Someone who knows #Haskell and ML: is there a writeup somewhere explaining how first-class modules (a la ML) can do similar things to Haskell type classes? I'm finding it hard to figure that out.
To give a more concrete case: suppose I wanted to write something like Control.Applicative, which provides an 'interface' Applicative with some methods, as well as functions that work for any Applicative. How would I do this with ML-style first-class modules?
@koz I would like to see such a comparison post too. In the meantime I found this stackoverflow question which contains a way to do it using an ML functor: https://stackoverflow.com/questions/48989663/monads-and-sml-modules. The obvious downside is that you have to explicitly state which monad to use at some point.
Another lesser known difference is that I believe you can't instantiate an ML signature with a polymorphic type. For example you can't write an instance of that MAPPABLE signature for a type like Map k v. At least not such that it is still polymorphic over the key type k.
@koz Not quite your case, but “The next 500 module systems” paper gives a nice overview of the problem, bridging modules, type classes and records (and scopes!).
Best tip I have is to pay more attention to the 'forall's. Compose / . / <<< "fixes" the 'forall', which can cause type checking to fail elsewhere or, if "a" is higher-rank, there (it forces "b" to be monomorphic; higher-rank "a" might require a polymorphic "b'). Application / '$' (in GHC) doesn't "fix" the forall.
I think the difference might be "deeper", but for me it's able where the "choice" for the forall is made.
I'm going to return to #haskell after a very long time. Back then, the #cabal hell was excruciating. But now, thanks to #nix, setting up a project is like two seconds from the time you decide to create it to the point you start coding.
@lxsameer Not really dependent on Nix, I'd say. You can use Nix if you want to, sure, but also cabal(-install) itself is much better than it used to be.
I think the only thing that needs to be done is to come up with a clever type class that does some flipping for you, based on the arguments. It’s not entirely trivial but might work. #haskell
I've been trying to make this work for a few days and finally I achieved it, the most basic form of a wayland client using unix sockets, and well in other languages it was not difficult at all, I did it in hare, c, typescript (deno), and in the end I wanted to try with a language that I had never used, Haskell, and I learned many things but I still don't know what a monod is, anyway, here I leave a link to the code for those who are interested: https://gitlab.com/-/snippets/3711372 #haskell#programming#wayland
"Duality" is the idea that two concepts are "similar but opposite" in some precise sense. The discovery of a duality enables us to use our understanding of one concept to help us understand the dual concept, and vice versa. It is a powerful technique in many disciplines, including computer science. In this episode of the Haskell...
Well-Typed is releasing the materials for my video-based #Haskell intro course to the public, starting today and continuing over the next few weeks. Initially, parts 1 (Introduction) and 2 (Datatypes and Functions) are available.
Great to see this effort on improving template #Haskell! I think that figuring out why people don’t use quotes more is partly answered by the volume of deficiencies already identified. When you find that a quote doesn’t do something you need, it’s not totally uncommon to switch away from them altogether. https://informal.codes/posts/stabilising-th/
This is the second of a two-part series of blog posts focused on GHC’s specialization optimization. Part 1 acts as a reference manual documenting exactly how, why, and when specialization works in GHC. In this post, we will finally introduce the new tools and techniques we’ve developed to help us make more precise,...
"A strict binding (with a top level !) should not be thought of as a regular pattern binding that happens to have a bang pattern [...] on the LHS. Rather, the top level ! should be considered part of the let-binding, rather than part of the pattern."
I didn't know about this distinction! Found out about it when fiddling with linear let-bindings in GHC 9.10.1.
Removing the reexports from mtl was, while I really like it conceptually, quite the breaking change, apparently it had become a habit in my team to just import Control.Monad.Except to get access to Control.Monad and Control.Monad.IO.Class… On that note: why’s there no Control.Monad.IO, why do I have to type .Class all the time.
