- Haskell-Cafe - Haskell.org

gtk2hs and hmake websites
by Joachim Breitner 12 Dec '10

12 Dec '10

Hi, I get regular error message from some Debian tools that check for new upstream versions that it cannot find http://haskell.org/hmake, and http://haskell.org/gtk2hs seems to be gone as well since the recent move of haskell.org. Is that temporary or will these projects have to find new homes? Greetings, Joachim -- Joachim "nomeata" Breitner mail: mail(a)joachim-breitner.de | ICQ# 74513189 | GPG-Key: 4743206C JID: nomeata(a)joachim-breitner.de | http://www.joachim-breitner.de/ Debian Developer: nomeata(a)debian.org

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The Monad Reader links are broken
by Jason Dagit 12 Dec '10

12 Dec '10

Hello, I noticed today that the links in this article point to Haskell.org and they are broken: http://themonadreader.wordpress.com/previous-issues/ Maybe someone can fix this? Thanks! Jason

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Avoiding the Y combinator for self-referencing types
by Florian Weimer 12 Dec '10

12 Dec '10

Suppose I've got some named objects which reference other objects by name: > data NodeS = NodeS {nameS :: String, refsS :: [String]} Through name resolution, the strings are translated to the actual nodes they denote: > data Node = Node {name :: String, refs :: [Node]} > resolve :: [NodeS] -> Map String Node NodeS and Node are quite similar, so they should probably be the same parametrized type. However, if I turn the type of the references into a type parameter, I need the type-level Y combinator to avoid an infinite type, and manipulating nodes turns a bit more tedious because of increased syntactic overhead. Is there a third choice, beyond manually expanding the type definition or using Y?

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ANN: improve-0.2.2
by Tom Hawkins 12 Dec '10

12 Dec '10

ImProve [1] is an imperative DSL for high assurance, embedded applications. This release includes a new compositional proof framework where users can leverage previously proved theorems to aid the proof of new theorems. This new addition was inspired from discussions with Lee Pike [2]. Lee also recommended the strategy of building disjunctive invariants to reduce, if not eliminate the need for multi step induction, thus dramatically reducing proof time. Using these new strategies with ImProve, we where able to verify several realtime safety properties of an Eaton Hybrid Hydraulic program. -Tom [1] http://hackage.haskell.org/package/improve [2] http://groups.google.com/group/fp-embedded/browse_thread/thread/63cd023e8f1…

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Contexts for type family instances
by Stephen Tetley 12 Dec '10

12 Dec '10

Hello all I've a type family DUnit that I use to allow the unit type, usually a Double, of geometric things (points, vectors...) to be parametric: > type family DUnit a :: * E.g for Points > data Point u = P2 u u > type instance (Point u) = u I can make an type instance for Maybe like this, using DUnit on the right hand side: > type instance DUnit (Maybe a) = DUnit a But pair is a problem. Is there a way to assert both parts of a pair should have the same DUnit? The code below won't compile but it should illustrate what I'm trying to do. > type instance (DUnit a ~ DUnit b) => DUnit (a,b) = DUnit a I don't want to pick an arbitrary side, e.g: > type instance DUnit (a,b) = DUnit a or > type instance DUnit (a,b) = DUnit b Thanks Best wishes Stephen

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How can i insert graphic into a haddock document?
by Poprádi Árpád 12 Dec '10

12 Dec '10

Hi, I have found nothing about this topic in the haddock documentation. Is there a light way to do that? Best regards, Árpád

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haskell2010 and state question.
by Magicloud Magiclouds 12 Dec '10

12 Dec '10

Hi, Formerly, I had IORef and some state monad to do the task of keeping states. Now in haskell 2010, I cannot find anything about it. Do I have to use ghc base package for this function? -- 竹密岂妨流水过山高哪阻野云飞

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dot-ghci files
by Tony Morris 12 Dec '10

12 Dec '10

I teach haskell quite a lot. I recommend using .ghci files in projects. Today I received complaints about the fact that ghci will reject .ghci if it is group-writeable. I didn't offer an opinion on the matter. I am wondering if these complaints have legitimate grounds i.e. maybe you want to have group write on that file for some reason. I'd appreciate some comments on this issue. Thanks. -- Tony Morris http://tmorris.net/

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haskell-2010 binary IO
by Permjacov Evgeniy 12 Dec '10

12 Dec '10

Does haskell 2010 include binary IO? If no, what was the reason?

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Issues Installing Vacuum-Cairo 0.4.1, gtk-0.12.0, GHC 6.12.3, Cairo 0.12.0
by aditya siram 11 Dec '10

11 Dec '10

Hi all, When I try to cabal install vacuum-cairo, I get the following error message : Resolving dependencies... Configuring vacuum-cairo-0.4.1... Preprocessing library vacuum-cairo-0.4.1... Building vacuum-cairo-0.4.1... [1 of 1] Compiling System.Vacuum.Cairo ( System/Vacuum/Cairo.hs, dist/build/System/Vacuum/Cairo.o ) System/Vacuum/Cairo.hs:239:17: Ambiguous occurrence `G.eventKeyName' It could refer to either `G.eventKeyName', imported from Graphics.UI.Gtk at System/Vacuum/Cairo.hs:21:0-36 or `G.eventKeyName', imported from Graphics.UI.Gtk.Gdk.Events at System/Vacuum/Cairo.hs:22:0-47 System/Vacuum/Cairo.hs:261:16: Ambiguous occurrence `G.eventKeyName' It could refer to either `G.eventKeyName', imported from Graphics.UI.Gtk at System/Vacuum/Cairo.hs:21:0-36 or `G.eventKeyName', imported from Graphics.UI.Gtk.Gdk.Events at System/Vacuum/Cairo.hs:22:0-47 cabal: Error: some packages failed to install: vacuum-cairo-0.4.1 failed during the building phase. The exception was: exit: ExitFailure 1 Can anyone shed some light? -deech

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