November 2021 - Haskell-Cafe

Type inference for lambda function
by Matthias Güdemann 04 Nov '21

04 Nov '21

Hi cafe, today while explaining lambda functions I came across this case which I don't really understand. This is what I get using ghci λ> :t (\a b -> a + b) (\a b -> a + b) :: Num a => a -> a -> a but when loading a .hs file with just this function (without signature) add = \a b -> a + b I get λ> :t add add :: Integer -> Integer -> Integer but I can explicitly define add to have this type: add :: Num a => a -> a -> a add = \a b -> a + b Also ghc infers this polymorphic type for example for add0 a = \b -> a + b Why is the type of add without a signature inferred to Integer and not Num a? Best regards Matthias

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TOP is hiring Functional Programmers for developing multi-user web applications
by rinus plasmeijer 03 Nov '21

03 Nov '21

Dear Haskell Fans, TOP Software Technology (top-software.com <http://top-software.com>) is a recently founded (2018) spin-off company located in the Netherlands, building on decades of research on Functional Programming at the Radboud University of Nijmegen (clean.cs.ru.nl <http://clean.cs.ru.nl>). By using advanced Functional Programming techniques and tools, we develop collaborative, distributed, multi-user / multi-system / multi-platform, web-oriented software applications for industry. We focus on Command and Control type of applications such as VIIA <https://top-software.nl/VIIA.html> <https://top-software.nl/VIIA.html> where real-time information is used for monitoring vessels. We use Clean, a Haskell like pure and lazy functional language, and the iTask system offering Task Oriented Programming (TOP), a special flavour of Functional Programming to construct reliable software applications for our customers at a high-level of abstraction on an Agile manner. We are looking for Experienced Functional Programmers to join our team. See the attached pdf. More information on what we do can be found ontop-software.com <http://top-software.com>. Mail torinus(a)top-software.com <mailto:rinus@top-software.com> orrinus(a)cs.ru.nl <mailto:rinus@cs.ru.nl> if you are interested. Greetings, Rinus Plasmeijer

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[ANN] text-display 0.0.1.0: A typeclass for user-facing output
by Hécate 02 Nov '21

02 Nov '21

Hi everyone, I am proud to release the first version of text-display¹, a typeclass for user-facing output. `Display` is a typeclass that doesn't abide by the rules of `Show` & `Read`, and brings with it a nice and ergonomic way to derive instances through `DerivingVia` when they already have a `Show` instance: ```haskell {-# LANGUAGE DerivingVia #-} data AutomaticallyDerived = AD -- We derive 'Show' deriving Show -- We take advantage of the 'Show' instance to derive 'Display' from it deriving Display via (ShowInstance AutomaticallyDerived) ``` But let's say you want to redact an instance of `Display`? You can do it locally, through the `OpaqueInstance` helper. It is most useful to hide tokens or passwords: ```haskell data UserToken = UserToken UUID deriving Display via (OpaqueInstance "[REDACTED]" UserToken) display $ UserToken "7a01d2ce-31ff-11ec-8c10-5405db82c3cd" -- => "[REDACTED]" ``` I hope you will have fun with this library! Cheers! ¹ https://hackage.haskell.org/package/text-display-0.0.1.0 -- Hécate ✨ 🐦: @TechnoEmpress IRC: Hecate WWW: https://glitchbra.in RUN: BSD

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Call for Contributions: BOB 2022 [March 11, Deadline Dec 6]
by Stefan Wehr 02 Nov '21

02 Nov '21

================================================================================ BOB Conference 2022 "What happens when we use what's best for a change?" http://bobkonf.de/2022/cfc.html Berlin, Mar 11 Call for Contributions Deadline: December 6, 2021 ================================================================================ You are actively engaged in advanced software engineering methods, solve ambitious problem with software and are open to cutting-edge innovation? Attend this conference, meet people that share your goals, and get to know the best software tools and technologies available today. We strive to offer a day full of new experiences and impressions that you can use to immediately improve your daily life as a software developer. If you share our vision and want to contribute, submit a proposal for a talk or tutorial! NOTE: The conference fee will be waived for presenters. Travel expenses will not be covered (for exceptions see "Speaker Grants"). Online or Onsite ---------------- We expect we'll be able to hold BOB 2022 in Berlin. If that is not possible, we'll make BOB a successful online event, like BOB 2021. Should BOB happen online, we will likely ask for pre-recorded talks to make room for questions and social interactions during the actual conference day. (Of course, we'll provide assistance making those recordings.) Tutorials will likely happen as a live-session. Shepherding ----------- The program committee offers shepherding to all speakers. Shepherding provides speakers assistance with preparing their sessions. Specifically: - advice on structure and presentation - review of talk slides - assistance with recording - review of recording, if applicable Speaker Grants -------------- BOB has Speaker Grants available to support speakers from groups under-represented in technology. We specifically seek women speakers, speakers of color, and speakers who are not able to attend the conference for financial reasons. Topics ------ We are looking for talks about best-of-breed software technology, e.g.: - functional programming - persistent data structures and databases - event-based modelling and architecture - "fancy types" (dependent types, gradual typing, linear types, ...) - formal methods for correctness and robustness - abstractions for concurrency and parallelism - metaprogramming - probabilistic programming - math and programming - controlled side effects - program synthesis - next-generation IDEs - effective abstractions for data analytics - … everything really that isn’t mainstream, but you think should be. Presenters should provide the audience with information that is practically useful for software developers. Challenges ---------- Furthermore, we seek contributions on successful approaches for solving hard problems, for example: - bias in machine-learning systems - digital transformation in difficult settings - accessibiltity - systems with critical reliability requirements - ecologically sustainable software development We're especially interested in experience reports. Other topics are also relevant, e.g.: - introductory talks on technical background - overviews of a given field - demos and how-tos Requirements ------------ We accept proposals for presentations of 45 minutes (40 minutes talk + 5 minutes questions), as well as 90 minute tutorials for beginners. The language of presentation should be either English or German. Your proposal should include (in your presentation language of choice): - An abstract of max. 1500 characters. - A short bio/cv - Contact information (including at least email address) - A list of 3-5 concrete ideas of how your work can be applied in a developer's daily life - additional material (websites, blogs, slides, videos of past presentations, …) - Don't be confused: The system calls a submission event. Organisation ------------ - Direct questions to contact at bobkonf dot de - Proposal deadline: December 6, 2021 - Notification: December 17, 2021 - Program: December 22, 2021 Submit here: https://bobcfc.active-group.de/en/bob2022/cfp Program Committee ----------------- (more information here: https://bobkonf.de/2022/programmkomitee.html) - Matthias Fischmann, Wire - Matthias Neubauer, SICK AG - Nicole Rauch, Softwareentwicklung und Entwicklungscoaching - Michael Sperber, Active Group - Stefan Wehr, Hochschule Offenburg Scientific Advisory Board - Annette Bieniusa, TU Kaiserslautern - Torsten Grust, Uni Tübingen - Peter Thiemann, Uni Freiburg

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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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