August 2018 - Haskell-Cafe

Is there a library that has a strict version of `sum`?
by Damian Nadales 14 Aug '18

14 Aug '18

I thought the answer would be easy to find on the internet, but I cannot find any package that features a strict version of `sum`. Do you know if such a function is defined anywhere? (like a custom prelude for instance) I know it is trivial to define, but I would prefer not to repeat myself (and somebody else). Thanks!

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First Call for Participation for IFL 2018 (Implementation and Application of Functional Languages)
by Jurriaan Hage 14 Aug '18

14 Aug '18

Hello, Please, find below the 1st call for participation for IFL 2018. 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 --- CALL FOR PARTICIPATION: ================================================================================ IFL 2018 30th Symposium on Implementation and Application of Functional Languages University of Massachusetts Lowell, MA, USA September 5th-7th, 2018 http://iflconference.org September 5th: Haskell Mini-Course by Galois, Inc, see details below. ================================================================================ ### 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 2018 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. ### Keynote Speakers * Adam Chlipala, Massachusetts Institute of Technology CSAIL * Arjun Guha, University of Massachusetts Amherst ### Haskell Mini-Course (September 5th, 2018) Mini-course on Haskell by Galois, Inc, presented by David Thrane Christiansen and Jose Manuel Calderon Trilla. Register: Attendance at the course is free, but you must RSVP. (Link to RSVP form can be found at http://iflconference.org) Course Description: Recent versions of the GHC compiler for Haskell feature support for a number of advanced type system features, including pattern-matching functions in the type system (type families), indexed families (generalized algebraic datatypes, or GADTs), type-level data structures (data kinds), and general compile-time metaprogramming (Template Haskell). At Galois, we use these features in a number of our projects, which allows us to build deep embeddings of programming languages and have GHC enforce the target language's type system for us. This style of programming ensures that we only produce well-typed terms, including that we do not forget any of the run-time checks that are necessary to preserve our invariants when accepting input from untyped sources such as files. In the course of developing these projects, some common problems and programming patterns emerged. We developed the `parameterized-utils` library to codify solutions to these problems, and provide necessary generalizations of interfaces from the standard library (Eq, Applicative, Traversable, etc.) We will expect that participants in the course have used Haskell before, but we will not expect everyone to be experts. We will introduce GADTs, type families, and data kinds, and then show how to use them together with the tools from parameterized-utils with an implementation of the simply-typed lambda calculus, including basic AST definitions, evaluation, and parsing. ### 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: Jay McCarthy & Matteo Cimini, University of Massachusetts Lowell, USA Program Committee: * Arthur Chargueraud, Inria, FR * Ben Delaware, Purdue University, USA * Christos Dimoulas, Northwestern University, USA * David Darais, University of Vermont, USA * Dominic Orchard, University of Kent, UK * Ekaterina Komendantskaya, Heriot-Watt University, UK * Garrett Morris, University of Kansas, USA * Heather Miller, EPFL & Northeastern University, CH & USA * Jeremy Yallop, University of Cambridge, UK * Keiko Nakata, SAP Innovation Center Potsdam, DE * Laura Castro, University of A Coruna, ESP * Magnus Myreen, Chalmers University of Technology, SWE * Natalia Chechina, Bournemouth University, UK * Peter Achten, Radboud Universiteit Nijmegen, NL * Peter-Michael Osera, Grinnell College, USA * Richard Eisenberg, Bryn Mawr College, USA * Trevor McDonell, University of New South Wales, AUS * Yukiyoshi Kameyama, University of Tsukuba, JAP ### Venue The 30th IFL is organized by the University of Massachusetts Lowell. The City of Lowell is located at the heart of the Merrimack Valley just 30 miles northwest of Boston. Lowell can be easily reached by train or taxi. See the website for more information on the venue.

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What is the right way to use unsafeCoerce?
by Cosmia Fu 14 Aug '18

14 Aug '18

Hi all, I have noticed that unsafeCoerce is able to > Prelude> import Unsafe.Coerce > Prelude Unsafe.Coerce> data P = P Int Double deriving Show > Prelude Unsafe.Coerce> data Q a b = Q a b deriving Show > Prelude Unsafe.Coerce> unsafeCoerce (P 23 2.33) :: Q Int Double > Q 23 2.33 And it works even for sum type, and the first constructor always wins. > Prelude Unsafe.Coerce> data M a = J a deriving Show > Prelude Unsafe.Coerce> unsafeCoerce (J "qwe") :: Either String String > Left "qwe" > Prelude Unsafe.Coerce> unsafeCoerce (Just "qwe") :: M String > J "qwe" And the documenation for unsafeCoerce# says > Casting between two types that have the same runtime representation. One case is when the two types differ only in "phantom" type parameters, for example Ptr Int to Ptr Float, or [Int] to [Float] when the list is known to be empty. Also, a newtype of a type T has the same representation at runtime as T. > http://hackage.haskell.org/package/base-4.11.1.0/docs/GHC-Exts.html#v:unsaf… But info tables for different constructors are different. Why does the code above work? And is it safe to use unsafeCoerce like this? Thanks, Cosmia Fu

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Learning & Haskell Job Board
by Alex Mesropians 13 Aug '18

13 Aug '18

Hey All, Just wanted to share Workshub <http://t.sidekickopen13.com/e1t/c/5/f18dQhb0S7lC8dDMPbW2n0x6l2B9nMJW7t5XZs5…> with you all for those looking to hire Haskell engineers or want to see for yourself whats out there! We also have a learn section which is forever growing with new FP related content! We are always also looking for people to contribute to! thanks, Alex

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Google Summer of Code : CodeWorld
by Krystal Maughan 12 Aug '18

12 Aug '18

Hi All, I wrote a blog post on features I worked on this summer for Google Summer of Code in CodeWorld. Hope you enjoy it! Thank you for giving me the opportunity to work in Haskell this summer! https://medium.com/@krystal.maughan/breaking-the-space-time-barrier-with-ha… Best, Krystal

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cpphs broken on GHC 8.6.1
by Vanessa McHale 12 Aug '18

12 Aug '18

As of the latest release of GHC 8.6.1, cpphs no longer compiles. Anyone happen to know what's going on? Thanks! -- *Vanessa McHale* Functional Compiler Engineer | Chicago, IL Website: www.iohk.io <http://iohk.io> Twitter: @vamchale PGP Key ID: 4209B7B5 Input Output <http://iohk.io> Twitter <https://twitter.com/InputOutputHK> Github <https://github.com/input-output-hk> LinkedIn <https://www.linkedin.com/company/input-output-global> This e-mail and any file transmitted with it are confidential and intended solely for the use of the recipient(s) to whom it is addressed. Dissemination, distribution, and/or copying of the transmission by anyone other than the intended recipient(s) is prohibited. If you have received this transmission in error please notify IOHK immediately and delete it from your system. E-mail transmissions cannot be guaranteed to be secure or error free. We do not accept liability for any loss, damage, or error arising from this transmission

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hs-boot and (micro)lenses
by Francesco Ariis 11 Aug '18

11 Aug '18

Hello cafe, I have some problem setting up an appropriate .hs-boot module. I attach a .tar.gz'd cabal folder, so you can immediately test it with `cabal new-repl`. I had a file like this -- datatypes data A = A { _i :: Int, _b :: B } type AS a = State A a data B = B (AS ()) makeLenses ''A -- functions f :: B f = B $ i .= 18 So I decided to split it up in 2 files to test hs-boot in the wild: -- A.hs ------- data A = A { _i :: Int, _b :: B } type AS a = State A a makeLenses ''A -- B.hs ------- data B = B (AS ()) f :: B f = B $ i .= 18 Well, I don't know how to write A.hs-boot. I tried this: module A where import Lens.Micro.Platform data A b :: Lens' A B but ghc rightfully complains that he doesn't know about B, and if I slap an `import B` in the .hs-boot then I have another import-cycle. What's the way out of that? The project I am dealing with is bigger than this problem and I would really love to keep functions and related datatypes nearby for mental sanity. As I wrote above, attached you can find a .tar.gz with everything set up to replicate this -F

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Fwd: [Haskell] [ANNOUNCE] GHC 8.6.1-beta1 available
by Dan Burton 11 Aug '18

11 Aug '18

I've generated a stack.yaml which should allow most stack users to install this ghc release via stack. https://gist.github.com/DanBurton/43b5f5155fdd1affd02f6e86f37da9ae e.g. $ mkdir test-new-ghc && cd test-new-ghc $ wget https://gist.github.com/DanBurton/43b5f5155fdd1affd02f6e86f37da9 ae/raw/6cb25068fcfae7d70739b7927248a80518192ad6/stack.yaml $ stack setup $ stack repl Once installed in this way, you can simply use: compiler: ghc-8.6.0.20180810 compiler-check: match-exact In any project's stack.yaml in order to build with this version of ghc. -- Dan Burton ---------- Forwarded message ---------- From: Ben Gamari <ben(a)well-typed.com> Date: Fri, Aug 10, 2018 at 7:31 PM Subject: [Haskell] [ANNOUNCE] GHC 8.6.1-beta1 available To: GHC developers <ghc-devs(a)haskell.org>, GHC users < glasgow-haskell-users(a)haskell.org>, Haskell Cafe < haskell-cafe(a)googlegroups.com>, haskell(a)haskell.org Hello everyone, The GHC development team is very pleased to announce the first beta leading up to GHC 8.6.1 release. The usual release artifacts are available from https://downloads.haskell.org/~ghc/8.6.1-beta1 This beta fixes most of the bugs reported in the first two alphas and brings all of the core libraries up to their final release versions. The 8.6 release fixes over 300 bugs from the 8.4 series and introduces a number of exciting features. These most notably include: * Significantly better handling of macOS linker command size limits, avoiding linker errors while linking large projects * A new deriving mechanism, `deriving via`, providing a convenient way for users to extend Haskell's typeclass deriving mechanism * Quantified constraints, allowing forall quantification in contexts * An early version of the GHCi `:doc` command * The `ghc-heap-view` package, allowing introspection into the structure of GHC's heap * Valid hole fit hints, helping the user to find terms to fill typed holes in their programs * The BlockArguments extension, allowing the `$` operator to be omitted in some unambiguous contexts * The next phase of the MonadFail proposal, enabling -XMonadFailDesugaring by default A full list of the changes in this release can be found in the release notes: https://downloads.haskell.org/~ghc/8.6.1-beta1/docs/html/ users_guide/8.6.1-notes.html This will very likely be the last release before the final 8.6.1 so do give it a thorough testing and, as always, report any issues you encounter. Thanks for your help! Cheers, - Ben _______________________________________________ Haskell mailing list Haskell(a)haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell

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Aeson memory use
by Lana Black 09 Aug '18

09 Aug '18

Hello Cafe, Recently while trying to optimize some code, I noticed that aeson requires quite a substantial amount of memory when parsing map-like structures. The quick example I crafted [1] is quite surprising. In order to parse an 11 megabyte file aeson requires around 300 megabytes of memory (according to the heap profiler), and the total memory footprint (according to htop) jumps to around 700 megabytes. Is there a way to reduce this number to something less insane? I suspect that I might be doing something wrong here, but I can't exactly see what. [1] https://github.com/greydot/aeson-example

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Call for Participation: ICFP 2018
by Lindsey Kuper 07 Aug '18

07 Aug '18

*** Early registration ends 27 August. *** ===================================================================== Call for Participation ICFP 2018 23rd ACM SIGPLAN International Conference on Functional Programming and affiliated events September 23 - September 29, 2018 St. Louis, Missouri, USA http://icfp18.sigplan.org/ ===================================================================== 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 Strange Loop! Considering attending ICFP for the first time? See our brief explainer: https://icfp18.sigplan.org/attending/introduction-to-icfp * Overview and affiliated events: http://icfp18.sigplan.org/home * Program: http://icfp18.sigplan.org/program/program-icfp-2018 * Accepted papers: http://icfp18.sigplan.org/track/icfp-2018-papers * Registration is available via: https://regmaster4.com/2018conf/ICFP18/register.php Early registration ends 27 August, 2018. * Programming contest results: https://icfpcontest2018.github.io/ * Student Research Competition: https://icfp18.sigplan.org/track/icfp-2018-Student-Research-Competition * Follow us on Twitter for the latest news: http://twitter.com/icfp_conference In addition to Strange Loop (9/26-9/28), there are several events co-located with ICFP: * Erlang Workshop (9/29) * Functional Art, Music, Modeling and Design (9/29) * Functional High-Performance Computing (9/29) * Haskell Implementors' Workshop (9/23) * Haskell Symposium (9/27-9/28) * Higher-order Programming with Effects (9/23) * ICFP Tutorials (9/27-9/29) * ML Family Workshop (9/28) * Numerical Programming in Functional Languages (9/27) * OCaml Workshop (9/27) * Programming Languages Mentoring Workshop (9/23) * Scala Symposium (9/28) * Scheme Workshop (9/28) * Type-Driven Development (9/27) Conference Organizers: General Chair: Robby Findler (Northwestern University, USA) Program Chair: Matthew Flatt (University of Utah, USA) Accessibility Chair: Alan Jeffrey (Mozilla Research, USA) Artefact Evaluation Co-Chair: Simon Marlow (Facebook, UK) Industrial Relations Chair: Alan Jeffrey (Mozilla Research, USA) PLMW Co-Chair: Dan Licata (Wesleyan University, USA) PLMW Co-Chair: David Van Horn (University of Maryland, USA) PLMW Co-Chair: Niki Vazou (University of Maryland, USA) Programming Contest Organizer: Matthew Fluet (Rochester Institute of Technology, USA) Publications Co-Chair: Alex Potanin (Victoria University of Wellington, New Zealand) Publicity Chair: Lindsey Kuper (UC Santa Cruz, USA) Student Research Competition Chair: Ravi Chugh (University of Chicago, USA) Student Volunteer Co-Captain: Jakub Zalewski (University of Edinburgh, UK) Student Volunteer Co-Captain: Spencer P. Florence (Northwestern University, USA) Treasurer and Conference Manager: Annabel Satin (P.C.K., UK) Video Co-Chair Jamie Willis (University of Bristol, UK) Video Co-Chair: Jose Calderon (Galois, USA) Workshops Co-Chair: Christophe Scholliers (Ghent University, Belgium) Workshops Co-Chair: David Christiansen (Galois, USA) Sponsors and industrial partners: Platinum supporters: Ahrefs Jane Street Standard Chartered X Gold supporters: DFINITY Facebook Mozilla McCormick School of Engineering, Northwestern University Silver supporters: Bloomberg Cal Poly Computer Science & Software Engineering Digital Asset Galois Microsoft Research Oracle Labs Tweag I/O Bronze supporters: Google IntelliFactory Kadena Obsidian Systems Systor Vest Well-Typed

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