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Haskell function composition commutivity?
by Galaxy Being 13 Apr '21

13 Apr '21

I'm in chapter 4 of Bird's very interesting *Thinking Functionally with Haskell *and he has a problem at the end of the chapter where he lists these equations map f . take n = take n . map f map f . reverse = reverse . map f map f . sort = sort . map f map f . filter p = map fst . filter snd . map (fork (f,p)) filter (p . g) = map (invertg) . filter p . map g reverse . concat = concat . reverse . map reverse filter p . concat = concat . map (filter p) adding this caveat for the 3rd equation iff x <= y <=> f x <= f y and this for the 4th equation fork (f,g) x = (f x, g x) and for the 5th invertg satisfies invertg . g = id My confusion is over the commutative-ness of most of this but only anecdotally. With the particularly dense map f . filter p = map fst . filter snd . map (fork (f,p)) We have > :t (map myF . filter myP) Integral b => [b] -> [b] > :t (map fst . filter snd . map (myFork (myF,myP))) Integral b => [b] -> [b] Is there anything universal to be drawn from these anecdotal examples of seeming commutativity? My breakdown of the third equation shows the same type definition for both sides. Is this a way to find equality? All in all, Bird doesn't indicate that there are any underlying truths, just "almost" commutativity. LB

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Re: [Haskell-cafe] What's the modern way to apply a polymorphic function to a Dynamic value in GHC 8.8 and onwards?
by YueCompl 13 Apr '21

13 Apr '21

Thanks to Vlad and Jaro, your solution of `apD` compiles, I think it should work. But unfortunately my real case is a little different / more complex, a MWE appears like this: ```hs holdEvent :: Dynamic -> Dynamic holdEvent (Dynamic t evs') = withTypeable t $ Dynamic typeRep (hcHoldEvent evs') where hcHoldEvent :: forall a. EventSink a -> IO (TimeSeries a) hcHoldEvent !evs = do !holder <- newIORef Nothing listenEvents evs $ writeIORef holder . Just return $ TimeSeries $ readIORef holder data EventSink a = EventSink { listenEvents :: (a -> IO ()) -> IO (), closeStream :: IO () } instance Functor EventSink where fmap = undefined newtype TimeSeries a = TimeSeries {readTimeSeries :: IO (Maybe a)} instance Functor TimeSeries where fmap = undefined ``` Now I'm clueless how to use the `withTypeable` trick to apply my polymorphic `hcHoldEvent` to `Dynamic`, naively written as in above, the error is: ```log src/PoC/DynPoly.hs:20:49: error: • Couldn't match expected type ‘EventSink a0’ with actual type ‘a’ ‘a’ is a rigid type variable bound by a pattern with constructor: Dynamic :: forall a. base-4.13.0.0:Data.Typeable.Internal.TypeRep a -> a -> Dynamic, in an equation for ‘holdEvent’ at src/PoC/DynPoly.hs:19:12-25 • In the first argument of ‘hcHoldEvent’, namely ‘evs'’ In the second argument of ‘Dynamic’, namely ‘(hcHoldEvent evs')’ In the second argument of ‘($)’, namely ‘Dynamic typeRep (hcHoldEvent evs')’ • Relevant bindings include evs' :: a (bound at src/PoC/DynPoly.hs:19:22) t :: base-4.13.0.0:Data.Typeable.Internal.TypeRep a (bound at src/PoC/DynPoly.hs:19:20) | 20 | withTypeable t $ Dynamic typeRep (hcHoldEvent evs') | ^^^^ ``` Thanks with best regards, Compl > On 2021-04-12, at 22:04, Jaro Reinders <jaro.reinders(a)gmail.com> wrote: > > I have no experience in this area, but this compiles: > > ``` > {-# LANGUAGE RankNTypes, ScopedTypeVariables #-} > import Type.Reflection > import Data.Dynamic > > appD :: forall f. Typeable f => (forall a. a -> f a) -> Dynamic -> Dynamic > appD f (Dynamic rep (x :: a)) = withTypeable rep (toDyn (f x)) > ``` > > Cheers, > > Jaro > On 2021-04-12, at 21:06, Vladislav Zavialov <vladislav(a)serokell.io> wrote: > > Would something like this work for you? > > import Type.Reflection > import Data.Dynamic > > apD :: Typeable f => (forall a. a -> f a) -> Dynamic -> Dynamic > apD f (Dynamic t a) = withTypeable t $ Dynamic typeRep (f a) > > - Vlad > >> On 12 Apr 2021, at 14:34, YueCompl via ghc-devs <ghc-devs(a)haskell.org> wrote: >> >> Dear Cafe and GHC devs, >> >> >> There used to be a "principled way with pattern match on the constructor": >> >> ```hs >> data Dynamic where >> Dynamic :: Typeable a => a -> Dynamic >> >> apD :: Typeable f => (forall a. a -> f a) -> Dynamic -> Dynamic >> apD f (Dynamic a) = Dynamic $ f a >> ``` >> Source: https://www.reddit.com/r/haskell/comments/2kdcca/q_how_to_apply_a_polymorph… >> >> >> But now with GHC 8.8 as in my case, `Dynamic` constructor has changed its signature to: >> >> ```hs >> Dynamic :: forall a. TypeRep a -> a -> Dynamic >> ``` >> >> Which renders the `apD` not working anymore. >> >> >> And it seems missing dependencies now for an older solution Edward KMETT provides: >> >> ```hs >> apD :: forall f. Typeable1 f => (forall a. a -> f a) -> Dynamic -> Dynamic >> apD f a = dynApp df a >> where t = dynTypeRep a >> df = reify (mkFunTy t (typeOf1 (undefined :: f ()) `mkAppTy` t)) $ >> \(_ :: Proxy s) -> toDyn (WithRep f :: WithRep s (() -> f ())) >> ``` >> Source: https://stackoverflow.com/questions/10889682/how-to-apply-a-polymorphic-fun… >> >> >> So, how can I do that nowadays? >> >> Thanks, >> Compl >> >> _______________________________________________ >> ghc-devs mailing list >> ghc-devs(a)haskell.org >> http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs >

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What's the modern way to apply a polymorphic function to a Dynamic value in GHC 8.8 and onwards?
by YueCompl 12 Apr '21

12 Apr '21

Dear Cafe and GHC devs, There used to be a "principled way with pattern match on the constructor": ```hs data Dynamic where Dynamic :: Typeable a => a -> Dynamic apD :: Typeable f => (forall a. a -> f a) -> Dynamic -> Dynamic apD f (Dynamic a) = Dynamic $ f a ``` Source: https://www.reddit.com/r/haskell/comments/2kdcca/q_how_to_apply_a_polymorph… But now with GHC 8.8 as in my case, `Dynamic` constructor has changed its signature to: ```hs Dynamic :: forall a. TypeRep a -> a -> Dynamic ``` Which renders the `apD` not working anymore. And it seems missing dependencies now for an older solution Edward KMETT provides: ```hs apD :: forall f. Typeable1 f => (forall a. a -> f a) -> Dynamic -> Dynamic apD f a = dynApp df a where t = dynTypeRep a df = reify (mkFunTy t (typeOf1 (undefined :: f ()) `mkAppTy` t)) $ \(_ :: Proxy s) -> toDyn (WithRep f :: WithRep s (() -> f ())) ``` Source: https://stackoverflow.com/questions/10889682/how-to-apply-a-polymorphic-fun… So, how can I do that nowadays? Thanks, Compl

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[ANN] tasty-bench-0.2.5: featherlight benchmark framework
by Andrew Lelechenko 11 Apr '21

11 Apr '21

I'm happy to announce a release of tasty-bench-0.2.5. It is a featherlight benchmark framework with API mimicking criterion and gauge. https://github.com/Bodigrim/tasty-bench#readme https://hackage.haskell.org/package/tasty-bench-0.2.5 * It supports GHCs from 7.0 to 9.2 alpha. Running benchmarks on a bleeding edge GHC is important to identify potential performance degradation before a compiler is released. * A build on a clean machine is 16 times faster than criterion and 4 times faster than gauge. A build without dependencies is 6 times faster than criterion and 8 times faster than gauge. One can build benchmarks on CI without wasting excessive resources. * Benchmarks can be written together with tests, and can itself be turned into a performance regression test suite. In fact our benchmarks are just regular tasty tests. * Comparisons between benchmarks are readily available out of the box: no external tools (like criterion-compare or bench-show) are required. One can compare results between runs and between individual benchmarks instead of squinting at absolute numbers. Best regards, Andrew

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Taking over scenegraph
by Pippijn van Steenhoven 10 Apr '21

10 Apr '21

Hi all, I've revived http://hackage.haskell.org/package/scenegraph: https://github.com/homectl/lambdaray/tree/main/scenegraph. I'd like to take over maintenance of that package. I can't reach the original author (email address no longer exists). Also, I'm looking for people who would like to join me in working on it and a 3D rendering pipeline based on GPipe. Currently hanging out in #implicitcad on freenode. Cheers, Pippijn

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[ANN] network-packet-linux 0.1.1.0
by Mads Rolsdorph 10 Apr '21

10 Apr '21

Dear Cafe, The network package [0] provides an extensible API for working with sockets. I'm pleased to announce network-packet-linux [1], a small helper package containing the types needed to use the network package with Linux packet sockets [2]. The documentation [3] provides a short example of using network and network-packet-linux for a simple packet sniffer. Have a great weekend! Mads [0] https://hackage.haskell.org/package/network [1] https://hackage.haskell.org/package/network-packet-linux [2] https://man7.org/linux/man-pages/man7/packet.7.html [3] https://hackage.haskell.org/package/network-packet-linux-0.1.1.0/docs/Netwo…

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FMBC 2021 - 2nd Call for Papers
by Bruno Bernardo 10 Apr '21

10 Apr '21

[ Please distribute, apologies for multiple postings. ] ======================================================================== 3rd International Workshop on Formal Methods for Blockchains (FMBC) - Second 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 -------------------------------- David Dill, Lead Researcher, Blockchain, Novi/Facebook, USA https://research.fb.com/people/dill-david/ -------------------------------- -------------------------------- 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 * Wolfgang Ahrendt (Chalmers University of Technology, Sweden) * Lacramioara Astefanoei (Nomadic Labs, France) * Massimo Bartoletti (University of Cagliari, Italy) * Joachim Breitner (Dfinity Foundation, Germany) * Achim Brucker (University of Exeter, UK) * Zaynah Dargaye (Nomadic Labs, France) * Jérémie Decouchant (TU Delft, Netherlands) * Dana Drachsler Cohen (Technion, Israel) * Ansgar Fehnker (University of Twente, Netherlands) * Maurice Herlihy (Brown University, USA) * Lars Hupel (INNOQ, Germany) * Florian Kammueller (Middlesex University London, UK) * Igor Konnov (Informal Systems, Austria) * Andreas Lochbihler (Digital Asset, Switzerland) * Simão Melo de Sousa (Universidade da Beira Interior, Portugal) * Karl Palmskog (KTH, Sweden) * Maria Potop-Butucaru (Sorbonne Université, France) * Andreas Rossberg (Dfinity Foundation, Germany) * César Sanchez (Imdea, Spain) * Clara Schneidewind (TU Wien, Austria) * Ilya Sergey (Yale-NUS College/NUS, Singapore) * Mark Staples (CSIRO Data61, Australia) * Meng Sun (Peking University, China) * Simon Thompson (University of Kent, UK) * Josef Widder (Informal Systems, Austria)

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ML Family Workshop 2021: first call for short abstracts and presentations
by Jonathan Protzenko 09 Apr '21

09 Apr '21

(tl;dr) The ML family workshop is back, and will be held virtually along with ICFP 2021. The workshop does not have proceedings, making it the perfect venue to run some ideas with the community or present some work in progress within a friendly environment. The PC has a broad expertise and submissions are 3 pages long: when in doubt, just submit! (long version) We are happy to announce that the ML Family Workshop is back for its 2021 edition, which we will be held online on Thursday August 26th, in conjunction with ICFP 2021. The ML family workshop warmly welcomes submission touching on the programming languages traditionally seen as part of the "ML family" (Standard ML, OCaml, F#, CakeML, SML#, Manticore, MetaOCaml, etc.). The scope of the workshop includes all aspects of the design, semantics, theory, application, implementation, and teaching of the members of the ML family. We also encourage presentations from related languages (such as Haskell, Scala, Rust, Nemerle, Links, Koka, F*, Eff, ATS, etc), to exchange experience of further developing ML ideas. ## Submission details Submissions must be at most three pages long; see the full call for papers <https://icfp21.sigplan.org/home/mlfamilyworkshop-2021#Call-for-Presentations> for details. Submission site: https://ml21.hotcrp.com/ ## Important dates Thu, May 27th 2021 (AoE): submission deadline Thu, Jun 17th 2021 (AoE): author notification Thu, Aug 26th: workshop (time slots TBD) ## Program committee Danel Ahman (University of Ljubljana) Robert Atkey (University of Strathclyde) Frédéric Bour (Tarides) Ezgi Çiçek (Facebook London) Youyou Cong (Tokyo Institute of Technology) Richard A. Eisenberg (Tweag I/O) Martin Elsman (University of Copenhagen, Denmark) Ohad Kammar (University of Edinburgh) Naoki Kobayashi (University of Tokyo, Japan) Benoît Montagu (Inria) Jonathan Protzenko (Microsoft Research) (Chair) Kristina Sojakova (INRIA Paris) Don Syme (Microsoft) Matías Toro (University of Chile) Katsuhiro Ueno (Tohoku University)

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haskell text://protocol client?
by Petite Abeille 09 Apr '21

09 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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