April 2018 - Haskell-Cafe

Object assignment and equivalence
by Alfred Matthews 26 Apr '18

26 Apr '18

Numerically, wondering if there are design implications to or via defining integers (1,12) as let mod(1)=0, 0<x<=12 as opposed to let mod(1):=0, 0<x<=12 or 0<x<=12, let mod(1)==0 I think I mean mathematically, since none are anything more than Haskell pseudocode. Possibly this makes only metaphorical sense. Thanks in advance. Alfred.

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Block editor for Haskell
by Alex McLean 26 Apr '18

26 Apr '18

Hi all, I'm wondering if anyone has made a 'block editor' for Haskell, i.e. a syntax-aware text editor where you make a program by snapping together type-compatible words, usually with a mouse. Something similar to Scratch for example: https://scratch.mit.edu/ Any leads appreciated! Best wishes alex

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HaRe : informal poll
by Alan & Kim Zimmerman 26 Apr '18

26 Apr '18

Currently HaRe (on hackage) supports GHC 7.10 and 8.0 There is a new version ready to roll, with GHC 8.2 and 8.4 support. But due to the complexities of the build environment (details here[1] for anyone who cares) it will not be able to support earlier GHC versions. Will this be a problem for anyone? Alan [1] https://github.com/haskell/cabal/pull/5275

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Numerical Programming in Functional Languages (CfP)
by dominic＠steinitz.org 26 Apr '18

26 Apr '18

I’m the chair this year for the first(!) ACM SIGPLAN International Workshop on Numerical Programming in Functional Languages (NPFL), which will be co-located with ICFP this September in St. Louis, Missouri, USA. Please consider submitting something! All you have to do is submit between half a page and a page describing your talk. There will be no proceedings so all you need do is prepare your slides or demo. We do plan to video the talks for the benefit of the wider world. We have Eva Darulova <https://people.mpi-sws.org/%7Eeva/> giving the keynote. The submission deadline is Friday 13th July but I and the Committee would love to see your proposals earlier. See here <https://icfp18.sigplan.org/track/npfl-2018-papers> for more information. Please contact me if you have any questions! Dominic Steinitz dominic(a)steinitz.org http://idontgetoutmuch.wordpress.com Twitter: @idontgetoutmuch

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need to find generated reflex/reflex-dom docs
by Michael Litchard 25 Apr '18

25 Apr '18

I've installed reflex-platform on ubuntu via nix, and am pretty sure I have local docs installed. I located this file /nix/store/hv5zkh1gmhklk4sgwhd8gy1q79l37zpc-reflex-dom-0.4-doc/share/doc/html/index.html But it doesn't lead to very much. I'm thinking I didn't do a full doc install. I'd like some advice on how to make sure I've got a complete local install of reflex docs.

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how to catch/bracket in yesod-1.6?
by waldmann 25 Apr '18

25 Apr '18

Dear Cafe, I wonder what's the recommended way to catch an exception, clean up resources, etc., in a yesod Handler. I was using Control.Monad.Catch.bracket_ in legacy code but now I get "No instance for (Control.Monad.Catch.MonadMask (HandlerFor App))" - J

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ML4PL '18, 1st Call for Submissions
by Artem Pelenitsyn 25 Apr '18

25 Apr '18

******************************************************************************** | | | The 2nd International Workshop on Machine Learning Techniques | | for Programming Languages (ML4PL '18) | | | | July 18th 2018, Amsterdam, Netherlands | | Collocated with ECOOP & ISSTA | | | ******************************************************************************** A workshop on machine learning techniques applied to programming language-related research and development. This workshop puts an emphasis on identifying open problem rather than presenting solution, and encourages discussion amongst the participants. Attendance will be limited to ensure that meeting retains an interactive character. Workshop web-site: https://conf.researchr.org/track/ecoop-issta-2018/ML4PL-2018-papers Submission web-site: https://ml4pl18.hotcrp.com/ ********************************** SCOPE *********************************** Over the last years, we have seen a rapid growth in the use of machine-learning technologies in programming languages and systems. This growth is driven by the need to design programming languages to analyze, detect patterns, and make sense of Big Data, along with the increasing complexity of programming language tools, including analyzers and compilers, and computer architectures. The scale of complexity in available unstructured data and system tools has reached a stage where simple heuristics and solutions are no longer feasible or do not deliver adequate performance. At the same time, statistical and machine learning techniques have become mainstream. This workshop is a broad forum to bring together researchers with interests in the intersection of programming languages and system tools with machine learning. Topics of interest include (but are not limited to): * Program analysis + machine learning * Programming languages + machine learning * Compiler optimizations + machine learning * Computer architecture + machine learning * Probabilistic programming languages * Design space exploration Submissions should take the form of talk abstract or 2-page problem statements. Materials of accepted talks will be published in ACM DL. --------------- IMPORTANT DATES --------------- Submission deadline: Wednesday, May 18th, 2018, AOE Notification (tentative): Monday, June 1st, 2018 ML4PL Workshop: Wednesday, July 18th, 2018 ----------------- PROGRAM COMMITTEE ----------------- * Miltiadis Allamanis (Microsoft Research, Cambridge, United Kingdom) * Lasse Blaauwbroek (Czech Institute for Informatics Robotics and Cybernetics, Czech Republic) * Yoav Goldberg (Bar Ilan University, Israel) * Georgy Lukyanov (Newcastle University, United Kingdom) * Alex Polozov (Microsoft Research, United States) * Mark Santolucito (Yale University, United States) * Meital Zilberstein (Technion, Israel) ------------------------------ ORGANIZING COMMITTEE & CONTACT ------------------------------ * Hila Peleg (Technion, Israel) * Artem Pelenitsyn (Czech Technical University in Prague, Czech Republic) Please, address any questions to Artem (a.pelenitsyn(a)gmail.com)

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WST 2018 - Last Call for Papers (deadline: April 30, 2018)
by Salvador Lucas 25 Apr '18

25 Apr '18

========================================================================== WST 2018 - Call for Papers 16th International Workshop on Termination July 18-19, 2018, Oxford, United Kingdom http://wst2018.webs.upv.es/ ========================================================================== NEW: James Worrell and Akihisa Yamada, WST 2018 invited speakers The Workshop on Termination (WST) traditionally brings together, in an informal setting, researchers interested in all aspects of termination, whether this interest be practical or theoretical, primary or derived. The workshop also provides a ground for cross-fertilization of ideas from the different communities interested in termination (e.g., working on computational mechanisms, programming languages, software engineering, constraint solving, etc.). The friendly atmosphere enables fruitful exchanges leading to joint research and subsequent publications. The workshop is held as part of the 2018 Federated Logic Conference (FLoC 2018) http://www.floc2018.org/ IMPORTANT DATES: * submission deadline: April 30, 2018 * notification: May 28, 2018 * final version due: June 11, 2018 * workshop: July 18-19, 2018 TOPICS: The 16th International Workshop on Termination welcomes contributions on all aspects of termination. In particular, papers investigating applications of termination (for example in complexity analysis, program analysis and transformation, theorem proving, program correctness, modeling computational systems, etc.) are very welcome. Topics of interest include (but are not limited to): * abstraction methods in termination analysis * certification of termination and complexity proofs * challenging termination problems * comparison and classification of termination methods * complexity analysis in any domain * implementation of termination methods * non-termination analysis and loop detection * normalization and infinitary normalization * operational termination of logic-based systems * ordinal notation and subrecursive hierarchies * SAT, SMT, and constraint solving for (non-)termination analysis * scalability and modularity of termination methods * termination analysis in any domain (lambda calculus, declarative programming, rewriting, transition systems, etc.) * well-founded relations and well-quasi-orders INVITED SPEAKERS: James Worrell - University of Oxford "Termination Checking and Invariant Synthesis for Affine Programs" Akihisa Yamada - NII Japan "Towards a Unified Method for Termination" COMPETITION: Since 2003, the catalytic effect of WST to stimulate new research on termination has been enhanced by the celebration of the Termination Competition and its continuously developing problem databases containing thousands of programs as challenges for termination analysis in different categories, see http://termination-portal.org/wiki/Termination_Competition In 2018, the Termination Competition will run in parallel with FLoC 2018. More details will be provided in a dedicated announcement on the competition. PROGRAM COMMITTEE: Cristina Borralleras - U. de Vic Ugo Dal Lago - U. degli Studi di Bologna Carsten Fuhs - Birkbeck, U. of London Samir Genaim - U. Complutense de Madrid Juergen Giesl - RWTH Aachen Raul Gutiérrez - U. Politecnica de València Keiichirou Kusakari - Gifu University Salvador Lucas (chair) - U. Politecnica de Valencia Fred Mesnard - U. de La Reunion Aart Middeldorp - U. of Innsbruck Albert Rubio - U. Politecnica de Catalunya Rene Thiemann - U. of Innsbruck Caterina Urban - ETH Zürich SUBMISSION: Submissions are short papers/extended abstracts which should not exceed 5 pages. There will be no formal reviewing. In particular, we welcome short versions of recently published articles and papers submitted elsewhere. The program committee checks relevance and provides additional feedback for each submission. The accepted papers will be made available electronically before the workshop. Papers should be submitted electronically via the submission page: https://easychair.org/conferences/?conf=wst2018 Please, use LaTeX and the LIPIcs style file http://drops.dagstuhl.de/styles/lipics/lipics-authors.tgz to prepare your submission.

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In which format should GHC expose documentation via its .hi-files?
by Simon Jakobi 24 Apr '18

24 Apr '18

Hi! In preparation for the coding phase of the Hi Haddock proposal that I want to implement, I need a decision on the format in which we should expose haddocks in GHC's .hi interface files. Please visit https://github.com/haskell/haddock/issues/805, ask questions, make suggestions and help me find a timely decision! :) Cheers, Simon

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Selda: confused about type signtures
by Marc Busqué 24 Apr '18

24 Apr '18

Hi! I'm using [selda](https://hackage.haskell.org/package/selda) package in order to deal with database backends. Selda uses `TypeOperators` language extension, and it introduces `:*:` type operator constructor which take concrete types like `RowID` or `Text` . It also has a `Table` type constructor which takes anything built with `:*:`). On the other hand, `SeldaM` is selda custom monad transformer with `IO` at the bottom. I have following helper function which just wraps a call to the SQLite backend. `dBPath` is just the database file path: ``` withDB :: SeldaM a -> IO a withDB act = do path <- dBPath withSQLite path act ``` I want to wrap selda API in custom functions to be more resilient to changes. Right now I'm trying to abstract selecting all rows for a given table (maybe it seems brittle, but it is just a toy project in order to learn Haskell): ``` list table = withDB $ query (select table) ``` Not adding a type signature to `list` produces following compilation error: ``` • Non type-variable argument in the constraint: selda-0.1.12.1:Database.Selda.Column.Columns (selda-0.1.12.1:Database.Selda.Column.Cols s a) (Use FlexibleContexts to permit this) • When checking the inferred type list :: forall s a. (selda-0.1.12.1:Database.Selda.Column.Columns (selda-0.1.12.1:Database.Selda.Column.Cols s a), selda-0.1.12.1:Database.Selda.Compile.Result (selda-0.1.12.1:Database.Selda.Column.Cols s a)) => Table a -> IO [selda-0.1.12.1:Database.Selda.Compile.Res (selda-0.1.12.1:Database.Selda.Column.Cols s a)] ``` If I try to add what I think would be the correct signature: ``` list :: Table a -> IO [a] ``` The error changes to: ``` • Couldn't match type ‘a’ with ‘selda-0.1.12.1:Database.Selda.Compile.Res (selda-0.1.12.1:Database.Selda.Column.Cols s0 a)’ ‘a’ is a rigid type variable bound by the type signature for: list :: forall a. Table a -> IO [a] at src/Hedger/Category.hs:35:1-25 Expected type: SeldaM [a] Actual type: selda-0.1.12.1:Database.Selda.Backend.Internal.SeldaT IO [selda-0.1.12.1:Database.Selda.Compile.Res (selda-0.1.12.1:Database.Selda.Column.Cols s0 a)] • In the second argument of ‘($)’, namely ‘query (select table)’ In the expression: withDB $ query (select table) In an equation for ‘list’: list table = withDB $ query (select table) • Relevant bindings include table :: Table a (bound at src/Hedger/Category.hs:36:6) list :: Table a -> IO [a] (bound at src/Hedger/Category.hs:36:1) | 36 | list table = withDB $ query (select table) ``` However, if I constraint the type signature to act just for a given table, it compiles without errors: ``` type CategoriesSchema = RowID:*:Text list :: Table CategoriesSchema -> IO [CategoriesSchema] ``` Why is that it works with concrete types but not with a type variable that takes the same concrete type in its both placeholders? Thanks in advance, Marc Busqué http://waiting-for-dev.github.io/about/

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