July 2016 - Haskell-Cafe

Re: [Haskell-cafe] Haskell-Cafe Digest, Vol 154, Issue 27
by Vlad Lopatin 02 Jul '16

02 Jul '16

Re: up-to-date glfw examples (briand(a)aracnet.com) Hey, Brian Here's a bare-bones example of modern OpenGL(4.5) (VBO's, vertex/fragment shaders), using GLFW-b to handle windows/input and Yampa for animation. Shader-loading is handled by Sven Panne's code: https://github.com/madjestic/Haskell-OpenGL-Tutorial/tree/master/Mandelbrot… Cheers, Vlad

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haskell-browser-mods - v0.1
by Erik Rantapaa 02 Jul '16

02 Jul '16

Hi everyone, I've created a browser extension to aid in navigating around Haskell-related websites. The extension adds information to visited pages, create links to other relevent pages and adds keyboard shortcuts and conveniences. The sites the extension knows about include: - haskellnews.org - hdiff.luite.com - hackage.haskell.org - packdeps.haskellers.com - hayoo.fh-wedel.de The extension is currently available for Safari and Chrome. For more information and downloads visit: https://github.com/erantapaa/haskell-browser-mods Feedback, suggestions, bug reports and PRs are very welcome. Erik

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type level Min function for GHC.TypeLits?
by Baojun Wang 01 Jul '16

01 Jul '16

Hi Cafe, I'm trying to do some basic type level tricks, I wonder whether it is possible to get ``vZipWith`` in below code snippet working: {-# LANGUAGE DataKinds #-} {-# LANGUAGE PolyKinds #-} {-# LANGUAGE KindSignatures #-} {-# LANGUAGE TypeOperators #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE RankNTypes #-} {-# LANGUAGE GADTs #-} {-# LANGUAGE StandaloneDeriving #-} {-# LANGUAGE UndecidableInstances #-} {-# OPTIONS_GHC -fplugin GHC.TypeLits.Normalise #-} import GHC.TypeLits import Data.Proxy data Vect :: (Nat -> * -> *) where VNil :: Vect 0 a VCons :: a -> Vect n a -> Vect (1+n) a deriving instance (Show a) => Show (Vect n a) vlength :: forall n a . KnownNat n => Vect n a -> Integer vlength _ = natVal (Proxy :: Proxy n) vconcat :: Vect n a -> Vect m a -> Vect (n+m) a -- Need type checker plugin vconcat VNil ys = ys vconcat xs VNil = xs vconcat (VCons x xs) ys = VCons x (vconcat xs ys) type family Min3 (t :: Bool) (m :: Nat) (n :: Nat) :: Nat type instance Min3 'True m n = m type instance Min3 'False m n = n type Min m n = Min3 (m <=? n) m n vZipWith :: (a -> b -> c) -> Vect m a -> Vect n b -> Vect (Min m n) c vZipWith f VNil _ = VNil vZipWith f _ VNil = VNil vZipWith f (VCons x xs) (VCons y ys) = f x y `VCons` vZipWith f xs ys As I got errors: /home/wangbj/downloads/stack/vect/src/Vect.hs:51:21: Could not deduce (Min3 (m <=? 0) m 0 ~ 0) from the context (n ~ 0) bound by a pattern with constructor VNil :: forall a. Vect 0 a, in an equation for ‘vZipWith’ at /home/wangbj/downloads/stack/vect/src/Vect.hs:51:14-17 Expected type: Vect (Min m n) c Actual type: Vect 0 c Relevant bindings include vZipWith :: (a -> b -> c) -> Vect m a -> Vect n b -> Vect (Min m n) c (bound at /home/wangbj/downloads/stack/vect/src/Vect.hs:50:1) In the expression: VNil In an equation for ‘vZipWith’: vZipWith f _ VNil = VNil /home/wangbj/downloads/stack/vect/src/Vect.hs:52:40: Could not deduce (Min3 (m <=? n) m n ~ (1 + Min3 (n1 <=? n2) n1 n2)) from the context (m ~ (1 + n1)) bound by a pattern with constructor VCons :: forall a (n :: Nat). a -> Vect n a -> Vect (1 + n) a, in an equation for ‘vZipWith’ at /home/wangbj/downloads/stack/vect/src/Vect.hs:52:13-22 or from (n ~ (1 + n2)) bound by a pattern with constructor VCons :: forall a (n :: Nat). a -> Vect n a -> Vect (1 + n) a, in an equation for ‘vZipWith’ at /home/wangbj/downloads/stack/vect/src/Vect.hs:52:26-35 Expected type: Vect (Min m n) c Actual type: Vect (1 + Min n1 n2) c Relevant bindings include ys :: Vect n2 b (bound at /home/wangbj/downloads/stack/vect/src/Vect.hs:52:34) xs :: Vect n1 a (bound at /home/wangbj/downloads/stack/vect/src/Vect.hs:52:21) vZipWith :: (a -> b -> c) -> Vect m a -> Vect n b -> Vect (Min m n) c (bound at /home/wangbj/downloads/stack/vect/src/Vect.hs:50:1) In the expression: f x y `VCons` vZipWith f xs ys In an equation for ‘vZipWith’: vZipWith f (VCons x xs) (VCons y ys) = f x y `VCons` vZipWith f xs ys Failed, modules loaded: none. Also I tried https://github.com/yav/type-nat-solver but got error like: *** Exception: user error (Unexpected result from the SMT solver: Expected: success Result: (error "line 57 column 16: unknown constant tn_0" ) Which I have no idea what it really means. Is there any way to get ``vZipWith`` working without too much hassle? Thanks baojun

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Type-class predicates head-normal forms
by sheng chen 01 Jul '16

01 Jul '16

Hello, I got a question about what the form of types in Haskell are allowed. Specifically, what are the requirements of the context of a type? The paper Typing Haskell in Haskell required the type to be in the form P => t, where P to be in head-normal form or in other words shouldn't be something like Num Bool. Now what about multi-parameter classes? The paper Type classes: an exploration of the design space listed several potential choices but didn't say exactly what. The Haskell 2010 report covered single-parameter type classes only. Given the following definition. class Collects ce e | ce -> e where empty :: ce insert :: e -> ce -> ce insert2 c = insert True (insert False c) The function insert2 has the following type insert2 :: Collects ce Bool => ce -> ce This shows that the definition of head-normal forms for multi-parameter class differs from that for single-parameter classes. Is there any definite specification about the context of Haskell types? Thank you, Sheng

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ICFP 2016 Student Research Competition: Call for Submissions
by Lindsey Kuper 01 Jul '16

01 Jul '16

====================================================================== CALL FOR SUBMISSIONS SRC at ICFP 2016 Nara, Japan 18-24 September 2016 http://conf.researchr.org/info/icfp-2016/student-research-competition Co-located with the International Conference on Functional Programming (ICFP 2016) ====================================================================== Student Research Competition ---------------------------- This year ICFP will host a Student Research Competition where undergraduate and postgraduate students can present posters. The SRC at ICFP 2016 consists of three rounds: * Extended abstract round. All students are encouraged to submit an extended abstract of up to 800 words outlining their research. * Poster session. Based on the abstracts, a panel of judges will select the most promising entrants to participate in the poster session which will take place at ICFP. Students who make it to this round will be eligible for some travel support to attend the conference. In the poster session, students will have the opportunity to present their work to the judges, who will select three finalists in each category (graduate/undergraduate) to advance to the next round. * ICFP presentation. The last round will consist of an oral presentation at ICFP to compete for the final award. Prizes ------ * The top three graduate and the top three undergraduate winners will receive prizes of $500, $300, and $200, respectively. * All six winners will receive award medals and a two-year complimentary ACM student membership, including a subscription to ACM's Digital Library. * The names of the winners will be posted on the ACM SRC web site. * The first-place winners will be invited to participate in the ACM SRC Grand Finals, an on-line round of competition among the winners of conference-hosted SRCs. * Grand Finalists and their advisors will be invited to the Annual ACM Awards Banquet for an all-expenses-paid trip, where they will be recognized for their accomplishments along with other prestigious ACM award winners, including the winner of the Turing Award (also known as the Nobel Prize of Computing). * The top three graduate Grand Finalists will receive an additional $500, $300, and $200. Likewise, the top three undergraduate Grand Finalists will receive an additional $500, $300, and $200. All six Grand Finalists will receive Grand Finalist certificates. * The ACM, Microsoft Research, and our industrial partners provide financial support for students attending the SRC. You can find more information about this on the ACM website. Eligibility ----------- The SRC is open to both undergraduate (not in a PhD programme) and graduate students (in a PhD programme). Upon submission, entrants must be enrolled as a student at their universities, and are ACM student members. Furthermore, there are some constraints on what kind of work may be submitted. Previously published work: Submissions should consist of original work (not yet accepted for publication). If the work is a continuation of previously published work, the submission should focus on the contribution over what has already been published. We encourage students to see this as an opportunity to get early feedback and exposure for the work they plan to submit to the next ICFP or POPL. Collaborative work: Students are encouraged to submit work they have been conducting in collaboration with others, including advisors, internship mentors, or other students. However, submissions are individual, so they must focus on the contributions of the student. Submission Details ------------------ Each submission should include the student author's name, institutional affiliation, e-mail address, and postal address; research advisor's name; ACM student member number; category (undergraduate or graduate); research title; and an extended abstract addressing the following: * Problem and Motivation: Clearly state the problem being addressed and explain the reasons for seeking a solution to this problem. * Background and Related Work: Describe the specialized (but pertinent) background necessary to appreciate the work. Include references to the literature where appropriate, and briefly explain where your work departs from that done by others. * Approach and Uniqueness: Describe your approach in attacking the problem and clearly state how your approach is novel. * Results and Contributions: Clearly show how the results of your work contribute to computer science and explain the significance of those results. The abstract must describe the student's individual research and must be authored solely by the student. If the work is collaborative with others and/or part of a larger group project, the abstract should make clear what the student's role was and should focus on that portion of the work. The extended abstract must not exceed 800 words and must not be longer than 2 pages. The reference list does not count towards these limits. To submit an abstract, please register through the submission page and follow the instructions. Abstracts submitted after the deadline may be considered at the committee's discretion, but only after decisions have been made on all abstracts submitted before the deadline. If you have any problems, don't hesitate to contact the competition chair. Please submit your abstract at the EasyChair submission page: https://easychair.org/conferences/?conf=icfp2016src Important Dates --------------- * Deadline for submission: 3 August * Notification of acceptance: 10 August Selection Committee ------------------- To include: Chair: David Van Horn, University of Maryland Ronald Garcia, University of British Columbia Ilya Sergey, University College London

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Deadline extended: Commercial Users of Functional Programming Call For Tutorials
by Lindsey Kuper 01 Jul '16

01 Jul '16

The 2016 Commercial Users of Functional Programming (CUFP) call for tutorials have passed the initial deadlines, but we have more seat for tutors. CUFP tutorial is a good opportunity if you have some idea you want to spread to the real world, say, your favorite programming language (Clojure, Erlang, F#, F*, Haskell, ML, OCaml, Scala, Scheme...), concepts (e.g. Lens, Liquid-Haskell, Proof Assistance, ...), applications (Web, high-performance computing, finance...,) tools and techniques (QuickCheck, Elm, ...), or theories. If you are interested, we kindly invite you to submit a proposal for the Call For Tutorials from here: http://cufp.org/2016/call-for-tutorials.html , before July 3rd. If you have any questions, please do not hesitate to contact us: Roman Gonzalez: roman(a)unbounce.com Takayuki Muranushi: muranushi(a)gmail.com best regards, Takayuki

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