- Haskell-Cafe - Haskell.org

Code-completion problem with emacs, ghc-mod and auto-complete
by Илья Бирюков 18 Jan '15

18 Jan '15

Hi, Cafe! I'm struggling to configure my emacs for haskell development with ghc-mod and auto-complete. It works well for the most part, but I've run into the issue when completing qualified names. In the following example I don't get any completion after BS: module Playground where import qualified Data.ByteString.Lazy as BL doWork :: BL.By -- no completion after dot Completion for unqualified names and module name in imports works just fine. Maybe someone has run into this issue before? My .emacs: (ac-config-default) (auto-complete-mode t) (add-hook 'haskell-mode-hook 'turn-on-haskell-indentation) (autoload 'ghc-init "ghc" nil t) (add-hook 'haskell-mode-hook (lambda () (ghc-init))) (defun my-ac-haskell-mode () (setq ac-sources (append ac-sources '(ac-source-ghc-mod)))) (add-hook 'haskell-mode-hook 'my-ac-haskell-mode) (add-hook 'haskell-mode-hook 'turn-on-haskell-doc-mode) (add-hook 'haskell-mode-hook 'turn-on-haskell-indent) (ac-define-source ghc-mod '((depends ghc) (candidates . ghc-select-completion-symbol) (symbol . "s") (cache))) -- Regards, Ilya Biryukov.

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haskell.org slow
by Hector Urroz 16 Jan '15

16 Jan '15

Anyone know when haskell.org <http://haskell.org/> will be usable again? Page loads take 20+ seconds. Info at https://status.haskell.org <https://status.haskell.org/> indicates there's a DB problem, but there's no ETA and performance has been bad for over 10 days.

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Number of widgets extant and displayed varying over time? (FRP, reactive-banana)
by Jeffrey Brown 16 Jan '15

16 Jan '15

Dear list, I want to write an application in which the set of widgets in existence, and the subset of them that is displayed, depends on user input. I am using reactive-banana. So far the simplest spec I have imagined for it is this: Initially there is just a text entry box and an empty (hence invisible) collection of labels. The user can do two things: enter the word "add", or enter an integer. Entering the word "add" causes a label to be added to the collection, but not displayed. The labels require no text content. Entering an integer N causes the first N labels to be displayed onscreen. The text entry box remains visible. I am totally baffled. In particular, the Behavior paradigm, though it is elegant and beautiful whenever I study it, I have no idea how to apply. Thank you, Jeff

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Undefined symbols when trying to use SDL-mixer
by Peter Reiner Fels 15 Jan '15

15 Jan '15

I'm trying to use SDL-mixer v0.6.1. When I add a dependency to my cabal file and run cabal repl I get the following error: Loading package SDL-mixer-0.6.1 ... <command line>: can't load .so/.DLL for: /home/prf/haskell/link-problem/.cabal-sandbox/lib/x86_64-linux-ghc-7.8.3/SDL-mi xer-0.6.1/libHSSDL-mixer-0.6.1-ghc7.8.3.so (/home/prf/haskell/link-problem/.cab al-sandbox/lib/x86_64-linux-ghc-7.8.3/SDL-mixer-0.6.1/libHSSDL-mixer-0.6.1-ghc7 .8.3.so: undefined symbol: Mix_FreeChunk) I can see these undefined symbols when I run: nm -D SDL-mixer-0.6.1/libHSSDL-mixer-0.6.1-ghc7.8.3.so | grep Free U Mix_FreeChunk U Mix_FreeMusic Running ldd on this file and grepping for SDL gives libHSSDL-0.6.5-ghc7.8.3.so => /home/prf/haskell/link-problem/.cabal-sandbox/lib /x86_64-linux-ghc-7.8.3/SDL-0.6.5/libHSSDL-0.6.5-ghc7.8.3.so (0x00007fb20b30600 0) libSDL-1.2.so.0 => /usr/lib64/libSDL-1.2.so.0 (0x00007fb20a232000) It seems like a dependency to /usr/lib64/libSDL_mixer.so is missing. Line 1815 of SDL-mixer-0.6.1/configure contains the following definition of SDL_LIBS: SDL_LIBS="-L`$SDL_CONFIG --prefix`/lib -lSDL_mixer" This refers to the 32 bit lib directory, but I'm on a 64 bit system. I unpacked SDL-mixer and changed this line to refer to the 64 bit lib directory. Next I recreated my cabal sandbox from scratch and added the patched version of SDL-mixer as a dependency. When I run cabal repl again I get the same error as mentioned above. What am I doing wrong? How do I get SDL-mixer to build against /usr/lib64/libSDL_mixer.so? Thanks, Peter

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uu-parsinglib - Greedy Parser
by Marco Vassena 15 Jan '15

15 Jan '15

In the uu-parsinglib the choice combinator (<|>) is symmetric and does not commit to any alternative. If the grammar being parsed is ambiguous, the corresponding parser will fail at run time on an ambiguous input. Consider for instance this html parser. pTag = pOpenTag <|> pCloseTag <|> pCommentTag <|> pContent pContent = Content <$> some (satisfy (/= '<')) pHtml = some pTag This parser will fail on "<a>123</a>", because this may be interpreted as: [ [Open a , Content "123", Close a], [Open a, Content "12", Content "3", Close a], [Open a, Content "1", Content "2", Content "3", Close a] ... ] In other parsing libraries such as parsec the choice operator <|> is greedy and commits to the first alternative that makes any progress, so that some is greedy and Content "123" would be parsed. The operator <<|> in uu-parsinglib has the same greedy behaviour. I would like to disambiguate the grammar so that the first result ([Open a, Content "123", Close a]) is selected (longest matching rule). I suppose that this may be done using <<|> to define a greedySome to be used in in pContent, however I am wondering whether there is another way to do this, without using such operator <<|>. Any help is appreciated. All the best, Marco

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1/15/2015 3:46:00 PM
by Diony Rosa 15 Jan '15

15 Jan '15

http://www.1367.co.nz/basjaupc/pebrbhpjthzcrumhnityftkmrmxbjau.myfduxbsyxon… Diony Rosa 1/15/2015 3:46:00 PM

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ParallelListComp strange behavior
by Michael Jones 14 Jan '15

14 Jan '15

I am trying to use ParallelListComp and have code that compiles but only produces one value, but I am not clear why. The code is something like: gen :: (a -> b) -> [MyType] gen f = [MyType (Just []) (Just c) (Just d) Nothing | c <- f | d <- [1,2,3,4] When the gen function is used with take or any other function, only one value is returned. Is there something here that can’t desugar properly to mzip that will still compile? Note I did not test this specific code, I am just writing it here to represent the different pieces of a larger piece of real code which is below. Mike ———— Real Code ———— data Config = Config { onOffControl::Maybe [DEVICE_ON_OFF_CONTROL_BITS] , seqUpPos::[Maybe ([DEVICE_SEQ_UP_POSITION_BITS], Word16)] , seqDownPos::[Maybe ([DEVICE_SEQ_DOWN_POSITION_BITS], Word16)] , tonTimers::[Maybe ([DEVICE_TON_TIMERS_BITS], Word16)] , toffTimers::[Maybe ([DEVICE_TOFF_TIMERS_BITS], Word16)] , vRange::Maybe [DEVICE_V_RANGE_BITS] , vThresh::[Maybe (Word16, Word16)] , rstbConfig::Maybe [DEVICE_RSTB_CONFIG_BITS] , faultResponse::Maybe [DEVICE_FAULT_RESPONSE_BITS] , breakpoint::Maybe ([DEVICE_BREAK_POINT_BITS], Word16) , writeProtect::Maybe ([DEVICE_WRITE_PROTECTION_BITS], Word16) , specialLot::Maybe Word16 , deviceId::Maybe Word16 , statusInfo::Maybe ([DEVICE_STATUS_INFORMATION_BITS]) , monitorStatus::Maybe ([DEVICE_MONITOR_STATUS_BITS]) , monitorStatusHistory::Maybe ([DEVICE_MONITOR_STATUS_HISTORY_BITS]) , monitorBackup::Maybe ([DEVICE_MONITOR_BACKUP_BITS]) , seqPosCount::Maybe ([DEVICE_SEQ_POSITION_COUNT_BITS], Word16) generateConfigs seqValues delayValues threshValues = return [Config (Just []) -- On off ([Just (suPol, suPos),Just (suPol, suPos),Just (suPol, suPos),Just (suPol, suPos),Just (suPol, suPos),Just (suPol, suPos)]) ([Just (sdPol, sdPos),Just (sdPol, sdPos),Just (sdPol, sdPos),Just (sdPol, sdPos),Just (sdPol, sdPos),Just (sdPol, sdPos)]) ([Just ([tonMax], tonDelay),Just ([tonMax], tonDelay),Just ([tonMax], tonDelay),Just ([tonMax], tonDelay),Just ([tonMax], tonDelay),Just ([tonMax], tonDelay)]) ([Just ([toffMax], toffDelay),Just ([toffMax], toffDelay),Just ([toffMax], toffDelay),Just ([toffMax], toffDelay),Just ([toffMax], toffDelay),Just ([toffMax], toffDelay)]) (Just [rng1, rng2, rng3, rng4, rng5, rng6]) ([Just (threshOv, threshUv),Just (threshOv, threshUv),Just (threshOv, threshUv),Just (threshOv, threshUv),Just (threshOv, threshUv),Just (threshOv, threshUv)]) (Just ([rst_en] ++ [rst_time])) (Just ([fault_number] ++ [fault_action] ++ [fault_delay] ++ fault_other ++ [fault_count])) (Just ([], 0)) (Just ([], 0)) (Just 0) Nothing Nothing Nothing Nothing Nothing Nothing | suPol <- [DEVICE_seq_up_position_bits] | suPos <- seqValues | sdPol <- [DEVICE_seq_down_position_bits] | sdPos <- seqValues | tonMax <- DEVICE_ton_timers_bits | tonDelay <- delayValues | toffMax <- DEVICE_toff_timers_bits | toffDelay <- delayValues | rng1 <- DEVICE_v_range_bits1 | rng2 <- DEVICE_v_range_bits2 | rng3 <- DEVICE_v_range_bits3 | rng4 <- DEVICE_v_range_bits4 | rng5 <- DEVICE_v_range_bits5 | rng6 <- DEVICE_v_range_bits6 | threshOv <- threshValues | threshUv <- threshValues | rst_time <- DEVICE_rstb_config_bits_time | rst_en <- DEVICE_rstb_config_bits_en | fault_number <- DEVICE_fault_response_bits_retry_number | fault_other <- [DEVICE_fault_response_bits_other] | fault_count <- DEVICE_fault_response_bits_count | fault_delay <- DEVICE_fault_response_bits_delay | fault_action <- DEVICE_fault_response_bits_action ] generateSeqValues :: IO [Word16] generateSeqValues = do vs <- replicateM 10 (randomRIO (0x0000, 0x03FF)) return vs generateDelayValues :: IO [Word16] generateDelayValues = do vs <- replicateM 10 (randomRIO (0x0000, 0x1FFF)) return vs generateThreshValues :: IO [Word16] generateThreshValues = do vs <- replicateM 10 (randomRIO (0x0000, 0x00FF)) return vs

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Re: [Haskell-cafe] working my way through Data.Type.Equality...my head hurts...
by oleg＠okmij.org 14 Jan '15

14 Jan '15

Richard Eisenberg wrote: > `~` is simply equality on types. The constraint `a ~ b` means that `a` > is the same type as `b`. We could have spelled it `=` if that weren't > used elsewhere. Before `~` was added to GHC, it might have been > implemented like this: > class Equals a b | a -> b, b -> a > instance Equals x x > -- no other instances! Actually, `~' has been implemented, back in 2004, and the implementation quite a bit more involved than the above (although still taking a couple of lines). The `~' constrain was called TypeCast back then, and there is a page about it explaining the benefits and peculiarities of the implementation. http://okmij.org/ftp/Haskell/typecast.html Perhaps the many examples of TypeCast make it less mysterious.

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Deploying Scotty App to AWS
by Stephen Portanova 14 Jan '15

14 Jan '15

I'm having trouble running my Scotty binary on amazon web services... I'm using Ubuntu 15.04, this gist (https://gist.github.com/yantonov/10083524) to install the haskell platform dependencies, and then I do a git pull to my repo and build my binary. Everything compiles, but when I do ./cabal-sandbox/bin/app or ./dist/build/app/app, nothing happens. No error messages or anything - the terminal just goes to the next line and hangs (on my Mac development machine the server starts up fine and prints a startup message). Any ideas or experience with deploying Scotty / Haskell apps would be really appreciated, thanks! - Stephen

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Future of the boxes package--call for ideas
by David Feuer 13 Jan '15

13 Jan '15

I've just taken over maintainership of the boxes package, and will be making a maintenance release shortly (as soon as I figure out how and get added to the maintainers group). The package, however, currently suffers from a paucity of bug reports (no problem) and feature requests (not so great). To keep things lively, I need a bit of help from two groups of people. If you use the package but wish it could do something more for you, I want to know about it. If you considered using the package but rejected it because it couldn't quite handle your job, I want to know about that too. I'd prefer if people would open issues and pull requests at https://github.com/treeowl/boxes/issues but I will also accept requests by email. Thanks, David

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