- Haskell-Cafe - Haskell.org

Fun with type functions
by Simon Peyton-Jones 02 Jul '09

02 Jul '09

Friends Ken, Oleg, and I have finished Version 2 of our paper "Fun with Type Functions", which gives a programmer's tour of what type functions are and how they are useful. http://haskell.org/haskellwiki/Simonpj/Talk:FunWithTypeFuns If you have a moment to look at, and wanted to help us improve it, the above link goes to a wiki page where you can comment on the paper or discuss it. We still have time to improve it. Thanks Simon

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ghc static linking on Windows
by Günther Schmidt 02 Jul '09

02 Jul '09

Hi, I tried to compile an app that uses sqlite3.dll with the -optl-static flag and the error message is: C:\ghc\ghc-6.10.3\gcc-lib\ld.exe: cannot find -lsqlite3 collect2: ld returned 1 exit status

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Suggestions for simulating Object ID
by Hemanth Kapila 01 Jul '09

01 Jul '09

Hello all, Can some one please suggest something on simulating some sort of "object-Ids" in Haskell? I mean, something like the following relation will hold: > a1 == a2 = (objectID a1) == (objectID a2) Currently I have something like > import Data.Hash >import qualified Data.ByteString.Char8 as B > newtype UniqueID = UniqueID (Hash, B.ByteString) I have a type class called Identifiable, the instances of which are supposed to give a unqiue bytestring representation of the instance which can be arbitrarily long but should satisfy the condition mentioned earlier. > class Identifiable a where > instanceID :: a -> B.ByteString and finally, the required funtion objectID is defined as : > objectID :: (Hashable a, Identifiable a) => a -> UniqueID > objectID a1 = UniqueID (hash a1, instanceID a1) while comparing object Ids, I compare the hash values first (which can be faster for arbitrary values). Only if they are equal then I compare the instanceIDs and count on laziness for avoiding the construction of the bytestrings where they are not needed. Can you please suggest a better approach? I also toyed with the idea of storing all the data 'objects' in an array and use the index as the identifier but the trouble is I am not aware of all the number of instances before hand under all the circumstances. Many thanks Hemanth K

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Happy GLR mode build failures
by Cetin Sert 01 Jul '09

01 Jul '09

Hi, It's not possible to build the Happy glr examples using GHC 6.10.3 and Happy 1.18.4: cetin@unique:~/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr$ make make loop CMD=run make[1]: Entering directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr' for d in expr-eval expr-tree expr-monad hidden-leftrec highly-ambiguous packing nlp bio-eg; do (cd $d && make run); done make[2]: Entering directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/expr-eval' # might want to run happy with --ghc ghc -I../common -i../common -package data -O -cpp -fglasgow-exts -package lang -o expr --make Main.lhs <command line>: unknown package: data make[2]: *** [expr] Error 1 make[2]: Leaving directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/expr-eval' make[2]: Entering directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/expr-tree' # might want to run happy with --ghc ghc -I../common -i../common -package data -O2 -cpp -fglasgow-exts -package lang -o expr --make Main.lhs <command line>: unknown package: data make[2]: *** [expr] Error 1 make[2]: Leaving directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/expr-tree' make[2]: Entering directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/expr-monad' ghc -I../common -i../common -package data -cpp -fglasgow-exts -package lang -o expr --make Main.lhs <command line>: unknown package: data make[2]: *** [expr] Error 1 make[2]: Leaving directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/expr-monad' make[2]: Entering directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/hidden-leftrec' ghc -I../common -i../common -package data -cpp -fglasgow-exts -package lang -o expr --make Main.lhs <command line>: unknown package: data make[2]: *** [expr] Error 1 make[2]: Leaving directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/hidden-leftrec' make[2]: Entering directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/highly-ambiguous' ghc -I../common -i../common -package data -cpp -fglasgow-exts -package lang -o expr --make Main.lhs <command line>: unknown package: data make[2]: *** [expr] Error 1 make[2]: Leaving directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/highly-ambiguous' make[2]: Entering directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/packing' Makefile:8: warning: overriding commands for target `.y.hs' ../Makefile.defs:15: warning: ignoring old commands for target `.y.hs' ghc -I../common -i../common -package data -cpp -fglasgow-exts -package lang -o expr --make Main.lhs <command line>: unknown package: data make[2]: *** [expr] Error 1 make[2]: Leaving directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/packing' make[2]: Entering directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/nlp' ghc -I../common -i../common -package data -cpp -fglasgow-exts -package lang -o english --make Main.lhs <command line>: unknown package: data make[2]: *** [english] Error 1 make[2]: Leaving directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/nlp' make[2]: Entering directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/bio-eg' Making BioData.hs WITHOUT optimisation (for speed) ghc -I../common -i../common -package data -cpp -fglasgow-exts -package lang -funfolding-use-threshold0 -fno-strictness -c BioData.hs <command line>: unknown package: data make[2]: *** [BioData.hi] Error 1 make[2]: Leaving directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/bio-eg' make[1]: *** [loop] Error 2 make[1]: Leaving directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr' make: *** [all] Error 2 cetin@unique:~/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr$ cabal update Downloading the latest package list from hackage.haskell.org cetin@unique:~/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr$ cabal install data cabal: There is no package named data cetin@unique:~/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr$ happy --version; ghc --version Happy Version 1.18.4 Copyright (c) 1993-1996 Andy Gill, Simon Marlow (c) 1997-2005 Simon Marlow Happy is a Yacc for Haskell, and comes with ABSOLUTELY NO WARRANTY. This program is free software; you can redistribute it and/or modify it under the terms given in the file 'LICENSE' distributed with the Happy sources. The Glorious Glasgow Haskell Compilation System, version 6.10.3 or GHC 6.10.1 and Happy 1.18.2: cetin@sweethome:~/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr$ makemake loop CMD=run make[1]: Betrete Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr' for d in expr-eval expr-tree expr-monad hidden-leftrec highly-ambiguous packing nlp bio-eg; do (cd $d && make run); done make[2]: Betrete Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/expr-eval' # might want to run happy with --ghc ghc -I../common -i../common -package data -O -cpp -fglasgow-exts -package lang -o expr --make Main.lhs <command line>: unknown package: data make[2]: *** [expr] Fehler 1 make[2]: Verlasse Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/expr-eval' make[2]: Betrete Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/expr-tree' # might want to run happy with --ghc ghc -I../common -i../common -package data -O2 -cpp -fglasgow-exts -package lang -o expr --make Main.lhs <command line>: unknown package: data make[2]: *** [expr] Fehler 1 make[2]: Verlasse Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/expr-tree' make[2]: Betrete Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/expr-monad' ghc -I../common -i../common -package data -cpp -fglasgow-exts -package lang -o expr --make Main.lhs <command line>: unknown package: data make[2]: *** [expr] Fehler 1 make[2]: Verlasse Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/expr-monad' make[2]: Betrete Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/hidden-leftrec' ghc -I../common -i../common -package data -cpp -fglasgow-exts -package lang -o expr --make Main.lhs <command line>: unknown package: data make[2]: *** [expr] Fehler 1 make[2]: Verlasse Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/hidden-leftrec' make[2]: Betrete Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/highly-ambiguous' ghc -I../common -i../common -package data -cpp -fglasgow-exts -package lang -o expr --make Main.lhs <command line>: unknown package: data make[2]: *** [expr] Fehler 1 make[2]: Verlasse Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/highly-ambiguous' make[2]: Betrete Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/packing' Makefile:8: Warnung: Die Befehle für das Ziel ».y.hs« werden überschrieben ../Makefile.defs:15: Warnung: Alte Befehle für das Ziel ».y.hs« werden ignoriert ghc -I../common -i../common -package data -cpp -fglasgow-exts -package lang -o expr --make Main.lhs <command line>: unknown package: data make[2]: *** [expr] Fehler 1 make[2]: Verlasse Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/packing' make[2]: Betrete Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/nlp' ghc -I../common -i../common -package data -cpp -fglasgow-exts -package lang -o english --make Main.lhs <command line>: unknown package: data make[2]: *** [english] Fehler 1 make[2]: Verlasse Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/nlp' make[2]: Betrete Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/bio-eg' Making BioData.hs WITHOUT optimisation (for speed) ghc -I../common -i../common -package data -cpp -fglasgow-exts -package lang -funfolding-use-threshold0 -fno-strictness -c BioData.hs <command line>: unknown package: data make[2]: *** [BioData.hi] Fehler 1 make[2]: Verlasse Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/bio-eg' make[1]: *** [loop] Fehler 2 make[1]: Verlasse Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr' make: *** [all] Fehler 2 cetin@sweethome:~/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr$ happy --version; ghc --version Happy Version 1.18.2 Copyright (c) 1993-1996 Andy Gill, Simon Marlow (c) 1997-2005 Simon Marlow Happy is a Yacc for Haskell, and comes with ABSOLUTELY NO WARRANTY. This program is free software; you can redistribute it and/or modify it under the terms given in the file 'LICENSE' distributed with the Happy sources. The Glorious Glasgow Haskell Compilation System, version 6.10.1 When I try to manually build something out of a .y file, I keep getting: cetin@sweethome:~/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr$ find | grep -E "y$" | xargs -n 1 echo happy -gcal happy -gcal ./packing/Expr.y happy -gcal ./highly-ambiguous/Expr.y happy -gcal ./expr-eval/Expr.y happy -gcal ./expr-monad/Expr.y happy -gcal ./nlp/English.y happy -gcal ./hidden-leftrec/Expr.y happy -gcal ./expr-tree/Expr.y happy -gcal ./bio-eg/Bio.y cetin@sweethome:~/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr$ find | grep -E "y$" | xargs -n 1 happy -gcal reduce/reduce conflicts: 2 happy: src/ProduceGLRCode.lhs:190:11-76: Irrefutable pattern failed for pattern (pre, drop_me : post) shift/reduce conflicts: 7 reduce/reduce conflicts: 1 happy: src/ProduceGLRCode.lhs:190:11-76: Irrefutable pattern failed for pattern (pre, drop_me : post) shift/reduce conflicts: 9 happy: src/ProduceGLRCode.lhs:190:11-76: Irrefutable pattern failed for pattern (pre, drop_me : post) shift/reduce conflicts: 9 happy: src/ProduceGLRCode.lhs:190:11-76: Irrefutable pattern failed for pattern (pre, drop_me : post) shift/reduce conflicts: 2 happy: src/ProduceGLRCode.lhs:190:11-76: Irrefutable pattern failed for pattern (pre, drop_me : post) shift/reduce conflicts: 4 reduce/reduce conflicts: 1 happy: src/ProduceGLRCode.lhs:190:11-76: Irrefutable pattern failed for pattern (pre, drop_me : post) shift/reduce conflicts: 9 happy: src/ProduceGLRCode.lhs:190:11-76: Irrefutable pattern failed for pattern (pre, drop_me : post) unused rules: 20 shift/reduce conflicts: 35 reduce/reduce conflicts: 68 happy: src/ProduceGLRCode.lhs:190:11-76: Irrefutable pattern failed for pattern (pre, drop_me : post) Does anyone have solution for this? The irrefutable pattern failure issue is especially bothersome for me as I ran into it in a Fortran grammar I'm writing and got stuck. Best Regards, Cetin Sert

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List spine traversal
by Tony Morris 01 Jul '09

01 Jul '09

Is there a canonical function for traversing the spine of a list? I could use e.g. (seq . length) but this feels dirty, so I have foldl' (const . const $ ()) () which still doesn't feel right. What's the typical means of doing this? -- Tony Morris http://tmorris.net/

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gtk2hs tray icon disappears when using GHCi
by Deniz Dogan 01 Jul '09

01 Jul '09

Hi I'm just trying out gtk2hs for the first time and I quite like it. However, for some reason my tray icon (...Gtk.Display.StatusIcon) disappears after a split second when I run my program using GHCi. What's the reason for this? Perhaps this is even a bug? It works just fine if I compile an .exe. I'm using Windows XP with GHC 6.10.3 and gtk2hs 0.10.1. import Graphics.UI.Gtk import Graphics.UI.Gtk.Display.StatusIcon main :: IO () main = do initGUI window <- windowNew tray <- statusIconNewFromFile "c:/Program Files/TortoiseHg/icons/commit.png" window `onDestroy` mainQuit widgetShowAll window mainGUI -- Deniz Dogan

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Haskell on JVM
by Greg Meredith 01 Jul '09

01 Jul '09

Simon, et al, It might be interesting to look at CAL<http://labs.businessobjects.com/cal/>as a non-blank-slate beginning for Haskell on the JVM. To my mind there are three things that this needs to make it a real winner: - Much, much better Java interop. Basically, the bar to meet here is Scala/Java interop. - Better support for "std" Haskell syntax - and better support for some of the basic (semantic and syntactic) extensions - Figuring out what of Hackage it is reasonable to support Best wishes, --greg Date: Tue, 23 Jun 2009 15:16:03 +0100 > From: Simon Peyton-Jones <simonpj(a)microsoft.com> > Subject: RE: [Haskell-cafe] Haskell on the iPhone > To: Rick R <rick.richardson(a)gmail.com>, Haskell Cafe > <haskell-cafe(a)haskell.org> > Message-ID: > < > 638ABD0A29C8884A91BC5FB5C349B1C33F4BAAFA41(a)EA-EXMSG-C334.europe.corp.microsoft.com > > > > Content-Type: text/plain; charset="us-ascii" > > Good news about the iPhone port! > > There seems to be quite a bit more interest now in supporting platforms > other than win/*nix on x86 these days*. Maybe now there will be sufficient > motivation to make the fundamental changes required. Caveat: I have > absolutely no idea of the scope or complexity of said changes. I will look > through the LambdaVM code (and iPwn when available) to get an idea. > > There is definitely an opportunity here for someone to make an impact. > There is no reason in principle why Haskell can't run on a JVM or .net or > other platform. But it's not just a simple matter of absorbing some patch > or other. Here's a summary I wrote a little while ago: > > http://haskell.org/haskellwiki/GHC:FAQ#Why_isn.27t_GHC_available_for_.NET_o… > > The short summary is: > > * There is interesting design work to do; and then interesting > engineering work to make it a reality. > > * We (at GHC HQ) would love to see that happen, but are not likely > to drive it. > > * If someone, or a small group, wanted to take up the cudgels and > work on it, we'd be happy to advise. > > * We'd certainly consider folding the results into the HEAD, > provided the author(s) are willing to maintain it, and we feel that the > result is comprehensible and maintainable. > > * But another viable route might well be to use the GHC API, which > means that the result wouldn't be part of GHC at all, just a client of the > API. That would make it much easier to distribute upgrades etc, just as a > Cabal package. > > Simon > -- L.G. Meredith Managing Partner Biosimilarity LLC 1219 NW 83rd St Seattle, WA 98117 +1 206.650.3740 http://biosimilarity.blogspot.com

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ANN: package Boolean: Generalized booleans
by Conal Elliott 30 Jun '09

30 Jun '09

I just uploaded a new package [1] for generalized booleans, which provides type classes with generalizations of boolean values & operations, if-then-else, Eq and Ord. These values & types come up for me with every new deep DSEL, and I think they do for others as well. The design space has some tricky trade-offs, and I'm not positive I've found the optimum yet. Users & comments are very welcome. Please direct discussion to the haskell-cafe list (rather than haskell list). [1]: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Boolean - Conal

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Re: [Haskell-cafe] Monoid wants a (++) equivalent
by Bryan O'Sullivan 30 Jun '09

30 Jun '09

On Tue, Jun 30, 2009 at 9:50 AM, David Leimbach <leimy2k(a)gmail.com> wrote: > I actually worry that this will make people think, more incorrectly, that > Monoids are about appending stuff only. > I think that adding a graphical operator as a synonym for mappend would actually help to address that, since the magic word "append" would no longer be nearly as common in source code, and that textual name certainly is (unhelpfully) suggestive of a specific semantics.

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Re: [Haskell-cafe] Making a strict (non-lazy) GCL Interpreter
by Hector Guilarte 30 Jun '09

30 Jun '09

Thanks Ketil, I'll try to give that a try, but as I said beforen, I don't know anything about monads, and since this project is for next monday and I have many other projects for the University for next week too I can't learn them right now... What I need to do is randomly select an element from a List... Any Ideas? Also, I had another question in my original e-mail... Any ideas about that? ------Original Message------ From: Ketil Malde To: Hector Guilarte Cc: haskell-cafe(a)haskell.org Subject: Re: [Haskell-cafe] Making a strict (non-lazy) GCL Interpreter Sent: Jun 30, 2009 05:00 Hector Guilarte <hectorg87(a)gmail.com> writes: > I need to randomly select ONE of the valid conditions and execute it's > instruction. I know there is a Random Monad, but it returns an IO > Int, No, this is not right. Values in the Random monad are computations that rely on randomness, but they can produce values of arbitrary type. (The 'a' in 'Random a', no?) > Is there anyway I can do some Random that doesn't involve IO? or any other > solution? Some options are: 1. Use the IO monad 2. Use the Random monad 3. Pass around a RandomGen explicitly 4. Generate an infinite stream of random values, and pass that around I think option 2 is the nicest, but option 4 may work if the use of randomness is limited. No. 3 does the same as 2 (I presume, I never looked) but with a lot more noise in your code, and no. 1 erases the separation between real IO, and computations -- which IME includes a lot of them -- that happen to depend on randomness (but require no other IO). -k -- If I haven't seen further, it is by standing in the footprints of giants

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