3 ms·

What's the advantage of the Monad approach? Doesn't the render function still have to check whether those Maybes contain values or not?

valenterry 3y ago
If you just have 1 step then there is no advantage. If you have multiple steps then the advantage is that you never have to unpack "in the middle" and you don't have to care - and the compiler has your back. Classical example: show the street number of the user or show <None> if there is no street number. There can be multiple things missing on the way and multiple transformations might happen on the way. E.g. the user might not even have an adress saved alltogether. In that case, you only have to "check whether those Maybes contain values or not" once at the very end.
steeleduncan 3y ago
I dont think there is any advantage when the language lacks syntax level support for Monads. E.g. in Haskell (which does) it would look roughly like: getUser :: Maybe User getUser = ... getFriends :: Maybe [User] getFriends = do user <- getUser let friends = getFriendsForUser user return friends bestFriends :: Maybe [User] bestFriends = do friends <- getFriends let besties = filter isBestFriend friends return besties render :: IO () render = do let bffs = getBestFriends case bffs of Just besties -> renderBestFriends besties Nothing -> renderNoFriends The Maybe monad itself contains the equivalent of runSafely from the article, and the syntax propagates the failure case transparently from getUser down to the choice of render function used. All without either the hassle of handling null cases, or the danger that you might forget to handle them and the code crash. Without syntax level support, its not obviously an improvement to me
- chrischen 3y ago
  It saves you from having to write the null check code for other cases.

valenterry 3y ago

If you just have 1 step then there is no advantage. If you have multiple steps then the advantage is that you never have to unpack "in the middle" and you don't have to care - and the compiler has your back. Classical example: show the street number of the user or show <None> if there is no street number. There can be multiple things missing on the way and multiple transformations might happen on the way. E.g. the user might not even have an adress saved alltogether. In that case, you only have to "check whether those Maybes contain values or not" once at the very end.

steeleduncan 3y ago

I dont think there is any advantage when the language lacks syntax level support for Monads. E.g. in Haskell (which does) it would look roughly like: getUser :: Maybe User getUser = ... getFriends :: Maybe [User] getFriends = do user <- getUser let friends = getFriendsForUser user return friends bestFriends :: Maybe [User] bestFriends = do friends <- getFriends let besties = filter isBestFriend friends return besties render :: IO () render = do let bffs = getBestFriends case bffs of Just besties -> renderBestFriends besties Nothing -> renderNoFriends The Maybe monad itself contains the equivalent of runSafely from the article, and the syntax propagates the failure case transparently from getUser down to the choice of render function used. All without either the hassle of handling null cases, or the danger that you might forget to handle them and the code crash. Without syntax level support, its not obviously an improvement to me

chrischen 3y ago
It saves you from having to write the null check code for other cases.