never executed always true always false

    1 module HelVM.HelMA.Automata.Piet.Types.Hue
    2   ( Hue (..)
    3   , calculate
    4   , hueChange
    5   ) where
    6 
    7 import           HelVM.HelMA.Automata.Piet.Types.Extra
    8 
    9 calculate ∷ Maybe Hue → Maybe Hue → Maybe Int
   10 calculate (Just x) (Just y) = Just $ (fromEnum y - fromEnum x + 6) `mod` 6
   11 calculate _        _        = Nothing
   12 
   13 hueChange ∷ Hue → Hue → Hue
   14 hueChange = changeDiff 6
   15 
   16 data Hue
   17   = Red
   18   | Yellow
   19   | Green
   20   | Cyan
   21   | Blue
   22   | Magenta
   23   deriving stock (Bounded, Enum, Eq, Ord, Read, Show)