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>2. got amazing, highly flexible and generalized iterator and monad support (you can use iterator methods on monads), basically second only to Haskell itself, t

>2. got amazing, highly flexible and generalized iterator and monad support (you can use iterator methods on monads), basically second only to Haskell itself, that compiles down to the equivalent of hand written assembly code loops As I understand it, Rust lacks do-notation and higher-kinded types, making it hard to have true monads in Rust. Scala would be the language with monad support comparable to Haskell.

logicprog 3y ago
I actually had this objection in mind when I wrote that, so thank you for giving me the opportunity to expand on what I meant a little bit. Yes, it is very much true that rust cannot yet represent monads as type classes directly, since it does not have any form of higher kinded types yet — which is the reason why I said second only to Haskell. If it could represent monads directly, than I would have placed it equal to Haskell — as I would have placed scala! But I do think it is important to highlight that it does have pervasive useful monad use in the language, and an interface that allows you to use a very large common set of powerful transformations on them via the iterator trait, and it uses the monads that exist in the language and the ability to use that trait on any monad a lot to increase the power of the language in a way no other language besides ones with superior monad support does that I know of. So I would argue that while it is still second to Haskell, it is still far above almost any other language not equal to Haskell in this respect. Which is what I meant by saying second only to haskell! Also, HKTs are something that the rust team seems to be very actively looking to rectify with an in progress implementation currently available in nightly, so that won't be true for very long.
nicoburns 3y ago
My understanding is that Rust lacks the ability to have a generic Monad abstraction like Haskell and Scala, but that it certainly has monads (e.g Option, Result, Vec, etc). And indeed that even languages like JavaScript have lots of monads (e.g. Promise) it's just that these are likewise not abstractable. I believe that a monad is basically any container that has both a constructor and a flat_map function (and there may be one other requirement that I've forgotten). The special ability that Haskell has is the ability to write code that is generic over any such container.
- nyssos 3y ago
  > (and there may be one other requirement that I've forgotten) `map: forall a b . (a -> b) => (m a -> m b)` and `pure: forall a . a -> m a`, plus some (mostly very natural) compatibility conditions between the three: `flatMap(pure)` does nothing, `map` takes the identity to the identity, etc.

logicprog 3y ago

I actually had this objection in mind when I wrote that, so thank you for giving me the opportunity to expand on what I meant a little bit. Yes, it is very much true that rust cannot yet represent monads as type classes directly, since it does not have any form of higher kinded types yet — which is the reason why I said second only to Haskell. If it could represent monads directly, than I would have placed it equal to Haskell — as I would have placed scala! But I do think it is important to highlight that it does have pervasive useful monad use in the language, and an interface that allows you to use a very large common set of powerful transformations on them via the iterator trait, and it uses the monads that exist in the language and the ability to use that trait on any monad a lot to increase the power of the language in a way no other language besides ones with superior monad support does that I know of. So I would argue that while it is still second to Haskell, it is still far above almost any other language not equal to Haskell in this respect. Which is what I meant by saying second only to haskell! Also, HKTs are something that the rust team seems to be very actively looking to rectify with an in progress implementation currently available in nightly, so that won't be true for very long.

nicoburns 3y ago

My understanding is that Rust lacks the ability to have a generic Monad abstraction like Haskell and Scala, but that it certainly has monads (e.g Option, Result, Vec, etc). And indeed that even languages like JavaScript have lots of monads (e.g. Promise) it's just that these are likewise not abstractable. I believe that a monad is basically any container that has both a constructor and a flat_map function (and there may be one other requirement that I've forgotten). The special ability that Haskell has is the ability to write code that is generic over any such container.

nyssos 3y ago
> (and there may be one other requirement that I've forgotten) `map: forall a b . (a -> b) => (m a -> m b)` and `pure: forall a . a -> m a`, plus some (mostly very natural) compatibility conditions between the three: `flatMap(pure)` does nothing, `map` takes the identity to the identity, etc.