- Haskell-Cafe - Haskell.org

No "fields of ... not initialized" warning with RecordWildCards and Void?
by Markus Läll 01 Nov '21

01 Nov '21

Hi! Would it make sense to suppress the "fields of ... not initialized" when the type of the field is Void, or any other type with no data constructors? As the only way to construct void would be `undefined :: Void`, and the field already is undefined. Regards, -- Markus Läll

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ghci's choice of names for type variables
by Julian Bradfield 01 Nov '21

01 Nov '21

I have tried to answer this by google and the list archives, but without success, though it wouldn't surprise me if there is a post buried somewhere. This is GHCI 8.10.7. When ghci infers types, it sometimes produces types with "a", with "t", and with "p" (and maybe others), as in the following set of examples: Prelude> h (x : xs) = x Prelude> :t h h :: [a] -> a Prelude> foo f x = not(f x) Prelude> :t foo foo :: (t -> Bool) -> t -> Bool Prelude> bar f x = (f x) + 1 Prelude> :t bar bar :: Num a => (t -> a) -> t -> a Prelude> barb f x g y = (f x)+(g y) Prelude> :t barb barb :: Num a => (t1 -> a) -> t1 -> (t2 -> a) -> t2 -> a Prelude> gar f x = f x Prelude> :t gar gar :: (t1 -> t2) -> t1 -> t2 Prelude> fooa x = x Prelude> :t fooa fooa :: p -> p What is its rationale? I have attempted to find it in the typechecker code, and I see things that suggest "t" is something to do with tau types (monotypes?), and "p" has something to do with levels, but going from basic Haskell and a modest theoretical acquaintance with System F to being able to read the GHCi type-checker is several steps too far! Can somebody give me a brief explanation of what's going on? In particular, is there actual information about the types in the choice of letters, or is it just incidental information about the way type inference proceeded? Thanks, Julian. -- The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336.

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Trojan source
by Henning Thielemann 01 Nov '21

01 Nov '21

Hide malicious code behind Unicode with reversed text direction: https://github.com/nickboucher/trojan-source They are missing the Haskell examples.

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German live interview about experiences with functional programming, today 12:00
by Henning Thielemann 01 Nov '21

01 Nov '21

https://www.heise.de/news/software-architektur-tv-Funktionale-Programmierun…

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Journal of Functional Programming - Call For PhD Abstracts
by Graham Hutton 01 Nov '21

01 Nov '21

Dear all, If you or one of your students recently completed a PhD in the area of functional programming, please submit the dissertation abstract for publication in JFP: simple process, no refereeing, open access, 200 published to date, deadline 30th November 2021. Please share! Best wishes, Graham Hutton ============================================================ CALL FOR PHD ABSTRACTS Journal of Functional Programming Deadline: 30th November 2021 http://tinyurl.com/jfp-phd-abstracts ============================================================ PREAMBLE: Many students complete PhDs in functional programming each year. As a service to the community, twice per year the Journal of Functional Programming publishes the abstracts from PhD dissertations completed during the previous year. The abstracts are made freely available on the JFP website, i.e. not behind any paywall. They do not require any transfer of copyright, merely a license from the author. A dissertation is eligible for inclusion if parts of it have or could have appeared in JFP, that is, if it is in the general area of functional programming. The abstracts are not reviewed. Please submit dissertation abstracts according to the instructions below. We welcome submissions from both the PhD student and PhD advisor/supervisor although we encourage them to coordinate. ============================================================ SUBMISSION: Please submit the following information to Graham Hutton <graham.hutton(a)nottingham.ac.uk> by 30th November 2021. o Dissertation title: (including any subtitle) o Student: (full name) o Awarding institution: (full name and country) o Date of PhD award: (month and year; depending on the institution, this may be the date of the viva, corrections being approved, graduation ceremony, or otherwise) o Advisor/supervisor: (full names) o Dissertation URL: (please provide a permanently accessible link to the dissertation if you have one, such as to an institutional repository or other public archive; links to personal web pages should be considered a last resort) o Dissertation abstract: (plain text, maximum 350 words; you may use \emph{...} for emphasis, but we prefer no other markup or formatting; if your original abstract exceeds the word limit, please submit an abridged version within the limit) Please do not submit a copy of the dissertation itself, as this is not required. JFP reserves the right to decline to publish abstracts that are not deemed appropriate. ============================================================ PHD ABSTRACT EDITOR: Graham Hutton School of Computer Science University of Nottingham Nottingham NG8 1BB United Kingdom ============================================================ This message and any attachment are intended solely for the addressee and may contain confidential information. If you have received this message in error, please contact the sender and delete the email and attachment. Any views or opinions expressed by the author of this email do not necessarily reflect the views of the University of Nottingham. Email communications with the University of Nottingham may be monitored where permitted by law.

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GHC 9.2.x error on m1 Mac?
by Stuart Hungerford 01 Nov '21

01 Nov '21

Hi, I've been trying out the latest GHC (9.2.1) on an m1 Mac running macOS 12.0.1. I'm seeing this error when building an existing project: Failed to build wcwidth-0.0.2. Build log ( /Users/stu/.cabal/logs/ghc-9.2.1/wcwdth-0.0.2-232d390d.log ): Warning: wcwidth.cabal:47:45: version operators used. To use version operators the package needs to specify at least 'cabal-version: >= 1.8'. Warning: wcwidth.cabal:30:45: version operators used. To use version operators the package needs to specify at least 'cabal-version: >= 1.8'. Configuring wcwidth-0.0.2... Preprocessing library for wcwidth-0.0.2.. Building library for wcwidth-0.0.2.. [1 of 1] Compiling Data.Char.WCWidth ( Data/Char/WCWidth.hs, dist/build/Data/Char/WCWidth.o, dist/build/Data/Char/WCWidth.dyn_o ) In file included from /var/folders/2q/ym4rpn7j6v9d6jhpt0wnk03r0000gn/T/ghc7111_0/ghc_3.c:4:0: error: In file included from /Users/stu/.ghcup/ghc/9.2.1/lib/ghc-9.2.1/lib/../lib/aarch64-osx-ghc-9.2.1/rts-1.0.2/include/ffi.h:66:0: error: /Users/stu/.ghcup/ghc/9.2.1/lib/ghc-9.2.1/lib/../lib/aarch64-osx-ghc-9.2.1/rts-1.0.2/include/ffitarget.h:6:10: error: fatal error: 'ffitarget_arm64.h' file not found | 6 | #include "ffitarget_arm64.h" | ^ #include "ffitarget_arm64.h" ^~~~~~~~~~~~~~~~~~~ 1 error generated. Am I missing a package or system library/header that provides that ffitarget_arm64.h file? TIA, Stu

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New CLC proposal process
by Andrew Lelechenko 30 Oct '21

30 Oct '21

I'm happy to announce that Core Libraries Committee has completed post-election reboot and now has a new home at https://github.com/haskell/core-libraries-committee <https://github.com/haskell/core-libraries-committee> and a new GitHub-based process: https://github.com/haskell/core-libraries-committee/blob/main/PROPOSALS.md <https://github.com/haskell/core-libraries-committee/blob/main/PROPOSALS.md>. From now on proposals to change base should be raised as GitHub issues instead of emails to libraries@. Best regards, Andrew

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Re: [Haskell-cafe] ghci's choice of names for type variables
by Johannes Waldmann 30 Oct '21

30 Oct '21

Just from observing the behaviour (not the source) - it seems that ghci tries to use the variables from the declaration of the/a function, type, or class that is being used. Prelude> data T c = T c Prelude> h x y = (T x, T y) Prelude> :t h h :: c1 -> c2 -> (T c1, T c2) Prelude> f :: foo -> foo ; f x = x Prelude> g = f Prelude> :t g g :: foo -> foo In the Haskell Standard, type variables are a, b, ... mostly (always?), hence you get `a` for anything with lists and Num. If there's no type to refer to, then your examples show that it's using t or p, but I don't know how. Prelude> i x = x Prelude> :t i i :: p -> p Prelude> k x y = x Prelude> :t k k :: p1 -> p2 -> p1 Prelude> s x y z = x z (y z) Prelude> :t s s :: (t1 -> t2 -> t3) -> (t1 -> t2) -> t1 -> t3 interesting! - J.W.

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Re: [Haskell-cafe] simple word processor
by Olaf Klinke 27 Oct '21

27 Oct '21

> 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. Let me try to break your problem into sub-problems. 1. You have text where some patterns have meaning to your particular application (e.g. "\Section{title}{id}"). 2. When knowing this structure, you want to transform it from front to back while updating some counters. 3. Once that transformation is done, you want to write the structure back into a plain text. How to approach: 1. is addressed with parsers. There are plenty to choose from, e.g. parsec, attoparsec, megaparsec to name just tree applicative-style libraries. A parser looks for patterns in plain text and transforms it into a more stuctured type. The structured type may be somethig like data Block a = SomeText Text | Section Text a | Table Text s | etc. The parsing function will have a type similar to Text -> Either ParseError [Block ()] where () stands for a numbering that is not yet known. 2. May be modeled as a stateful traversal. First define a state with all the counters, say data Counters = Counters { theSection :: Int, theTable :: Int} Next define a traversal function Block () -> State Counters (Block Text) where the unknown numbering () is replaced with the appropriate Text- representation of theSection or (theSection,theTable) etc. Finally, traverse your parsed list of Blocks with this traversal. 3. essentially requires a Show instance for your (Block Text) type together with concatenation. Steps 1-3 will be combined like follows. fmap ((=<<) show . flip evalState start . traverse number) . parse where parser :: Text -> Either ParseError [Block ()] start :: Counters number :: Block () -> State Counters (Block Text) "traversal" -> hoogle for Data.Traversable "stateful" -> hoogle for Control.Monad.State Olaf

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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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