- Libraries - Haskell.org

can't understand the Cabal manual. flag, manual
by Roman Beslik 25 Nov '12

25 Nov '12

Hello. http://www.haskell.org/cabal/users-guide/developing-packages.html#package-d… {{{ manual: boolean (default: False) By default, Cabal will first try to satisfy dependencies with the default flag value and then, if that is not possible, with the negated value. However, if the flag is manual, then the default value (which can be overridden by commandline flags) will be used. }}} Can I interpret this as {{{ First, Cabal tries to satisfy dependencies with the default flag value. Second, if the flag is manual, Cabal tries to satisfy dependencies with the negated flag value. }}} ? {{{ This file should contain of a number global property descriptions and several sections. }}} Maybe it's my English, but I can only think of "descriptions of global properties of a number" which does not make sense.

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Adding swap/compose functions to Data.Tuple and Data.Function
by John Wiegley 24 Nov '12

24 Nov '12

Moving discussion from http://hackage.haskell.org/trac/ghc/ticket/7435: I propose adding the following three functions to Data.Tuple and Data.Function, respectively: swap :: (a,b) -> (b,a) swap = snd &&& fst Fairly obvious, but strangely missing. compose :: [(a -> a)] -> a -> a compose = foldr (.) id composeM :: [(a -> m a)] -> a -> m a composeM = foldr (<=<) return This can be done with Endo, of course, but the result is awkward. The idiom of composing a list of endomorphisms occurs often enough that you can Google for it. -- John Wiegley FP Complete Haskell tools, training and consulting http://fpcomplete.com johnw on #haskell/irc.freenode.net

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Proposal: Allow gunfold for Data.Map, Data.IntMap, etc.
by Edward Kmett 22 Nov '12

22 Nov '12

I would like to propose improving the Data instances for a number of currently completely opaque data types in the containers package, by using virtual constructors. The instance for Data.Map already uses fromList for gfoldl, it just stops there. Extending it to be able to gunfold and mention the name of that constructor would enable generic traversal libraries like uniplate, etc. to work over the contents of the Map, rather than bailing out in fear or crashing at the sight of a mkNoRepType. An example of the changes for Data.Map are highlighted below. instance (Data k, Data a, Ord k) => Data (Map k a) where gfoldl f z m = z fromList `f` toList m toConstr _ = fromListConstr gunfold k z c = case constrIndex c of 1 -> k (z fromList) _ -> error "gunfold" dataTypeOf _ = mapDataType dataCast2 f = gcast2 f fromListConstr :: Constr fromListConstr = mkConstr mapDataType "fromList" [] Prefix mapDataType :: DataType mapDataType = mkDataType "Data.Map.Map" [fromListConstr] I've used this approach for years on my own libraries to great effect. Discussion Period: 3 Weeks (I added a week for ICFP) -Edward

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Re: Proposal: Add (&) to Data.Function
by John Lato 22 Nov '12

22 Nov '12

> > From: David Menendez <dave(a)zednenem.com> > > On Tue, Nov 20, 2012 at 11:59 AM, Yitzchak Gale <gale(a)sefer.org> wrote: > > > It is a common idiom to write a sequence of composed combinators in > > reverse order to the way they would be written with ($) or (.). That > > naturally expresses the idea of the combinators as operations being > > applied in the given order. > > > > I think the bar should be pretty high before we add a third way to write > function application to base. How common is this? Common among whom? Why > can't the existing idioms of (.) and ($) work just as well? > I guardedly agree with Dave Menendez. There are a very limited number of convenient 1-character operators available, and I'm not certain that function application should take up 3 of them. On the other hand, this is a common enough idiom to have emerged in both diagrams and lens at least. (I'm not taking a position at this time) John L.

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Proposal: Add setEnv/unsetEnv to "base"
by Simon Hengel 20 Nov '12

20 Nov '12

Hi, setting environment variables is possible on both POSIX and Windows systems. Currently this functionally is missing from System.Environment; the "unix" package provides an implementation for POSIX systems. I propose to add setEnv/unsetEnv to System.Environment, so that it is easier to write applications that behave the same on POSIX and Windows systems. I implemented both in a way, so that they behave exactly the same on POSIX and Windows (modulo case sensitivity on Windows). For now I prepared a standalone implementation [1] and corresponding tests [2]. That implementation depends on the "unix" package. If the proposal is accepted, I will prepare a patch against "base" that includes the relevant code from "unix". Discussion Period: 2 Weeks Cheers, Simon [1] https://github.com/sol/setenv/blob/master/src/System/SetEnv.hs [2] https://github.com/sol/setenv/blob/master/test/System/SetEnvSpec.hs

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intersectionSet, differenceSet
by Henning Thielemann 16 Nov '12

16 Nov '12

When using the new Data.Map.fromSet function I encountered that I use it many times in connection with Map.intersection and Map.difference like so Map.intersection m (Map.fromSet (const ()) s) Map.difference m (Map.fromSet (const ()) s) Actually the element types of the second operands of Map.intersection and Map.difference are completely independent and the values of these maps are not touched. Thus I think that intersection and difference with a Set are the more natural operation. How about adding Map.intersectionSet :: Ord k => Map k a -> Set k -> Map k a Map.differenceSet :: Ord k => Map k a -> Set k -> Map k a to Data.Map?

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Cabal: download dependencies for later offline build
by Bram Neijt 15 Nov '12

15 Nov '12

Dear reader, I'm experimenting with creating my own little build server using disk images as job input/output and KVM to run them[1]. As a security measure, the build process does not have any network access during the build, so I need to make sure everything is available before the build starts. What is the easiest way to "take a cabal build offline" as it were, so I can make sure a cabal build will work without a network connection? Greetings, Bram [1] https://github.com/bneijt/construir/

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mtl-2.1 severly broken, cabal needs blacklisting
by Andreas Abel 15 Nov '12

15 Nov '12

After 2 days of shrinking 251 modules of source code to a few lines I realized that modify in MonadState causes <<loop>> in mtl-2.1. http://hackage.haskell.org/packages/archive/mtl/2.1/doc/html/src/Control-Mo… The bug has been fixed, apparently seven month ago. https://github.com/ekmett/mtl/pull/1 However, the "malicious" mtl-2.1 still lingers on: it is available from hackage and installed in many systems. This calls for a means of blacklisting broken or malicious packages. cabal update should also pull a blacklist of packages that will never be selected by cabal install (except maybe by explicit user safety overriding). I think such a mechanism is not only necessary for security purposes, but also to safe the valuable resources of our community. Cheers, Andreas -- Andreas Abel <>< Du bist der geliebte Mensch. Theoretical Computer Science, University of Munich Oettingenstr. 67, D-80538 Munich, GERMANY andreas.abel(a)ifi.lmu.de http://www2.tcs.ifi.lmu.de/~abel/

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Re: [Haskell-cafe] hackageDB haddock errors
by Andreas Abel 14 Nov '12

14 Nov '12

I found that for the recently uploaded Agda-2.3.2 there is no haddockumentation. Stumbling over the build protocol by chance http://hackage.haskell.org/packages/archive/Agda/2.3.2/logs/success/ghc-7.6 I searched for whether haddock had been executed and found, yes, but also, it failed: ... 40% ( 2 / 5) in 'Agda.Syntax.Abstract.Pretty' haddock: internal error: /tmp/ghc17357_0/ghc17357_126.s: hPutBuf: resource exhausted (No space left on device) Q: Could this build be run again, with sufficient disk space? For gtk-0.12.4 there is another explanation: it has build failures: http://hackage.haskell.org/packages/archive/gtk/0.12.4/logs/failure/ghc-7.6 On 13.11.2012 16:41, timothyhobbs(a)seznam.cz wrote: > Hello, > There are several packages without haddock documentation on hackage. > The one that bugs me right now, is the latest version of gtk2hs: > http://hackage.haskell.org/package/gtk > I've been told that this may be due to hackage updating docs with an > infrequent cron job, so that new packages don't get their docs for a > long time. Whatever is causing it, the fact that hayoo > http://holumbus.fh-wedel.de/hayoo/hayoo.html always uses the most > frequent docs, means that I cannot currently search for anything gtk2hs > related :( > > Can someone please look into prodding this cron job so it doesn't take > days to run, or look into resolving any errors that might be causing > this unfortunate behaviour? > > Thank you for your time, > and happy hacking, > Timothy -- Andreas Abel <>< Du bist der geliebte Mensch. Theoretical Computer Science, University of Munich Oettingenstr. 67, D-80538 Munich, GERMANY andreas.abel(a)ifi.lmu.de http://www2.tcs.ifi.lmu.de/~abel/

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Proposal: Remove Control.Concurrent{QSem,QSemN,,SampleVar,mergeIO,nmergeIO} from base
by Ian Lynagh 13 Nov '12

13 Nov '12

Hi all, I propose that we remove Control.Concurrent.QSem Control.Concurrent.QSemN Control.Concurrent.SampleVar Control.Concurrent.mergeIO Control.Concurrent.nmergeIO from base. Rationale: There is no real need for them to be in base, and they are not being well-maintained there (e.g. see [3160]). Chris Kuklewicz has already made a SafeSemaphore package that provides fixed versions of the 3 modules. Patch is attached (but basically it just removes the above). Suggested discussion deadline: Fri 22 June 2012. [3160] http://hackage.haskell.org/trac/ghc/ticket/3160 Thanks Ian

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