Aeson Convert Array to Object

Question

What is the best way Data.Aeson FromJSON instance Convert Array to Object:

import Data.Aeson

data MixArray = MixArray {                                                                                                                                                                                         
  vStr :: String,                                                                                                                                                                                                   
  vNum :: Int,
  vBool :: Bool                                                                                                                                                                                                  
} deriving Show   

main = do
  jsonStr = ["a",1,true]
  mix <- eitherDecode $ jsonStr :: IO (Either String [MixArray])
  show mix

to:

MixArray { vStr = "a", vNum = 1, vBool= true}

Answer 1

You can reuse the FromJSON instance for lists and the Value type, and then construct your type after pattern matching. If the pattern match fails, the parser will fail.

import Data.Text (unpack)

instance FromJSON MixArray where
  parseJSON jsn = do
    [String s, Number n, Bool b] <- parseJSON jsn
    return MixArray { vStr = unpack s, vNum = truncate n, vBool = b }