- Haskell-Cafe - Haskell.org

state monad transformer that adds or combines state
by Dennis Raddle 15 May '18

15 May '18

I find myself using the state and exception monads at large scale in my programs. For instance I often keep a pseudorandom generator as the state, and use exception handling. In local computations, I may want to use some additional state. Is there a way to add a little extra state temporarily? Let's say I have data State1 = State1 StdGen type M1 = State State1 data State2 = State2 State1 Int type M2 = State State2 runM2 :: M2 a -> Int -> M1 a someFunc :: M1 Double someFunc = do r <- <compute something pseudorandomly> r2 <- runM2 (deeperFunc r) 3 <..etc..> deeperFunc :: Double -> M2 Double

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template haskell library for OO-like selector syntax?
by Dennis Raddle 15 May '18

15 May '18

In my current application, I'm really missing the ability from OO to do things like someData.field1.field2 = "foo" What's do I mean? - field selectors are scoped so that names don't clash with each other or global names - this way of selecting data can be used both for reading it, and for updating specific fields of some data deep in a data hierarchy (In Haskell, if using immutable data, this would requiring doing a data update on every level). Any attempt to do this in Haskell, for me anyway, results in an explosion of names and a lot of boilerplate code and a resulting heavy syntax. Is there a way of obtaining OO-like concise syntax, perhaps with Template Haskell? Dennis

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Failing build for HaXml
by Vanessa McHale 15 May '18

15 May '18

Does anyone know how to submit patches for HaXml? The .cabal file does not list any upstream source repo and it's currently breaking with GHC 8.4.2, which in turn breaks cabal-debian. Thanks -- *Vanessa McHale* Functional Compiler Engineer | Chicago, IL Website: www.iohk.io <http://iohk.io> Twitter: @vamchale PGP Key ID: 4209B7B5 Input Output <http://iohk.io> Twitter <https://twitter.com/InputOutputHK> Github <https://github.com/input-output-hk> LinkedIn <https://www.linkedin.com/company/input-output-global>

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GHC TV station?
by Sylvester Hazel 15 May '18

15 May '18

White space in "do notation" is no longer supported by GHC but I had to guess it the hard way seeing my solutions to Hutton's book and then his own code produce "Parse error" and irritating hint "Possibly caused by a missing 'do'?". So, Hutton 2ed is outdated, Haskell Platform is dropped exhausted then perhaps GHC should have a TV station? Fun is best when it can be shared. Regards, Sylvester

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Haskell eXchange 2018 CFP (London, Thursday, 11th - Friday, 12th October)
by Oliver Charles 15 May '18

15 May '18

Hi all, The Haskell eXchange is an annual conference created for and by the Skills Matter community. An opportunity for Haskellers to meet, learn and share skills, discover emerging technologies and help evolve the Haskell ecosystem. Everyone is welcome to join, whether you are an expert or a beginner, whether you are a commercial user, an academic or a hobbyist, we'd love it if you join us this year at the Haskell eXchange! For 2018, we are planning to have three types of sessions: 1. Regular talks (35 minutes) 2. Hands-on workshops (approximately 90 minutes) 3. Lightning talks (5-10 minutes to be determined in the formal confirmation) The Haskell eXchange is a broad conference, and we'll consider anything with a clear Haskell connection. For example, talks about Haskell libraries and applications, experience reports of using Haskell for work, and tutorials on programming techniques are all fantastic proposals - but please feel free to submit anything that you think is interesting. The committee are happy to work with you if you're unsure if your talk is a good fit, and can be reached at haskellx(a)skillsmatter.com Most importantly, we're looking for talks that inspire and educate. If your proposal doesn't fit into any of the above categories, it doesn't matter! To submit, please see the form in https://skillsmatter.com/conferences/10237-haskell-exchange-2018#get_involv… We look forward to your submissions!

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Maintaining cpphs
by Markus Ongyerth 15 May '18

15 May '18

Hi Malcolm, Are you still interested in maintaining cpphs? I have posted an issue to your github tracker [1] (linked at [2]) and didn't get any response in a week. While that's not a terribly long time, the reason for this patch is trickling down to different distributions repositories (arch and debian-sid) which is making it harder for me to support users because of a dependency. If you are not planing to maintain cpphs in future, I'd like to take over the package on hackage. Cheers, ongy [1] https://github.com/malcolmwallace/cpphs/issues/16 [2] http://hackage.haskell.org/package/cpphs

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PSA for Cabal 2.2 new-* users regarding .ghc.environment files
by Gershom B 14 May '18

14 May '18

There is an important change in the cabal new- commands for 2.2 that the release docs should have highlighted more significantly. Cabal new-* commands now produce a .ghc.environment file by default. These files [1] are picked up by ghc and ghci automatically (since 8.0.1), and allow them to operate directly with the same package environment used by the new-* commands. This lets you, for example, run `ghci` in a project where you are using `new-build` and get the proper dependencies in scope. Herbert has written an experimental tool to make it easier to create and manipulate these environments [2]. However: there is a drawback (on which some discussion at [3] and [4]. In particular, there is not good information provided by ghc about when these files are picked up and used. So if you are admixing new-* commands and other commands for the time being, jumping between the two, or admixing ghc and ghcjs, etc., then you may run into unexpected behavior! [5] The simplest solution for now is to delete the local .ghc.environment file in those cases (i.e. where you're mixing commands and get unexpected behavior). A particular gotcha is that these files are picked up not just in the current directory but also in any parent directory. Cheers, Gershom [1] documented at https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/packages.ht… [2] https://github.com/hvr/cabal-env [3] https://github.com/haskell/cabal/issues/4542 [4] https://ghc.haskell.org/trac/ghc/ticket/13753 [5] Error messages may be like ".cabal/store/ghc-8.0.2/package.db/package.cache: openBinaryFile: does not exist (No such file or directory)" or complaints about missing inplace dependencies.

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Re: [Haskell-cafe] Problem with submitting papers for haskell 2018
by Nicolas Wu 14 May '18

14 May '18

Hello Winter, Thanks for getting in touch, I’m glad to hear that you’re preparing a submission to the Haskell Symposium this year. You haven’t missed any deadlines: we’re still reviewing the early track papers and so EasyChair is closed for regular submissions until notifications for those papers are released. This will happen on 18 May 2018. Best wishes, Nick Dr Nicolas Wu Department of Computer Science University of Bristol > On 14 May 2018, at 14:19, Brent Yorgey <byorgey(a)gmail.com> wrote: > > Hi Nick, > > Did you see this message that was sent to haskell-cafe a few hours ago? > > -Brent > > ---------- Forwarded message --------- > From: winter <drkoster(a)qq.com> > Date: Mon, May 14, 2018 at 4:15 AM > Subject: [Haskell-cafe] Problem with submitting papers for haskell 2018 > To: <haskell-cafe(a)haskell.org> > > > Dear all, > > Currently i and my friends @sighingnow are writing a paper on our > new I/O manager based on libuv. We planed to submit it to Haskell 2018, > and according to the official site's info, the deadline should be next > month: https://icfp18.sigplan.org/track/haskellsymp-2018-papers > > But here is my problem, i registered an account on easychair as Haskell > 2019 required and logged in, but when i click the submit link, a page > with following info are provided: > > > Paper submission for Haskell 2018 is closed.,,You seem to have no > previous roles at Haskell 2018, so > you cannot enter its pages. If you > have questions about the conference, please contact Haskell 2018 > chairs. > > What does this mean? Did i miss the submission window? Or do i have to > do some extra preparations? Please help! > > > Cheers~ > > Winter > > > > _______________________________________________ > Haskell-Cafe mailing list > To (un)subscribe, modify options or view archives go to: > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe > Only members subscribed via the mailman list are allowed to post.

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Current state of dependent types in Haskell
by Serguey Zefirov 14 May '18

14 May '18

Can anyone kindly point me at blog posts and/or articles on the subject? I would like to brush off my Haskell skills in that area with whatever new things that are hot. I once implemented type-level arithmetic in Haskell for sizing various hardware things but it is ages ago now. I would like to experiment with current state of affairs with type-level arithmetic and possibly experiment with adding structured values into the constraints.

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Problem with submitting papers for haskell 2018
by winter 14 May '18

14 May '18

Dear all, Currently i and my friends @sighingnow are writing a paper on our new I/O manager based on libuv. We planed to submit it to Haskell 2018, and according to the official site's info, the deadline should be next month: https://icfp18.sigplan.org/track/haskellsymp-2018-papers But here is my problem, i registered an account on easychair as Haskell 2019 required and logged in, but when i click the submit link, a page with following info are provided: > Paper submission for Haskell 2018 is closed.,,You seem to have no previous roles at Haskell 2018, so > you cannot enter its pages. If you have questions about the conference, please contact Haskell 2018 > chairs. What does this mean? Did i miss the submission window? Or do i have to do some extra preparations? Please help! Cheers~ Winter

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