{-# language LambdaCase #-}

data Choice = ChoiceA | ChoiceB | ChoiceC | ChoiceD deriving Show

choiceToString = \case
  ChoiceA -> "string for A"
  ChoiceB -> "string for B"
  ChoiceC -> "string for C"
  ChoiceD -> "string for D"
  
stringToChoice = \case
  "string for A" -> Right ChoiceA
  "string for B" -> Right ChoiceB
  "string for C" -> Right ChoiceC
  "string for D" -> Right ChoiceD
  unknown -> Left unknown

main = do
  print . stringToChoice $ choiceToString ChoiceA