mmap.hs

-- what does this function do?

someFn :: (a -> b) -> [a] -> [b]

-- map!

map :: (a -> b) -> [a] -> [b]

-- not only lists are mappable

data Maybe a = Totes a | Nada

mapMaybe :: a -> b -> Maybe a -> Maybe b
mapMaybe f (Totes x) = Totes (f x)
mapMaybe f Nada      = Nada

-- abstraction \o/

class Mappable m where
  mmap :: (a -> b) -> m a -> m b

instance Mappable List where
  mmap = map

instance Mappable Maybe where
  mmap f (Totes x) = Totes (f x)
  mmap f Nada      = Nada

-- what do we know about this function without looking at implementations?

someFn :: Mappable m, Num a => m a => m a

-- either it returns its input or it applies a numerical operation to all items contained in it

-- e.g.:

someFn stuff = mmap (*2) stuff

maybe i could reverse things and start with the desired function type

how about adding Joinable?

class Joinable j where
  join :: j (j a) -> j a

and then? hm.