> You could invent a total different implementation for the list monad, for the maybe monad, etc (if you respect the laws).
Could you show such a different implementation for either list or maybe?
Could you show such a different implementation for either list or maybe?
newtype HeadList a = HeadList { getHeadList :: [a] }
instance Monad HeadList where
return a = HeadList [a]
m >>= f = HeadList $ fmap (head . getHeadList . f) (getHeadList m)
But you could imagine putting any function that returns one result. min max avg normalize, etc
-- const [] for a HeadList
quux :: a -> HeadList a
quux = HeadList . (const [])
*Main> HeadList "hello... no wait" >>= quux
HeadList {getHeadList = "*** Exception: Prelude.head: empty list