March 2007 - Haskell-Cafe

Re: [Haskell] Summer of Code questions
by Malcolm Wallace 08 Mar '07

08 Mar '07

Wolfgang Jeltsch <g9ks157k(a)acme.softbase.org> writes: > First, what organization is Haskell.org? That would be us, right here. Anyone who is interested enough in Haskell to be involved in mailing lists, IRC, distributing library code and tools, whatever. > Is this a real organization, i.e., a legal entity? No. (Unlike e.g. the Apache Foundation.) > Does Haskell.org get the $ 500 for each successful project? > If yes, what does Haskell.org do with this money? Yes, we get the money. Last year, Galois kindly served as the account holder that received the cheque. The mentors involved get to decide what happens to it. I think we are planning to spend last year's on machine/bandwidth for hosting hackage.haskell.org. > Furthermore, the Google Summer of Code FAQ talks about *the* project of a > organization which seems to indicate that each organization has only > one SoC project. The model is that an open-source organisation does indeed usually have one focus, e.g. apache, Linux kernel, GTK, Gnome, Python. But of course there can be smaller tools and focuses within each overarching theme. > What is the project of the Haskell.org organization then? Is this > the general project "The Haskell language plus associated libraries and > tools"? Exactly so. > The FAQ says "Mentor organizations must be organizations or individuals > running an active and viable open source or free software project". Does > this mean that the above-mentioned general project has to be active and > viable (which it is) or that each concrete idea has to be part of an active > and viable project? The former. Decisions about concrete ideas are made collectively by the organisation, and we could certainly decide to go for a relatively immature concrete idea, if it looks both viable and of sufficient value to the community as a whole. > That is, is it allowed to start a new concrete project > by letting a student code for it as part of the SoC or wouldnât this be > possible since a new project isnât yet active and viable? Yes, you can do. It will have to compete with other ideas for top ranking. > Who decides which ideas will be worked on and who decides which student > works on which? Each organisation (in practice, this means a group of people prepared to be mentors) reads and ranks student proposals. After a certain date, Google tell us how many projects they will fund, and the top N are given the money. > What are the obligations of a mentor? (a) To carefully read and vote on quite a lot of student proposals. (b) If chosen to mentor a funded project, to guide the student throughout the project time, primarily by email (and/or IRC). Also to write two reports on progress (mid-term and final), that directly determine whether the student gets paid. > Is it okay to create an idea, become the mentor for this idea > and propose a concrete student for it? Sure. But your idea and student will need to compete for ranking. > What do I have to do to become a mentor? Start by adding yourself to the wiki. > What are Haskell.org's criteria for selecting mentors? According to the > above-mentioned FAQ, Google wants to know these criteria as specifically as > possible. I'm not sure we have definite criteria. I guess that the community generally recognises your name as a contributor to the Haskell language, libraries, tools, or whatever. Regular and visible engagement with the community would count for a lot. > Finally, should the ideas be chosen so that they are solvable by a student > working full time on them during the three months of the SoC? Exactly so. This year, Google have set things up with a greater time period between notification of acceptance, and the official beginning of coding, so that students have more preparation time before full-time work starts. > The problem is that at many German universities lectures go until > July. At our university, for example, lecture time ends in mid of July > and is followed by two weeks for exams. So a faithful student would > only have the last month for working full time on the SoC. Google have indeed set up the timetable largely with US universities in mind. So yes, it is certainly a disadvantage to a German student that they cannot work full-time for the three months. Regards, Malcolm

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open a browser from the command line, wait a few seconds, and shut it. (ie, translate forking from bash to haskell)
by Thomas Hartman 08 Mar '07

08 Mar '07

I have a bash script that opens a browser for a few seconds, and then closes it. Could someone point me up the equivelant(s) in haskell, h4sh, hsh, etc,0 and friends? I reckon this amounts to, what's the process for translating forking from bash to haskell. ******** #!/bin/bash konqueror http://www.google.com & pid=$! # give the page some time to load sleep 5 kill $pid ******** By the way, this isn't an academic question -- I'm using this simple script to verify various html downloads by checking the konqueror html cache for text strings I'm interested in, for pages that can't be easily downloaded with wget/web mechanize because of javascript and redirect nastiness. Also, for those interested in shell-equivelance strategies, I posted essentially the same question to perlmonks at http://perlmonks.org/?node_id=603868

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Re: [Haskell-cafe] TVars & throw
by Thomas Conway 08 Mar '07

08 Mar '07

On 3/8/07, Chris Kuklewicz <haskell(a)list.mightyreason.com> wrote: > What happens in your throw/catch case if I have > stm1 = do some_stm_code_that_throws_your_exception > stm2 = return Foo > and I run "atomically (stm1 `orElse` stm2)" ? > Answer: The exception will prevent running stm2. In the *specific* case of the external dictionary code, there is no orElse case to worry about since the algorithms are deterministic in this sense. For a more general case, it is an interesting problem to consider. You might want something like throwIfNothingElseSeemsLikeAGoodIdea, so that you can attempt any alternatives, and if none succeed then throw (and I guess choose the first if more than one alternative wants to throw - I like determinism). > > Um, is > > unsafeIOToSTM $ atomically trans > > going to run you into problems? > > YES! My point is that onRetry really wants to be not "IO t" but "IO_execpt_STM t", but there's no way of ensuring that, which unfortunately antagonizes modularity in the same kind of way that locks do. It requires you to know how the implementation of the IO actions you use work, in case they use STM inside. Since the actions may come out of a library somewhere, you need to know how the library is implemented. <sigh> Why are tricky problems tricky? I thought Haskell was supposed to make everything easy. ;-) T. -- Dr Thomas Conway You are beautiful; but learn to work, drtomc(a)gmail.com for you cannot eat your beauty. -- Congo proverb

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EnumSet and EnumMap
by Chris Kuklewicz 08 Mar '07

08 Mar '07

I could not quickly find anyone else writing this boiler plate, so I have posted this useful wrapper on the Haskell wiki at http://haskell.org/haskellwiki/EnumSet_EnumMap This uses a cheap newtype to wrap IntSet and IntMap so that you can store any Enum in them. It saves either writing many toEnum/fromEnum functions or using the slower and more generic Data.Set and Data.Map. The original motivation was to go from Map Char to IntMap. And as a bonus, the type signature of the newtype is the same kind as Data.Set and Data.Map (which matters when declaring instances...) > newtype EnumSet e = EnumSet {unEnumSet :: S.IntSet} > deriving (Monoid,Eq,Read,Show,Ord) > newtype EnumMap k a = EnumMap {unEnumMap :: M.IntMap a} > deriving (Eq,Read,Show,Ord,Monoid,Foldable,Functor) This has been quickly tested with GHC 6.6 and may contain typographical errors I have not caught yet. -- Chris

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Re: [Haskell-cafe] Usage of . and $
by David House 08 Mar '07

08 Mar '07

On 07/03/07, Thomas Conway <drtomc(a)gmail.com> wrote: > Of course, what really gets me, is when I start trying to use $ in > type signatures and declarations: > ... Map ByteString $ foo (bar baz) qux .... It's almost possible! GHC gives us infix type synonyms: type a $ b = a b (Probably needs -fglasgow-exts.) Sadly we don't have a fixity system for type operators :( -- -David House, dmhouse(a)gmail.com

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Re: problems installing ghc 6.6 with extralibs (bad interface file)
by Thomas Hartman 08 Mar '07

08 Mar '07

Thanks. I incorporated these changes, and it cranks longer now before failing. But still fails, now with a seg fault. Does this just mean I don't have enough ram, or cpu, or ... Any ideas? thomas. ************* thartman@linodewhyou:~/haskellInstalls$ tail -n13 out.txt ../compiler/ghc-inplace -H16m -O -istage2/utils -istage2/basicTypes -istage2/types -istage2/hsSyn -istage2/prelude -istage2/rename -istage2/typecheck -istage2/deSugar -istage2/coreSyn -istage2/specialise -istage2/simplCore -istage2/stranal -istage2/stgSyn -istage2/simplStg -istage2/codeGen -istage2/main -istage2/profiling -istage2/parser -istage2/cprAnalysis -istage2/ndpFlatten -istage2/iface -istage2/cmm -istage2/nativeGen -istage2/ghci -Istage2 -DGHCI -DBREAKPOINT -package template-haskell -threaded -package readline -DUSE_READLINE -cpp -fglasgow-exts -fno-generics -Rghc-timing -I. -Iparser -package unix -package Cabal -package regex-compat -ignore-package lang -recomp -Rghc-timing -H16M '-#include "cutils.h"' -package-name ghc-6.6 -fgenerics -fno-cse -c main/DriverPipeline.hs -o stage2/main/DriverPipeline.o -ohi stage2/main/DriverPipeline.hi <<ghc: 489718944 bytes, 1371 GCs, 11780600/23325480 avg/max bytes residency (7 samples), 59M in use, 0.00 INIT (0.00 elapsed), 3.40 MUT (18.69 elapsed), 3.69 GC (3.91 elapsed) :ghc>> ../compiler/ghc-inplace -H16m -O -istage2/utils -istage2/basicTypes -istage2/types -istage2/hsSyn -istage2/prelude -istage2/rename -istage2/typecheck -istage2/deSugar -istage2/coreSyn -istage2/specialise -istage2/simplCore -istage2/stranal -istage2/stgSyn -istage2/simplStg -istage2/codeGen -istage2/main -istage2/profiling -istage2/parser -istage2/cprAnalysis -istage2/ndpFlatten -istage2/iface -istage2/cmm -istage2/nativeGen -istage2/ghci -Istage2 -DGHCI -DBREAKPOINT -package template-haskell -threaded -package readline -DUSE_READLINE -cpp -fglasgow-exts -fno-generics -Rghc-timing -I. -Iparser -package unix -package Cabal -package regex-compat -ignore-package lang -recomp -Rghc-timing -H16M '-#include "cutils.h"' -package-name ghc-6.6 -fgenerics -c main/GHC.hs -o stage2/main/GHC.o -ohi stage2/main/GHC.hi gcc: Internal error: Segmentation fault (program cc1) Please submit a full bug report. See <URL:http://gcc.gnu.org/bugs.html> for instructions. For Debian GNU/Linux specific bug reporting instructions, see <URL:file:///usr/share/doc/gcc-4.0/README.Bugs>. <<ghc: 595874452 bytes, 1818 GCs, 14564135/30202688 avg/max bytes residency (8 samples), 74M in use, 0.00 INIT (0.00 elapsed), 5.10 MUT (17.37 elapsed), 5.80 GC (12.08 elapsed) :ghc>> make[1]: *** [stage2/main/GHC.o] Error 1 make: *** [install] Error 1 ~/haskellInstalls thartman@linodewhyou:~/haskellInstalls$ sudo ./install-ghc-6.6.sh 2>&1 | tee out.txt thartman@linodewhyou:~/haskellInstalls$ cat install-ghc-6.6.sh if [ ! -f ghc-6.6-src.tar.bz2 ]; then wget http://www.haskell.org/ghc/dist/6.6/ghc-6.6-src.tar.bz2 fi if [ ! -f ghc-6.6-src-extralibs.tar.bz2 ]; then wget http://www.haskell.org/ghc/dist/6.6/ghc-6.6-src-extralibs.tar.bz2 fi tar -tvjf ghc-6.6-src.tar.bz2 tar -tvjf ghc-6.6-src-extralibs.tar.bz2 pushd ghc-6.6 (cd compat && make clean && make UseStage1=YES) (cd utils && make clean && make UseStage1=YES) ./configure make make install popd thartman@linodewhyou:~/haskellInstalls$ 2007/2/27, Thomas Hartman <tphyahoo(a)gmail.com>: > I incorporated these changes to my install script, and now it cranks > longer before failing, but still fails. Now with a seg fault. > > For some odd reason the final crash snipped below didn't get written > to out.txt, otherwise I would have attached it. > > Any ideas to get it working? > > Thanks, thomas. > > ********************************** > > thartman@linodewhyou:~/haskellInstalls$ cat install-ghc-6.6.sh > if [ ! -f ghc-6.6-src.tar.bz2 ]; then > wget http://www.haskell.org/ghc/dist/6.6/ghc-6.6-src.tar.bz2 > fi > > if [ ! -f ghc-6.6-src-extralibs.tar.bz2 ]; then > wget http://www.haskell.org/ghc/dist/6.6/ghc-6.6-src-extralibs.tar.bz2 > fi > > > tar -tvjf ghc-6.6-src.tar.bz2 > tar -tvjf ghc-6.6-src-extralibs.tar.bz2 > pushd ghc-6.6 > (cd compat && make clean && make UseStage1=YES) > (cd utils && make clean && make UseStage1=YES) > ./configure > make > make install > popd > thartman@linodewhyou:~/haskellInstalls$ > > thartman@linodewhyou:~/haskellInstalls$ sudo ./install-ghc-6.6.sh 2>&1 > | tee out.txt > > .... > > ../compiler/ghc-inplace -H16m -O -istage2/utils -istage2/basicTypes > -istage2/types -istage2/hsSyn -istage2/prelude -istage2/rename - > istage2/typecheck -istage2/deSugar -istage2/coreSyn > -istage2/specialise -istage2/simplCore -istage2/stranal > -istage2/stgSyn -istage2 > /simplStg -istage2/codeGen -istage2/main -istage2/profiling > -istage2/parser -istage2/cprAnalysis -istage2/ndpFlatten > -istage2/iface > -istage2/cmm -istage2/nativeGen -istage2/ghci -Istage2 -DGHCI > -DBREAKPOINT -package template-haskell -threaded -package readline > -DUSE_R > EADLINE -cpp -fglasgow-exts -fno-generics -Rghc-timing -I. -Iparser > -package unix -package Cabal -package regex-compat -ignore-package > lang > -recomp -Rghc-timing -H16M '-#include "cutils.h"' -package-name > ghc-6.6 -fgenerics -c main/GHC.hs -o stage2/main/GHC.o -ohi > stage2 > /main/GHC.hi > gcc: Internal error: Segmentation fault (program cc1) > Please submit a full bug report. > See <URL:http://gcc.gnu.org/bugs.html> for instructions. > For Debian GNU/Linux specific bug reporting instructions, see > <URL:file:///usr/share/doc/gcc-4.0/README.Bugs>. > > <<ghc: 595874452 bytes, 1818 GCs, 14564135/30202688 avg/max bytes > residency (8 samples), 74M in use, 0.00 INIT (0.00 elapsed), 5.10 MUT > (17 > .37 elapsed), 5.80 GC (12.08 elapsed) :ghc>> > make[1]: *** [stage2/main/GHC.o] Error 1 > make: *** [install] Error 1 > ~/haskellInstalls > > > > 2007/2/27, Simon Marlow <simonmarhaskell(a)gmail.com>: > > Thomas Hartman wrote: > > > I installed ghc 6.6 from source ok. But then when I tried installing > > > it with the "extralibs" to get all the functionality that had been > > > unbundled in 6.6, I hit a glitch. > > > > > > Anyone ever seen anything like this? > > > > > > In case it matters, this is ssh-ed in to a virtualized user mode linux > > > session. > > > > > > ***************************************** > > > > > > thartman@linodewhyou:~/haskellInstalls$ cat install-ghc-6.6.sh > > > if [ ! -f ghc-6.6-src.tar.bz2 ]; then > > > wget http://www.haskell.org/ghc/dist/6.6/ghc-6.6-src.tar.bz2 > > > fi > > > > > > if [ ! -f ghc-6.6-src-extralibs.tar.bz2 ]; then > > > wget http://www.haskell.org/ghc/dist/6.6/ghc-6.6-src-extralibs.tar.bz2 > > > fi > > > > > > > > > tar -tvjf ghc-6.6-src.tar.bz2 > > > tar -tvjf ghc-6.6-src-extralibs.tar.bz2 > > > pushd ghc-6.6 > > > ./configure > > > make > > > make install > > > popd > > > thartman@linodewhyou:~/haskellInstalls$ sudo ./install-ghc-6.6.sh 2>&1 > > > | tee out.txt > > > thartman@linodewhyou:~/haskellInstalls$ tail -n20 out.txt > > > ------------------------------------------------------------------------ > > > make[2]: Nothing to be done for `install'. > > > ------------------------------------------------------------------------ > > > == make install - --no-print-directory -r; > > > in /home/thartman/haskellInstalls/ghc-6.6/utils/ghc-pkg > > > ------------------------------------------------------------------------ > > > Creating a symbolic link from ghc-pkg-6.6 to ghc-pkg in /usr/local/bin > > > for i in ghc-pkg-6.6; do \ > > > /usr/bin/install -c -m 755 $i /usr/local/bin; \ > > > done > > > /usr/local/bin/ghc -H16m -O -cpp -Wall -fno-warn-name-shadowing > > > -fno-warn-unused-matches -i../../compat -ignore-package Cabal > > > -Rghc-timing -c Main.hs -o Main.o -ohi Main.hi > > > > > > Main.hs:19:0: > > > Bad interface file: ../../compat/Distribution/InstalledPackageInfo.hi > > > mismatched interface file versions: expected 6060, found 6 > > > <<ghc: 24591324 bytes, 4 GCs, 106128/106128 avg/max bytes residency (1 > > > samples), 16M in use, 0.00 INIT (0.02 elapsed), 0.25 MUT (0.42 > > > elapsed), 0.10 GC (0.12 elapsed) :ghc>> > > > make[2]: *** [Main.o] Error 1 > > > make[1]: *** [install] Error 1 > > > make: *** [install] Error 1 > > > > I'm guessing what happened is that during the install the build system decided > > to rebuild ghc-pkg (I'm not sure why), but by that time you had already > > installed the new compiler, and the previous interface files weren't compatible > > with the new compiler. (I don't know why that would be the case either, since > > both compilers are 6.6...). > > > > You might be able to work around it by > > > > $ (cd compat && make clean && make UseStage1=YES) > > $ (cd utils && make clean && make UseStage1=YES) > > > > Cheers, > > Simon > > > > >

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LDFLAGS
by unknown＠example.com 08 Mar '07

08 Mar '07

I have built ghc-6.6 twice for 64-bit OpenBSD 4.0 with LDFLAGS=-L/usr/local/lib set as an environmental variable. Both times the built ghc did not find -lgmp until I modified lib/ghc-6.6/package.conf by adding "-L/usr/local/lib" to ldOptions. What do I set in order to have ldOptions set properly at the conclusion of make;make install? Thanks, Dave Feustel

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TVars & throw
by Thomas Conway 08 Mar '07

08 Mar '07

Hi All, Consider the following: foo = do v <- newTVar "hi there!" throwDyn v main = do catchDyn (atomically foo) \v -> do x <- atomically (readTVar v) putStr x I.e. throw information that gets rolled back from inside a transaction, catch it and use it. This looks like bad. I assume it actually works, but should it? T. -- Dr Thomas Conway You are beautiful; but learn to work, drtomc(a)gmail.com for you cannot eat your beauty. -- Congo proverb

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lhs2TeX
by Thomas Conway 07 Mar '07

07 Mar '07

Hi all, I noticed that in the polycode mode, lhs2TeX produces odd looking output for hex constants. E.g. \begin{code} wibble = 0x7F \end{code} It produces a nice little gap between the 0 and the x. Inspecting the latex source, it even goes to some effort to do so: \mathrm{0}\;\Varid{x7F} I couldn't see anything in the manual to show me how. Anyone? -- Dr Thomas Conway You are beautiful; but learn to work, drtomc(a)gmail.com for you cannot eat your beauty. -- Congo proverb

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Usage of . and $
by Jefferson Heard 07 Mar '07

07 Mar '07

Usually, I can do this, but today, my brain is weak, and I'm just trying to get this piece of code out the door. My code looks like this: weight = sum (IntMap.elems (IntMap.intersectionWith (\x y -> x*y) queryVector rationalProjection)) I know that this will work (ignoring indentation): sum $ IntMap.elems $ IntMap.intersectionWith (\x y -> x*y) queryVector rationalProjection But why won't this?: sum . IntMap.elems . IntMap.IntersectionWith ... Is there a difference between the "elegance" of function composition versus application?

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