February 2016 - Haskell-Cafe

Is there a way to generate instances from the GHCi REPL?
by Christopher Done 05 Feb '16

05 Feb '16

Good evening, Is there a way with TH to generate instances for a class in GHCi? I want to generate instances for a serialization class. I tried to write some TH to do it, but $(foo) in GHCi’s REPL says that it can only be Q Exp, not Q [Dec]. Sadness. I found qAddTopDecls. I tried to add the class declarations via $(foo >>= qAddTopDecls; stringE "OK!") and it says “Only function, value, and foreign import declarations may be added with addTopDecl". Woe. I could create a file and then load in that file, but loading modules loses all GHCi's state, which would defeat the purpose of using a REPL in the first place. Any hope? Ciao!

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Re: [Haskell-cafe] Can we improve Show instance for non-ascii charcters?
by Miguel Mitrofanov 04 Feb '16

04 Feb '16

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Re: [Haskell-cafe] Can we improve Show instance for non-ascii charcters?
by Miguel Mitrofanov 04 Feb '16

04 Feb '16

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Haskell game to translate
by Sergey Mironov 04 Feb '16

04 Feb '16

Hi, Cafe. My friend wants to improve her collaboration skills in the area of game development. She is a Translator and the plan is to learn Git by contributing some Russian/English/French (and maybe simple Korean) translations to a GitHub project. Could you recommend me (and my friend) some game project wich needs translation? Note, that It should support multylang features in some form, understandable for non-programmer. I'll help with required workplace setup. Haskell, Linux, etc. is OK. Regards, Sergey

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Hackage Docs
by Geraldus 04 Feb '16

04 Feb '16

Hi friends! Apologize, a lot of Hackage docs issues discussed here already, but I'll decided to bring this question one more time. I'm facing missing docs during last few weeks, both Hoogle and Hayoo links to Hackage and usual response I see is "Not found". Stackage helps a lot, but most of the time I have to manually search same term on Stackage again. Can we improve this sad situation finally?

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Month in Haskell Mode January 2016
by Gracjan Polak 04 Feb '16

04 Feb '16

Welcome Haskell Mode users, Haskell Mode progress report for January 2016. For previous issue see December 2015 <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-December…>. Reddit discussion <https://www.reddit.com/r/haskell/comments/441ukg/month_in_haskell_mode_janu…> . <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-January-…>What is Haskell Mode? Haskell Mode is an umbrella project for multiple Emacs tools for efficient Haskell development. Haskell Mode is an open source project developed by a group of volunteers constantly looking for contributions. For more information how to help see https://github.com/haskell/haskell-mode. <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-January-…>Important developments Haskell Mode 2015 retrospective <https://github.com/haskell/haskell-mode/wiki/Haskell-Mode-2015-retrospective> was published. Emacs 23 support was dropped. Last stable haskell-mode release that supports Emacs 23 is haskell-mode version 13.18 <https://github.com/haskell/haskell-mode/releases/tag/v13.18>. We have added code coverage reporting and it already helped to nail down some missing cases in our test suite for indentation and font locking. We are currently at 30% coverage. <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-January-…> Request Haskell Mode web presence is none at this point. I'd like to ask a volunteer to create a static web page deployed on github pages that will serve as Haskell Mode home page. Any takers? <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-January-…>Current project focus Current project focus is to lower entry barrier for newcomers by defining bite-sized tasks. Get 50 'well-defined-tasks' done as by the metric: https://github.com/haskell/haskell-mode/issues?q=is%3Aissue+label%3Awell-de… A 'well-defined-task' is a category of tasks that have the field cleared for them, questions already sorted out and detailed information how to get them done. So you can just sit, search for 'well-defined-task' label and enjoy the coding! The point is to lower the entry barrier for new users, new issue reporters and advanced programmers but Emacs lisp beginners to contribute to the project. Current status: 14 well-defined-tasks closed <https://github.com/haskell/haskell-mode/issues?q=is%3Aissue+label%3Awell-de…> plus 13 more open <https://github.com/haskell/haskell-mode/issues?q=is%3Aissue+label%3Awell-de…> . If only you can help with reaching our targets please do so! <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-January-…>Issues closed in January - [Discussion] Character class for apostrophe #549 <https://github.com/haskell/haskell-mode/issues/549> - Debugger triggered on "match c of", a typo for "case c of" #599 <https://github.com/haskell/haskell-mode/issues/599> - Interactive mode recognizes some lines as compiler errors incorrectly #635 <https://github.com/haskell/haskell-mode/issues/635> - make check should recompile files properly #709 <https://github.com/haskell/haskell-mode/issues/709> - haskell-process-suggest-pragma hangs emacs #754 <https://github.com/haskell/haskell-mode/issues/754> - ghc-mod / stack / dist dir #801 <https://github.com/haskell/haskell-mode/issues/801> - [Discussion] REPL vs IDE #809 <https://github.com/haskell/haskell-mode/issues/809> - haskell-mode becomes unresponsive when adding a language pragma #820 <https://github.com/haskell/haskell-mode/issues/820> - Drop Emacs 23 support #847 <https://github.com/haskell/haskell-mode/issues/847> - Can't press enter in haskell interactive mode #876 <https://github.com/haskell/haskell-mode/issues/876> - Mac OS X El Capitan: no such file or directory, ghci #908 <https://github.com/haskell/haskell-mode/issues/908> - Emacs hangs when typing behind whitespace #980 <https://github.com/haskell/haskell-mode/issues/980> - haskell-process-load-file error (wrong-type-argument number-or-marker-p nil) when code has an error #1004 <https://github.com/haskell/haskell-mode/issues/1004> - Regression quasi-quotes are not highlighted anymore #1041 <https://github.com/haskell/haskell-mode/issues/1041> - Custom Haskell variables don't retain their customization #1043 <https://github.com/haskell/haskell-mode/issues/1043> - Indentation point missing for record data declarations #1044 <https://github.com/haskell/haskell-mode/issues/1044> - Font lock Role annotations #1057 <https://github.com/haskell/haskell-mode/issues/1057> - Use undercover.el and https://coveralls.io/ #1062 <https://github.com/haskell/haskell-mode/issues/1062> - haskell-cabal-strip-list and haskell-cabal-listify #1076 <https://github.com/haskell/haskell-mode/issues/1076> - Indentation of guards does not work sensibly with haskell-indentation #1079 <https://github.com/haskell/haskell-mode/issues/1079> - Indentation of first data constructor does not work with haskell-indent #1080 <https://github.com/haskell/haskell-mode/issues/1080> - Annoying indentation behaviour when declaring data types #1081 <https://github.com/haskell/haskell-mode/issues/1081> - Can't indent, gets error. #1082 <https://github.com/haskell/haskell-mode/issues/1082> - [Discussion] Make haskell-indentation external, editor agnostic project #1086 <https://github.com/haskell/haskell-mode/issues/1086> - haskell-cabal-subsection-arrange-lines inserts superfluous commas #1094 <https://github.com/haskell/haskell-mode/issues/1094> - haskell-indentation misbehaves for comments #1101 <https://github.com/haskell/haskell-mode/issues/1101> - haskell-process-path-* now allowed to be lists #1112 <https://github.com/haskell/haskell-mode/issues/1112> - Wrong completion-at-point in Haskell interpreter with helm #1113 <https://github.com/haskell/haskell-mode/issues/1113> <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-January-…>Pull requests merged in January - Record indentation should follow tibell style #1047 <https://github.com/haskell/haskell-mode/pull/1047> - Defcustoms should not be autoloaded #1048 <https://github.com/haskell/haskell-mode/pull/1048> - Define url and some keywords/tags for haskell-mode #1049 <https://github.com/haskell/haskell-mode/pull/1049> - Make quasi quote more visible #1051 <https://github.com/haskell/haskell-mode/pull/1051> - Lexeme parsing improvements #1052 <https://github.com/haskell/haskell-mode/pull/1052> - Skip an indentation test for Emacs 25 #1053 <https://github.com/haskell/haskell-mode/pull/1053> - Require at least Emacs 24.1 #1055 <https://github.com/haskell/haskell-mode/pull/1055> - Add font lock type/data family declarations #1056 <https://github.com/haskell/haskell-mode/pull/1056> - User manual updates #1058 <https://github.com/haskell/haskell-mode/pull/1058> - Add literate font lock tests, remove unused parts #1059 <https://github.com/haskell/haskell-mode/pull/1059> - Fix typos in documentation strings #1060 <https://github.com/haskell/haskell-mode/pull/1060> - Use plain string face for quasi quotes #1061 <https://github.com/haskell/haskell-mode/pull/1061> - Add code coverage #1063 <https://github.com/haskell/haskell-mode/pull/1063> - Add keybinding for haskell-cabal-visit-file #1064 <https://github.com/haskell/haskell-mode/pull/1064> - Add type role to font lock #1066 <https://github.com/haskell/haskell-mode/pull/1066> - Add test for SQL font-lock #1067 <https://github.com/haskell/haskell-mode/pull/1067> - Add test for 'type role' font-lock #1068 <https://github.com/haskell/haskell-mode/pull/1068> - Remove turn-on/off-haskell-font-lock #1069 <https://github.com/haskell/haskell-mode/pull/1069> - More font lock tests #1070 <https://github.com/haskell/haskell-mode/pull/1070> - Add tests and fix for classify by first char #1071 <https://github.com/haskell/haskell-mode/pull/1071> - Disallow leading spaces in error regexp in interactive mode #1072 <https://github.com/haskell/haskell-mode/pull/1072> - Add some tests for indentation #1073 <https://github.com/haskell/haskell-mode/pull/1073> - Inline haskell-mode-jump-to-loc #1075 <https://github.com/haskell/haskell-mode/pull/1075> - Increase haskell-cabal.el coverage #1077 <https://github.com/haskell/haskell-mode/pull/1077> - Define haskell-package struct's slots #1083 <https://github.com/haskell/haskell-mode/pull/1083> - Utils coverage #1089 <https://github.com/haskell/haskell-mode/pull/1089> - Utils coverage #1090 <https://github.com/haskell/haskell-mode/pull/1090> - Improve haskell-utils-reduce-string. Add tests #1092 <https://github.com/haskell/haskell-mode/pull/1092> - Add post-command-hook related tests #1093 <https://github.com/haskell/haskell-mode/pull/1093> - Test utils #1095 <https://github.com/haskell/haskell-mode/pull/1095> - Add string tests #1096 <https://github.com/haskell/haskell-mode/pull/1096> - Follow comma style when arranging a Cabal section #1098 <https://github.com/haskell/haskell-mode/pull/1098> - Detect comma style #1099 <https://github.com/haskell/haskell-mode/pull/1099> - Implement haskell-goto-first-error #1100 <https://github.com/haskell/haskell-mode/pull/1100> - Bump version to 16.1-git #1102 <https://github.com/haskell/haskell-mode/pull/1102> - Honor equals on its own line in data decl #1105 <https://github.com/haskell/haskell-mode/pull/1105> - Honor equals on separate line after guards #1106 <https://github.com/haskell/haskell-mode/pull/1106> - Remove a stray parenthesis #1108 <https://github.com/haskell/haskell-mode/pull/1108> - Tidy up haskell-load.el: untabify, reindent. Fix some warnings. #1111 <https://github.com/haskell/haskell-mode/pull/1111> - Allow haskell-process-path-* to be lists. #1114 <https://github.com/haskell/haskell-mode/pull/1114> - Add haskell-indent tests #1115 <https://github.com/haskell/haskell-mode/pull/1115> - Prevent haskell-doc-mode to hang Emacs during user input waiting #1116 <https://github.com/haskell/haskell-mode/pull/1116> - Remove haskell-interactive-mode-completion-cache #1119 <https://github.com/haskell/haskell-mode/pull/1119> <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-January-…>Contributors active in January Arthur Fayzrakhmanov (Артур Файзрахманов), Bozhidar Batsov, Dan Aloni, Daniel Bergey, Fice-T, Gracjan Polak, Herbert Valerio Riedel, Kirill Ignatiev, Mike Sperber, Thomas Winant, U-Yuriy-PCYuriy, issue-dispenser, mrBliss <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-January-…> Contributing Haskell Mode needs volunteers like any other open source project. For more information see: https://github.com/haskell/haskell-mode/wiki Also drop by our IRC channel: #haskell-emacs at irc.freenode.net. Thanks!

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Building / cross compile GHC for OpenBSD/macppc.
by Christoph R. Murauer 03 Feb '16

03 Feb '16

Hello ! I am new here - sorry, if I ask something what was asked before. OpenBSD provides for amd64 and other platforms GHC and, also the haskell-platform which works very good. I try to get one of the old PowerMac's with a G5 CPU and saw, that there is no GHC (yes, there is a very old version - something like 3.x) for OpenBSD/macppc. I got some informations about to cross compile and saw also the wiki at https://ghc.haskell.org/trac/ghc/wiki/Building/CrossCompiling now my main question is, are there more informations about it ? Available for cross compile is GHC and haskell-platform 7.10.3, gcc 4.2.1 20070719, llvm 3.5.20140228 all on amd64. The planned target platforms are Mac's / PowerMac's with G3, G4 and G5 CPU's. All versions of OpenBSD/macppc are 32 bit only (including the G5). A cross compile from Mac OS X is no option because the OpenBSD project should be able to cross build on their machines (security reasons). Thanks for informations and tips. Regards, Christoph

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Problems with cabal and stackage
by David Turner 03 Feb '16

03 Feb '16

Hi, Overnight there seems to have been a change to stackage where it's now issuing redirects from http to https URLs: ~$ cabal update Downloading the latest package list from stackage-lts-2.22 Warning: http error: Unable to handle redirect, unsupported scheme: https://www.stackage.org/snapshot/lts-2.22/00-index.tar.gz cabal: Failed to download http://www.stackage.org/snapshot/lts-2.22/00-index.tar.gz : ErrorMisc "Error HTTP code: 301" My cabal doesn't seem to like https and I think it's a recentish version: $ cabal --version cabal-install version 1.22.0.0 using version 1.22.0.0 of the Cabal library I'm probably using a bit of an old workflow (and I know that LTS-2 is pretty old too) but is there any simple way of getting this working again? Cheers,

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Accessing and Inspecting StgBindings in Ghci
by Michael Christensen 03 Feb '16

03 Feb '16

Hi all, I'm currently trying to understand how STG works, and my goal right now is to be able to inspect StgBinding values. I've written a short program, based on the wiki article GHC/As a library <https://wiki.haskell.org/GHC/As_a_library>, like below: -- Code.hs -- module Lib (printSTG, dumpSTG) where import Control.Monad.Ghc (lift, runGhcT) import CorePrep (corePrepPgm) import CoreToStg (coreToStg) import DynFlags (defaultFatalMessager, defaultFlushOut) import GHC hiding (runGhcT) import GHC.Paths (libdir) import HscMain (newHscEnv) import HscTypes (hsc_dflags, typeEnvTyCons) import Outputable (interppSP, showSDoc) import System.Environment (getArgs) import StgSyn (StgBinding) dumpSTG :: String -> IO [StgBinding] dumpSTG fileName = defaultErrorHandler defaultFatalMessager defaultFlushOut $ runGhcT (Just libdir) $ do sess <- getSession let dflags = hsc_dflags sess setSessionDynFlags dflags cm <- compileToCoreModule fileName let md = cm_module cm ml <- fmap ms_location $ getModSummary $ moduleName md lift $ do cp <- corePrepPgm sess ml <$> cm_binds <*> (typeEnvTyCons . cm_types) $ cm coreToStg dflags md cp printSTG = getArgs >>= \x -> case x of [] -> putStrLn "usage: Main <file.hs>" (fileName:_) -> do bindings <- dumpSTG fileName str <- runGhcT (Just libdir) $ do dflags <- getSessionDynFlags return $ showSDoc dflags $ interppSP bindings putStrLn str This works when I compile it to print out a Haskell file in STG format. However, *my question is*, is there a way so that I can call dumpSTG to get back that list of StgBindings, *from within Ghci*? Whenever I do so within Ghci, i.e. ghci> :l code.hs ghci> bindings <- dumpSTG "fileToTest.hs" <interactive>: panic! (the 'impossible' happened) (GHC version 7.10.3 for x86_64-unknown-linux): no package state yet: call GHC.setSessionDynFlags I know that it's saying I need to set the session dyn flags, but I'm not sure how that can get done from within Ghci, especially because that needs to get done within the GhcMonad. Part of my problem may stem from having a inadequate understanding of monads. Any help or pointers would be greatly appreciated! Thank you very much, Mike

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Is there a type class for boring types?
by David Feuer 03 Feb '16

03 Feb '16

Or, alternatively, some common class that lets me express that a type is boring (i.e., inhabited by precisely one fully-defined value)? lens has Settable, whose law ensures the type involved has a boring representation (in the sense of representable functor), but is there a more fundamental way? class Boring x where inhabitant :: x instance Boring () where inhabitant = () instance Boring (Proxy a) where inhabitant = Proxy instance Boring y => Boring (x -> y) where inhabitant = const inhabitant instance (Boring x, Boring y) => Boring (x, y) where inhabitant = (inhabitant, inhabitant) instance Boring x => Boring (Const x y) where inhabitant = Const inhabitant instance Boring x => Boring (Identity x) where inhabitant = Identity inhabitant ...

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