June 2015 - Haskell-Cafe

Haskell users on Chile
by Ruben Astudillo 18 Jun '15

18 Jun '15

Hi all I would like to see how many haskellers are living on Chile with hopes of forming a user group. If you are in here, you should reply this thread and see how many of us there are. You can also contact me to my mail. -- Ruben Astudillo. pgp: 0x3C332311 , usala en lo posible :-) Crear un haiku, en diecisiete silabas, es complica...

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phantom types and record syntax
by Dimitri DeFigueiredo 18 Jun '15

18 Jun '15

Hi All, My apologies if this is not the right forum, but am not satisfied with my current understanding. I am surprised that this program compiles in GHC: ----- data UserSupplied = UserSupplied -- i.e. unsafe data Safe = Safe data Username a = Username { first :: String, last :: String} sanitize :: Username UserSupplied -> Username Safe sanitize name = name { first = "John" } main = putStrLn "Hi!" ----- My trouble is that it seems the record syntax is*implicitly* converting from one type to the other. It seems I would have to remove the phantom type by adding a tag to avoid this: ----- data Username a = Username { first :: String, last :: String, tag :: a } sanitize :: Username UserSupplied -> Username Safe sanitize name = name { first = "John" } -- FAIL as expected!! :-) ----- But this makes me unwilling to use phantom types for security as I would be worried of unwittingly making the conversion. Could somebody sprinkle some insight into why this is "converted automatically" for phantom types? Is there another way around this? Thanks! Dimitri

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Haskell and Spark
by Vasili I. Galchin 18 Jun '15

18 Jun '15

Hello, There was a posting from a Polish guy(Wojcieh .,,,, been trying to contact him) on implementing a library/wrapper for Spark. Does anybody know the status? Vasili

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RFC: "Native -XCPP" Proposal
by Herbert Valerio Riedel 18 Jun '15

18 Jun '15

Hello *, As you may be aware, GHC's `{-# LANGUAGE CPP #-}` language extension currently relies on the system's C-compiler bundled `cpp` program to provide a "traditional mode" c-preprocessor. This has caused several problems in the past, since parsing Haskell code with a preprocessor mode designed for use with C's tokenizer has caused already quite some problems[1] in the past. I'd like to see GHC 7.12 adopt an implemntation of `-XCPP` that does not rely on the shaky system-`cpp` foundation. To this end I've created a wiki page https://ghc.haskell.org/trac/ghc/wiki/Proposal/NativeCpp to describe the actual problems in more detail, and a couple of possible ways forward. Ideally, we'd simply integrate `cpphs` into GHC (i.e. "plan 2"). However, due to `cpp`s non-BSD3 license this should be discussed and debated since affects the overall-license of the GHC code-base, which may or may not be a problem to GHC's user-base (and that's what I hope this discussion will help to find out). So please go ahead and read the Wiki page... and then speak your mind! Thanks, HVR [1]: ...does anybody remember the issues Haskell packages (& GHC) encountered when Apple switched to the Clang tool-chain, thereby causing code using `-XCPP` to suddenly break due to subtly different `cpp`-semantics?

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Canberra Functional Programming Group
by Ivan Lazar Miljenovic 18 Jun '15

18 Jun '15

In case you live in Canberra, Australia and were unaware of this already, Alex Mason (aka Axman6) is helping to arrange/organise a new functional programming group. The first meeting for it is next week on 24 June (including free pizza!). For more information please see http://www.meetup.com/CanFPG/ -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com http://IvanMiljenovic.wordpress.com

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Haskell Weekly News
by Kim-Ee Yeoh 17 Jun '15

17 Jun '15

*Top Picks:* - Andrew Gibiansky <http://www.reddit.com/r/haskell/comments/37uqqk/ihaskell_online_help_choose…> announces the Mathematica-inspired REPL 2.0 IHaskell as a web-app you can play with right now <http://try.jupyter.org/>. Bouquets include: "This is an awesome step up from the tryhaskell window." Also, "I love IHaskell. I've already started preferring it to ghci since it's so much easier to use." More /r/haskell love here <https://www.reddit.com/r/haskell/comments/376aqh/ihaskell_on_tryjupyterorg/> . - Mihai Maruseac and Alejandro Serrano Mena publish the 28th Haskell Communities and Activities Report <https://www.haskell.org/communities/05-2015/html/report.html>. Top comment on HN <https://news.ycombinator.com/item?id=9627260>: "Haskell is backed by a truly amazing community. Haskell will continue to inspire people to build better, safer software. I hope that the values of tolerance, respect and benevolence that most of the Haskell community is supporting will also contribute to make tech a more friendly and equal place for everyone." - Bicycling in circles just to find parking in Utrecht? Bas van Dijk launches a city-wide monitoring system that guides you to a space that's free, dry, and safe <https://bicycledutch.wordpress.com/2015/06/09/bicycle-parking-guidance-syst…>. Written in Haskell 'natch, even the front-end leverages GHCJS. Devops'ed in NixOS. He tips off his fellow redditors <http://www.reddit.com/r/haskell/comments/3959r0/haskellbased_bicycle_parkin…> about using blaze-react to wrap Facebook's React library. HN-worthy <https://news.ycombinator.com/item?id=9690683>. - Announcing on haskell-cafe <http://haskell.1045720.n5.nabble.com/A-Dockerfile-to-provision-a-build-envi…> and /r/haskell <http://www.reddit.com/r/haskell/comments/387uct/building_an_android_game_wr…>, Sean Seefried open sources a Docker script that instantly gets you a Haskell build environment for Android game development <https://github.com/sseefried/docker-epidemic-build-env>. No more fiddling with cross-compiles. He even gives you an open source game <https://github.com/sseefried/open-epidemic-game> all mobile-ready. Thanks, Sean! - Vincent Hanquez releases cryptonite <http://hackage.haskell.org/package/cryptonite>, a single package that consolidates 10-20 other crypto packages. Why? Because maintaining multiple packages is a pain involving fiddling with dependency version bounds and changelog/cabal/version metadata. Benefit for the user? Easier discovery of crypto widgets now that they are all in one haddock, as opposed to hidden in a package whose name eludes you. Kibbitz on /r/haskell <http://www.reddit.com/r/haskell/comments/389tpg/announcing_cryptonite/>. - Joe Nelson <https://news.ycombinator.com/item?id=9642665#up_9643923>discovered Haskell two years ago <http://www.wagonhq.com/blog/first-two-weeks-haskell-wagon> and calls it "moon language." Now he works full-time at Wagon, an all-Haskell start-up offering "a modern data collaboration tool." He's proud of his team that "excels at debugging gnarly issues, including a memory leak caused by a useful yet tricky language feature called lazy evaluation." But what's the buzz that HN <https://news.ycombinator.com/item?id=9703500> and /r/haskell <http://www.reddit.com/r/haskell/comments/39izi6/my_first_two_weeks_of_haske…> latch on? Answer: The pros and cons of effectful point-free refactoring. - Fredrik Olsen migrates from Ruby on Rails (RoR) to Haskell <https://medium.com/@folsen/haskell-in-production-bdellium-1df48de40e19> at fintech start-up Bdellium. Unlike RoR where he "always had a much harder time" with an existing codebase, he testifies that "Haskell let me quickly browse the code, read the types and almost instantly understand the structure and layout of the program." Hiring for RoR nets him "a few hundred applications" where only "10–20% I’d say are people that I’d actually be interested in hiring." Hiring for Haskell gets "50 responses to the Reddit post, all of them were people that I could have hired. Many of the applicants were even grossly over-qualified and were willing to take the job just because it would let them work in Haskell." Ben Ford of Fynder.io corroborates Fredrik in the top comment on /r/haskell <http://www.reddit.com/r/haskell/comments/38nooh/haskell_in_production_bdell…> . Phil Wadler reblogs <http://wadler.blogspot.com/2015/06/haskell-in-production-bdellium.html> the story and zooms in on how Fredrik gained 3.7x parallelism from 4 cores by merely tweaking a single line of code. Control.Parallel.Strategies <http://hackage.haskell.org/package/parallel-3.2.0.6/docs/Control-Parallel-S…> ftw! - Arnaud Bailly <https://news.ycombinator.com/item?id=9642665#up_9643923> shares on HN that he had "no issue finding talent" for Haskell jobs in Singapore. "150 qualified applicants (i.e. passed the test, which was to design an inventory management system in Haskell) for ~10 positions, all foreign; the majority came from the US, Germany and Scandinavia." - If type errors can be deferred, why not also "name not found"? Tom Ellis asks <http://haskell.1045720.n5.nabble.com/fdefer-more-errors-tp5809991.html>. He thinks it would make Haskell "gentler for newcomers." For veterans: even more stub-driven-dev opportunities. Coincidentally, Dan Burton spitballed the same on /r/haskell <http://www.reddit.com/r/haskell/comments/37km7e/fdeferscopeerrors_anyone/>. This idea has a history stretching back at least 3 years: see trac ticket #5910 <https://ghc.haskell.org/trac/ghc/ticket/5910#comment:19>. - David Luposchainsky proposes to move the fail method out of the Monad type class <https://github.com/quchen/articles/blob/master/monad_fail.md>. With the deeply thought out blueprint he provides, /r/haskell reports <http://www.reddit.com/r/haskell/comments/397k1a/monadfail_proposal_mfp_movi…> that the community's already working on it. Discussion on libraries list <http://haskell.1045720.n5.nabble.com/MonadFail-proposal-MFP-Moving-fail-out…> . - Anthony Cowley proposes a shorter syntax for imports on haskell-cafe <http://haskell.1045720.n5.nabble.com/Proposal-Shorter-Import-Syntax-td58104…> and trac <https://ghc.haskell.org/trac/ghc/ticket/10478>. He withdraws his proposal five days later because the "disdainful mockery" and "strongly worded rebuttals" have him overwhelmed on what is only a "nights and weekends project." Reddit discussion here <https://www.reddit.com/r/haskell/comments/38vsef/proposal_shorter_import_sy…> . - Henk-Jan van Tuyl <http://haskell.1045720.n5.nabble.com/a-files-not-found-td5810165.html> runs smack into a library .a-extension File Not Found problem when installing data-default-instances-old-locale on 7.10. Culprit? Windows! And its %&@#! 255-character filepath limit. He is not alone <https://github.com/haskell/cabal/issues/2502>. Why is 7.8 ok? Because package names in the filepath used to be abbreviated. Workaround? Instead of cabal install X, download it first: cabal get X, then cabal install ./X. Thanks to Matej Borovec and Michal Antkiewicz for sorting it out. - FP Complete announces Stack <https://www.fpcomplete.com/blog/2015/06/announcing-first-public-beta-stack>, a replacement for cabal-install <https://hackage.haskell.org/package/cabal-install> the command-line tool (not Cabal the library infrastructure). Stack leverages Stackage <https://www.stackage.org/> Long-Term Support (LTS) releases for a speedy escape from cabal hell. Warmly received on /r/haskell <http://www.reddit.com/r/haskell/comments/3957e1/announcing_first_public_bet…>. Dan Burton blogs on how Stack eases development by removing the need to remember a sequence of cabal commands <http://www.reddit.com/r/haskell/comments/3a6p9h/how_stack_lowers_the_barrie…>. HN-worthy <https://news.ycombinator.com/item?id=9687274> and a troll that Haskell's "an esoteric language that no one uses" provokes many a valiant, evidence-backed defense <https://news.ycombinator.com/item?id=9687274#up_9688248>. - Redditor beerdude26 nudges folks on /r/haskell <http://www.reddit.com/r/haskell/comments/37y1yi/my_approach_to_centralizing…> to continue cultivating the haskell wiki <https://wiki.haskell.org/Haskell>. He sets an example by splicing in the common newtype workaround <https://wiki.haskell.org/Orphan_instance#Common_workaround> into the entry on orphan instances. - In HN news <https://news.ycombinator.com/item?id=9662705>: Cloud Haskell <http://haskell-distributed.github.io/> -- Erlang-style concurrent and distributed programming. Top comment notes that whereas the web site suggests that activity stopped in 2014, CH actually thrives on Github <https://github.com/haskell-distributed>. - In HN news <https://news.ycombinator.com/item?id=9696086>: Haskell wiki entry on Frag <https://wiki.haskell.org/Frag>, a 2005 undergrad project by Mun Hon Cheong who recreated a Quake3-like First-Person Shooter (FPS) game using Yampa FRP. Although a decade old, Cody Goodman <https://news.ycombinator.com/item?id=9696086#up_9696700> reports that he's gotten it to compile. - In HN news <http://news.ycombinator.com/item?id=9704851>: APL lives! A functional programmer investigates APL <http://theburningmonk.com/2015/06/fear-and-loathing-with-apl/>, discovers that it "looks every bit as mind-bending and unbelievable as scenes from Johnny Depp’s *Fear and Loathing in L**as Vegas*", and summarizes the syntax for the benefit of all. *Quotes of the Week:* - A typeclass with only one instance is nonsensical, and often a symptom of trying to use typeclasses as OO classes. -- Brandon Allbery <http://haskell.1045720.n5.nabble.com/Disambiguating-a-Num-RealFrac-instance…> - That Haskell shows the developer things about themselves even they didn't know is enough to make it worth learning. It's mind-bending and ideology-exposing. -- Redditor on /r/haskell <http://www.reddit.com/r/haskell/comments/39ci9j/coming_from_php_working_in_…> - Haskell's great for writing an ugly solution and fixing it later because refactoring is so cheap. No need to get it right the first time. -- Gabriel Gonzalez on Twitter <https://twitter.com/GabrielG439/status/606831084655902720> -- Kim-Ee nights and weekends project

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More instances for Identity?
by Niklas Hambüchen 17 Jun '15

17 Jun '15

Hi, I just noticed that Data.Functor.Identity [1] lacks many useful instances like Eq, Ord, Show ... etc. Is there a reason for this? Otherwise, shouldn't we make a proposal for it? In my opinion, if the seven-tuple has an instance, then Identity deserves it as well. Niklas [1]: https://downloads.haskell.org/~ghc/7.8.3/docs/html/libraries/transformers-0…

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About my commitment to my passions, Haskell and the world
by Jesus Gonzalez 17 Jun '15

17 Jun '15

Hi everybody, I have a very important announcement. I’ve decided to dedicate the next big part of my life to improve the world through Haskell. And you can help! (I’m not asking for money…) I plan to go to live at a “poor” village where my grandparents live. Poor because it is very hard to get a higher education. My grandfather founded some time ago some schools nearby the village, but if people wanted to have a bright future, they had to leave the village. My father moved to the nearest capital city. The story repeated. My father and my mother (together with other people) founded a school at the city where I was born. I left this city to get an even higher education at one of the best universities of my continent. At college, I got the opportunity to study a year as an exchange student at one of the best CS universities in the world. Knowing that probably I would never be able to study at such a good university again, I took the hardest subjects I could. The first semester, I took 2 undergrad courses an 2 grad courses (Program Transformations, Software Design, etc…) This first semester was hard, but at the end I got ok grades, so I thought that maybe I could give a little bit more. For the next semester, I tried to encode the knowledge I acquired as clearly as I could. Very quickly, I got more interested in how to model this knowledge more than the knowledge itself. When I failed with Java, I turned to Haskell and so it begun. I did enjoy my time also. I got to see the inauguration of the Gates Computer Science Building, I found the time to play the piano and learned how to drive the bike without hands very well. When I returned, my parents kindly forced me to finish colleague. When I graduated, I got a scholarship for grad school (that I took, but I left 3 months later) and a job making iOS and Android apps. I couldn’t use Haskell but I did work some months with F#. Now that I’ve seen the world, the good, the bad and the ugly things, Now that I’ve tasted the impoverishing money and repented, Now I’m ready, I flipped the arrows. The hardest thing so far has been to finish my NDA… I’m still on it… It looks like the story will repeat once more. I want to retreat my self and found a next generation school where my grandparents live. I believe that we need to create high performant Haskellers and that we owe to teach children as young and fast as they can happily take it. I would appreciate encouragement, tutorials for all ages and levels of math encoded in Haskell, advice, anything good. I’m already burning bridges! I’ll keep reporting.

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[Hiring] Infrastructure Engineer @ Elastic (makers of Elasticsearch) Location: Anywhere
by Joe Hillenbrand 16 Jun '15

16 Jun '15

Although not strictly a Haskell developer position. Haskel experience/interest is a huge plus. https://www.elastic.co/about/careers/engineering/infrastructure-engineer?id… (Note: the id param is required or else you'll get a 404)

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Type constraint with RankNTypes gradually slows down function?
by Ben Gunton 16 Jun '15

16 Jun '15

When I write a function with the type constraint "embedded" in the function's type declaration, instead of at the beginning, the function takes longer each time it is run. The simplest example I could write is this: http://lpaste.net/134563. "run1" is near instantaneous the first time, but gets marginally slower after each iteration... after thousands of iterations it takes about a millisecond to run (and keeps getting worse). "run2" is always near instantaneous. What is happening in "run1" that makes it slow down? PS: The example is fairly contrived, I know "run1"'s type declaration wouldn't be used in practice. Thanks for any guidance! {-# LANGUAGE RankNTypes #-} {-# LANGUAGE FlexibleContexts #-} module Main where import Control.Monad.State.Strict import qualified Data.Time.Clock as Clock import Control.Exception run1 :: (Int -> (Num Int => State Int Bool)) -> Int -> IO () run1 f state = do t1 <- Clock.getCurrentTime evaluate $ runState (f 1) state t2 <- Clock.getCurrentTime print $ Clock.diffUTCTime t2 t1 run1 f state run2 :: Num s => (Int -> State s Bool) -> s -> IO () run2 f state = do t1 <- Clock.getCurrentTime evaluate $ runState (f 1) state t2 <- Clock.getCurrentTime print $ Clock.diffUTCTime t2 t1 run2 f state main :: IO () main = run1 (const $ return False) 1 --main = run2 (const $ return False) 1

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