- Haskell-Cafe - Haskell.org

Is Data.Pool not thread-safe or have I done something silly?
by Cody Gman 14 Mar '21

14 Mar '21

I wrote some code with a Data.Pool that has 1 stripe, 1 max resource, and then basically did `Async.replicateConcurrently_ . withResource $ \res -> f res`. I expect withResource to block in each of those threads until the first thread spawned is done with that Resource and releases. To be clear, I get output like: ```shell /tmp $ stack exec --resolver lts-17.5 --package resource-pool --package stm --package hslogger --package time --package concurrent-output -- ghc -O2 -threaded -fwarn-unused-imports testpool.hs && ./testpool acquire 0 - .81428 acquire 1 - .81431 acquire 2 - .81438 acquire 3 - .81440 acquire 4 - .81448 ThreadId 8: processing 1 - .82460 ThreadId 17: processing 4 - .82461 ThreadId 11: processing 2 - .82464 ThreadId 14: processing 3 - .82464 ThreadId 5: processing 0 - .82465 anything else? release 4 - .14427 release 3 - .14430 release 2 - .14431 release 1 - .14431 release 0 - .14432 anything else? anything else? ``` I expect output like: ```shell /tmp $ stack exec --resolver lts-17.5 --package resource-pool --package stm --package hslogger --package time --package concurrent-output -- ghc -O2 -threaded -fwarn-unused-imports testpool.hs && ./testpool [1 of 1] Compiling Main ( testpool.hs, testpool.o ) Linking testpool ... acquire 0 ThreadId 5: processing 0 - .01129 release 0 acquire 1 -- I thought this would have blocked until 0 was released ThreadId 8: processing 1 - .01120 release 1 acquire 2 ThreadId 11: processing 2 - .01123 release 2 acquire 3 ThreadId 14: processing 3 - .01129 release 3 acquire 4 ThreadId 17: processing 4 - .01129 release 4 anything else? anything else? anything else? ``` Here is the code: ``` #!/usr/bin/env stack -- stack script --resolver lts-17.5 --package resource-pool --package stm --package hslogger --package time --package concurrent-output import Control.Concurrent import Control.Concurrent.Async import Control.Concurrent.STM import Data.Pool import Data.Time import System.Console.Concurrent import System.Clock main :: IO () main = do counter <- newTVarIO 0 let acquire = do k <- atomically $ do k <- readTVar counter writeTVar counter (k + 1) return k now <- getTime Monotonic outputConcurrent ("acquire " ++ show k ++ " - "++ show now ++ "\n") return k release k = do now <- getTime Monotonic outputConcurrent ("acquire " ++ show k ++ " - "++ show now ++ "\n") withConcurrentOutput $ do -- create a pool that only allows 1 resource pool <- createPool acquire release 1 500 1 replicateConcurrently_ 5 $ do useResourceFor (seconds 10) pool -- Why do you need these to see the release messages? putStrLn "anything else?" >> threadDelay (seconds 5) putStrLn "anything else?" >> threadDelay (seconds 5) putStrLn "anything else?" >> threadDelay (seconds 5) useResourceFor waitSeconds pool = withResource pool $ \i -> do threadDelay waitSeconds tid <- myThreadId now <- getTime Monotonic outputConcurrent $ show tid <> ": " <> " processing " <> show i <> " - " <> show now <> "\n" seconds = (* 1000000) ``` I'm hoping someone could help explain what I did wrong or confirm it's a bug. Thanks, Cody

2 1

Re: [Haskell-cafe] naturally, length :: a -> Int
by Olaf Klinke 14 Mar '21

14 Mar '21

Which bugs can be caught at compile-time by having length return natural numbers? Regarding space, Int instead of Word only wastes the sign bit, doesn't it? I like the idea that Johannes Waldmann and Jaro Reinders brought up: Why is length :: Foldable a => a -> Int so convenient? Short answer: Because of "affine" things like `availableSpace - length xs'. There are indeed two types involved here, as the foundation package points out: relative offsets (like a tangent space?) and absolute counts. Think of NominalDiffTime versus UTCTime, or the two interpretations of vectors as points/movements in space. In this light one could regard the current length as "the relative offset of the end of the list" which can readily be subtracted from another relative offset. In mathematical terms: Int the free group over the monoid of cardinal lengths. While we're at it: Can there be a Fractional type permitting only positive numbers, as the positive real numbers are closed under division? Can there be a type of rationals between 0 and 1 (which is closed under multiplication) where (/x) is the right adjoint to (*x)? Olaf

4 6

Property checks and PostgreSQL?
by Ignat Insarov 14 Mar '21

14 Mar '21

Note: I posted this [elsewhere] — I hope it is permissible to also post here. There seems to be no single right venue for Haskell questions at this time. [elsewhere]: https://discourse.haskell.org/t/property-checks-and-postgresql/2078 So, I have a three layer stack: PostgreSQL data base, Haskell back end, PureScript front end. And there is a fault somewhere in this stack: sometimes some items present in the data base do not make it to the front end. A small fortune in programmer hours has been spent searching for the fault but there is no progress. No one can figure out even roughly where the fault is. Our last hope is to property check the whole thing, from end to end, verifying that any things put into the data base can be retrieved by the front end. We have in place a fixture that creates a new PostgreSQL cluster, runs the back end on it and makes some scripted HTTP requests. We use it to run unit tests, such like _«if I make this `PUT` request and then that `GET` request to the same end point, I should get back the same thing as I put in»_. In principle it would not be a problem to make a property check out of this property. Practically, tearing down the cluster, building a new pristine one and initializing the data base anew takes seconds, so this way even a trivial property check would take minutes to run. Theoretically, we can carefully reset the data base back to the initial state after each run of the property check. Given that only a small amount of data is modified, it would take imperceptibly little time. But it is hard to know what exactly should be reset, and it is easy to get it wrong if done by hand! One trick we do use is SQL transactions. We take a single connexion, start a transaction, perform a check and then roll the transaction back. Unfortunately, even this is not completely safe: it looks as though sequences used to draw primary keys from are not reset to their previous values! _(Or maybe we are doing something wrong — I am not really a PostgreSQL guru so I am not too sure of myself.)_ But even ignoring this problem _(it is irrelevant to most checks)_, there is another, more severe problem: transactions guarantee that uncommitted data is only visible inside the same connexion. So, there is no way to request it from the HTTP API. This trick is suitable for fuzzing the data base – back end layer, but nothing beyond that. Another thing I heard being done is to selectively drop and re-create exactly the tables affected by a run of a property check. This seems challenging to automate though. How can I know in a general way if a table has been touched? And then, how can I re-create exactly the affected tables given that the data base initialization code is an opaque blob? I wonder if this problem is already solved. In any case, any advice is welcome!

5 9

Package Takeover: `toml`
by Emily Pillmore 14 Mar '21

14 Mar '21

To whom it may concern, I'd like to take over maintenance of the package `toml`. I have a burning need. I tried to contact Spiros a year ago, but no response has come. The last release was 2017, and it's safe to say the package is totally abandoned. My hackage user is topos. Cheers, E

20 51

data kinds and exhaustiveness of typeclass instances
by Paul Brauner 13 Mar '21

13 Mar '21

Hello, the following program doesn't typecheck in GHC 9: data Tag = A | B data Foo (a :: Tag) = Foo class C a where f :: a -> Int instance C (Foo A) where f x = 1 instance C (Foo B) where f x = 2 g :: Foo a -> Int g = f Yet one could argue that for all a :: Tag, C (Foo a) holds because a :: Tag can only take two values: A or B, and C (Foo A) and C (Foo B) hold. Is there a way to somehow convince GHC of that fact so that g typechecks? Cheers, Paul

6 7

[ANN] singletons-3.0, singletons-th-3.0, and singletons-base-3.0
by Ryan Scott 12 Mar '21

12 Mar '21

I'm happy to announce the 3.0 release of the singletons library, as well as the debut of its companion libraries, singletons-th and singletons-base. There's been a fair bit of improvements, cleanup, and reorganization since the last release, so I thought it appropriate to give this release a super-major version bump. This announcement will go over some highlights of the new releases, but if you want the full details, you can consult the changelog entries for each library below: * singletons-3.0: http://hackage.haskell.org/package/singletons-3.0/changelog * singletons-th-3.0: http://hackage.haskell.org/package/singletons-th-3.0/changelog * singletons-base-3.0: http://hackage.haskell.org/package/singletons-base-3.0/changelog ########################## ## Why three libraries? ## ########################## Instead of there just being one singletons library, there are now _three_ libraries: * singletons: A small, foundational library that defines basic singleton-related types and definitions. The new singletons library supports GHC 8.0 or later, does not depend on any external libraries, and does not make use of Template Haskell. * singletons-th: A library that defines Template Haskell functionality for promoting term-level functions to type-level equivalents and singling functions to dependently typed equivalents. This library requires bleeding-edge GHC features, and as a result, it only supports GHC 9.0 or later. * singletons-base: A library that uses singletons-th to define promoted and singled functions from the base library, including the Prelude. Similarly to singletons-th, this library only supports GHC 9.0 or later. Previous singletons releases combined all of this functionality into a single library. However, discussions with singletons users revealed that this was a frequent source of pain: * The total time it took to compile the old singletons library dissuaded some from using it, especially for those who only wanted to use a small part of the library. * Some users wished to use singletons in environments where Template Haskell is not an option. * Some users wanted to use core definitions from Data.Singletons, but because the old singletons library only ever supported one GHC at a time, this was impractical. The new package structure in the 3.0 release is an attempt to address some of these pain points. In particular, most of the code which results in extensive compile times is now confined to the singletons-base library. For the full discussion that led up to this, see [1]. ########################### ## Module reorganization ## ########################### Splitting up singletons into smaller packages provided a rare opportunity to clean up the module naming conventions, which were confusing and inconsistent in many places. The 3.0 releases now use the following conventions: * All modules in singletons now begin with Data.Singletons.*. * All modules in singletons-th now begin with Data.Singletons.TH.*. * Most modules in singletons-base now reflect the modules from base from which they take inspiration. For example, the Prelude module now has a Prelude.Singletons counterpart in singletons. Similarly, there are also modules like Control.Monad.Singletons, GHC.TypeLits.Singletons, etc. All other modules that do not correspond to something in base now begin with Data.Singletons.Base.*. The convention now used in singletons-base was inspired by the conventions used in the lens library. The end result is that is now somewhat easier to figure out what parts of singletons-base to import. Because this is a significant departure from previous singletons releases, if you want to continue supporting pre-3.0 releases, you will likely need to put something like this in your .cabal file: flag singletons-3-0 description: Use @singletons-3.0@ or later. default: True library ... if flag(singletons-3-0) build-depends: singletons-base >= 3.0 -- You may also need to depend on singletons >= 3.0 or singletons-th >= 3.0 else build-depends: singletons < 3.0 ################### ## Other changes ## ################### Besides the package and module reorganization mentioned above, singletons-{,th,base}-3.0 feature a variety of new quality-of-life improvements. Here are a handful of the more notable improvements: * The OptionsM type, used for configuring how the Template Haskell machinery in singletons-th works, is now an instance of Quote. This avoids the need to use the Control.Monad.Trans.Class.lift function to lift quoted declarations into OptionsM. [2] * Data.Singletons.TH.Options now defines a promotedDataTypeOrConName option. Overriding this option can be useful in situations where one wishes to promote types such as `Nat`, `Symbol`, or data types built on top of them. [3] * The internals of the ShowSing class have been refactored to allow deriving Show instances for Sing types (e.g., deriving instance ShowSing a => Show (SList (z :: [a]))). [4] * Improve the quality of GHCi's output when using :kind on types defined by singletons-th. [5] If you encounter any issues, feel free to leave a bug report at https://github.com/goldfirere/singletons/issues. Happy (type-level) hacking, Ryan S. ----- [1] https://github.com/goldfirere/singletons/issues/420 [2] https://github.com/goldfirere/singletons/pull/484 [3] https://github.com/goldfirere/singletons/pull/462 [4] https://github.com/goldfirere/singletons/pull/486 [5] https://github.com/goldfirere/singletons/pull/446

2 1

ANN: hledger-1.21
by Simon Michael 10 Mar '21

10 Mar '21

I'm very pleased to announce hledger 1.21 ! http://hledger.org/release-notes.html#hledger-1-21 describes the user-visible changes. Highlights include: - About 10% faster/more space-efficient, and much more in some cases - Jump to any topic in the manuals from the command line - More polish for valuation and balance reports, and a new value change report - Improvements to check, print and other commands. Thank you to the following release contributors this time around: Dmitry Astapov, Arnout Engelen, Damien Cassou, aragaer, Doug Goldstein, Caleb Maclennan, Felix Van der Jeugt, heavy first time contributor Vladimir Zhelezov, and especially Stephen Morgan. hledger (http://hledger.org) is a robust, cross-platform, plain text accounting tool, with command-line, terminal and web UIs. It is an actively maintained, largely compatible reimplementation of Ledger CLI with many improvements. You can use it to track money, time, investments, cryptocurrencies, inventory and more. See also the Plain Text Accounting site (http://plaintextaccounting.org) http://hledger.org/download shows all the ways to install hledger on mac, windows or unix (stack, cabal, brew, nix, CI binaries, your package manager..). Or, run this bash script to install or upgrade to the latest release: $ curl -sO https://raw.githubusercontent.com/simonmichael/hledger/master/hledger-insta… $ less hledger-install.sh # security review $ bash hledger-install.sh New users, check out https://hledger.org/quickstart. To get help, see http://hledger.org#help-feedback, and join our chat channel via Freenode (#hledger, http://irc.hledger.org) or Matrix (#freenode_#hledger:matrix.org, http://matrix.hledger.org) Beginners and experts, contributors, sponsors, and all feedback are most welcome! Wishing you health and prosperity, -Simon

1 0

Multitier Haskell?
by Adriaan Leijnse 09 Mar '21

09 Mar '21

Dear Café, Are there any techniques for compiling a single client-server program such that clients are not distributed any server code? I'm currently looking at implementing an FRP library with a type system like Gavial's [0]. The types will make it clear on which side code belongs. My current thinking is to have Client and Server instances of a ClientServer type class which can safely implement the functions of the other side as no-ops/bottom, but I imagine that would at leastrequire a dead code elimination step after compilation to get the desired effect? Adriaan [0] https://arxiv.org/pdf/2002.06188.pdf

1 0

Re: [Haskell-cafe] FMBC 2021 - 1st CFP
by Bruno Bernardo 09 Mar '21

09 Mar '21

Apologies for the poor formatting of my previous message. You'll find below a hopefully more readable version.Sorry again for the noise. ==================================== [ Please distribute, apologies for multiple postings. ] ======================================================================== 3rd International Workshop on Formal Methods for Blockchains (FMBC) 2021 - First Call https://fmbc.gitlab.io/2021 July 18 or 19 (TBA), 2021 Co-located with the 33nd International Conference on Computer-Aided Verification (CAV 2021) http://i-cav.org/2021/ ------------------------------------------------------------- IMPORTANT DATES -------------------------------- Abstract submission: April 22, 2021 Full paper submission: April 29, 2021 Notification: June 10, 2021 Camera-ready: July 8, 2021 Workshop: July 18 or 19 (TBA), 2021 Deadlines are Anywhere on Earth: https://en.wikipedia.org/wiki/Anywhere_on_Earth -------------------------------- -------------------------------- TOPICS OF INTEREST -------------------------------- Blockchains are decentralized transactional ledgers that rely on cryptographic hash functions for guaranteeing the integrity of the stored data. Participants on the network reach agreement on what valid transactions are through consensus algorithms. Blockchains may also provide support for Smart Contracts. Smart Contracts are scripts of an ad-hoc programming language that are stored in the Blockchain and that run on the network. They can interact with the ledger’s data and update its state. These scripts can express the logic of possibly complex contracts between users of the Blockchain. Thus, Smart Contracts can facilitate the economic activity of Blockchain participants. With the emergence and increasing popularity of cryptocurrencies such as Bitcoin and Ethereum, it is now of utmost importance to have strong guarantees of the behavior of Blockchain software. These guarantees can be brought by using Formal Methods. Indeed, Blockchain software encompasses many topics of computer science where using Formal Methods techniques and tools are relevant: consensus algorithms to ensure the liveness and the security of the data on the chain, programming languages specifically designed to write Smart Contracts, cryptographic protocols, such as zero-knowledge proofs, used to ensure privacy, etc. This workshop is a forum to identify theoretical and practical approaches of formal methods for Blockchain technology. Topics include, but are not limited to: * Formal models of Blockchain applications or concepts * Formal methods for consensus protocols * Formal methods for Blockchain-specific cryptographic primitives or protocols * Design and implementation of Smart Contract languages * Verification of Smart Contracts -------------------------------- -------------------------------- SUBMISSION -------------------------------- Submit original manuscripts (not published or considered elsewhere) with a page limit of 12 pages for full papers and 6 pages for short papers (excluding bibliography and short appendix of up to 5 additional pages). Alternatively you may also submit an extended abstract of up to 3 pages (including bibliography) summarizing your ongoing work in the area of formal methods and blockchain. Authors of selected extended-abstracts are invited to give a short lightning talk. Submission link: https://easychair.org/conferences/?conf=fmbc2021 Authors are encouraged to use LaTeX and prepare their submissions according to the instructions and styling guides for OASIcs provided by Dagstuhl. Instructions for authors: https://submission.dagstuhl.de/documentation/authors#oasics At least one author of an accepted paper is expected to present the paper at the workshop as a registered participant. -------------------------------- -------------------------------- PROCEEDINGS -------------------------------- All submissions will be peer-reviewed by at least three members of the program committee for quality and relevance. Accepted regular papers (full and short papers) will be included in the workshop proceedings, published as a volume of the OpenAccess Series in Informatics (OASIcs) by Dagstuhl. -------------------------------- -------------------------------- INVITED SPEAKER -------------------------------- To be confirmed -------------------------------- -------------------------------- PROGRAM COMMITTEE -------------------------------- PC CO-CHAIRS * Bruno Bernardo (Nomadic Labs, France) (bruno(a)nomadic-labs.com) * Diego Marmsoler (University of Exeter, UK) (D.Marmsoler(a)exeter.ac.uk) PC MEMBERS To be confirmed

1 0

FMBC 2021 - 1st CFP
by Bruno Bernardo 09 Mar '21

09 Mar '21

[ Please distribute, apologies for multiple postings. ]========================================================================3rd International Workshop on Formal Methods for Blockchains (FMBC) 2021 - First Callhttps://fmbc.gitlab.io/2021July 18 or 19 (TBA), 2021Co-located with the 33nd International Conference on Computer-Aided Verification (CAV 2021)http://i-cav.org/2021/------------------------------------------------… DATES--------------------------------Abstract submission: April 22, 2021Full paper submission: April 29, 2021Notification: June 10, 2021Camera-ready: July 8, 2021Workshop: July 18 or 19 (TBA), 2021Deadlines are Anywhere on Earth:https://en.wikipedia.org/wiki/Anywhere_on_Earth----------------------… OF INTEREST--------------------------------Blockchains are decentralized transactional ledgers that rely oncryptographic hash functions for guaranteeing the integrity of thestored data. Participants on the network reach agreement on what validtransactions are through consensus algorithms.Blockchains may also provide support for Smart Contracts. SmartContracts are scripts of an ad-hoc programming language that arestored in the Blockchain and that run on the network. They caninteract with the ledger’s data and update its state. These scriptscan express the logic of possibly complex contracts between users ofthe Blockchain. Thus, Smart Contracts can facilitate the economicactivity of Blockchain participants.With the emergence and increasing popularity of cryptocurrencies suchas Bitcoin and Ethereum, it is now of utmost importance to have strongguarantees of the behavior of Blockchain software.These guarantees can be brought by using Formal Methods. Indeed,Blockchain software encompasses many topics of computer science whereusing Formal Methods techniques and tools are relevant: consensusalgorithms to ensure the liveness and the security of the data on thechain, programming languages specifically designed to write SmartContracts, cryptographic protocols, such as zero-knowledge proofs,used to ensure privacy, etc.This workshop is a forum to identify theoretical and practicalapproaches of formal methods for Blockchain technology. Topicsinclude, but are not limited to:* Formal models of Blockchain applications or concepts* Formal methods for consensus protocols* Formal methods for Blockchain-specific cryptographic primitives or protocols* Design and implementation of Smart Contract languages* Verification of Smart Contracts----------------------------------------------------------------SUBMISSION--------------------------------Submit original manuscripts (not published or considered elsewhere)with a page limit of 12 pages for full papers and 6 pages for shortpapers (excluding bibliography and short appendix of up to 5additional pages).Alternatively you may also submit an extended abstract of up to 3pages (including bibliography) summarizing your ongoing work in thearea of formal methods and blockchain. Authors of selectedextended-abstracts are invited to give a short lightning talk.Submission link: https://easychair.org/conferences/?conf=fmbc2021Authors are encouraged to use LaTeX and prepare their submissionsaccording to the instructions and styling guides for OASIcs providedby Dagstuhl.Instructions for authors: https://submission.dagstuhl.de/documentation/authors#oasicsAt least one author of an accepted paper is expected to present thepaper at the workshop as a registered participant.----------------------------------------------------------------PROCEEDINGS--------------------------------All submissions will be peer-reviewed by at least three members of theprogram committee for quality and relevance. Accepted regular papers(full and short papers) will be included in the workshop proceedings,published as a volume of the OpenAccess Series in Informatics (OASIcs)by Dagstuhl.----------------------------------------------------------------INVITED SPEAKER--------------------------------To be confirmed----------------------------------------------------------------PROGRAM COMMITTEE--------------------------------PC CO-CHAIRS* Bruno Bernardo (Nomadic Labs, France) (bruno(a)nomadic-labs.com)* Diego Marmsoler (University of Exeter, UK) (D.Marmsoler(a)exeter.ac.uk)PC MEMBERSTo be confirmed

1 0

[ANN] Copilot 3.2.1 - hard realtime C runtime verification
by Frank Dedden 08 Mar '21

08 Mar '21

Dear all, We are very pleased to announce the release of Copilot 3.2.1, a stream-based DSL for writing and monitoring embedded C programs, with an emphasis on correctness and hard realtime requirements. Copilot is typically used as a high-level runtime verification framework, and supports temporal logic (LTL, PTLTL and MTL), clocks and voting algorithms. Among others, Copilot has been used at the Safety Critical Avionics Systems Branch of NASA Langley Research Center for monitoring test flights of drones. In collaboration with the development team at Galois, Inc., the new release introduces a backend to their What4 solver frontend. With this addition, it is now possible to prove properties of Copilot specifications using What4 [4]. We thank Galois for their help and their contribution. The second big focus of this release was the documentation: the public API documentation has been improved and completed. Additionally, several small improvements and fixes are made in the C99 code generator. The newest release is available on hackage [1]. For more information, including documentation, examples and links to the source code, please visit the webpage [2]. Current emphasis is on facilitating the use with other systems, and improving the codebase in terms of stability and test coverage. Users are encouraged to participate by opening issues and asking questions via our github repo [3]. Kind regards, The Copilot developers: - Frank Dedden - Alwyn Goodloe - Ivan Perez [1] http://hackage.haskell.org/package/copilot [2] https://copilot-language.github.io [3] https://github.com/Copilot-Language/copilot [4] https://github.com/GaloisInc/what4

1 0

Second Call for Papers for the Haskell Symposium 2021
by Hage, J. (Jurriaan) 08 Mar '21

08 Mar '21

Dear all, This is the second call for papers for the upcoming Haskell Symposium. The deadline of the first round is approaching fast. Please forward to anyone that you believe might be interested. Apologies for receiving multiple copies of this announcement. Best regards, Jurriaan Hage Chair ================================================================================ ACM SIGPLAN CALL FOR SUBMISSIONS Haskell Symposium 2021 ** virtual ** Thu 26 -- Fri 27 August, 2021 http://www.haskell.org/haskell-symposium/2021/ ================================================================================ The ACM SIGPLAN Haskell Symposium 2021 will be co-located with the 2021 International Conference on Functional Programming (ICFP). Due to COVID-19 it will take place **virtually** this year. Like last year, we will be using a lightweight double-blind reviewing process. See further information below. Different from last year is that we offer a new submission category: the tutorial. Details can be found below. The Haskell Symposium presents original research on Haskell, discusses practical experience and future development of the language, and promotes other forms of declarative programming. Topics of interest include: * Language design, with a focus on possible extensions and modifications of Haskell as well as critical discussions of the status quo; * Theory, such as formal semantics of the present language or future extensions, type systems, effects, metatheory, and foundations for program analysis and transformation; * Implementations, including program analysis and transformation, static and dynamic compilation for sequential, parallel, and distributed architectures, memory management, as well as foreign function and component interfaces; * Libraries, that demonstrate new ideas or techniques for functional programming in Haskell; * Tools, such as profilers, tracers, debuggers, preprocessors, and testing tools; * Applications, to scientific and symbolic computing, databases, multimedia, telecommunication, the web, and so forth; * Functional Pearls, being elegant and instructive programming examples; * Experience Reports, to document general practice and experience in education, industry, or other contexts; * Tutorials, to document how to use a particular language feature, programming technique, tool or library within the Haskell ecosystem; * System Demonstrations, based on running software rather than novel research results. Regular papers should explain their research contributions in both general and technical terms, identifying what has been accomplished, explaining why it is significant, and relating it to previous work, and to other languages where appropriate. Experience reports and functional pearls need not necessarily report original academic research results. For example, they may instead report reusable programming idioms, elegant ways to approach a problem, or practical experience that will be useful to other users, implementers, or researchers. The key criterion for such a paper is that it makes a contribution from which other Haskellers can benefit. It is not enough simply to describe a standard solution to a standard programming problem, or report on experience where you used Haskell in the standard way and achieved the result you were expecting. A new submission category for this year's Haskell Symposium is the tutorial. Like with the experience report and the functional pearl, the key criterion for such a paper is that it makes a contribution from which other Haskellers can benefit. What distinguishes a tutorial is that its focus is on explaining an aspect of the Haskell language and/or ecosystem in a way that is generally useful to a Haskell audience. Tutorials for many such topics can be found online; the distinction here is that by writing it up for formal review it will be vetted by experts and formally published. System demonstrations should summarize the system capabilities that would be demonstrated. The proposals will be judged on whether the ensuing session is likely to be important and interesting to the Haskell community at large, whether on grounds academic or industrial, theoretical or practical, technical, social or artistic. Please contact the program chair with any questions about the relevance of a proposal. If your contribution is not a research paper, please mark the title of your experience report, functional pearl, tutorial or system demonstration as such, by supplying a subtitle (Experience Report, Functional Pearl, Tutorial Paper, System Demonstration). Submission Details ================== Early and Regular Track ----------------------- The Haskell Symposium uses a two-track submission process so that some papers can gain early feedback. Strong papers submitted to the early track are accepted outright, and the others will be given their reviews and invited to resubmit to the regular track. Papers accepted via the early and regular tracks are considered of equal value and will not be distinguished in the proceedings. Although all papers may be submitted to the early track, authors of functional pearls and experience reports are particularly encouraged to use this mechanism. The success of these papers depends heavily on the way they are presented, and submitting early will give the program committee a chance to provide feedback and help draw out the key ideas. Formatting ---------- Submitted papers should be in portable document format (PDF), formatted using the ACM SIGPLAN style guidelines. Authors should use the `acmart` format, with the `sigplan` sub-format for ACM proceedings. For details, see: http://www.sigplan.org/Resources/Author/#acmart-format It is recommended to use the `review` option when submitting a paper; this option enables line numbers for easy reference in reviews. Functional pearls, experience reports, tutorials and demo proposals should be labelled clearly as such. Lightweight Double-blind Reviewing ---------------------------------- Haskell Symposium 2021 will use a lightweight double-blind reviewing process. To facilitate this, submitted papers must adhere to two rules: 1. Author names and institutions must be omitted, and 2. References to authors' own related work should be in the third person (e.g., not "We build on our previous work" but rather "We build on the work of "). The purpose of this process is to help the reviewers come to an initial judgment about the paper without bias, not to make it impossible for them to discover the authors if they were to try. Nothing should be done in the name of anonymity that weakens the submission or makes the job of reviewing the paper more difficult (e.g., important background references should not be omitted or anonymized). In addition, authors should feel free to disseminate their ideas or draft versions of their paper as they normally would. For instance, authors may post drafts of their papers on the web or give talks on their research ideas. A reviewer will learn the identity of the author(s) of a paper after a review is submitted. Page Limits ----------- The length of submissions should not exceed the following limits: Regular paper: 12 pages Functional pearl: 12 pages Tutorial: 12 pages Experience report: 6 pages Demo proposal: 2 pages There is no requirement that all pages are used. For example, a functional pearl may be much shorter than 12 pages. In all cases, the list of references is not counted against these page limits. Deadlines --------- Early track: Submission deadline: 19 March 2021 (Fri) Notification: 23 April 2021 (Fri) Regular track and demos: Submission deadline: 21 May 2021 (Fri) Notification: 23 June 2021 (Wed) Deadlines are valid anywhere on Earth. Submission ---------- Submissions must adhere to SIGPLAN's republication policy (http://sigplan.org/Resources/Policies/Republication/) and authors should be aware of ACM's policies on plagiarism (https://www.acm.org/publications/policies/plagiarism) Program Committee members are allowed to submit papers, but their papers will be held to a higher standard. The paper submission deadline and length limitations are firm. There will be no extensions, and papers violating the length limitations will be summarily rejected. Papers should be submitted through HotCRP at: https://haskell21.hotcrp.com/ Improved versions of a paper may be submitted at any point before the submission deadline using the same web interface. Supplementary material: Authors have the option to attach supplementary material to a submission, on the understanding that reviewers may choose not to look at it. This supplementary material should not be submitted as part of the main document; instead, it should be uploaded as a separate PDF document or tarball. Supplementary material should be uploaded at submission time, not by providing a URL in the paper that points to an external repository. Authors can distinguish between anonymized and non-anonymized supplementary material. Anonymized supplementary material will be visible to reviewers immediately; non-anonymized supplementary material will be revealed to reviewers only after they have submitted their review of the paper and learned the identity of the author(s). Resubmitted Papers: authors who submit a revised version of a paper that has previously been rejected by another conference have the option to attach an annotated copy of the reviews of their previous submission(s), explaining how they have addressed these previous reviews in the present submission. If a reviewer identifies him/herself as a reviewer of this previous submission and wishes to see how his/her comments have been addressed, the conference chair will communicate to this reviewer the annotated copy of his/her previous review. Otherwise, no reviewer will read the annotated copies of the previous reviews. Proceedings =========== Accepted papers will be included in the ACM Digital Library. Their authors will be required to choose one of the following options: - Author retains copyright of the work and grants ACM a non-exclusive permission-to-publish license (and, optionally, licenses the work with a Creative Commons license); - Author retains copyright of the work and grants ACM an exclusive permission-to-publish license; - Author transfers copyright of the work to ACM. For more information, please see ACM Copyright Policy (http://www.acm.org/publications/policies/copyright-policy) and ACM Author Rights (http://authors.acm.org/main.html) Accepted proposals for system demonstrations will be posted on the symposium website but not formally published in the proceedings. Publication date: The official publication date of accepted papers is the date the proceedings are made available in the ACM Digital Library. This date may be up to two weeks prior to the first day of the conference. The official publication date affects the deadline for any patent filings related to published work. Artifacts ========= Authors of accepted papers are encouraged to make auxiliary material (artifacts like source code, test data, etc.) available with their paper. They can opt to have these artifacts published alongside their paper in the ACM Digital Library (copyright of artifacts remains with the authors). If an accepted paper's artifacts are made permanently available for retrieval in a publicly accessible archival repository like the ACM Digital Library, that paper qualifies for an Artifacts Available badge (https://www.acm.org/publications/policies/artifact-review-badging#available) Applications for such a badge can be made after paper acceptance and will be reviewed by the PC chair. Program Committee ================= Edwin Brady University of St Andrews Koen Claessen Chalmers University of Technology Dominique Devriese Vrije Universiteit Brussel Andy Gill University of Kansas Jurriaan Hage (chair) Universiteit Utrecht Zhenjiang Hu Peking University Ranjit Jhala University of California Patricia Johann Appalachian State University Yukiyoshi Kameyama University of Tsukuba George Karachalias Tweag Ralf Laemmel University of Koblenz-Landau Daan Leijen Microsoft Research Ben Lippmeier Ghost Locomotion Neil Mitchell Facebook Alberto Pardo Universidad de la Republica, Uruguay Matt Roberts Macquarie University Janis Voigtlaender University of Duisburg-Essen Nicolas Wu Imperial College London If you have questions, please contact the chair at: j.hage(a)uu.nl ================================================================================

1 0

Announcing `passveil` 0.0.1.0
by raichoo 08 Mar '21

08 Mar '21

Hi everyone, My company antei (https://antei.de) has developed a password manager for our internal usage and we have decided to open source it. We drew a lot of inspiration from the well established `password-store`. It's build in Haskell and uses `darcs` for versioning the password store. We have chosen `darcs` because of its powerful merging capabilities which turned out to be useful for our use case. Apart from that, we have implemented a trust system, that can be used to transfer knowledge of a password to other people having access to the store, so we do not have to rely on transmitting sensitive data via insecure channels (https://sysadminotaur.devolutions.net/30-vault) Please note that `passveil` is in an early state and has only been tested and used internally. We strongly believe in open source and making our tools available to others and are constantly working on improving our code and want share our progress with everyone. Check out: https://passveil.antei.de for more information. Kind regards, raichoo

1 0

Profiling analyzing ghc compilation
by Martin Heuschober 05 Mar '21

05 Mar '21

Hi, Is there a way to profile (time/space) GHC compilation itself, I'd be interested in what compilation steps in compiling my project take long and how much RAM it uses/why it uses so much RAM, so I can identify what to rewrite, remove, and split to get a leaner build. Thanks, Martin PS.: I hope this is the right place to ask this.

3 2

Haskell.org Call For Nominations
by Rebecca Skinner 05 Mar '21

05 Mar '21

Dear Haskellers, As you may know, Emily Pillmore has recently stepped down from her role on the Haskell.org committee as she focuses full time on her new role as the CTO of the Haskell Foundation. We are currently seeking nominations for anyone interested in filling her vacated seat on the committee. The term for this seat will end in October of 2021, so it will be a good opportunity for anyone who is interested in serving for a short time, perhaps to get a better idea of whether they would like to be re-nominated for a full term at the end of the year. The role is about setting policy, providing direction/guidance for Haskell.org infrastructure, planning for the long term, and being fiscally responsible with the Haskell.org funds and donations. As overseers for policy regarding the open source side of Haskell, committee members must also be able to set aside personal or business related bias and make decisions with the good of the open source Haskell community in mind. For more information about the haskell committee please visit https://www.haskell.org/haskell-org-committee/ To nominate yourself, please send an email to committee(a)haskell.org no later than 12 March 2021. Q: If selected for this role, will I serve a normal 3-year term? A: No, you will serve the remainder of the term for the seat, which will end in October of 2021. Q: If I was nominated for a seat during the 2021 election and was not selected, am I eligible for re-nomination? A: We had a number of great candidates for the recent election and we would welcome anyone who was not selected to re-nominate themselves for this seat. Q: If selected, am I eligible for re-nomination at the end of the year? A: Yes, if you are selected and serve you may be re-nominated for a full 2022-2025 term. Q: Who can be nominated to serve on the committee? A: Anyone who has something to contribute. Committee members do not need to be deep technical Haskell experts. Instead we look for enthusiasm towards improving the Haskell community. We aim to represent the different facets of the community. We aim to be diverse in terms of industry or research, and in terms of gender, race and location. Q: What should I include in my nomination? A: Tell us a bit about who you are, and how you think you can help. Feel free to include anything that you think will help us make a better decision. Q: What is involved in membership? A: Being a member of the committee does not necessarily require a significant amount of time, but committee members should aim to be responsive during discussions when the committee is called upon to make a decision. For more information, or any other questions, please reach out to the committee by email. - Rebecca Skinner on behalf of the Haskell.org Committee

1 0

Re: [Haskell-cafe] naturally, length :: a -> Int
by Olaf Klinke 05 Mar '21

05 Mar '21

> Date: Thu, 4 Mar 2021 11:36:14 +0100 > From: Ben Franksen <ben.franksen(a)online.de> > To: haskell-cafe(a)haskell.org > Subject: Re: [Haskell-cafe] naturally, length :: a -> Int > Message-ID: <s1qd6u$l43$1(a)ciao.gmane.io> > Content-Type: text/plain; charset=utf-8 > > Am 03.03.21 um 16:17 schrieb Olaf Klinke: > > Which bugs can be caught at compile-time by having length return > > natural numbers? Regarding space, Int instead of Word only wastes the > > sign bit, doesn't it? > > > > I like the idea that Johannes Waldmann and Jaro Reinders brought up: > > Why is length :: Foldable a => a -> Int so convenient? Short answer: > > Because of "affine" things like `availableSpace - length xs'. > > > > There are indeed two types involved here, as the foundation package > > points out: relative offsets (like a tangent space?) and absolute > > counts. Think of NominalDiffTime versus UTCTime, or the two > > interpretations of vectors as points/movements in space. > > > > In this light one could regard the current length as > > "the relative offset of the end of the list" which can readily be > > subtracted from another relative offset. In mathematical terms: Int the > > free group over the monoid of cardinal lengths. > > Hm, interesting point. > > If we do embrace that viewpoint, then I'd say we should go all the way > and interpret indices modulo (non-negative) structure size! This makes > (safe) indexing total (for non-empty structures) and allows things like > xs !! (-1) == last xs as in Perl and some other languages. Unsafe > indexing (as in the vector package) could remain as is for performance > critical code. > > Cheers > Ben I like Haskell particularly for not being like Matlab, where virtually any well-bracketed indexing syntax does produce a result, but not necessarily what you intended or expected. Besides, for some structures length is expensive but index is not so much, so I wonder whether one can modulo-index into a lazy container without evaluating its entire spine. I just wanted to understand/justify why Int is so convenient, and the Time-DiffTime analogy sprang to mind. Following the free group route, one immediately sees that there is an embedding from cardinalities to offsets, but no inverse. We could, of course, bring other categories into the picture such as ordered sets. Then there is an embedding-projection pair between Int and Natural, where all Ints < 0 are mapped to 0. The base functions such as take and drop adhere to this interpretation. Olaf

2 1

Serious bug with Natural in GHC 9.0.1
by Sylvain Henry 05 Mar '21

05 Mar '21

Hi Café, I've made a mistake while implementing constant folding for Natural numbers in GHC 9.0.1 that hasn't been caught before the release. It's a rather serious bug as any number converted into `Natural` with `fromIntegral` can be truncated to Word range if a bogus rule is triggered (see #19345 and #19411 for more details). It is already fixed in HEAD and the fix will be present in GHC 9.0.2 which should be released soon. In the meantime you can check if the rule is triggered with `-ddump-rule-firings`. If it shows that the following rule has fired, then your code may be badly modified: |Rule fired: fromIntegral/Int->Natural (GHC.Real)| (the issue is that despite its name the rule isn't correctly constrained to convert Ints into Natural, but any numeric type...). Sorry about that! Sylvain #19345: https://gitlab.haskell.org/ghc/ghc/-/issues/19345 #19411: https://gitlab.haskell.org/ghc/ghc/-/issues/19411

2 1

naturally, length :: a -> Int
by Johannes Waldmann 04 Mar '21

04 Mar '21

Dear Cafe - let's fight Int. In a lot of code I write (for research, teaching, production), a lot of numbers are in fact natural numbers - because I am counting (e.g., number of elements in a collection) or pointing into what I just counted (e.g., Data.Set.elemAt). But Haskell's "most natural" type is - Int. At least that's my impression from current usage in libraries and teaching examples (see functions length, replicate, ... ). I've developed a horror of reading and writing "length something :: Int". As I will be teaching an introductory class on FP soon, I am looking for ways to handle this. One option is presented in Bird/Gibbons: Algorithm Design with Haskell, which has "type Nat = Int" on page 6. Actually, that's the very first code example that appears in the book! The footnote there refers to a remark in Data.Word that has since been dropped? Now there is Numeric.Natural, (cf. https://mail.haskell.org/pipermail/libraries/2014-November/024203.html ) and numeric literals are already overloaded, so we can just use that? Well, yes and no - we still have to write a type conversion each time we use some library function that insists on Int, or, write cumbersome "genericLength". Also (but that is the lesser concern), Numeric.Natural is for arbitrary-length numbers (corresponding to Integer), while I might sometimes know that numbers are representable in a machine word, and I don't want to pay for the implied pattern match (data Natural = NatS Word | NatJ BigNat). I am willing to pay for underflow checks (on subtraction), and for overflow checks (if there's an upper bound). If I want to live risky (no checks) I could use Data.Word. So, what do you do? (Yes, Peano numerals ...) Or, how do we convince ourselves (and our students) of keeping the current status? NB: here is another practical argument for Natural (from production code, an auto-grading system for student homework) We use datatype-generic parsers heavily. For data Foo = Foo { ... :: Nat ... }, bad input will be rejected by the parser already, and I need no extra checks later on. Less code! I sometimes even use "Pos(itive)". That's all fine and dandy - until I call some library function... - J.W.

8 8

aeson: instance FromJSON IntMap
by Olaf Klinke 03 Mar '21

03 Mar '21

Dear Cafe, why is Aeson's instance FromJSON IntMap so different from the instance of Map? Apparently the Map instance expects an Object (the dictionary) while the IntMap instance [1] is implemented using IntMap.fromList, so it expects an array. I can of course decode the JSON as (Map Int) and then use IntMap.fromAscList . Map.assocs but how efficient is that? And it also relies on Map.assocs producing the list in the order expected by fromAscList which (unlikely) could be broken in a future version of containers. Thanks Olaf [1] https://hackage.haskell.org/package/aeson-1.5.6.0/docs/src/Data.Aeson.Types…

3 2

International Conference on Applied Data Science and Intelligence - (ADSI 2021) Prague
by matteo＠confscience.com 03 Mar '21

03 Mar '21

Call for papers ************************************************* International Conference on Applied Data Science and Intelligence - (ADSI 2021) Prague- Czech Republic, October 14-15, 2021 https://confscience.com/adsi/ Submission deadline: April 1, 2021 All papers accepted in ADSI 2021 will be published in Springer CCIS (Communications in Computer and Information Science). CCIS is abstracted/indexed in Scopus, SCImago, EI-Compendex, Mathematical Reviews, DBLP, Google Scholar, and Thomson Reuters Conference Proceedings Citation (Former ISI Proceedings) *************************************************************************** IMPORTANT DATES: - Paper Submission: April 1, 2021 - Acceptance Notification: July 1, 2021 - Final Manuscript Due: September 1, 2021 *************************************************************************** The ADSI 2021 conference will be held in Conjunction with: International Conference on Recent Theories and Applications in Transportation and Mobility (RTATM 2021) International Conference on Informatics Revolution for Smarter Healthcare (IRSH 2021) *************************************************************************** TOPICS: Authors are invited to submit their original papers to address the topics of the conference, including but not limited to: FUNDAMENTALS AND THEORIES - Theoretical Models - Spatial and temporal multi-models - Multi-dimensional data - Data acquisition and pre-processing - Data inference - Data Classification and Taxonomy - Data Metrics - New approaches for collaboration and competition - Self-organization, self-healing, fault-tolerance approaches - Spatial reasoning - Context awareness - Intelligent mobility - New approaches to supervised and unsupervised learning - New approaches for security, privacy, trust, and ethics in data science - Real-time data analytics - Multi-Agent Systems for data science - Distributed data analytics - Data authenticity - New theories and approaches for Deep learning - New approaches for Business Intelligence - Fuzzy logic - Decision trees - Support vector machines - Evolutionary computation - Statistical methods - Collaborative filtering - Data engineering - Content mining - Indexing schemes - Information retrieval - Metadata use and management INTELLIGENT DATA PROCESSING AND ANALYTICS - Multi-level data processing - Data analytics optimization - Smart data mining - Machine Learning - Deep Learning - Bio-Inspired Computing - Secure data analytics - Privacy in data analytics - Trust in Big Data - Business intelligence - Visualization Analytics - Intelligence as a Service (IaaS) - Data Science as a Service (DSaaS) - Natural Language Processing - Signal Processing - Simulation and Modeling - Data-Intensive Computing SYSTEMS AND INFRASTRUCTURES - Data storage infrastructure - Data warehouses - Data Query and Indexing Technologies - Software Defined Infrastructures - Software Defined Networks (SDN) - Distributed data systems - Smart grid computing - Intelligent data management - Big Data computing - Smart data networking - Internet of Things - Cyber Physical Systems - Blockchain - Fog and Edge intelligence - Parallel Computing systems - Open Source systems for data science - Embedded intelligence - Embedded data science - In-Memory computing - Intelligent drones - Internet of Drones - Real-time data acquisition systems APPLICATIONS - Intelligent Hazard management - Intelligent data science in healthcare - Intelligent data science in farming - Intelligent data science in Oil and Gas - Smart logistics - Intelligent data science in transportation - Intelligent data science in surveillance - Xtech (Fintech, Agritech, etc.) - Intelligent drones - Digital transformation - Bioinformatics - Marketing - Social Science - E-learning and E-services *************************************************************************** OUTSTANDING PAPERS: Based on the peer review scores as well as the presentations at the conference, the authors of outstanding papers will be invited to extend their works for a potential publication in journals special issues with high impact factors. *************************************************************************** PAPER SUBMISSION: Papers must be submitted electronically as PDF files via easychair (https://easychair.org/conferences/?conf=adsi2021) All papers will be peer reviewed. Length of Full papers: 12-15 pages long (written in the LNCS/CCIS one-column page format, 400 words per page) Length of Short papers: less than 12 pages For more information, please refer to the conference website: https://confscience.com/adsi/ *************************************************************************** CONTACT For more information, please send an email to info-adsi(a)confscience.com

5 5

International Conference on Informatics Revolution for Smarter Healthcare (IRSH 2021) Prague
by matteo＠confscience.com 03 Mar '21

03 Mar '21

Call for papers ************************************************* International Conference on Informatics Revolution for Smarter Healthcare (IRSH 2021) Prague- Czech Republic, October 14-15, 2021 https://confscience.com/irsh/ Submission deadline: April 1, 2021 All papers accepted in IRSH 2021 will be published in Springer CCIS (Communications in Computer and Information Science). CCIS is abstracted/indexed in Scopus, SCImago, EI-Compendex, Mathematical Reviews, DBLP, Google Scholar, and Thomson Reuters Conference Proceedings Citation (Former ISI Proceedings) *************************************************************************** IMPORTANT DATES: - Paper Submission: April 1, 2021 - Acceptance Notification: July 1, 2021 - Final Manuscript Due: September 1, 2021 *************************************************************************** The IRSH 2021 conference will be held in Conjunction with: International Conference on Applied Data Science and Intelligence (ADSI 2021) International Conference on Recent Theories and Applications in Transportation and Mobility - (RTATM 2021) *************************************************************************** TOPICS: Authors are invited to submit their original papers to address the topics of the conference, including but not limited to: FUNDAMENTALS AND THEORIES - Interoperability and Data Integration - Confidentiality and Data Security - Data protection - Data Sharing - Security, Privacy, and Trust - Emergent healthcare standards - Emergent healthcare architectures - ICT, Ageing and Disability - Physiological and behavioural modelling - Pandemic and disease modeling - Usability and user experience of medical devices - Human behaviour - Clinical investigation regulatory frameworks - Integrated healthcare approaches - eHealth data standards and interoperability (e.g. HL7/FHIR) - Databases and data warehousing - Big Data and Open Data for healthcare - Design and Development of Methodologies for Healthcare - Emergent Communication Technologies - Real-time interaction theories - Emergent Technologies for Ambient Assisted Living - User Interface Design for healthcare - Sustainability - New approaches for accuracy and effectiveness - Data mining and bioinformatics - Enhanced living environments - Analysis and evaluation of healthcare systems INTELLIGENT HEALTHCARE - Pattern recognition and Machine - Learning for healthcare - Cognitive Informatics - Big Data in Healthcare - Wellbeing Informatics - Data Mining and Data Analytics - Data Visualization - Smart environments - Smart Ambient Assisted Living - Intelligent healthcare solutions - Agent-based solutions for healthcare - Collaboration systems - Intelligent Electronic Health Records - Internet of Things for healthcare - Cyber-Physical Systems for healthcare - Ambient Computing and Reasoning - Context Awareness - Smart devices for eldercare - Autonomy and active ageing - Emergent technologies for intelligent Computer Vision - Service production and delivery - Gamification - Multi-modal interaction - Computer-aided detection and diagnosis - Crowdsourcing for smarted healthcare SERVICES, SYSTEMS, AND INFRASTRUCTURES - Emergent healthcare services - Pervasive health systems and services - Remote healthcare management - Emergent healthcare infrastructure - Industry Revolution 4.0 for healthcare - eHealth - Electronic health records - Assistive technologies - Disease surveillance and patient monitoring systems - Prevention and detection systems - Home monitoring - Healthcare management systems - ICT-based therapeutic systems - ICT-based rehabilitation technologies - Wearable health informatics - Emergent technologies for data analytics - Ambient Assisted Leaving (AAL) - Decision Support Systems - Emergent Technologies for Remote AAL Monitoring - Emergent Technologies and Accessibility - 5G for healthcare - Healthcare supply chain and logistics - Wireless Body Networks - Telemedicine and mobile telemedicine - Mobile Systems - Software Defined infrastructures - Patient empowerment systems - Smart technology for remote patient visits - Biosensors - Medical devices APPLICATIONS - eHealth applications - Application of health informatics in clinical cases - Mobile technologies for healthcare applications - Software Systems in healthcare - Social networking and healthcare - Case Studies - Personalization and patient experience - AR and VR applications - Patient billing - Accounting systems - Personnel and payroll - Materials management - Voice recognition systems - Asset management solutions - Disease management - Feedback integration - Clinical software - Crowd-computing applications - Future directions - Drone-based solutions - Software Defined Networks for healthcare *************************************************************************** OUTSTANDING PAPERS: Based on the peer review scores as well as the presentations at the conference, the authors of outstanding papers will be invited to extend their works for a potential publication in journals special issues with high impact factors. *************************************************************************** PAPER SUBMISSION: Papers must be submitted electronically as PDF files via easychair (https://easychair.org/conferences/?conf=irsh2021) All papers will be peer reviewed. Length of Full papers: 12-15 pages long (written in the LNCS/CCIS one-column page format, 400 words per page) Length of Short papers: less than 12 pages For more information, please refer to the conference website: https://confscience.com/irsh/ *************************************************************************** CONTACT For more information, please send an email to info-irsh(a)confscience.com

1 0

Re: [Haskell-cafe] naturally, length :: a -> Int
by Johannes Waldmann 02 Mar '21

02 Mar '21

Dear Cafe, thanks for ideas and arguments. > [Ben Franksen] I would support a move Int->Word in all libraries > where that makes sense. I find it hard to think of a library where that does NOT make sense... The following is somewhat related but actually orthogonal: I mentioned that numbers often arise as cardinalities (so they are natural, by definition) and serve as pointers. The next step is then: pointer type safety. Vincent Hanquez' Foundation https://hackage.haskell.org/package/foundation-0.0.25 defines class (IsList c, Item c ~ Element c) => Collection c where length :: c -> CountOf (Element c) class ( ... Collection c) => Sequential c where take :: CountOf (Element c) -> c -> c with newtype CountOf ty (and there's also newtype Offset ty) I tend to agree. The phantom type argument for CountOf would catch errors like adding the number of students to the number of exercises (in my application). (Well and the next step after that would be to have the size of the collection in the (dependent) type as well.) Current implementation is newtype CountOf ty = CountOf Int and the author adds (and that was also the point I was making) "Int is a terrible backing type which is hard to get away from, considering that GHC/Haskell are mostly using this for [counting and] offset. Trying to bring some sanity by a lightweight wrapping." NB: I found out about this from Michael Snoyman's (very much entertaining, and too much true) https://www.snoyman.com/blog/2020/12/haskell-bad-parts-3/ Best regards, J.W.

2 1

Puzzling instance method definitions in Data.Sequence.Internal
by Viktor Dukhovni 02 Mar '21

02 Mar '21

In `containers`, Data.Sequence.Internal defines a Foldable instance for `Seq` with method definitions for `length` and `null` that I'm struggling to understand: https://github.com/haskell/containers/blob/master/containers/src/Data/Seque… #if MIN_VERSION_base(4,8,0) length = length {-# INLINE length #-} null = null {-# INLINE null #-} #endif further down the file there are also explicit top-level definitions for these functions: https://github.com/haskell/containers/blob/master/containers/src/Data/Seque… -- | $ O(1) $. Is this the empty sequence? null :: Seq a -> Bool null (Seq EmptyT) = True null _ = False -- | $ O(1) $. The number of elements in the sequence. length :: Seq a -> Int length (Seq xs) = size xs So the intent seems clear, but I don't understand how the instance method definitions are valid. The imports of Both Prelude and Data.Foldable don't include `length` or `null`: https://github.com/haskell/containers/blob/master/containers/src/Data/Seque… So the RHS definitions should plausibly resolve to the top-level functions, but when I try to define a similar type class instance GHC tells me: ‘method’ is not a (visible) method of class ‘Class’ and in any case I'd expect `length = length` to yield an infinite loop, regardless of any other bindings in the outer scope. How is Data.Sequence.Internal getting away with this??? -- Viktor.

2 2

DatatypeContexts / alternative
by CASANOVA Juan 01 Mar '21

01 Mar '21

Hello again, Haskell Cafe, Here again with another doubt on how am I supposed to. This one should be fairly easier, I believe. In short, I would like to have a functor type that can only be applied to certain type parameters. Why? Well, something like this: module DatatypeContextsExample where import Data.Map import Data.Bifunctor data Foo t = Foo (Map t t) instance Functor Foo where fmap f (Foo m) = Foo (fromList (fmap (bimap f f) (toList m))) This does not compile, because I am using toList and fromList, which require (Ord t). But I cannot really have Foo be a functor in this way without it. The thing is, every time I am going to use it, t is actually going to be Ord. But how do I tell Haskell to have this constraint? DatatypeContexts seems to be the extension that allows this: data Ord t => Foo t = Foo (Map t t) But this has two issues. First, DatatypeContexts is deprecated. Second, more importantly, it still does not type check! It produces the exact same error, saying that Ord t could not be inferred. It should be inferred from the very fact that I am using the type Foo, but GHC does not seem to want to understand this. I could also try with GADTs: data Foo t where Foo :: Ord t => Map t t -> Foo t But this still gives the same error on the fmap definition, stating it cannot use Foo without Ord. But I am pattern-matching against it, shouldn't that be enough to know that (Ord t) is going to hold? I don't understand it. Is there anything simple I am missing? Any other simple way to achieve this? Any fundamental problem with what I am trying to do? Thanks as usual, Juan. The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336. Is e buidheann carthannais a th' ann an Oilthigh Dhùn Èideann, clàraichte an Alba, àireamh clàraidh SC005336.

5 14

Re: [Haskell-cafe] Not too extensible records?
by Anthony Clayden 01 Mar '21

01 Mar '21

Hi Ignat, as an example of what an extensible records system might look like in Haskell, you could play with Hugs.Trex -- https://www.haskell.org/hugs/pages/hugsman/exts.html#sect7.2 To match a few of its features to your post: > suppose I have two functions: one is a layout algorithm that assigns to nodes some spatial positions, and the second is a topological algorithm that discerns roots and leaves. These two functions are conceptually independent and ... r1 = (label = blah1) r2 = (topology = blah2 | r1) r3 = (v2 = blah3 :: Double | r2) The `( ... | r1)` means extend `r1` with some extra field or fields comma-separated. This is an 'extensible' 'anonymous' records system -- 'anonymous' in that you don't pre-declare your record types via `data`. You can name your record types, either with a `type` decl or with a `newtype` that provides a constructor for known-in-advance types. > may be applied in any order, Yes you can extend an existing record with arbitrary fields, the result is always a 'flat' tuple with the labels-value pairs forming a set: two records are same type providing they have the same set of labels and the same field types at each label, irrespective of how the labels got added. > I would like to make sure their fields are not mixed. > I need to be able to add more and more fields to labels, but in such a way that it is impossible to assign an unsuitable field. There's a so-called 'lacks' constraint you can put on record operations (written with backslash): foo :: r1\topology => Rec r1 -> a -> Rec (edges :: a | r1) is the type of a function that will extend record type `r1` lacking label 'topology' with a field `edges` at type `a`. You can put record types with lacks constraints on instances: instance (r2\v2) => Foo (Rec (label :: String | r2)) (Rec (v2 :: Double, label :: String | r2)) where ... holds for any record that includes label `label` at `String`, and possibly other labels in `r2`, but lacks `v2`. (I'm presuming there's a FunDep on Foo so the second instance parameter is the return type.) > a huge number of `HasThis` and `HasThat` instances That instance head is in effect a `Has` `label` constraint. There's also a shorthand `#label` that generates a function to extract the value at `label` **from any record with a `label`** -- that is, Hugs infers the `Has` constraint for you. > it seems to me that some smart technology is needed to make this manageable. I'm not seeing Trex as 'smart'. It follows conventional relational algebra semantics; was developed ~1996; last release of Hugs was 2006. I'd have thought GHC would come up with something comparable by now. As Olaf's and Henning's replies show, you could fake it with "a lot of boilerplate" and/or some dubious type trickery. AntC

1 0

Desktop GUI in Haskell
by A. Mc. 28 Feb '21

28 Feb '21

Hello, I'm attempting to use GTK+3 to create a Desktop, but I am having a problem installing all of the dependencies. I keep getting the following error: GUI cabal: version >=0.9.0 of pkg-config is required I am using Cygwin on a Windows 10 operating system. What is needed to fix this? Is this the best way to do a desktop GUI in Haskell? Thanks in advance and thank you for your time.

7 6

[ANN] HGeometry-0.12
by Lemmih 28 Feb '21

28 Feb '21

It is our great pleasure to announce version 0.12 of HGeometry! HGeometry is a swiss army knife for computational geometry. Wondering if a point is inside a polygon? HGeometry will tell you. Looking for the shortest path inside a maze? HGeometry will light your way. Planning a museum heist? HGeometry will show you the camera blindspots in O(n log n) time! Check out our website for more: https://hgeometry.org/ HGeometry is open to contributors at all levels of Haskell experience and we have a list of weekend-sized projects. Ask in the Discord server for guidance and/or pair programming. New in 0.12: - Algorithms: - Visibility polygon in O(n log n). - Earclip triangulation in O(n^2) worst case, O(n) expected case. - Single-source shortest path in O(n). - Planar point locator in O(log n). - Point set diameter in O(n log n). - Convex hull of a polygon in O(n). - Diameter of a convex polygon in O(n). - Check if a point lies inside a convex polygon in O(n). - Bug fixes and improved numerical robustness. - Property testing and several methods for generating random polygons. - See changelog.org for an exhaustive list of changes. Future developments: - Bring Haddock documentation coverage up to 100%. Currently, we're in the low eighties. - A holistic approach to demonstrating correctness: - Proven algorithms. - Unit testing for hand-picked corner cases. - Property testing with randomly generated polygons / geometric data. - Exhaustive property testing with real-world datasets (osm). - Benchmarks to show the relative performance of HGeometry's many algorithms. Contributors: - Frank Staals, @noinia - David Himmelstrup, @Lemmih - Hunter DeMeyer, @1ndy Website: https://hgeometry.org GitHub: https://github.com/nionia/hgeometry Hackage: https://hackage.haskell.org/package/hgeometry Discord: https://discord.gg/HQwbD9jWqg

1 0

What is your favourite graph library?
by Ignat Insarov 28 Feb '21

28 Feb '21

Hello! I really like graphs. People seem to like thinking in terms of dots and arrows, and graph theory provides a formalization for this. (Homogeneous binary) relations, finite state automata, networks and categories are sorts of graphs too. But unfortunately it is not possible to represent a graph as an algebraic type. For example, a list is a fixed point of a maybe tuple, and every usual linear container _(an array, a vector, a sequence…)_ is isomorphous to a list, so we have an easy time prototyping and specifying the behaviour of any such thing. With graphs, we have a hard time! The most popular library for graphs in Haskell is `fgl`. Unfortunately, it is really easy to get weird behaviour with it, because folds tear away the limbs from contexts so that your observation of said contexts depends on the order of folding. I have been poking at it, trying to make graphs resemble a comonad… but of course you can have an empty graph, and a comonad cannot be empty. There is also `alga` — it seemed promising, but now it is deprecated for some reason… The usual `containers` also provide something they call a graph, but it does not offer much in terms of instances and algorithms — a graph is merely a type alias to an array. So, is there any cool library that I missed? Or some promising research? Do you know of any packages that use graphs heavily and in interesting ways? Are you curious to see progress in this area?

6 5

Re: [Haskell-cafe] Not too extensible records?
by Olaf Klinke 27 Feb '21

27 Feb '21

> I have a situation that I think is a good case to apply extensible records to. I > have two kinds of entities that are both extensible but in different ways — I > would like to make sure their fields are not mixed. At the same time, I want to > be able to extend the sets of fields across several modules. Is it possible and > is it practical? > My case is that I have a type for graphs that is a bifunctor — in node labels > and edge labels. > So, I need to be able to add more and more fields to labels, but in such a way > that it is impossible to assign an unsuitable field. If your graph is already a bifunctor, why not use a disctinct label or node type in each use case/module? That certainly fits the requirement of not mixing fields. Then you could go the old-fashioned way of type classes, e.g. class HasTopology label where topology :: label -> Topology instance HasTopology Topology where topology = id instance HasTopology label => HasTopology (label,moreInfo) where topology = topology.fst Or for updateable fields, use a Lens Topology. This is a lot of boilerplate, I admit, but you have fine-grained control over what your types have in common. Nested pairs are type- level polymorphic lists and with the right type classes can be used as such, if the list of types is known at compile-time. It is similar to what mtl does with the MonadFoo classes. Olaf

3 3

Not too extensible records?
by Ignat Insarov 27 Feb '21

27 Feb '21

Hello! I have a situation that I think is a good case to apply extensible records to. I have two kinds of entities that are both extensible but in different ways — I would like to make sure their fields are not mixed. At the same time, I want to be able to extend the sets of fields across several modules. Is it possible and is it practical? My case is that I have a type for graphs that is a bifunctor — in node labels and edge labels. I want to gradually decorate these labels with more and more information. For nodes, it may be the number of outgoing edges or the position of the node in space. For edges, it may be whether an edge is directed or not, or whether it was added by some computation, like say transitive closure. So, I need to be able to add more and more fields to labels, but in such a way that it is impossible to assign an unsuitable field. It would be nonsense if a node was said to be undirected or for an edge to be declared a leaf. I would also like not to provide all the labels ahead of time, but rather define whatever labels are needed in the module that defines the corresponding decorating functions. An example for the sort of things I have in mind: class Suitable label type | label → type … data Topology = Root | Internal | Leaf instance Suitable Topology NodeLabels detectTopology ∷ graph someNodeLabels whateverEdgeLabels → graph (someNodeLabels + Topology) whateverEdgeLabels I looked into `extensible` and `vinyl`. * `extensible` does not seem to fit because it defines field labels to be type level strings, making them all interchangeable — there is no way to enforce the distinction between labels suitable for nodes and for edges. * `vinyl` seems to be more flexible and low level, but this also means that it is steeper to learn. The example from the repository uses an enumeration to define a set of labels for a type of records, and this means that the set of labels cannot be extended across modules — this is a problem for me and I am not sure if it can be solved within `vinyl`. What should I do?

1 0

Is there a StateT but with resulting pair swapped?
by Javran Cheng 26 Feb '21

26 Feb '21

Hi cafe, I'm playing with alex recently and noticed that: newtype Alex a = Alex {unAlex :: AlexState -> Either String (AlexState, a)} which is almost StateT AlexState (Except String), and looks like I can make a MonadError instance out of it. Therefore I'm curious if there's any existing package that has newtype StateT' s m a = StateT' (s -> m (s, a)) -- note the swapped pair here so that I can just deriving (MonadError String) via StateT' AlexState (Except String) to implement MonadError. Thanks! -- Javran (Fang) Cheng

2 1

Re: [Haskell-cafe] Problem with stack
by Olaf Klinke 25 Feb '21

25 Feb '21

> Are you building on a networked filesystem? > > Here's a somewhat similar report where switching to a completely local > filesystem has resolved the issue. Speaking of which, is there a specification about what filesystem features stack and its sub-tools expect? I can not build stack projects on a remote cifs share, but on the local filesystem it works fine. The error is Encountered error while migrating Stack database: SQLite3 returned ErrorBusy while attempting to perform step: database is locked Please report this on https://github.com/commercialhaskell/stack/issues I suspect that things like symlinks are expected to work, which samba does not support despite the target drive being ext4. Olaf

4 5

International Conference on Recent Theories and Applications in Transportation and Mobility - (RTATM 2021) Prague
by matteo＠confscience.com 25 Feb '21

25 Feb '21

Call for papers ************************************************* International Conference on Recent Theories and Applications in Transportation and Mobility - (RTATM 2021) Prague - Czech Republic, October 14-15, 2021 https://confscience.com/rtatm/ Submission deadline: April 1, 2021 All papers accepted in RTATM 2021 will be published in Springer CCIS (Communications in Computer and Information Science). CCIS is abstracted/indexed in Scopus, SCImago, EI-Compendex, Mathematical Reviews, DBLP, Google Scholar, and Thomson Reuters Conference Proceedings Citation (Former ISI Proceedings) *************************************************************************** IMPORTANT DATES: - Paper Submission: April 1, 2021 - Acceptance Notification: July 1, 2021 - Final Manuscript Due: September 1, 2021 *************************************************************************** The RTATM 2021 conference will be held in Conjunction with: International Conference on Applied Data Science and Intelligence (ADSI 2021) International Conference on Informatics Revolution for Smarter Healthcare (IRSH 2021) *************************************************************************** TOPICS: Authors are invited to submit their original papers to address the topics of the conference, including but not limited to: FUNDAMENTALS AND THEORIES - Modelling and Simulation Algorithms - Vehicular Wireless Medium Access Control - V2X communications - Routings and Protocols for Connected Vehicles - Mobility Models and Architectures - Distribution Strategies - Traffic Incident Management Systems - Bio-Inspired Approaches - Optimization and Collaboration - Automatic Control in Vehicular Networks - Energy-aware Connected Mobility - Programming Languages - Sustainable Transportation - Multimodal Transportation Networks and Systems - Systemsb Integration - Driver Behavior Models and Simulation - Human Factors and Travel Behaviour - Green Mobility - Regulations and Bylaws for Intelligent - Transportation and Mobility SMART TRANSPORTATION AND LOGISTICS - Mobility Management - Connected Vehicles - VANETs - Predictive Logistics - Spatio-Temporal Event Tracking - Decision Support Systems - Emergency Management - Logistics and E-Commerce - Supply Chain Design and Execution - Supply Chain Management - Advanced Planning Systems - Fleet Management - Multi-Agent Systems - Machine Learning for Smart Logistics - Intelligent Infrastructures - Real-time Analysis of Comprehensive Supply Chain Data - Smart Synchronization of Logistics Processes - New Approaches for Cost Transparency - Big Data for Smart Logistics - Logistics 4.0 - Mobile Networks - Next-Generation Smart Logistics - Performance Management Approaches - Tests and Deployment - Software Defined Networks - Smart Freight Management - Smart Shipment Management - Smart Warehousing - Smart Inventory management DATA AND SERVICES - Real-Time transportation Data Acquisition - Event Detection and Monitoring - Data Warehouses for connected mobility - Data mining and Data analytics - Data Worthiness in Connected Vehicles - Data Trustworthiness for effective transportation and mobility - Road Traffic Data Analytics - Structured and Unstructured Data for Connected Mobility - Volunteered Geographic Information (VGI) - Data Representation for Connected Mobility - Transportation Data Mining - Transportation and mobility Data Visualization - Cognitive and Context-aware Intelligence - Transportation Decision Support Systems - Mobility as a Service (MaaS) - Intelligent Transportation Services - Smart Mobility Services - Big Data and Vehicle Analytics - Massive Data Management - Collective and connected Intelligence - Next Generation Services - Driver Behaviour Analysis - Geo-Spatial Services - Service-Oriented Architecture (SOA) - Web and Mobile Services SAFETY, SECURITY, AND HAZARD MANAGEMENT - Security Issues in Vehicular Communications - Safety Applications of Connected Vehicles - Weather-related Safety solutions - V2V, V2I and I2V Road Safety Applications - Connected Mobility for Hazard Management - Risk Management - Road Traffic Crashes Analytics - Traffic Jam Prediction - Resource Allocation for Hazard Management - Trust and Privacy Issues in Logistics - Management of Exceptional Events - New approaches to Networking Security for Transportation Applications - Failure modes, human factors, software safety - Automated Failure Analysis - Performance and Human Error Analysis - Design and Reliability of Control Systems - Dispersion Modelling Software - Quantification of Risk *************************************************************************** OUTSTANDING PAPERS: Based on the peer review scores as well as the presentations at the conference, the authors of outstanding papers will be invited to extend their works for a potential publication in journals special issues with high impact factors. *************************************************************************** PAPER SUBMISSION: Papers must be submitted electronically as PDF files via easychair (https://easychair.org/conferences/?conf=rtatm2021) All papers will be peer reviewed. Length of Full papers: 12-15 pages long (written in the LNCS/CCIS one-column page format, 400 words per page) Length of Short papers: less than 12 pages For more information, please refer to the conference website: https://confscience.com/rtatm/ *************************************************************************** CONTACT For more information, please send an email to info-rtatm(a)confscience.com

1 0

F-IDE 2021 - Last Call for Papers - Extended Deadline
by Andrei Paskevich 24 Feb '21

24 Feb '21

****************************************************************** F-IDE 2021: 6th Workshop on Formal Integrated Development Environment Affiliated with NASA Formal Methods 2021 May 24-25, 2021 -- held online https://cister-labs.pt/f-ide2021 ****************************************************************** Keynotes * Prof. Jan Friso Groote, Eindhoven Univ. of Technology, the Netherlands * Benoît Rognier, Edukera, France Important Dates * Abstract submission - extended: Mon, Mar 8, 2021 * Full paper submission - extended: Mon, Mar 15, 2021 * Notification: Mon, Apr 19, 2021 * Camera-ready: Mon, May 3, 2021 * Workshop: May 24-25, 2021 Overview High levels of safety, security, and privacy standards require the use of formal methods to specify and develop compliant software (sub)systems. Any standard comes with an assessment process, which requires a complete documentation of the application to ease the justification of design choices and the review of code and proofs. Ideally, an F-IDE dedicated to such developments should comply with several requirements. The first one is to associate a logical theory with a programming language, in a way that facilitates the tightly coupled handling of specification properties and program constructs. The second is to offer a language and/or an environment simple enough to be usable by most developers, even if they are not fully acquainted with higher-order logics or set theory, in particular by making development of proofs as easy as possible. The third is to offer automated management of application documentation. It may also be expected that developments done with such an F-IDE are reusable and modular. Tools for testing and static analysis may be embedded within F-IDEs to support the assessment process. Topics The workshop is open to contributions on all aspects of a system development process, including specification, design, implementation, analysis, and documentation. It welcomes the presentation of tools, methods, techniques, and experiments. Topics of interest include, but are not limited to, the following: * F-IDE building: design and integration of languages, development of user-friendly front-ends * How to make high-level logical and programming concepts palatable to industrial developers * Integration of object-oriented and modularity features * Integration of static analyzers * Integration of automated proof tools, theorem provers, and testing tools * Documentation tools * Impact of tools on certification * Experience reports on developing F-IDEs * Experience reports on using F-IDEs * Experience reports on formal methods-based assessments in industrial applications Submission Guidelines We accept both long (15 pages) and short (6 pages) paper submissions. The page limit does not include the bibliography. Submitted papers must present original contributions whose main results and conclusions have not been published or submitted elsewhere. Each submission will be reviewed by at least three members of the Program Committee. We expect that one author of every accepted paper will present their work at the workshop. Submitted papers must be written in English and follow the EPTCS LaTeX format (http://style.eptcs.org) Authors are invited to submit the following types of contributions: * Research papers providing new concepts and results * Experience reports * Position papers and research perspectives * Tool presentations Papers should be submitted via EasyChair at F-IDE 2021's workshop page: https://easychair.org/conferences/?conf=f-ide2021. Preliminary proceedings will be made available in electronic form at the workshop. Post-proceedings will be published in the Electronic Proceedings in Theoretical Computer Science (EPTCS). Program Committee * Andrew Reynolds, University of Iowa, USA * Damien Doligez, Inria, France * Bernhard Rumpe, RWTH Aachen University, Germany * Carlo A. Furia, Chalmers University of Technology, Sweden * César Muñoz, NASA Langley, USA * Cinzia Bernardeschi, University of Pisa, Italy * Claudio Sacerdoti Coen, University of Bologna, Italy * Enrico Tassi, Inria, France * François Pessaux, ENSTA ParisTech, France * José Creissac Campos, University of Minho, Portugal * Kenneth Lausdahl, Aarhus University, Denmark * Laurent Voisin, Systerel, France * Lucas Wagner, Collins Aerospace, USA * Makarius Wenzel, sketis.net * Markus A. Kuppe, Microsoft Research, USA * Mattias Ulbrich, Karlsruhe Institute of Technology, Germany * Pierre-Yves Strub, LIX, École Polytechnique, France * Rosemary Monahan, Maynooth University, Ireland * Silvia Lizeth Tapia Tarifa, University of Oslo, Norway * Simão Melo de Sousa, Universidade Beira Interior, Portugal * Stefan Mitsch, Carnegie Mellon University, USA * Stephan Merz, Inria, France * Virgile Prevosto, Institut List, CEA Tech, Université Paris-Saclay, France * Yannick Moy, AdaCore, France * Yi Zhang, Massachusetts General Hospital, USA PC Chairs * Andrei Paskevich, Université Paris-Saclay, France * José Proença, CISTER/ISEP, Portugal Steering Committee * Catherine Dubois, Samovar, ENSIIE, France * Paolo Masci, US National Institute of Aerospace (NIA), USA * Dominique Méry, LORIA, Université de Lorraine, France

1 0

Problem with stack
by Seph Shewell Brockway 24 Feb '21

24 Feb '21

Hi all, A system update (on Arch Linux) seems to have broken my stack installation. It’s started producing linker errors that look like this: dns > /usr/bin/ld.gold: error: /mnt/data/home/seph/.stack/snapshots/x86_64-linux-tinfo6/0ae0d61c27cd61876740871252be93ed57cf041b2170a9014507e77ea977085d/8.10.4/lib/x86_64-linux-ghc-8.10.4/libHScryptonite-0.27-G0nFpwexMw39Vj7zbfAUBq-ghc8.10.4.so:1:1: invalid character dns > collect2: error: ld returned 1 exit status dns > `gcc' failed in phase `Linker'. (Exit code: 1) This seems to happen no matter what snapshot I’m using, although not necessarily with the same packages. Does anyone have any idea what might be going on? Regards, Seph -- Seph Shewell Brockway, BSc MSc (Glas.) Pronouns: she/her

2 3

[ANN] cabal-install-3.4.0.0
by Emily Pillmore 24 Feb '21

24 Feb '21

The Cabal team is excited to announce the release of cabal-install 3.4. This is the third release of the 3.0 release series, bringing a support for the `Cabal-Version: 3.4` `.cabal` file format. This introduces a number of user-facing features including: - Support for GHC 9.0 - Package sublibrary dependency syntax - Allowing omission of the `default-language` declaration - A mixins field allowing the user to specify a sublibrary - [Many other features]( https://cabal.readthedocs.io/en/latest/file-format-changelog.html#cabal-ver… ) In addition, the `cabal-install` frontend itself has gained a number of new features including: - New `active-repositories` `cabal.project` fields allowing users to specify an order and various ways of combining package repositories - Improvements to `cabal init` - A rework of the `cabal v2-sdist` command. `cabal v1-sdist` is removed as of this version - `source-repository-package` directories are no longer local - A new `list-bin` command - `cabal sandbox` is now removed in favor of default nix-style builds - `cabal list` now accepts regular expressions - More rich `index-state` syntax. `v2-freeze` saves `index-state` I'd also like to thank the many contributors who offered patches, tickets, and other help in the preparation of this release. We appreciate all of your help! For a full set of release notes, see https://github.com/haskell/cabal/blob/master/release-notes/cabal-install-3.…. If you have issues, we'd love to hear about there here: https://github.com/haskell/cabal/issues. Happy hacking! Emily

2 2

Cabal 3.2.0.0, run okay with profiling enabled, but installed exe NO profiling enabled
by YueCompl 23 Feb '21

23 Feb '21

Dear Cafe, I'm not sure it is a bug or just designed behavior? But I can't install profiling-enabled exe with cabal 3.2.0.0, while direct running works correctly. $ cabal --version cabal-install version 3.2.0.0 compiled using version 3.2.0.0 of the Cabal library $ cabal run --enable-profiling --enable-executable-profiling exe:els -- +RTS --info Up to date [("GHC RTS", "YES") ,("GHC version", "8.8.4") ,("RTS way", "rts_thr_p") ,("Build platform", "x86_64-apple-darwin") ,("Build architecture", "x86_64") ,("Build OS", "darwin") ,("Build vendor", "apple") ,("Host platform", "x86_64-apple-darwin") ,("Host architecture", "x86_64") ,("Host OS", "darwin") ,("Host vendor", "apple") ,("Target platform", "x86_64-apple-darwin") ,("Target architecture", "x86_64") ,("Target OS", "darwin") ,("Target vendor", "apple") ,("Word size", "64") ,("Compiler unregisterised", "NO") ,("Tables next to code", "YES") ,("Flag -with-rtsopts", "-maxN31 -qg") ] $ cabal install --enable-profiling --overwrite-policy=always --enable-executable-profiling exe:els && els +RTS --info Wrote tarball sdist to ... Resolving dependencies... Up to date Copying 'els' [("GHC RTS", "YES") ,("GHC version", "8.8.4") ,("RTS way", "rts_thr") ,("Build platform", "x86_64-apple-darwin") ,("Build architecture", "x86_64") ,("Build OS", "darwin") ,("Build vendor", "apple") ,("Host platform", "x86_64-apple-darwin") ,("Host architecture", "x86_64") ,("Host OS", "darwin") ,("Host vendor", "apple") ,("Target platform", "x86_64-apple-darwin") ,("Target architecture", "x86_64") ,("Target OS", "darwin") ,("Target vendor", "apple") ,("Word size", "64") ,("Compiler unregisterised", "NO") ,("Tables next to code", "YES") ,("Flag -with-rtsopts", "-maxN31 -qg") ] $ cabal install --enable-profiling --overwrite-policy=always --enable-executable-profiling exe:els && els +RTS -p Wrote tarball sdist to ... Resolving dependencies... Up to date Copying 'els' els: the flag -p requires the program to be built with -prof els: els: Usage: <prog> <args> [+RTS <rtsopts> | -RTS <args>] ... --RTS <args> els: ... Is there other options to get a profiling enabled exe installed? Thanks with regards, Compl

2 2

[ANN] zlib-0.6.2.3
by Emily Pillmore 21 Feb '21

21 Feb '21

Hello Everyone, I'm pleased to announce zlib-0.6.2.3, which adds support for the bytestring-0.11 work, and unblocks a decent number of packages to the next bytestring versions. I would also like to announce that two new maintainers have been added to the zlib team: Andrew Lelechenko (bodigrim), and myself (topos). Cheers, Emily

1 0

Munich Virtual Haskell Meeting, 2021-02-23 @ 19:30
by Leah Neukirchen 21 Feb '21

21 Feb '21

Dear all, Next week, our monthly Munich Haskell Meeting will take place again on Tuesday, Feburary 23 on Google Meet at 19:30 CET. **Due to meetup limitations in Bavaria, this meeting will take place online!** For details see here: https://muenchen.haskell.bayern/dates.html A Google Meet link to join the room is provided on the page. Everybody is welcome, especially the Haskellers from Bavaria that do not usually come to our Munich meetings due to travel distance! cu, -- Leah Neukirchen <leah(a)vuxu.org> https://leahneukirchen.org/

1 0

dyre-0.9.0 release candidate and call for testing
by Fraser Tweedale 21 Feb '21

21 Feb '21

Dyre is a tool for Haskell program configuration by (re)compilation. After years of project dormancy, I am pleased to announce a Dyre 0.9 release candidate[1]. If you are interested and able to test this candidate release, you can report results at [2]. For more details including changelog, see the accompanying blog post[3]. [1] https://hackage.haskell.org/package/dyre-0.9.0/candidate [2] https://github.com/willdonnelly/dyre/issues/39 [3] https://frasertweedale.github.io/blog-fp/posts/2021-02-21-dyre-0.9-rc.html Thanks, Fraser

1 0

More Efficient Recursion
by A. Mc. 21 Feb '21

21 Feb '21

Hello, I'm just starting off, but I'm wondering if anyone has any suggestions. I've made a recursive function that's goal is to handle a base raised to a very large power. modLoop :: Integer -> Integer -> Integer -> Integer -> Integer -> Integer modLoop iterator exponent result base modulus | (iterator == exponent) = result | (iterator < exponent) = modLoop (iterator + 1) (exponent) (mod (result * base) modulus) base modulus | (iterator > exponent) = (-1) However, it flat breaks or takes a long time when using large numbers. I need to get better at using strict functions, however, I compiled with ghc -o (as it tends to implement the strict version - ?) and I still have the same problem. What's a better way? Thanks in advance and thank you for your time.

3 2

help with existential type signature?
by Ken T Takusagawa 20 Feb '21

20 Feb '21

{- I am experimenting with type-level naturals and with moving values known at runtime to type space. Is there a type signature that I can add to f1 below so that this will compile (maybe also requiring some additional LANGUAGE pragmas)? If I were to change the return value of f1 from "x" to "show x", then the program does compile, suggesting that there's nothing inherently wrong with "x". But I'd prefer the option to compose the output of f1 with other computations separately, e.g., "show . f1" . Thanks, Ken -} {-# LANGUAGE KindSignatures, ScopedTypeVariables, DataKinds, Rank2Types #-} import qualified GHC.TypeLits as TypeLits; import Data.Proxy(Proxy); main = undefined; data Foo (fn :: TypeLits.Nat) = Mkfoo deriving (Show); --f1 :: TypeLits.SomeNat -> ? ; f1 mynat = case mynat of { TypeLits.SomeNat (_ :: Proxy n) -> let { x :: Foo n; x = Mkfoo; } in x }; {- typelits.hs:27:8: error: * Couldn't match expected type `p' with actual type `Foo n' because type variable `n' would escape its scope This (rigid, skolem) type variable is bound by a pattern with constructor: TypeLits.SomeNat :: forall (n :: TypeLits.Nat). TypeLits.KnownNat n => Proxy n -> TypeLits.SomeNat, in a case alternative at smalltypelits2.hs:24:3-33 * In the expression: x In the expression: let x :: Foo n x = Mkfoo in x In a case alternative: TypeLits.SomeNat (_ :: Proxy n) -> let x :: Foo n x = Mkfoo in x * Relevant bindings include x :: Foo n (bound at smalltypelits2.hs:26:5) f1 :: TypeLits.SomeNat -> p (bound at smalltypelits2.hs:23:1) | 27 | } in x | ^ -}

2 1

Grapheme length?
by amindfv＠mailbox.org 20 Feb '21

20 Feb '21

Does there exist a Haskell library or function for getting grapheme lengths of String/Text values? e.g. right now, Prelude.length ("ä" :: String) == 2 Data.Text.length ("ä" :: Text) == 2 But I'd like, either for String or Text, to get 1 instead (there are 2 code points but only 1 grapheme). Thanks, Tom

2 6

Sizes in memory?
by Dušan Kolář 20 Feb '21

20 Feb '21

Dear café, I don't know, whether this is the right place to ask, but I'll try :-) If I would like to know size of the list in the memory (after complete evaluation, e.g. deepseq). The type is [( Int, [([Int],[Int])] )]. So we have K tuples of the type (Int,[([Int],[Int])]) Each tuple has N tuples of the type ([Int],[Int]) and each of these lists M elements long (yes, both a are of the same length). Top level list needs (on 64bit CPU) 8 bytes for pointer to elements, 8 bytes to point to another element, some more "expenses", probably yes, tag, anything else? So we have K*(16+XXX), where XXX is for size of (Int,[([Int],[Int])]). Tuple needs 8 bytes for each pointer, so XXX = 16 + YYY, where YYY is the size of the [([Int],[Int])] list. It needs 8 + 8 bytes on the list, we have N such elements, thus YYY = N * (16 + ZZZ), where ZZZ is size of the ([Int],[Int]). Again tuple, so 16 bytes + 2*(M * (16 + 8)) -- 16 bytes for 2 tuple elements -- 2 for two lists -- every list 16 bytes for list itself -- 8 bytes for Int So ZZZ = 16 + 2*(M * (16 + 8)), thus YYY = N * (16 + 16 + 2*(M * (16 + 8))), thus XXX = 16 + N * (16 + 16 + 2*(M * (16 + 8))), thus size = K * (16 + 16 + N * (16 + 16 + 2*(M * (16 + 8)))) = K* (32 + N* (32 + M*48) ) Am I right? Roughly right? Or totally wrong? E.g. for K = 25, N = 10000, M = 7 we get cca 88MiB ? Why am I asking? In reality the memory consumption is much higher, so I must be missing some extras, e.g. each memory chunk extra 8 bytes for GC, extra for tag, extra to point to VMT? Regards, Dušan

2 1

How to deal with type family applications in type equalities?
by Jakob Brünker 18 Feb '21

18 Feb '21

Imagine you want to have a type level function that calculates the element-wise OR on two bitstrings, encoded as length-indexed vectors filled with Bools (this is a simplification of something I need for a project). The vectors should be "aligned to the right" as it were, such that the new right-most value is True if the right-most value of the first vector OR the right-most value of the second vector was True. Example (replacing True and False with 1 and 0 for readability): ElementwiseOr [1,0,1,1] [0,1,1,0,0,0,0,1] = [0,1,1,0,1,0,1,1] Its type would be something like ElementwiseOr :: Vec n Bool -> Vec m Bool -> Vec (Max n m) Bool I have written the following code: --------------------------------------------------------------------------- {-# LANGUAGE TypeFamilies, GADTs, DataKinds, StandaloneKindSignatures, PolyKinds, TypeOperators, RankNTypes, TypeApplications, UndecidableInstances #-} import Data.Kind import Data.Type.Equality data Nat = Z | S Nat infixr 5 :< type Vec :: Nat -> Type -> Type data Vec n a where Nil :: Vec Z a (:<) :: a -> Vec n a -> Vec (S n) a type Cong :: forall f -> a :~: b -> f a :~: f b type family Cong f p where Cong f Refl = Refl type Max :: Nat -> Nat -> Nat type family Max n m where Max Z m = m Max n Z = n Max (S n) (S m) = S (Max n m) -- The reason for this slightly convoluted Ordering type is that it seems -- to make the "right-alignment" easier. type NatOrdering :: Ordering -> Nat -> Nat -> Type data NatOrdering o n m where NOLTE :: NatOrdering EQ n m -> NatOrdering LT n (S m) NOLTS :: NatOrdering LT n m -> NatOrdering LT n (S m) NOEQZ :: NatOrdering EQ Z Z NOEQS :: NatOrdering EQ n m -> NatOrdering EQ (S n) (S m) NOGTE :: NatOrdering EQ n m -> NatOrdering GT (S n) m NOGTS :: NatOrdering GT n m -> NatOrdering GT (S n) m type MaxSIsSMaxEQ :: forall n m . NatOrdering EQ n m -> Max n (S m) :~: S (Max n m) type family MaxSIsSMaxEQ o where MaxSIsSMaxEQ NOEQZ = Refl MaxSIsSMaxEQ (NOEQS o) = Cong S (MaxSIsSMaxEQ o) type TransportVec :: n :~: m -> Vec n a -> Vec m a type family TransportVec p v where TransportVec Refl v = v type ElementwiseOr :: NatOrdering o n m -> Vec n Bool -> Vec m Bool -> Vec (Max n m) Bool type family ElementwiseOr o u v where ElementwiseOr (NOLTE o) u (s :< v) = TransportVec (MaxSIsSMaxEQ o) (s :< ElementwiseOr o u v) -- XXX -- other equations ommitted --------------------------------------------------------------------------- To me, the equation at the end marked with XXX seems like it should work. However, it produces the following error: • Couldn't match kind: Max n ('S m) with: 'S (Max n m) Expected kind ‘'S (Max n m) :~: 'S (Max n m)’, but ‘MaxSIsSMaxEQ o’ has kind ‘Max n ('S m) :~: 'S (Max n m)’ • In the first argument of ‘TransportVec’, namely ‘(MaxSIsSMaxEQ o)’ So it expects something of kind `S (Max n m) :~: S (Max n m)` - it seems like Refl fits that bill, but that doesn't work either, because replacing (MaxSIsSMaxEQ o) with Refl means that TransportVec returns a type of the wrong kind, producing a very similar error. I suspect the reason this doesn't work is because type equality isn't equipped to properly handle type family applications. I could potentially work around this if I defined Max as data Max n m r where MaxZZ :: Max Z Z Z MaxSZ :: Max (S n) Z (S n) MaxZS :: Max Z (S m) (S m) MaxSS :: Max n m r -> Max (S n) (S m) (S r) However, dealing with a proof object like this is a lot less convenient than just being able to use a type family for most purposes, so I'd like to avoid this if possible. Is there a way to make this work while sticking with type families? Thanks Jakob

2 3

Blog post about masking asynchronous exceptions
by coot＠coot.me 18 Feb '21

18 Feb '21

Hello Haskell-Caffee, I wrote a blog post about masking asynchronous exceptions and interruptible operations: https://coot.me/posts/mask.html Best regards, Marcin Szamotulski

2 2

First Call for Papers for the Haskell Symposium 2021
by Hage, J. (Jurriaan) 17 Feb '21

17 Feb '21

Dear all, This is the first call for papers for the upcoming Haskell Symposium. Please forward to anyone that you believe might be interested. Apologies for receiving multiple copies of this announcement. Best regards, Jurriaan Hage Chair PS. Note that the website is not up yet (but will be soon). ================================================================================ ACM SIGPLAN CALL FOR SUBMISSIONS Haskell Symposium 2021 ** virtual ** Thu 26 -- Fri 27 August, 2021 http://www.haskell.org/haskell-symposium/2021/ ================================================================================ The ACM SIGPLAN Haskell Symposium 2021 will be co-located with the 2021 International Conference on Functional Programming (ICFP). Due to COVID-19 it will take place **virtually** this year. Like last year, we will be using a lightweight double-blind reviewing process. See further information below. Different from last year is that we offer a new submission category: the tutorial. Details can be found below. The Haskell Symposium presents original research on Haskell, discusses practical experience and future development of the language, and promotes other forms of declarative programming. Topics of interest include: * Language design, with a focus on possible extensions and modifications of Haskell as well as critical discussions of the status quo; * Theory, such as formal semantics of the present language or future extensions, type systems, effects, metatheory, and foundations for program analysis and transformation; * Implementations, including program analysis and transformation, static and dynamic compilation for sequential, parallel, and distributed architectures, memory management, as well as foreign function and component interfaces; * Libraries, that demonstrate new ideas or techniques for functional programming in Haskell; * Tools, such as profilers, tracers, debuggers, preprocessors, and testing tools; * Applications, to scientific and symbolic computing, databases, multimedia, telecommunication, the web, and so forth; * Functional Pearls, being elegant and instructive programming examples; * Experience Reports, to document general practice and experience in education, industry, or other contexts; * Tutorials, to document how to use a particular language feature, programming technique, tool or library within the Haskell ecosystem; * System Demonstrations, based on running software rather than novel research results. Regular papers should explain their research contributions in both general and technical terms, identifying what has been accomplished, explaining why it is significant, and relating it to previous work, and to other languages where appropriate. Experience reports and functional pearls need not necessarily report original academic research results. For example, they may instead report reusable programming idioms, elegant ways to approach a problem, or practical experience that will be useful to other users, implementers, or researchers. The key criterion for such a paper is that it makes a contribution from which other Haskellers can benefit. It is not enough simply to describe a standard solution to a standard programming problem, or report on experience where you used Haskell in the standard way and achieved the result you were expecting. A new submission category for this year's Haskell Symposium is the tutorial. Like with the experience report and the functional pearl, the key criterion for such a paper is that it makes a contribution from which other Haskellers can benefit. What distinguishes a tutorial is that its focus is on explaining an aspect of the Haskell language and/or ecosystem in a way that is generally useful to a Haskell audience. Tutorials for many such topics can be found online; the distinction here is that by writing it up for formal review it will be vetted by experts and formally published. System demonstrations should summarize the system capabilities that would be demonstrated. The proposals will be judged on whether the ensuing session is likely to be important and interesting to the Haskell community at large, whether on grounds academic or industrial, theoretical or practical, technical, social or artistic. Please contact the program chair with any questions about the relevance of a proposal. If your contribution is not a research paper, please mark the title of your experience report, functional pearl, tutorial or system demonstration as such, by supplying a subtitle (Experience Report, Functional Pearl, Tutorial Paper, System Demonstration). Submission Details ================== Early and Regular Track ----------------------- The Haskell Symposium uses a two-track submission process so that some papers can gain early feedback. Strong papers submitted to the early track are accepted outright, and the others will be given their reviews and invited to resubmit to the regular track. Papers accepted via the early and regular tracks are considered of equal value and will not be distinguished in the proceedings. Although all papers may be submitted to the early track, authors of functional pearls and experience reports are particularly encouraged to use this mechanism. The success of these papers depends heavily on the way they are presented, and submitting early will give the program committee a chance to provide feedback and help draw out the key ideas. Formatting ---------- Submitted papers should be in portable document format (PDF), formatted using the ACM SIGPLAN style guidelines. Authors should use the `acmart` format, with the `sigplan` sub-format for ACM proceedings. For details, see: http://www.sigplan.org/Resources/Author/#acmart-format It is recommended to use the `review` option when submitting a paper; this option enables line numbers for easy reference in reviews. Functional pearls, experience reports, tutorials and demo proposals should be labelled clearly as such. Lightweight Double-blind Reviewing ---------------------------------- Haskell Symposium 2021 will use a lightweight double-blind reviewing process. To facilitate this, submitted papers must adhere to two rules: 1. Author names and institutions must be omitted, and 2. References to authors' own related work should be in the third person (e.g., not "We build on our previous work" but rather "We build on the work of "). The purpose of this process is to help the reviewers come to an initial judgment about the paper without bias, not to make it impossible for them to discover the authors if they were to try. Nothing should be done in the name of anonymity that weakens the submission or makes the job of reviewing the paper more difficult (e.g., important background references should not be omitted or anonymized). In addition, authors should feel free to disseminate their ideas or draft versions of their paper as they normally would. For instance, authors may post drafts of their papers on the web or give talks on their research ideas. A reviewer will learn the identity of the author(s) of a paper after a review is submitted. Page Limits ----------- The length of submissions should not exceed the following limits: Regular paper: 12 pages Functional pearl: 12 pages Tutorial: 12 pages Experience report: 6 pages Demo proposal: 2 pages There is no requirement that all pages are used. For example, a functional pearl may be much shorter than 12 pages. In all cases, the list of references is not counted against these page limits. Deadlines --------- Early track: Submission deadline: 19 March 2021 (Fri) Notification: 23 April 2021 (Fri) Regular track and demos: Submission deadline: 21 May 2021 (Fri) Notification: 23 June 2021 (Wed) Deadlines are valid anywhere on Earth. Submission ---------- Submissions must adhere to SIGPLAN's republication policy (http://sigplan.org/Resources/Policies/Republication/) and authors should be aware of ACM's policies on plagiarism (https://www.acm.org/publications/policies/plagiarism) Program Committee members are allowed to submit papers, but their papers will be held to a higher standard. The paper submission deadline and length limitations are firm. There will be no extensions, and papers violating the length limitations will be summarily rejected. Papers should be submitted through HotCRP at: https://haskell21.hotcrp.com/ Improved versions of a paper may be submitted at any point before the submission deadline using the same web interface. Supplementary material: Authors have the option to attach supplementary material to a submission, on the understanding that reviewers may choose not to look at it. This supplementary material should not be submitted as part of the main document; instead, it should be uploaded as a separate PDF document or tarball. Supplementary material should be uploaded at submission time, not by providing a URL in the paper that points to an external repository. Authors can distinguish between anonymized and non-anonymized supplementary material. Anonymized supplementary material will be visible to reviewers immediately; non-anonymized supplementary material will be revealed to reviewers only after they have submitted their review of the paper and learned the identity of the author(s). Resubmitted Papers: authors who submit a revised version of a paper that has previously been rejected by another conference have the option to attach an annotated copy of the reviews of their previous submission(s), explaining how they have addressed these previous reviews in the present submission. If a reviewer identifies him/herself as a reviewer of this previous submission and wishes to see how his/her comments have been addressed, the conference chair will communicate to this reviewer the annotated copy of his/her previous review. Otherwise, no reviewer will read the annotated copies of the previous reviews. Proceedings =========== Accepted papers will be included in the ACM Digital Library. Their authors will be required to choose one of the following options: - Author retains copyright of the work and grants ACM a non-exclusive permission-to-publish license (and, optionally, licenses the work with a Creative Commons license); - Author retains copyright of the work and grants ACM an exclusive permission-to-publish license; - Author transfers copyright of the work to ACM. For more information, please see ACM Copyright Policy (http://www.acm.org/publications/policies/copyright-policy) and ACM Author Rights (http://authors.acm.org/main.html) Accepted proposals for system demonstrations will be posted on the symposium website but not formally published in the proceedings. Publication date: The official publication date of accepted papers is the date the proceedings are made available in the ACM Digital Library. This date may be up to two weeks prior to the first day of the conference. The official publication date affects the deadline for any patent filings related to published work. Artifacts ========= Authors of accepted papers are encouraged to make auxiliary material (artifacts like source code, test data, etc.) available with their paper. They can opt to have these artifacts published alongside their paper in the ACM Digital Library (copyright of artifacts remains with the authors). If an accepted paper's artifacts are made permanently available for retrieval in a publicly accessible archival repository like the ACM Digital Library, that paper qualifies for an Artifacts Available badge (https://www.acm.org/publications/policies/artifact-review-badging#available) Applications for such a badge can be made after paper acceptance and will be reviewed by the PC chair. Program Committee ================= Edwin Brady University of St Andrews Koen Claessen Chalmers University of Technology Dominique Devriese Vrije Universiteit Brussel Andy Gill University of Kansas Jurriaan Hage (chair) Universiteit Utrecht Zhenjiang Hu Peking University Ranjit Jhala University of California Patricia Johann Appalachian State University Yukiyoshi Kameyama University of Tsukuba George Karachalias Tweag Ralf Laemmel University of Koblenz-Landau Daan Leijen Microsoft Research Ben Lippmeier Ghost Locomotion Neil Mitchell Facebook Alberto Pardo Universidad de la Republica, Uruguay Matt Roberts Macquarie University Janis Voigtlaender University of Duisburg-Essen Nicolas Wu Imperial College London If you have questions, please contact the chair at: j.hage(a)uu.nl ================================================================================

1 0

Final Call for Participation: BOB 2021 (February 26, online)
by Stefan Wehr 17 Feb '21

17 Feb '21

Subject: Final Call for Participation: BOB 2021 (February 26, online) ============================================================================ BOB 2021 Conference “What happens if we simply use what’s best?” February 26, 2021, online (UTC+0100) http://bobkonf.de/2021/ Program: http://bobkonf.de/2021/program.html Registration: http://bobkonf.de/2021/registration.html ============================================================================ BOB conference is a place for developers, architects and decision-makers to explore technologies beyond the mainstream in software development, and to find the best tools available to software developers today. Our goal is for all participants of BOB to return home with new insights that enable them to improve their own software development experience. The program features 14 talks and 8 tutorials on current topics: http://bobkonf.de/2021/program.html The subject range includes functional programming, logic programming, revision control, formal methods, mindfulness, event sourcing, front-end development, and more. Jeremy Gibbons will give the keynote talk. BOB 2021 will take place online. We are working towards fostering lively exchange of exciting ideas and enable meaningful social interactions. Registration is open online: http://bobkonf.de/2021/registration.html Registration is €30 for a regular ticket, €15 for a student ticket. (If you need financial aid, let us know.) We intend to make this the most diverse, colorful, fun BOB ever!

1 0

International Conference on Informatics Revolution for Smarter Healthcare (IRSH 2021) Prague
by matteo＠confscience.com 15 Feb '21

15 Feb '21

Call for papers ************************************************* International Conference on Informatics Revolution for Smarter Healthcare (IRSH 2021) Prague- Czech Republic, October 14-15, 2021 https://confscience.com/irsh/ Submission deadline: April 1, 2021 All papers accepted in IRSH 2021 will be published in Springer CCIS (Communications in Computer and Information Science). CCIS is abstracted/indexed in Scopus, SCImago, EI-Compendex, Mathematical Reviews, DBLP, Google Scholar, and Thomson Reuters Conference Proceedings Citation (Former ISI Proceedings) *************************************************************************** IMPORTANT DATES: - Paper Submission: April 1, 2021 - Acceptance Notification: July 1, 2021 - Final Manuscript Due: September 1, 2021 *************************************************************************** The IRSH 2021 conference will be held in Conjunction with: International Conference on Applied Data Science and Intelligence (ADSI 2021) International Conference on Recent Theories and Applications in Transportation and Mobility - (RTATM 2021) *************************************************************************** TOPICS: Authors are invited to submit their original papers to address the topics of the conference, including but not limited to: FUNDAMENTALS AND THEORIES - Interoperability and Data Integration - Confidentiality and Data Security - Data protection - Data Sharing - Security, Privacy, and Trust - Emergent healthcare standards - Emergent healthcare architectures - ICT, Ageing and Disability - Physiological and behavioural modelling - Pandemic and disease modeling - Usability and user experience of medical devices - Human behaviour - Clinical investigation regulatory frameworks - Integrated healthcare approaches - eHealth data standards and interoperability (e.g. HL7/FHIR) - Databases and data warehousing - Big Data and Open Data for healthcare - Design and Development of Methodologies for Healthcare - Emergent Communication Technologies - Real-time interaction theories - Emergent Technologies for Ambient Assisted Living - User Interface Design for healthcare - Sustainability - New approaches for accuracy and effectiveness - Data mining and bioinformatics - Enhanced living environments - Analysis and evaluation of healthcare systems INTELLIGENT HEALTHCARE - Pattern recognition and Machine - Learning for healthcare - Cognitive Informatics - Big Data in Healthcare - Wellbeing Informatics - Data Mining and Data Analytics - Data Visualization - Smart environments - Smart Ambient Assisted Living - Intelligent healthcare solutions - Agent-based solutions for healthcare - Collaboration systems - Intelligent Electronic Health Records - Internet of Things for healthcare - Cyber-Physical Systems for healthcare - Ambient Computing and Reasoning - Context Awareness - Smart devices for eldercare - Autonomy and active ageing - Emergent technologies for intelligent Computer Vision - Service production and delivery - Gamification - Multi-modal interaction - Computer-aided detection and diagnosis - Crowdsourcing for smarted healthcare SERVICES, SYSTEMS, AND INFRASTRUCTURES - Emergent healthcare services - Pervasive health systems and services - Remote healthcare management - Emergent healthcare infrastructure - Industry Revolution 4.0 for healthcare - eHealth - Electronic health records - Assistive technologies - Disease surveillance and patient monitoring systems - Prevention and detection systems - Home monitoring - Healthcare management systems - ICT-based therapeutic systems - ICT-based rehabilitation technologies - Wearable health informatics - Emergent technologies for data analytics - Ambient Assisted Leaving (AAL) - Decision Support Systems - Emergent Technologies for Remote AAL Monitoring - Emergent Technologies and Accessibility - 5G for healthcare - Healthcare supply chain and logistics - Wireless Body Networks - Telemedicine and mobile telemedicine - Mobile Systems - Software Defined infrastructures - Patient empowerment systems - Smart technology for remote patient visits - Biosensors - Medical devices APPLICATIONS - eHealth applications - Application of health informatics in clinical cases - Mobile technologies for healthcare applications - Software Systems in healthcare - Social networking and healthcare - Case Studies - Personalization and patient experience - AR and VR applications - Patient billing - Accounting systems - Personnel and payroll - Materials management - Voice recognition systems - Asset management solutions - Disease management - Feedback integration - Clinical software - Crowd-computing applications - Future directions - Drone-based solutions - Software Defined Networks for healthcare *************************************************************************** OUTSTANDING PAPERS: Based on the peer review scores as well as the presentations at the conference, the authors of outstanding papers will be invited to extend their works for a potential publication in journals special issues with high impact factors. *************************************************************************** PAPER SUBMISSION: Papers must be submitted electronically as PDF files via easychair (https://easychair.org/conferences/?conf=irsh2021) All papers will be peer reviewed. Length of Full papers: 12-15 pages long (written in the LNCS/CCIS one-column page format, 400 words per page) Length of Short papers: less than 12 pages For more information, please refer to the conference website: https://confscience.com/irsh/ *************************************************************************** CONTACT For more information, please send an email to info-irsh(a)confscience.com

1 0

Kind pairs and kind currying/uncurrying
by CASANOVA Juan 13 Feb '21

13 Feb '21

Hello again, At this point, I think what I am trying to do is simply not possible in Haskell, not even with as many extensions as I would want. Perhaps with template Haskell, but that's ground that I am still afraid to tread. But I thought I would ask anyway. (All the code in the rest of the email assumes as many extensions as GHC asks me to compile). The background is more complicated and controversial than the question itself, but I'll give a little bit of it so that you know why I'm trying to do this. I am trying to define a type class that takes other type classes as arguments. That is fairly straightforward by itself. A single parameter type-class has kind (k -> Constraint). So I can write my class SecondOrderClass (cl :: k -> Constraint) The problem, however, is that I want to use this class for multi-parameter type classes as well. A two parameter type class has kind (k1 -> k2 -> Constraint) The most general unifier of these two kinds is, unfortunately, a free kind (k), which thus includes kinds that are not type classes (like types). Therefore, it is not possible to directly specify a class that takes as parameter a type class with any number of arguments. So, thus I thought: I've seen this before. This is currying and uncurrying. Except I'm doing it with kinds except of with types. A brief search didn't yield me any library that would do this. So I thought: This should be fairly easy to do by myself if I throw enough extensions at it. Well, I failed. I tried two variations and neither worked. To be clear, what I tried to do is to * Define a type synonym that would produce a kind representing a pair of two given kinds. * Define type synonyms for currying and uncurrying kinds using the pair kind. The first variation I tried I feel is the most semantically accurate, as it is clear from the beginning of what I am trying to do. The main "insight" I used was using/assuming extensionality of kinds (and partial application of type synonyms) to define a kind pair: type KindPair (a :: ka) (b :: kb) (f :: ka -> kb -> *) = f a b A pair of kinds is simply anything that "owes the two kinds to the type checker". Thus, if given anything expecting those two kinds, it would feed them to it. This by itself compiles fine. But then when trying to define currying and uncurrying, it won't type check: type KCurry (tf :: (KindPair ka kb) -> kc) (ta :: ka) (tb :: kb) = kc type KUncurry (tf :: ka -> kb -> kc) (tp :: (KindPair ka kb)) = kc The error I get is: The type synonym ‘KindPair’ should have 3 arguments, but has been given 2 Partial application of type synonyms is fine, I use it all the time. But it seems it is not fine when it is "kind synonyms"??? It is not even asking me for any extension to allow it. So I tried a more syntactic approach, abusing the notion that GHC treats kinds and types very similarly: type KindPair (a :: ka) (b :: kb) = ((ka -> kb -> *) -> *) type KCurry (tf :: (KindPair ka kb) -> kc) = ka -> kb -> kc type KUncurry (tf :: ka -> kb -> kc) = (KindPair ka kb) -> kc This type checks, but it is just a mirage. If you check the kinds of KCurry and KUncurry it does not look good: (KindPair ka kb -> kc) -> * Uhh... that's not what I said. It's taking the right hand side entirely as a type, not as a kind. This becomes obvious when we try to use them: ftest :: KCurry (KUncurry (,)) Int Int -> (Int, Int) This does not type check, regardless of the definition (ideally ftest = id would work, but we do not even get that far). The error is: Expected kind ‘* -> * -> *’, but ‘KCurry (KUncurry (,))’ has kind ‘*’ So, my question is: Is what I am trying to do possible in Haskell? Is what I am trying to do completely absurd? I do not think it is, but maybe I am being naive? Thanks in advance, and sorry for the long email (again). I tried to be as straight to the point as possible. Juan. The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336.

3 4