October 2021 - Haskell-Cafe

xmonad 0.17.0, xmonad-contrib 0.17.0 released!
by Brandon Allbery 27 Oct '21

27 Oct '21

━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ XMONAD AND XMONAD-CONTRIB 0.17.0 ARE AVAILABLE ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ New versions of xmonad and xmonad-contrib have been released. Check out our [download page] for instructions on where to get them. It's been a little over 3 years since xmonad 0.15, and a little over 2 years since xmonad-contrib 0.16. A lot has happened. This post is an overview of the most important changes. To celebrate this milestone, we would like to announce a contest for a new xmonad logo (see section 3). Last but not least, in section 4 we're looking to raise funds to keep the XMonad project and community alive and relevant in the next decade. With the [final X.Org Server 21.1 release] being announced today, there are some obvious challenges ahead of us. [download page]: <https://xmonad.org/download.html> [final X.Org Server 21.1 release]: <https://lists.x.org/archives/xorg-announce/2021-October/060799.html> 1 xmonad 0.17.0 ═══════════════ This release includes 156 non-merge commits by 22 contributors! For a full summary of all the changes, see [xmonad's CHANGES.md] file. [xmonad's CHANGES.md]: <https://github.com/xmonad/xmonad/blob/v0.17.0/CHANGES.md> 1.1 Major Breaking Changes ────────────────────────── • `util/GenerateManpage.hs' is no longer distributed in the tarball. 1.2 Selected Features and Improvements ────────────────────────────────────── • Migrated `X.L.LayoutCombinators.(|||)' into `XMonad.Layout', providing the ability to directly jump to a layout with the `JumpToLayout' message. • Improved handling of XDG directories. 1. If all three of xmonad's environment variables (`XMONAD_DATA_DIR', `XMONAD_CONFIG_DIR', and `XMONAD_CACHE_DIR') are set, use them. 2. If there is a build script called `build' (see [here] for usage examples) or configuration `xmonad.hs' in `~/.xmonad', set all three directories to `~/.xmonad'. 3. Otherwise, use the `xmonad' directory in `XDG_DATA_HOME', `XDG_CONFIG_HOME', and `XDG_CACHE_HOME' (or their respective fallbacks). These directories are created if necessary. In the cases of 1. and 3., the build script or executable is expected to be in the config dir. Additionally, the xmonad config binary and intermediate object files were moved to the cache directory (only relevant if using XDG or `XMONAD_CACHE_DIR'). • Recompilation now detects `stack.yaml' (can be a symlink) alongside `xmonad.hs' and switches to using `stack ghc'. Additionally, deprecation warnings during recompilation are no longer suppressed. These can still be suppressed manually using an `OPTIONS_GHC' pragma with `-Wno-deprecations'. [here]: <https://github.com/xmonad/xmonad-testing/tree/master/build-scripts> 2 xmonad-contrib 0.17.0 ═══════════════════════ This release includes 582 non-merge commits by 57 contributors! For a full summary of all the changes, see [xmonad-contrib's CHANGES.md] file. [xmonad-contrib's CHANGES.md]: <https://github.com/xmonad/xmonad-contrib/blob/v0.17.0/CHANGES.md> 2.1 Major Breaking Changes ────────────────────────── • All modules that export bitmap fonts as their default • If xmonad is compiled with XFT support (the default), use an XFT font instead. The previous default expected an X11 misc font (PCF), which is not supported in pango 1.44 anymore and thus some distributions have stopped shipping these. • All modules still exporting a `defaultFoo' constructor • All of these were now removed. You can use the re-exported `def' from `Data.Default' instead. • `XMonad.Hooks.StatusBar', `XMonad.Hooks.StatusBar.PP' (previously `XMonad.Hooks.DynamicLog') and `XMonad.Util.Run' • `spawnPipe' no longer uses binary mode handles and defaults to the current locale encoding instead, `xmonadPropLog' and `xmonadPropLog'' now encode their input string in UTF-8, and `dynamicLogString' no longer encodes its output in UTF-8. When these functions are used together, everything should continue to work as it always has, but in isolation behaviour might change. To get the old `spawnPipe' behaviour, `spawnPipeWithNoEncoding' can now be used, and `spawnPipeWithUtf8Encoding' was added as well to force UTF-8 regardless of locale. • `XMonad.Hooks.DynamicLog' will be deprecated soon in favor of `XMonad.Hooks.StatusBar' which offers a nicer and easier to use interface for status bars. Laptop users who (dis)connect external monitors dynamically should definitely try this new interface: `XMonad.Hooks.DynamicBars' has been deprecated already. • `XMonad.Hooks.EwmhDesktops' • It is no longer recommended to use standalone hooks directly: Instead of `ewmhDesktopsStartup', `ewmhDesktopsLogHook(Custom)' and `ewmhDesktopsEventHook(Custom)', users should now use the `ewmh' combinator. The `Custom' variants have been replaced by a [more composable interface] which now also allows simply marking windows that request focus as urgent instead of immediately focusing them. Instead of `fullscreenEventHook', use `ewmhFullscreen', which now advertises fullscreen support to applications, fixing fullscreen in [mpv] and many others. • `XMonad.Hooks.Script' • `execScriptHook' now has an `X' constraint (was: `MonadIO'), due to changes in how the xmonad core handles XDG directories. • `XMonad.Actions.WorkspaceNames' • The type of `getWorkspaceNames' was changed to fit into the new `ppRename' field of `PP'. [more composable interface]: <https://xmonad.github.io/xmonad-docs/xmonad-contrib-0.17.0/XMonad-Hooks-Ewm…> [mpv]: <https://mpv.io/> 2.2 Selected Features and Improvements ────────────────────────────────────── • `XMonad.Actions.EasyMotion' A new module that allows selection of visible screens using a key chord—inspired by [vim-easymotion]. See the animation in the vim-easymotion repo to get some idea of the functionality of this EasyMotion module. • `XMonad.Prompt.OrgMode' A prompt for interacting with [org-mode]. It can be used to quickly save TODOs, NOTEs, and the like with the additional capability to schedule/deadline a task, or use the primary selection as the contents of the note. • `XMonad.Hooks.StatusBar' A new module, providing a nicer, composable interface for status bars that replaces `XMonad.Hooks.DynamicLog' and `XMonad.Hooks.DynamicBars'. Supports property-based as well as pipe-based status bars, multiple status bars (Xinerama), and takes care of restarting the bars as needed. • `XMonad.Hooks.Rescreen' A new module, providing custom hooks for screen (xrandr) configuration changes. These are used internally by `XMonad.Hooks.StatusBar' to restart status bars/systrays after xrandr, and can also be used to invoke xrandr or autorandr when an output is (dis)connected. • `XMonad.Util.Hacks' A collection of hacks and fixes that should be easily accessible to users, like a fix for the fullscreen behaviour of chromium based applications when using windowed fullscreen, or a fix to make certain Java applications play more nicely with xmonad. • `XMonad.Hooks.WindowSwallowing' A new module to implement window swallowing; optionally via sublayouting. Hide parent windows like terminals when opening other programs (like image viewers) from within them, restoring them once the child application closes. • `XMonad.Util.ClickableWorkspaces' A new module providing `clickablePP', which when applied to the `PP' pretty-printer used by `XMonad.Hooks.StatusBar.PP', will make the workspace tags clickable in XMobar (for switching focus). Note that `XMonad.Layout.IndependentScreens' and `XMonad.Actions.WorkspaceNames' now also use the same composable `ppRename' interface as `XMonad.Util.ClickableWorkspaces' so it's much easier to use them with one another. • `XMonad.Util.Loggers' • Added `logTitles' to log all window titles (focused and unfocused ones) on the focused workspace, as well as `logTitlesOnScreen' as a screen-specific variant thereof. • `XMonad.Actions.TopicSpace' • Added `TopicItem', as well as the helper functions `topicNames', `tiActions', `tiDirs', `noAction', and `inHome' for a drastically simpler specification of topics. • `XMonad.Hooks.ServerMode' • To make it easier to use, the `xmonadctl' client is now included in `scripts/'. [vim-easymotion]: <https://github.com/easymotion/vim-easymotion> [org-mode]: <https://orgmode.org/> 3 Logo Contest ══════════════ We'd also like to announce a contest to create a new xmonad logo to replace the current one. If you want to participate, please submit at most /three/ logos (in SVG format) to [this GitHub Discussion] by the 31st of January. Please do not vote for a logo yet—voting will start after the above deadline. Your logo will need to be licensed under a suitable freely distributable license; for example, the CC BY-SA 4.0. The prize for the winner is `$100'! For voting, we will use an [instant-runoff] type system. In short: • Users rank a minimum of three submissions according to their preferences in decreasing order. • If a logo wins a majority of first-preference votes (> 50%) it is chosen. • If not, we eliminate the logo with the least amount of first preference votes, exposing the second preference of those who voted for it. • Rinse and repeat until we have a majority. • If at the end of all that we still don't have a majority, we will act as a tiebreaker and internally vote for a winner from the remaining logos. We will retain veto power in case of inappropriate logos. Team members whose submitted entries are amongst the remaining choices will not partake in the potential tiebreaking vote. [this GitHub Discussion]: https://github.com/xmonad/xmonad/discussions/343 [instant-runoff]: <https://en.wikipedia.org/wiki/Instant-runoff_voting> 4 Looking for Funding ═════════════════════ TL;DR: We would love your support to keep xmonad alive! You can support us via [GitHub Sponsors] and the [Open Collective] is our fiscal host such that our funds are fully transparent. [GitHub Sponsors]: <https://github.com/sponsors/xmonad> [Open Collective]: <https://opencollective.com/xmonad> XMonad has been around since 2007 and has a great track record in stability. There's an active, vibrant community of users and developers who help each other and contribute fixes and extensions. Keeping this community organized, reviewing and merging contributions and responding to bug reports is almost a full-time job, however, not to mention doing actual development. We've been struggling to find volunteers to do all this work, especially the less exciting bits like documentation. Despite that struggle, we managed to repay a portion of our technological and organizational debt over the last year, and to pick up the [pace of development]. We're worried about the sustainability of that pace, however. As with the previous generations of maintainers, our studies and sabbaticals won't last forever. Your help is needed to keep the project alive and well! We'd like to raise enough funds to enable at least one core developer to work on XMonad full-time (or several part-time). To learn more about our plans for the future, see our [GitHub Sponsors] profile. Thanks to [one unexpected appearance on the Hacker News front page], we already gathered a couple dozen sponsors who donate in total over $300 a month. We're incredibly grateful for this support! Our fiscal host is the [Open Source Collective], so our budget is fully transparent on [our Collective's page]. If you also want to aid our efforts going forward, please consider becoming a supporter as well. We accept both monthly and one-time donations through [GitHub Sponsors] and [Open Collective]. Thank you! [pace of development]: https://xmonad.org/images/xmonad-0-17/commits.svg [GitHub Sponsors]: <https://github.com/sponsors/xmonad> [one unexpected appearance on the Hacker News front page]: <https://news.ycombinator.com/item?id=28793941> [Open Source Collective]: <https://www.oscollective.org/> [our Collective's page]: <https://opencollective.com/xmonad> [Open Collective]: <https://opencollective.com/xmonad> -- brandon s allbery kf8nh allbery.b(a)gmail.com

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type inference and FFI
by PICCA Frederic-Emmanuel 27 Oct '21

27 Oct '21

Hello, I have a bunch of C method that I need to call like this c'foo_unit16_t :: Ptr Word16 -> IO r c'foo_uint32_t :: Ptr Word32 -> IO r ... These methodes are called from a method like this process :: NativeType t => Dataframe t => IO r process df = do ... <pseudo code> case typeof t of WORD16 -> c'foo_unit16_t ... WORD32 -> c'foo_uint32_t ... Since there is type erasure, I would like to know what is the best way to write this process method. thanks for you help Frederic

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simple word processor
by Dennis Gaita 26 Oct '21

26 Oct '21

-1 <https://stackoverflow.com/posts/69702739/timeline> I am new to haskell and I need to create a simple word processor. It needs to read text from the cmd and implement functions that would edit functions found in the text so some other text.All functions in the text are odered. Each function i.e section,table,figures and ref must be located and numbered independently based on the order of occurence. Since tables and figures are within the sections function(just like a book), when a new section is encountered you will reset the value of tables and figures. So i did a loop where the tables and figures are inside the section loop when searching for the functions. The functions all start with this '' character (escape character) and must be replaced with text using this method: \Section{title}{id}: -> "Section n: title". Where n is the section number. \table{title}{id} : -> "Table n.m : title". Where n is the number of the last section encountered and m is the table number. And so on. I need help because my code isn't running.This is the code: import Text.Format import Data.Text.Internal.Search import Data.Text s = count . "section" -- count number of occurences of a certain word t = count . "table" f = count . "Figure" r = count . "ref" forLoop :: Int - Int - Int - Int forLoop s value = if i < s then forLoop (i + 1) format "Section{title}{id}" [show i, show {title}] then replace "Section{i}{title}" "Section {i}:{title}" else value forLoop t value = if j < t then forLoop (j + 1) format "table{title}{id}" [show i.j, show {title}] --change the text then replace "table{i}.{j}{title}" "Table {i}.{j} : {title}" else value forLoop f value = if k < f then forLoop (k + 1) format "figure{title}{id}" [show i.k, show {title}] --change the text then replace "Figure{title}{id}" "Figure {i}.{k} : {title}" else value if "ref{id}" == "table{title}" then forLoop r value = if l < r then forLoop (l + 1) format "ref{id}" [show {title}] --change the text then replace "ref{id}" "see {title} {i}.{j}" else value else Nothing if "ref{id}" == "Figure{title}" then forLoop r value = if m < r then forLoop (m + 1) format "ref{id}" [show {title}] --change the text then replace "ref{id}" "see {title} {i}.{m}" else value else Nothing if "ref{id}" == "Section{title}" then forLoop r value = if n < r then forLoop(n+1) format "ref{id}" [show{title}] then replace "ref{id}" "see {title} {i}" else value else nothing

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Numerics (was: Re: Trouble with asinh)
by Barak A. Pearlmutter 25 Oct '21

25 Oct '21

The numerics in Haskell have not been carefully vetted, for a variety of reasons. Not just under MS Windows, even under Linux. Here's an example: atan has drastic loss of precision in the imaginary direction around zero in the complex domain. $ ghci GHCi, version 8.8.4: https://www.haskell.org/ghc/ :? for help Prelude> :m + Data.Complex Prelude Data.Complex> tan (1e-20 :+ 0) 1.0e-20 :+ 0.0 Prelude Data.Complex> atan (1e-20 :+ 0) 1.0e-20 :+ (-0.0) Prelude Data.Complex> tan (0 :+ 1e-20) 0.0 :+ 1.0e-20 Prelude Data.Complex> atan (0 :+ 1e-20) 0.0 :+ (-0.0) Although there have been amazing efforts to use fancy PLT methods to improve the numerics of programs using source-to-source transformations and such, the boring janitorial work of checking and fixing numeric issues in the standard library doesn't seem to attract people. To be fair, it isn't my cup of tea either...

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[ANN] hslua 2.0.0, bridging Haskell and Lua
by Albert Krewinkel 23 Oct '21

23 Oct '21

I am pleased to announce the release of [HsLua] 2.0.0; a collection of packages offering (bidirectional) glue and abstractions bridging Haskell and Lua. HsLua is a featureful framework, enabling Haskell programmers to combine the embeddable scripting language Lua with code written Haskell. This new release is an almost complete rewrite and offers better performance, cleaner types, and adds more abstraction helpers. It supports exposing data and functions from Haskell to Lua in a convenient and structured way. Probably the best-known real world use case of HsLua is [pandoc], the universal document converter, where it serves as the central building block for [Lua filters] and custom writers. Contributions are welcome. [HsLua]: https://hslua.org [pandoc]: https://pandoc.org [Lua filters]: https://pandoc.org/lua-filters.html -- Albert Krewinkel GPG: 8eed e3e2 e8c5 6f18 81fe e836 388d c0b2 1f63 1124

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Munich Haskell Meeting, 2021-10-26 @ 19:30
by Leah Neukirchen 22 Oct '21

22 Oct '21

Dear all, next week, our monthly Munich Haskell Meeting will take place again on Tuesday, October 26 at Augustiner-Gaststätte Rumpler(!!) at 19h30. For details see here: http://muenchen.haskell.bayern/dates.html If you plan to join, please add yourself to this dudle until Tuesday 12:00 so we can reserve enough seats! 3G rules apply. It is OK to add yourself to the dudle anonymously or pseudonymously. https://dudle.inf.tu-dresden.de/haskell-munich-oct-2021/ Everybody is welcome! cu, -- Leah Neukirchen <leah(a)vuxu.org> https://leahneukirchen.org/

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unexpected compile error with wrapped HList
by Zoran Bošnjak 22 Oct '21

22 Oct '21

Hello members, I am struggling to compile the snippet below. GHC version is 8.10.4. If I try to construct the 'Variation' (with the type signature), I am getting an unexpected error. (see the comments in the code below). The error is only present if the HList is empty. I would appreciate a suggestion how to fix it. regards, Zoran --- {-# LANGUAGE DataKinds #-} {-# LANGUAGE GADTs #-} {-# LANGUAGE FlexibleContexts #-} {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE TypeOperators #-} {-# LANGUAGE PolyKinds #-} module Test where import Data.Kind data (a::k1) :<< (b::k2) infixr 5 :<< data HList (ts :: [Type]) where HNil :: HList '[] HCons :: x -> HList xs -> HList (x ': xs) data TVariation = TVariation1 | TVariation2 data Variation vt where Variation1 :: HList ts -> Variation ('TVariation1 :<< ts) Variation2 :: HList ts -> Variation ('TVariation2 :<< ts) -- This works as expected, including the explicit type signature. x1 :: Variation ('TVariation1 :<< '[()]) x1 = Variation1 (HCons () HNil) -- But the following 2 cases do not work as expected. -- 1. problem: -- This 'x0' type is inferred by GHC, -- but when specified as such, it won't compile. {- • Couldn't match type ‘k’ with ‘*’ ‘k’ is a rigid type variable bound by the type signature for: x0 :: forall k. Variation ('TVariation1 :<< '[]) at adhoc/test.hs:39:1-38 Expected type: Variation ((:<<) @TVariation @[k] 'TVariation1 ('[] @k)) Actual type: Variation ((:<<) @TVariation @[*] 'TVariation1 ('[] @*)) • In the expression: Variation1 HNil In an equation for ‘x0’: x0 = Variation1 HNil • Relevant bindings include x0 :: Variation ('TVariation1 :<< '[]) (bound at adhoc/test.hs:40:1) -} x0 :: Variation ('TVariation1 :<< '[]) x0 = Variation1 HNil class Empty t where mkEmpty :: t -- 2. problem: -- This instance declaration reports the same problem (as in x0 above). instance Empty (Variation ('TVariation1 :<< '[])) where mkEmpty = Variation1 HNil

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Downsides to disabling unticked-promoted-constructor warning?
by Markus Läll 21 Oct '21

21 Oct '21

Hi! Is there any consensus on unticked promoted constructors -- are they generally safe to use? Currently the warning is part of -Wall, but having promoted constructors unticked is just aesthetically nicer. Thanks, -- Markus Läll

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You're invited to the October virtual Haskell CoHack
by Chris Smith 19 Oct '21

19 Oct '21

Hi everyone, This Saturday, I’m once again hosting a virtual Haskell CoHack. In the past, we’ve had a great time with groups here working on various projects, whether it’s learning Haskell, hacking on GHC, writing documentation, making progress on personal projects, or just hanging out to chat with like-minded folk. You should consider coming if you would be excited to meet fellow Haskell programmers and work or learn together with them. There are details, including times, on the meetup page: https://www.meetup.com/NY-Haskell/events/280998863

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GDB and ticks
by Henning Thielemann 18 Oct '21

18 Oct '21

I am stepping through a Haskell program using the GNU debugger GDB and see function calls to handle_tick, handleProfTick, stopTicker all over the place. It sounds like they would manage profiling, but I compiled the executable without profiling.

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