October 2019 - Haskell-Cafe

Re: [Haskell-cafe] Publish slides of talks in HIW 2019 (Or whom to ask about it)
by Yuji Yamamoto 07 Oct '19

07 Oct '19

Confirmed my profile and the link to the slides. Thanks! 2019年10月7日(月) 19:10 niki.vazou <niki.vazou(a)imdea.org>: > Hi Yuji, Richard, > > Yuji, I added the link to your lightning talk here: > https://icfp19.sigplan.org/home/hiw-2019#event-overview > > I did not collect links for the slides this year, but if more speakers > want to share their slides, will be happy to upload them. > > Best, > Niki > > > On 02.10.2019 10:59, Richard Eisenberg wrote: > > I have cc'd Niki Vazou, the chair of this year's HIW. She'll have the > > best answers. > > > > Richard > > > >> On Oct 2, 2019, at 2:39 AM, Yuji Yamamoto > >> <whosekiteneverfly(a)gmail.com> wrote: > >> > >> Hello Haskellers, > >> > >> I'm not sure where is the best place to ask about this, > >> so please tell me if there is better place. > >> > >> Does anyone know when the slides of HIW 2019 will be published in > >> the web site [1] like the last year's [2]? > >> I see some of the talks are "File Attached", but most of them are > >> not. > >> > >> In addition, can I attach the URL of my lightning talk slides > >> https://the.igreque.info/slides/2019-08-23-indexed-applicative.html > >> to the web site? > >> > >> According to the last year's page, some of the lightning talks are > >> also "File Attached" or "Media Attached". > >> > >> Thanks in advance! > >> > >> -- > >> > >> 山本悠滋 > >> twitter: https://twitter.com/igrep > >> GitHub: https://github.com/igrep > >> GitLab: https://gitlab.com/igrep > >> Facebook: http://www.facebook.com/igrep > >> _______________________________________________ > >> 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. > > > > > > > > Links: > > ------ > > [1] https://icfp19.sigplan.org/home/hiw-2019#program > > [2] https://icfp18.sigplan.org/track/hiw-2018-papers#event-overview > -- 山本悠滋 twitter: https://twitter.com/igrep GitHub: https://github.com/igrep GitLab: https://gitlab.com/igrep Facebook: http://www.facebook.com/igrep

2 1

Problematic fixed "stack ghci" temporary script (parent) directory
by Viktor Dukhovni 06 Oct '19

06 Oct '19

When I run "stack ghci", an attempt is made to create a temporary directory named: /tmp/haskell-stack-ghci/<unique-subdir> in which various temporary artefacts are stored. The parent directory is created with permissions (0777 & ~umask). Security issues aside, this can't work reliably on a multi-user system. Does anyone know whether this is something peculiar to my FreeBSD setup, or a systemic issue with "stack ghci"? I don't see the same behaviour with "stack script", though if I create a script to run in "/tmp", then ghc is, somewhat unexpectely, executed with "-i/tmp/", which also has security implications... -- Viktor.

3 4

hie + neovim + coc.nvim on NixOS
by Marc Busqué 05 Oct '19

05 Oct '19

Hi Cafe, this is an adapted version of a question I already posted on NixOS discussion forum, so far with no luck [1]: I’m trying to replicate the configuration from an article on a NixOS machine [2]. That’s, I’m trying to use hie on neovim, through coc.nvim, with NixOS as operating system. For now, I want it to work for a project which uses GHC 8.6.5 through Stack. So far I’ve been able to: - Install hie version for GHC 8.6.5: ``` let all-hies = import (fetchTarball "https://github.com/infinisil/all-hies/tarball/master") {}; in { environment.systemPackages = with pkgs; [ (all-hies.selection { selector = p: { inherit (p) ghc865; }; }) ]; ``` - Install neovim 4.x to have floating window feauture, which is only available in master, as far as I know: ``` let nixPkgsMaster = import (fetchTarball "https://github.com/NixOS/nixpkgs/tarball/master") {}; in { environment.systemPackages = with pkgs; [ nixPkgsMaster.neovim ]; } ``` - I configured coc.nvim [3] to use hie, together with `haskell-vim` plugin. I'm using Plug for this: ``` Plug 'neoclide/coc.nvim', { 'do': 'yarn install --frozen-lockfile' } Plug 'neovimhaskell/haskell-vim' ``` And I have configured coc.nvim as its documentation suggests [4]. - I found that having hie for GHC 8.6.5 was not enough and that I had to install manually the compiler for 8.6.5. I think it is needed in NixOS. If I’m wrong, please, tell me. So, I added `haskell.compiler.ghc865` in `environment.systemPackages`. - Besides, I have following haskell tools: `haskellPackages.hlint`, `haskellPackages.apply-refact` and `haskellPackages.hindent`. With all of that, hie is somehow working on neovim, but there are a lot of things missing. For example, one thing that is working is `:call CocAction('format')`. It also points me to some hlint warnings underlying their lines. However, there are a lot of functionalities missing. - Autocompletion is anything but intellisense. - I can’t quickfix hlint warnings. It says `[coc.nvim] No quickfix action available` - Trying to rename returns `[coc.nvim] Error on 'rename': rename: "HaRe: file not loaded for refactoring"` - It gives me no type information when I press K on a word (being K mapped as coc.nvim suggests) I think that my NixOS configuration is the culprit here, because I’m not too experienced with it and I see it needs to be very specific when configuring haskell. I’m wondering if I’m missing some extra haskell package. I tried with `haskell.packages.ghc865.hoogle` hoping it would make a difference in showing me types or documentation, but no luck here. Thanks for any insight you can give me. - [1] https://discourse.nixos.org/t/configuration-needed-for-haskell-ide-environm… - [2] http://marco-lopes.com/articles/Vim-and-Haskell-in-2019/ - [3] https://github.com/neoclide/coc.nvim - [4] https://github.com/neoclide/coc.nvim#example-vim-configuration Marc Busqué http://waiting-for-dev.github.io/about/

1 0

Parametric polymorphism and promoted types
by Marcin Szamotulski 04 Oct '19

04 Oct '19

Hello Haskell Cafe, It seems that GHC has a trouble recognising that a variable of type `forall (x :: (a, b))` can be reduced to `forall ((u, v) :: (a, b))`. For example in the following snippet `unsafeCoerce` is unavoidable: ``` data P a = P data Proxy (p :: (a, b)) where Proxy :: P a -> P b -> Proxy '(a, b) both0 :: forall (s :: (a, b)). Proxy s both0 = unsafeCoerce (Proxy P P) ``` A slightly nicer solution can be written with type families: ``` type family Fst (p :: (a, b)) :: a where Fst '(x, y) = x type family Snd (p :: (a, b)) :: b where Snd '(x, y) = y data Dict (a :: k) (b :: k) where Dict :: a ~ b => Dict a b instance Category Dict where id = Dict Dict . Dict = Dict proof :: forall (s :: (a, b)). Dict s '(Fst s, Snd s) proof = unsafeCoerce Dict both1 :: forall (s :: (a, b)). Proxy s both1 = case proof :: Dict s '(Fst s, Snd s) of Dict -> Proxy P P ``` Did I missed how to avoid `unsafeCoerce` all together? Best regards, Marcin Szamotulski

4 4

LGtk
by Seph Shewell Brockway 04 Oct '19

04 Oct '19

Does anyone know what happened to the LGtk project? I really like its declarative approach to writing GUIs, but it doesn’t seem to be being actively maintained. -- Seph Shewell Brockway, BSc MSc (Glas.) Pronouns: she/her

1 0

Publish slides of talks in HIW 2019 (Or whom to ask about it)
by Yuji Yamamoto 02 Oct '19

02 Oct '19

Hello Haskellers, I'm not sure where is the best place to ask about this, so please tell me if there is better place. Does anyone know when the slides of HIW 2019 will be published in the web site <https://icfp19.sigplan.org/home/hiw-2019#program> like the last year's <https://icfp18.sigplan.org/track/hiw-2018-papers#event-overview>? I see some of the talks are "File Attached", but most of them are not. In addition, can I attach the URL of my lightning talk slides https://the.igreque.info/slides/2019-08-23-indexed-applicative.html to the web site? According to the last year's page, some of the lightning talks are also "File Attached" or "Media Attached". Thanks in advance! -- 山本悠滋 twitter: https://twitter.com/igrep GitHub: https://github.com/igrep GitLab: https://gitlab.com/igrep Facebook: http://www.facebook.com/igrep

2 2

New book: Haskell from the Very Beginning
by John Whitington 01 Oct '19

01 Oct '19

Hello, I've prepared a new book "Haskell from the Very Beginning", which has now been published. A printed copy may be obtained from Amazon for $29.99: https://www.amazon.com/dp/095767113X/ (or your equivalent local Amazon) Alternatively, a PDF copy may be obtained for $19.99 from the book's website: https://www.haskellfromtheverybeginning.com Thanks to all those who have helped in recent weeks with useful comments on an earlier draft. And of course, thank-you for Haskell! Here's the blurb: In Haskell from the Very Beginning John Whitington takes a no-prerequisites approach to teaching the basics of a modern general-purpose programming language. Each small, self-contained chapter introduces a new topic, building until the reader can write quite substantial programs. There are plenty of questions and, crucially, worked answers and hints. Haskell from the Very Beginning will appeal both to new programmers, and to experienced programmers eager to explore functional languages such as Haskell. It is suitable both for formal use within an undergraduate or graduate curriculum, and for the interested amateur. Thanks, -- John Whitington Director, Coherent Graphics Ltd

1 0

hackage issues
by Richard Senington 01 Oct '19

01 Oct '19

Hi list, I have been trying to set up an account on Hackage to upload a project. I have created the account, but cannot get in contact with trustees to enable uploading. My mail servers (a university server) says that it cannot deliver the messages. Can anyone advise or assist? Richard

2 1