I get it! (Thanks, playing around with actual code helped a ton.) For example, in Typescript you're saying you can add a default value simply: # old fu

I get it! (Thanks, playing around with actual code helped a ton.) For example, in Typescript you're saying you can add a default value simply: # old function f(x: number): number { return 2 * x; } # new function f(x: number|null): number { x = x || 3; return 2 * x; } # usage # old f(2) # new f(2) # still works! But in Haskell this requires changing the call sites: -- old f :: Int -> Int f = (*2) -- new f :: Maybe Int -> Int f = maybe 0 (*2) -- usage -- old f 2 -- new f (Just 2) -- different! But I actually feel this is an antipattern in Haskell (and maybe TypeScript too), and a separate wrapper function avoids refactoring while making things even more user friendly. -- old f :: Int -> Int f = (*2) -- new fMaybe :: Maybe Int -> Int fMaybe = maybe 3 f -- usage -- old f 2 -- new f 2 -- still works! fMaybe Nothing -- works too! Here's some wrappers for general functions (not that they're needed, they're essentially just raw prelude functions): maybeIn :: b -> (a -> b) -> (Maybe a -> b) maybeIn = maybe maybeOut :: (a -> b) -> (a -> Maybe b) maybeOut = fmap Just maybeBoth :: b -> (a -> b) -> (Maybe a -> Maybe b) maybeBoth d = maybeOut . maybeIn d Added bonus, this approach avoids slowing down existing code with the null checks we just added.