August 2007 - Haskell-Cafe

Re: [Haskell-cafe] let and fixed point operator
by Dan Piponi 30 Aug '07

30 Aug '07

On 8/30/07, jerzy.karczmarczuk(a)info.unicaen.fr <jerzy.karczmarczuk(a)info.unicaen.fr> wrote: > Dan Piponi writes: > > In Haskell, there is no box. > > Well, there are boxes... > But there also thunks and latent, yet-unevaluated graphs... But the point of Haskell is to provide an abstraction that hides these details from you. (Though ultimately it's a leaky abstraction and there comes a point where you do need to know about these things.) > Anyway, I believe strongly that ALL people who have problems with the > Haskell protocole, and they are numerous, I teach a good sample of them, > should be encouraged to learn Prolog. I'd second that. It's hard to see the difference between declarative and imperative programming when you only have one instance of a declarative language from which to generalise. -- Dan

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happs on ghc 6.7 won't work because of dependency on Data.Binary (everything that depends on Data.Binary broken at present) ( unknown symbol `stg_uncheckedShiftRL64' )
by Thomas Hartman 30 Aug '07

30 Aug '07

happs on ghc 6.7 won't work because of dependency on Data.Binary, since everything that depends on Data.Binary is broken at present. This is for Data.Binary installed via cabal from darcs get --partial http://darcs.haskell.org/binary . Cabal installed without any errors, but perhaps there should have been one since it appears broke. So I think my project of using the ghc debugger to help understand happs is on ice until this gets resolved. Unless this has been fixed since August 16. (Anyone out there got a more recent version?) $ cat UseDataBinary.hs import Data.Binary main = putStrLn "hello world" $ /usr/local/bin/ghc-6.6.1 -e 'main' UseDataBinary.hs hello world $ /usr/local/bin/ghc-6.7.20070816 -e 'main' UseDataBinary.hs <interactive>: /usr/local/lib/binary-0.3/ghc-6.7.20070816/HSbinary-0.3.o: unknown symbol `stg_uncheckedShiftRL64' ghc-6.7.20070816: unable to load package `binary-0.3' $ /usr/local/bin/ghc-6.7.20070816 -e '' UseDataBinary.hs --- This e-mail may contain confidential and/or privileged information. If you are not the intended recipient (or have received this e-mail in error) please notify the sender immediately and destroy this e-mail. Any unauthorized copying, disclosure or distribution of the material in this e-mail is strictly forbidden.

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redirecting stdout
by Chad Scherrer 30 Aug '07

30 Aug '07

Is it possible to write a function redirect :: Handle -> IO () -> IO () so that "redirect h action" is just like action, except that all the output written to stdout now gets sent to h instead? Thanks, Chad

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cabal install of HDBC-odbc fails on ghc 6.7, -I flag causes problems
by Thomas Hartman 30 Aug '07

30 Aug '07

problemw with the -I flag to ghc are causing cabal install to fail for hdbc-odbc (darcs head). man ghc still reports that -I is a valid flag after installing ghc 6.7 from darcs head a couple days ago. I think the problem might be the space after the -I flag (which is bad for both 6.6.1 and 6.7) hartthoma@linuxpt:~/installs/HDBC-odbc-head/hdbc-odbc>/usr/local/bin/ghc-6.7.20070816 -I. -e '' Setup.hs hartthoma@linuxpt:~/installs/HDBC-odbc-head/hdbc-odbc>/usr/local/bin/ghc-6.7.20070816 -I/ -e '' Setup.hs hartthoma@linuxpt:~/installs/HDBC-odbc-head/hdbc-odbc>/usr/local/bin/ghc-6.7.20070816 -I / -e '' Setup.hs ghc-6.7.20070816: unrecognised flags: -I just a guess... anothing thing is it seems like there's a new INCLUDE pragma in 6.7. perhaps this should be used in one of the source files to get it to compile. but which one? I couldn't figure out what was causing ghc -c -I dist/build/Database/HDBC/ODBC/Connection_hsc_make.c -o dist/build/Database/HDBC/ODBC/Connection_hsc_make.o to be run. (I did try grepping on ghc but no luck, below.) Any tips on debugging this cabal install would be appreciated. thanks, thomas ************* $ runghc Setup.hs configure; runghc Setup.hs build ..... configure: Using tar found on system at: /bin/tar Reading parameters from /home/hartthoma/installs/HDBC-odbc-head/hdbc-odbc/HDBC-odbc.buildinfo Preprocessing library HDBC-odbc-1.1.2hartthoma@linuxpt:~/installs/HDBC-odbc-head/hdbc-odbc>darcs whatsnew.0... ghc-6.7.20070816: unrecognised flags: -I Usage: For basic information, try the `--help' option. compiling dist/build/Database/HDBC/ODBC/Connection_hsc_make.c failed command was: ghc -c -I dist/build/Database/HDBC/ODBC/Connection_hsc_make.c -o dist/build/Database/HDBC/ODBC/Connection_hsc_make.o ........ hartthoma@linuxpt:~/installs/HDBC-odbc-head/hdbc-odbc>darcs whatsnew { hunk ./Setup.hs 8 -main = defaultMainWithHooks defaultUserHooks{preConf = conf, postConf = ok} - where ok _ _ _ _ = return ExitSuccess +--main = defaultMainWithHooks defaultUserHooks{preConf = conf, postConf = ok} +-- where ok _ _ _ _ = return ExitSuccess +main = do + let ok _ _ _ _ = do return ExitSuccess + return () + in defaultMainWithHooks defaultUserHooks{preConf = conf, postConf = ok} + return () + } ..... hartthoma@linuxpt:~/installs/HDBC-odbc-head/hdbc-odbc>grep -i ghc * HDBC-odbc.buildinfo:ghc-prof-options: HDBC-odbc.buildinfo:ghc-options: HDBC-odbc.cabal:GHC-Options: -O2 Makefile:GHCPARMS := -fglasgow-exts Makefile:all: setup # GHC build Makefile: ghc -package Cabal Setup.hs -o setup Makefile: cd testsrc && ghc --make -package mtl -package HUnit -package MissingH -package HDBC -lodbc $(GHCPARMS) -o runtests -i../dist/build:.. ../d\ ist/build/hdbc-odbc-helper.o runtests.hs Makefile:test-ghc6: testsrc/runtests Makefile:interact-ghci: all Makefile: ghci -idist/build -Ldist/build $(GHCPARMS) Makefile:test: test-ghc6 test-hugs README.txt:You'll need either GHC 6.4.1 or above, or Hugs 2005xx or above. If README.txt:2) ghc --make -o setup Setup.lhs README.txt:To use with GHC, you'll want to use: --- This e-mail may contain confidential and/or privileged information. If you are not the intended recipient (or have received this e-mail in error) please notify the sender immediately and destroy this e-mail. Any unauthorized copying, disclosure or distribution of the material in this e-mail is strictly forbidden.

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2D game graphics library for Haskell?
by peterv 30 Aug '07

30 Aug '07

I’m currently playing around with SOE to make some simple interactive math exercises for students. This worked fine, although I could have done this much faster using C# (which I know very well), but since I’m addicted to Haskell now, I used the latter language ;) Furthermore, I hope that one day, I will know enough Haskell to learn it to the students, because I feel that functional programming should not be given in the last bachelor or master years, since most software engineering students then know OO programming extremely well and have a horrible time with FP (I currently did not meet anyone in my sector of game development that liked FP, and many of those people had a masters degree and some were PhDs) Anyway, SOE is great for learning Haskell, but it lacks a couple of fundamental functions to make it really attractive, like: - Support for images - Support for rendering to an “offscreen graphics surface” and reading the pixels from that surface (for pixel-wise collision detection) - Support for detecting non-ASCII key presses (cursor keys, etc) - Support for joysticks Concurrent Clean seems to have a nice 2D game library and PLT/DrScheme also has nice support for basic 2D graphics, but somehow I feel Haskell is more mature and more elegant. So before digging into “advanced” APIs (like GTK itself, which I know nothing about, I’m a Win32 GDI/XNA/WPF expert), I should ask the question if something similar exists? It has to be as simple as SOE. Would it be possible to extend the GTK SOE with support for the features mentioned above? Is this insanely difficult for someone like me who knows a lot about Win32 but little Haskell? Thanks, Peter Verswyvelen No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.484 / Virus Database: 269.12.4/969 - Release Date: 23/08/2007 16:04

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Re: [Haskell-cafe] Haskell on the Playstation 3? :-)
by Miguel 30 Aug '07

30 Aug '07

> Hmmm, random thought along similar lines, I mean I know the answer to > this thought is no, but I'm curious: could we get Haskell to run on a > graphics card??? I mean, I'm guessing the answer is no (not a > difficult guess ;-) ), but curious what it would take to make a > graphics card able to run Haskell? What about running Haskell on a PostScript printer? PostScript IS Turing-complete.

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Bug in Gtk2HS 0.9.12/SOE on WinXP? Or is it just me?
by Peter Verswyvelen 30 Aug '07

30 Aug '07

First of all, I'm really excited that GTK2HS 0.9.12 now allows launching SOE apps using GHCI. However, in the code below the blue and green triangle should render on top of each other, but the green triangle is rendered incorrectly. Being a newbie, I hesitate to file a bug report... Can anyone reproduce this? Maybe it works fine on unix? Thanks, Peter module Main where import Graphics.SOE.Gtk shape = [(200,100), (200,200), (100,200), (200,100)] main = runGraphics $ do w <- openWindow "Buggy polgon fill?" (300,300) setGraphic w $ (withColor Red $ polyline shape) `overGraphic` (withColor Green $ drawRegion $ createPolygon shape) drawInWindow w $ (withColor Red $ polyline shape) `overGraphic` (withColor Blue $ polygon shape) waitForClose w closeWindow w waitForClose w = do e <- getWindowEvent w case e of Closed -> return () otherwise -> waitForClose w

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GHC optimisations
by Andrew Coppin 30 Aug '07

30 Aug '07

Does GHC do stuff like converting (2*) into (shift 1) or converting x + x into 2*x? If I do x * sin 12, is GHC likely to compute sin 12 at compile-time?

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compiling happs under 6.7 (unbound implicit parameter error)
by Thomas Hartman 29 Aug '07

29 Aug '07

After much progress and learning, I'm stuck again trying to get happs to compile under ghc 6.7. (Hoping that running happs under the new ghc debugger will help me understand it better.) I was trying to compile from the "stable" 8.8 version, unzipped and with just a few modifications. (see attached zip). The problem has to do with an "unbound implicit parameter" [53 of 72] Compiling HAppS.Protocols.MessageWrap.W ( src/HAppS/Protocols/MessageWrap/W.hs, dist/build/HAppS/Protocols/MessageWrap/W.o ) src/HAppS/Protocols/MessageWrap/W.hs:209:63: Unbound implicit parameter (?style::Element -> XML Element) arising from a use of `xmlWrapM' at src/HAppS/Protocols/MessageWrap/W.hs:209:63-72 In the expression: xmlWrapM v In the definition of `ehShow'': ehShow' (DynException e) | Just (DynErr' v) <- fromDynamic e = xmlWrapM v I'd appreciate any advice. thomas. --- This e-mail may contain confidential and/or privileged information. If you are not the intended recipient (or have received this e-mail in error) please notify the sender immediately and destroy this e-mail. Any unauthorized copying, disclosure or distribution of the material in this e-mail is strictly forbidden.

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trouble compiling regex posix head (I think >0.92) on ghc 6.7
by Thomas Hartman 29 Aug '07

29 Aug '07

I'm trying to compile regex-posix on ghc 6.7. (Ultimate goal: happs on 6.7). First, I patched by changing the cabal file to be compatible with the new libraries broken out of base. I also had to add HsRegexPosixConfig.h to include/regex (I just copied it from somewhere else on my hard drive where I guess it had been put by an earlier regex-posix install, I don't know if it's compatible here but at least it permitted things to compile further.) Setup.hs build -v3 had a lot of warnigs but didn't seem to fail. However, Setup.hs install -v3 didn't work. the problem in build seems to occur around "upsweep partially failed or main not exported"... [6 of 6] Compiling Text.Regex.Posix ( Text/Regex/Posix.hs, dist/build/Text/Regex/Posix.o ) *** Parser: *** Renamer/typechecker: Text/Regex/Posix.hs:57:2: Warning: The export item `module Text.Regex.Posix.String' exports nothing Text/Regex/Posix.hs:59:2: Warning: The export item `module Text.Regex.Posix.Sequence' exports nothing Text/Regex/Posix.hs:61:2: Warning: The export item `module Text.Regex.Posix.ByteString' exports nothing Text/Regex/Posix.hs:63:2: Warning: The export item `module Text.Regex.Posix.ByteString.Lazy' exports nothing *** Deleting temp files: Deleting: /tmp/ghc9618_0/ghc9618_0.s Warning: deleting non-existent /tmp/ghc9618_0/ghc9618_0.s Upsweep partially successful. *** Deleting temp files: Deleting: link(batch): upsweep (partially) failed OR Main.main not exported; not linking. *** Deleting temp files: Deleting: *** Deleting temp dirs: Deleting: /tmp/ghc9618_0 complete output (along with patch) is attached. I'd appreciate any advice. best, thomas. --- This e-mail may contain confidential and/or privileged information. If you are not the intended recipient (or have received this e-mail in error) please notify the sender immediately and destroy this e-mail. Any unauthorized copying, disclosure or distribution of the material in this e-mail is strictly forbidden.

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