Recurisive foldable... more or less

recursive-foldable.hs

{-# LANGUAGE DeriveFoldable #-}

module Main where

import Data.Map (Map)
import qualified Data.Map as Map
import Data.Foldable

data Object a
  = Value a
  | Dictionary (Map String (Object a))
  deriving (Show, Foldable)

obj :: Object String
obj = Dictionary (Map.fromList
  [ ( "Foo"
    , Dictionary (Map.fromList
        [ ("Bar", Value "Baz")
        , ("Qux", Dictionary (Map.fromList [("Qux", Value "BAHHHH")]))
        ])
    )
  ])

main :: IO ()
main = print (foldr (:) [] obj)

-- outputs ["Baz","BAHHHH"]