- Haskell-Cafe - Haskell.org

Documenting Examples for a library
by Guru Devanla 17 Mar '18

17 Mar '18

Hello, I am close to releasing a new version of the https://hackage.haskell.org/package/pptable library I have been working on off late. I am a little confused on what approach I need to take regarding providing good documentation and working examples. Please, note that I am not referring to the API documentation attached to the code. For API documentation I will continue to use haddock and generate documentation as I build. The approaches I have in mind to provide clear examples are as follows: 1. Provide a README.md and document all usage examples in markdown format. Allow github to produce the HTML. 2. Create and ship an Example.hs file along with library. Using a .hs file allows haddock to build the documentation as part of the package. I took this approach for the previous release. Here is an example: https://hackage.haskell.org/package/pptable-0.2.0.0/docs/Text-PrettyPrint-T…. 3. Using Example.lhs. I like this approach since it lets me load the code in ghci and test out the examples seamlessly. But, I am hitting roadblocks with this, since I am not able to include this file as part of my stack project. `stack haddock` fails too. When I include .lhs file in a stack project, I get the following error File name does not match module name: Saw: ‘Main’ Expected: ‘Text.PrettyPrint.Tabulate.Example’ I like (3) because I can make sure my examples run successfully, (using stack ghci Example.lhs), before I publish them. With options (1) and (2), I need to manually copy/past code into ghci to make sure there are no errors. Is there a better way to do this? Please could the group provide any recommendations and guidance on what approach I should be taking and why. Thanks

2 2

[Google Summer of Code 2018] Student Applications are now open
by Jasper Van der Jeugt 16 Mar '18

16 Mar '18

Hey all, As we've previously announced through different channels, Haskell.org was accepted into Google Summer of Code 2018 [1]. Students application have now opened. Students can submit their proposal at the Summer of Code Dashboard [2]. We are also seeking mentors for possible projects. This year, we would like to assign a back-up mentor for each student. If you are interested in mentoring, please contact us [3] so we can add you to the mentor list directly. Having good mentors is an important factor in making the students feel welcome and guiding them to a succesful completion of their projects. If you would like to apply but you don't know how to start your proposal, have a look at our ideas list [4] and this great guide [5]. Lastly, we recognize that inclusion is an important part of our mission to promote Haskell. Therefore, we strongly encourage applications from people in communities that are underrepresented in functional programming, including but not limited to women; people of color; people in gender, sexual and romantic minorities; people with disabilities; people residing in Asia, Africa, or Latin America; and people who have never taken part in similar programs before. Kind regards, Jasper Van der Jeugt & George Wilson on behalf of the Haskell.org Committee [1]: https://summerofcode.withgoogle.com/organizations/5706672807346176/ [2]: https://summerofcode.withgoogle.com/ [3]: https://summer.haskell.org/contact.html [4]: https://summer.haskell.org/ideas.html [5]: http://write.flossmanuals.net/gsocstudentguide/writing-a-proposal/

1 0

Using Backpack for initial and final encodings
by David Laing 15 Mar '18

15 Mar '18

Hi everyone, Ed Kmett recently pointed me towards his usage of Backpack to write some code in the tagless final style, and I've been playing with it and riffing on it for a while. There's a solution to the expression problem in there involving classy Prisms (and now Backpacky Prisms) that seems pretty neat. I've written it up here: https://qfpl.io/posts/backpack-for-initial-and-final-encodings/ Hopefully some of you find it interesting. Cheers, Dave

1 0

[ANNOUNCE] GHC 8.4.1 released
by Ben Gamari 14 Mar '18

14 Mar '18

The GHC developers are very happy to announce the 8.4.1 release of Glasgow Haskell Compiler. Binary and source distributions can be found at https://downloads.haskell.org/~ghc/8.4.1/ This is the third major release in the GHC 8 series. As such, the focus of this release is performance, stability, and consolidation. Consequently numerous cleanups can be seen throughout the compiler including, * Further refinement of TypeInType, including significant improvements in error messages. * Improvements in code generation resulting in noticable performance improvements in some types of programs. * Core library improvements, including phase 2 of the Semigroup/Monoid proposal * Many improvements to instance deriving * The resolution of nearly 300 other tickets A more thorough list of the changes in this release can be found in the release notes, https://downloads.haskell.org/~ghc/8.4.1/docs/html/users_guide/8.4.1-notes.… There are a few changes in release-engineering matters that should be noted, * This is GHC's first release on it's new, accelerated release schedule. From now on GHC will produce one release every six months. * While we typically strive to produce OpenBSD builds, the gcc shipped with OpenBSD 6.1 is unfortunately too old to compile this release. * FreeBSD builds are still in progress This release has been the result of approximately six months of work by over one hundred code contributors. Thanks to everyone who has helped in writing patches, testing, reporting bugs, and offering feedback over the last year. As always, let us know if you encounter trouble. How to get it ~~~~~~~~~~~~~ The easy way is to go to the web page, which should be self-explanatory: http://www.haskell.org/ghc/ We supply binary builds in the native package format for many platforms, and the source distribution is available from the same place. Packages will appear as they are built - if the package for your system isn't available yet, please try again later. Background ~~~~~~~~~~ Haskell is a standard lazy functional programming language. GHC is a state-of-the-art programming suite for Haskell. Included is an optimising compiler generating efficient code for a variety of platforms, together with an interactive system for convenient, quick development. The distribution includes space and time profiling facilities, a large collection of libraries, and support for various language extensions, including concurrency, exceptions, and foreign language interfaces. GHC is distributed under a BSD-style open source license. A wide variety of Haskell related resources (tutorials, libraries, specifications, documentation, compilers, interpreters, references, contact information, links to research groups) are available from the Haskell home page (see below). On-line GHC-related resources ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Relevant URLs on the World-Wide Web: GHC home page http://www.haskell.org/ghc/ GHC developers' home page http://ghc.haskell.org/trac/ghc/ Haskell home page http://www.haskell.org/ Supported Platforms ~~~~~~~~~~~~~~~~~~~ The list of platforms we support, and the people responsible for them, is here: http://ghc.haskell.org/trac/ghc/wiki/Contributors Ports to other platforms are possible with varying degrees of difficulty. The Building Guide describes how to go about porting to a new platform: http://ghc.haskell.org/trac/ghc/wiki/Building Developers ~~~~~~~~~~ We welcome new contributors. Instructions on accessing our source code repository, and getting started with hacking on GHC, are available from the GHC's developer's site run by Trac: http://ghc.haskell.org/trac/ghc/ Mailing lists ~~~~~~~~~~~~~ We run mailing lists for GHC users and bug reports; to subscribe, use the web interfaces at http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-tickets There are several other haskell and ghc-related mailing lists on www.haskell.org; for the full list, see https://mail.haskell.org/cgi-bin/mailman/listinfo Some GHC developers hang out on #haskell on IRC, too: http://www.haskell.org/haskellwiki/IRC_channel Please report bugs using our bug tracking system. Instructions on reporting bugs can be found here: http://www.haskell.org/ghc/reportabug

3 3

Append after index and update items after inserted item with lens
by Cody Goodman 13 Mar '18

13 Mar '18

Hello, I'm trying to insert a new elemnt into a list after a given index and increment the orderId accordingly with the lens library. I'm a bit confused at why this code isn't working: ``` import Control.Lens data A = A { _customOrderId :: Int } deriving Show things = [ A {_customOrderId = 0} , A {_customOrderId = 1} , A {_customOrderId = 2} , A {_customOrderId = 3} ] main = print $ things & ( (_drop 2 %~ ((A 22)<|)) . ((traversed . indices (> 2) . customerOrderIdLens) %~ (+ 1)) ) ``` The first portion works to insert where desired, but the second portion `((traversed . indices (> 2) . customerOrderIdLens) %~ (+ 1))` only increments the order id in indices 4. Any idea why this is happening? Thanks, Cody Goodman

2 2

Call for Contributions: Type-Driven Development 2018
by Niki Vazou 13 Mar '18

13 Mar '18

Hello, The first call for contributions for TyDe is out. Forward it to anyone who might be interested. Best, Niki Vazou ============================================== CALL FOR CONTRIBUTIONS Type 2018: Type-Driven Development https://icfp18.sigplan.org/track/tyde-2018 23-29 Sep, 2018, St. Louis, Missouri (co-located with ICFP) ============================================== *Call for Contributions* We welcome all contributions, both theoretical and practical, on a range of topics including: dependently typed programming; generic programming; design and implementation of programming languages, exploiting types in novel ways; exploiting typed data, data dependent data, or type providers; static and dynamic analyses of typed programs; tools, IDEs, or testing tools exploiting type information; pearls, being elegant, instructive examples of types used in the derivation, calculation, or construction of programs. *Important Dates* Regular paper deadline: Wednesday, June 6, 2018 Extended abstract deadline: Wednesday, June 13, 2018 Author notification: Friday, June 29, 2018 Deadline for camera ready version: August 5, 2018 Workshop: Thursday, September 27, 2018 *Program Committee* - Guillaume Allais, Radboud University Nijmegen, Netherlands - Zena M. Ariola, University of Oregon, USA - David Darais, University of Vermont, USA - Richard Eisenberg, Bryn Mawr College, USA (co-chair) - Jennifer Hackett, University of Nottingham, UK - Shin-ya Katsumata, National Institute of Informatics, Japan - Daan Leijen, Microsoft Research, USA - Shin-Cheng Mu, Academia Sinica, Taiwan - Dominic Orchard, University of Kent, UK - Peter-Michael Osera, Grinnell College, USA - Zoe Paraskevopoulou, Princeton University, USA - Alberto Pardo, Universidad de la Republica, Uruguay - Matthieu Sozeau, University of Paris Diderot, Paris 7, France - Niki Vazou, University of Maryland, USA (co-chair) *Submission details* Submissions should fall into one of two categories: - Regular research papers (12 pages) - Extended abstracts (2 pages) The bibliography will not be counted against the page limits for either category. Regular research papers are expected to present novel and interesting research results, and will be included in the formal proceedings. Extended abstracts should report work in progress that the authors would like to present at the workshop. Extended abstracts will be distributed to workshop attendees but will not be published in the formal proceedings. We welcome submissions from PC members (with the exception of the two co-chairs), but these submissions will be held to a higher standard. Submission is handled through HotCRP: https://tyde18.hotcrp.com/ All submissions should be in portable document format (PDF) and formatted using the ACM SIGPLAN style guidelines: http://www.sigplan.org/Resources/Author/ Note that the ACM SIGPLAN style guidelines have changed from previous years! In particular, submissions should use the new ‘acmart’ format and the two-column ‘sigplan’ subformat (not to be confused with the one-column ‘acmlarge’ subformat!). Extended abstracts must be submitted with the label ‘Extended abstract’ clearly in the title.

1 0

1st CfP: IFL 2018 (30th Symposium on Implementation and Application of Functional Languages)
by Jurriaan Hage 13 Mar '18

13 Mar '18

Hello, Please, find below the first call for papers 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 --- ================================================================================ IFL 2018 30th Symposium on Implementation and Application of Functional Languages University of Massachusetts Lowell, MA, USA September 5th-7th, 2018 http://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 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. 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 ### Submissions and peer-review Differently from previous editions of IFL, IFL 2018 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 2018. 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: May 25, 2018 Submission of draft papers: July 17, 2018 Regular and draft papers notification: July 20, 2018 Deadline for early registration: August 8, 2018 Submission of pre-proceedings version: August 29, 2018 IFL Symposium: September 5-7, 2018 Submission of papers for post-proceedings: November 7, 2018 Notification of acceptance: December 22, 2018 Camera-ready version: February 10, 2019 ### 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=ifl2018 ### 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 Chargu√©raud, 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 Coru√±a, 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 will take place at the UMass Lowell Inn & Conference Center in Lowell (MA), in association with 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. ### 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 2018 format and CFP language that describes conditionally accepted papers has been adapted from call-for-papers of OOPSLA conferences.

1 0

Serialising data between Haskell and C#
by Clinton Mead 13 Mar '18

13 Mar '18

Hi All I want to integrate Haskell into an existing C# project, initially by creating one C# class that basically does all it's "work" in Haskell (and just provides a C# interface). There will be a few types passed in and out of this Haskell module from/to C#. On the C# side, there are classes with members, who's types are probably going to be either Strings, Ints, or lists of Strings/Ints, or lists of other objects. I'd like to have the same types on the Haskell side. It would be nice if I could just magically pass one of these C# types to Haskell and on the Haskell side it will appear as a Haskell type I assume what I'll have to do is serialise the type on the C# side and deserialise on the Haskell side. C# allows one to serialise any data type to XML. Haskell has plenty of serialisation libraries as well. However, the problem I presume is that if I just serialise to XML on the C# side, and deserialise from XML on the Haskell side, if my types are just slightly different, or even if the exact serialisers/deserialises represent their data in different ways, it isn't going to work. It seems like passing complex data to/from Haskell may be a common problem other people experience, so I'm looking for any suggestions on a clean way of doing this.

5 4

Midlands Graduate School 2018 - final call for participation
by Graham Hutton 12 Mar '18

12 Mar '18

Dear all, There are just a few days left now to register for this years Midlands Graduate School (MGS) in Nottingham: eight fantastic courses on dependently typed programming, categories, lambda calculus, semantics, and more. Registration closes on Friday 16th March. Please share! http://tinyurl.com/MGS18NOTT Best wishes, Graham Hutton and Henrik Nilsson ========================================================== Midlands Graduate School 2018 9-13 April 2018, Nottingham, UK http://tinyurl.com/MGS18NOTT BACKGROUND: The Midlands Graduate School (MGS) in the Foundations of Computing Science provides an intensive course of lectures on the mathematical foundations of computing. The MGS has been running since 1999, and is aimed at PhD students in their first or second year of study, but the school is open to everyone, and has increasingly seen participation from industry. We welcome participants from all over the world! COURSES: Eight courses will be given. Participants usually take all the introductory courses and choose additional options from the advanced courses depending on their interests. Invited course - Type-Driven Development with Idris, Edwin Brady Introductory courses - Lambda Calculus, Venanzio Capretta - Category Theory, Roy Crole - Domain Theory and Denotational Semantics, Achim Jung Advanced courses - Univalent Foundations, Benedikt Ahrens - Coalgebra, Alexander Kurz - Separation Logic, Georg Struth - Machine Learning, Michel Valstar REGISTRATION: Registration is £550 for student, academic and independent participants, and £850 for industry participants. The fee includes 5 nights single en-suite accommodation (Sun-Thu), lunch and coffee breaks, and the conference dinner. The registration deadline is ** Friday 16th March **. Spaces are limited, so please register early to secure your place. SPONSORSHIP: We offer a range of sponsorship opportunities for industry (bronze, silver, gold and platinum), each with specific benefits. Please see the website for further details. ========================================================== 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.

1 0

Midlands Graduate School 2018 - final call for participation
by Graham Hutton 12 Mar '18

12 Mar '18

Dear all, There are just a few days left now to register for this years Midlands Graduate School (MGS) in Nottingham: eight fantastic courses on dependently typed programming, categories, lambda calculus, semantics, and more. Registration closes on Friday 16th March. Please share! http://tinyurl.com/MGS18NOTT Best wishes, Graham Hutton and Henrik Nilsson ========================================================== Midlands Graduate School 2018 9-13 April 2018, Nottingham, UK http://tinyurl.com/MGS18NOTT BACKGROUND: The Midlands Graduate School (MGS) in the Foundations of Computing Science provides an intensive course of lectures on the mathematical foundations of computing. The MGS has been running since 1999, and is aimed at PhD students in their first or second year of study, but the school is open to everyone, and has increasingly seen participation from industry. We welcome participants from all over the world! COURSES: Eight courses will be given. Participants usually take all the introductory courses and choose additional options from the advanced courses depending on their interests. Invited course - Type-Driven Development with Idris, Edwin Brady Introductory courses - Lambda Calculus, Venanzio Capretta - Category Theory, Roy Crole - Domain Theory and Denotational Semantics, Achim Jung Advanced courses - Univalent Foundations, Benedikt Ahrens - Coalgebra, Alexander Kurz - Separation Logic, Georg Struth - Machine Learning, Michel Valstar REGISTRATION: Registration is £550 for student, academic and independent participants, and £850 for industry participants. The fee includes 5 nights single en-suite accommodation (Sun-Thu), lunch and coffee breaks, and the conference dinner. The registration deadline is ** Friday 16th March **. Spaces are limited, so please register early to secure your place. SPONSORSHIP: We offer a range of sponsorship opportunities for industry (bronze, silver, gold and platinum), each with specific benefits. Please see the website for further details. ========================================================== 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.

1 0