February 2017 - Haskell-Cafe

Read my thesis draft on Backpack!
by Edward Z. Yang 23 Feb '17

23 Feb '17

Hello all, I have finished a draft of my thesis on Backpack, a new module system for Haskell (building on top of the work of Scott Kilpatrick et al). This thesis also doubles as the definitive manual on Backpack, which will be released with the upcoming GHC 8.2. I've posted a copy of the draft here: https://github.com/ezyang/thesis/releases and I would love it if you took a look at it, gave it a read perhaps, and told me about anything that was unclear or not well explained. You can file an issue on the GitHub, or shoot me an email or tweet. Looking forward to your comments. Thanks, Edward

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ghc on xeon phi?
by Johannes Waldmann 23 Feb '17

23 Feb '17

Dear Cafe - would a program compiled by ghc, or ghc itself, run as-is on Intel Xeon Phi (KNL)? I found this reference http://stackoverflow.com/questions/22253311/running-haskell-on-xeon-phi but it seems to be about the pre-KNL version. Thanks - J.

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Trends in Functional Programming in Education ITFPIE) 2017, call for papers
by Simon Thompson 23 Feb '17

23 Feb '17

TFPIE 2017 Trends in Functional Programming in Education, 2017 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). 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). 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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-Werror -Woverlapping-patterns -fglasgow-exts ?
by Johannes Waldmann 23 Feb '17

23 Feb '17

Dear Cafe, I want to chase overlapping patterns in a larger code base. So I use -Werror -Woverlapping-patterns . But the code also needs -fglasgow-exts and this makes compilation stop right at the beginning, with "warning: -fglasgow-exts is deprecated: ..." which will be turned into an error because of -Werror -Wno-warnings-deprecations does not help, apparently that warning is not a deprecation. Is there a way to get -Werror for specific warnings? - J.

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Size-indexed monoids
by Kosyrev Serge 22 Feb '17

22 Feb '17

Good day! What is the proper type class for stronger-typed (size-indexed) monoids: - that is, monoids carrying their "size" in the type - preferably as GHC.TypeLits.Nat - preferably on Hackage ? I'm quite prepared to the idea that a monoid is an entirely wrong abstraction, from a category-theoretic standpoint, so I would gladly learn of a better one : -) Use case: > {-# LANGUAGE DataKinds, GADTs, KindSignatures, TypeOperators, UnicodeSyntax, StandaloneDeriving #-} > > module Understanding.Types where > > import GHC.TypeLits > > data T (depth ∷ Nat) p where > TZ ∷ T 0 p > TS ∷ (Show p, CmpNat (m + 1) n ~ EQ) ⇒ > { payload ∷ p > , next ∷ T m a } → T n a > deriving instance Show p ⇒ Show (T d p) > > instance Monoid (T d p) where > mempty = TZ > mappend TZ TZ = TZ > mappend TZ t@(TS _ _) = t > mappend t@(TS _ _) TZ = t > mappend tl@(TS pl nl) tr = TS pl $ mappend nl tr As it is, even the mempty case rejects such a blatant violation of polymorphism, since `T 0 p` cannot unify with `T n p`. So, ideally (I think), I would like something like this: > class TypedMonoid a where > tmempty ∷ a 0 > tmappend ∷ a n → a m → a (n + m) -- с уважениeм / respectfully, Косырев Сергей -- “Most deadly errors arise from obsolete assumptions.” -- Frank Herbert, Children of Dune

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CFP: International Workshop on OCL and Textual Modeling (OCL 2017)
by Achim D. Brucker 22 Feb '17

22 Feb '17

(Apologies for duplicates) 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=ocl17). 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: April 28, 2017 - 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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Takeover of http-client-lens
by Simon Hafner 22 Feb '17

22 Feb '17

Hello I wanted to take over http-client-lens. The corresponding email address is out of service: > 550 5.1.1 The email account that you tried to reach does not exist. Please try double-checking the recipient's email address for typos or unnecessary spaces. https://github.com/reinh/http-client-lens/issues/2 Posting here in another attempt to reach the original author. Cheers, Simon

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ghc on xeon phi?
by Dominic Steinitz 22 Feb '17

22 Feb '17

> Hi Levent, > >> The whole point of the Xeon-phi is the availability of >> large-vector sized floating-point support and many-many cores. > > Sure, that's what I'm contemplating - use the many options > of writing parallel and concurrent Haskell programs. > > So, GHC's RTS should "just work"? > > I was hoping someone already had actually seen this > on their machine. > > - J. I recall we thought about using a Xeon phi for our application but abandoned the attempt for reasons I cannot recall. I’ll see if I can find out. But maybe you would better using something like accelerate-llvm? I think you wrote your application was numerical. BTW I am currently adding a small improvement to ghc floating point code generation but I am beginning to think it’s going to be difficult to get ghc to generate really good numerical / floating point code and I am experimenting with accelerate-llvm. Dominic

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A question about GHC test coverage
by Olaf Klinke 21 Feb '17

21 Feb '17

You should not have to write tests for functions you did not define. Correct me if I'm wrong, but any property of max can be derived from the properties of <=. Sadly, the laws for Ord are not stated in the documentation of Data.Ord. (Because there is no consensus?) They are: Reflexive: if x == y then x <= y Transitive: if x <= y and y <= z then x <= z Antisymmetric: if x <= y and y <= x then x == y Olaf

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What is this applicative functor?
by Joachim Breitner 20 Feb '17

20 Feb '17

Hi, I recently wrote this applicative functor: data OneStep a = OneStep a [a] instance Functor OneStep where fmap f (OneStep o s) = OneStep (f o) (map f s) instance Applicative OneStep where pure x = OneStep x [] OneStep f fs <*> OneStep x xs = OneStep (f x) (map ($x) fs ++ map f xs) takeOneStep :: OneStep t -> [t] takeOneStep (OneStep _ xs) = xs This was useful in the context of writing a shrink for QuickCheck, as discussed at http://stackoverflow.com/a/41944525/946226. Now I wonder: Does this functor have a proper name? Does it already exist in the libraries somewhere? Should it? Greetings, Joachim -- Joachim “nomeata” Breitner mail(a)joachim-breitner.de • https://www.joachim-breitner.de/ XMPP: nomeata(a)joachim-breitner.de • OpenPGP-Key: 0xF0FBF51F Debian Developer: nomeata(a)debian.org

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