users-guide/

name:                Lens-Aeson-test
version:             0.1.0.0
-- synopsis:
-- description:
license:             MIT
license-file:        LICENSE
author:              cosmo0920
-- maintainer:
-- copyright:
category:            Text
build-type:          Simple
cabal-version:       >=1.8

executable Lens-Aeson-test
  main-is: Main.hs
  -- other-modules:
  build-depends:       base       >= 4.5 && < 5
                     , aeson      >= 0.6
                     , lens       >= 3.9 && < 4
                     , lens-aeson >= 0.1
  extensions: OverloadedStrings
              ExtendedDefaultRules
              NoImplicitPrelude
              CPP
              GADTs

Main.hs

import Data.Aeson (decode, Value)
import Data.Maybe
import Prelude
import Control.Lens
import Control.Lens.Aeson

main :: IO ()
main = do
  fstr <- readFile "test.json"
  let v = fstr :: String
  let a = fstr ^? key "a"
      b = fstr ^? key "b"
  putStrLn $ unlines [ "a value: " ++ (show $ fromJust a)
                     , "b value: " ++ (show $ fromJust b)]

output.log

% ./dist/build/Lens-Aeson-test/Lens-Aeson-test
a value: Number 1
b value: Number 3

test.json

{"a": 1, "b": 3}