4 ms·
> Scala's for/yield has surprising behaviour ... because it doesn't have a categorical grounding Not sure what you're talking about, but for/yield is syntactic
by bad_user 9y ago
> Scala's for/yield has surprising behaviour ... because it doesn't have a categorical grounding
Not sure what you're talking about, but for/yield is syntactic sugar for map/flatMap, just like the "do notation" is in Haskell. Of course it has theoretical grounding, because it wouldn't work without flatMap being the monadic bind.
> mixing lists and sets
Again, not entirely sure what you're talking about, but if true, it's entirely unrelated to for/yield.
- JD557 9y agoI believe that he's referring to the fact that Scala's Set is not a monad, so it "shouldn't" have a .flatMap operation. Scala has other containers that have a .flatMap operation that are not real monads, such as Future and Try. That can lead to surprising behavior on for/yeld loops. Disclaimer: I do work in Scala and enjoy the language.
- lmm 9y agoI mean if you write something like: (for { x <- List(1, 1, 1) y <- Set(x) z <- List(y, y) } yield z).length the answer will be rather surprising, because in Scala for/yield is not necessarily monadic.
- ionforce 9y agoIt's only surprising if you ascribe monadic properties to that syntax versus understanding it as literal syntactic sugar and absolutely nothing else.
- clhodapp 9y agoI would say: it is `Set` and `List` that are wrong in that example, not `for`. That said, `for` really does have some issues (enter https://github.com/oleg-py/better-monadic-for/blob/master/README.md https://github.com/oleg-py/better-monadic-for/blob/master/RE...)