never executed always true always false

    1 module Data.ReversedList where
    2 
    3 {-|
    4 ReversedList can be used to avoid accidentally forgetting to reverse a list
    5 (this most commonly occurs when implementing recursive algorithms that build up a
    6 list that needs to be reversed in the termination case).
    7 -}
    8 
    9 newtype Reversed a = Reversed [a]
   10 
   11 
   12 empty :: Reversed a
   13 empty =
   14     Reversed []
   15 
   16 
   17 push :: a -> Reversed a -> Reversed a
   18 push a (Reversed list) =
   19     Reversed (a : list)
   20 
   21 
   22 isEmpty :: Reversed a -> Bool
   23 isEmpty (Reversed []) = True
   24 isEmpty _ = False
   25 
   26 
   27 toList :: Reversed a -> [a]
   28 toList (Reversed list) =
   29     reverse list