August 2017 - Haskell-Cafe

Investigating single-letter type variables
by Jeffrey Brown 10 Aug '17

10 Aug '17

Haskellers tend to use uninformative single-letter type variables. A case in point: Megaparsec> :i ParsecT type role ParsecT nominal nominal representational representational newtype ParsecT e s (m :: * -> *) a ... I've gotten used to the conventions that "a" stands for anything and "m" stands for monad -- but without digging into the code it wasn't initially obvious to me whether "s" stood for stream or state. Single-letter type variables don't seem to always be the standard, though: Megaparsec> :i between between :: Applicative m => m open -> m close -> m a -> m a -- Defined in ‘Control.Applicative.Combinators’ My questions are: (1) Are the brevity gains worth the confusion costs? (2) If I'm looking at a new library for the first time and trying to figure out what a type variable stands for, is there a canonical way to do it? Flailing through documentation at random? Unifying types by hand? -- Jeff Brown | Jeffrey Benjamin Brown Website <https://msu.edu/~brown202/> | Facebook <https://www.facebook.com/mejeff.younotjeff> | LinkedIn <https://www.linkedin.com/in/jeffreybenjaminbrown>(spammy, so I often miss messages here) | Github <https://github.com/jeffreybenjaminbrown>

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DSLDI 2017: Final Call for Talk Proposals (deadline extended)
by Lindsey Kuper 08 Aug '17

08 Aug '17

********************************************************************* FINAL CALL FOR TALK PROPOSALS DSLDI 2017 Fifth Workshop on Domain-Specific Language Design and Implementation October 22, 2017 Vancouver, Canada Co-located with SPLASH http://2017.splashcon.org/track/dsldi-2017 https://twitter.com/wsdsldi ********************************************************************* **Deadline for talk proposals extended to Friday, 11 August 2017** Well-designed and implemented domain-specific languages (DSLs) can achieve both usability and performance benefits over general-purpose programming languages. By raising the level of abstraction and exploiting domain knowledge, DSLs can make programming more accessible, increase programmer productivity, and support domain-specific optimizations. ## Workshop Goal Domain-Specific Language Design and Implementation (DSLDI) is a workshop intended to bring together researchers and practitioners interested in discussing how DSLs should be designed, implemented, supported by tools, and applied in realistic contexts. The focus of the workshop is on all aspects of this process, from soliciting domain knowledge from experts, through the design and implementation of the language, to evaluating whether and how a DSL is successful. More generally, we are interested in continuing to build a community that can drive forward the development of modern DSLs. ## Workshop Format DSLDI is a single-day workshop and will consist of an invited speaker followed by moderated audience discussions structured around a series of short talks. The role of the talks is to facilitate interesting and substantive discussion. Therefore, we welcome and encourage talks that express strong opinions, describe open problems, propose new research directions, and report on early research in progress. Proposed talks should be on topics within DSLDI’s area of interest, which include but are not limited to: * solicitation and representation of domain knowledge * DSL design principles and processes * DSL implementation techniques and language workbenches * domain-specific optimizations * human factors of DSLs * tool support for DSL users * community and educational support for DSL users * applications of DSLs to existing and emerging domains * studies of usability, performance, or other benefits of DSLs * experience reports of DSLs deployed in practice ## Call for Talk Proposals We solicit talk proposals in the form of short abstracts (max. 2 pages). A good talk proposal describes an interesting position, open problem, demonstration, or early achievement. The submissions will be reviewed on relevance and clarity, and used to plan the mostly interactive sessions of the workshop day. Publication of accepted abstracts and slides on the website is voluntary. * Deadline for talk proposals: August 11th, 2017 * Notification: September 11th, 2017 * Workshop: October 22nd, 2017 * Submission website: https://dsldi17.hotcrp.com/ ## Workshop Organization Co-chairs: * Lindsey Kuper (lindsey(a)composition.al) Intel Labs * Eric Walkingshaw (eric.walkingshaw(a)oregonstate.edu) Oregon State University Follow us on Twitter at https://twitter.com/wsdsldi Program committee: * Nada Amin (EPFL/University of Cambridge) * Eric Holk (Google) * Gabriele Keller (Data61, CSIRO (formerly NICTA) and UNSW) * Rebekah Leslie-Hurd (Intel Labs) * Chris Martens (NCSU) * Lee Pike (Galois) * Jonathan Ragan-Kelley (UC Berkeley) * Jesús Sánchez Cuadrado (Autonomous University of Madrid) * Vincent St-Amour (Northwestern University) * Philip Wadler (University of Edinburgh)

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Combining pool and Conduit
by Pieter Laeremans 07 Aug '17

07 Aug '17

Hello, I would like to combine a "Connection Pool" with the conduit library. I have an application were a stream of results from a web api needs to be analysed and stored in a database. Since the analysis is composed of different parts, I combine some parts together ( .|) Some of those parts need a database connection to do their work. Initially I created a Connection and passed it around to each part that needed it, this is sub-optimal. So I wanted to try the "resource-pool" library to address this problem. (https://hackage.haskell.org/package/resource-pool) So instead of a Connection I pass around a (Pool Connection) But I run into problems , and I don't know how to fix them. Here is a simple snippet of code that demonstrates the problem: ------------------------------------------- {-# LANGUAGE RankNTypes #-} module Lib where import Data.Pool import Database.HDBC import Database.HDBC.ODBC import Data.Conduit import Conduit createConnectionPool :: Pool Connection createConnectionPool = undefined processFoo :: Pool Connection -> Consumer String IO () processFoo pool = withResource pool $ \conn -> do mapM_C print ------------------------- I can not get this to compile: src/Lib.hs:15:19: error: • No instance for (MonadBaseControl IO (ConduitM String o IO)) arising from a use of ‘withResource’ • In the expression: withResource pool In the expression: withResource pool $ \ conn -> do { mapM_C print } In an equation for ‘processFoo’: processFoo pool = withResource pool $ \ conn -> do { mapM_C print } But I have no Idea how to tackle this problem. Any suggestions ? Thanks, Pieter -- Pieter Laeremans pieter(a)laeremans.org

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Extended deadline: IFL 2017 (29th Symposium on Implementation and Application of Functional Languages)
by publicityifl＠gmail.com 07 Aug '17

07 Aug '17

<div dir="ltr">Hello, Please, find below the third call for papers for IFL 2017. Note that some of the deadlines have been extended. Details are given below. 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 2017 - CALL FOR PAPERS: DEADLINES EXTENDED ============================================== 29th SYMPOSIUM ON IMPLEMENTATION AND APPLICATION OF FUNCTIONAL LANGUAGES ======================================================================= University of Bristol, UK In cooperation with ACM SIGPLAN Wednesday 30 August - Friday 1 September, 2017 <a href="http://iflconference.org/">http://iflconference.org/</a> 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 2017 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. Peer-review ----------- Following the IFL tradition, IFL 2017 will use a post-symposium review process to produce the formal proceedings. All participants of IFL 2017 are invited to submit either a draft paper or an extended abstract describing work to be presented at the symposium. At no time may work submitted to IFL be simultaneously submitted to other venues; submissions must adhere to ACM SIGPLAN's republication policy: <a href="http://www.sigplan.org/Resources/Policies/Republication">http://www.sigplan.org/Resources/Policies/Republication</a> The submissions will be screened by the program committee chair to make sure they are within the scope of IFL, and will appear in the draft proceedings distributed at the symposium. Submissions appearing in the draft proceedings are not peer-reviewed publications. Hence, publications that appear only in the draft proceedings are not subject to the ACM SIGPLAN republication policy. After the symposium, authors 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 review process. From the revised submissions, the program committee will select papers for the formal proceedings considering their correctness, novelty, originality, relevance, significance, and clarity. The formal proceedings will appear in the International Conference Proceedings Series of the ACM Digital Library. Important dates --------------- Note that the original deadlines for submission and registration have been extended. | | | | ----------------------| -----------------------------------------------------------| | Thu 17 August 2017 | Submission deadline draft papers | | Fri 18 August 2017 | Notification of acceptance for presentation | | Mon 21 August 2017 | Early registration deadline | | Mon 21 August 2017 | Submission deadline for pre-symposium proceedings | | Fri 25 August 2017 | Late registration deadline | | Wed 30 August 2017 - Fri 1 September 2017 | IFL Symposium | | Mon 4 December 2017 | Submission deadline for post-symposium proceedings | | Wed 31 January 2018 | Notification of acceptance for post-symposium proceedings | | Mon 12 March 2018 | Camera-ready version for post-symposium proceedings | Submission details ------------------ Prospective authors are encouraged to submit papers or extended abstracts to be published in the draft proceedings and to present them at the symposium. All contributions must be written in English. Papers must use the new ACM two columns conference format, which can be found at: <a href="http://www.acm.org/publications/proceedings-template">http://www.acm.org/publications/proceedings-template</a> For the pre-symposium proceedings we adopt a 'weak' page limit of 12 pages. For the post-symposium proceedings the page limit of 12 pages is firm. Authors submit through EasyChair: <a href="https://easychair.org/conferences/?conf=ifl2017">https://easychair.org/conferences/?conf=ifl2017</a> Topics ------ IFL welcomes submissions describing practical and theoretical work as well as submissions describing applications and tools in the context of functional programming. If you are not sure whether your work is appropriate for IFL 2017, please contact the PC chair at <a href="mailto:nicolas.wu@bristol.ac.uk">nicolas.wu(a)bristol.ac.uk</a>. Topics of interest 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 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. Programme committee ------------------- Chair: Nicolas Wu, University of Bristol, UK - Kenichi Asai, Ochanomizu University, Japan - Sandrine Blazy, University of Rennes 1, France - Carlos Camarao, Universidade Federal de Minas Gerais, Brazil - Stephen Dolan, University of Cambridge, UK - Jurriaan Hage, Utrecht University, Netherlands - Yukiyoshi Kameyama, University of Tsukuba, Japan - Benjamin Lerner, Brown University, USA - Bas Lijnse, Radboud University, Netherlands - Garrett Morris, University of Kansas, USA - Miguel Pagano, Universidad Nacional de C√≥rdoba, Argentina - Tomas Petricek, Alan Turing Institute, UK - Maciej Pir√≥g, University of Wroclaw, Poland - Exequiel Rivas, Universidad Nacional de Rosario, Argentina - Neil Sculthorpe, Nottingham Trent University, UK - Melinda Toth, Eotvos Lorand University, Hungary - Phil Trinder, Glasgow University, UK - Kanae Tsushima, National Institute of Informatics, Japan - Marcos Viera, Universidad de la Republica, Uruguay - Meng Wang, University of Kent, UK Venue ----- The IFL 2017 will be held in association with the Department of Computer Science, University of Bristol, UK. Bristol is located in South West England, and can be easily reached from Bristol Airport. See the website for more information on the venue. </div>  <a style='display: block; margin: 32px 0 40px 0; padding: 10px; font-size: 1em; text-align: center; border: 0; border-top: 1px solid gray; ' href='https://goo.gl/2ksdRv'>powered by GSM. Free mail merge and email marketing software for Gmail.</a>

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Convert Data.Vector.Unboxed.Mutable.MVector to Data.Vector.Unboxed.Vector
by Cody Goodman 06 Aug '17

06 Aug '17

I want to do this so I can use the Data.Vector.Unboxed.Generic functions requiring the Vector constraint, namely the maxIndex function. Implementing maxIndex for Data.Vector.Unboxed.Mutable.MVector would be useful as well, but I'm even more confused at how to do that or where to begin. Here is some stubbed out code demonstrating this. {-# Language ScopedTypeVariables #-} module Main where import Control.Monad.Primitive import qualified Data.Vector.Unboxed import qualified Data.Vector.Generic as VG import qualified Data.Vector.Unboxed.Mutable as VM import qualified Data.Vector.Unboxed as V toImmutable :: VM.MVector RealWorld Int -> V.Vector Int toImmutable = undefined main :: IO () main = do v :: VM.MVector RealWorld Int <- VM.new 1 VM.write v 0 (3 :: Int) x <- VM.read v 0 -- y <- VG.head . toImmutable $ v -- print y print $ VM.length v {- Thanks, Cody -}

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Job opening: compiling to categories
by Conal Elliott 05 Aug '17

05 Aug '17

I have a job opening to work closely with me (at Target Digital) on the GHC plugin described in the paper *Compiling to Categories* <http://conal.net/papers/compiling-to-categories> as well as on applications, including machine learning. I’m especially looking for someone used to working inside of GHC and/or on GHC plugins. Mathematically oriented, solid background in programming language theory, denotationally inclined. Remote work is perfectly fine (and is what I do). – Conal

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ANN: stack-1.5.1 released
by Emanuel Borsboom 05 Aug '17

05 Aug '17

See https://haskellstack.org for installation and upgrade instructions. Bug fixes: * Stack eagerly tries to parse all cabal files related to a snapshot. Starting with Stackage Nightly 2017-07-31, snapshots are using GHC 8.2.1, and the `ghc.cabal` file implicitly referenced uses the (not yet supported) Cabal 2.0 file format. Future releases of Stack will both be less eager about cabal file parsing and support Cabal 2.0. This patch simply bypasses the error for invalid parsing.

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Re: [Haskell-cafe] Running ghci in a Cabal sandbox
by Emil Axelsson 04 Aug '17

04 Aug '17

Thanks for your reply! But I actually don't want `cabal repl`. The bigger picture is explained here: http://fun-discoveries.blogspot.com/2017/08/building-haskell-projects-with-… Towards the end of that post I suggest using `cabal exec` to integrate with a Cabal sandbox; however, as Daniel Trstenjak pointed out, that shouldn't be needed since `cabal-cargs` already sets the `-package-db` flag for GHC. So my question is why `cabal exec` is needed (in this particular case) even though `-package-db` is given? I know `cabal exec` sets a few environment variables (`CABAL_SANDBOX_CONFIG`, `CABAL_SANDBOX_PACKAGE_PATH` and `GHC_PACKAGE_PATH`). I've checked that these are all set correctly, so Cabal seems to be doing its job. But it's not clear why ghci gets confused when these variables are not set (and `-package-db` is given), but not when the variables are set. Cheers / Emil Den 2017-08-04 kl. 15:31, skrev nek0: > Hi Emil, > > What you want is hidden behind the `cabal repl` command, which starts > ghci with the package-db of the sandbox. > > Greetings, > > nek0 > > On 4.8.2017 13:41, Emil Axelsson wrote: >> Hi! >> >> I have a small file Test.hs alone in a directory: >> >> {-# LANGUAGE DeriveGeneric #-} >> >> module Test where >> >> import Data.Hashable >> import Data.Scientific >> import GHC.Generics >> >> data Sc = Sc Scientific deriving (Generic) >> >> instance Hashable Sc >> >> To be able to load this file, I set up a Cabal sandbox: >> >> $ ghc --numeric-version >> 8.0.2 >> >> $ cabal --numeric-version >> 1.24.0.2 >> >> $ cabal sandbox init >> ... >> >> $ cabal install hashable-1.2.6.0 scientific >> ... >> >> (Note: not the latest version of hashable.) >> >> Now, if I try to run GHCi and point it to the sandbox' package database >> I get this error: >> >> $ ghci >> -package-db=.cabal-sandbox/x86_64-linux-ghc-8.0.2-packages.conf.d >> Test.hs GHCi, version 8.0.2: http://www.haskell.org/ghc/ :? for help >> [1 of 1] Compiling Test ( Test.hs, interpreted ) >> >> Test.hs:12:14: error: >> • No instance for (Hashable Scientific) >> arising from a use of >> ‘hashable-1.2.6.1:Data.Hashable.Class.$dmhashWithSalt’ >> • In the expression: >> hashable-1.2.6.1:Data.Hashable.Class.$dmhashWithSalt @Sc >> In an equation for ‘hashWithSalt’: >> hashWithSalt >> = hashable-1.2.6.1:Data.Hashable.Class.$dmhashWithSalt @Sc >> In the instance declaration for ‘Hashable Sc’ >> >> Somehow it mixes in version 1.2.6.1 of hashable, even though this >> package isn't installed (neither in the sandbox nor the global database). >> >> It turns out that wrapping the command in `cabal exec` fixes the problem: >> >> $ cabal exec -- ghci >> -package-db=.cabal-sandbox/x86_64-linux-ghc-8.0.2-packages.conf.d Test.hs >> GHCi, version 8.0.2: http://www.haskell.org/ghc/ :? for help >> [1 of 1] Compiling Test ( Test.hs, interpreted ) >> Ok, modules loaded: Test. >> *Test> >> >> Any idea what's going on? >> >> / Emil >> _______________________________________________ >> Haskell-Cafe mailing list >> To (un)subscribe, modify options or view archives go to: >> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe >> Only members subscribed via the mailman list are allowed to post.

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Call for participation: FARM (early reg ends today)
by Mark Santolucito 04 Aug '17

04 Aug '17

5th ACM SIGPLAN International Workshop on Functional Art, Music, Modelling and Design Oxford, UK September 9, 2017 (co-located with ICFP 2017) http://functional-art.org/2017 The ACM SIGPLAN International Workshop on Functional Art, Music, Modelling and Design (FARM) gathers together people who are harnessing functional techniques in the pursuit of creativity and expression. Functional Programming has emerged as a mainstream software development paradigm, and its artistic and creative use is booming. A growing number of software toolkits, frameworks and environments for art, music and design now employ functional programming languages and techniques. FARM is a forum for exploration and critical evaluation of these developments, for example to consider potential benefits of greater consistency, tersity, and closer mapping to a problem domain. This year FARM presents paper and demo sessions during the day, as well as a performance in the evening. The evening performance feature computer music performances of artists integrating functional programming techniques into their work. To register for FARM, visit the ICFP registration page - early registration ends August 4. Some funding support is available for the main ICFP conference and related workshops like FARM. This information can be found on the travel support page. Registration ------------ You can register via the ICFP 2017 registration:http://icfp17.sigplan.org/attending/registration Early registration deadline is August 4. Program --------------- 9:00 - 9:10 Welcome Michael Sperber, Jean Bresson 09:10 - 10:00 A Categorial Grammar for Music and Its Use in Automatic Melody Generation Halley Young Demo - Representation of Musical Notation in Haskell Edward Lilley 10:30 - 11:30 Demo - The Arpeggigon: A Functional Reactive Musical Automaton Henrik Nilsson Demo - Vivid: Sound Synthesis with Haskell and SuperCollider Tom Murphy Demo - African Polyphony and Polyrhythm Chris Ford 12:00 - 12:30 Modelling the Way Mathematics Is Actually Done Joe Corneli, Ursula Martin, Dave Murray-Rust, Alison Pease, Raymond Puzio, Gabriela Rino Nesin 14:00 - 15:00 FAUST Tutorial for Functional Programmers Yann Orlarey, Stéphane Letz, Dominique Fober, Romain Michon 15:30 - 16:20 GALE: A Functional Graphic Adventure Library and Engine Ivan Perez Demo - Ait: A Concatenative Language for Creative Programming Stian Veum Mollersen 16:50 - 17:40 Unified Media Programming: An Algebraic Approach Simon Archipoff, David Janin Demo - Octopus: A High-Level Fast 3D Animation Language Simon Archipoff, David Janin Performances 19:30-22:00 @ Old Fire Station Workshop Organisation --------------------- - Workshop Chair: Mike Sperber, Active Group GmbH - Program Chair: Jean Bresson, UMR STMS IRCAM/CNRS/UPMC Sorbonne UniversitÃ©s - Publicity Chair: Mark Santolucito, Yale University - Performance Chair: Alex McLean, Deutsches Museum, Munich Program Committee: --------------------- - Renick Bell, Tama Art University, Tokyo - Beatrice Berard, LIP6, Universite Pierre et Marie Curie - Jean Bresson, UMR STMS IRCAM/CNRS/UPMC Sorbonne Universités - Richard Gabriel, IBM Research - Jean-Louis Giavitto, UMR STMS IRCAM/CNRS/UPMC Sorbonne Universités - Stéphane Letz, Grame - José Pedro Magalhães, Standard Chartered Bank - Ivan Perez Dominguez, University of Nottingham - Donya Quick, Southern Methodist University - Christophe Rhodes, Goldsmiths, University of London - Andrew Sorensen, Australian National University - Michael Sperber, Active Group GmbH - Charlotte Truchet, LINA, UMR 6241, Université de Nantes

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[ANN] brittany - haskell source code formatting tool - hackage release
by lennart spitzner 04 Aug '17

04 Aug '17

Greetings, I am happy to (finally) announce the first hackage release of brittany, a configurable haskell source code formatter based on ghc-exactprint [2]. https://hackage.haskell.org/package/brittany https://github.com/lspitzner/brittany *Introduction* Brittany aims to nicely layout the code and retain empty lines and comments as they appear in the input. For that it uses a fundamentally different approach (see [7]/theory) than other formatters. The project is not finished, yet it already is usable and produces better results than other formatters in many cases. Of course these words come from its creator, so see for yourself: I have included some examples at the bottom of this mail; see [3] and [4] for some more. I wish to stress that this project will only progress at a very slow speed barring support from the community. I hereby offer to work on this and ask for funding. See the "future" paragraph below. *Changelog* Since the "alpha-release" announced previously [5] the most important changes are: - Release under the AGPL-v3; - Release on hackage; - Make horizontal alignment less aggressive by default (see example [6]); - Add high-level documentation (see [7]). This might be of interest to anyone considering to write a formatter (haskell or even otherwise); - Improve testsuite setup; - Improve layouting in many many cases and fix various bugs; - Add a library interface (this integrates with haskell-ide-engine [8]); Brittany still.. - does not touch anything other than top-level type signatures and bindings (imports, classes, instances, data decls, .. are not modified); - contains some bugs (but it checks its own output for validity and aborts); - does not handle many "uncommon" syntactic constructs/extentions (e.g. arrow notation); In preparation of this release the `butcher` and `czipwith` packages were published on hackage as well. I will cover those in separate announcements. *Building* Brittany currently requires ghc-8.0 (no support for previous ghc versions is planned, but 8.2 will be). Now that this package is on hackage, cabal users should be able to install it directly; stack users will currently have to clone and go from there (a stack.yaml is provided). Detailed building guides for cabal, cabal-new and stack are in the project README. Inclusion in stackage is coming as soon as all dependencies are included. *Known issues* - Bad performance for large inputs (really noticeable at >1k loc). The cause is already determined - quadratic instead of linear complexity in one specific function (see issue #34 [9]). Should be fixable and has high priority. - The config (file) lacks documentation. - Comments are not always reproduced exactly when reformatting. There is a lack of testcases for comments in the testsuite. There is the known case of comments in List/MonadComprehensions that currently breaks idempotency (the comments move further left each roundtrip through brittany) where a solution will most likely involve some non-trivial changes in ghc-exactprint (see [10]). - As mentioned above: only certain module elements are transformed, and not all syntactical constructs are supported. re-layouting of imports, data decls, classes and instances are on the radar, but all require a good amount of work. - CPP is not officially supported. This is mostly a WONTFIX. One can enable it by force, and it works to a degree, but it is relatively easy to find cases where it will break (conditional code not being reformatted, leading to syntax errors and theoretically also to change semantics)). - No fine-grained (per file or even per-function) control/configuration, e.g. it is not yet possible to add some pragma/comment to disable reformatting this one carefully layouted-by-hand function that brittany messes up. - No adaption to ghc-8.2 yet. *Future/Outlook* As far as I can tell brittany already works rather well - I use it all the time, even though I still run into issues from time to time. Still, brittany is not finished (these projects never really are, are they?). Up on my list are ghc-8.2 adaption, fixing the performance bug mentioned above, layouting of data decls, layouting of instances, and controlling behaviour/config via flags in the source (as comments). But implementing new functionality costs a lot of time, even with the DSL used internally: One has to understand the GHC AST (which is not always documented), think of all possible interactions ("do users really use record syntax when having more than one constructor?" "are GADT records a thing?"), write the layouting transformation and test it. I have already invested a good amount of my free time into this project but its scope is too large and I decided to put a limit on my personal investment. This means that barring some form of support from the community I don't see new features being implemented at any certain pace. This leaves the following paths: 1) This project is supported monetarily: I hereby offer to (part-time) work on this provided appropriate funding. I am not sure who exactly might be interested in providing this kind of support - I am no student anymore so GSoC is out of the question. Feel free to contact me on- or off-list if interested. 2) (More) Contributors add tests, report (and maybe fix) bugs and most importantly implement new functionality (layouting for any syntactic constructs of the haskell language not yet supported, etc.) I realize that this is not a trivial project to dive into, and there is a good amount of stuff one has to get familiar with before one can start making use of the abstractions (the DSL) provided. On the other hand, I _think_ that the project source code is relatively well-structured (although in-source comments are really sparse, admittedly) and the high-level (markdown) documentation <strike>will scare everyone away due to their length</strike> will allow understanding the project relatively quickly. 3) The project will progress only rather slowly. Regardless I plan to continue maintaining this project, fix bugs as they come up and also work on expanding functionality when I find the time. *Contributing* In ascending order of involvement, you can contribute by: - Reporting issues, especially instances of bad layouting (especially when it is not a pure matter of opinion); - Add to the testsuite, specifically to the `tests.blt` file of the `littests` test. It contains a large number of tests already, but the coverage is not very good. - If you want to really help implementing more stuff, the high-level docs [7] are the right place to get a rough overview, especially the theory document [11]. I have not documented how to write new layouters yet, so for now I recommend looking at the existing ones, e.g. in `Expr.hs`. -- lennart [1] https://hackage.haskell.org/package/brittany https://github.com/lspitzner/brittany/ [2] https://mpickering.github.io/posts/2015-07-23-ghc-exactprint.html https://hackage.haskell.org/package/ghc-exactprint [3] https://github.com/lspitzner/brittany/blob/da692a4341399390018fb03773e15865… [4] https://github.com/lspitzner/brittany/tree/master/doc/showcases [5] https://mail.haskell.org/pipermail/haskell-cafe/2016-September/124793.html [6] https://github.com/lspitzner/brittany/blob/da692a4341399390018fb03773e15865… [7] https://github.com/lspitzner/brittany/blob/master/doc/implementation/index.… [8] https://github.com/haskell/haskell-ide-engine [9] https://github.com/lspitzner/brittany/issues/34 [10] https://github.com/alanz/ghc-exactprint/issues/53 [11] https://github.com/lspitzner/brittany/blob/master/doc/implementation/theory… -- some layouting examples - would be (re)produced in exactly this way by brittany: > main = do > > now <- getCurrentTime > let (_, _, week) = toWeekDate . utctDay $ now > putStrLn $ ("it's "++) $ case week of > 6 -> "the weekend" > 7 -> "the weekend" > _ -> "a weekday" > > localtime <- utcToLocalZonedTime now > let hr = todHour . localTimeOfDay . zonedTimeToLocalTime $ localtime > case hr of > _ | hr < 12 -> putStrLn "it's before noon" > | otherwise -> putStrLn "it's after noon" > -- Newlines are used sparingly: Only after "do" and when the > -- `liftBaseOpDiscard` application would lead to overflowing 80 columns. > main :: IO () > main = do > pool <- createPostgresqlPool (toS databaseConnectionString) 10 > initiate $ \chan -> forever $ do > flip runDbConn pool $ do > makeSureQueueIsFull chan > void $ liftBaseOpDiscard (consumeMsgs chan responseQueue Ack) > (uncurry processMsg) > threadDelay 1000000 > -- Alignment of patterns > go [] "" = True > go [WildCard ] "" = True > go (WildCard :rest) (c:cs) = go rest (c : cs) || go (WildCard : rest) cs > go (Union globs:rest) cs = any (\glob -> go (glob ++ rest) cs) globs > go [] (_:_) = False > go (_:_) "" = False

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