April 2017 - Haskell-Cafe

[ANN] Karps-0.2.0 Haskell frontend and optimizer for Apache Spark's dataframes and datasets
by Karps 11 Apr '17

11 Apr '17

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How does GHC avoid "<stderr>: hPutChar: invalid argument (invalid character)"?
by Yuji Yamamoto 11 Apr '17

11 Apr '17

Hello Haskellers, Currently, I’m working on this issue <https://github.com/haskell/haddock/pull/566>, where haddock crashes when printing the Unicode “bullet character” <http://www.fileformat.info/info/unicode/char/2022/index.htm> on stderr whose character encoding is not UTF-8. In the beforementioned pull request, I just added hSetEncoding stderr utf8 as a quick-and-dirty workaround. But GHC actually doesn’t do so: GHC prints “?” instead of the bullet character when stderr is not Unicode-compatible. So, I believe there’s a better way to handle the case, and GHC knows it. Then, how does GHC detect the handle’s character encoding and convert incompatible characters (such as the bullet character) into “?” to avoid the error? I couldn’t get it by reading the source of GHC a bit. Thanks in advance!

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Journal of Functional Programming - Call for PhD Abstracts
by Graham Hutton 11 Apr '17

11 Apr '17

Dear all, If you or one of your students recently completed a PhD in the area of functional programming, please submit the dissertation abstract for publication in JFP: simple process, no refereeing, deadline 30th April 2017. Please share! Best wishes, Graham Hutton ============================================================ CALL FOR PHD ABSTRACTS Journal of Functional Programming Deadline: 30th April 2017 http://tinyurl.com/jfp-phd-abstracts ============================================================ PREAMBLE: Many students complete PhDs in functional programming each year. As a service to the community, the Journal of Functional Programming publishes the abstracts from PhD dissertations completed during the previous year. The abstracts are made freely available on the JFP website, i.e. not behind any paywall. They do not require any transfer of copyright, merely a license from the author. A dissertation is eligible for inclusion if parts of it have or could have appeared in JFP, that is, if it is in the general area of functional programming. The abstracts are not reviewed. Please submit dissertation abstracts according to the instructions below. We welcome submissions from both the PhD student and PhD advisor/supervisor although we encourage them to coordinate. ============================================================ SUBMISSION: Please submit the following information to Graham Hutton <graham.hutton(a)nottingham.ac.uk> by 30th April 2017. o Dissertation title: (including any subtitle) o Student: (full name) o Awarding institution: (full name and country) o Date of PhD award: (month and year; depending on the institution, this may be the date of the viva, corrections being approved, graduation ceremony, or otherwise) o Advisor/supervisor: (full names) o Dissertation URL: (please provide a permanently accessible link to the dissertation if you have one, such as to an institutional repository or other public archive; links to personal web pages should be considered a last resort) o Dissertation abstract: (plain text, maximum 1000 words; you may use \emph{...} for emphasis, but we prefer no other markup or formatting in the abstract, but do get in touch if this causes significant problems) Please do not submit a copy of the dissertation itself, as this is not required. JFP reserves the right to decline to publish abstracts that are not deemed appropriate. ============================================================ PHD ABSTRACT EDITOR: Graham Hutton School of Computer Science University of Nottingham Nottingham NG8 1BB United Kingdom ============================================================ This message and any attachment are intended solely for the addressee and may contain confidential information. If you have received this message in error, please send it back to me, and immediately delete it. Please do not use, copy or disclose the information contained in this message or in any attachment. Any views or opinions expressed by the author of this email do not necessarily reflect the views of the University of Nottingham. This message has been checked for viruses but the contents of an attachment may still contain software viruses which could damage your computer system, you are advised to perform your own checks. Email communications with the University of Nottingham may be monitored as permitted by UK legislation.

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2nd CFP - Only Two Weeks Left: International Workshop on OCL and Textual Modeling (OCL 2017)
by Achim D. Brucker 10 Apr '17

10 Apr '17

(Apologies for duplicates) -- Dr. Achim D. Brucker | Software Assurance & Security | University of Sheffield https://www.brucker.ch | https://logicalhacking.com/blog @adbrucker | @logicalhacking

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Same code, system, but different arch using Win32 for reading registry.
by Akos Marton 10 Apr '17

10 Apr '17

Dear Haskellers, The setup: Having a binary compiled on either x86 or x64 system (same installation, utilizing stack) in order to preserve compatibility against x64 systems. Actually, not to have 2 separate executable for each, that would be the overall goal. However it surprises me when running the x86 .exe utilizing Win32-2.5.4.1 package with ghc-8.0.2, reading out a registry key fails on x64 system with the following:/ / /me.exe: RegOpenKey: invalid argument (The system cannot find the file specified.)/ That would be fine, however the key does exists. When same code, same system, but the .exe built to be x64 it runs like a charm. A couple of question, which some of them eventually will not make sense, but still: - Can it be ghc code optimization issue? - but this is a runtime check in IO, if so, how? - Yes, I could use a built-in windows system command and parse the input of that; unless absolutely necessary I would not introduce another dependency (system package). Would love to solve it with the currently utilized weapons. - the issue just puzzles me... I would know the answer if possible. - Is it more library (Win32), ghc, binary I generate, issue? What library can I use to detect a system's architecture which works in this scenario? Another thing which convoluted in the issue... The function, /getSystemInfo :: IO SYSTEM_INFO, /can read out the underlying architecture. When compiled on x86 and run on x64 it would tell me: "I am running on x86". That's failure. Most importantly: what is the obvious I am missing? Thank you for your insights! Best, Akos Ps.: Would you/we need sample code to puzzle about I can quickly weld one. - not sure if necessary.

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Call for Presentations: CUFP 2017, September 7-9, Oxford, UK
by Jasper Van der Jeugt 10 Apr '17

10 Apr '17

This CFP and the form for submitting presentations proposals can be found at: http://cufp.org/2017/call-for-presentations.html ------------------------------------------------------------------------ 2017 Call for Presentations Workshop for Commercial Users of Functional Programming 2017 Sponsored by SIGPLAN CUFP 2017 Co-located with ICFP 2017 Oxford, UK September 7-9 Talk Proposal Submission Deadline: 9 June 2017 The annual CUFP event is a place where people can see how others are using functional programming to solve real world problems; where practitioners meet and collaborate; where language designers and users can share ideas about the future of their favorite language; and where one can learn practical techniques and approaches for putting functional programming to work. ------------------------------------------------------------------------ Giving a CUFP Talk If you have experience using functional languages in a practical setting, we invite you to submit a proposal to give a talk at the event. We're looking for two kinds of talks: Retrospective reports are typically 25 minutes long. Now that CUFP has run for more than a decade, we intend to invite past speakers to share what they’ve learned after a decade spent as commercial users of functional programming. We will favour experience reports that include technical content. Technical talks are also 25 minutes long, and should focus on teaching the audience something about a particular technique or methodology, from the point of view of someone who has seen it play out in practice. These talks could cover anything from techniques for building functional concurrent applications, to managing dynamic reconfigurations, to design recipes for using types effectively in large-scale applications. While these talks will often be based on a particular language, they should be accessible to a broad range of programmers. We strongly encourage submissions from people in communities that are underrepresented in functional programming, including but not limited to women; people of color; people in gender, sexual and romantic minorities; people with disabilities; people residing in Asia, Africa, or Latin America; and people who have never presented at a conference before. We recognize that inclusion is an important part of our ission to promote functional programming. So that CUFP can be a safe environment in which participants openly exchange ideas, we abide by the SIGPLAN Conference Anti-Harassment Policy: http://www.sigplan.org/Resources/Policies/Anti-harassment If you are interested in offering a talk, or nominating someone to do so, please submit your presentation before 09 June 2017 via the CUFP 2017 Presentation Submission Form: https://goo.gl/forms/KPloANxHHwdiaoVj2 You do not need to submit a paper, just a short proposal for your talk. There will be a short scribe's report of the presentations and discussions but not of the details of individual talks, as the meeting is intended to be more of a discussion forum than a technical interchange. Nevertheless, presentations will be recorded and presenters will be expected to sign an ACM copyright release form. Note that we will need presenters to register for the CUFP workshop and travel to Oxford at their own expense. There are some funds available to would-be presenters who require assistance in this respect. ------------------------------------------------------------------------ Program Committee Alex Lang (Tsuru Capital), co-chair Rachel Reese (Mulberry Labs), co-chair Garrett Smith (Guild AI) Danielle Sucher (Jane Street) Jasper Van der Jeugt (Fugue) Yukitoshi Suzuki (Ziosoft) Evelina Gabasova (University of Cambridge) Brian Mitchell (Jet.com) ------------------------------------------------------------------------ More information For more information on CUFP, including videos of presentations from previous years, take a look at the CUFP website at http://cufp.org. Note that presenters, like other attendees, will need to register for the event. Acceptance and rejection letters will be sent out by July 15th. Guidance on giving a great CUFP talk Focus on the interesting bits: Think about what will distinguish your talk, and what will engage the audience, and focus there. There are a number of places to look for those interesting bits. Setting: FP is pretty well-established in some areas, including formal verification, financial processing, and server-side web services. An unusual setting can be a source of interest. If you're deploying FP-based mobile UIs or building servers on oil rigs, then the challenges of that scenario are worth focusing on. Did FP help or hinder in adapting to the setting? Technology: The CUFP audience is hungry to learn about how FP techniques work in practice. What design patterns have you applied, and to what areas? Did you use functional reactive programming for user interfaces, or DSLs for playing chess, or fault-tolerant actors for large-scale geological data processing? Teach us something about the techniques you used, and why we should consider using them ourselves. Getting things done: How did you deal with large-scale software development in the absence of pre-existing support tools that are often expected in larger commercial environments (IDEs, coverage tools, debuggers, profilers) and without larger, proven bodies of libraries? Did you hit any brick walls that required support from the community? Don't just be a cheerleader: It's easy to write a rah-rah talk about how well FP worked for you, but CUFP is more interesting when the talks also cover what doesn't work. Even when the results were all great, you should spend more time on the challenges along the way than on the parts that went smoothly.

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Does this function have a name?
by Paul Brauner 10 Apr '17

10 Apr '17

Hello Haskell Cafe, I had to write the following function and I was wondering if it (or its generalization to Alternative or Traversable) was exposed by some library under a different name: first [] = Nothing first (t:ts) = fmap (:ts) (s t) <|> fmap (t:) (first ts) Somehow it is to "traverse" as "any" is to "all". Cheers, Paul

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Eliminating phantom type
by Timotej Tomandl 09 Apr '17

09 Apr '17

Hi, I have stumbled upon the Control-Monad-ST2 package by Kevin Backhouse, I have decided to expand the code with a run function and replace IO with ST s; and as of now I have removed the functions working on arrays and conversion to IO for the sake of simplicity. Here is the code in its modified form with newtype wrappers removed: {-# LANGUAGE RankNTypes #-} {-# LANGUAGE DeriveFunctor #-} -- Copyright 2013 Kevin Backhouse. -- Copyright 2017 Timotej Tomandl. Modifications import Data.STRef import Control.Monad.ST import Control.Applicative import Control.Monad newtype ST2 r w s a = ST2 { unwrapST2 :: ST s a } deriving (Functor) instance Monad (ST2 r w s) where return x = ST2 $ return x (ST2 m) >>= f = ST2 $ do x <- m unwrapST2 (f x) instance Applicative (ST2 r w s) where pure = return (<*>) = ap -- | This function checks that the sub-computation is polymorphic in -- both type parameters. This means that the sub-computation does not -- read or write any state from the enclosing context. {-# INLINE pureST2 #-} pureST2 :: (forall r w. ST2 r w s a) -> ST2 r' w' s a pureST2 m = m -- | This function checks that the computation is polymorphic in -- both parameters and then returns a pure value {-# INLINE runST2 #-} runST2 :: (forall r w s. ST2 r w s a) -> a runST2 m=runST $ unwrapST2 m -- | This function checks that the sub-computation is polymorphic in -- the @w@ type parameter. This means that the sub-computation does -- not write any state from the enclosing context (but read-only -- operations are permitted). {-# inline readOnlyST2 #-} readOnlyST2 :: (forall w. ST2 r w s a) -> ST2 r w' s a readOnlyST2 m = m -- | Mutable reference. 'ST2Ref' is actually just a newtype of an -- 'STRef', but the @r@ and @w@ type parameters allow the read and -- write dependencies to be tracked by the type system. newtype ST2Ref r w s a = ST2Ref (STRef s a) -- | Create a new reference. The @r@ and @w@ type parameters of the -- reference are unified with the 'ST2' monad to indicate that new -- state is created in the enclosing context. {-# INLINE newST2Ref #-} newST2Ref :: a -> ST2 r w s (ST2Ref r w s a) newST2Ref x = ST2 $ do r <- newSTRef x >>= \ var -> return var return (ST2Ref r) -- | Read a reference. The @w@ type parameter of the reference is not -- unified with the 'ST2' monad to indicate that this access is -- read-only. {-# INLINE readST2Ref #-} readST2Ref :: ST2Ref r w s a -> ST2 r w' s a readST2Ref (ST2Ref r) = ST2 $ readSTRef r -- | Write to a reference. The @w@ type parameter of the reference is -- unified with the 'ST2' monad to indicate that state is written in -- the enclosing context. {-# INLINE writeST2Ref #-} writeST2Ref :: ST2Ref r w s a -> a -> ST2 r w s () writeST2Ref (ST2Ref r) x = ST2 $ writeSTRef r x -- | Modify a reference. {-# INLINE modifyST2Ref #-} modifyST2Ref :: ST2Ref r w s a -> (a -> a) -> ST2 r w s () modifyST2Ref (ST2Ref r) f = ST2 $ modifySTRef r f But as you can see, now all my types got tainted by s even though sharing the same r or w implies sharing the same s. Is there a way how to hide s from the type signatures, but still preserve an ability to write runST2 without resorting to IO/RealWorld? I have tried writing such a function and failed. Timotej Tomandl

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State monad exit
by p75213＠gmail.com 08 Apr '17

08 Apr '17

Hi, I am playing around with the State monad and queues. At the moment I have the following code: {-# LANGUAGE ViewPatterns, FlexibleContexts #-} module Main where import Criterion.Main import Control.Monad.State.Lazy import Data.Maybe (fromJust) import Data.Sequence ((<|), ViewR ((:>))) import qualified Data.Sequence as S -------------------------------------------------------- data Queue a = Queue { enqueue :: [a], dequeue :: [a] } deriving (Eq, Show) -- adds an item push :: a -> Queue a -> Queue a push a q = Queue (a:enqueue q) (dequeue q) pop :: Queue a -> Maybe (a, Queue a) pop q = if null (dequeue q) then go $ Queue [] (reverse (enqueue q)) else go q where go (Queue _ []) = Nothing go (Queue en (x:de)) = Just (x, Queue en de) queueTst :: Int -> Queue Int -> Queue Int queueTst 0 q = q queueTst n q | even n = queueTst (n - 1) (push (100 + n) q) | otherwise = queueTst (n - 1) (if popped == Nothing then q else snd (fromJust popped)) where popped = pop q ------------------------------------------------------------- pushS :: a -> S.Seq a -> S.Seq a pushS a s = a <| s pushS' :: a -> State (S.Seq a) (Maybe a) pushS' a = do s <- get put (a <| s) return Nothing pushS'' :: a -> State (S.Seq a) (Maybe a) pushS'' a = get >>= (\g -> put (a <| g)) >> return Nothing popS :: S.Seq a -> Maybe (a, S.Seq a) popS (S.viewr -> S.EmptyR) = Nothing popS (S.viewr -> s:>r) = Just (r,s) popS' :: State (S.Seq a) (Maybe a) popS' = do se <- get let sl = popS'' se put $ snd sl return $ fst sl where popS'' (S.viewr -> S.EmptyR) = (Nothing, S.empty) popS'' (S.viewr -> beg:>r) = (Just r, beg) queueTstS :: Int -> S.Seq Int -> S.Seq Int queueTstS 0 s = s queueTstS n s | even n = queueTstS (n - 1) (pushS (100 + n) s) | otherwise = queueTstS (n - 1) (if popped == Nothing then s else snd (fromJust popped)) where popped = popS s queueTstST :: Int -> State (S.Seq Int) (Maybe Int) queueTstST n = if (n > 0) then if even n then pushS' (100 + n) >> queueTstST (n - 1) else popS' >> queueTstST (n - 1) else return Nothing main1 :: IO () main1 = defaultMain [ bench "Twin Queue" $ whnf (queueTst 550) (Queue [500,499..1] []) , bench "Sequence Queue" $ whnf (queueTstS 550) (S.fromList [500,499..1]) , bench "State Queue" $ whnf (runState (queueTstST 550)) (S.fromList [500,499..1]) ] -------------------------------------------------------------------------------------------------------------------------------------------------- In the function "queueTstST" is there a way to exit while retaining the last "Maybe value" rather than with "Nothing"?

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LambdaConf standard registration opens
by Salas Sanchez-Bennasar 07 Apr '17

07 Apr '17

http://lambdaconf.us/events/2017/lcusc.html LambdaConf is one of the largest functional programming conferences in the world, focused on foundational concepts (such as lambda calculus, type theory, category theory), functional programming languages (Haskell, Scala, PureScript, F#, Clojure, Elixir, and more), new languages and approaches in functional programming, functional programming libraries, and related areas such as dependent types, proof systems, parallel array programming, functional GPU processing, and more. Standard registration is now open at Eventbrite: https://www.eventbrite.com/e/lambdaconf-2017-registration-29839799644 A complete list of sessions is online, including the following highlights: * 6 keynotes, including one on using Haskell to model life on the blockchain, one on how programmers brains work, and one on the axes of abstraction; * 8 leap workshops, including an in-depth workshop on category theory, one on optics, and one on building front-ends using PureScript Halogen; * 12 hop workshops, including one introducing Coq, another diving into recursion schemes, and another teaching functional data processing; * 9 de novo sessions, including on one formally specified digital logic, one on algebraic and monadic composability for distributed computing, and one on type-level REST programming; * 21 educational sessions, including one on Free monads, one on high-performance Haskell, one on codata and corecursion, one on FP on Android using Frege, and another on dependently-typed programming in Haskell; * 21 inspire sessions, including one on dependent-pairs, one on generative design, and one on type singletons. This is more than 110 hours of content, with enough variety and difficulty level for everyone. Speakers are book authors, contributors to open source libraries, researchers, and practicing functional programmers. The conference takes place in Boulder, Colorado, from May 25 - 27, at the University of Colorado Boulder in the foothills of the Rocky Mountains. Conference registration includes all sessions (including workshops), locally-catered breakfast and lunch on Thursday, Friday, and Saturday; a conference dinner on Friday night; a choice from a variety of networking activities on Sunday; free childcare and STEM workshops for children; all-gender restrooms and handicapped-accessible venues. Videos from some previous events can be found here: https://www.youtube.com/ channel/UCEtohQeDqMSebi2yvLMUItg; and here: https://www.youtube.com/ watch?v=JxC1ExlLjgw&list=PLE7tQUdRKcybh21_zOg8_y4f2oMKDHpUS The conference is preceded by commercial training opportunities on Monday - Tuesday, including: * Up & Running with Elixir & Phoenix, by Brooklyn Zelenka * Applied Haskell, by Michael Snoyman * Advanced FP in Scala, by John A. De Goes * Introduction to FP, by David Koontz * Mastering Apache Spark, by Pawel Szulc * Mastering Elm, by Isaac Shapira On Wednesday, several free mini-conferences are co-located with LambdaConf: * PureScript Conf 2017 * Introduction to FP with Haskell For more information on LambdaConf, the commercial training workshops, or the mini-conferences, please visit the website: http://lambdaconf.us/events/2017/lcusc.html

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