never executed always true always false

    1 module HelVM.HelMA.Automaton.WrapTokenList where
    2 
    3 import qualified Text.Read
    4 import qualified Text.Show
    5 
    6 newtype WrapTokenList a
    7   = WrapTokenList { unWrapTokenList :: a }
    8   deriving stock (Eq)
    9 
   10 ----
   11 
   12 instance Show a ⇒ Show (WrapTokenList [a]) where
   13   show (WrapTokenList tokens) = show =<< tokens
   14 
   15 instance Read a ⇒ Read (WrapTokenList [a]) where
   16   readsPrec _ source = [( WrapTokenList $ maybeToList . readMaybe . one =<< source , "")]