mycroftholmessGolang be like
I wonder what portion of all go code written is
if err != nil { return err }
It’s gotta be at least 20%
Swift and Rust have a far more elegant solution. Swift has a pseudo throw / try-catch, while Rust has a Result<> and if you want to throw it up the chain you can use a ? notation instead of cluttering the code with error checking.
The exception handling question mark, spelled
? and abbreviated and pronounced eh?, is a half-arsed copy of monadic error handling. Rust devs really wanted the syntax without introducing HKTs, and admittedly you can’t do foo()?.bar()?.baz()? in Haskell so it’s only theoretical purity which is half-arsed, not ergonomics.
NevoicNote: Lemmy code blocks don’t play nice with some symbols, specifically < and & in the following code examples
This isn’t a language level issue really though, Haskell can be equally ergonomic.
The weird thing about ?. is that it’s actually overloaded, it can mean:
- call a function on
A?that returnsB? - call a function on
A?that returnsB
you’d end up with B? in either case
Say you have these functions
toInt :: String -> Maybe Int double :: Int -> Int isValid :: Int -> Maybe Intand you want to construct the following using these 3 functions
fn :: Maybe String -> Maybe Intin a Rust-type syntax, you’d call
str?.toInt()?.double()?.isValid()in Haskell you’d have two different operators here
str >>= toInt <&> double >>= isValidhowever you can define this type class
class Chainable f a b fb where (?.) :: f a -> (a -> fb) -> f b instance Functor f => Chainable f a b b where (?.) = (<&>) instance Monad m => Chainable m a b (m b) where (?.) = (>>=)and then get roughly the same syntax as rust without introducing a new language feature
str ?. toInt ?. double ?. isValidthough this is more general than just Maybes (it works with any functor/monad), and maybe you wouldn’t want it to be. In that case you’d do this
restricting it to only maybes could also theoretically help type inference.
I was thinking along the lines of “you can’t easily get at the wrapped type”. To get at b instead of Maybe b you need to either use do-notation or lambdas (which do-notation is supposed to eliminate because they’re awkward in a monadic context) whereas Rust will gladly hand you that b in the middle of an expression, and doesn’t force you to name the point.
Or to give a concrete example, if foo()? {…} is rather awkward in Haskell, you end up writing things like
, though of course baz is completely generic and can be factored out. I think I called it “cap” in my Haskell days, for “consequent-alternative-predicate”.
Flattening Functors and Monads syntax-wise is neat but it’s not getting you all the way. But it’s the Haskell way: Instead of macros, use tons upon tons of trivial functions :)