- Haskell-Cafe - Haskell.org

haskell text://protocol client?
by Petite Abeille 10 Apr '21

10 Apr '21

Hello, Would you know of any haskell text://protocol clients? Or servers? [1][2][3] Thanks in advance. [1] https://textprotocol.org [2] https://github.com/textprotocol/public [3] https://github.com/textprotocol/publictext

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Haskell Joke of the Year 2020
by Nick Rudnick 09 Apr '21

09 Apr '21

Dear all, recently, I was confronted with a question what the Haskell joke of the year 2020 is – for anybody else, whose attention, like mine, this slipped completely, here it is, since it really is quite a bit funny, Haskellers don't make money… :-/ If anybody knows jokes of the other years, I'd be happy to know those, too! Cheers, and thanks in advance, Nick

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Z.Haskell project announced
by Dong Han 07 Apr '21

07 Apr '21

Dear Haskellers: After having a discussion with HF guys, I decide to announce [Z.Haskell]( http://z.haskell.world/) project, It's available on Hackage and very much usable now, the document is also pretty adequate. To recap the document from Z.Haskell, Z.Haskell provides: + Array, vector(array slice), sorting, searching + Text based UTF-8, basic Unicode manipulating, regex + FFI utilities + Fast parsing and building monad + JSON encoding and decoding + IO resource management, resource pool + File system operations + Network: DNS, TCP, UDP and IPC + Buffered input and output + Process management + Environment settings + High performance logger + High performance low-resolution timer The project's goal is not to compete with the base, but to provide an alternative engineering toolkit, which is more suitable for writing practical network/storage services. Similar to [netty](https://netty.io/) for java or [nodejs](https://nodejs.org/) for javascript. Welcome to join Z.Haskell if you have a similar use case. Currently, we're heading with the following roadmap: + Crypto library based on [botan](https://github.com/ZHaskell/z-botan). + TLS network stack. + HTTP framework. + Distributed system algorithms. Happy hacking! Z.Haskell Contributors

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Get proof of injectivity for an injective type family
by Andreas Källberg 07 Apr '21

07 Apr '21

Is there any way to get hold of a proof of injectivity for an injective type family? In other words, given this type family type family F a = b | b -> a can I get the term fInj :: F a ~ F b => (a ~ b => r) -> r in any way (without using unsafeCoerce)?

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[ANN] aws-arn-0.1.0.0 - Library and optics for munging Amazon Resource Names (ARNs)
by Jack Kelly 07 Apr '21

07 Apr '21

I have just pushed an initial release of aws-arn[1] to Hackage. This library provides a type representing Amazon Resource Names (ARNs)[2], and parsing/unparsing functions for them. The provided optics make it very convenient to rewrite parts of ARNs. An example, from the documentation: API Gateway Lambda Authorizers are given the ARN of the requested endpoint and method, and are expected to respond with an IAM Policy Document. It is sometimes useful to manipulate the given ARN when describing which resources to authorize: -- Returns "arn:aws:execute-api:us-east-1:123456789012:my-spiffy-api/stage/*" let authorizerSampleARN = "arn:aws:execute-api:us-east-1:123456789012:my-spiffy-api/stage/GET/some/deep/path" in over (_ARN . arnResource . slashes) (\parts -> take 2 parts ++ ["*"]) authorizerSampleARN The code is available on GitHub[3]; bug reports and pull requests are welcome. There is some additional support for parsing specific resource types -- PRs to support more resource types are especially welcome. Best, -- Jack [1]: https://hackage.haskell.org/package/aws-arn-0.1.0.0 [2]: https://docs.aws.amazon.com/general/latest/gr/aws-arns-and-namespaces.html [3]: https://github.com/bellroy/aws-arn

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Looking for a toy imperative language implementation in Haskell for research
by Igor Moreno Santos 07 Apr '21

07 Apr '21

Hi, I'm looking for a toy imperative language implementation in Haskell for research purposes. I imagine something like the language of arithmetic expressions from TAPL ch. 3 augmented with - while-loop (so the CFG has loops) - blocks (sequence of statements to put inside loops and conditionals) - assignment (otherwise we can't show any effects from sequences) I think there's probably nothing exactly like that so we might end up doing it ourselves but maybe there's already something out there. Thank you in advance. Regards, Igor Moreno

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A functor for two Peano systems
by Galaxy Being 07 Apr '21

07 Apr '21

I'm just not understanding the concept of a functor in this context: I have this plus :: Int -> Int -> Int plus n m = if (n == 0) then m else sCessor (plus (pCessor n) m) where sCessor x = x + 1 pCessor x = if (x == 0) then error "too small" else (x - 1) and this data MyNum = MNZero | OneMoreThan MyNum deriving (Show,Eq,Ord) plus2 :: MyNum -> MyNum -> MyNum plus2 n m = if (n == MNZero) then m else sCessor (plus2 (pCessor n) m) where sCessor x = (OneMoreThan x) pCessor x = if (x == MNZero) then (error "too small") else (oneLess x) oneLess MNZero = MNZero oneLess (OneMoreThan myn) = myn It seems there should be just one plus, function that would handle both an Int-based Peano and the MyNum-based Peano, not two. But in this definition fmap :: (a -> b) -> f a -> f b The (a -> b) should be "lifted" over the f a -> f b But I can't conceive of how this should all fit together, i.e., to create just one generic plus that would handle both the plus :: Int -> Int -> Int and the plus2 :: MyNum -> MyNum -> MyNum. Trying to get started, I would assume I need some sort of instance Functor MyNum describing, yeah, what? Or am I barking up the completely wrong tree here, i.e., this isn't a functor issue? LB

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How to ensure optimization for large immutable vectors to be shared w.r.t. Referential Transparency
by YueCompl 06 Apr '21

06 Apr '21

Hello Cafe and respected GHC Devs, I would like to ensure some immutable vectors (can be quite large) are always shared instead of copied, and I think that should be straight forward w.r.t. referential transparency we enjoy. In an attempt to determine whether two immutable vectors can be treated as the same one to enable specific optimizations for that case, I tried to use ST to determine their respective backing foreign ptrs for comparison. But appears it can be copied when wrapped in a newtype, I wonder why it is the case, and how to avoid the copy? Here's my minimum reproducible snippet: ```hs λ> :set -XBangPatterns λ> λ> :set -package vector package flags have changed, resetting and loading new packages... λ> λ> import Prelude λ> λ> import Control.Monad.ST λ> import qualified Data.Vector.Storable as VS λ> λ> :{ λ| λ| newtype SomeVector = SomeVector (VS.Vector Int) λ| λ| isSameVector :: SomeVector -> SomeVector -> Bool λ| isSameVector (SomeVector !x) (SomeVector !y) = runST $ do λ| mx@(VS.MVector !x'offset !x'fp) <- VS.unsafeThaw x λ| my@(VS.MVector !y'offset !y'fp) <- VS.unsafeThaw y λ| _ <- VS.unsafeFreeze mx λ| _ <- VS.unsafeFreeze my λ| return $ x'offset == y'offset && x'fp == y'fp λ| λ| :} λ> λ> let !v = VS.fromList [3,2,5] in isSameVector (SomeVector v) (SomeVector v) False λ> λ> let !v = SomeVector (VS.fromList [3,2,5]) in isSameVector v v True λ> ``` Thanks with best regards, Compl

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International Conference on Recent Theories and Applications in Transportation and Mobility - (RTATM 2021) Prague
by matteo＠confscience.com 06 Apr '21

06 Apr '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/ 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 20, 2021 (extended) - 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

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Re: [Haskell-cafe] A functor for two Peano systems
by Anthony Clayden 06 Apr '21

06 Apr '21

> This whole exercise is my attempt to translate *The Littler MLer* and its last chapter where they go into functors. That approach isn't working for you, and it's trying the patience of the cafe. (These are sub-beginner level q's, please use the Beginners' forum. And I'd forgotten that's what you're doing. Your first post in this thread should have said you're talking about ML functors. https://stackoverflow.com/questions/2030863/in-functional-programming-what-…. says "most beginning programmers have difficulty with [functors]".) I suggest you first go through a Haskell tutorial, and get your knowledge secure of idiomatic Haskell. Even so, I just don't believe you're coming from idiomatic ML. Unless 'The Little MLer' is giving it as obfuscated code, and the objective is to de-obfuscate it. I'd code your `plus2` with pattern-matching: > plus2 :: MyNum -> MyNum -> MyNum > plus2 MNZero m = m > plus2 (OneMoreThan n') m = OneMoreThan $ plus2 n' m Your test for `(x == MNZero)` inside helper function `pCessor` is useless: flow-of-control doesn't take the outer `else` branch unless `x` (i.e. `n`) is _not_ equal `MNZero`. Similar redundant code in the case for `Int`. But that has bigger problems, as Olaf points out: `Int`s can be negative. So if `plus` is called with a negative `n`, it'll call `pCessor` repeatedly until stack overflow (or numeric underflow). AntC

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