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How can I find out which functions can be run on an expression?
by Julian Leviston 30 Apr '17

30 Apr '17

I'd like to programmatically find out which functions in a module could possibly apply to a particular expression. I also posted this to stack overflow. To make this concrete: {-# LANGUAGE TemplateHaskell #-} module Test where -- we'll import template-haskell from Lens -- so we can create prisms automatically for our 'AST' import qualified Control.Lens.TH as LTH --- some 'AST' in a toy language data CExp = CLit Int -- a literal integer | CAdd CExp CExp -- addition | CMul CExp CExp -- multiplication | CSub CExp CExp -- subtraction deriving Show -- an eval for our AST eval :: CExp -> Int eval exp = case exp of CLit i -> i CAdd e1 e2 -> eval e1 + eval e2 CMul e1 e2 -> eval e1 * eval e2 CSub e1 e2 -> eval e1 - eval e2 -- a function to build a sum using add with our AST, from a list of Int values listToSums :: [Int] -> CExp listToSums = foldr CAdd (CLit 0) . fmap CLit -- here we make prisms for looking at particular values -- in the CExp AST LTH.makePrisms ''CExp -- let's have an expression: theList1 :: CExp theList1 = listToSums [1..38] Now, at this point, I'd like a function that can give me a list of all the top level functions of a particular module (including this one) that are able to be applied to the expression theList1. This will include the prisms that were created with makePrisms. It would be fine if it uses the hint library's Interpreter monad. I've been experimenting with it a bit, and while I can get a list of all of the definitions at the top level of any module, and I can find the types of them, too (more or less), I'm a bit lost about how to pass an expression in as an argument to these functions then check if that exprssions will typecheck. If I can do that, I can run filter across all of the functions in a module, which lets me find out which ones are applicable. Many thanks in advance.

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State of Haskell IDE Engine
by Alan & Kim Zimmerman 30 Apr '17

30 Apr '17

Some of you have been wondering what has happened to the haskell-ide-engine[1], and whether it may perhaps have died. Development has resumed, based mainly on the existence of an enabling technology in the Language Server Protocol[2] which is starting to have implementations for IDEs and Languages[3]. It was always the intention to leverage off common infrastructure at the IDE side, and this protocol is making that possible. The current state for haskell-ide-engine is that support is provided in master[4], which has been tested in emacs using[5] (and [6] until the branch is merged). It is also tested against vscode[7] using the vscode-hie-server plugin[8]. Current features include - diagnostics provided via hlint and ghc-mod (using flycheck in emacs) - hover support giving the type under the cursor - ability to apply hlint suggestions as codeActions, via apply-refact - HaRe refactorings exposed in the emacs version. The vscode plugin lags in this, my skills are limited There is a lot of development happening on the emacs lsp-mode, as it benefits many languages, not just haskell, and so developers from other languages are also contributing. The LSP support for haskell-ide-engine is supplied by a separate library[9] which is being used in at least 3 other LSP servers to my knowledge. These will be made public when/if it suits their creators to do so. The general plan going forward is to focus HIE on being an LSP server. Other transports will not be removed, but the driving paradigm will be LSP support. The longer term plan is to use this as a platform to drive more interactivity back into GHC, starting with exploring incremental parsing driven by the document change notifications provided in the LSP protocol, and supported in haskell-lsp[9]. Alan [1] https://github.com/haskell/haskell-ide-engine/issues/218 [2] https://github.com/Microsoft/language-server-protocol [3] https://github.com/Microsoft/language-server-protocol/wiki/Protocol-Impleme… [4] https://github.com/haskell/haskell-ide-engine [5] https://github.com/alanz/lsp-haskell [6] https://github.com/alanz/lsp-mode/tree/project-ask [7] http://code.visualstudio.com/ [8] https://github.com/alanz/vscode-hie-server [9] https://github.com/alanz/haskell-lsp

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Deadline Extension: International Workshop on OCL and Textual Modeling (OCL 2017)
by Achim D. Brucker 29 Apr '17

29 Apr '17

(Apologies for duplicates) New Deadline: May 7, 2017 CALL FOR PAPERS 17th International Workshop on OCL and Textual Modeling Co-located with STAF 2017 SOFTWARE TECHNOLOGIES: APPLICATIONS AND FOUNDATIONS July 20, 2017, Marburg, Germany http://oclworkshop.github.io Modeling started out with UML and its precursors as a graphical notation. Such visual representations enable direct intuitive capturing of reality, but they have weaknesses: for example, detailed visual representations bear the risk of becoming overcrowded faster than textual models and some of the visual features lack the level of precision required to create complete and unambiguous specifications. These weaknesses of graphical notations encouraged the development of text-based modeling languages that either integrate with or replace graphical notations for modeling. Typical examples of such languages are OCL, textual MOF, Epsilon, and Alloy. Textual modeling languages have their roots in formal language paradigms like logic, programming and databases. The goal of this workshop is to create a forum where researchers and practitioners interested in building models using OCL or other kinds of textual languages can directly interact, report advances, share results, identify tools for language development, and discuss appropriate standards. In particular, the workshop will encourage discussions for achieving synergy from different modeling language concepts and modeling language use. The close interaction will enable researchers and practitioners to identify common interests and options for potential cooperation. ## Topics of interest Topics of interest include (but are not limited to): - Mappings between textual modeling languages and other languages/formalisms - Algorithms, evaluation strategies and optimizations in the context of textual modeling languages for: - validation, verification, and testing, - model transformation and code generation, - meta-modeling and DSLs, and - query and constraint specifications - Alternative graphical/textual notations for textual modeling languages - Evolution, transformation and simplification of textual modeling expressions - Libraries, templates and patterns for textual modeling languages - Tools that support textual modeling languages (e.g., verification of OCL formulae, runtime monitoring of invariants) - Complexity results for textual modeling languages - Quality models and benchmarks for comparing and evaluating textual modeling tools and algorithms - Successful applications of textual modeling languages - Case studies on industrial applications of textual modeling languages - Experience reports: - usage of textual modeling languages and tools in complex domains, - usability of textual modeling languages and tools for end-users - Empirical studies about the benefits and drawbacks of textual modeling languages - Innovative textual modeling tools - Comparison, evaluation and integration of modeling languages - Correlation between modeling languages and modeling tasks This year, we particularly encourage submissions describing applications and case studies of textual modeling as well as test suites and benchmark collections for evaluating textual modeling tools. ## Venue This workshop will be organized as a part of STAF 2017 Conferenze in Marburg, Germany. It was previously organized as part of the MODELS conference. Similar to its predecessors , the workshop addresses both people from academia and industry . The aim is to provide a forum for addressing integration of OCL and other textual modeling languages , as well as tools for textual modeling , and for disseminating good practice and discussing the new requirements for textual modeling . ## Workshop Format The workshop will include short (about 15 min) presentations, parallel sessions of working groups, and sum-up discussions. ## Submissions Two types of papers will be considered: * Short contributions (between 6 and 8 pages) describing new ideas, innovative tools or position papers. * Full papers (between 12 and 16 pages). in LNCS format. Submissions should be uploaded to [EasyChair](https://easychair.org/conferences/?conf=ocl2017). The program committee will review the submissions (minimum 2 reviews per paper, usually 3 reviews) and select papers according to their relevance and interest for discussions that will take place at the workshop. Accepted papers will be published online in a post-conference edition of [CEUR](http://www.ceur-ws.org). ## Important Dates - Submission of papers: May 7, 2017 (extended) - Notification: May 25, 2017 - Workshop date: July 20, 2017 -- Dr. Achim D. Brucker | Software Assurance & Security | University of Sheffield https://www.brucker.ch | https://logicalhacking.com/blog @adbrucker | @logicalhacking

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th-abstraction: A new library for inspecting datatypes from Template Haskell
by Eric Mertens 28 Apr '17

28 Apr '17

Hello, I've uploaded a new library to Hackage that helps normalize the information one can get by reifying the type constructor of a type declared with data or newtype. https://hackage.haskell.org/package/th-abstraction https://github.com/glguy/th-abstraction I've found that I was duplicating a lot of code when trying to maintain compatibility across a range of Template Haskell versions when using the 'reify' operation. Currently I'm testing against GHC versions as old as 7.4.2 and as new as 8.2.1-rc1. This package eliminates some of the noise that comes from reify's syntax-oriented constructors and eliminates the differences across normal and GADT syntax. I expect to add more Template Haskell functionality to this package over time as needed with a focus on being able to maintain compatibility across a wide range of template-haskell package versions. I hope others are able to find it useful! Best regards, Eric Mertens "glguy"

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ANN: wxHaskell 0.92.3.0
by Henk-Jan van Tuyl 28 Apr '17

28 Apr '17

L.S., I am happy to announce a new version of wxHaskell: 0.92.3.0 Windows users can still use wxInstall Achelanne 0.1 to install this new version of wxHaskell.[0][1] Changes in wxHaskell since 0.92.2: - Improvements for compilation on BSD platform - Improved commandline handling - Sample program PaintGC.hs added - Compilation can now be done with an alternative wx-config.exe - Simplification of Windows build process with Stack - Several bugs solved Thanks to everyone who contributed! What is wxHaskell? ------------------ wxHaskell[2] is a portable and native GUI library for Haskell. The goal of the project is to provide an industrial strength GUI library for Haskell, but without the burden of developing (and maintaining) one ourselves. wxHaskell is therefore built on top of wxWidgets[3] – a comprehensive C++ library that is portable across all major GUI platforms; including GTK, Windows, X11, and MacOS X. Furthermore, it is a mature library (in development since 1992) that supports a wide range of widgets with the native look-and-feel. Links ----- See the homepage of wxHaskell for more information: https://wiki.haskell.org/WxHaskell Repository: https://github.com/wxHaskell/wxHaskell Tickets: https://sourceforge.net/p/wxhaskell/_list/tickets The packages are: - wxc https://hackage.haskell.org/package/wxc - wxdirect https://hackage.haskell.org/package/wxdirect - wxcore https://hackage.haskell.org/package/wxcore - wx https://hackage.haskell.org/package/wx Regards, Henk-Jan van Tuyl [0] http://sourceforge.net/projects/wxhaskell/files/wxInstall/ [1] https://wiki.haskell.org/WxHaskell/Windows#Installing_the_easy_way [2] https://wiki.haskell.org/WxHaskell [3] https://wxwidgets.org/ -- 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://folding.stanford.edu/ http://Van.Tuyl.eu/ http://members.chello.nl/hjgtuyl/tourdemonad.html Haskell programming --

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bounty for vty on Windows
by Simon Michael 28 Apr '17

28 Apr '17

Hi all, vty is a nice full-screen curses-style API, and the basis for the nice higher-level brick TUI (text UI) framework, that builds on POSIX platforms only. All agree that it would be nice to make it work on Windows too. This would allow building cross-platform TUIs with haskell. Also there are things in vty, such as the Graphics.Vty.Attributes, that would be useful for CLIs too. I summarised current status and have kicked off a bounty towards getting Windows support added to the vty lib. I'm sending this to raise interest and invite your help, be you a person with a Windows machine, a potential bounty donor, or someone interested in improving Haskell's portability and applicability. https://github.com/jtdaugherty/vty/pull/1#issuecomment-297143444 <https://github.com/jtdaugherty/vty/pull/1#issuecomment-297143444> My particular interest is in making hledger-ui[1] cross platform, and in being able to use vty's higher-level terminal styles in CLI tools on all platforms. Best! Simon [1] http://hledger.org/hledger-ui.html <http://hledger.org/hledger-ui.html>

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Should I report a bug on GHC 7.10.3, or is it past it's end-of-life?
by Ramin Honary 28 Apr '17

28 Apr '17

I'm getting an "internal error: evacuate: strange closure type" in GHC 7.10.3. Should I report it? Would it even do any good? It doesn't seem there is any more development on the 7.10 branch anymore. If it is still being developed, should I try updating my GHC to a more recent build of 7.10.3? Looking at the core dump file, it appears to be a problem in the garbage collector. I've done a bit of work trying get around the bug, including using -dcore-lint and -O0, and updating my dependency libraries, and I can still reproduce the issue very regularly in my own environment by calling a single method in my code base, either in GHCi or in a compiled binary test program.

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Trends in Functional Programming in Education TFPIE 2017, Canterbury 22 June, SECOND CALL FOR PAPERS
by Simon Thompson 28 Apr '17

28 Apr '17

TFPIE 2017 Trends in Functional Programming in Education, 2017 https://www.cs.kent.ac.uk/people/staff/sjt/TFPIE2017/ The sixth workshop on Trends in Functional Programming in Education, 2017, which is to be held on the Canterbury campus of the University of Kent on Thursday, 22 June, following the 2017 TFP meeting on 19–21 June. TFPIE workshops have previously been held in St Andrews, Scotland (2012), Provo Utah, USA (2013), Soesterberg, The Netherlands (2014), and Sophia-Antipolis, France (2015), College Park, USA (2016). A particular topic of this year's TFPIE will be MOOCs and other online learning, and as well as a session on this, we're looking forward to announcing a keynote speaker in this area very soon. The goal of TFPIE is to gather researchers, teachers and professionals that use, or are interested in the use of, functional programming in education. TFPIE aims to be a venue where novel ideas, classroom-tested ideas and work-in-progress on the use of functional programming in education are discussed. The one-day workshop will foster a spirit of open discussion by having a review process for publication after the workshop. The program chair of TFPIE 2017 will screen submissions to ensure that all presentations are within scope and are of interest to participants. After the workshop, presenters will be invited to submit revised versions of their articles for publication in the journal Electronic Proceedings in Theoretical Computer Science (EPTCS). Second call for papers TFPIE 2017 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. Submission Potential presenters are invited to submit an extended abstract (4-6 pages) or a draft paper (up to 16 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=tfpie2017 After the workshop, presenters will be invited to submit (a revised version of) their article for review. The PC will select the best articles for publication in the journal Electronic Proceedings in Theoretical Computer Science (EPTCS). Articles rejected for presentation and extended abstracts will not be formally reviewed by the PC. Programme committee Dr Laura Castro, University of A Coruña Prof Ralf Lämmel, University of Koblenz-Landau Dr Elena Machkasova, University of Minnesota, Morris Prof Michel Mauny, Inria, Paris Dr Jeremy Singer, University of Glasgow Prof Simon Thompson, University of Kent (chair) Important dates Submissions of draft papers: 10 May, 2017 Notification: 17 May, 2017 Registration: 11 June, 2017 Workshop: 22 June 2017 Submission for formal review: 18 August, 2017 Notification of acceptance: 6 October, 2017 Camera ready paper: 3 November, 2017 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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Looking for maintainers or comaintainers on my Haskell projects
by Christopher Done 28 Apr '17

28 Apr '17

Hi all, The short version is: I’ve been battling RSI in my fingers for some years. I’m doing various things to mitigate that problem, but I have very limited finger bandwidth these days; enough to work at my usual pace at my job, but not much in the evenings and weekends, and so I can’t manage to do much on my hobby projects. I’m also not as motivated these days to work on my set of open source projects, and am turning my attention to different things. It’s not great, but that’s life. I don’t think that the users of my packages are getting the best maintainership deal. Rather than be “the absentee maintainer”, I’d prefer a straight-forward transition of maintainership or ownership to someone who can put the right energy and time in. In terms of packages, there are really two that have a significant maintenance burden and users aren’t being served very well: - HIndent <https://github.com/chrisdone/hindent> has a significant amount of issues opened for it regularly, and many of them require discussion and debate. If someone would like to become a co-maintainer, let me know. It may (eventually) make sense to move it to a more general GitHub organization like commercialhaskell or haskell. - Intero <https://github.com/commercialhaskell/intero/issues>, which seems to have been a success, has a pretty big maintenance burden on “this doesn’t work” kind of issues which require investigation. There’s some Emacs Lisp work to do on it, and some Haskell work on the intero binary, and a whole lot of platform-specific problems or tooling not working together. On the other hand people really like this project, and there’s a lot of tooling potential. If you want to take xeno <https://github.com/chrisdone/xeno> and make it into a publishable package, please do so. The rest of my projects that are on Stackage are: labels <https://hackage.haskell.org/package/labels>, ace <https://hackage.haskell.org/package/ace>, ical <https://hackage.haskell.org/package/ical>, check-email <https://hackage.haskell.org/package/check-email>, freenect <https://hackage.haskell.org/package/freenect>, frisby <https://hackage.haskell.org/package/frisby>, gd <https://hackage.haskell.org/package/gd>, ini <https://hackage.haskell.org/package/ini>, lucid <https://hackage.haskell.org/package/lucid>, osdkeys <https://hackage.haskell.org/package/osdkeys>, pdfinfo <https://hackage.haskell.org/package/pdfinfo>, present <https://hackage.haskell.org/package/present>, pure-io <https://hackage.haskell.org/package/pure-io>, scrobble <https://hackage.haskell.org/package/scrobble>, shell-conduit <https://hackage.haskell.org/package/shell-conduit>, sourcemap <https://hackage.haskell.org/package/sourcemap>, descriptive <https://hackage.haskell.org/package/descriptive>, wrap <https://hackage.haskell.org/package/wrap>, path <https://hackage.haskell.org/package/path>, weigh <https://hackage.haskell.org/package/weigh>, haskell-docs <https://hackage.haskell.org/package/haskell-docs>, and structured-haskell-mode <https://hackage.haskell.org/package/structured-haskell-mode>. If you’re interested in taking over or co-maintaining any of them, let me know. Some are interesting, others are boring, some are trivial. I have other packages on Hackage, but they’re mostly dead or experiments that don’t need maintenance anyway. I’ve started the process of adding or changing maintainers on my public services: - Haskell News <https://github.com/haskellnews> is now a GitHub organization. Luke Murphy is a co-owner, and has full access to the DigitalOcean account that is running the service. So if you want to work on that project, I’m not in the way. - lpaste <https://github.com/lpaste/lpaste> has been moved to its own DigitalOcean account too. If anyone is interested in taking over the project or co-running it, let me know. - tryhaskell <https://github.com/chrisdone/tryhaskell> doesn’t really require any maintenance, but it’s also on its own DigitalOcean account now too. - IRCBrowse <https://github.com/chrisdone/ircbrowse> is now on its own DigitalOcean account too. It requires maintenance once in a while. If anyone is interested in taking over the project or co-running it, let me know. Cheers!

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Re: [Haskell-cafe] Partial type family application
by Oleg 27 Apr '17

27 Apr '17

If the goal is to write higher-order type families, we can do that already -- and were able to do for a long time. For example, please see http://okmij.org/ftp/Haskell/TTypeable/TTypeable.hs that was written in 2012 for http://okmij.org/ftp/Haskell/typeEQ.html It shows the type-level function that checks for a membership in a type-level using the equality function supplied by a user as the first argument. Incidentally, here is the definition type instance Member f x NIL = HFalse type instance Member f x (h :/ t) = ORELSE (Apply f (x,h)) (CLOS AC_Member (f,x,t)) It was written before the modern syntax for type-level lists and booleans. This is an example of the general technique of defunctionalization.

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