An exmple of a simple Haskell that has a small bug

Main.hs

{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE DeriveGeneric #-}

-- This file will not compile - there is a small error you need to fix. 
-- Follow the guidelines about how to set up a new stack project and copy 
-- this file, then run stack build to try and compile.

-- To have the dependencies available you have to add this fragment to the package.yaml of
-- your stack project:
-- - aeson
-- - bytestring

module Main where

import Prelude hiding (readFile)
import Data.ByteString.Lazy (readFile)
import Data.Aeson
import GHC.Generics

data Person = MkPerson {
  firstName :: String
  , lastName :: String
  , interests :: [String]
  }
  deriving (Show, Eq, Generic)

instance ToJSON Person
instance FromJSON Person

readAndDecode :: FilePath -> (Either String Person)
readAndDecode path = do
  content <- readFile path
  return (eitherDecode content :: Either String Person)

main = do
  result <- readAndDecode "test.json"
  putStrLn (show result)