GetIn.hs

{-# LANGUAGE OverloadedStrings #-}

module GetIn where

import Data.Aeson          ( Value( Array
                                  , Null
                                  , Object
                                  )
                           , decode
                           )
import Data.HashMap.Strict ( lookupDefault )
import Data.List           ( foldl' )
import Data.Maybe          ( fromMaybe )
import Data.Text           ( Text
                           , unpack
                           )
import Data.Vector         ( (!?) )
import Text.Read           ( readMaybe )

getIn :: [Text] -> Value -> Value
getIn = flip . foldl' $ \v k -> case v of
  Object m -> lookupDefault Null k m
  Array  a -> maybe Null (fromMaybe Null . (a !?)) . readMaybe . unpack $ k
  _        -> Null

example :: Value
example = fromMaybe (error "boom") . decode
  $ "{\"a\":{\"b\":{\"c\":[\"foo\",\"bar\",\"baz\"]}}}"

example2 :: Value
example2 = fromMaybe (error "boom") . decode
  $ "{\"a\":{\"b\":{\"c\":[\"foo\",{\"d\":7},\"baz\"]}}}"

-- λ> getIn ["a", "b", "c"] example
-- Array [String "foo",String "bar",String "baz"]

-- λ> getIn ["a", "b", "c", "1"] example
-- String "bar"

-- λ> getIn ["a", "b", "c", "1", "d"] example2
-- Number 7.0