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Crashing - First Graphics Program in Haskell School of Expression(HSOE)
by Raja Koduru 10 Apr '09

10 Apr '09

Hi, I am a beginner. Help me. Here is my "main.hs", sample code from the book HSOE. ---------------------------------------------------------------- module Main where import SOE main = runGraphics ( do w <- openWindow "My First Graphics Program" (300, 300) drawInWindow w (text (100, 100) "Hello Graphics World") k <- getKey w closeWindow w ) ------------------------------------------------------------------ When this is run, a window pops up but it immediately crashes. I call "main" function after loading the above src file (main.hs) in ghci I am on XP, using GHC-6.10.2. It crashed on GHC-6.10.1 also. I downloaded the HSOE code from here: http://haskell.org/soe/software1.htm Used cabal to install OpenGL(-2.2.1.1) and GLFW(0.3). ghc-pkg list output: d:/ghc/ghc-6.10.2\package.conf: Cabal-1.6.0.3, GLFW-0.3, HUnit-1.2.0.3, OpenGL-2.2.1.1, QuickCheck-1.2.0.0, Win32-2.2.0.0, array-0.2.0.0, base-3.0.3.1, base-4.1.0.0, bytestring-0.9.1.4, containers-0.2.0.1, directory-1.0.0.3, (dph-base-0.3), (dph-par-0.3), (dph-prim-interface-0.3), (dph-prim-par-0.3), (dph-prim-seq-0.3), (dph-seq-0.3), filepath-1.1.0.2, (ghc-6.10.2), ghc-prim-0.1.0.0, haddock-2.4.2, haskell-src-1.0.1.3, haskell98-1.0.1.0, hpc-0.5.0.3, html-1.0.1.2, integer-0.1.0.1, mtl-1.1.0.2, network-2.2.1, old-locale-1.0.0.1, old-time-1.0.0.2, packedstring-0.1.0.1, parallel-1.1.0.1, parsec-2.1.0.1, pretty-1.0.1.0, process-1.0.1.1, random-1.0.0.1, regex-base-0.72.0.2, regex-compat-0.71.0.1, regex-posix-0.72.0.3, rts-1.0, stm-2.1.1.2, syb-0.1.0.1, template-haskell-2.3.0.1, xhtml-3000.2.0.1 ----------------------------------------------------------------------------------------- regards, raja

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WX: linking to system libraries statically
by FFT 10 Apr '09

10 Apr '09

I noticed that even simple WX demos like "Layout" are linked dynamically against 59 libraries on Linux. This would make distributing the binaries a nightmare. Is there a simple way to make a (mostly) statically linked binary?

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GHC: compile using multiple cores?
by Peter Verswyvelen 10 Apr '09

10 Apr '09

Is it possible to use all CPU cores when compiling with GHC and/or Cabal?

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ANN: network-bytestring 0.1.2
by Johan Tibell 10 Apr '09

10 Apr '09

I am pleased to announce a new release of network-bytestring, a Haskell library for fast socket I/O using ByteStrings. New in this release is support for scatter/gather I/O (also known as vectored I/O). Scatter/gather I/O provides more efficient I/O by using one system call to send several separate pieces of data and by avoiding unnecessary copying. I would like to thank Brian Lewis, Bryan O'Sullivan, and Thomas Schilling for contributing patches for this release. Get it: cabal install network-bytestring And on Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/network-bytestri… Windows hackers needed: I've made sure that the library builds on Windows but since I don't use Windows myself I haven't implemented scatter/gather I/O support for Windows. It should be straightforward to add and I'd be happy to review the patches. Cheers, Johan

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ghci *.hs
by Paul Keir 10 Apr '09

10 Apr '09

Hi all, I like to use ghci *.hs to start my session, but I then have to type :m +Main to bring the Main module into scope. Is there a command-line switch to control which modules are initially in scope with ghci? Thanks, Paul

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Re: [Haskell-cafe] Referential Transparency and Monads
by Luke Palmer 10 Apr '09

10 Apr '09

2009/4/9 Mark Spezzano <mark.spezzano(a)chariot.net.au> > Or does RT ignore the encapsulated data and just view the “action” > performed by the monad as the “value” of the monad? > If I understand you right, this is more-or-less correct. You may as well think of IO as some sort of algebraic type that you are building and returning. A value of type "IO Integer" is not, itself, an integer. Thus: main = let r = print "hello" in return () Prints nothing. RT steps in in a similar scenario: main = let r = print "hello" in do { r; r } Replacing "r" with its definition: main = do { print "hello"; print "hello" } As expected. Luke > > Just curious as to the rationale behind referential transparency and how it > applies to monads. > > > > Cheers, > > > > Mark Spezzano > > > > No virus found in this outgoing message. > Checked by AVG. > Version: 7.5.557 / Virus Database: 270.11.48/2048 - Release Date: 8/04/2009 > 7:02 PM > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > >

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Re: [Haskell-cafe] Referential Transparency and Monads
by Paul Keir 10 Apr '09

10 Apr '09

I think this topic is covered in Andrew Gordon's dissertation/book: Functional programming and input/output by Andrew D. Gordon You can read it online. Cheers, Paul

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Referential Transparency and Monads
by Mark Spezzano 09 Apr '09

09 Apr '09

Hi, How exactly do monads “solve” the problem of referential transparency? I understand RT to be such that a function can be replaced with a actual value. Since a monad could potentially encapsulate any other value—say, data read from a keyboard—doesn’t that violate the assumption of RT on monads? Or does RT ignore the encapsulated data and just view the “action” performed by the monad as the “value” of the monad? Just curious as to the rationale behind referential transparency and how it applies to monads. Cheers, Mark Spezzano No virus found in this outgoing message. Checked by AVG. Version: 7.5.557 / Virus Database: 270.11.48/2048 - Release Date: 8/04/2009 7:02 PM

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Problems getting errors with HXT
by rodrigo.bonifacio 09 Apr '09

09 Apr '09

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Debugging compile times (Template Haskell)
by Henning Günther 09 Apr '09

09 Apr '09

Hi, as the author of the encoding package[1] I'm quite annoyed by the extreeme long time it takes to compile a certain module (JISX0208). This module uses template haskell to generate both a Map (Map Char (Word8,Word8)) and an Array (UArray (Word8,Word8) Int) for character conversion. The file has about 6000 entries and the generated array has 8649 entries. Generating the syntax for the array and map is very fast (under a second) but compiling the code seems to take forever. Is there any way to find out why that is the case? I've tried pinpointing the problem but couldn't... [1] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/encoding

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OFX libs available ?
by Simon Michael 09 Apr '09

09 Apr '09

Has anyone got code for OFX financial data handling they could share ? Best - Simon

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ANN: tree-monad 0.2
by Sebastian Fischer 09 Apr '09

09 Apr '09

I am pleased to announce version 0.2 of the package tree-monad that provides instances of MonadPlus that represent the search space of non- deterministic computations as a tree. In version 0.2 I have implemented an optimized CPS version of the tree monad based on the idea described in "Asymptotic Improvement of Computations over Free Monads" [^1]. The package is on Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/tree-monad The sources are on Github: http://github.com/sebfisch/tree-monad Installation and usage instructions are at: http://sebfisch.github.com/tree-monad A possible application of search trees is parallel search as described in the blog post: http://www-ps.informatik.uni-kiel.de/~sebf/haskell/speedup-search-with-para… The package parallel-tree-search by Fabian Reck and myself http://hackage.haskell.org/cgi-bin/hackage-scripts/package/parallel-tree-se… implements the search described in the above blog post based on the hereby announced package tree-monad. Cheers, Sebastian [^1]: http://wwwtcs.inf.tu-dresden.de/~voigt/mpc08.pdf

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Ghc: -O harmful?
by Petr Skovron 09 Apr '09

09 Apr '09

Hello all, I have a haskell program that runs an order of magnitude slower when compiled with optimisations turned on. This happens on 6.8.2 as well as 6.10.1: petr@r4at184:/tmp[1]% ghc --make -fforce-recomp -o out buga.hs [1 of 1] Compiling Main ( buga.hs, buga.o ) Linking out ... petr@r4at184:/tmp% time ./out < 3-med.in >|/dev/null ./out < 3-med.in >| /dev/null 0,03s user 0,00s system 99% cpu 0,038 total petr@r4at184:/tmp% ghc --make -fforce-recomp -o out buga.hs -O [1 of 1] Compiling Main ( buga.hs, buga.o ) Linking out ... petr@r4at184:/tmp% time ./out < 3-med.in >|/dev/null ./out < 3-med.in >| /dev/null 0,99s user 0,01s system 99% cpu 1,001 total petr@r4at184:/tmp[1]% ghc --make -fforce-recomp -o out buga.hs -O2 [1 of 1] Compiling Main ( buga.hs, buga.o ) Linking out ... petr@r4at184:/tmp% time ./out < 3-med.in >|/dev/null ./out < 3-med.in >| /dev/null 0,99s user 0,01s system 99% cpu 1,004 total petr@r4at184:/tmp% ghc --version The Glorious Glasgow Haskell Compilation System, version 6.8.2 psxxxxxx:/tmp$ ghc --make -fforce-recomp -o out buga.hs [1 of 1] Compiling Main ( buga.hs, buga.o ) Linking out ... psxxxxxx:/tmp$ time ./out < 3-med.in >|/dev/null real 0m0.028s user 0m0.011s sys 0m0.007s psxxxxxx:/tmp$ ghc --make -fforce-recomp -o out buga.hs -O [1 of 1] Compiling Main ( buga.hs, buga.o ) Linking out ... psxxxxxx:/tmp$ time ./out < 3-med.in >|/dev/null real 0m0.252s user 0m0.225s sys 0m0.011s psxxxxxx:/tmp$ ghc --make -fforce-recomp -o out buga.hs -O2 [1 of 1] Compiling Main ( buga.hs, buga.o ) Linking out ... Vazeny pane, cekam na Vase rozkazy. psxxxxxx:/tmp$ time ./out < 3-med.in >|/dev/null real 0m0.239s user 0m0.225s sys 0m0.010s psxxxxxx:/tmp$ ghc --version The Glorious Glasgow Haskell Compilation System, version 6.10.1 The GHC documentation states that > -O2: > Means: "Apply every non-dangerous optimisation, even if it means > significantly longer compile times." The avoided "dangerous" > optimisations are those that can make runtime or space worse if > you're unlucky. They are normally turned on or off individually. If I understand this correctly, the dangerous optimisations should not be performed with -O. Am I doing anything wrong? Am I hitting a bug in GHC optimiser? A known one? The program source: -------------- petr@r4at184:/tmp$ cat buga.hs {-# LANGUAGE FlexibleContexts #-} import Control.Monad import Control.Monad.State data Predpoc a = Nic | Kus { delka :: Int, levy :: Predpoc a, pravy :: Predpoc a } deriving Show gList i = Kus 1 Nic Nic gPredpoc kus1 kus2 = Kus (delka kus1 + delka kus2) kus1 kus2 pop :: MonadState [a] m => m a pop = get >>= \(x:xs) -> put xs >> return x mbuild :: MonadState [Int] m => Int -> m (Predpoc Int) mbuild 1 = gList `liftM` pop mbuild n = liftM2 gPredpoc (mbuild n1) (mbuild n2) where n1 = n`div`2 n2 = n - n1 build n li = evalState (mbuild n) li best :: Predpoc Int -> Int -> Int -> Int best kus i j | i == 1 && j == delka kus = delka kus | j <= del1 = best (levy kus) i j | i > del1 = best (pravy kus) (i-del1) (j-del1) | otherwise = best (levy kus) i del1 + best (pravy kus) 1 (j-del1) where del1 = delka (levy kus) main = do n <- read `liftM` getLine pole <- liftM (build n . map read . words) getLine replicateM_ 100 $ do getLine print $ best pole 42 420 -------------- The sample input file (30k) can be downloaded from http://pikomat.mff.cuni.cz/petr/3-med.in I suspect that the main's variable "pole" (which is a large binary tree of type Predpoc Int) may be built from scratch in each iteration of the replicateM_ loop. Petr

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Functions from Data.Hashtable
by Peter Verswyvelen 09 Apr '09

09 Apr '09

These functions have their arguments reversed when compare to e.g. Map For example Data.HashTable.lookup<http://haskell.org/ghc/docs/latest/html/libraries/base/Data-HashTable.html#…> :: HashTable<http://haskell.org/ghc/docs/latest/html/libraries/base/Data-HashTable.html#…> key val -> key -> IO<http://haskell.org/ghc/docs/latest/html/libraries/base/System-IO.html#t%3AIO> (Maybe<http://haskell.org/ghc/docs/latest/html/libraries/base/Data-Maybe.html#t%3A…> val) Data.Map.lookup<http://hackage.haskell.org/packages/archive/containers/0.2.0.0/doc/html/Dat…> :: Ord<http://hackage.haskell.org/packages/archive/base/4.0.0.0/doc/html/Data-Ord.…> key => key -> Map<http://hackage.haskell.org/packages/archive/containers/0.2.0.0/doc/html/Dat…> key val -> Maybe<http://hackage.haskell.org/packages/archive/base/4.0.0.0/doc/html/Data-Mayb…> val I find this a bit odd. Is this by design?

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A challenge
by Thomas Davie 09 Apr '09

09 Apr '09

We have two possible definitions of an "iterateM" function: iterateM 0 _ _ = return [] iterateM n f i = (i:) <$> (iterateM (n-1) f =<< f i) iterateM n f i = sequence . scanl (>>=) (return i) $ replicate n f The former uses primitive recursion, and I get the feeling it should be better written without it. The latter is quadratic time – it builds up a list of monadic actions, and then runs them each in turn. Can anyone think of a version that combines the benefits of the two? Bob

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stream fusion -- multi-module programs
by Jason Dusek 09 Apr '09

09 Apr '09

In the paper "Stream Fusion: From Streams To Lists To Nothing At All", we find: For large multi-module programs, the results are less clear, with just as many programs speeding up as slowing down. We ﬁnd that for larger programs, GHC has a tendency to miss optimisation op- portunities for stream fusible functions across module boundaries, which is the subject of further investigation. What's the state of these things? Is this still an issue for stream fusion? -- Jason Dusek

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Re: A challenge
by Thomas Davie 08 Apr '09

08 Apr '09

Woops, the second version there applies it one too many times, it should have been replicate (n-1) f. Bob

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Parallel combinator, performance advice
by Neil Mitchell 08 Apr '09

08 Apr '09

Hi, I've written a parallel_ function, code attached. I'm looking for criticism, suggestions etc on how to improve the performance and fairness of this parallel construct. (If it turns out this construct is already in a library somewhere, I'd be interested in that too!) The problem I'm trying to solve is running system commands in parallel. Importantly (unlike other Haskell parallel stuff) I'm not expecting computationally heavy Haskell to be running in the threads, and only want a maximum of n commands to fire at a time. The way I'm trying to implement this is with a parallel_ function: parallel_ :: [IO a] -> IO () The semantics are that after parallel_ returns each action will have been executed exactly once. The implementation (attached) creates a thread pool of numCapabililties-1 threads, each of which reads from a task pool and attempts to do some useful work. I use an idempotent function to ensure that all work is done at most one, and a sequence_ to ensure all work is done at least once. Running a benchmark of issuing 1 million trivial tasks (create, modify, read and IO ref) the version without any parallelism is really fast (< 0.1 sec), and the version with parallelism is slow (> 10 sec). This could be entirely due to space leaks etc when queueing many tasks. I'm useful for any thoughts people might have! Thanks in advance, Neil

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Monad transformer to consume a list
by Stephan Friedrichs 08 Apr '09

08 Apr '09

Hello, is there a monad transformer to consume an input list? I've got external events "streaming into the monad" that are consumed on demand and I'm not sure if there's something better than a StateT. //Stephan -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr

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How to cut a file effciently?
by Magicloud Magiclouds 08 Apr '09

08 Apr '09

Hi, Let us say I have a text file of a million lines, and I want to cut it into smaller (10K lines) ones. How to do this? I have tried a few ways, none I think is lazy (I mean not reading the file all at the start). -- 竹密岂妨流水过山高哪阻野云飞

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Painful Data Abstraction
by Brad Larsen 08 Apr '09

08 Apr '09

I asked this earlier on #haskell, but it was quiet hour. Here goes. Suppose I have an abstract data type for prefix dictionaries of bytestrings. I define a typeclass in a module PrefixDict.Class: module PrefixDict.Class where import qualified Data.ByteString.Char8 as B type Word = B.ByteString class PrefixDict d where empty :: d isEmpty :: d -> Bool insert :: Word -> d -> d delete :: d -> Word -> d hasWord :: d -> Word -> Bool hasPrefix :: d -> Word -> Bool I then write several implementations, including a naive list implementation, and a trie implementation, in the modules PrefixDict.ListDict and PrefixDict.TrieDict, both looking something like this: module PrefixDict.ListDict where import PrefixDict.Class data ListDict = ListDict [Word] instance PrefixDict ListDict where ... Now, there are many properties that should be satisfied by any implementation of PrefixDict, that are not easily captured in the type system. Trying to be a good coder, I write up some generic QuickCheck properties, such as prop_insert_idempotent :: (Eq d, PrefixDict d) => d -> Word -> Bool prop_insert_idempotent d w = insert w d' == d' where d' = insert w d The problem is this: I can't think of a non-kludged way of checking that TrieDict and ListDict satisfy this abstract property without having to add explicit type signatures, e.g. quickCheck (prop_insert_idempotent :: TrieDict -> Word -> Bool) I have many abstract properties, and I *really* don't like having to put an explicit signature on each one. I came up with a hackishway that minimizes the number of signatures required, by checking all abstract properties in one, generic function, reflecting a type as a value, and using scoped type variables: testAbstractProperties :: forall d. (PrefixDict d) => d -> IO () testAbstractProperties _ = do quickCheck (prop_insert_idempotent :: d -> Word -> Bool) quickCheck (prop_delete_works :: d -> Word -> Property) ... I then call this function from a "test suite" function written for each module, e.g. testTrieDict :: IO () testTrieDict = do testAbstractProperties (undefined :: TrieDict) testTrieDictSpecificProperties This means I only have to write the type signatures on the properties in one place, but it is still less than ideal. Is there a better way of doing this, or is Haskell simply not good at this kind of data abstraction? Best, Brad Larsen

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cabal on mac os x (gmp problem)
by brian 08 Apr '09

08 Apr '09

For future reference: Solved, I just created a symlink to libgmp.dylib in /usr/local, and the zlib package was able to build.

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Generating arbitrary function in QuickCheck
by Yusaku Hashimoto 08 Apr '09

08 Apr '09

Hi, today, I want to ask about QuickCheck. I have known recently that arbitrary works on functions as well. I played on this for a while, and met a strange behavior. I tried to write property for sortBy. import Test.QuickCheck import Data.List instance Show (a -> b) where show _ = "<<function>>" instance Arbitrary Ordering where arbitrary = elements [LT,EQ,GT] mySortBy :: (Ord a) => (a -> a -> Ordering) -> [a] -> [a] mySortBy = sortBy prop_mysortby_sorted :: (Int -> Int -> Ordering) -> [Int] -> Property prop_mysortby_sorted cmp ls = null ls `trivial` all eq_or_lt (zipWith cmp sorted (tail sorted)) where sorted = mySortBy cmp ls eq_or_lt ord = ord == EQ || ord == LT I had thought Arbitrary instance for Ord and property for sortBy both fine. But checking fails: ghci> quickCheck prop_mysortby_sorted Falsifiable, after 2 tests: <<function>> [2,3] I guess arbitrary for (Int -> Int -> Ordering) generates a non-sense function like this: -- let (arb_compare :: Int -> Int -> Ordering) generated function. arb_compare 0 1 = GT arb_compare 1 0 = GT arb_compare _ _ = EQ Then, I want to ask two questions. 1. Is my guessing in function generated by arbitrary right? 2. If so, How do I generate right function? Thanks, Yusaku Hashimoto

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ANN: HCard -- A library for implementing card-like structures.
by Joe Fredette 08 Apr '09

08 Apr '09

HCard, is a library which supports a card-like data structures, it uses associated types [1] to provide shuffling, dealing, and other facilities. It's general enough to support many different types of playing cards, it currently comes with the common "French Deck" (4-suit, 13 card deck that is very common in the US) implemented and an example (though untested) cribbage scoring application. You can find HCard here [2,3], and a post about it's use of associated types here [1]. On another note, I can't think of a good reason I should be using associated types, as I explain in [1]. Well, no good reason other than the "cool factor" -- can anyone enlighten me on a possible practical benefit of using Assoc types as opposed to a simple indexed record? Anyway, enjoy HCard! /Joe Fredette [1] http://lowlymath.net/2009/card-games-scorekeeping-and-associated-datatypes/ [2] darcs get http://patch-tag.com/publicrepos/HCard [3] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HCard

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ghci/i386/dragonfly: unhandled ELF relocation(Rel) type 15
by G.Isenmann 08 Apr '09

08 Apr '09

Hi, I am trying to get a useable ghc on i386 dragonfly2.2.0. My current problem: $ /var/tmp/ghc-6.10.2/bin/ghci GHCi, version 6.10.2: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer ... linking ... done. ghc: /var/tmp/ghc-6.10.2/lib/ghc-6.10.2/base-4.1.0.0/HSbase-4.1.0.0.o: unhandled ELF relocation(Rel) type 15 Loading package base ... linking ... ghc: unable to load package `base' Looks like HSbase-4.1.0.0.o uses three different relocation types $ objdump -r lib/ghc-6.10.2/base-4.1.0.0/HSbase-4.1.0.0.o \ | awk '{print $2}' | sort -u | grep R_ R_386_32 R_386_PC32 R_386_TLS_IE but the ghc rts/Linker.c only supports two $ grep R_386_ rts/Linker.c # define R_386_32 RELOC_32 # define R_386_PC32 RELOC_PC32 case R_386_32: *pP = value; break; case R_386_PC32: *pP = value - P; break; The third seems to be the access to thread local errno $ objdump -r lib/ghc-6.10.2/base-4.1.0.0/HSbase-4.1.0.0.o \ | grep R_386_TLS_IE 001c2682 R_386_TLS_IE errno 001c2b5b R_386_TLS_IE errno 001c2f36 R_386_TLS_IE errno The difference to linux and freebsd seems to be that the access to the errno location is not hidden inside dragonflys libc but is visible for the caller similar to $ cat t.c static __thread int tls; int *get() { return &tls; } $ gcc -c t.c $ objdump -r t.o t.o: file format elf32-i386 RELOCATION RECORDS FOR [.text]: OFFSET TYPE VALUE 0000000b R_386_TLS_LE tls What would be the best or easiest way to deal with this situation? -- Goetz

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strange performance issue with takusen 0.8.3
by Marko Schütz 08 Apr '09

08 Apr '09

Dear All, I have an application where some simple data extracted from some source files is inserted into a PostgreSQL database. The application uses Takusen and is compiled with GHC 6.8.3. Some (59 in the test data) of the selects take on average 460ms each for a total time for this sample run of 30s. I prepare one select statement at the beginning of the run into which I then bind the specific values for every one of the selects. It does not seem to make a difference whether I do this or whether I just use a new statement for every select. For comparison, I have collected the SQL statements in a file with PREPARE ... and DEALLOCATE for _every_ select and then run this file through psql. This takes 2s! During the run of the GHC-compiled executable the cpu load goes up. In top I see %CPU of above 72%. Any ideas that might enlighten are welcome. Best regards, Marko

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Re: Configuring cabal dependencies at install-time
by John Lato 08 Apr '09

08 Apr '09

> From: Jeff Heard <jefferson.r.heard(a)gmail.com> > > Is there a way to do something like autoconf and configure > dependencies at install time? Building buster, I keep adding > dependencies and I'd like to keep that down to a minimum without the > annoyance of littering Hackage with dozens of packages. For instance, > today I developed an HTTP behaviour and that of course requires > network and http, which were previously not required. I'm about to > put together a haxr XML-RPC behaviour as well, and that of course > would add that much more to the dependency list. HaXml, haxr, and > haxr-th most likely. > > so... any way to do that short of making a bunch of separate packages > with one or two modules apiece? Otherwise I'm thinking of breaking > things up into buster, buster-ui, buster-network, buster-console, and > buster-graphics to start and adding more as I continue along. > I'd be interested in hearing answers to this as well. I'm not a fan of configure-style compile-time conditional compilation, at least for libraries. It makes it much harder to specify dependencies. With this, if package Foo depends on buster and the HTTP behavior, it's no longer enough to specify "build-depends: buster" because that will only work if buster was configured properly on any given system. I think that the proper solution is to break up libraries into separate packages as Jeff suggests (buster, buster-ui, etc.), but then the total packages on hackage would explode. I don't feel great about doing that with my own packages either; is it a problem? If so, maybe there could be just one extra package, e.g. buster and buster-extras. Is there a better solution I'm missing? John Lato

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threadDelay granularity
by Ulrik Rasmussen 08 Apr '09

08 Apr '09

Hello. I am writing a simple game in Haskell as an exercise, and in the rendering loop I want to cap the framerate to 60fps. I had planned to do this with GHC.Conc.threadDelay, but looking at it's documentation, I discovered that it can only delay the thread in time spans that are multiples of 20ms: http://www.haskell.org/ghc/docs/6.4/html/libraries/base/Control.Concurrent.… I need a much finer granularity than that, so I wondered if it is possible to either get a higher resolution for threadDelay, or if there is an alternative to threadDelay? I noticed that the SDL library includes the function "delay", which indeed works with a resolution down to one millisecond. However, since I'm using HOpenGL and GLUT, I think it would be a little overkill to depend on SDL just for this :). Thanks, Ulrik Rasmussen

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advice on space efficient data structure with efficient snoc operation
by Manlio Perillo 07 Apr '09

07 Apr '09

Hi. I'm still working on my Netflix Prize project. For a function I wrote, I really need a data structure that is both space efficient (unboxed elements) and with an efficient snoc operation. I have pasted a self contained module with the definition of the function I'm using: http://hpaste.org/fastcgi/hpaste.fcgi/view?id=3453 The movie ratings are loaded from serialized data, and the result is serialized again, using the binary package: transcodeIO :: IO () transcodeIO = do input <- L.hGetContents stdin let output = encodeZ $ transcode $ decodeZ input L.hPut stdout output (here encodeZ and decodeZ are wrappers around Data.Binary.encode and Data.Binary.decode, with support to gzip compression/decompression) This function (transcodeIO, not transcode) takes, on my Core2 CPU T7200 @ 2.00GHz: real 30m8.794s user 29m30.659s sys 0m10.313s 1068 Mb total memory in use The problem here is with snocU, that requires a lot of copying. I rewrote the transcode function so that the input data set is split in N parts: http://hpaste.org/fastcgi/hpaste.fcgi/view?id=3453#a3456 The mapReduce function is the one defined in the Real World Haskell. The new function takes (using only one thread): real 18m48.039s user 18m30.901s sys 0m6.520s 1351 Mb total memory in use The additional required memory is probably caused by unionsWith, that is not strict. The function takes less time, since array copying is optimized. I still use snocU, but on small arrays. GC time is very high: 54.4% Unfortunately I can not test with more then one thread, since I get segmentation faults (probably a bug with uvector packages). I also got two strange errors (but this may be just the result of the segmentation fault, I'm not able to reproduce them): tpp.c:63: __pthread_tpp_change_priority: Assertion `new_prio == -1 || (new_prio >= __sched_fifo_min_prio && new_prio <= __sched_fifo_max_prio)' failed. internal error: removeThreadFromQueue: not found (GHC version 6.8.2 for i386_unknown_linux) Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug Now the question is: what data structure should I use to optimize the transcode function? IMHO there are two solutions: 1) Use a "lazy" array. Something like ByteString.Lazy, and what is available in storablevector package. Using this data structure, I can avoid the use of appendU. 2) Use an "unboxed" list. Something like: http://mdounin.ru/hg/nginx-vendor-current/file/tip/src/core/ngx_list.h That is: a linked list of unboxed arrays, but unlike the lazy array solution, a snoc operation avoid copying if there is space in the current array. I don't know if this is easy/efficient to implement in Haskell. Any other suggestions? Thanks Manlio Perillo

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CFP: JFP Special Issue on Generic Programming
by Matthew Fluet (ICFP Publicity Chair) 07 Apr '09

07 Apr '09

OPEN CALL FOR PAPERS JFP Special Issue on Generic Programming Deadline: 1 October 2009 http://www.comlab.ox.ac.uk/ralf.hinze/JFP/cfp.html Scope ----- Generic programming is about making programs more adaptable by making them more general. Generic programs often embody non-traditional kinds of polymorphism; ordinary programs are obtained from them by suitably instantiating their parameters. In contrast to normal programs, the parameters of a generic program are often quite rich in structure; for example they may be other programs, types or type constructors, classes, concepts, or even programming paradigms. This special issue aims at documenting state-of-the-art research, new developments and directions for future investigation in the broad field of Generic Programming. It is an outgrowth of the series of Workshops on Generic Programming, which started in 1998 and which continues this year with an ICFP affiliated workshop in Edinburgh. Participants of the workshops are invited to submit a suitably revised and expanded version of their paper to the special issue. The call for papers is, however, open. Other contributions are equally welcome and are, indeed, encouraged. All submitted papers will be subjected to the same quality criteria, meeting the standards of the Journal of Functional Programming. The special issue seeks original contributions on all aspects of generic programming including but not limited to o adaptive object-oriented programming, o aspect-oriented programming, o case studies, o concepts (as in the STL/C++ sense), o component-based programming, o datatype-generic programming, o generic programming with dependent types, o meta-programming, o polytypic programming, and o programming with modules. Submission details ------------------ Manuscripts should be unpublished works and not submitted elsewhere. Revised versions of papers published in conference or workshop proceedings that have not appeared in archival journals are eligible for submission. Deadline for submission: 1 October 2009 Notification of acceptance or rejection: 15 January 2010 Revised version due: 15 March 2010 For submission details, please consult http://www.comlab.ox.ac.uk/ralf.hinze/JFP/cfp.html or see the Journal's web page http://journals.cambridge.org/jfp Guest Editor ------------ Ralf Hinze University of Oxford Computing Laboratory Wolfson Building, Parks Road, Oxford OX1 3QD, UK. Telephone: +44 (1865) 610700 Fax: +44 (1865) 283531 Email: ralf.hinze(a)comlab.ox.ac.uk WWW: http://www.comlab.ox.ac.uk/ralf.hinze/ -------------------------------------------------------------------------------

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Re: [Haskell-cafe] threadDelay granularity
by Ulrik Rasmussen 07 Apr '09

07 Apr '09

On Tue, Apr 07, 2009 at 04:01:01PM +0200, Peter Verswyvelen wrote: > Are you on Windows? Because this might be because GHC is not using a high > resolution timer for doing its scheduling, I don't know... No, Ubuntu 8.10. That may very well be, I'm not that much into the details of GHC. I'm thinking about importing a system dependent delay method through the FFI to get more control over the delay interval, but that seems like overkill too. Also, I don't know if that would introduce some nasty problems, again, I'm not that into the inner workings of GHC. For now I'll just allow the application to render as fast as possible, the primary motivation for capping the framerate was to prevent my laptop from getting so hot that I can't have it in my lap :). (I see that I replied to you instead of to the list by accident. I'm CC'ing the message to the list now) /Ulrik > On Tue, Apr 7, 2009 at 3:21 PM, Ulrik Rasmussen <haskell(a)utr.dk> wrote: > > > On Tue, Apr 07, 2009 at 02:53:20PM +0200, Peter Verswyvelen wrote: > > > I think this is an RTS option. > > > > > http://www.haskell.org/ghc/docs/latest/html/users_guide/using-concurrent.ht… > > > > Ahh, I found it now. Seems like the `-C' option didn't work because it > > still limited by the master tick interval. Using `+RTS -V0.001' helps. > > It is a bit inaccurate at that resolution though. > > > > > > > > > > > > > > On Tue, Apr 7, 2009 at 1:41 PM, Ulrik Rasmussen <haskell(a)utr.dk> wrote: > > > > > > > Hello. > > > > > > > > I am writing a simple game in Haskell as an exercise, and in the > > > > rendering loop I want to cap the framerate to 60fps. I had planned to > > do > > > > this with GHC.Conc.threadDelay, but looking at it's documentation, I > > > > discovered that it can only delay the thread in time spans that are > > > > multiples of 20ms: > > > > > > > > > > > > > > http://www.haskell.org/ghc/docs/6.4/html/libraries/base/Control.Concurrent.… > > > > > > > > I need a much finer granularity than that, so I wondered if it is > > > > possible to either get a higher resolution for threadDelay, or if there > > > > is an alternative to threadDelay? > > > > > > > > I noticed that the SDL library includes the function "delay", which > > > > indeed works with a resolution down to one millisecond. However, since > > > > I'm using HOpenGL and GLUT, I think it would be a little overkill to > > > > depend on SDL just for this :). > > > > > > > > > > > > Thanks, > > > > > > > > Ulrik Rasmussen > > > > _______________________________________________ > > > > Haskell-Cafe mailing list > > > > Haskell-Cafe(a)haskell.org > > > > http://www.haskell.org/mailman/listinfo/haskell-cafe > > > > > >

1 0

System.Process.Posix
by Cristiano Paris 07 Apr '09

07 Apr '09

Is it me or the above package is not included in Hoogle? Cristiano

7 8

tail recursion
by Daryoush Mehrtash 07 Apr '09

07 Apr '09

Is the call to "go" in the following code considered as tail recursion? data DList a = DLNode (DList a) a (DList a) mkDList :: [a] -> DList a mkDList [] = error <http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:error> "must have at least one element" mkDList xs = let (first,last <http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:last>) = go last <http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:last> xs first in first where go :: DList a -> [a] -> DList a -> (DList a, DList a) go prev [] next = (next,prev) go prev (x:xs) next = let this = DLNode prev x rest (rest,last <http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:last>) = *go this xs next* in (this,last <http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:last>) Daryoush

2 1

automatically inserting type declarations
by FFT 07 Apr '09

07 Apr '09

I remember hearing about a Haskell mode for Vim, Emacs, Yi or VisualHaskell that inserts type declarations automatically (it's lazier to just check the type than to write it manually), but I can't remember any details. What editor mode / IDE was it? What do most people use with GHC on Linux? I'm more used to Vim than to Emacs. Yi sounds like something I might like. Is it stable enough to solve more problems than it would create? (I hate buggy and broken stuff)

3 2

replicateM should be called mreplicate?
by Sjoerd Visscher 07 Apr '09

07 Apr '09

Considering these naming conventions: http://haskell.org/ghc/docs/latest/html/libraries/base/Control-Monad.html#3 • A postfix 'M' always stands for a function in the Kleisli category: The monad type constructor m is added to function results (modulo currying) and nowhere else. So, for example, filter :: (a -> Bool) -> [a] -> [a] filterM :: (Monad m) => (a -> m Bool) -> [a] -> m [a] • A postfix '_' changes the result type from (m a) to (m ()). Thus, for example: sequence :: Monad m => [m a] -> m [a] sequence_ :: Monad m => [m a] -> m () • A prefix 'm' generalizes an existing function to a monadic form. Thus, for example: sum :: Num a => [a] -> a msum :: MonadPlus m => [m a] -> m a replicateM has the following type: replicateM :: Monad m => Int -> m a -> m [a] Am I missing something or should this have been called mreplicate? greetings, -- Sjoerd Visscher sjoerd(a)w3future.com

4 4

Infix tuple comma query (,)
by Paul Keir 07 Apr '09

07 Apr '09

module Main where data (:%^&) a b = a :%^& b deriving (Show) main = do print $ 18 :%^& (Just 99) print $ (,) 9 10 print $ 9 , 10 The last line in the code above causes a compile error. Why does infix use of the comma (tuple constructor?) function fail without brackets? Thanks, Paul

4 3

Lazy vs correct IO [Was: A round of golf]
by oleg＠okmij.org 07 Apr '09

07 Apr '09

Lennart Augustsson wrote > main = do > name:_ <- getArgs > file <- readFile name > print $ length $ lines file Given the stance against top-level mutable variables, I have not expected to see this Lazy IO code. After all, what could be more against the spirit of Haskell than a `pure' function with observable side effects. With Lazy IO, one indeed has to choose between correctness and performance. The appearance of such code is especially strange after the evidence of deadlocks with Lazy IO, presented on this list less than a month ago. Let alone unpredictable resource usage and reliance on finalizers to close files (forgetting that GHC does not guarantee that finalizers will be run at all). Is there an alternative? -- Counting the lines in a file import IterateeM count_nl = liftI $ IE_cont (step 0) where step acc (Chunk str) = liftI $ IE_cont (step $! acc + count str) step acc stream = liftI $ IE_done acc stream count [] = 0 count ('\n':str) = succ $! count str count (_:str) = count str main = do name:_ <- getArgs IE_done counter _ <- unIM $ enum_file name >. enum_eof ==<< count_nl print counter The function count_nl could have been in the library, but I'm a minimalist. It is written in a declarative rather than imperative style, and one easily sees what it does. The above code as well as the IterateeM library is Haskell98. It does not use any unsafe Haskell functions whatsoever. time wc -l /usr/share/dict/words 235882 /usr/share/dict/words real 0m0.024s user 0m0.022s sys 0m0.000s time ~/Docs/papers/DEFUN08/Wc /usr/share/dict/words 235882 real 0m0.141s user 0m0.126s sys 0m0.008s To compare with lazy IO, the code using readFile gives time ~/Docs/papers/DEFUN08/Wc /usr/share/dict/words 235882 real 0m0.297s user 0m0.262s sys 0m0.023s So, choosing correctness does not mean losing in performance; in fact, one may even gain. Can enumerators compose? Well, we already seen the example above (enum_file name >. enum_eof) where the operation (>.) e1 >. e2 = (==<<) e2 . e1 is a flipped composition if monadic bind were considered a flipped application. Here is a more interesting example: count words in all the files whose names are given on the command line. There may be many files given, thousands of them. -- Count the stream. Again, could have been in the library stream_count :: Monad m => IterateeGM el m Int stream_count = liftI $ IE_cont (step 0) where step acc (Chunk []) = liftI $ IE_cont (step acc) step acc (Chunk [_]) = liftI $ IE_cont (step $! succ acc) step acc (Chunk ls) = liftI $ IE_cont (step $! acc + length ls) step acc stream = liftI $ IE_done acc stream main = do names <- getArgs let enumerators = foldr (\name -> (enum_file name >.)) enum_eof names IE_done (IE_done counter _) _ <- unIM $ enumerators ==<< enum_words stream_count print counter We notice that the composition of enumerators corresponds to the `concatenation' of their sources. Declaratively, the meaning of the above code is: -- all the given files are concatenated -- the resulting stream of characters is converted to a stream of words -- the stream of words is counted. Operationally, the code does not open more than one file at a time. More importantly, the code *never* reads more than 4096 characters at a time. A block of the file is read, split into words, counted, and only then another chunk is read. After one file is done, it is closed, and another file is processed. One can see that only one file is being opened at a time by enabling traces. The processing is fully incremental. /usr/local/share/doc/ghc6> find . -name \*.html -print | time xargs ~/Docs/papers/DEFUN08/Wc 3043421 16.99 real 15.83 user 0.71 sys BTW, the program has counted words in 1169 files. It is interesting to compare the above main function with the corresponding lazy IO: main'' = do names <- getArgs files <- mapM readFile names print $ length $ words (concat files) The number of lines is comparable. The execution is not. If we try to run the lazy IO code, we get: /usr/local/share/doc/ghc6> find . -name \*.html -print | time xargs ~/Docs/papers/DEFUN08/Wc Wc: ./libraries/Win32/Graphics-Win32-GDI-Path.html: openFile: resource exhausted (Too many open files)

9 12

Volunteer
by Xiao-Yong Jin 07 Apr '09

07 Apr '09

Hi, I learned that no one is doing generic unix source tarball, right now, and thought I might help to get it start. I have decent skills on Makefile, but knows very little about auto-tools. I can only spent a few hours every week on it, because I don't have too much spare time as a PhD student. But I still want to help, since it is quite important for Haskell to distribute as widely as possible. So, how should I start? I learned that ghc supports quite a lot of platforms in its tier2 support list through community supporters. I'm not sure what is the most convenient way to combine these into a generic source tarball. And what do we use to bootstrap ghc? Some pre-compiled binary? I'm not sure how I should start. Any insight? Best, Xiao-Yong P.S. I tried to send to haskell-platform, but got rejected. What's going on? ---------- begin error message ---------- ... while talking to community.haskell.org.: >>> DATA <<< 550 Unrouteable address 550 5.1.1 <haskell-platform(a)projects.haskell.org>... User unknown <<< 503 valid RCPT command must precede DATA ---------- end error message ---------- -- c/* __o/* <\ * (__ */\ <

2 1

Configuring cabal dependencies at install-time
by Jeff Heard 07 Apr '09

07 Apr '09

Is there a way to do something like autoconf and configure dependencies at install time? Building buster, I keep adding dependencies and I'd like to keep that down to a minimum without the annoyance of littering Hackage with dozens of packages. For instance, today I developed an HTTP behaviour and that of course requires network and http, which were previously not required. I'm about to put together a haxr XML-RPC behaviour as well, and that of course would add that much more to the dependency list. HaXml, haxr, and haxr-th most likely. so... any way to do that short of making a bunch of separate packages with one or two modules apiece? Otherwise I'm thinking of breaking things up into buster, buster-ui, buster-network, buster-console, and buster-graphics to start and adding more as I continue along. -- Jeff

1 0

GHC accepts libraries compiled with Visual Studio?
by Peter Verswyvelen 07 Apr '09

07 Apr '09

To my surprise GHC seems to accept .lib files (produced by e.g. Visual Studio on Windows) directly; I don't need to convert these to .a files using e.g. reimp That's really cool. Is this by design or did I miss something? The manual does not seem to mention this.

2 1

Re: Linking hmatrix without LAPACK
by Duane Johnson 07 Apr '09

07 Apr '09

Hi Alberto! Thanks for your informative reply. I looked in to the versions of liblapack on my system... it turns out there is indeed a liblapack.dylib that (apparently) comes with Mac OS X. How to tell ghc to link to that instead is still in question. I can run simple matrix operations in ghci as you suggest (in fact, "runTests 20" succeeds wonderfully); however, I created the following simple module (test.hs) and it fails: > module Main where > import Numeric.LinearAlgebra.Tests > > main = do > runTests 20 I tried plain "--make", as well as the "-dynamic" flag, and then I tried the "-L" shell argument to point to the /usr/lib dir where the liblapack.dylib library is located: > $ ghc --make test.hs -o test > [1 of 1] Compiling Main ( test.hs, test.o ) > Linking test ... > ld: in /opt/local/lib/liblapack.a( > ), not a valid archive member > collect2: ld returned 1 exit status > > $ ghc --make -dynamic test.hs -o test > Linking test ... > ld: library not found for -lHShmatrix-0.5.0.1-ghc6.10.1 > collect2: ld returned 1 exit status > > $ ghc --make -L/usr/lib test.hs -o test > Linking test ... > Undefined symbols: > "_zgemm_", referenced from: > _multiplyC in libHShmatrix-0.5.0.1.a(lapack-aux.o) > "_zgesv_", referenced from: > _linearSolveC_l in libHShmatrix-0.5.0.1.a(lapack-aux.o) > "_zpotrf_", referenced from: > _chol_l_H in libHShmatrix-0.5.0.1.a(lapack-aux.o) > "_dpotrf_", referenced from: > _chol_l_S in libHShmatrix-0.5.0.1.a(lapack-aux.o) > "_dgemm_", referenced from: > _multiplyR in libHShmatrix-0.5.0.1.a(lapack-aux.o) > "_dgesv_", referenced from: > _linearSolveR_l in libHShmatrix-0.5.0.1.a(lapack-aux.o) > "_zgetrf_", referenced from: > _lu_l_C in libHShmatrix-0.5.0.1.a(lapack-aux.o) > "_zgetrs_", referenced from: > _luS_l_C in libHShmatrix-0.5.0.1.a(lapack-aux.o) > "_dgetrf_", referenced from: > _lu_l_R in libHShmatrix-0.5.0.1.a(lapack-aux.o) > "_dgetrs_", referenced from: > _luS_l_R in libHShmatrix-0.5.0.1.a(lapack-aux.o) > ld: symbol(s) not found > collect2: ld returned 1 exit status I attempted to install hmatrix with the "-faccelerate" option, but when using "ghc --make" for the above test code, I received the same error messages noted previously. Is there a way to tell if the "- faccelerate" was acknowledged and that the alternate library was used? One more clue: I took a look at the directions found on the page at mit.edu/harold... it turns out I had installed atlas/lapack unnecessarily. That explains the mysterious "not a valid archive member" message. Nevertheless, I am still befuddled by the "Undefined symbols" above. ghc --make is still unable to figure out where the liblapack.dylib file is in spite of ghci's success. Any suggestions from here? Regards, Duane Johnson P.S. I'm CC'ing the Haskell Cafe so that our journey so far can be archived. On Apr 6, 2009, at 12:22 PM, Alberto Ruiz wrote: > Hi Duane, > > I have seen your messages to Haskell Cafe but I am still thinking > about the problem... :) > > Can you run simple matrix operations in ghci? > > $ ghci > Prelude> import Numeric.LinearAlgebra > Prelude Numeric.LinearAlgebra> let m = (2><2) [1..4 :: Double] > > (...Loading packages...) > > Prelude Numeric.LinearAlgebra> m <> m > (2><2) > [ 7.0, 10.0 > , 15.0, 22.0 ] > > If so, some version of blas/lapack can be found in your system, it > is strange that ghc --make doesn't find them. > > Perhaps the problem is that dynamic libraries like liblapack.so are > required instead of static ones like liblapack.a. (In ubuntu they > are in the "devel" packages for blas/lapack.) > > I am not familiar with Mac OS, but if you can use the "accelerate > framework" in your system you may try the -faccelerate configuration > option for hmatrix: > > cabal install hmatrix -faccelerate > > See also the following page (steps 3-8). It explains how to install > hmatrix on Mac OS (required for other project). > > http://mit.edu/harold/Public/easyVisionNotes.html > > Please let me know if any of these methods works for you. > > Thanks for your message, > > Alberto > > > > Duane Johnson wrote: >> Hi Alberto, >> I've been very happy with hmatrix as I've used it in ghci, and I >> should first thank you for making such an excellent package. I've >> had trouble when linking it using "ghc --make" on Mac OS >> (Leopard). Below are two messages I sent to the Haskell Cafe >> mailing list. Do you have any insight into either question: >> 1. How to link without atlas/lapack >> 2. What the "not a valid archive member" message means? >> Thank you! >> Duane Johnson >> Brigham Young University >> Provo, UT >> Begin forwarded message: >>> From: Don Stewart <dons(a)galois.com> >>> Date: April 5, 2009 11:48:38 PM MDT >>> To: Duane Johnson <duane.johnson(a)gmail.com> >>> Subject: Re: [Haskell-cafe] Re: Linking hmatrix without LAPACK >>> >>> It would be best to contact the author of hmatrix directly. >>> >>> >>> duane.johnson: >>>> On a related note, I've installed Atlas, and I get the following >>>> error >>>> when linking: >>>> >>>>> Linking SilkwormGame ... >>>>> ld: in /opt/local/lib/liblapack.a(), not a valid archive member >>>>> collect2: ld returned 1 exit status >>>> >>>> How would I go about diagnosing this? I've never seen an ld >>>> error like >>>> that. >>>> >>>> Thanks again! >>>> Duane Johnson >>>> >>>> >>>> On Apr 5, 2009, at 11:02 PM, Duane Johnson wrote: >>>> >>>>> I'm curious if there is a quick fix to this. I installed GLS and >>>>> hmatrix, and it runs wonderfully together in ghci. When I run >>>>> ghc -- >>>>> make, however, I run into the following link dependency: >>>>> >>>>> Linking SilkwormGame ... >>>>> Undefined symbols: >>>>> "_dgemm_", referenced from: >>>>> _multiplyR in libHShmatrix-0.5.0.1.a(lapack-aux.o) >>>>> "_dgesv_", referenced from: >>>>> _linearSolveR_l in libHShmatrix-0.5.0.1.a(lapack-aux.o) >>>>> ... etc >>>>> >>>>> Is there a way to tell ghc to not link these? Or am I making a >>>>> poor >>>>> assumption that if my code runs in ghci, it does not need LAPACK? >>>>> >>>>> Thanks, >>>>> Duane Johnson >>>> >>>> _______________________________________________ >>>> Haskell-Cafe mailing list >>>> Haskell-Cafe(a)haskell.org >>>> http://www.haskell.org/mailman/listinfo/haskell-cafe

1 1

Re: [Haskell-cafe] Combining sequences
by michael rice 07 Apr '09

07 Apr '09

Thanks. It looks like mergeBy will do the job, but is it available in Hugs? Michael --- On Sun, 4/5/09, Henning Thielemann <lemming(a)henning-thielemann.de> wrote: From: Henning Thielemann <lemming(a)henning-thielemann.de> Subject: Re: [Haskell-cafe] Combining sequences To: "michael rice" <nowgate(a)yahoo.com> Cc: haskell-cafe(a)haskell.org Date: Sunday, April 5, 2009, 9:09 PM On Sat, 4 Apr 2009, michael rice wrote: > Is there a simple way to combine two sequences that are in ascending order into a single > sequence that's also in ascending order? An example would be the squares [1,4,9,16,25..] > combined with the cubes [1,8,27,64,125..] to form [1,1,4,8,9,16,25,27..]. http://hackage.haskell.org/packages/archive/utility-ht/0.0.4/doc/html/Data-…

3 2

ghc --make unable to find dynamic library, but ghci can
by Duane Johnson 07 Apr '09

07 Apr '09

Hi Haskellers, This is related to my previous message, "Linking hmatrix without LAPACK". Apparently, ghc --make is not finding the lapack.dylib library where ghci is (dylib is Mac OS X specific) . For example, the following test module does NOT work when compiled with ghc --make: > module Main where > import Numeric.LinearAlgebra.Tests > > main = do > runTests 20 But the following runs fine in ghci: > $ ghci > GHCi, version 6.10.1: http://www.haskell.org/ghc/ :? for help > [...loading packages...] > Prelude> :m Numeric.LinearAlgebra.Tests > Prelude Numeric.LinearAlgebra.Tests> runTests 20 > [...loading packages...] > ------ mult > OK, passed 100 tests. > OK, passed 100 tests. > [...more tests pass...] Can anyone point me in the right direction? Thank you, Duane Johnson

1 0

Re: [Haskell-cafe] Combining sequences
by nowgate＠yahoo.com 07 Apr '09

07 Apr '09

Hi Daniel, Thanks, but apparently no go. This isn't critical, as I already have a function that will combine two sequences. Michael ============= Michael [michael@localhost untitled folder]$ cd utility-ht-0.0.4 [michael@localhost utility-ht-0.0.4]$ ls LICENSE Setup.lhs src utility-ht.cabal [michael@localhost utility-ht-0.0.4]$ ./Setup.lhs configure --hugs /usr/bin/env: runhaskell: No such file or directory --OOPS! [michael@localhost utility-ht-0.0.4]$ su Password: [root@localhost utility-ht-0.0.4]# ./Setup.lhs configure --hugs /usr/bin/env: runhaskell: No such file or directory [root@localhost utility-ht-0.0.4]# --- On Mon, 4/6/09, Daniel Fischer <daniel.is.fischer(a)web.de> wrote: From: Daniel Fischer <daniel.is.fischer(a)web.de> Subject: Re: [Haskell-cafe] Combining sequences To: haskell-cafe(a)haskell.org Cc: "michael rice" <nowgate(a)yahoo.com> Date: Monday, April 6, 2009, 12:04 PM Am Montag 06 April 2009 17:12:42 schrieb michael rice: > I downloaded it and it appears more complicated than just adding files to a > directory. There's a setup and a build, and no assurances it will work with > Hugs. > > I think I'll wait for more information. > > Michael > Try installing it with Cabal: ./Setup.lhs configure --hugs if that doesn't say otherwise, chances are that it will work, so try ./Setup.lhs build sudo ./Setup.lhs install If it doesn't work, you can copy the code from Data.List.HT

2 1

community.haskell.org unreachable?
by Claus Reinke 07 Apr '09

07 Apr '09

I seem to be having problems reaching anything on that server. Does anyone know what is going on, or who to contact? It would help if the haskellwiki page http://www.haskell.org/haskellwiki/Haskell.org_domain would mention the admin address directly, instead of referring to http://community.haskell.org/admin/ which is also unreachable. Claus

2 2

Re: [Haskell-cafe] ANN: SVGFonts 0.1
by Tillmann Vogt 07 Apr '09

07 Apr '09

John Van Enk schrieb: > This sounds very cool. Is is just a program, or is there a library sitting > behind it? From your .cabal file, it seems to be just a binary program. > > Is this correct? > > http://hackage.haskell.org/packages/archive/SVGFonts/0.1/SVGFonts.cabal > > On Mon, Apr 6, 2009 at 1:22 PM, Tillmann Vogt > <Tillmann.Vogt(a)rwth-aachen.de>wrote: > It is a real library made of pure Haskell. What is wrong with my .cabal file?

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Making videos of your project
by Don Stewart 07 Apr '09

07 Apr '09

Hey guys, I've been making quick youtube videos of projects to convey what they do. Here, for example, using Tim Docker's Charts library in ghci: http://www.youtube.com/watch?v=2Lqzygxvus0 (Click on the HD button for higher res). Or one of Neil Brown's "SG" OpenGL graphics library, http://www.youtube.com/watch?v=tJ6AtfcorkY You can create your own really simply: 1. install 'recordmydesktop' I use: recordmydesktop --no-sound --v_bitrate 2000000 2. type 'recordmydesktop' 3. do something with haskell 4. hit control-C 5. upload out.ogv to youtube If you're a library author of one of the 2 or 3D packages, please consider video along with other "why I want to use this" material. -- Don

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ANN: SVGFonts 0.1
by Tillmann Vogt 07 Apr '09

07 Apr '09

I hereby publish my first library in Haskell. SVGFonts 0.1 It parses the pretty unknown SVG Font format to produce outlines of characters. The big advantage of this format is that it is XML, which means easy parsing and manipulating. Because I haven't found any svg-files on the Internet the typical way is to convert a more popular format (i.e. .ttf) into SVG Font via fontforge. This library may be useful if you want to have a direct access to specific algorithms which is of course harder when using a binding (i.e. Jeff Heards FTGL binding). The speed is improvable (see TO DO list) and since since this is my first library there might some errors which I am not aware of (please tell me). I also wonder why the library doesn't appear under graphics on hackage, although there is Category: Graphics in my cabal file. Depending on which library I like more, I will maybe integrate SVGFonts into LambdaCube or Fieldtrip Cheers, Tillmann

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Re: [Haskell-cafe] Combining sequences
by michael rice 07 Apr '09

07 Apr '09

I downloaded it and it appears more complicated than just adding files to a directory. There's a setup and a build, and no assurances it will work with Hugs. I think I'll wait for more information. Michael --- On Mon, 4/6/09, Thomas Hartman <tphyahoo(a)gmail.com> wrote: From: Thomas Hartman <tphyahoo(a)gmail.com> Subject: Re: [Haskell-cafe] Combining sequences To: "michael rice" <nowgate(a)yahoo.com> Cc: "Henning Thielemann" <lemming(a)henning-thielemann.de>, haskell-cafe(a)haskell.org Date: Monday, April 6, 2009, 12:26 AM It's not in hugs, nor in ghc. It's just in hackage. However, by the looks of it, you should probably be able to use it in hugs. I didn't actually check this, but the cabal file didn't name any fancy extensions, so it looks pretty cross-compiler. You can just go to http://hackage.haskell.org/cgi-bin/hackage-scripts/package/utility-ht-0.0.4 wget http://hackage.haskell.org/packages/archive/utility-ht/0.0.4/utility-ht-0.0… untar and put them with the rest of the files your hugs compiler uses for package import. (I don't actually know how package installation works in hugs... isn't it just put the files into a dir?) thomas. 2009/4/5 michael rice <nowgate(a)yahoo.com>: > Thanks. It looks like mergeBy will do the job, but is it available in Hugs? > > Michael > > > --- On Sun, 4/5/09, Henning Thielemann <lemming(a)henning-thielemann.de> > wrote: > > From: Henning Thielemann <lemming(a)henning-thielemann.de> > Subject: Re: [Haskell-cafe] Combining sequences > To: "michael rice" <nowgate(a)yahoo.com> > Cc: haskell-cafe(a)haskell.org > Date: Sunday, April 5, 2009, 9:09 PM > > > On Sat, 4 Apr 2009, michael rice wrote: > >> Is there a simple way to combine two sequences that are in ascending order >> into a single >> sequence that's also in ascending order? An example would be the squares >> [1,4,9,16,25..] >> combined with the cubes [1,8,27,64,125..] to form [1,1,4,8,9,16,25,27..]. > > http://hackage.haskell.org/packages/archive/utility-ht/0.0.4/doc/html/Data-… > > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > >

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Unary Minus
by Paul Keir 06 Apr '09

06 Apr '09

If I use :info (-) I get information on the binary minus. Is unary minus also a function? Thanks, Paul

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