Which is awfully similar to Haskell's Maybe. Ignoring boilerplate and comments, the entire module is just [0]: data Maybe a = Nothing | Just a deriving (

Which is awfully similar to Haskell's Maybe. Ignoring boilerplate and comments, the entire module is just [0]: data Maybe a = Nothing | Just a deriving ( Eq, Ord ) And the deriving line isn't really nessasary. The Monad module is larger and contains code specific to Maybe [1]: instance Monad Maybe where (Just x) >>= k = k x Nothing >>= _ = Nothing (>>) = (*>) fail _ = Nothing (Only the first 2 lines are needed. The 3rd is an optimization, the 4th is a historical wart that will be removed in future versions (moved to MonadFail) [0] https://hackage.haskell.org/package/base-4.12.0.0/docs/src/GHC.Maybe.html#Maybe https://hackage.haskell.org/package/base-4.12.0.0/docs/src/G... [1] https://hackage.haskell.org/package/base-4.12.0.0/docs/src/GHC.Base.html#line-854 https://hackage.haskell.org/package/base-4.12.0.0/docs/src/G...