- Haskell-Cafe - Haskell.org

project compile with multi-versions of alex
by Zilin Chen 18 Jan '16

18 Jan '16

Hi Cafe, I have a Haskell project which has ~90 dependencies (transitively) and is managed with plain cabal (w/o stackage, etc.). I try to keep it compile with a few latest releases of GHC (so right now 7.8.4, 7.10.1, 7.10.2 and 7.10.3). It was tractable with conditionals in the cabal config file with minor annoyance. But recently I found this issue:language-c-quote-0.11.3 does not compile with alex 3.1.5 [1]. I was wondering if I should also allow a few versions of executables, like alex, happy, etc (I can see though it will be a huge pain); or should I force all users to use the latest versions of them (I don't know if they are compatible with old ghc versions)? What's the common practice for other projects? Any hints? What should I write in my cabal config? Thanks, Zilin [1]https://github.com/mainland/language-c-quote/issues/57

2 1

ANN: stack-1.0.2
by Emanuel Borsboom 18 Jan '16

18 Jan '16

New version released of Stack, a build tool. See haskellstack.org for installation and upgrade instructions. Release notes: - Arch Linux: Stack has been adopted into the official community repository <https://www.archlinux.org/packages/community/x86_64/stack/>, so we will no longer be updating the AUR with new versions. See the install/upgrade guide <http://docs.haskellstack.org/en/stable/install_and_upgrade.html#arch-linux> for current download instructions. Major changes: - stack init and solver overhaul #1583 <https://github.com/commercialhaskell/stack/pull/1583> Other enhancements: - Disable locale/codepage hacks when GHC >=7.10.3 #1552 <https://github.com/commercialhaskell/stack/issues/1552> - Specify multiple images to build for stack image container docs <http://docs.haskellstack.org/en/v1.0.2/yaml_configuration.html#image> - Specify which executables to include in images for stack image container docs <http://docs.haskellstack.org/en/v1.0.2/yaml_configuration.html#image> - Docker: pass supplemantary groups and umask into container - If git fetch fails wipe the directory and try again from scratch #1418 <https://github.com/commercialhaskell/stack/issues/1418> - Warn if newly installed executables won’t be available on the PATH #1362 <https://github.com/commercialhaskell/stack/issues/1362> - stack.yaml: for stack image container, specify multiple images to generate, and which executables should be added to those images - GHCI: add interactive Main selection #1068 <https://github.com/commercialhaskell/stack/issues/1068> - Care less about the particular name of a GHCJS sdist folder #1622 <https://github.com/commercialhaskell/stack/issues/1622> - Unified Enable/disable help messaging #1613 <https://github.com/commercialhaskell/stack/issues/1613> Bug fixes: - Don’t share precompiled packages between GHC/platform variants and Docker #1551 <https://github.com/commercialhaskell/stack/issues/1551> - Properly redownload corrupted downloads with the correct file size. Mailing list discussion <https://groups.google.com/d/msg/haskell-stack/iVGDG5OHYxs/FjUrR5JsDQAJ> - Gracefully handle invalid paths in error/warning messages #1561 <https://github.com/commercialhaskell/stack/issues/1561> - Nix: select the correct GHC version corresponding to the snapshot even when an abstract resolver is passed via --resolver on the command-line. #1641 <https://github.com/commercialhaskell/stack/issues/1641> - Fix: Stack does not allow using an external package from ghci #1557 <https://github.com/commercialhaskell/stack/issues/1557> - Disable ambiguous global ‘—resolver’ option for ‘stack init’ #1531 <https://github.com/commercialhaskell/stack/issues/1531> - Obey --no-nix flag - Fix: GHCJS Execute.hs: Non-exhaustive patterns in lambda #1591 <https://github.com/commercialhaskell/stack/issues/1591> - Send file-watch and sticky logger messages to stderr #1302 <https://github.com/commercialhaskell/stack/issues/1302> #1635 <https://github.com/commercialhaskell/stack/issues/1635> - Use globaldb path for querying Cabal version #1647 <https://github.com/commercialhaskell/stack/issues/1647>

1 0

Haskell Weekly News
by Kim-Ee Yeoh 15 Jan '16

15 Jan '16

*Top Picks:* - Team GHC announces the first release candidate of version 8.0 <http://haskell.1045720.n5.nabble.com/ANNOUNCE-Glasgow-Haskell-Compiler-8-0-…>. New features include: - Strict and StrictData extensions - TypeFamilyDependencies extension for injective type families <https://ghc.haskell.org/trac/ghc/wiki/InjectiveTypeFamilies> - TypeInType extension for more dependent typing hackery - explicit type application in plain Haskell, not Core - Applicative do-notation - a spanking new pattern-match checker - modularization of the ghci interpreter: it can now run as an independent process Note that the announcement includes a list of bugs linked to the new features. - The engineers at an Australian real estate listings website explain how they "used Category Theory to solve a problem in Java." <http://techblog.realestate.com.au/how-we-used-category-theory-to-solve-a-pr…> They face the problem of their search API having grown gnarly and inextensible. First they offer a monoid tutorial culminating in SearchResults -> SearchResults endomorphisms. Then they regularize their database lookups as Kleisli-composable instances of a monomorphic state monad of type (DataSource, SearchResults) -> SearchResults. Finally, they profunctorize the state monad for mereological development of the DataSource. So how was the blog post received? A vocal section of the HN community express skepticism <https://news.ycombinator.com/item?id=10892696>. One haskell subredditor found it "an excellent article." <https://www.reddit.com/r/haskell/comments/40s85b/how_we_used_category_theor…> - Verity Stob <https://en.wikipedia.org/wiki/Verity_Stob>, the doyen of information technology satire, skewers the cargo culting of Functional Programming <http://www.theregister.co.uk/2016/01/13/stob_remember_the_monoids/> and by the by writes a monad tutorial (omg!). Haskell redditors chuckle and cluck at the hatchet job <https://www.reddit.com/r/haskell/comments/40wqzf/learn_you_func_prog_on_fiv…> . - Team Wander Nauta creates Viskell <https://github.com/wandernauta/viskell>, "an experimental visual programming environment for a typed (Haskell-like) functional programming language." Programming with touch tablets in mind, he implements Viskell in Java 8 because "Haskell lacks suitable GUI libraries, and we need good multi-touch support." A slides PDF contains more screenshots. <https://github.com/wandernauta/viskell/blob/master/viskell-nlfpday.pdf> Well-received on both Hacker News <https://news.ycombinator.com/item?id=10874294> and /r/haskell <https://www.reddit.com/r/haskell/comments/406au9/viskell_visual_programming…> . *Quotes of the Week:* - Tom Ellis: <https://news.ycombinator.com/item?id=10870488#up_10874714> In Haskell you don't fight the type system. It fights your bugs. - Jeremy Bowers: <https://news.ycombinator.com/item?id=10892293#up_10896419> The reason I find Haskell interesting is precisely that it's the only place I know where the theoretically-minded and the practically-minded get together and interpollinate. Everywhere else the one group pretty much just sneers at the other. - Redditor lukewarm: <https://www.reddit.com/r/haskell/comments/40aa4n/how_to_make_industry_quali…> Yes, you can write industry quality software in Haskell. Do all your computations in the IO monad, keep intermediate results in MVars. Use only Int and String types. Use exceptions to handle errors. Write yourself custom constructs to emulate for and while loops, preferably using Template Haskell. -- Kim-Ee

1 0

repa parallelization results
by Anatoly Yakovenko 14 Jan '16

14 Jan '16

https://gist.github.com/aeyakovenko/bf558697a0b3f377f9e8 so i am seeing basically results with N4 that are as good as using sequential computation on my macbook for the matrix multiply algorithm. any idea why? Thanks, Anatoly

5 19

Call for Participation: BOB 2016 (February 19, Berlin)
by Stefan Wehr 14 Jan '16

14 Jan '16

Quick reminder: the early registration deadline for BOB 2016 is this Sunday! We have some interesting Haskell talks and tutorials at BOB 2016! ================================================================ BOB 2016 Conference "What happens if we simply use what's best?" February 19, 2016 Berlin http://bobkonf.de/2016/ Program: http://bobkonf.de/2016/program.html Registration: http://bobkonf.de/2016/registration.html ================================================================ BOB is the conference for developers, architects and decision-makers to explore technologies beyond the mainstream in software development, and to find the best tools available to software developers today. Our goal is for all participants of BOB to return home with new insights that enable them to improve their own software development experiences. The program features 14 talks and 8 tutorials on current topics: http://bobkonf.de/2016/program.html The subject range of talks includes functional programming, advanced front-end development, data management, and sophisticated uses of types. The tutorials feature introductions to Erlang, Haskell, Scala, Isabelle, Purescript, Idris, Akka HTTP, and Specification by Example. Elise Huard will hold the keynote talk - about Languages We Love. Registration is open online: http://bobkonf.de/2016/registration.html NOTE: The early-bird rates expire on January 17, 2016! BOB cooperates with the :clojured conference on the following day. There is a registration discount available for participants of both events. http://www.clojured.de/

1 0

Hiring: Haskell at Biotech Startup!
by Andrew Gibiansky 13 Jan '16

13 Jan '16

Hello haskell-cafe, I'm an engineer at Karius, a "stealth-mode" biotech startup in Menlo Park, CA, and we're looking to hire a few folks to write software (and we use Haskell!). Currently only hiring locally or with relocation (though that could change in the future, so feel free to get in touch regardless!). We are a team of crazy biologists, engineers, data scientists and clinicians on a mission to change forever the way infectious diseases are diagnosed and treated. We face incredibly interesting challenges in software engineering, machine learning and molecular biology, as we push the limits of diagnostics and genomic technologies. We're hiring computational biologists, software engineers and data scientists. If you're a software engineer, we're looking for experience in front-end, back-end, web development, intrastructure, devops, bioinformatics, and machine learning. We have a varied list of challenges; we build large data processing pipelines to analyze data from in-house DNA sequencers, separate the signal from the noise and extract what we need, and visualize this in ways that are helpful for scientists and doctor; we build web apps and tools for biologists and doctors to use to plan, conduct, and analyze experiments; we work closely with molecular biologists to analyze data generated by these experiments and develop novel computational biology methods. Our technology stack, as of right now: - Python (for bioinformatics) - Rails (for one backend codebase in maintenance mode) - React and ES6 (for front-end interfaces) - Haskell (for infrastructure and new development) - Backed by AWS and Docker We just put our first large Haskell application into production and are planning on continuing with Haskell; this is an opportunity to use Haskell at a cutting-edge biotechnology startup. If any of this sounds exciting to you, please don't hesitate to get in touch with us by emailing Greg Stock atgstock(a)kariusdx.com. Take a look at our job postings on AngelList <https://angel.co/karius/jobs> for more detail, though they won't say much about Haskell. You may know me personally from my work with IHaskell <http://github.com/gibiansky/IHaskell> and my hindent style <http://github.com/chrisdone/hindent>; Greg Weber is also here at Karius, whom you may know from his contributions to Persistent <http://github.com/yesodweb/persistent>, Yesod <http://github.com/yesodweb/yesod>, and Shelly <https://github.com/yesodweb/Shelly.hs>. -- Andrew Gibiansky

1 0

7.10.3 source link missing
by aditya siram 13 Jan '16

13 Jan '16

Hi all, Just wanted to make haskell.org maintainers aware that 7.10.3 release does not provide a link to the source distribution on the Download page. https://www.haskell.org/ghc/download_ghc_7_10_3#sources. Thanks! -deech

1 1

New release of the book Haskell Programming from first principles
by Christopher Allen 13 Jan '16

13 Jan '16

I'd been reticent in the past to announce the book on the mailing list, but it's pretty comprehensive now and we have enough ecstatic readers learning Haskell with it that I thought I'd share what we've been up to. We're writing this Haskell book (http://haskellbook.com/) because many have found learning Haskell to be difficult and it doesn't have to be. We have a strong focus on writing it to be a book for learning and teaching - it's not just a reference or review of topics. Particularly, we strive to make the book suitable for self-learners. We think Haskell is a really nice language and learning Haskell should be as nice as using it is. The new release puts the book at 26 chapters and 1,156 pages. You can track our progress here: http://haskellbook.com/progress.html The latest release included parser combinators, composing types, and monad transformers. My coauthor Julie Moronuki has never programmed before learning Haskell to work with me on this book. She has written about using the book to teach her 10 year old son as well - https://superginbaby.wordpress.com/2015/04/08/teaching-haskell-to-a-10-year… Julie has also written about learning Haskell more generally - https://superginbaby.wordpress.com/2015/05/30/learning-haskell-the-hard-way/ If you've been reading the book, please speak up and share your thoughts. We have some reader feedback on the site at http://haskellbook.com/feedback.html We'll be looking for a press to do a print run of the book soon as it's about 80% done. If anyone has any pointers or recommendations on whom to work with, particularly university presses, please email me. Cheers everyone, Chris Allen

6 8

Why does shift's function return result in Cont and reset reinsert result into Cont again?
by Dmitriy Matrosov 12 Jan '16

12 Jan '16

Hi. I've read "Introduction to Programming with Shift and Reset" by Kenichi Asai and Oleg Kiselyov , where shift and reset defined as > import Control.Monad.Cont > > shift :: ((a -> w) -> Cont w w) -> Cont w a > shift f = cont (flip runCont id . f) > > reset :: Cont a a -> Cont w a > reset = return . flip runCont id > > shiftT :: Monad m => ((a -> m w) -> ContT w m w) -> ContT w m a > shiftT f = ContT (flip runContT return . f) > > resetT :: Monad m => ContT a m a -> ContT w m a > resetT = lift . flip runContT return But why should function f return result in Cont, which i'll unwrap immediately? And why should i reinsert delimited continuation's result into Cont again in reset? Wouldn't it be simpler (better?) to just define shift/reset like > shift' :: ((a -> w) -> w) -> Cont w a > shift' = cont > > reset' :: Cont w w -> w > reset' m = runCont m id > > shiftT' :: ((a -> m w) -> m w) -> ContT w m a > shiftT' = ContT > > resetT' :: Monad m => ContT w m w -> m w > resetT' m = runContT m return Moreover, Bubble-up semantics proof of Cont bubble elimination is (literally) correct only with reset' (below is my bubble implementation, may be i've written it wrong?): > data Bubble w a b = Bubble (a -> Bubble w a b) ((a -> w) -> Bubble w a w) > | Value b > > instance Monad (Bubble w a) where > return x = Value x > Value x >>= h = h x > Bubble k f >>= h = Bubble (\x -> k x >>= h) f > > convBub'2 :: Bubble w a b -> Cont w b > convBub'2 (Value x) = return x > convBub'2 (Bubble k f) = cont $ \t -> runCont (fC (\x -> runCont (kC x) t)) id > where > --fC :: (a -> w) -> Cont w w > fC = convBub'2 . f > --kC :: a -> Cont w b > kC = convBub'2 . k > > bubbleResetProp :: Eq w => Bubble w a w -> Bool > bubbleResetProp b@(Value x) = reset' (convBub'2 b) == x > bubbleResetProp b@(Bubble k f) = > reset' (convBub'2 b) == reset' (fC (\x -> reset' (kC x))) > where > --fC :: (a -> w) -> Cont w w > fC = convBub'2 . f > --kC :: a -> Cont w b > kC = convBub'2 . k > > infixl 0 === > (===) :: a -> a -> a > (===) = const > > bubbleResetProof :: Bubble w a w -> w > bubbleResetProof (Bubble k f) = > reset' (cont $ \t -> runCont (fC (\x -> runCont (kC x) t)) id) > === runCont (cont $ \t -> runCont (fC (\x -> runCont (kC x) t)) id) id > === (\t -> runCont (fC (\x -> runCont (kC x) t)) id) id > === runCont (fC (\x -> runCont (kC x) id)) id > === reset' (fC (\x -> reset' (kC x))) > where > --fC :: (a -> w) -> Cont w w > fC = convBub'2 . f > --kC :: a -> Cont w b > kC = convBub'2 . k -- Dmitriy Matrosov

2 1

Re: [Haskell-cafe] New release of the book Haskell Programming from first principles
by Johannes Waldmann 12 Jan '16

12 Jan '16

Chris - Impressive amount of work! Since this is "cafe" ... allow me to put my standard rant here: Browsing your table of contents, I certainly agree that lambda calculus is a first principle. But when I teach (beginners or not) I put algebraic data types and pattern matching even before functions. Because I want to first describe data, then transformation of data. (Yes, I know, we can simulate data with functions. We can also simulate lambda calculus with term rewriting. No winner there..) And testing really should go as early as possible (lecture 1 or 2, ideally). I don't really know how to do this from first principles and early, because we need some type-classes here (deriving Eq and Show, and also Serial, for automated test case generation. Which should be a strong selling point.) And I do avoid numbers, lists and strings. Really. Functional programming tragically over-uses lists, and by extension, strings. (Of course, other languages also tragically over-use strings.) When I need a list, I have the students write down the data declaration. When I need numbers (mostly I don't), it's Peano numbers. Yes, lazy lists have a purpose in Haskell (expressing control) but this only works if they're being fused away. Later, when we have modules and type classes (for abstract data types), students can learn to use different representations for sequences. But if you start feeding them lists/strings, they'll think it's natural, and have a hard time switching to Data.Sequence, Data.Vector, Data.Text ... I know I did. Well. I'm sure you've given this a lot of thought. I see that you refer to Brent Yorgey's course https://github.com/bitemyapp/learnhaskell#yorgeys-cis194-course and there we have "data"/"case" in lecture 2. Oh, and I do have to read up on how he sells Applicative/Monad. For me, Monad feels more natural, but that's just because I learned it earlier, and now I have to unlearn it. And that illustrates the point I'm making about lists and strings. Best - Johannes.

2 1