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> It doesn't do higher-kinded polymorphism, no. That's what I referred to. > ... The point is that you can't leverage all the existing monad/functor/applicat

• louthy 11y ago
  > all the existing monad/functor/applicative/free/yoneda... libraries out there–they don't exist Agreed. I can only hope one day that the CLR team decide it's a reasonable thing to support so that C# (and F#) can both support it. It seems to be the blockage to the language teams (they won't move without it, even if they could implement it in a weaker/slower way on top of the existing type system). I've jumped through many hoops to get as much of a functional 'base class library' as possible in C# (I needed it for a very large C# project I maintain and want to bring more stability to), but language support would be preferred.
• daxfohl 11y ago
  Just out of curiosity what kind of reusable monad libraries are out there for Scala/Haskell? Given the scope of everything between Maybe and IO, I've never understood what one could make that would be useful to "monads" in general (beyond the sugar for do-notation).
  • runT1ME 11y ago
    https://github.com/scalaz/scalaz https://github.com/scalaz/scalaz Monad Transformers for one. Traverse/Sequence are another super common (amazing) pattern that requires abstracting over types. http://eed3si9n.com/learning-scalaz-day12 http://eed3si9n.com/learning-scalaz-day12 is a nice tutorial series on it.
    • louthy 11y ago
      Monad transformers in C# [1] (but yes, only works with the monads in the library) [1] https://github.com/louthy/language-ext/blob/master/LanguageExt.Tests/OptionTTests.cs https://github.com/louthy/language-ext/blob/master/LanguageE...
    • daxfohl 11y ago
      Ah, light bulb moment (perhaps). So in F# I've been using specialized asyncSeq and asyncMaybe libraries. With monad transformers (and thus HKT's), would those come largely for free? And you could traverse a list<maybe<list<_>> combo like [Some [Some [1; 2]; None; Some [3]]; None; Some [None; Some [4]]] with no more difficulty than a regular list-of-lists?
      • runT1ME 11y ago
        Exactly! You can also write a generic "sequence" over a list, for instance, so that any 'monad' (task/future, maybe/option, state, either/disjunction etc.) can 'swap places'. So your List<Future<A>> can become Future<List<A>>. But you only need to write it once. Then it doesn't matter what the inner type of the List is, as long as it's a monad (applicative, really, but all monads are applicatives).
        • daxfohl 11y ago
          Crazy, I'd always considered monad transformers a sore thumb on, well, all that stuff. The fact that monads weren't enough but then you had to go reproduce all that stuff in monad transformers as well. The whole thing just reeked of code duplication and bad smells so I didn't really look into it further. Now looking at the Scalaz impl, the transformers are actually the core thing, and monads themselves are just transformers over Identity. So it all fits and isn't redundant. Certainly changes a lot of perspective.
          • daxfohl 11y ago
            That said, I'd still put LINQ as 99% of "the deal" per the original comment. The extra abstractions allowed by HKT's, while "necessary" mathematically, still only save me about 1% of the work required to implement asyncSeq and asyncMaybe, and in 15 years of pro experience those are the only real uses of HKT's I've ever had the need for.
  • chongli 11y ago
    For one example, in Haskell, all Monads are also Functors. This means you can `fmap` a function over a Maybe Foo just as you would over a [Foo] (read list of Foo) or Vector Foo or indeed an IO Foo.
  • tome 11y ago
    lens, for example (which is not really a "reusable monad library" but very much of that flavour).