- Haskell-Cafe - Haskell.org

a simpler way to declare typeclass instances
by Alexey Muranov 29 Oct '14

29 Oct '14

Hello, i am trying to understand how typeclasses work. I know that they can be used as follows (from the manual): data Foo = Foo {x :: Integer, str :: String} instance Eq Foo where (Foo x1 str1) == (Foo x2 str2) = (x1 == x2) && (str1 == str2) I am wondering, why is the following seemingly unambiguous syntax not allowed too? data Foo = Foo { x :: Integer, str :: String } instance Eq Foo (Foo x1 str1) == (Foo x2 str2) = (x1 == x2) && (str1 == str2) If it was allowed, it seems that it could also be applied to records: class HasName r where name :: r -> String data Bird = Bird { name :: String, wingNumber :: Integer } data Person = Person { name :: String, likesBirds :: Bool } instance HasName Bird instance HasName Person Alexey.

3 4

Polymorphic case for this lens transformer?
by Hans Höglund 28 Oct '14

28 Oct '14

Hi all, I have been using this lens transformer http://lpaste.net/113159. However, I can't seem to find a way to implement the polymorphic case (i.e. Lens instead of Lens'). What am I missing? Hans - Hans Höglund Composer, conductor and developer hans [at] hanshoglund.se hanshoglund.com https://twitter.com/hanshogl https://soundcloud.com/hanshoglund http://github.com/hanshoglund

2 1

Tracking down where an instance comes from
by Mateusz Kowalczyk 28 Oct '14

28 Oct '14

Hi, I'm in a situation where we have a 140+ module program (Yi) with some 30+ packages of dependencies and somewhere along the lines, this little guy gets in: instance [safe] Show (a -> b) -- Defined in ‘Text.Show.Functions’ Of course this automatically infects everything to import Yi. This is bad. What would be the best way to track down through which import this actually comes in? There's nothing directly importing Text.Show.Functions and I wonder if there's a better way than ‘remove imports one by one going deeper each time you hit it’ which might take a while, especially as there seems to be no way to unload instances except restarting GHCi. -- Mateusz K.

4 3

pontarius-xmpp with tls
by Никита Тимофеев 27 Oct '14

27 Oct '14

Who can show a working example code creates a client Session with the server with enabled TLS? -- Timofeev N.D.

1 0

inlinable vs inline
by Charlie Durham 27 Oct '14

27 Oct '14

Hi, I wanted to get some clarifications on how inlinable and inline behave. One particular case is where you have a module exporting some functions with helper functions that are not exported. You go ahead and add inlinable to the exported functions so that the call site can specialize on them. Is there any penalty to adding inline vs inlinable to the helper functions? For example, are there cases where a helper function will not inline and thus can not be specailized at the call site and it would be better to declare the helper function inlinable? I would be interested to hear any nuances related to the differences and practical consequences of these pragmas. Thanks! Charlie Durham

1 0

Wiki Account
by Alper Tekinalp 27 Oct '14

27 Oct '14

Hi. In wiki page it says: " If you would like an account please email "nominolo" (at the email service from Google) or on the haskell-cafe mailing list." I want to create a wiki account. My preferred user name: alpert Can anyone help? Best regards. -- Alper Tekinalp atekinalp.blogspot.com

1 0

Haskell Cheat Sheet
by Rudy Matela 26 Oct '14

26 Oct '14

Hello, All, Some time ago, I was looking for a Haskell Cheat Sheet, to help me remember Haskell's syntax and common functions. I've found one, but it was quite long (14 pages), not what I was looking for. So, I've started building a Haskell Cheat Sheet with the most common language features condensed in two pages. It still needs a lot of improvement (and some content). I'm using LaTeX and I've built a "cls" (so it can be used to create Sheets for other languages as well), it is kind of a hack for now. If someone wants to use it as a reference, the first version can be found on [1] and the TeX source can be found on GitHub [2]. I would appreciate help on it: feel free to fork and make pull requests with new additions (or mail me asking for push permissions). Regards, Rudy [1]: https://matela.com.br/pub/cheat-sheets/haskell-ucs-0.1.pdf [2]: https://github.com/rudymatela/ultimate-cheat-sheets

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Call-for-help: Add XDGBDS support to `directory` package
by Herbert Valerio Riedel 25 Oct '14

25 Oct '14

Hello *, I'd like to invite everyone with knowledge of the XDG Base Directory Specification[1] to contribute to https://github.com/haskell/directory/issues/6 >From what I gathered, it appears to me that adhering to the XDGBD Spec (on Linux at least) is desirable and "strongly encouraged" by Linux distributions[2], so I think this ought to be implemented sooner rather than later (maybe even in time to be part of GHC 7.10.1) This issue was originally filed against GHC, since it affects the location of the `~/.ghc` folder (and fwiw this would also affect cabal's `~/.cabal` folder location). Thanks, hvr [1]: http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html [2]: https://wiki.debian.org/XDGBaseDirectorySpecification

1 0

Parse CSV / TSV file in Haskell - Unicode Characters
by Volker Strobel 24 Oct '14

24 Oct '14

Hi, I'm trying to parse a tab-delimited file using cassava/Data.Csv in Haskell. However, I get problems if there are "strange" (Unicode) characters in my CSV file. I'll get a parse error (endOfInput) then. According to the command-line tool "file", my file has a "UTF-8 Unicode text" decoding. My Haskell code looks like this: {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE OverloadedStrings #-} import qualified Data.ByteString as C import qualified System.IO.UTF8 as U import qualified Data.ByteString.UTF8 as UB import qualified Data.ByteString.Lazy.Char8 as DL import qualified Codec.Binary.UTF8.String as US import qualified Data.Text.Lazy.Encoding as EL import qualified Data.ByteString.Lazy as L import Data.Text.Encoding as E -- Handle CSV / TSV files with ... import Data.Csv import qualified Data.Vector as V import Data.Char -- ord csvFile :: FilePath csvFile = "myFile.txt" -- Set delimiter to \t (tabulator) myOptions = defaultDecodeOptions { decDelimiter = fromIntegral (ord '\t') } main :: IO () main = do csvData <- L.readFile csvFile case EL.decodeUtf8' csvData of Left err -> print err Right dat -> case decodeWith myOptions NoHeader $ EL.encodeUtf8 dat of Left err -> putStrLn err Right v -> V.forM_ v $ \ (category :: String , user :: String , date :: String, time :: String, message :: String) -> do print message I tried using decodingUtf8', preprocessing (filtering) the input with predicates from Data.Char, and much more. However the endOfFile error persists. My CSV-file looks like this: a - - - RT USE " Kenny" • Hahahahahahahahaha. #Emmen #Brandstapel a - - - Uhm .. wat dan ook ????!!!! 👋 Or more literally: a\t-\t-\t-\tRT USE " Kenny" • Hahahahahahahahaha. #Emmen #Brandstapel a\t-\t-\t-\tUhm .. wat dan ook ????!!!! 👋 The problem chars are the 👋 and • (and in my complete file, there are many more of similar characters). What can I do, so that cassava / Data.Csv can read my file properly? I've also posted this question at StackOverflow a few days ago: http://stackoverflow.com/questions/26499831/parse-csv-tsv-file-in-haskell-u… Best, Volker

2 1

Timing execution of individual functions in ghci?
by Magnus Therning 24 Oct '14

24 Oct '14

When playing around with various implementations of a single function it would be nice to time the execution. Is there some way to do that easily from within GHCi? Or am I forced to look to criterion for that? /M -- Magnus Therning OpenPGP: 0xAB4DFBA4 email: magnus(a)therning.org jabber: magnus(a)therning.org twitter: magthe http://therning.org/magnus Heuristic is an algorithm in a clown suit. It’s less predictable, it’s more fun, and it comes without a 30-day, money-back guarantee. -- Steve McConnell, Code Complete

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pattern matches are overlapped
by briand＠aracnet.com 23 Oct '14

23 Oct '14

This works fine keyboardAct a d p (SpecialKey KeyLeft) Down Modifiers {shift=Down, ctrl=Up, alt=Up} = do (x,y) <- get p p $= (x-0.1, y) This keyboardAct a d p (SpecialKey KeyLeft) Down shiftDown = do (x,y) <- get p p $= (x-0.1, y) where, shiftDown = Modifiers {shift=Down, ctrl=Up, alt=Up} gives me : KeyBindings.hs:32:1: Warning: Pattern match(es) are overlapped In an equation for `keyboardAct': keyboardAct angle delta p (SpecialKey KeyLeft) Down Modifiers {shift = Up, ctrl = Up, alt = Up} = ... keyboardAct is used several times via pattern matching, e.g. keyboardAct angle delta p (SpecialKey KeyLeft) Down Modifiers {shift=Up, ctrl=Up, alt=Up} = do (x,y) <- get p a <- get angle d <- get delta angle $= a+d and there are several more. So clearly, the pattern match is overlapped, just like the warning says. The question is why I don't get the same warning before I make use of shiftDown. Thanks Brian

2 1

acid-state problem.
by Magicloud Magiclouds 23 Oct '14

23 Oct '14

Hi, I have following code. In init, I called update, createCheckpoint, and close. So every time the code runs, if the DB did not exist, it would ask some configurations and create one. But actually it asks for init every time. How should I use it? state <- openLocalStateFrom dbFolder $ State ConfNone conf <- query state QueryState case conf of ConfNone -> init state m c -> process state m c -- 竹密岂妨流水过山高哪阻野云飞 And for G+, please use magiclouds#gmail.com.

1 1

Haskell Weekly News: Issue 310
by Daniel Santa Cruz 23 Oct '14

23 Oct '14

Welcome to issue 310 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers from October 5 to 18, 2014 Quotes of the Week * spopejoy: That [Spineless Tagless G Machine] will always sound like the villian in an upcoming Ghostbusters sequel to me :) * pigworker: When you can make data out of potatoes, why would you want to encode them as functions? * fishcorn: When someone mentions lens on freenode... [1]zeus-lens! * neelk: So constructively we know this style can be used to meet hard performance deadlines in domains where the penalty for failure is literally radioactive flaming death. * edwardkmett: At one point we had a type in lens where one of its arguments started taking parameters of the form i m a s t a b u. Upon reflection, we let it win the argument and decided not to implement the function. * Ivan Appel: ... while the popular opinion says that the main reason to pick Haskell is "to have fun hacking," in fact it's not so fun to hack in Haskell because there's not such much hacking to do at the first place. For instance, you don't need to spend lots of effort tracing and fixing obscure bugs, so if your definition of "hacking" includes heroic bugfixing, you'd be better off with JavaScript or Perl. Top Reddit Stories * From 60 Frames per Second to 500 in Haskell Domain: keera.co.uk, Score: 116, Comments: 82 Original: [2] http://goo.gl/tiA202 On Reddit: [3] http://goo.gl/sl8TTl * Note: Erik Meijer's MOOC - "Introduction to Functional Programming" starts next Wednesday Domain: edx.org, Score: 109, Comments: 34 Original: [4] http://goo.gl/QNXb5M On Reddit: [5] http://goo.gl/sVfmE4 * The New Haskell.org Domain: blog.haskell.org, Score: 98, Comments: 72 Original: [6] http://goo.gl/TbBGrW On Reddit: [7] http://goo.gl/kdaLFq * New Haskell Book: Thinking Functionally with Haskell Domain: amazon.com, Score: 95, Comments: 39 Original: [8] http://goo.gl/oj35Ox On Reddit: [9] http://goo.gl/rYKq6c * Some notes on reimplementing a NodeJS service in Haskell Domain: gist.github.com, Score: 67, Comments: 5 Original: [10] http://goo.gl/ZoSy2a On Reddit: [11] http://goo.gl/kQ6mOs * Release of threepenny-gui 0.5.0.0: easy UI in Haskell! Domain: apfelmus.nfshost.com, Score: 65, Comments: 1 Original: [12] http://goo.gl/NClc0o On Reddit: [13] http://goo.gl/qDos1R * Bake: a Continuous Integration System Domain: neilmitchell.blogspot.fr, Score: 64, Comments: 34 Original: [14] http://goo.gl/u5bznA On Reddit: [15] http://goo.gl/7oC0N8 * On concerns about Haskell's Prelude favoring Foldable/Traversable Domain: yesodweb.com, Score: 62, Comments: 101 Original: [16] http://goo.gl/yJ7yMJ On Reddit: [17] http://goo.gl/M1M6we * Making GHCi awesomer? Domain: haskell.org, Score: 57, Comments: 3 Original: [18] http://goo.gl/KUkSQ7 On Reddit: [19] http://goo.gl/GRxzb6 * lens over tea, part 1: lenses 101, traversals 101, and some implementation details Domain: artyom.me, Score: 56, Comments: 25 Original: [20] http://goo.gl/rH0tdJ On Reddit: [21] http://goo.gl/jgsBeN * A neat trick for GHCi Domain: mega-nerd.com, Score: 54, Comments: 12 Original: [22] http://goo.gl/o9yrqJ On Reddit: [23] http://goo.gl/oB8Nhb * Shaking up GHC Domain: blogs.ncl.ac.uk, Score: 53, Comments: 21 Original: [24] http://goo.gl/jkRnPn On Reddit: [25] http://goo.gl/byWnxV * FRP Zoo: the TodoMVC of FRP libraries Domain: github.com, Score: 53, Comments: 12 Original: [26] http://goo.gl/JyKRtL On Reddit: [27] http://goo.gl/wJV4Vt * [Video] Simon Peyton Jones - Zero-Cost Coercions in Haskell at Haskell eXchange Domain: skillsmatter.com, Score: 50, Comments: 46 Original: [28] http://goo.gl/yXp43E On Reddit: [29] http://goo.gl/l0mo5O * Bryan O'Sullivan - Performance Measurement and Optimization in Haskell [video] Domain: skillsmatter.com, Score: 49, Comments: 23 Original: [30] http://goo.gl/HO4Sjy On Reddit: [31] http://goo.gl/4sqGgX * How to Rewrite the Prelude Domain: neilmitchell.blogspot.it, Score: 42, Comments: 81 Original: [32] http://goo.gl/PnnoO2 On Reddit: [33] http://goo.gl/EP9CaL * Generalizing function composition Domain: jaspervdj.be, Score: 42, Comments: 31 Original: [34] http://goo.gl/vCfmqT On Reddit: [35] http://goo.gl/GXb4gt * C structures in Haskell FFI Domain: ghc.haskell.org, Score: 40, Comments: 19 Original: [36] http://goo.gl/OT7UFH On Reddit: [37] http://goo.gl/uKJWCl * Yi 0.10, Anniversary Edition Domain: haskell.org, Score: 38, Comments: 16 Original: [38] http://goo.gl/T58nN6 On Reddit: [39] http://goo.gl/Fz6NQo * Curry-Howard, the Ontological Ultimate Domain: psnively.github.io, Score: 38, Comments: 28 Original: [40] http://goo.gl/HpPhXz On Reddit: [41] http://goo.gl/LlYUiM Top StackOverflow Questions * Is it possible to directly invoke Haskell code from Bash and output to stdout? votes: 17, answers: 3 Read on SO: [42] http://goo.gl/jkG0vv * Why does foldr use a helper function? votes: 16, answers: 4 Read on SO: [43] http://goo.gl/hsmIsF * Why do hGetBuf, hPutBuf, etc. allocate memory? votes: 14, answers: 2 Read on SO: [44] http://goo.gl/G40NfW * Is it possible to get the Kind of a Type Constructor in Haskell? votes: 10, answers: 1 Read on SO: [45] http://goo.gl/Pajd4R * Printing out Haskell's evaluation (rewriting) steps for educational/learning purposes. Is it possible? votes: 9, answers: 3 Read on SO: [46] http://goo.gl/Wlfeol Until next time, [47]+Daniel Santa Cruz References 1. https://s3.amazonaws.com/fishcorn/zeus-lens.gif 2. http://keera.co.uk/blog/2014/10/15/from-60-fps-to-500/ 3. http://www.reddit.com/r/haskell/comments/2jbl78/from_60_frames_per_second_t… 4. https://www.edx.org/course/delftx/delftx-fp101x-introduction-functional-212… 5. http://www.reddit.com/r/haskell/comments/2ixpcf/note_erik_meijers_mooc_intr… 6. https://blog.haskell.org/post/the_new_haskell_org/ 7. http://www.reddit.com/r/haskell/comments/2j4sim/the_new_haskellorg/ 8. http://www.amazon.com/Thinking-Functionally-Haskell-Richard-Bird/dp/1107087… 9. http://www.reddit.com/r/haskell/comments/2jele8/new_haskell_book_thinking_f… 10. https://gist.github.com/paf31/9c4d402d400d61a49656 11. http://www.reddit.com/r/haskell/comments/2j8lhd/some_notes_on_reimplementin… 12. http://apfelmus.nfshost.com/blog/2014/10/04-threepenny-gui-0-5.html 13. http://www.reddit.com/r/haskell/comments/2idep2/release_of_threepennygui_05… 14. http://neilmitchell.blogspot.fr/2014/10/bake-continuous-integration-system.… 15. http://www.reddit.com/r/haskell/comments/2in244/bake_a_continuous_integrati… 16. http://www.yesodweb.com/blog/2014/10/classy-base-prelude 17. http://www.reddit.com/r/haskell/comments/2if0fu/on_concerns_about_haskells_… 18. http://www.haskell.org/pipermail/ghc-devs/2014-October/006771.html 19. http://www.reddit.com/r/haskell/comments/2jm4nk/making_ghci_awesomer/ 20. http://artyom.me/lens-over-tea-1 21. http://www.reddit.com/r/haskell/comments/2igp1v/lens_over_tea_part_1_lenses… 22. http://www.mega-nerd.com/erikd/Blog/CodeHacking/Haskell/ghci-trick.html 23. http://www.reddit.com/r/haskell/comments/2jketr/a_neat_trick_for_ghci/ 24. https://blogs.ncl.ac.uk/andreymokhov/shaking-up-ghc/ 25. http://www.reddit.com/r/haskell/comments/2j07m0/shaking_up_ghc/ 26. https://github.com/gelisam/frp-zoo#readme 27. http://www.reddit.com/r/haskell/comments/2j0u4h/frp_zoo_the_todomvc_of_frp_… 28. https://skillsmatter.com/skillscasts/5296-safe-zero-cost-coercions-in-haske… 29. http://www.reddit.com/r/haskell/comments/2iqrr5/video_simon_peyton_jones_ze… 30. https://skillsmatter.com/skillscasts/5466-bryan-o-sullivan 31. http://www.reddit.com/r/haskell/comments/2is5am/bryan_osullivan_performance… 32. http://neilmitchell.blogspot.it/2014/10/how-to-rewrite-prelude.html 33. http://www.reddit.com/r/haskell/comments/2icjmf/how_to_rewrite_the_prelude/ 34. http://jaspervdj.be/posts/2014-10-17-generalizing-function-composition.html 35. http://www.reddit.com/r/haskell/comments/2jivxa/generalizing_function_compo… 36. https://ghc.haskell.org/trac/ghc/wiki/CStructures 37. http://www.reddit.com/r/haskell/comments/2jefui/c_structures_in_haskell_ffi/ 38. http://www.haskell.org/pipermail/haskell-cafe/2014-October/116463.html 39. http://www.reddit.com/r/haskell/comments/2j8pfv/yi_010_anniversary_edition/ 40. http://psnively.github.io/blog/2014/10/14/Curry-Howard-the-Ontological-Ulti… 41. http://www.reddit.com/r/haskell/comments/2jb1n7/curryhoward_the_ontological… 42. http://stackoverflow.com/questions/26417136/is-it-possible-to-directly-invo… 43. http://stackoverflow.com/questions/26243014/why-does-foldr-use-a-helper-fun… 44. http://stackoverflow.com/questions/26333815/why-do-hgetbuf-hputbuf-etc-allo… 45. http://stackoverflow.com/questions/26291740/is-it-possible-to-get-the-kind-… 46. http://stackoverflow.com/questions/26214586/printing-out-haskells-evaluatio… 47. https://plus.google.com/105107667630152149014/about

1 0

Yosemite
by Kazu Yamamoto 23 Oct '14

23 Oct '14

Hi, Has anybody tried GHC on Yosemite? I cannot afford to do it by myself this time. So, I would like to know. --Kazu

10 11

Precise timing
by Jeffrey Brown 23 Oct '14

23 Oct '14

Hi, An earlier version of this question is cross-posted at StackOverflow <http://stackoverflow.com/questions/26437770/timing-inaccuracy-in-haskell-th…> . What should I use for precise (and eventually, concurrency-compatible) timing in Haskell? I want to make rhythms. I tried the following to produce a repeating rhythm in which one note is twice as long as the other two. (That rhythm is encoded by the list [1,1,2].) import Control.Concurrent import Text.Printf import Control.Monad main = mapM_ note (cycle [1,1,2]) beat = round (10^6 / 4) -- measured in microseconds note :: Int -> IO () note n = do threadDelay $ beat * n printf "\BEL\n" When I run it the long note is three times as long as the others, not twice. If I speed it up, by changing the number 4 to a 10, the rhythm is destroyed completely: the notes all have the same length. threadDelay is guaranteed <http://hackage.haskell.org/package/base-4.7.0.1/docs/Control-Concurrent.htm…> to wait at least as long, but potentially longer than, what the caller specifies. Another potential problem could be buffering in printf. (Eventually I intend to replace the printf statement with OSC output to a sound generator.) Thanks, Jeff

10 23

a textured quad/triangle
by Vlad Lopatin 22 Oct '14

22 Oct '14

Hello, I am looking for a working example of texture binding, using VBOs and OpenGL4+ standard. A textured quad/triangle would be great. Does anybody have one? Regards, Vlad

2 2

How to send a string somewhere via UDP
by Jeffrey Brown 22 Oct '14

22 Oct '14

Chapter 27 of Real World Haskell <http://book.realworldhaskell.org/read/sockets-and-syslog.html> explains a way to send a message over UDP. From a folder containing the two files "syslogclient.hs" and "SyslogTypes.hs" (which are attached to this email, and also available here <http://book.realworldhaskell.org/read/sockets-and-syslog.html>), supposedly one can run these three commands from GHCI, to send the message "This is my message" to localhost, port number 514: :load syslogclient.hs h <- openlog "localhost" "514" "testprog" syslog h USER INFO "This is my message" I have a Max/MSP patch that accepts UDP on localhost port number 9000. I substitute 514 -> 9000 and run that, and I get nothing. I know the Max/MSP "udpreceive" object is working, because from Python, using the aiosc module, I can run aiosc.send(('127.0.0.1', 9000), "This is a message from Python") ) and "This is a message from Python" reaches Max. There is a UDP library <http://hackage.haskell.org/package/network-conduit-0.6.1.1/docs/Data-Condui…> for Haskell, which I presume could serve as an alternative to the RWH code, but I don't understand it. I run OS X 10.9 on an early 2011 MBP. Many thanks, Jeff

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Limit elements of a list to a certain value
by Vlatko Basic 21 Oct '14

21 Oct '14

Hello Cafe, I have these datatypes data Event = E1 {...} | E2 {...} | E3 {...} data Parsed = PEvent Event | PLine Text | PHeader Text I'd like to split the list of Parsed values into separate lists with a guaranty that each of those lists contains only the elements of the same type, as in [PEvent E1] [PEvent E2] [PLine Text] ... How can that be achieved on type level (without creating newtypes for each case)? I tried with type families, but failed. Also, an explanation of why the Event above (or "data Q = Q1 | Q2 String") is not promotable to kind level would be welcome. best regards, vlatko

2 2

Recommended way to install, use and maintain haskell tools on OS X
by Nicola Gigante 20 Oct '14

20 Oct '14

Hi I know this question might be a little old, but I happen to have a from scratch installation of OS X (yosemite) on my machine and I want to install the haskell tools in the currently best way. So I summarize the options that I understand are available: 1) A non-option first: the Homebrew formula for haskell-platform is no longer available, but… 2) There are formulas for GHC (7.8.x) and cabal, so I can install those and install the other packages with the homebrew cabal. 3) I can install the binary distribution of the Haskell Platform for OS X directly from the website, and then install any needed package with cabal. 4) I’ve heard of Nix, what is this all about? 5) Installing manually the binary distributions of ghc and cabal. No thanks. That said, what is the recommended way to manage packages once I have cabal and ghc? 1) Installing everything locally into ~/Library/Haskell, which afaik is the default behavior of cabal. That also means having ~/Library/Haskell/bin in the PATH. But do I have to also have ~/.cabal/bin in the PATH? Why having two different local bin directories? What happens to the packages installed by haskell platform system-wide? They are left there, shadowed by the local ones, and never again touched nor updated? 2) Installing everything globally, changing the cabal configuration to make it the default. Afaik bad idea, but then I don’t have obsoleted packages installed system-wide. 3) Installing nothing, and relying on sandboxes to install exactly what is needed for any single package I need. This option is still a bit mysterious to me. 3a) If I need to install a package I need for development, I do cabal sandbox init in my source tree and then if I install something from inside it, cabal installs it in the sandbox. Am I correct? 3a) If I need to install a package I need to _use_, instead, what to do? Sorry for the confusion and thanks for the clarification. Bye, Nicola

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ANN: Haskell plugin for IntelliJ
by Rik van der Kleij 20 Oct '14

20 Oct '14

Hi everyone, I'm glad to announce initial version of Haskell plugin for IntelliJ. It's available in the plugin repository. This plugin is written mainly in Scala and is not mentioned to support GHC/Cabal directly. This plugin support sandbox projects and expects that the Cabal init/install/build is done on command-line. Features - Syntax highlighting (which can be customised); - Error/warning highlighting; - Find Usages of identifiers; - Resolving references of identifiers (also to library code if library source code is added to project and resolves inside import declaration); - Code completion by resolving references; - Renaming variables (which first shows preview so refactoring scope can be adjusted); - View type info from (selected) expression; - View expression info; - View quick documentation; - View quick definition; - Structure view; - Navigate to declaration (called `Class` in IntelliJ menu); - Navigate to identifier (called `Symbol` in IntelliJ menu); - Code completion by looking to import declarations; - Simple form of code formatting; A lot of features are with the help of ghc-mod and ghc-modi. Documentation is provided by haskell-docs. See for more information and getting started: https://github.com/rikvdkleij/intellij-haskell Any feedback is welcome! Regards, Rik

1 0

Eval forgotten unless type specified?
by Jeffrey Brown 19 Oct '14

19 Oct '14

In this passage, after the seq call, :sprint reveals x and y to be evaluated: let x = 1 + 2 :: Int let y = x + 1 :sprint x :sprint y seq y () :sprint x :sprint y The above is a verbatim quote of Marlow's Concurrency book, chapter 2. In the below, however, :sprint shows them unevaluated both before and after the seq call. let x = 1 + 2 let y = x + 1 :sprint x :sprint y seq y () :sprint x :sprint y Why?

2 1

Profiling with an interpreter
by Corentin Dupont 18 Oct '14

18 Oct '14

Hi, I'm trying to profile my game (Nomyx) but I get: "You can't call hscCompileCoreExpr in a profiled compiler". I figured out it's because I'm embbeding an intrepreter. Is there a way to avoid that and profile anyway? Maybe ignoring the calls to the interpreter or something... Cheers Corentin

1 0

What happened to hugs?
by Thorsten Rangwich 18 Oct '14

18 Oct '14

Hi, I suppose this question is not new, but neither google nor a manual search file be file through the archives brought enlightement. www.haskell.org/hugs still exists, but none of the links there does work. Documentation and source point to cvs.haskell.org ("server does not exist") and development points to http://hackage.haskell.org/trac/hugs ("page does not exist"). Was it migrated to somewhere else or is it dead - in latter case the page would not make sense any more. "Raskell" (iPad app) provided a development environment usinh hugs, so I would at least like to install hugs on my Mac as well... Thank you very much in advance. Thorsten. Sent from my mobile phone

4 5

Best way to Introduce FP into a dev team with many C, C++ and Java developers?
by Birmjin In 18 Oct '14

18 Oct '14

Hi, Recently our development team had decided to attempt using Haskell or Scala as one of our programming language. (We had hoped some of our problem will be addressed through taking advantage of some element of FP, like immutability and Rx) Most of our team members have fairly good knowledge of C, C++ and Java. And few of them, including myself, have been self-studying a FP language like Haskell and Scala since last year. Besides some early starters, functional programming is quite new to us. When we held a lecture on FP, we found many of our developers were struggling in grasping some idea of FP. They fumbled with writing functional programming style code. We kept on lecturing several times, but still not quite successful. It seems more difficult than it looks - thinking in functional programming way for the long time C, C++ and Java developers. Does anyone had an experience with initiating FP adoption into a large dev team without pain? Our development team has around 300+ people. Thanks.

8 8

beginnners book
by Roelof Wobben 17 Oct '14

17 Oct '14

Hello, What is a good book to learn Haskell with a lot of exercises so I can check if I understand everything right ? Roelof

3 5

2^770000 triggers Bus Error?
by Erik Rantapaa 17 Oct '14

17 Oct '14

Running ghci under OSX I am seeing the following behavior: Prelude> 2^750000 {... lots of digits...} Prelude> 2^760000 Segmentation Fault: 11 Prelude> 2^770000 Bus Error: 10 and I'm curious why this happens. More details: $ ghci --version The Glorious Glasgow Haskell Compilation System, version 7.8.3 I'm using the 64-bit version of the Haskell Platform (x86_64-darwin-7.8.3).

4 3

Haskell software engineering master thesis
by Jon Kristensen 17 Oct '14

17 Oct '14

Hi, everyone! I'm about to write a software engineering/management master thesis at the IT University of Gothenburg, and I'm considering to do research into the Haskell world. It should probably be in one of the following five fields: empirical software engineering, requirements engineering, software architecture, model-driven engineering or quality management. The focus should probably be more towards an empirical study, rather than something more computer science-related. It should also add to general body of knowledge, and not be too tied to, for example, a specific implementation. Does anyone have any suggestions of relevant topics that I could write about, or perhaps some related papers that I could read? Thanks! Warm regards, Jon Kristensen

1 0

Splicing type signature in TH
by Hugo Pacheco 17 Oct '14

17 Oct '14

Hi list, I am 99.9% sure that this is currently not possible, but I might as well ask: - Is there a way to lift type variables into Template Haskell type splices? What I had in mind would be something like this (erroneous) code: liftT :: a -> Q Type liftT (_::a) = [t| $a |] I have no idea how hard it would be to implement such a feature, or if it is remotely doable. Naively, it seems to me that TH would have to delay evaluating the splice until the type variable is fully expanded, but all the necessary information would still be available at some point during compilation. Cheers, hugo -- www.cs.cornell.edu/~hpacheco

3 5

Converting a Constraint to Bool
by Ivan Lazar Miljenovic 17 Oct '14

17 Oct '14

Using the Constraint type and the ConstraintKinds extension, is there any way we can determine if a Constraint is satisfied (i.e. a type-level function of type Constraint -> Bool using DataKinds)? -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com http://IvanMiljenovic.wordpress.com

4 4

Unicode symbols in operators
by Niklas Hambüchen 16 Oct '14

16 Oct '14

(I'm trying to improve Sublime Text's Haskell lexer.) https://www.haskell.org/onlinereport/haskell2010/haskellch10.html says uniSymbol → any Unicode symbol or punctuation What is meant here, is "Unicode symbol" literally \p{Symbol} in regex, or more? So uniSymbol = \p{Symbol} | \p{Punctuation} Thanks!

2 1

Hiding platform packages in Cabal sandboxes
by Sven Panne 15 Oct '14

15 Oct '14

As a maintainer of the various OpenGL-related packages I have the following problem: The Haskell platform has those packages (OpenGLRaw, GLURaw, ...) exposed, which is the right thing to do in general. When I want to work on those packages, I'd like to use Cabal sandboxes to avoid screwing up the platform versions of them, but things get a bit tricky then. Consider e.g. the GLURaw package, which depends on the OpenGLRaw package. Assume that I'd like to add some stuff to the OpenGLRaw package and use that in GLURaw. With cabal sandboxes I'll have to fight a little bit, because versions of these packages are already exposed: ----------------------------------------------------------------------------------------------------------------------- svenpanne@svenpanne[master]:~/repos/haskell-packages/GLURaw$ cabal sandbox init Writing a default package environment file to /usr/local/google/home/svenpanne/repos/haskell-packages/GLURaw/cabal.sandbox.config Creating a new sandbox at /usr/local/google/home/svenpanne/repos/haskell-packages/GLURaw/.cabal-sandbox svenpanne@svenpanne[master]:~/repos/haskell-packages/GLURaw$ cabal sandbox add-source ../OpenGLRaw ----------------------------------------------------------------------------------------------------------------------- No problem so far. But the next step is not so OK: ----------------------------------------------------------------------------------------------------------------------- svenpanne@svenpanne[master]:~/repos/haskell-packages/GLURaw$ cabal install --only-dependencies Resolving dependencies... All the requested packages are already installed: Use --reinstall if you want to reinstall anyway. ----------------------------------------------------------------------------------------------------------------------- Hmmm, obviously cabal sees the globally exposed OpenGLRaw and ignores that I've done add-source above. OK, next try with --constraint added: ----------------------------------------------------------------------------------------------------------------------- svenpanne@svenpanne[master]:~/repos/haskell-packages/GLURaw$ cabal install --only-dependencies --constraint='OpenGLRaw source' Resolving dependencies... In order, the following would be installed: OpenGLRaw-1.5.0.0 (reinstall) cabal: The following packages are likely to be broken by the reinstalls: OpenGL-2.9.2.0 GLUT-2.5.1.1 GLURaw-1.4.0.1 Use --force-reinstalls if you want to install anyway. ----------------------------------------------------------------------------------------------------------------------- (Is there any documentation about --constraint? I figured that out by actually reading the cabal sources. :-/ ) Better, but still not OK, so let's add --force-reinstalls: ----------------------------------------------------------------------------------------------------------------------- svenpanne@svenpanne[master]:~/repos/haskell-packages/GLURaw$ cabal install --only-dependencies --constraint='OpenGLRaw source' --force-reinstalls Resolving dependencies... Warning: The following packages are likely to be broken by the reinstalls: OpenGL-2.9.2.0 GLUT-2.5.1.1 GLURaw-1.4.0.1 Continuing even though the plan contains dangerous reinstalls. Notice: installing into a sandbox located at /usr/local/google/home/svenpanne/repos/haskell-packages/GLURaw/.cabal-sandbox Configuring OpenGLRaw-1.5.0.0... Building OpenGLRaw-1.5.0.0... Installed OpenGLRaw-1.5.0.0 ----------------------------------------------------------------------------------------------------------------------- That works, so after that I could actually build/install GLURaw. So in a nutshell what I have to do is: cabal sandbox init cabal sandbox add-source ../OpenGLRaw cabal install --constraint='OpenGLRaw source' --force-reinstalls --enable-documentation --haddock-hyperlink-source And for other packages I even have to add several --constraint flags, because they depend on several locally modified packages. This seems a bit weird. Is this the recommended workflow? How do other maintainers of platform packages handle this? What one *actually* wants is hiding some of the globally exposed packages while being in the sandbox (--constraint and --force-reinstalls could go away then), but I've found no way to do that. Cheers, S.

5 4

Deriving vs. type constructors
by Michael Sperber 15 Oct '14

15 Oct '14

I'm struggling with a problem related to generic programming, boiling down to this: ----snip---- {-# LANGUAGE StandaloneDeriving, KindSignatures, UndecidableInstances #-} data Foo (v :: * -> *) = Foo (v Bar) deriving instance (Show (v Bar)) => Show (Foo v) data Bar = Bar deriving Show ----snip---- So the Show instance for Foo v wants the rather specific Show instance for v Bar. But now imagine that v is always something like Maybe, itself done using something like this presumably: instance Show a => Show (Maybe a) where ... Can I somehow state as a constraint that Foo v has a Show instance if v is a type constructor like Maybe, i.e. once with a Show instances for any arguments that has a Show instance? (You can't see *why* I want to do this in this example - I actually have something like 100 nested datatypes which thread v through, and *every single one of them* adds to the context I need for every one of them.) I feel I want to write something like this: deriving instance (Show a => Show (v a)) => Show (Foo v) Is there a way to do this? Help would be much appreciated! -- Regards, Mike

3 3

Missing or undocumented ARM architecture controls
by Jon Schneider 15 Oct '14

15 Oct '14

I worked around a problem of a build of a simple cross ghc not finding (shared) libraries by setting the LIBRARY_PATH environment variable. Not ideal. Then I came to a problem with StcCRun.c using vldmia and related instructions which are part of ARMv6. I worked around this by putting #defines for arm_HOST_ARCH_PRE_ARMv6 and arm_HOST_ARCH_PRE_ARMv7 in mk/config.h Now it seems to make use of llvm at a later stage and that fails with "inplace/bin/ghc-stage1" -static -H64m -O0 -Iincludes -Iincludes/dist -Iincludes/dist-derivedconstants/header -Iincludes/dist-ghcconstants/header -Irts -Irts/dist/build -DCOMPILING_RTS -package-name rts -dcmm-lint -i -irts -irts/dist/build -irts/dist/build/autogen -Irts/dist/build -Irts/dist/build/autogen -O2 -c rts/Exception.cmm -o rts/dist/build/Exception.o '+v7' is not a recognized feature for this target (ignoring feature) UNREACHABLE executed! UNREACHABLE executed! Stack dump: 0. Program arguments: /usr/bin/llc -O3 -relocation-model=static /tmp/ghc20998_0/ghc20998_4.bc -o /tmp/ghc20998_0/ghc20998_5.lm_s --enable-tbaa=true -mattr=+v7,+vfp3 1. Running pass 'Function Pass Manager' on module '/tmp/ghc20998_0/ghc20998_4.bc'. 2. Running pass 'ARM Instruction Selection' on function '@stg_unmaskAsyncExceptionszh_ret_info' Now the thing that sticks out there is the +v7,+vfp3 option. Again it seems to be making incorrect assumptions about the exact ARM architecture. Ours is a v5TE/926. What is the correct way to specify this ? Thanks, Jon

2 1

Building cross compiler fails
by Jon Schneider 15 Oct '14

15 Oct '14

I am after a ghc cross compiler. I have been cross compiling stuff for years and also built cross-compiling gcc from time to time but am having trouble building a cross-compiling ghc. I have read https://ghc.haskell.org/trac/ghc/wiki/CrossCompilation and associated pages. In the ghc-7.8.3 directory I do ./configure --target=arm-linux-gnueabi -with-gcc=arm-linux-gnueabi-gcc but make eventually fails (in stage 1) configure: error: in `/home/jon/build/ghc-7.8.3/libraries/terminfo': configure:3386: arm-linux-gnueabi-gcc -o conftest -fno-stack-protector conftest.c -lncurses >&5 /usr/lib/gcc/arm-linux-gnueabi/4.6/../../../../arm-linux-gnueabi/bin/ld: cannot find -lncurses Firstly the requirement for termcap is surely unnecessary. We don't need it as the target will just be processing data. We do have an libncurses kicking about and I know _exactly_ what -L option to pass to (in this case) arm-linux-gnueabi-gcc to make this work but where to specify it to ghc's build system escapes me. I have tried setting CFLAGS, LDFLAGS, CONF_GCC_LINKER_OPTS_STAGE1 the configure commandline and also mk/build.mk . >From searching it is clear this has tripped people up time and time again and that there is something missing from the documentation. So in summary please could https://ghc.haskell.org/trac/ghc/wiki/CrossCompilation be updated to show where to specify the CFLAGS and LDFLAGS that should accompany the compiler specified with -with-gcc (or derived from --target). Also more generally could the build documentation show how to omit frills like curses and termcap if at all possible. Jon

2 1

Optimizing Haskell games with minimal changes.
by Ivan Perez 15 Oct '14

15 Oct '14

Hi Café, As you know, we are building Android games in Haskell, and efficiency is crucial. I often find myself trying to explain to other game programmers that the price to be paid in speed in exchange for the robustness and the clarity of the language is minimal; and that optimising and parallelising can be very easy. In our game we only had to apply very basic techniques (RWH, Chapter 25; Parallel & Concurrent Haskell, Chapter 2) to obtain a x7 speedup and reduce memory consumption from hundreds to 3MB on desktop. The number of changes to the codebase was minimal. I hope it helps support the case that using Haskell even for CPU demanding code is worth it. Our game now also runs smoothly on Android. Hopefully this will also help others trying to achieve the same thing. http://keera.co.uk/blog/2014/10/15/from-60-fps-to-500/ Cheers Ivan -- Facebook: https://www.facebook.com/keerastudios Twitter: https://twitter.com/KeeraStudios Web: http://www.keera.co.uk

1 0

foreign libraries, dylibs, OS X Mavericks and GHC 7.8.3 woes
by Alfredo Di Napoli 15 Oct '14

15 Oct '14

Hello Cafe, I will let this gist talk for me: https://gist.github.com/adinapoli/d4c33a9d1ea85bcaebdf Even though there is a solution, it seems extremely unsatisfying having to specify such paths manually. I always had very good experiences with FFI, OS X and GHC in the past, so this strikes me as a surprise. I have read a bit here and there about GHC 7.8.3 introducing the -dynamic flag (not sure about the specific problem it aims to solve, though) and changing some internal when it comes to library linking, but information is scattered and fragmented. I would like to: 1) Shed some light on my specific use case: Can I do better here? (aka have GHC figure out automatically all the nitty gritty details) 2) Any sort of pointers to documentation, tutorials, papers, everything to "teach me to fish”? Many thanks, Alfredo

4 6

Slides for "Adventures with Types" @ Functional Programming Exchange 2013?
by Erik Rantapaa 15 Oct '14

15 Oct '14

Hi, Does anyone know if the slides for Simon Peyton Jones' keynote talk at the Skillsmatter Functional Programming Exchange 2013 are available somewhere? Link to the video: https://skillsmatter.com/skillscasts/3842-keynote-3842 Thanks!

4 3

value vs object orientation
by Rustom Mody 15 Oct '14

15 Oct '14

I was trying to explain to a colleague the difference in outlook between value and object orientation. I find some references like C#'s 'value-objects' vs the more usual 'reference-objects' But these kinds of references are very OOP-tilted. OTOH there are a few writings eg by Peter Wegner argung that the millennial philosophy divide between 'rationalism' and 'empiricism' corresponds to the division in programming between FP and OOP. Im looking for some more middle ground stuff -- not too stuck on one technological platform and yet not overly philosophical

3 6

Re: [Haskell-cafe] Getting the haddocks back
by Carter Schonwald 14 Oct '14

14 Oct '14

you have to add your acls curl -X DELETE https://$username:$ pwd(a)hackage.haskell.org/package/linear-1.10.1.2/docs something like that, suitably adjusted for the libs in question On Tue, Oct 14, 2014 at 3:00 PM, Johannes Waldmann < johannes.waldmann(a)htwk-leipzig.de> wrote: > Hi Carter, > > > https://hackage.haskell.org/api > > Aha. How do I authenticate? I'm getting this (no surprise) > > [waldmann@R630 ~]$ curl -i -X DELETE -H "Accept: application/json" > https://hackage.haskell.org/package/satchmo-2.8.1/docs > > HTTP/1.1 401 Unauthorized > > - J. > >

1 0

ANN: yi-0.10.0 , the text editor written in Haskell
by Mateusz Kowalczyk 14 Oct '14

14 Oct '14

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 We're glad to announce Yi 0.10.0. Yi is 10 years old today! Our main repository is at [1]. Yi compiles with GHC 7.6.3 all the way up to GHC 7.8.3. There have been many changes since the latest Hackage release (0.8.2). I inline the relevant part of the changelog at the bottom. We are slowly trying to populate the documentation pages: we have recently started using GitHub pages[2] for this purpose. Please have a look! On top of the issues listed in the changelog, a lot of issues were closed separately. If you had a pending issue, please check the issue tracker. As always we're looking for contributors: we have tasks in just about any area. Note that you don't even need to know Haskell to help us. Visit us on #yi on Freenode: be prepared to stay for more than 5 minutes. Installation instructions are available at [2]. If you're using nix, Yi 0.10.0 will be packaged shortly. 0.10.0 - ------ * Unicode syntax highlighting fixed (issue #82) * Hook to GTK Window exposed (#557) * Multiple components moved out to separate packages (oo-prototypes, word-trie, yi-languages, yi-string) * Replace a lot of the API to use YiString/Text instead of String improving performance * Greatly improve performance in the pango front-end as long as line-wrapping is on (default) * Recognise read-only files (#145) * Various Vim keymap improvements and fixes * Use lens instead of uniplate, replace some boilerplate with lens * Improve test framework to handle windows interactions, e.g. scrolling. * Use GHC.Generics instead of derive on GHC 7.8 * Remove bitrotten ghcapi and scion flags. * Support non-qwerty vim users * Support eventlog profiling with -feventlog * Eliminate idle CPU consumption in vty frontend * General cleanup * Make C-w closer to actual emacs behaviour (#612) * Make M-h behave more like emacs (#611) * Hint with buffer names when using C-k with emacs keymap (#606) * Fix display of paths starting with / (#528) * Don't mark buffer as changed if nothing was killed (#618) * Nicer findFile &c behaviour in dired buffers (#149) * Implement C-a for CUA (#167) * Fix dired for directories with unicode files/dirs (#445) * Fix vim indenting under some circumstances (#621) * Allow the font size to be changed per buffer (#608) * Double-click and triple-click selection in pango (#100 and #101) * Count columns properly in presence of tabs (#440) * Extra marking operations in dired Contributors: Alan Zimmerman, Anders Papitto, Anthony Quizon, Ben Armston, Benno Fünfstück, Carter Charbonneau, Corey O'Connor, Cray Elliott, Dmitry Ivanov, fiendfan1, Ilya Smelkov, Jakub Arnold, Jared Hance, jetho, Mateusz Kowalczyk, Richard Goulter, Ryan Desfosses, Siddhanathan Shanmugam 0.9.0 - ----- * Vim keymap removed. Vim2 is now called Vim. [1]: https://github.com/yi-editor/yi [2]: http://yi-editor.github.io/ - -- Mateusz K. -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iQIcBAEBAgAGBQJUPWXYAAoJEM1mucMq2pqXgzcP/0iljWag1qweflSYIqKa+FOc n/NYTqUV3HIYSGxolUvnm5HMfJ1uFFYmV7BVEtC7VcdntdP/bUCxu2gdOA9XxIrL JFwV3tzvLFqPYsm0bBVwq+lqRaBF2ICK95gmZpE+Osw7lrIK0SwibGAuLL+niRoo Qf5duTZXMBw0gQxay47zAb1XPwUhLYQUThSnbcOAG1raRI3OCV/eyMky+l5WMLTy 3RK5j2ZsWnps9k1XOFBVR/pQ6kJiFrButfLY7c3RBbfY9+uHQDN1ba3hr3wHsXUP fw4PiM6WmHecezH1Q7TSzH0XL+Mh5miM+g2QGphKAjeACOzskiCYRGcBpUCHSPsO EdxHe62oUvonEPAP747lCMRcYURknvoyVCDKjYzNKFBHJPFAizWW+tlv82QKKT1j CKECN7Lkra3nlLKzi11TdLHMUDGmatJeNHUMp4W1EDGG/hRbobrmD+2U2Yt/pRKH f/tSeE5Azk0xjDMNmYZBprqf1O1Q9tve4NrIHgQK0EXRWhkcFAsGIdqQBHP27Z0s JdCXdlMaRs4u2IfYoDevnFadMGF10oqQ1wUJPtIzcVvghgBkZEIMswsqbD5fTtPf Y/DFe2YcJl+lxPqgm/fq3aDnJABGYLftfJ05Rs1BGA909bnW29YqK0Si8JxAoH4R K6YQBTpqWULfHXh/ZQ68 =CAHP -----END PGP SIGNATURE-----

1 0

ANN: New version of graphmod (1.2.4)
by Iavor Diatchki 14 Oct '14

14 Oct '14

Hello, I am pleased to announce a new version of `graphmod`---a program that helps you visualize the import dependencies between the modules in your Haskell programs. The new feature in version 1.2.4 is support for pruning the dependency graph, which is enabled with the flag -p or --prune-edges. When this option is selected, `graphmod` will ignore imports to modules that are already imported by some of the dependencies of the module. For example, consider the following modules: module A where { import B; import C } module B where { import C } module C where { } When generated with `--prune-edges`, the resulting graph will be: A -> B -> C Note that there is no edge from `A` to `C`, because `C` is already imported by `B`. Happy hacking, -Iavor

5 7

Re: [Haskell-cafe] Pretty Printing Libraries with an Emphasis on Consistency
by Oliver Charles 14 Oct '14

14 Oct '14

Yes, hindent is exponential in its pretty printing and that's exactly the program I'm trying to speed up ;) To be specific, hindent has `sandbox` which runs a printer and then lets me make decisions on what the resulting state might be. I'm curious if there are other approaches. - ocharles On Sat, Oct 11, 2014 at 12:01 PM, Alan & Kim Zimmerman <alan.zimm(a)gmail.com> wrote: > Have you looked at hindent? > On 11 Oct 2014 11:52 AM, "Oliver Charles" <ollie(a)ocharles.org.uk> wrote: > >> Hi all, >> >> It seems that all of the pretty printing libraries on Hackage at the >> moment have an emphasis on being compact, but not necessarily consistent. >> By consistent, I mean that similar blocks of code are indented in the same >> fashion, even when not strictly necessary. >> >> Take for example, the start of "Pretty Printing with Lazy Dequeues". >> Here, the example is: >> >> if True >> then if True then True else True >> else >> if False >> then False >> else False >> >> I call this inconsistent, because the two sides of the top-level if have >> been formatted under different rules. A consistent formatting of this would >> be: >> >> if True >> then >> if True >> then True >> else True >> else >> if False >> then False >> else False >> >> The above can obviously be reached if you *always* format `if` in this >> style, but that's not what I'm after. If it's possible to format both sides >> on one-line, then that should be preferred. So an equally desirable output >> (that meets my "consistency" requirement) is: >> >> if True >> then if True then True else True >> else if True then True else True >> >> It doesn't seem that there is a library on Hackage that lets one express >> such a pretty printer. It seems that a pretty printer of this nature would >> need to have some sort of backtracking ability - I can imagine trying to >> print both sides of the if statement on one-line, and if this fails, try >> printing *both* on multiple lines. >> >> Curious to hear what people have to say on this matter, >> - ocharles >> >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> >>

4 3

Wiki account creation
by Pelumi Magbagbeola 14 Oct '14

14 Oct '14

Preferred Username is: Looms (I hope I have done this correctly)

1 0

Dependencies missing when building ghc.
by Magicloud Magiclouds 14 Oct '14

14 Oct '14

Hi, I am with my new Ubuntu Trusty box. I have installed ghc by apt-get. Then I wanted to build ghc from git to upgrade to 7.8.3. I did following commands. I tried 'make clean', or reget the source. No luck yet. $ git clone --recursive git://git.haskell.org/ghc.git $ ./sync-all -r git://git.haskell.org remote set-url origin $ git checkout ghc-7.8.3-release $ ./sync-all get $ rm -r libraries/time # as prompted by sync-all $ ./sync-all get $ ./boot $ ./configure $ make ===--- building phase 0 make -r --no-print-directory -f ghc.mk phase=0 phase_0_builds make[1]: Nothing to be done for `phase_0_builds'. ===--- building phase 1 make -r --no-print-directory -f ghc.mk phase=1 phase_1_builds "inplace/bin/ghc-cabal" check libraries/haskell98 "inplace/bin/ghc-cabal" configure libraries/haskell98 dist-install "" --with-ghc="/home/local/ANT/shida/src/git/ghc/inplace/bin/ghc-stage1" --with-ghc-pkg="/home/local/ANT/shida/src/git/ghc/inplace/bin/ghc-pkg" --disable-library-for-ghci --enable-library-vanilla --enable-library-profiling --enable-shared --configure-option=CFLAGS=" -fno-stack-protector " --configure-option=LDFLAGS=" " --configure-option=CPPFLAGS=" " --gcc-options=" -fno-stack-protector " --with-gcc="/usr/bin/gcc" --with-ld="/usr/bin/ld" --configure-option=--with-cc="/usr/bin/gcc" --with-ar="/usr/bin/ar" --with-ranlib="/usr/bin/ranlib" --with-alex="/usr/bin/alex" --with-happy="/usr/bin/happy" Configuring haskell98-2.0.0.4... ghc-cabal: At least the following dependencies are missing: base ==4.8.* make[1]: *** [libraries/haskell98/dist-install/package-data.mk] Error 1 make: *** [all] Error 2 -- 竹密岂妨流水过山高哪阻野云飞 And for G+, please use magiclouds#gmail.com.

3 4

Re: [Haskell-cafe] online tutorial
by Roelof Wobben 13 Oct '14

13 Oct '14

2 1

online tutorial
by Roelof Wobben 13 Oct '14

13 Oct '14

Hello, I want to learn haskell by using the fpcomplete site. Now I wonder if this ( https://www.fpcomplete.com/school/starting-with-haskell/haskell-fast-hard) is a good tutorial for a beginner. Roelof

1 0

documentation build failing in hackage?
by Alberto G. Corona 13 Oct '14

13 Oct '14

Sorry if this has been asked/discussed previously It seems that there are many packages in which the documentation is not generated. That is the visible effect since there is no indication if the build process failed or not. Could anyone give me some hints? I did a lazy look at the hackage2 documentation but I found nothing about that. Only that it is possible to upload the documentation if the build bot fails... -- Alberto.

11 15

New Functional Programming Job Opportunities
by Functional Jobs 13 Oct '14

13 Oct '14

Here are some functional programming job opportunities that were posted recently: Functional Software Engineer at Cake Solutions Ltd http://functionaljobs.com/jobs/8755-functional-software-engineer-at-cake-so… Software Engineer / Developer at Clutch Analytics/ Windhaven Insurance http://functionaljobs.com/jobs/8753-software-engineer-developer-at-clutch-a… Cheers, Sean Murphy FunctionalJobs.com

1 0

cabal sandbox using absolute path on symlinked dir
by Vlatko Basic 13 Oct '14

13 Oct '14

Hello Cafe, On Ubuntu, after creating a sandboxed project in a symlinked directory, cabal.sandbox.config contains absolute (canonical) paths of the directory, and not the symlinked paths. Is this a bug, and is there a way to correct that behavior? There is no way to move the project to a different place without recreating the whole sandbox. Best regards, vlatko

5 6

Library for URL/URI?
by Yuras Shumovich 12 Oct '14

12 Oct '14

Hello, Probably a silly question... But do we have good library for URL manipulations? I spent 2 days looking for library, that - has permissive license - doesn't use `String` everywhere - handles query part parsing/rendering - has minimal dependencies (Probably URL lib should not depend on anything outside Haskell Platform.) The best thing I found so far is https://github.com/Soostone/uri-bytestring It has few unnecessary dependencies (like http-types or errors,) but I can fork it and fix for my needs. Unfortunately it has unclear license -- BSD3 according to cabal file, but GPL-3 in source header. Are there better libs I missed? What are you using for URLs? Thanks, Yuras

2 2