Haskell playground created by essic - https://repl.it/@essic/Haskell-playground

Haskell playground.hs

{-# LANGUAGE NoImplicitPrelude #-}
import Data.List (find)
import Data.Monoid ((<>))
import Data.Either (Either(..))
import Data.Int (Int)
import System.IO (IO,putStrLn)
import Data.String (String)
import Text.Show (show,Show)
import Data.Maybe (maybe)
import Data.Function ( (.), ($))
import Data.Eq ((==))

data Employee =  Employee
  {
    id' :: Int
  }
  
instance Show Employee where
  show e = "manager with id " <> show (id' e)
  
newtype EmployeeResult = EmployeeResult (Either String Employee)

instance Show EmployeeResult where
  show (EmployeeResult (Left a)) = a
  show (EmployeeResult (Right v)) = show v


findManager :: [Employee] -> Employee -> EmployeeResult
findManager es e = 
  maybe (EmployeeResult . Left $ "Could not find " <> show e) (EmployeeResult . Right) (find (\m -> id' m == id' e) es)

inputs = [ Employee 1 , Employee 2 , Employee 3 ]

main :: IO()
main = do
  putStrLn . show $ findManager inputs (Employee 0)
  putStrLn . show $ findManager inputs (Employee 25)
  putStrLn $ "Found " <> show (findManager inputs (Employee 1))