- Haskell-Cafe - Haskell.org

Haskell internship at Tsuru Capital
by Mikhail Baykov 30 Aug '19

30 Aug '19

Hi Cafe It's that time of year again and we are looking for more interns. Haskell knowledge is required, experience with pricing futures/options would be nice but not necessary. Located in Tokyo, company language is English. Casual environment, nice monitors and a big coffee machine. Duration 3-6 months, starting at your convenience. We will help you with visa and looking for a place to stay. There's some salary. Details how to apply are on our website: http://www.tsurucapital.com/en/ Feel free to ask questions here, on Reddit or #tsurucapital on freenode. https://www.reddit.com/r/haskell/comments/cx8yei/tsuru_capital_is_looking_f…

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First call for draft papers for TFPIE 2020 (Trends in Functional Programming in Education)
by Jurriaan Hage 28 Aug '19

28 Aug '19

Hello, Please, find below the final call for draft papers for TFPIE 2020. Please forward these to anyone you think may be interested. Apologies for any duplicates you may receive. best regards, Jurriaan Hage Chair of TFPIE 2020 ======================================================================== TFPIE 2020 Call for papers http://www.staff.science.uu.nl/~hage0101/tfpie2020/index.html February 12th 2020, Krakow, Poland (co-located with TFP 2020 and Lambda Days) TFPIE 2020 welcomes submissions describing techniques used in the classroom, tools used in and/or developed for the classroom and any creative use of functional programming (FP) to aid education in or outside Computer Science. Topics of interest include, but are not limited to: FP and beginning CS students FP and Computational Thinking FP and Artificial Intelligence FP in Robotics FP and Music Advanced FP for undergraduates FP in graduate education Engaging students in research using FP FP in Programming Languages FP in the high school curriculum FP as a stepping stone to other CS topics FP and Philosophy The pedagogy of teaching FP FP and e-learning: MOOCs, automated assessment etc. Best Lectures - more details below In addition to papers, we are requesting best lecture presentations. What's your best lecture topic in an FP related course? Do you have a fun way to present FP concepts to novices or perhaps an especially interesting presentation of a difficult topic? In either case, please consider sharing it. Best lecture topics will be selected for presentation based on a short abstract describing the lecture and its interest to TFPIE attendees. The length of the presentation should be comparable to that of a paper. On top of the lecture itself, the presentation can also provide commentary on the lecture. Submissions Potential presenters are invited to submit an extended abstract (4-6 pages) or a draft paper (up to 20 pages) in EPTCS style. The authors of accepted presentations will have their preprints and their slides made available on the workshop's website. Papers and abstracts can be submitted via easychair at the following link: https://easychair.org/conferences/?conf=tfpie2020 . After the workshop, presenters will be invited to submit (a revised version of) their article for review. The PC will select the best articles that will be published in the Electronic Proceedings in Theoretical Computer Science (EPTCS). Articles rejected for presentation and extended abstracts will not be formally reviewed by the PC. Dates Submission deadline: January 14th 2020, Anywhere on Earth. Notification: January 17th 2020 TFPIE Registration Deadline: January 20th 2020 Workshop: February 12th 2020 Submission for formal review: April 19th 2020, Anywhere on Earth. Notification of full article: June 6th 2020 Camera ready: July 1st 2020 Program Committee Olaf Chitil - University of Kent Youyou Cong - Tokyo Institute of Technology Marko van Eekelen - Open University of the Netherlands and Radboud University Nijmegen Jurriaan Hage (Chair) - Utrecht University Marco T. Morazan - Seton Hall University, USA Sharon Tuttle - Humboldt State University, USA Janis Voigtlaender - University of Duisburg-Essen Viktoria Zsok - Eotvos Lorand University Note: information on TFP is available at http://www.cse.chalmers.se/~rjmh/tfp/

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GHC: Policy on -O flags?
by Andreas Klebinger 27 Aug '19

27 Aug '19

Hello ghc-devs and haskell users. I'm looking for opinions on when an optimization should be enabled by default. -O is currently the base line for an optimized build. -O2 adds around 10-20% compile time for a few % (around 2% if I remember correctly) in performance for most things. The question is now if I implement a new optimization, making code R% faster but slowing down the compiler down by C% at which point should an optimization be: * Enabled by default (-O) * Enabled only at -O2 * Disabled by default Cheap always beneficial things make sense for -O Expensive optimizations which add little make sense for -O2 But where exactly is the line here? How much compile time is runtime worth? If something slows down the compiler by 1%/2%/5% and speeds up code by 0.5%/1%/2% which combinations make sense for -O, -O2? Can there even be a good policy with the -O/-O2 split? Personally I generally want code to either: * Typecheck/Run at all (-O0, -fno-code, repl) * Not blow through all my RAM when adding a few Ints while developing: -O ? * Make a reasonable tradeoff between runtime/compiletime: -O ? * Give me all you got: -O2 (-O99999) The use case for -O0 is rather clear, so is -O2. But what do people consider the use case for -O What trade offs seem acceptable to you as a user of GHC? Is it ok for -O to become slower for faster runtimes? How much slower? Should all new improvements which might slow down compilation be pushed to -O2? Or does an ideal solution add new flags? Tell me what do you think. Cheers, Andreas Klebinger

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Munich Haskell Meeting, 2019-08-29 @ 19:30
by Leah Neukirchen 27 Aug '19

27 Aug '19

Dear all, This week, our monthly Munich Haskell Meeting will take place again on Thursday, August 29 at Augustiner-Gaststätte Rumpler at 19h30. For details see here: http://muenchen.haskell.bayern/dates.html If you plan to join, please add yourself to this dudle so we can reserve enough seats! It is OK to add yourself to the dudle anonymously or pseudonymously. https://dudle.inf.tu-dresden.de/haskell-munich-aug-2019/ Everybody is welcome! cu, -- Leah Neukirchen <leah(a)vuxu.org> https://leahneukirchen.org/

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ANN: bcp47
by Evan Borden 26 Aug '19

26 Aug '19

Announcing bcp47, http://hackage.haskell.org/package/bcp47-0.1.0.0 This library provides language tags as specified by https://tools.ietf.org/html/bcp47 As well it provides a trie like data structure for collecting and querying data that varies by language.

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First call for participation for IFL 2019 (Implementation and Application of Functional Languages)
by Jurriaan Hage 26 Aug '19

26 Aug '19

Hello, Please, find below the first call for participation for IFL 2019. Please forward these to anyone you think may be interested. Apologies for any duplicates you may receive. best regards, Jurriaan Hage Publicity Chair of IFL ================================================================================ IFL 2019 31st Symposium on Implementation and Application of Functional Languages National University of Singapore September 25th-27th, 2019 http://2019.iflconference.org ================================================================================ ### Scope The goal of the IFL symposia is to bring together researchers actively engaged in the implementation and application of functional and function-based programming languages. IFL 2019 will be a venue for researchers to present and discuss new ideas and concepts, work in progress, and publication-ripe results related to the implementation and application of functional languages and function-based programming. Topics of interest to IFL include, but are not limited to: - language concepts - type systems, type checking, type inferencing - compilation techniques - staged compilation - run-time function specialization - run-time code generation - partial evaluation - (abstract) interpretation - metaprogramming - generic programming - automatic program generation - array processing - concurrent/parallel programming - concurrent/parallel program execution - embedded systems - web applications - (embedded) domain specific languages - security - novel memory management techniques - run-time profiling performance measurements - debugging and tracing - virtual/abstract machine architectures - validation, verification of functional programs - tools and programming techniques - (industrial) applications ### Keynote Speaker * Olivier Danvy, Yale-NUS College ### Submissions and peer-review Differently from previous editions of IFL, IFL 2019 solicits two kinds of submissions: * Regular papers (12 pages including references) * Draft papers for presentations ('weak' limit between 8 and 15 pages) Regular papers will undergo a rigorous review by the program committee, and will be evaluated according to their correctness, novelty, originality, relevance, significance, and clarity. A set of regular papers will be conditionally accepted for publication. Authors of conditionally accepted papers will be provided with committee reviews along with a set of mandatory revisions. Regular papers not accepted for publication will be considered as draft papers, at the request of the author. Draft papers will be screened to make sure that they are within the scope of IFL, and will be accepted for presentation or rejected accordingly. Prior to the symposium: Authors of conditionally accepted papers and accepted presentations will submit a pre-proceedings version of their work that will appear in the draft proceedings distributed at the symposium. The draft proceedings does not constitute a formal publication. We require that at least one of the authors present the work at IFL 2019. After the symposium: Authors of conditionally accepted papers will submit a revised versions of their paper for the formal post-proceedings. The program committee will assess whether the mandatory revisions have been adequately addressed by the authors and thereby determines the final accept/reject status of the paper. Our interest is to ultimately accept all conditionally accepted papers. If you are an author of a conditionally accepted paper, please make sure that you address all the concerns of the reviewers. Authors of accepted presentations will be given the opportunity to incorporate the feedback from discussions at the symposium and will be invited to submit a revised full article for the formal post-proceedings. The program committee will evaluate these submissions according to their correctness, novelty, originality, relevance, significance, and clarity, and will thereby determine whether the paper is accepted or rejected. ### Publication The formal proceedings will appear in the International Conference Proceedings Series of the ACM Digital Library. At no time may work submitted to IFL be simultaneously submitted to other venues; submissions must adhere to ACM SIGPLAN's republication policy: http://www.sigplan.org/Resources/Policies/Republication ### Important dates Submission of regular papers: June 15, 2019 Submission of draft papers: August 1, 2019 Regular papers notification: August 1, 2019 Regular draft papers notification: August 7, 2019 Deadline for early registration: August 31, 2019 Submission of pre-proceedings version: September 15, 2019 IFL Symposium: September 25-27, 2019 Submission of papers for post-proceedings: November 30, 2019 Notification of acceptance: January 31, 2020 Camera-ready version: February 29, 2020 ### Submission details All contributions must be written in English. Papers must use the ACM two columns conference format, which can be found at: http://www.acm.org/publications/proceedings-template Authors submit through EasyChair: https://easychair.org/conferences/?conf=ifl2019 ### Peter Landin Prize The Peter Landin Prize is awarded to the best paper presented at the symposium every year. The honored article is selected by the program committee based on the submissions received for the formal review process. The prize carries a cash award equivalent to 150 Euros. ### Organization and Program committee Chairs: Jurrien Stutterheim (Standard Chartered Bank Singapore), Wei Ngan Chin (National University of Singapore) Program Committee: - Olaf Chitil, University of Kent - Clemens Grelck, University of Amsterdam - Daisuke Kimura, Toho University - Pieter Koopman, Radboud University - Tamás Kozsik, Eötvös Loránd University - Roman Leschinskiy, Facebook - Ben Lippmeier, The University of New South Wales - Marco T. Morazan, Seton Hall University - Sven-Bodo Scholz, Heriot-Watt University - Tom Schrijvers, Katholieke Universiteit Leuven - Alejandro Serrano, Utrecht University - Tony Sloane, Macquarie University - Simon Thompson, University of Kent - Marcos Viera, Universidad de la República - Wei Ngan Chin, NUS - Jurriën Stutterheim, Standard Chartered Bank ### Venue The 31st IFL is organized by the National University of Singapore. Singapore is located in the heart of South-East Asia, and the city itself is extremely well connected by trains and taxis. See the website for more information on the venue. ### Acknowledgments This call-for-papers is an adaptation and evolution of content from previous instances of IFL. We are grateful to prior organizers for their work, which is reused here. A part of IFL 2019 format and CFP language that describes conditionally accepted papers has been adapted from call-for-papers of OOPSLA conferences.

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ANN bitvec-1.0.0.1
by Andrew Lelechenko 23 Aug '19

23 Aug '19

Hello, I am happy to announce the stable release of bitvec-1.0.0.1. This package provides a "better" Vector instance for Bool. An unboxed Vector Bool spends 8 bits per boolean, while bitvec provides a newtype Bit and a custom instance of Vector, packing booleans densely and achieving 8x less memory footprint. Performance stays roughly the same, and certain bulk operations become up to 64x faster. http://hackage.haskell.org/package/bitvec-1.0.0.1 https://github.com/Bodigrim/bitvec#readme Best regards, Andrew

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Getting both the value and name of a variable in one expression
by Christopher Done 22 Aug '19

22 Aug '19

Hi all, Do we have already a syntax for ‘foo that also contains the typed value like TExp? I have e.g. an AST that I want to do more static checks on it that aren’t as convenient to do in the type system. Here’s an example: -- | Check the grammar spec to produce a grammar.checkGrammar :: (SchemaName, [(SchemaName, Schema)]) -> Q ExpcheckGrammar (toplevel, rules) = if M.size rulesMap /= length rules then error "Duplicate rule names in grammar." else lift (Grammar {grammarToplevel = toplevel, grammarRules = rulesMap}) where rulesMap = M.fromList rules -- | Grammar for Haskell.grammar :: Grammargrammar = $(checkGrammar $ runDefine $ mdo -- General expression expression <- rule "Expression" (ChoiceSchema [variable, constructor, parentheses ,tuple, let', application, string]) application <- rule "Application" (CompositeSchema [expression, expression]) parentheses <- rule "Parentheses" (CompositeSchema [openParenSchema, expression, closeParenSchema]) ... pure expression) Here I do a trivial check for duplicates. After I’ve checked the expression at compile-time, I Lift it so that it can be used at runtime. That’s pretty good. But some types like (a -> b) don’t Lift. So an alternative would be: grammar = $(checkGrammar_take2 thename 'thename) In which checkGrammar_take2 would: 1. Use thename at compile-time for a check. 2. If the check passes, then return (VarE thename) E.g. checkGrammar_take2 value name = if valueFine value then varE name elseerror "value isn't fine" That’s actually quite a good solution because it avoids a lift, and I didn’t transform the AST. It’s also more efficient than lifting. But there’s no checked relationship between thename and ‘thename. checkGrammar_take2 has no way of knowing that they refer to the same thing. See? Hence, if I could get e.g. `thename to produce both the value and a name for the value, that would be cool. My gist doesn’t go this far. It might look like this: checkGrammar_take2 namedValue = if valueFine (getValue namedValue) then getExp namedValue else error "value isn't fine" and call it like: mygrammar = checkGrammar_take2 `thename So the semantics would be roughly similar to [|| thename ||] :: TExp a but you’d get `thename :: Named a where data Named a = { namedThing :: a, nameOfThing :: Name } I feel like the more DSLs I design, the more I’d like something like this to perform my static checks. Cheers, Chris

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Question on inductive type-families
by Sylvain Henry 22 Aug '19

22 Aug '19

Hi, Suppose I have the following type family: type family Index (n :: Nat) (l :: [k]) = (r :: k) where Index 0 (x ': _ ) = x Index n (_ ': xs) = Index (n-1) xs I'm using it to define a Variant type: data V2 (vs :: [k]) where V2 :: forall vs (n :: Nat). KnownNat n => Proxy n -> Index n vs -> V2 vs Now I want to match on the Variant retrieving either the head or the tail (another Variant): splitV2 :: forall v vs. V2 (v:vs) -> Either v (V2 vs) splitV2 = \case V2 (n1 :: Proxy n) v -> case sameNat n1 (Proxy @0) of Just Refl -> Left v Nothing -> Right (V2 (Proxy @(n-1)) v) It fails to typecheck with: Couldn't match type ‘Index n (v : vs)’ with ‘Index (n - 1) vs’ Expected type: Index (n - 1) vs Actual type: Index n vs1 NB: ‘Index’ is a non-injective type family Is there a way to make this work? This is highly speculative as I'm not very familiar with type-checking: would it be sound to make the inductive Index family "weakly" injective? I.e. somehow produce a typing rule for the type family: forall n n' x xs xs'. Solving: Index n (x ': xs) ~ Index (n'-1) xs' Is equivalent to solving: if n /= 0 then (n ~ n', xs ~ xs') else (x ~ Index (n'-1) xs') Here we could know that "n /= 0" thanks to the match on "sameNat n1 (Proxy @0)". ("weakly" because we have some form of injectivity on the shape of the list but not on its contents) Any pointer on this kind of stuff in research papers, Coq, Agda, etc. ? Thanks, Sylvain

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Optimizations for list comprehension
by Emilio Francesquini 21 Aug '19

21 Aug '19

Hello Cafe, While investigating a performance problem I stumbled upon what I eventually reduced to the example below: module Main where import Data.Time.Clock outside :: Int -> Int outside n = sum [i + j | i <- range, j <- range] where range = [0..n-1] inside :: Int -> Int inside n = sum [i + j | i <- [0..n-1], j <- [0..n-1]] main :: IO () main = do t0 <- getCurrentTime print $ inside 10000 t1 <- getCurrentTime print $ outside 10000 t2 <-getCurrentTime print (diffUTCTime t1 t0) print (diffUTCTime t2 t1) Compiling with -O2, up to GHC 8.2.2, both `inside` and `outside` functions would take the same amount of time to execute. Somewhere between GHC 8.2.2 and 8.6.4 something changed (possibly some new optimization) making `inside` run ~4x faster on my machine. With LLVM the difference is even bigger. It is not that `outside` got slower, but that `inside` got much faster. I'm curious to what optimizations might be happening to the `inside` function that would not fire on the outside function. Any hints? Best regards, Emilio

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Permenent Faculty Position in PL at University of Bristol
by Meng Wang 19 Aug '19

19 Aug '19

Dear Haskellers, As part of a strategic expansion, the Department of Computer Science at the University of Bristol is hiring in the area of programming languages at the Lecturer (Assistant Professor) or Senior Lecturer/Reader (Associate Professor) level: http://www.bristol.ac.uk/jobs/find/details.html?nPostingID=51136&nPostingTa… Applications in the area of functional programming are especially encouraged. The deadline for application is 8 September 2019. Best wishes, Meng Wang, PhD Senior Lecturer (Associate Professor) Department of Computer Science University of Bristol Merchant Venturers Building, Woodland Road, Clifton BS8 1UB +44 (0) 117 954 5145 meng.wang(a)bristol.ac.uk

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Re: [Haskell-cafe] Unfolding alongside folding
by David Banas 19 Aug '19

19 Aug '19

I’m not certain, but think you might be describing hylomorphism: https://medium.com/@JosephJnk/hylomorphisms-43a5494729b7 <https://medium.com/@JosephJnk/hylomorphisms-43a5494729b7> -db > On Aug 19, 2019, at 5:00 AM, haskell-cafe-request(a)haskell.org wrote: > > Does a function of this general nature exist in some package already?

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Unfolding alongside folding
by David Feuer 19 Aug '19

19 Aug '19

Thinking about fusing indexed maps for lists led me to consider the following function, which generalizes mapWithIndex to allow arbitrary stateful computation foldWithUnfold :: (a -> s -> Maybe (b, s)) -> [a] -> s -> [b] foldWithUnfold f = go where go (a : as) s | Just (b, s') <- f a s = b : go as s' go _ _ = [] which we can fit into fold/build fusion like so: foldWithUnfold f as s0 = build $ \c n -> let go a k s | Just (b, s') <- f a s = b `c` k s' | otherwise = n in foldr go (const n) as s0 Does a function of this general nature exist in some package already? Also, I see that the type can be expressed foldWithUnfoldS :: (a -> StateT s Maybe b) -> [a] -> s -> [b] Is that a better or worse way to say it?

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MPC 2019 - Call for Participation
by Graham Hutton 19 Aug '19

19 Aug '19

Dear all, Registration is now open for the Mathematics of Program Construction (MPC) conference in Portugal. MPC 2019 will feature 15 research papers and 4 keynotes, and is co-located with Formal Methods 2019 and many other events. See you in Porto! https://tinyurl.com/MPC-Porto Best wishes, Graham Hutton Program Chair, MPC 2019 ====================================================================== *** CALL FOR PARTICIPATION -- MPC 2019 *** 13th International Conference on Mathematics of Program Construction 7-9 October 2019, Porto, Portugal Co-located with Formal Methods 2019 https://tinyurl.com/MPC-Porto ====================================================================== PROGRAM: https://tinyurl.com/yxvvc5vb ACCEPTED PAPERS: https://tinyurl.com/yyuhy8ze REGISTRATION AND TRAVEL: https://tinyurl.com/y4uetlsr KEYNOTE SPEAKERS: Assia Mahboubi (MPC) INRIA, France Annabelle McIver (MPC) Macquarie University, Australia Tony Hoare (UTP) Oxford University, UK Shriram Krishnamurthi (FM) Brown University, USA BACKGROUND: The International Conference on Mathematics of Program Construction (MPC) aims to promote the development of mathematical principles and techniques that are demonstrably practical and effective in the process of constructing computer programs. MPC 2019 will be held in Porto, Portugal from 7-9 October 2019, and is co-located with the International Symposium on Formal Methods, FM 2019. Previous conferences were held in Königswinter, Germany (2015); Madrid, Spain (2012); Québec City, Canada (2010); Marseille, France (2008); Kuressaare, Estonia (2006); Stirling, UK (2004); Dagstuhl, Germany (2002); Ponte de Lima, Portugal (2000); Marstrand, Sweden (1998); Kloster Irsee, Germany (1995); Oxford, UK (1992); Twente, The Netherlands (1989). PROGRAM COMMITTEE: Patrick Bahr IT University of Copenhagen, Denmark Richard Bird University of Oxford, UK Corina Cîrstea University of Southampton, UK Brijesh Dongol University of Surrey, UK João F. Ferreira University of Lisbon, Portugal Jennifer Hackett University of Nottingham, UK William Harrison University of Missouri, USA Ralf Hinze University of Kaiserslautern, Germany Zhenjiang Hu National Institute of Informatics, Japan Graham Hutton (chair) University of Nottingham, UK Cezar Ionescu University of Oxford, UK Mauro Jaskelioff National University of Rosario, Argentina Ranjit Jhala University of California, USA Gabriele Keller Utrecht University, The Netherlands Ekaterina Komendantskaya Heriot-Watt University, UK Chris Martens North Carolina State University, USA Bernhard Möller University of Augsburg, Germany Shin-Cheng Mu Academia Sinica, Taiwan Mary Sheeran Chalmers University of Technology, Sweden Alexandra Silva University College London, UK Georg Struth University of Sheffield, UK For any queries about the program please contact the program chair, Graham Hutton <graham.hutton(a)nottingham.ac.uk>. CONFERENCE VENUE: The conference will be held at the Alfândega Porto Congress Centre, a 150 year old former custom's house located in the historic centre of Porto on the bank of the river Douro. The venue was renovated by a Pritzer prize winning architect and has received many awards. LOCAL ORGANISER: José Nuno Oliveira University of Minho, Portugal For any queries about local issues please contact the local organiser, José Nuno Oliveira <jno(a)di.uminho.pt>. ====================================================================== This message and any attachment are intended solely for the addressee and may contain confidential information. If you have received this message in error, please contact the sender and delete the email and attachment. Any views or opinions expressed by the author of this email do not necessarily reflect the views of the University of Nottingham. Email communications with the University of Nottingham may be monitored where permitted by law.

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[ANN] express-0.1.2: manipulate dynamically typed Haskell expressions
by Rudy Matela 18 Aug '19

18 Aug '19

Hello Haskell-Café, I am happy to announce the [Express] library for Haskell. https://github.com/rudymatela/express Express allows manipulation of dynamically typed Haskell expressions. It is similar to Data.Dynamic but with support for encoding applications and variables. It provides an Expr type and over a hundred functions for building, evaluating, comparing, folding, canonicalizing and matching Exprs. [Express' Haddock documentation] is pretty comprehensive. The project [README] has a few examples showing how to use Express to: * create heterogeneous lists; * list valid applications between expressions; * generalize counterexamples; * automatically generate test properties. This library has its origins as an internal module of [Speculate] and [Extrapolate], I am now releasing it separetely hoping that it could be used for other purposes. To install it, just: $ cabal update $ cabal install express Then you're ready to use it: $ ghci > import Data.Express > let true = val True > :t true true :: Expr > print true True :: Bool > eval False true True -- Rudy [Express]: https://github.com/rudymatela/express [Express' Haddock documentation]: https://hackage.haskell.org/package/express/docs/Data-Express.html [README]: https://github.com/rudymatela/express#readme [Speculate]: https://github.com/rudymatela/speculate [Extrapolate]: https://github.com/rudymatela/extrapolate

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PhD position at Imperial College London
by Wu, Nicolas G 16 Aug '19

16 Aug '19

# PhD Position in Functional Programming: Effect Handlers at Imperial College London Applications are invited for a PhD student in Functional Programming under the supervision of Dr Nicolas Wu at Imperial College London. The project aims to enhance the applications of effects and handlers by developing scoped contextual operations and effects. There are two main interrelated topics: 1. Developing the foundations of operations and effects that are confined within a scope and that are sensitive to context, thus widening the applications of effect handlers. 2. Producing efficient implementations and demonstrating applications that allow programmers to combine and use such effects. Addressing these topics will deliver both theoretical insight to the academic community and practical benefits to software engineers. To apply for this position, you will need to have a strong background in at least one of the following areas: functional programming, programming language design, compilers, algebraic effects. A working understanding of Haskell is essential. Applicants are expected to have a First Class or Distinction Masters level degree, or equivalent, in a relevant scientific or technical discipline, such as computer science or mathematics. Applicants must be fluent in spoken and written English. The position is fully funded, covering tuition fees, travel funds and a stipend/bursary. The position is available to home, EU and overseas students. Studentship: Untaxed bursary of £17,009 per annum (2018/19 figure including London weighting plus home/EU fees) For more details on how to apply, please see the advertisement here: http://www.imperial.ac.uk/computing/prospective-students/courses/phd/schola… listed under "PhD Position in Functional Programming: Effect Handlers". Early applications are strongly encouraged. Please be in touch with informal inquiries about the position with Dr Nicolas Wu (n.wu(a)imperial.ac.uk)

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[TFP'20] first call for papers: Trends in Functional Programming 2020, 13-14 February, Krakow, Poland
by Peter Achten 15 Aug '19

15 Aug '19

------------------------------------------------------------------------- First call for papers 21st Symposium on Trends in Functional Programming tfp2020.org ------------------------------------------------------------------------- The symposium on Trends in Functional Programming (TFP) is an international forum for researchers with interests in all aspects of functional programming, taking a broad view of current and future trends in the area. It aspires to be a lively environment for presenting the latest research results, and other contributions. * TFP is moving to new winter dates, to provide an FP forum in between the annual ICFP events. * TFP offers a supportive reviewing process designed to help less experienced authors succeed, with two rounds of review, both before and after the symposium itself. Authors have an opportunity to address reviewers' concerns before final decisions on publication in the proceedings. * TFP offers two "best paper" awards, the John McCarthy award for best paper, and the David Turner award for best student paper. * This year we are particularly excited to co-locate with Lambda Days in beautiful Krakow. Lambda Days is a vibrant developer conference with hundreds of attendees and a lively programme of talks on functional programming in practice. TFP will be held in the same venue, and participants will be able to session-hop between the two events. Important Dates --------------- Submission deadline for pre-symposium review: 15th November, 2019 Submission deadline for draft papers: 10th January, 2020 Symposium dates: 13-14th February, 2020 Visit tfp2020.org for more information.

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Research Associate at Kent in Trustworthy Refactoring
by Simon Thompson 12 Aug '19

12 Aug '19

We are seeking to recruit an enthusiastic Research Associate to join the final year of the EPSRC project “Trustworthy Refactoring”. The overall goal of this project is to investigate the design and construction of trustworthy refactoring tools: this means that when refactorings are performed, the tools will provide strong evidence that the refactoring has not changed the behaviour of the code, built on a solid theoretical understanding of the semantics of the language, thus establishing a step change in the practice of refactoring. If you have have a PhD in Computer Science, awarded or nearing completion, experience in functional programming (e.g. Haskell/ML/Erlang/…) and experience of using a proof assistant (e.g. Coq/Isabelle/HOL/…), you have what we’re looking for. More details about the project are here: https://jobs.kent.ac.uk/vacancy.aspx?ref=STM-047-19 If you have any questions about the post do contact one of us by email: Scott Owens (s.a.owens(a)kent.ac.uk) and Simon Thompson (s.j.thompson(a)kent.ac.uk) : we look forward to hearing from you. Scott and Simon Simon Thompson | Professor of Logic and Computation School of Computing | University of Kent | Canterbury, CT2 7NF, UK s.j.thompson(a)kent.ac.uk | M +44 7986 085754 | W www.cs.kent.ac.uk/~sjt

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PADL 2020 (co-allocated with POPL 2020): first call for papers
by Ekaterina Komendantskaya 12 Aug '19

12 Aug '19

22nd International Symposium on Practical Aspects of Declarative Languages (PADL 2020)https://popl20.sigplan.org/home/PADL-2020,20-21 January 2019, New Orleans, Louisiana, United StatesCo-located with ACM POPL 2020 ( https://popl20.sigplan.org/) ------------------------------ *Declarative programming languages* is an umbrella term for functional, logic, answer-set and constraint-solving programming paradigms, as well as a range of verification and theorem proving methods that rely on such languages. These languages have been successfully applied to many different real-world situations, ranging from data base management and active networks to software engineering and decision support systems. New developments in theory and implementation have opened up new application areas. At the same time, applications of declarative languages to challenging problems raise new intriguing research questions, such as scalable design and implementation, language extensions for application deployment, and programming environments. Thus, applications drive the progress in the theory and implementation of declarative systems, and benefit from this progress as well. PADL is a well-established forum for researchers and practitioners to present original work emphasising novel applications and implementation techniques for all forms of declarative programming, including functional and logic programming, data-base and constraint programming, theorem proving. Topics of interest include, but are not limited to: - Innovative applications of declarative languages - Declarative domain-specific languages and applications - Practical applications of theoretical results - New language developments and their impact on applications - Declarative languages for software engineering - Evaluation of implementation techniques on practical applications - Practical experiences and industrial applications - Novel uses of declarative languages in the classroom - Practical languages and extensions such as probabilistic and reactive languages *PADL 2020 especially welcomes new ideas and approaches pertaining to applications, design and implementation of declarative languages going beyond the scope of the past PADL symposia, for example database languages and contract languages.* Important Dates and Submission Guidelines: - Abstracts due: 11 October 2019 - Papers due: 18 October 2019 - Notification to authors: 18 November 2019 - Camera-ready: 29 November 2020 Authors should submit an electronic copy of the full paper in PDF using the Springer LNCS format. The submission will be done through EasyChair conference system: https://easychair.org/conferences/?conf=padl2020 All submissions must be original work written in English. Submissions must be unpublished and not submitted for publication elsewhere. Work that already appeared in unpublished or informally published workshops proceedings may be submitted but the authors should notify the program chair about the place on which it has previously appeared. PADL 2020 will accept both technical and application papers: *Technical papers* must describe original, previously unpublished research results. Technical papers must not exceed 15 pages (plus one page of references) in Springer LNCS format. *Application papers* are a mechanism to present important practical applications of declarative languages that occur in industry or in areas of research other than Computer Science. Application papers are expected to describe complex and/or real-world applications that rely on an innovative use of declarative languages. Application descriptions, engineering solutions and real-world experiences (both positive and negative) are solicited. The limit for application papers is 8 pages in Springer LNCS format but such papers can also point to sites with supplemental information about the application or the system that they describe. *The proceedings of PADL 2020 will appear in the LNCS series of Springer Verlag: https://www.springer.com/gp/computer-science/lncs <https://www.springer.com/gp/computer-science/lncs>.* ************************************************************* For further questions, please contact the conference chairs: Ekaterina Komendantskaya <ek19(a)hw.ac.uk> and Annie Liu <liu(a)cs.stonybrook.edu >

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Unifying an IO read into a TChan?
by Adam 09 Aug '19

09 Aug '19

Hello Café! It's my first post here so do tell me if I get something wrong :) I'm in the process of writing an event database; it should adhere to ACID principles and is specifically aimed at persisting then broadcasting events in some event-driven system. The code is up on GitHub and I expect to build a Hackage package soon, for now I'm prototyping with Stack generating the .cabal file, but this will change when things settle down. My question is about a function I have: readEvents :: Word64 -> Connection -> IO ([IndexedEvent], TChan IndexedEvent) readEvents from conn = do (ec, chan) <- atomically $ (,) <$> (readTVar $ evCount conn) <*> (dupTChan $ readSubs conn) evsFromDisk <- readEventsRange from ec conn pure (evsFromDisk, chan) For context please see the whole file: https://github.com/ahri/eventdb/blob/4747afb/src/Database/EventDB.hs#L172-L… 1. What I'd like to understand is how I might unify the return type into a single `TChan IndexedEvent` which would contain first the `evsFromDisk` and then pull from the broadcast channel `chan`. The only way I can think to do it is to fork a thread to write to a new broadcast channel - which might be unexpected for a client of my API and seems quite heavyweight. I have a connected couple of questions too, related to lazy IO as I'm still learning Haskell! 2. does my `readEventsRange` function pull all events into memory or does lazy IO magically avoid this by streaming the data through from the disk? 3. if I did fork a thread and write the `evsFromDisk` and the sit in a ` forever` reading off `chan` and onto my new broadcast channel, would this result in all the written events being read into memory or does the laziness spread so that only when the client does a `readTChan` will the data flow through from the disk/`chan`? Thanks for reading, Adam

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Ambiguous types
by Dušan Kolář 07 Aug '19

07 Aug '19

Dear Café, I'm trying to solve a couple of examples and exercises just for me. I've come to the point, when I'm trying working code manipulating lists rewrite to work on Foldable (etc.). Nevertheless, I must be doing some mistake, overlooking something, as simple code like this: chkDup [] = False chkDup (0:ns) = chkDup ns chkDup (n:ns) = elem n ns || chkDup ns which works fine, type-checks, can be used within other code, I'm trying to replace with more generic, but probably less efficient and wrong code: chkDup ns = fst $ foldr f (False,mempty) ns where f _ res@(True,_) = res f v res@(_,vs) = if v==0 then (False, vs) else (elem v vs, pure v <> vs) which does not even type-check. Nevertheless, the error message is not too helpful, searching the Internet just confirms it's wrong and that adding AllowAmbiguousTypes would not work. The error message is: helper.hs:49:1: error: • Could not deduce (Foldable f0) from the context: (Eq a, Num a, Foldable t, Foldable f, Applicative f, Monoid (f a)) bound by the inferred type for ‘chkDup’: forall a (t :: * -> *) (f :: * -> *). (Eq a, Num a, Foldable t, Foldable f, Applicative f, Monoid (f a)) => t a -> Bool at helper.hs:(49,1)-(53,80) The type variable ‘f0’ is ambiguous • In the ambiguity check for the inferred type for ‘chkDup’ To defer the ambiguity check to use sites, enable AllowAmbiguousTypes When checking the inferred type chkDup :: forall a (t :: * -> *) (f :: * -> *). (Eq a, Num a, Foldable t, Foldable f, Applicative f, Monoid (f a)) => t a -> Bool | 49 | chkDup ns = | ^^^^^^^^^^^... So is there a nicer and working way, how to change my simple example? Is there a way, how to make it compile? Or is it useless to do that, original function is just fine... Best regards, Dušan

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Evaluating an AST with GADTs (and Type Families?)
by Hilco Wijbenga 07 Aug '19

07 Aug '19

Hi all, I'm trying to implement an evaluator with GADTs. This is about as far as I've gotten: https://pastebin.com/XjWBzgw7 . data Value = ValueBool Bool | ValueText String | ValueObject (Map String Value) data Expr t where ExprBool :: Bool -> Expr Bool ExprBoolOr :: Expr Bool -> Expr Bool -> Expr Bool ExprText :: String -> Expr String ExprTextAppend :: Expr String -> Expr String -> Expr String ExprObject :: Map String Value -> String -> Expr Value eval :: Expr t -> t eval (ExprBool value) = value eval (ExprBoolOr lft rgt) = eval lft || eval rgt eval (ExprText value) = value eval (ExprTextAppend lft rgt) = eval lft <> eval rgt eval (ExprObject map fieldName) = map ! fieldName Note that the Value data type was just an attempt and not (necessarily) what I'm looking for. And I'm ignoring all error handling for the moment to keep the example small. This compiles but obviously the object type is completely separate from the Expr Bool and Expr String types. Apparently, Type Familiies might help here? I could not find anything relevant that really explained it. I've been thinking about changing ExprObject to something like ExprObjectBool :: Map String Value -> String -> Expr Bool ExprObjectString :: Map String Value -> String -> Expr String ExprObjectObject :: Map String Value -> String -> Expr ??? but I can't figure out what ??? would be. And this would seem to explode if I add more "primitive" types, especially if I want to support lists and maps as well. (Maps and objects are very similar but not the same.) How would I go about making the object type useful here? Or should I go back to plain "Expr" and just error out when trying to, e.g., "or" 2 Strings? Cheers, Hilco

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cabal: Could not resolve dependencies
by Henk-Jan van Tuyl 07 Aug '19

07 Aug '19

L.S., I am trying to compile wxHaskell with GHC 8.8.0.20190721 and I get the following messages from cabal-install: > cabal new-build all --disable-documentation Resolving dependencies... cabal: Could not resolve dependencies: [__0] trying: samplesContrib-0.93.0.0 (user goal) [__1] trying: base-4.13.0.0/installed-4.1... (dependency of samplesContrib) [__2] trying: wxcore-0.93.0.0 (user goal) [__3] next goal: wxcore:setup.Cabal (dependency of wxcore) [__3] rejecting: wxcore:setup.Cabal-3.0.0.0/installed-3.0... (constraint from maximum version of Cabal used by Setup.hs requires <2.6 [...] What does this mean, how do I solve it? (There is a Setup.hs in package wxcore, but does it have its own Cabal file?) > cabal --version cabal-install version 2.4.1.0 compiled using version 2.4.1.0 of the Cabal library Regards, Henk-Jan van Tuyl -- Message from Stanford University: Folding@home What if you could share your unused computer power to help find a cure? In just 5 minutes you can join the world's biggest networked computer and get us closer sooner. Watch the video. http://foldingathome.stanford.edu/ -- http://members.chello.nl/hjgtuyl/tourdemonad.html Haskell programming --

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instance Monoid a => Monad ((,) a)
by Benjamin Franksen 06 Aug '19

06 Aug '19

I wanted to define a simple Monad instance for (Bool,) as instance Monad ((,) Bool) where return x = (False, x) (True, x) >>= k = (True, snd (k x)) (False, x) >>= k = k x -- or: (b, x) >>= k = let (c, y) = k x in (b||c, y) The idea was to keep track of whether functions change their input value or not. To my astonishment I found that this definition overlaps with an existing one. GHC tells me x.hs:2:10: error: • No instance for (Monoid Bool) arising from the superclasses of an instance declaration • In the instance declaration for ‘Monad ((,) Bool)’ | 2 | instance Monad ((,) Bool) where | ^^^^^^^^^^^^^^^^ x.hs:2:10: error: • Overlapping instances for Monad ((,) Bool) arising from a use of ‘GHC.Base.$dm>>’ Matching instances: instance Monoid a => Monad ((,) a) -- Defined in ‘GHC.Base’ instance Monad ((,) Bool) -- Defined at x.hs:2:10 • In the expression: GHC.Base.$dm>> @((,) Bool) In an equation for ‘>>’: (>>) = GHC.Base.$dm>> @((,) Bool) In the instance declaration for ‘Monad ((,) Bool)’ | 2 | instance Monad ((,) Bool) where | ^^^^^^^^^^^^^^^^ [one more similar overlap error elided] But I could not find the instance Monoid a => Monad ((,) a) documented anywhere in the base package. Should I look harder? Or is this instance accidentally leaking from GHC.Base? Eventually, through some experimenting I found that if I replace Bool with Any, then the existing instance seems to do what I want. Cheers Ben

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Performance best practices
by Todd Wilson 04 Aug '19

04 Aug '19

Dear Cafe: I'm getting to the point in my Haskell learning curve where I'm getting more interested in the fine points of programming for performance and would be grateful for some ideas of the tools and options available for exploring this. To make this concrete, let me give a simple example. Here are two different ways of coding the same list-splitting function: import Data.List (inits,tails) splits1, splits2 :: [a] -> [([a],[a])] splits1 xs = zip (inits xs) (tails xs) splits2 [] = [([],[])] splits2 xs@(x:xs') = ([],xs) : [(x:as,bs) | (as,bs) <- splits2 xs'] For example, splits1 [1,2,3] is [([],[1,2,3]),([1],[2,3]),([1,2],[3]),([1,2,3],[])]. How do these functions compare in their actual time and space usage? It seems that, asymptotically, tails is O(n) while inits is O(n^2) in both time and space (when fully evaluated), and splits2 is also O(n^2), but how would I go about comparing them in actual usage to get a more precise comparison? What profiling or run-time statistics could I gather to make a decision about which one to use in a situation where performance mattered (assuming for the sake of discussion that such a situation existed for this simple example)? And, out of curiosity, is there an even more efficient way to code this function? Thanks, Todd Wilson

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ANN: To Kata Haskellen Evangelion
by Cosmia Fu 02 Aug '19

02 Aug '19

Hi everyone, Though some of you might already knows, I'm pleased to announce a new Haskell book, *To Kata Haskellen Evangelion*. Link: https://cosmius.bitbucket.io/tkhe/ I believe that it does not have to be hard to learn Haskell. I begun to write the book in 2017 December, and... to be honest, I don't know what to write now, though I still think it incomplete. It will probably not be updated for quite a while. So I decide to announce it earlier. I am not a native English speaker, so it might be not fluent or even with a lot of grammar mistakes. It would be very nice of you if you can tell me the mistakes in it, factual, technical or grammar. And also feel free to tell me if you want to read some topic in it. Thank you ---- Cosmia Fu

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Request for Comments
by ibrahim Sagiroglu 01 Aug '19

01 Aug '19

Hello all, I have an attempt to present llvm assembly in [1]. Would you consider taking some time to comment on it? [1] https://github.com/ibrahimsag/rw

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Re: [Haskell-cafe] ANN: To Kata Haskellen Evangelion
by Olaf Klinke 01 Aug '19

01 Aug '19

Isn't the Eq vs Ord problem similar to all sub-classes, e.g. Applicative vs. Monad, Semigroup vs. Monoid, Foldable vs. Traversable? What is the recommended way of coding? The Traversable module for example has default implementations of fmap and foldMap, as Functor and Foldable are superclasses. This suggests it is okay to define the subclass method first and derive the superclass methods from them. But arguments have been put up against this practice in particular cases, e.g. for AMP [1]. Olaf [1] https://mail.haskell.org/pipermail/haskell-cafe/2019-July/131259.html

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RfA: wcwidth
by Jason Dusek 31 Jul '19

31 Jul '19

Hi All, This is a Request for Adoption for WCWidth, a low traffic package that provides the functionality of wcwidth(3) <http://man7.org/linux/man-pages/man3/wcwidth.3.html>: “The wcwidth() function returns the number of columns needed to represent the wide character c.” https://github.com/solidsnack/wcwidth/ Although there have been just 3 issues and 2 PRs in 10 years, that’s still indicative of a need for maintenance and life has drawn me away from these avocations. A contributor suggested I reach out with an RfA. Hopefully, the community can be better served with a new maintainer. Kind Regards, Jason

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Call for Participation: Summer BOB 2019 (August 21, Berlin)
by Stefan Wehr 31 Jul '19

31 Jul '19

Here's a quick reminder on the upcoming BOB conference, happening at the third day of ICFP at the same venue. For those going to ICFP anyway: your ticket also gives you access to all BOB talks. For those not going to ICFP: come to BOB conference and also get access to the ICFP talks of day 3! ======================================================================== Summer BOB 2019 Conference “What happens if we simply use what’s best?” August 21, 2019, Berlin co-located with ICFP 2019 http://bobkonf.de/2019-summer/ Program: http://bobkonf.de/2019-summer/program.html Registration: http://bobkonf.de/2019-summer/registration.html ======================================================================== Are you interested in technologies beyond the mainstream, that are a pleasure to use, and effective at getting the job done? BOB is the forum for developers, architects and builders to explore and discover the best tools available today for building software. Our goal is for all participants to leave the conference with new ideas to improve development back at the ranch. Summer BOB is a one-time-only event, in the spirit of the spectacular Winter BOB. The International Conference on Functional Programming is coming to town, and Summer BOB will be right in the middle of it, on the last day of ICFP proper, prior to all the workshops. Summer BOB will feature two tracks: one from practitioners, and one from researchers, and foster communication and cross-pollination between these communities. BOB features two tracks of seven talk each: One research track with invited talks, and one track by practitioners, designed to cross-pollinate and inspire.http://bobkonf.de/2019-summer/program.html Topics include distributed programming, testing, linear algebra, functional design patterns, type systems, formal methods, and interactive development. We are committed to diversity: We aim at exploring a wide range of tools in a welcoming and friendly crowd of diverse people. To that end, a number of support options for participants from groups under-represented in tech are available.http://bobkonf.de/2019-summer/registration.html

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Re: [Haskell-cafe] type variable is ambiguous in a non-injective type family
by Anthony Clayden 30 Jul '19

30 Jul '19

Anthony> I am interested in how you got into such a pickle in the first place: Anthony> Why set `AllowAmbiguousTypes`? Did you understand what that means? ----------------------^^^^^^^^^^^^^^^^^^^^ >I read > > https://stackoverflow.com/questions/49684655/how-dangerous-is-allowambiguou… > > > which seems to indicate that using it is "a perfectly reasonable thing" Hmm, I don't think that's how you got into the pickle. That SO answer (and there are plenty on the subject) says the "combination" of `AllowAmbiguousTypes` + `TypeApplications` is reasonable. But your first post had `AllowAmbiguousTypes` without `TypeApplications`. That is not "a perfectly reasonable thing"; no SO answer says it is. If you had already looked at that SO answer, how did you not use `TypeApplications`? Let me suggest how you got into the pickle, because there is a repeated experience here which is poor for learners: You wrote the method signature for `toBool`. That's ambiguous. GHC gave you an error message suggesting `AllowAmbiguousTypes` might get the method signature to compile -- which it did. `AllowAmbiguousTypes` works at the declaration site, not the usage site. Which is why: * It doesn't make sense to switch it on everywhere -- as one of the SO comments suggests. * It does need you to take action at the usage site, but GHC's message doesn't tell you that. * So your first post showed more `ambiguous` rejections at the usage site. * What's more there was a red herring about non-injective type families. * And to fix it per Li-yao's suggestion needs a whole bunch more extensions, * including the deeply flawed `ScopedTypeVariables`, * when the simpler `PatternSignatures` would be more appropriate -- except that's now deprecated. * `AllowAMbiguousTypes` is module-wide: that means you get no validation of any of your method sigs; although probably you mean only a few of the to be ambiguous. * Then any/every usage site for any method might turn out to be ambiguous. IMO GHC has got itself into a total mess in this bit of the language, and the error messages lead learners rapidly into deep water. I think `AllowAmbiguousTypes` might as well be spelled `AllhopeAbandonTypes`. Those other extensions might be the best approach for your full requirements, but might not. So as to other possible designs: * I didn't want to get into the FunDeps vs TypeFamilies war. * If method `toBool` is only going to be called on the result of `toSubAmbi`, I would go > toBool :: a -> Bool -- not ambiguous > > instance Ambi blah where > type SubAmbi blah = ... > toSubAmbi x = ... > toBool x = case toSubAmbi x of { ... -> True; _ -> False } Then in your `whatsWrong` function, call only `toBool`. So the instances are a little more verbose but the usage sites are more succinct and don't need all those extensions. AntC

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Re: [Haskell-cafe] type variable is ambiguous in a non-injective type family
by Henry Laxen 29 Jul '19

29 Jul '19

First, thank you Li-yao Xia for your clear and helpful response. I was able to continue thanks to you. Thanks for the question Anthony, I look forward to learning something. I hope I'll be explain this clearly. I am writing some games, which can share some code, such as logging in, and broadcasting messages to players. I started by writing just one game, with no consideration for how and what to share. This let to a gamestate which contained things like: newtype GameId = GameId Int data Game1 { _game1TimeStarted :: UTCTime, _game1PlayerId :: GameId, ... _game1RandomGen :: StdGen, _game1Commands :: [Game1Command] } the actual state is a more complicated than this, because I split it into a Static part and a Mutable part that is in a TVar (Map GameId Game1MutableState) Next I start writing Game2, which I discover will do the same kind of broadcasting of messages (Commands) as Game1. So I would like to use the same code in Game2 as in Game1 that handles the broadcasting. I came up with: (this is part of the actual class I am using) class Game a where type Command a :: * type Mutable a :: * type Static a :: * toGameId :: a -> GameId toMutable :: a -> IO (Maybe (Mutable a)) everyone :: Mutable a -> [Sink] instance Game Game1State where type Command Game1State = Game1Command type Mutable Game1State = Game1Mutable type Static Game1State = Game1Static toGameId ss = ss ^. game1Static . game1GameId toMutable ss = do let tVar = ss ^. game1Mutable gId = toGameId ss gm <- liftIO (readTVarIO tVar) return $ M.lookup gId (unGameMap gm) everyone = mapMaybe _game1Sink . M.elems . _game1SPMap similarly, I make Game2State an instance of Game. Now in the code that broadcasts commands I have: sendBroadCasts :: (Show (Command a) , Game a) => [BroadCast a] -> a -> IO () ... sendOneCommand :: (Show (Command a) , Game a) => a -> BroadCastReceiver -> Command a -> IO () sendOneCommand ss BroadCastToEveryone command = do mbMut <- toMutable ss case mbMut of Nothing -> return () Just mut -> do let sinks = everyone mut mapM_ (`sendCommand` command) sinks but GHC scolds me with: src/Games/BroadCasts.hs:53:12-23: error: … • Couldn't match type ‘Mutable a’ with ‘Mutable a0’ Expected type: IO (Maybe (Mutable a0)) Actual type: IO (Maybe (Mutable a)) NB: ‘Mutable’ is a non-injective type family The type variable ‘a0’ is ambiguous • In a stmt of a 'do' block: mbMut <- toMutable ss In the expression: ... After incorporating Li-yao Xia's suggestion, the code becomes: sendOneCommand :: forall a. (Show (Command a) , Game a) => ----------------- ^^^^^^^^^ this is added a -> BroadCastReceiver -> Command a -> IO () sendOneCommand _ (BroadCastToSome sinks) command = mapM_ (`sendCommand` command) sinks sendOneCommand ss BroadCastToEveryone command = do mbMut <- toMutable ss case mbMut of Nothing -> return () Just mut -> do let sinks = everyone @a mut -------------------------- ^^ this is added mapM_ (`sendCommand` command) sinks and GHC is happy. I hope I have explained this sufficiently clearly. I look forward to your insights. Best wishes, Henry Laxen >>>>> "Anthony" == Anthony Clayden <anthony_clayden(a)clear.net.nz> writes: Anthony> Hi Henry, both replies you've received are excellent, I won't expand on them. Anthony> I am interested in how you got into such a pickle in the first place: Anthony> Why set `AllowAmbiguousTypes`? Did you understand what that means? ----------------------^^^^^^^^^^^^^^^^^^^^ I read https://stackoverflow.com/questions/49684655/how-dangerous-is-allowambiguou… which seems to indicate that using it is "a perfectly reasonable thing" Anthony> Did you think it odd that despite having that set, you get error Anthony> `type variable ... is ambiguous`? Anthony> There are ways to achieve what you want without Anthony> `AllowAmbiguousTypes` nor `TypeApplications`, but that would need Anthony> a rather different design. So what lead you into this design? Anthony> AntC -- Nadine and Henry Laxen The rest is silence Villa Alta #6 Calle Gaviota #10 Never try to teach a pig to sing Chapala It wastes your time +52 (376) 765-3181 And it annoys the pig

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Re: [Haskell-cafe] type variable is ambiguous in a non-injective type family
by Anthony Clayden 29 Jul '19

29 Jul '19

> I really don't understand what is going on here. ... -------------------------------------------------------------------------------- > {-# LANGUAGE TypeFamilies #-} > {-# LANGUAGE AllowAmbiguousTypes #-} > {- > > src/Games/Ambiguous.hs:15:16: error: … > • Couldn't match expected type ‘SubAmbi a0’ > with actual type ‘SubAmbi a’ > NB: ‘SubAmbi’ is a non-injective type family > The type variable ‘a0’ is ambiguous > > -} Hi Henry, both replies you've received are excellent, I won't expand on them. I am interested in how you got into such a pickle in the first place: Why set `AllowAmbiguousTypes`? Did you understand what that means? Did you think it odd that despite having that set, you get error `type variable ... is ambiguous`? There are ways to achieve what you want without `AllowAmbiguousTypes` nor `TypeApplications`, but that would need a rather different design. So what lead you into this design? AntC

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[twilio] Project takeover initiation
by Brian C. Jones 28 Jul '19

28 Jul '19

Hello, I have attempted to contact the author via PR and direct email with no response in 3 weeks. This is my final attempt before engaging the Hackage admins. https://github.com/markandrus/twilio-haskell/pull/67 Brian Jones

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[language-dart] Package takeover initiation
by Sergey Bushnyak 28 Jul '19

28 Jul '19

Hi all, I tried to contact the author via github issues and direct email with no response in couple weeks. This is my statement on desire to takeover package maintainership forhttps://hackage.haskell.org/package/language-dart <https://hackage.haskell.org/package/language-dart> -- Sergey Bushnyak

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Munich Haskell Meeting, 2019-07-31 @ 19:30
by Leah Neukirchen 28 Jul '19

28 Jul '19

Dear all, Next week, our monthly Munich Haskell Meeting will take place again on Wednesday, July 31 at Augustiner-Gaststätte Rumpler at 19h30. For details see here: http://muenchen.haskell.bayern/dates.html If you plan to join, please add yourself to this dudle so we can reserve enough seats! It is OK to add yourself to the dudle anonymously or pseudonymously. https://dudle.inf.tu-dresden.de/haskell-munich-jul-2019/ Everybody is welcome! cu, -- Leah Neukirchen <leah(a)vuxu.org> https://leahneukirchen.org/

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type variable is ambiguous in a non-injective type family
by Henry Laxen 28 Jul '19

28 Jul '19

Dear Cafe, I really don't understand what is going on here. I've searched, but I don't really understand the links that I found. The closest I've come is: https://sulzmann.blogspot.com/2013/01/non-injective-type-functions-and.html but I don't understand it enough to see my way to a solution. Here is a minimal example of what I'm trying to do: -------------------------------------------------------------------------------- {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE AllowAmbiguousTypes #-} module Ambiguous where class Ambi a where type SubAmbi a :: * toSubAmbi :: a -> SubAmbi a toBool :: SubAmbi a -> Bool whatsWrong :: Ambi a => a -> IO () whatsWrong a = do let s = toSubAmbi a b = toBool s if b then print "True" else print "False" {- src/Games/Ambiguous.hs:15:16: error: … • Couldn't match expected type ‘SubAmbi a0’ with actual type ‘SubAmbi a’ NB: ‘SubAmbi’ is a non-injective type family The type variable ‘a0’ is ambiguous • In the first argument of ‘toBool’, namely ‘s’ In the expression: toBool s In an equation for ‘b’: b = toBool s • Relevant bindings include s :: SubAmbi a (bound at /home/henry/nadineloveshenry/bin/nlh/src/Games/Ambiguous.hs:14:5) a :: a (bound at /home/henry/nadineloveshenry/bin/nlh/src/Games/Ambiguous.hs:12:12) whatsWrong :: a -> IO () (bound at /home/henry/nadineloveshenry/bin/nlh/src/Games/Ambiguous.hs:12:1) | Compilation failed. -} -------------------------------------------------------------------------------- Could any of you Haskell sages please explain how to do this? Best wishes, Henry Laxen -- Nadine and Henry Laxen The rest is silence Villa Alta #6 Calle Gaviota #10 Never try to teach a pig to sing Chapala It wastes your time +52 (376) 765-3181 And it annoys the pig

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Final call for draft papers for IFL 2019 (Implementation and Application of Functional Languages)
by Jurriaan Hage 26 Jul '19

26 Jul '19

Hello, Please, find below the final call for draft papers for IFL 2019. Please forward these to anyone you think may be interested. Apologies for any duplicates you may receive. best regards, Jurriaan Hage Publicity Chair of IFL ================================================================================ IFL 2019 31st Symposium on Implementation and Application of Functional Languages National University of Singapore September 25th-27th, 2019 http://2019.iflconference.org ================================================================================ ### Scope The goal of the IFL symposia is to bring together researchers actively engaged in the implementation and application of functional and function-based programming languages. IFL 2019 will be a venue for researchers to present and discuss new ideas and concepts, work in progress, and publication-ripe results related to the implementation and application of functional languages and function-based programming. Topics of interest to IFL include, but are not limited to: - language concepts - type systems, type checking, type inferencing - compilation techniques - staged compilation - run-time function specialization - run-time code generation - partial evaluation - (abstract) interpretation - metaprogramming - generic programming - automatic program generation - array processing - concurrent/parallel programming - concurrent/parallel program execution - embedded systems - web applications - (embedded) domain specific languages - security - novel memory management techniques - run-time profiling performance measurements - debugging and tracing - virtual/abstract machine architectures - validation, verification of functional programs - tools and programming techniques - (industrial) applications ### Keynote Speaker * Olivier Danvy, Yale-NUS College ### Submissions and peer-review Differently from previous editions of IFL, IFL 2019 solicits two kinds of submissions: * Regular papers (12 pages including references) * Draft papers for presentations ('weak' limit between 8 and 15 pages) Regular papers will undergo a rigorous review by the program committee, and will be evaluated according to their correctness, novelty, originality, relevance, significance, and clarity. A set of regular papers will be conditionally accepted for publication. Authors of conditionally accepted papers will be provided with committee reviews along with a set of mandatory revisions. Regular papers not accepted for publication will be considered as draft papers, at the request of the author. Draft papers will be screened to make sure that they are within the scope of IFL, and will be accepted for presentation or rejected accordingly. Prior to the symposium: Authors of conditionally accepted papers and accepted presentations will submit a pre-proceedings version of their work that will appear in the draft proceedings distributed at the symposium. The draft proceedings does not constitute a formal publication. We require that at least one of the authors present the work at IFL 2019. After the symposium: Authors of conditionally accepted papers will submit a revised versions of their paper for the formal post-proceedings. The program committee will assess whether the mandatory revisions have been adequately addressed by the authors and thereby determines the final accept/reject status of the paper. Our interest is to ultimately accept all conditionally accepted papers. If you are an author of a conditionally accepted paper, please make sure that you address all the concerns of the reviewers. Authors of accepted presentations will be given the opportunity to incorporate the feedback from discussions at the symposium and will be invited to submit a revised full article for the formal post-proceedings. The program committee will evaluate these submissions according to their correctness, novelty, originality, relevance, significance, and clarity, and will thereby determine whether the paper is accepted or rejected. ### Publication The formal proceedings will appear in the International Conference Proceedings Series of the ACM Digital Library. At no time may work submitted to IFL be simultaneously submitted to other venues; submissions must adhere to ACM SIGPLAN's republication policy: http://www.sigplan.org/Resources/Policies/Republication ### Important dates Submission of regular papers: June 15, 2019 Submission of draft papers: August 1, 2019 Regular papers notification: August 1, 2019 Regular draft papers notification: August 7, 2019 Deadline for early registration: August 15, 2019 Submission of pre-proceedings version: September 15, 2019 IFL Symposium: September 25-27, 2019 Submission of papers for post-proceedings: November 30, 2019 Notification of acceptance: January 31, 2020 Camera-ready version: February 29, 2020 ### Submission details All contributions must be written in English. Papers must use the ACM two columns conference format, which can be found at: http://www.acm.org/publications/proceedings-template Authors submit through EasyChair: https://easychair.org/conferences/?conf=ifl2019 ### Peter Landin Prize The Peter Landin Prize is awarded to the best paper presented at the symposium every year. The honored article is selected by the program committee based on the submissions received for the formal review process. The prize carries a cash award equivalent to 150 Euros. ### Organization and Program committee Chairs: Jurrien Stutterheim (Standard Chartered Bank Singapore), Wei Ngan Chin (National University of Singapore) Program Committee: - Olaf Chitil, University of Kent - Clemens Grelck, University of Amsterdam - Daisuke Kimura, Toho University - Pieter Koopman, Radboud University - Tamás Kozsik, Eötvös Loránd University - Roman Leschinskiy, Facebook - Ben Lippmeier, The University of New South Wales - Marco T. Morazan, Seton Hall University - Sven-Bodo Scholz, Heriot-Watt University - Tom Schrijvers, Katholieke Universiteit Leuven - Alejandro Serrano, Utrecht University - Tony Sloane, Macquarie University - Simon Thompson, University of Kent - Marcos Viera, Universidad de la República - Wei Ngan Chin, NUS - Jurriën Stutterheim, Standard Chartered Bank ### Venue The 31st IFL is organized by the National University of Singapore. Singapore is located in the heart of South-East Asia, and the city itself is extremely well connected by trains and taxis. See the website for more information on the venue. ### Acknowledgments This call-for-papers is an adaptation and evolution of content from previous instances of IFL. We are grateful to prior organizers for their work, which is reused here. A part of IFL 2019 format and CFP language that describes conditionally accepted papers has been adapted from call-for-papers of OOPSLA conferences.

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Re: [Haskell-cafe] What is the most modern associative list in types?
by Daniel Díaz 24 Jul '19

24 Jul '19

Hi Serguey, I don’t know what extra functionality you require but, for what is worth, my library red-black-record features a Symbol-to-Type map . It’s implemented as a type-level red-black-tree. https://hackage.haskell.org/package/red-black-record-2.0.2.2/docs/Data-RBR.… The map can be manipulated with the Insert, Delete and Value associated type families. Regards, Daniel Díaz > Hello cafe. > > I am trying to express some environment in types to constrain program > behavour. For this I need associative list of types, something along the > lines of [(Symbol, *)] so that I can lookup on "variable" name and get type > associated with it. > > I looked into HList library but it does not provide one most generally > useful way (albeit there are dozen or so of ways in there). > > So where can I get most modern HList-like library? Or what should I read > to get most modern HList myself?

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What is the most modern associative list in types?
by Serguey Zefirov 24 Jul '19

24 Jul '19

Hello cafe. I am trying to express some environment in types to constrain program behavour. For this I need associative list of types, something along the lines of [(Symbol, *)] so that I can lookup on "variable" name and get type associated with it. I looked into HList library but it does not provide one most generally useful way (albeit there are dozen or so of ways in there). So where can I get most modern HList-like library? Or what should I read to get most modern HList myself?

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[ANNOUNCE] GHC 8.8.1 release candidate 1 is now available
by Ben Gamari 22 Jul '19

22 Jul '19

Hello everyone, The GHC team is pleased to announce the release candidate for GHC 8.8.1. The source distribution, binary distributions, and documentation are available at https://downloads.haskell.org/ghc/8.8.1-rc1 This release is the culmination of over 3000 commits by over one hundred contributors and has several new features and numerous bug fixes relative to GHC 8.6: * Profiling now works correctly on 64-bit Windows (although still may be problematic on 32-bit Windows due to platform limitations; see #15934) * A new code layout algorithm for amd64's native code generator * The introduction of a late lambda-lifting pass which may reduce allocations significantly for some programs. * Further work on Trees That Grow, enabling improved code re-use of the Haskell AST in tooling * More locations where users can write `forall` (GHC Proposal #0007) * A comprehensive audit of GHC's memory ordering barriers has been performed, resulting in a number of fixes that should significantly improve the reliability of programs on architectures with weakly-ordered memory models (e.g. PowerPC, many ARM and AArch64 implementations). * A long-standing linker limitation rendering GHCi unusable with projects with cyclic symbol dependencies has been fixed (#13786) * Further work on the Hadrian build system * Numerous bug-fixes As always, if anything looks amiss do let us know. Happy compiling! Cheers, - Ben [1] https://downloads.haskell.org/ghc/8.8.1-rc1/docs/html/users_guide/8.8.1-not…

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Translating a pre-image witness from agda to haskell
by Ruben Astudillo 22 Jul '19

22 Jul '19

Dear list I've been playing with agda lately, I've been following the tutorials on their homepage to get a grasp of dependent types. The exposition has been good and clear. Some techniques can be passed over to haskell by using GADTs and DataKinds. Some examples require singletons to have the same kind of quantification as in agda. Currently I am trying to write in haskell the following data type and function data Image {A B : Set} (f : A -> B) : B -> Set where im : (x : A) -> Image f (f x) inv : {A B : Set} (f : A -> B) (y : B) -> Image f y -> A inv f .(f x) (im x) = x The `Image` datatype correspond to the proposition that the function `f : A -> B` has a pre-image for certain element on `B`. This is witnessed only if the `im` data constructor exists. The `inv` function is there only to show how agda can know by the presence of the `im x` data constructor that the value of `y` cannot be other than `f x`, mind bending stuff. I've been trying to write this ADT on haskell. I haven't got luck in so far. The problem is that referring to a `type family` constructed from a term level function is not clear to me, even with singletons, as I cannot guarantee such type family is defined. Currently I got this data Image (f :: Type -> Type) Type where Im :: Proxy (Sing t1 -> Sing (f t1)) -> f t1 -> Image (Sing t1 -> Sing (f t1)) (f t1) Which isn't exactly what the agda version is. Does anyone has an idea on how to continue or has done this example before? I am perfectly OK with being told it's not possible yet or what should I read. -- -- Ruben -- PGP: 4EE9 28F7 932E F4AD

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Journeys in Computational Logic: Tributes to Roy Dyckhoff : CFP
by Ekaterina Komendantskaya 22 Jul '19

22 Jul '19

CALL FOR PARTICIPATION Journeys in Computational Logic: Tributes to Roy Dyckhoff at TABLEAUX 2019, the 28th International Conference on Automated Reasoning with Analytic Tableaux and Related Methods, Middlesex University, London https://tableaux2019.org/ Main conference: 3 September to 5 September 2019 Journeys in Computational Logic: 3 September 2019 Roy Dyckhoff (1948 - 2018) worked in logic and proof theory, having begun his career as a topologist and category theorist (for which one of his thesis advisors was Dana Scott). Much of his work concerned various aspects of intuitionistic logic, but he also contributed to work in programming languages, type theory, natural language processing, and model checking. The event will commemorate and celebrate Roy’s work, by speakers who have crossed paths with Roy, and/or whose work or scientific views have been influenced by him. The workshop will follow the Tableaux invited talks by Sara Negri and Stéphane Graham-Lengrand, also dedicated to Roy’s work and contribution to the field. The list of contributors is as follows: Marta Bilkova Alessio Guglielmi Jacob Howe Jael Kriener James McKinna Mehrnoosh Sadrzadeh Peter Schroeder-Heister Christian Urban SOCIAL EVENT The workshop will be followed by the Tableaux welcome reception. ORGANISERS If you have any questions, or wish to contribute a talk, please contact the organisers: Ekaterina Komendantskaya: http://www.macs.hw.ac.uk/~ek19/ Stephane Graham-Lengrand: http://www.csl.sri.com/users/sgl/ Mehrnoosh Sadrzadeh: https://msadrzadeh.com/

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ANNOUNCE: lens-family 2.0.0 anniversary edition!
by roconnor＠theorem.ca 20 Jul '19

20 Jul '19

In celebration of the 10th anniversary of Twan van Laarhoven's seminal blog post ``CPS based functional references''[1], I am releasing version 2.0 of lens-family[2] and lens-family-core[3] packages. This new release continues to explore the design of Van Laarhoven style optics with new support for adapters, grates, grids[4], and prisms. To bring support to these new optics necessarily means moving a little further away from syntactic compatibility with Kmett's lens library. In particular, lens-family's 'under' is unrelated to Kmett's lens library's 'under' combinator. Nonetheless the 'under' combinator plays a crucial role in lens-family as a dual to the 'over' combinator and this naming is hard to resist despite the conflict. This new version comes with some minor incompatibilities with the version 1.2 library that may require user updates. See <https://hackage.haskell.org/package/lens-family-2.0.0/changelog>. [1]<https://www.twanvl.nl/blog/haskell/cps-functional-references> [2]<https://hackage.haskell.org/package/lens-family-2.0.0> [3]<https://hackage.haskell.org/package/lens-family-core-2.0.0> [4]A grid is an optic that is both a grate and a traversal. -- Russell O'Connor <http://r6.ca/>

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Re: [Haskell-cafe] ANNOUNCE: lens-family 2.0.0 anniversary edition!
by roconnor＠theorem.ca 20 Jul '19

20 Jul '19

On Fri, 19 Jul 2019, Artyom Kazak wrote: > > Naturally, users can stick with the 1.2 release of lens-family if it > > suits their needs. > You can not easily have two versions of the same library in your dependency tree. So, only application developers will be able to stick to the 1.2 release without creating obstacles for > the rest of the ecosystem. I see. I hadn't given that much consideration. In that case, I apologize for the inconvience this upgrade may cause. I'll try to be more mindful of this in the future. -- Russell O'Connor <http://r6.ca/> ``My friends, love is better than anger. Hope is better than fear. Optimism is better than dispair. So let us be loving, hopeful and optimistic. And we'll change the world.'' -- Jack Layton

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[CC2020] Call for Papers for the ACM SIGPLAN 2020 International Conference on Compiler Construction
by Gabriel Rodríguez Álvarez 18 Jul '19

18 Jul '19

ACM SIGPLAN 2020 International Conference on Compiler Construction (CC'20) co-located with CGO, PPoPP and HPCA San Diego, CA, USA February 22 - 23, 2020 https://cc-conference.github.io The ACM SIGPLAN 2020 International Conference on Compiler Construction (CC 2020) is interested in work on processing programs in the most general sense: analyzing, transforming or executing input programs that describe how a system operates, including traditional compiler construction as a special case. Original contributions are solicited on the topics of interest which include, but are not limited to: - Compilation and interpretation techniques, including program representation, analysis, and transformation; code generation, optimization, and synthesis; the verification thereof - Run-time techniques, including memory management, virtual machines, and dynamic and just-in-time compilation - Programming tools, including refactoring editors, checkers, verifiers, compilers, debuggers, and profilers - Techniques for specific domains, such as secure, parallel, distributed, embedded or mobile environments - Design and implementation of novel language constructs, programming models, and domain-specific languages CC 2020 is the 29th edition of the conference. From this year onwards, CC is an ACM SIGPLAN conference and will implement guidelines and procedures recommended by SIGPLAN https://www.sigplan.org. ================================================================================================= To subscribe to the CC announce mailing list, see cc_conference_announce(a)googlegroups.com To subscribe to the CC announce Twitter account, see @cc2020conf (https://twitter.com/cc2020conf) ======================================================================================= IMPORTANT DATES Abstract Submission: 23 October 2019 Paper Submission : 30 October 2019 Rebuttal : 4-6 December 2019 Artifact Submission: 13 December 2019 Author Notification: 24 December 2019 Final papers due : 15 January 2020 Conference : 22–23 February 2020 Authors are encouraged to submit their artifacts for the Artifact Evaluation (AE). The Artifact Evaluation process is run by a separate committee whose task is to assess how the artifacts support the work described in the papers. To ease the organization of the AE committee, we kindly ask authors to submit their artifact at the latest 10 days after the rebuttal. Papers that go through the Artifact Evaluation process successfully will receive a seal of approval printed on the papers themselves. Additional information will be made available on the CC AE web page. ORGANIZERS General Chair Louis-Noel Pouchet Colorado State University <pouchet AT colostate.edu> Program Chair Alexandra Jimborean Uppsala University <alexandra.jimborean AT it.uu.se> Artifact Evaluation Chairs Michel Steuwer University of Glasgow <Michel.Steuwer AT glasgow.ac.uk> Martin Kong University of Oklahoma Publicity Chair Gabriel Rodriguez University of A Coruna Web Chair Mihail Popov Uppsala University Steering Committee Bjorn Franke University of Edinburgh <bfranke AT inf.ed.ac.uk> Sebastian Hack Saarland University Manuel Hermenegildo IMDEA SW Institute and Technical U. of Madrid Peng Wu Huawei America Research Lab Ayal Zaks Intel and Technion, Israel Jingling Xue University of New South Wales, Australia Christophe Dubach University of Edinburgh Nelson J. Amaral University of Alberta Milind Kulkarni Purdue University Program Committee Apan Qasem AMD/Texas State University Bernhard Scholz University of Sydney Bettina Heim Microsoft Bilha Mendelson Optitura Brian Demsky UC Irvine Changhee Jung Virginia Tech Christian Schulte KTH EJ Park Los Alamos National Laboratory Delphine Demange Inria Dongyoon Lee Virginia Tech Fernando Magno Quintao Pereira UFMG Brazil Haowei Wu Google Manuel Hermenegildo IMDEA and T.U. Madrid Matin Hashemi Sharif University of Technology Michel Steuwer University of Glasgow Mila Dalla Preda University of Verona Nelson J. Amaral University of Alberta Philippe Clauss University of Strasbourg Pavlos Petoumenos University of Edinburgh Rumyana Neykova Brunel London Santosh Nagarakatte Rutgers University Sebastian Hack University of Saarland Tomofumi Yuki Inria Xu Liu College of William and Mary

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MPC 2019 - Call for Participation
by Graham Hutton 18 Jul '19

18 Jul '19

Dear all, Registration is now open for the Mathematics of Program Construction (MPC) conference in Portugal. MPC 2019 will feature 15 research papers and 4 keynotes, and is co-located with Formal Methods 2019 and many other events. See you in Porto! https://tinyurl.com/MPC-Porto Best wishes, Graham Hutton ====================================================================== *** CALL FOR PARTICIPATION -- MPC 2019 *** 13th International Conference on Mathematics of Program Construction 7-9 October 2019, Porto, Portugal Co-located with Formal Methods 2019 https://tinyurl.com/MPC-Porto ====================================================================== PROGRAM: https://tinyurl.com/yxvvc5vb ACCEPTED PAPERS: https://tinyurl.com/yyuhy8ze REGISTRATION AND TRAVEL: https://tinyurl.com/y4uetlsr KEYNOTE SPEAKERS: Assia Mahboubi (MPC) INRIA, France Annabelle McIver (MPC) Macquarie University, Australia Tony Hoare (UTP) Oxford University, UK Shriram Krishnamurthi (FM) Brown University, USA BACKGROUND: The International Conference on Mathematics of Program Construction (MPC) aims to promote the development of mathematical principles and techniques that are demonstrably practical and effective in the process of constructing computer programs. MPC 2019 will be held in Porto, Portugal from 7-9 October 2019, and is co-located with the International Symposium on Formal Methods, FM 2019. Previous conferences were held in Königswinter, Germany (2015); Madrid, Spain (2012); Québec City, Canada (2010); Marseille, France (2008); Kuressaare, Estonia (2006); Stirling, UK (2004); Dagstuhl, Germany (2002); Ponte de Lima, Portugal (2000); Marstrand, Sweden (1998); Kloster Irsee, Germany (1995); Oxford, UK (1992); Twente, The Netherlands (1989). PROGRAM COMMITTEE: Patrick Bahr IT University of Copenhagen, Denmark Richard Bird University of Oxford, UK Corina Cîrstea University of Southampton, UK Brijesh Dongol University of Surrey, UK João F. Ferreira University of Lisbon, Portugal Jennifer Hackett University of Nottingham, UK William Harrison University of Missouri, USA Ralf Hinze University of Kaiserslautern, Germany Zhenjiang Hu National Institute of Informatics, Japan Graham Hutton (chair) University of Nottingham, UK Cezar Ionescu University of Oxford, UK Mauro Jaskelioff National University of Rosario, Argentina Ranjit Jhala University of California, USA Gabriele Keller Utrecht University, The Netherlands Ekaterina Komendantskaya Heriot-Watt University, UK Chris Martens North Carolina State University, USA Bernhard Möller University of Augsburg, Germany Shin-Cheng Mu Academia Sinica, Taiwan Mary Sheeran Chalmers University of Technology, Sweden Alexandra Silva University College London, UK Georg Struth University of Sheffield, UK For any queries about the program please contact the program chair, Graham Hutton <graham.hutton(a)nottingham.ac.uk>. CONFERENCE VENUE: The conference will be held at the Alfândega Porto Congress Centre, a 150 year old former custom's house located in the historic centre of Porto on the bank of the river Douro. The venue was renovated by a Pritzer prize winning architect and has received many awards. LOCAL ORGANISER: José Nuno Oliveira University of Minho, Portugal For any queries about local issues please contact the local organiser, José Nuno Oliveira <jno(a)di.uminho.pt>. ====================================================================== This message and any attachment are intended solely for the addressee and may contain confidential information. If you have received this message in error, please contact the sender and delete the email and attachment. Any views or opinions expressed by the author of this email do not necessarily reflect the views of the University of Nottingham. Email communications with the University of Nottingham may be monitored where permitted by law.

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Second Call for Participation: ICFP 2019
by Sam Tobin-Hochstadt 17 Jul '19

17 Jul '19

** The Early Registration deadline is tomorrow! ** ===================================================================== Call for Participation ICFP 2019 24th ACM SIGPLAN International Conference on Functional Programming and affiliated events August 18 - August 23, 2019 Berlin, Germany http://icfp19.sigplan.org/ Early Registration until July 18! ===================================================================== ICFP provides a forum for researchers and developers to hear about the latest work on the design, implementations, principles, and uses of functional programming. The conference covers the entire spectrum of work, from practice to theory, including its peripheries. This year, ICFP is co-located with BOBKonf! * Overview and affiliated events: http://icfp19.sigplan.org/home * Program: http://icfp19.sigplan.org/program/program-icfp-2019 * Accepted papers: http://icfp19.sigplan.org/track/icfp-2019-papers * Registration is available via: https://regmaster4.com/2019conf/ICFP19/register.php Early registration ends 18 July, 2019. * Programming contest: https://icfpcontest2019.github.io/ * Student Research Competition: https://icfp19.sigplan.org/track/icfp-2019-Student-Research-Competition * Follow us on Twitter for the latest news: http://twitter.com/icfp_conference In addition to BOBKonf (8/21), there are several events co-located with ICFP: * Erlang Workshop (8/18) * Functional Art, Music, Modeling and Design (8/23) * Functional High-Performance and Numerical Computing (8/18) * Haskell Implementors' Workshop (8/23) * Haskell Symposium (8/22-8/23) * miniKanren Workshop (8/22) * ML Family Workshop (8/22) * OCaml Workshop (8/23) * Programming Languages Mentoring Workshop (8/18) * Scheme Workshop (8/18) * Type-Driven Development (8/18) ### ICFP Organizers General Chair: Derek Dreyer (MPI-SWS, Germany) Artifact Evaluation Co-Chairs: Simon Marlow (Facebook, UK) Industrial Relations Chair: Alan Jeffrey (Mozilla Research, USA) Programming Contest Organiser: Ilya Sergey (Yale-NUS College, Singapore) Publicity and Web Chair: Sam Tobin-Hochstadt (Indiana University, USA) Student Research Competition Chair: William J. Bowman (University of British Columbia, Canada) Workshops Co-Chair: Christophe Scholliers (Universiteit Gent, Belgium) Jennifer Hackett (University of Nottingham, UK) Conference Manager: Annabel Satin (P.C.K.) ### PACMPL Volume 3, Issue ICFP 2019 Principal Editor: François Pottier (Inria, France) Review Committee: Lennart Beringer (Princeton University, United States) Joachim Breitner (DFINITY Foundation, Germany) Laura M. Castro (University of A Coruña, Spain) Ezgi Çiçek (Facebook London, United Kingdom) Pierre-Evariste Dagand (LIP6/CNRS, France) Christos Dimoulas (Northwestern University, United States) Jacques-Henri Jourdan (CNRS, LRI, Université Paris-Sud, France) Andrew Kennedy (Facebook London, United Kingdom) Daan Leijen (Microsoft Research, United States) Kazutaka Matsuda (Tohoku University, Japan) Bruno C. d. S. Oliveira (University of Hong Kong, China) Klaus Ostermann (University of Tübingen, Germany) Jennifer Paykin (Galois, United States) Frank Pfenning (Carnegie Mellon University, USA) Mike Rainey (Indiana University, USA) Chung-chieh Shan (Indiana University, USA) Sam Staton (University of Oxford, UK) Pierre-Yves Strub (Ecole Polytechnique, France) German Vidal (Universitat Politecnica de Valencia, Spain) External Review Committee: Michael D. Adams (University of Utah, USA) Robert Atkey (University of Strathclyde, IK) Sheng Chen (University of Louisiana at Lafayette, USA) James Cheney (University of Edinburgh, UK) Adam Chlipala (Massachusetts Institute of Technology, USA) Evelyne Contejean (LRI, Université Paris-Sud, France) Germán Andrés Delbianco (IRIF, Université Paris Diderot, France) Dominique Devriese (Vrije Universiteit Brussel, Belgium) Richard A. Eisenberg (Bryn Mawr College, USA) Conal Elliott (Target, USA) Sebastian Erdweg (Delft University of Technology, Netherlands) Michael Greenberg (Pomona College, USA) Adrien Guatto (IRIF, Université Paris Diderot, France) Jennifer Hackett (University of Nottingham, UK) Troels Henriksen (University of Copenhagen, Denmark) Chung-Kil Hur (Seoul National University, Republic of Korea) Roberto Ierusalimschy (PUC-Rio, Brazil) Ranjit Jhala (University of California, San Diego, USA) Ralf Jung (MPI-SWS, Germany) Ohad Kammar (University of Oxford, UK) Oleg Kiselyov (Tohoku University, Japan) Hsiang-Shang ‘Josh’ Ko (National Institute of Informatics, Japan) Ondřej Lhoták (University of Waterloo, Canada) Dan Licata (Wesleyan University, USA) Geoffrey Mainland (Drexel University, USA) Simon Marlow (Facebook, UK) Akimasa Morihata (University of Tokyo, Japan) Shin-Cheng Mu (Academia Sinica, Taiwan) Guillaume Munch-Maccagnoni (Inria, France) Kim Nguyễn (University of Paris-Sud, France) Ulf Norell (Gothenburg University, Sweden) Atsushi Ohori (Tohoku University, Japan) Rex Page (University of Oklahoma, USA) Zoe Paraskevopoulou (Princeton University, USA) Nadia Polikarpova (University of California, San Diego, USA) Jonathan Protzenko (Microsoft Research, USA) Tiark Rompf (Purdue University, USA) Andreas Rossberg (Dfinity, Germany) KC Sivaramakrishnan (University of Cambridge, UI) Nicholas Smallbone (Chalmers University of Technology, Sweden) Matthieu Sozeau (Inria, France) Sandro Stucki (Chalmers | University of Gothenburg, Sweden) Don Syme (Microsoft, UK) Zachary Tatlock (University of Washington, USA) Sam Tobin-Hochstadt (Indiana University, USA) Takeshi Tsukada (University of Tokyo, Japan) Tarmo Uustalu (Reykjavik University, Iceland) Benoit Valiron (LRI, CentraleSupelec, Univ. Paris Saclay, France) Daniel Winograd-Cort (University of Pennsylvania, USA) Nicolas Wu (University of Bristol, UK)

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Benefits and use cases for strong mobility in presence of closure serialization
by Станислав Черничкин 17 Jul '19

17 Jul '19

Benefits and use cases for strong mobility in presence of closure serialization I read a paper about strong mobility in Haskell http://www.dcs.gla.ac.uk/~trinder/papers/strongm.pdf and I wondering what benefits it gives in presence of closure serialization? I guess for some languages strong mobility could be only way to transfer execution state of program, e.g. [Mobile Pascal;)] program Test; var a: Integer; begin readln(a); // acquiring on current host moveTo("anotherHost"); // transfering state and terminating writeln(a); // printing on another host end. but in Haskell same program can be written just using rfork :: Host -> IO () -> IO (): main = do a <- readLn rfork AnotherHost $ do print a The difference comparing to moveTo :: Host -> IO () version is purely syntactic: main = do a <- readLn moveTo AnotherHost print a -- Sincerely, Stanislav Chernichkin.

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Re: [Haskell-cafe] Haskell-Cafe Digest, Vol 191, Issue 12
by Information The FLOSS 17 Jul '19

17 Jul '19

Bu ileti The FLOSS Information'a gönderdiğiniz ileti sonucunda otomatik olarak oluşturuldu. Bu iletiye yanıt vermenize gerek yoktur. Bu iletiyi gönderdiğiniz için teşekkür ederiz. 4 gün içerisinde yanıtlamaya çalışacağız. Eğer 4 gün içinde yanıt gelmezse tekrar ileti gönderebilirsiniz. Sık Sorulabilecek Sorular: https://theflossinformation.gitlab.io/sik-sorulabilecek-sorular.html Hakkımızda: https://theflossinformation.gitlab.io/hakkimizda.html Bize Ulaşın: https://theflossinformation.gitlab.io/bize-ulasin.html Saygılarımızla, The FLOSS Information https://theflossinformation.gitlab.io/

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