- Haskell-Cafe - Haskell.org

library for drawing charts
by Peter Gammie 05 Jun '08

05 Jun '08

Hello, Has anyone got some code for drawing charts? I don't mean graphs of functions, ala http://dockerz.net/twd/HaskellCharts and I don't mean calls to the Google Charts API ala http://community.livejournal.com/evan_tech/241080.html I would like something that can generate PNGs in memory, i.e. not directly to a file. This is close to what I have in mind: http://www.fred.net/brv/chart/ I'd like 2D pie charts, bar charts and something like a google-o-meter. Any pointers? cheers peter

4 5

Re: Having trouble with parallel Haskell
by Donnie Jones 05 Jun '08

05 Jun '08

Hello Bryan, 2008/6/4 Bryan O'Sullivan <bos(a)serpentine.com>: > I intended to write a half chapter or so about parallel programming in > Haskell for the book I'm working on, but I've been coming to the > conclusion that the time is not yet ripe for this. I hope it will be > helpful if I share my experiences here. > > Specifically, I was planning to write about parallel programming in pure > code: use of "par" and programming with strategies. > > The most substantial problem is that the threaded RTS in GHC 6.8.2 is > very crashy in the face of "par": about 90% of my runs fail with a > segfault or an assertion failure. Simon Marlow mentioned that this bug > is fixed, but I've been unsuccessful in building a GHC 6.8.3 release > candidate snapshot so far, so I can't verify this. > > When a run does go through, I have found it surprisingly difficult to > actually get both cores of a dual-core system to show activity. As > there are no tools I can use to see what is happening, I am stumped. It > is of course quite likely that I am doing something wrong that results > in unexpected dependencies, but I cannot find a means to gaining insight > into the problem. Although my Google Summer of Code project was not selected, I decided to go ahead and work on the Parallel Profiling Tools for GHC this Summer, with the help of Simon Marlow of course, for my Master's thesis. The work is nowhere near complete, as I just began working on it a couple of weeks ago. I was able to run the ParSort.hs program in your original post with my modified version of GHC HEAD that now supports parallel profiling. Hopefully, by the end of the Summer, Haskell's support for parallel profiling will be vastly improved. This is the example test I performed: ghc -parprof -threaded -o ParSort --make ParSort.hs time ./ParSort 1000000 +RTS -pN -N6 -RTS We have 1000000 elements to sort. Sorted all 1000000 elements. 28.04362s elapsed. real 0m36.060s user 0m44.107s sys 0m0.708s I have attached an Postscript file containing a graph that visualizes the parallel profiling data from the above test. A lot of work still needs to be done, but I just wanted to let you know that improvements are expected soon. Btw, ParSort.hs was taking advantage of both cores on my machine. Thank you. __ Donnie Jones

1 0

very hard to build darcs with win32 ghc-6.8.2!
by Tim Newsham 04 Jun '08

04 Jun '08

I built darcs for win32 recently and it was much more difficult than it should be. Probably most of the blame goes to ghc-6.8.2 binary release for win32. Half of the effort is getting the zlib prereq working. Previously to build zlib for win32 ghc I did the following: http://www.haskell.org/pipermail/haskell-cafe/2007-March/023059.html However, now, the gcc binary for ghc-6.8.2 does not work as well as I would like which requires a bit more effort: - It did not automatically add mingw headers during compilation, and to fix this I had to force some extra flags. I built a shell script "xcc": #!/bin/sh GHC=/ghc/ghc-6.8.2 PATH=/c$GHC/gcc-lib:$PATH export PATH /c$GHC/gcc -I $GHC/include -I $GHC/include/mingw \ -I $GHC/gcc-lib/include -L $GHC/gcc-lib "$@" - During linking it did not find crt2.o and adding it to PATH and -L did not help, so I just copied wholesale all of /c/ghc/ghc-6.8.2/gcc-lib into my zlib source directory. - At this point I was able to build with: CC=./xcc ./configure --prefix=/c/ghc/ghc-6.8.2 \ --libdir=/c/ghc/ghc-6.8.2 make make install Why is the gcc in ghc's directory so non-functional? Ok, so with zlib (the C library) installed, the zlib haskell package installs properly. Dependency resolved. Next, to build darcs I had to configure it without libcurl support (or alternately spend time chasing down that dep, pass for now). Using cygwin I ran "./configure" which falsely uses the cygwin gcc for configuration checks, but since gcc is never used directly during the compilation process, that doesn't matter that much. I could have tried the "xcc" trick here again, but didn't bother. I ran into two problems during the build: - -Werror is specified in the GNUMakefile and there are many warnings. I just removed -Werror for now. - During linking it was not able to resolve "SleepEx" from src/win32/System/Posix.hs. I could not figure out what is going on here. I tried adding "-lkernel32" and "-L /ghc/ghc-6.8.2/gcc-lib -Lkernel32" to the Makefile and it still did not work even though /ghc/ghc-6.8.2/gcc-lib/libkernel32.a has SleepEx@8 defined(!) Finally I bit the bullet and hacked around this by noticing that mingw headers have _sleep() defined. I replaced the code in Posix.hs with: foreign import ccall "_sleep" c_sleep :: CULong -> IO () sleep :: Integer -> IO CInt sleep n = c_sleep (fromIntegral n) >> return (toEnum $ fromIntegral n) At this point darcs builds and the binary seems to work (so far). I don't know the implication of my sleep hack (which doesn't return the actual time slept). Here's a small test program which uses FFI to SleepEx which I was not able to get working with win32 ghc-6.8.2. ------ {-# OPTIONS -fglasgow-exts -fffi #-} module Main where import Foreign.C.Types foreign import ccall "SleepEx" c_SleepEx :: CUInt -> CInt -> IO CInt main = do putStrLn "start" n <- c_SleepEx (2*1000) 1 print n ------- So, what is going on with ghc-6.8.2? Why is the gcc so hard to use now? Why can't I get FFI working with standard win32 functions? Why aren't there prebuilt win32 darcs binaries anymore? Tim Newsham http://www.thenewsh.com/~newsham/

3 2

[ANN] hs-pgms 0.1 -- Programmer's Minesweeper in Haskell
by Bertram Felgenhauer 04 Jun '08

04 Jun '08

Hi, I've just uploaded hs-pgms to hackage. It is a Haskell implementation of Programmer's Minesweeper [1], which allows programmers to implement minesweeper strategies and run them. (Note: ghc >= 6.8 is required.) hs-pgms uses MonadPrompt to achieve a clean separation between strategies, game logic, and presentation. There are two frontends, one command line frontend which is mainly useful for collecting statistics, and a GUI frontend, using gtk2hs, for watching the strategies in action. There's a git repo, see http://repo.or.cz/w/hs-pgms.git . enjoy, Bertram [1] http://www.ccs.neu.edu/home/ramsdell/pgms/index.html

1 0

ICFP2008 Call for Poster proposals
by Matthew Fluet (ICFP Publicity Chair) 04 Jun '08

04 Jun '08

ICFP 2008 poster session September 21, 2008 Call for presentation proposals ICFP 2008 will feature a poster session for researchers and practitioners, including students. The session will provide friendly feedback for work that is in gestation or ongoing, as well as opportunities to meet each other and exchange ideas. We welcome poster submissions on all ICFP topics, especially presentations of - applications of and to functional programming; - recent work presented at more distant venues; and - ongoing work, whether or not submitted to ICFP. There will be no formal proceedings, but presenters will be invited to submit working notes, demo code, and other materials to supplement their abstract and poster. These materials will be released informally on a Web page dedicated to the poster session. An accepted submission is not intended to replace conference or journal publication. Persons interested in presenting a poster are invited to submit a one-page abstract in SIGPLAN conference style http://www.acm.org/sigs/sigplan/authorInformation.htm to the Web site https://www.softconf.com/s08/icfp08-posters/submit.html by June 30, 2008. The program committee will review the submissions for relevance and interest, and notify the authors by July 14, 2008. Accepted posters must be presented by the authors in person on Sunday, September 21, 2008. Important dates: Submission: Monday, June 30, 2008 Notification: Monday, July 14, 2008 Presentation: Sunday, September 21, 2008 Program committee: Benjamin Pierce (University of Pennsylvania) Colin Runciman (University of York) Chung-chieh Shan (Rutgers University)

1 0

[ANNOUNCE] git-darcs-import 0.1
by Bertram Felgenhauer 04 Jun '08

04 Jun '08

Hi, I'm pleased to announce yet another tool for importing darcs repositories to git. Unlike darcs2git [1] and darcs-to-git [2], it's written in Haskell, on top of the darcs2 source code. The result is a much faster program - it can convert the complete ghc 6.9 branch (without libraries) in less than 15 minutes on my slightly dated machine (Athlon XP 2500+), which is quite fast [3]. Incremental updates work, too. The program is still rough around the edges, and there's some cosmetical work to do, especially with respect to converting author names. The program should recover from most errors, as long as nobody else modifies the destination repository. Nevertheless, it seems quite useable already. I hope somebody finds this useful. You can grab the source at http://int-e.home.tlink.de/haskell/git-darcs-import-0.1.tar.bz2 Look at the README for further information. Credits go to: David Roundy and all contributors for darcs2. The code base is surprisingly pleasant to work with. And of course, Linus Torvalds, Junio Hamano and all other git contributors. Enjoy, Bertram [1] http://repo.or.cz/w/darcs2git.git?a=shortlog [2] http://git.sanityinc.com/?p=darcs-to-git.git [3] http://nominolo.blogspot.com/2008/05/thing-that-should-not-be-or-how-to.html

8 15

Installing Haskore under Windows
by David 04 Jun '08

04 Jun '08

Hi! I'm currently running ghc under Windows XP and want to play around with Haskore, but I'm a little confused about how to install it, or if it's even possible to use it with ghc. The 'readme' file contains this note: "Note that the file ghc_add/IOExtensions.hs is a partial replacement of a library file of the same name under Hugs. It does not work yet on Windows/GHC (where one has to distinguish between binary and text IO)." Does this mean I have to use Hugs rather than ghc? I have both Hugs and ghc installed, but I'd prefer to use ghc if possible. In either case, I find the install instructions (for Haskore, that is) a little confusing, probably because I'm also new to Haskell. Any help would be greatly appreciated. Thanks.

2 1

problems with derive/TH
by Thomas Hartman 04 Jun '08

04 Jun '08

Haskellers/Chris, As part of my quest to better understand STM and eventually build a concurrent haskell server app, I checked out an embryonic haskell mud demo from Chris Smith's repo. It seemed like a great sample app. But I ran into a build issue that seems to have to do with derive/TH. I am assuming this used to work, but something changed, either in TH itself or switching from ghc6.6 to ghc6.8. From the error message (below) I surmise either a) M.Map based values used to automagically work with derive/TH, but no longer do... in which case I need to create this instance manually or b) this should still work, more or less... but I have to import the map instance via an additional module, or something like that. Any advice? Thomas. ***** This is the error I am getting: thartman@thartman-laptop:~/mud>cat _darcs/prefs/defaultrepo http://cdsmith.twu.net/demos/mud thartman@thartman-laptop:~/mud>ghc --version The Glorious Glasgow Haskell Compilation System, version 6.8.2 thartman@thartman-laptop:~/mud>runghc Setup.lhs configure; runghc Setup.lhs build Configuring mud-0.1... Preprocessing executables for mud-0.1... Building mud-0.1... [2 of 5] Compiling World ( World.hs, dist/build/mud/mud-tmp/World.o ) World.hs:42:0: No instances for (Eq (a (M.Map String Player)), Eq (a (M.Map ItemId Item)), Eq (a (M.Map PlayerId Player)), Eq (a (M.Map RoomId Room)), Eq (a RoomId)) arising from the 'deriving' clause of a data type declaration at World.hs:(42,0)-(50,14) Possible fix: add an instance declaration for (Eq (a (M.Map String Player)), Eq (a (M.Map ItemId Item)), Eq (a (M.Map PlayerId Player)), Eq (a (M.Map RoomId Room)), Eq (a RoomId)) When deriving the instance for (Eq (World a))

5 5

A simple beginner question
by Adam Smyczek 04 Jun '08

04 Jun '08

Example: data SampleType = A | B Int | C String | D -- .... etc. sampleTypes = [A, B 5, C "test"] :: [SampleType] How do I find for example element A in the sampleTypes list? Do I have to create e.g.: isA :: SampleType -> Bool isA A = True isA _ = False for every constructor and use find? It feels like this is not the quicker method. Thanks, Adam

8 9

Wouter-style expressions
by Ron Alford 04 Jun '08

04 Jun '08

Here's something that should be an easy extension of Wouter's approach to extensible datatypes, but I'm failing (possibly since it's 2:20am). I several classes of expressions I'm trying to represent (thus, Wouter's approach), and my first operation to implement over them is printing. Attached is a simplified version of what I'm doing. Expressions are composed of conjunctives (and) and atoms. Atoms are composed of a predicate string and a list of fillers (taken from 'Const' and 'Var'). For example (in a lisp like syntax): (and (pred c ?var1) (pred ?var1 ?var2)) To do this, I defined a 'Printable' class: class Functor f => Printable f where exprDoc :: f t -> Doc I think the 't' here will get me into trouble later. Combinations of printable types are also printable: instance (Printable f, Printable g) => Printable (f :+: g) where exprDoc (Inr x) = exprDoc x exprDoc (Inl y) = exprDoc y Constants, variables, and atoms are defined to be printable: instance Printable Var where exprDoc (Var name) = text ('?':name) instance Printable Const where exprDoc (Const name) = text name instance Printable f => Printable (Atomic (Expr f)) where exprDoc (Atomic p tl) = parens $ hsep $ (text p) : (map (\ (In t) -> exprDoc t) tl) But the obvious definition for conjunction doesn't work: instance Printable And where exprDoc (And el) = sep (map exprDoc el) GHC barfs, throwing: Couldn't match expected type `f t' against inferred type `t1' `t1' is a rigid type variable bound by the type signature for `exprDoc' at WouterTest.hs:62:17 Expected type: [f t] Inferred type: [t1] In the second argument of `map', namely `el' In the first argument of `sep', namely `(map exprDoc el)' I've attached the code. Compile and inspect with: $ ghci -fglasgow-exts -fallow-overlapping-instances WouterTest.hs test1 works great (other than needing some redundant typing, any hints?). test2 needs the definition of 'Printable And' to print, but I haven't gotten that to work yet. It also needs the redundant typing. -Ron However, I tried making more complex expression (conjunction, in this case), but I can't get the types to align. In particular, if I uncomment the obvious definition

2 1