- Haskell-Cafe - Haskell.org

HDBC Roadmap
by John Goerzen 06 Jan '06

06 Jan '06

I've had some questions about my intentions for HDBC. The Current Plan is: Release 1.0.0 next week. Before that happens, I want to have a stable and useful API. I have one feature request to implement yet (examinine properties of arbitrary tables in the database). I also want to finish the ODBC driver first, which should happen yet this week. After that, I will probably also release a MySQL backend. I hope that HDBC can be a community effort. Towards that end, I hope to be able to get some trac pages going on somebody's server and perhaps a mailing list where ideas and implementations for future enhancements can be discussed. I'd also like to be able to help people that would like to write backends for additional databases. (I also should announce hsql-testsuite, the common HUnit suite that is used to test each database backend.) The development time for a HDBC backend looks like about 1 day per database, including the amount of time it takes to learn that database's C API. (A bit more for ODBC because its API is weird and the documentation is unhelpful) Post 1.0.0, I will spend some time optimizing performance in the existing database drivers. There are several opportunities to do that, and they should yield significant results for certain use cases (such as inserting thousands or millions of rows of data at once.) Comments and suggestions are quite welcome. Patches too ;-) -- John

3 3

Fannkuch Entry
by David F. Place 06 Jan '06

06 Jan '06

Hi All, I've been enjoying following the thread about the "shootout" programs and trying to understand the performance of the entries, especially the Fannkuch benchmark. I've been comparing Sebastion's and Bertram's proposals found on the wiki. On my machine (PowerBook g4 (512M), GHC 6.4.1), Bertam's is about 3x faster. I think the main reason for the difference is that Bertram's conses much less and keeps much less data live on the heap. I don't find Bertram's version especially hard to read. I tripped on '>>=', but it was easy to look it up. You can substitute "concatMap" without penalty if you hate monads. The technique used in Bertram's `flop' is known to anyone who has been introduced to streams. I think Bertram solution is an idiomatic "engineered" Haskell program. Cheers, David ------------------------------------------------- [Marcel:~/pfann] david% time ./Sebastion 9 123456789 ... Pfannkuchen(9) = 30 8.132u 0.250s 0:08.89 94.2% 0+0k 0+2io 0pf+0w ------------------------------------------------- [Marcel:~/pfann] david% time ./Bertram 9 123456789 ... Pfannkuchen(9) = 30 2.629u 0.100s 0:03.10 87.7% 0+0k 0+4io 0pf+0w ------------------------------------------------- ------------------------------------------------- ./Sebastion 9 +RTS -K256m -c -sstderr 123456789 ... Pfannkuchen(9) = 30 911,697,700 bytes allocated in the heap 3,138,348 bytes copied during GC 5,172 bytes maximum residency (2 sample(s)) 3478 collections in generation 0 ( 0.28s) 2 collections in generation 1 ( 0.01s) 2 Mb total memory in use INIT time 0.00s ( 0.00s elapsed) MUT time 7.85s ( 8.52s elapsed) GC time 0.29s ( 0.44s elapsed) EXIT time 0.00s ( 0.00s elapsed) Total time 8.14s ( 8.96s elapsed) %GC time 3.6% (4.9% elapsed) Alloc rate 116,139,834 bytes per MUT second Productivity 96.4% of total user, 87.6% of total elapsed ------------------------------------------------- ./Bertram 9 +RTS -K256m -c -sstderr 123456789 ... Pfannkuchen(9) = 30 271,671,720 bytes allocated in the heap 818,676 bytes copied during GC 5,220 bytes maximum residency (1 sample(s)) 1036 collections in generation 0 ( 0.08s) 1 collections in generation 1 ( 0.00s) 1 Mb total memory in use INIT time 0.00s ( 0.01s elapsed) MUT time 2.56s ( 2.90s elapsed) GC time 0.08s ( 0.09s elapsed) EXIT time 0.00s ( 0.00s elapsed) Total time 2.64s ( 3.00s elapsed) %GC time 3.0% (3.0% elapsed) Alloc rate 106,121,765 bytes per MUT second Productivity 97.0% of total user, 85.3% of total elapsed ------------------------------------------------------ -------------------------------- David F. Place mailto:d@vidplace.com

3 2

bug in WinHugs Version 20051031?
by Bulat Ziganshin 06 Jan '06

06 Jan '06

Hello the following program fails to load in Hugs2005 with all Haskell extensions enabled: {-# OPTIONS_GHC -fglasgow-exts -fallow-undecidable-instances #-} class (Monad m) => Stream m h where class (Stream m h) => CharStream m h where vGetChar :: h -> m Char vGetContents :: h -> m String vGetContents h = func where func = do vGetChar h return "" class (Stream m h) => ByteStream m h where vGetByte :: h -> m () instance (CharStream m h) => ByteStream m h where vGetByte h = undefined instance (ByteStream m h) => CharStream m h where vGetChar = undefined message printed is: ERROR file:.\SystemStreamClasses.hs - *** The type checker has reached the cutoff limit while trying to *** determine whether: *** CharStream a b *** can be deduced from: *** () *** This may indicate that the problem is undecidable. However, *** you may still try to increase the cutoff limit using the -c *** option and then try again. (The current setting is -c40) this program compiles ok in GHC 6.4.1. if call to `func` is replaced with its body, then program loads ok: vGetContents h = do vGetChar h return "" can problem with loading my code in Hugs be resolved by giving to `func` some type signmature? i can't replace call with its body because code in real program is much more complicated: vGetContents h = let loop = let func = do c <- vGetChar h next <- loop c `seq` return (c : next) handler e = if isEOFError e then return [] else mError e in mCatch func handler in do firstchar <- vGetChar h rest <- loop return (firstchar : rest) class (Monad m) => MonadHelper m where mError :: IOError -> m a mCatch :: m a -> (IOError -> m a) -> m a class (Show h, MonadHelper m) => Stream m h | h -> m where .... -- Best regards, Bulat mailto:bulatz@HotPOP.com

2 2

Re[2]: Joels Time Leak
by Bulat Ziganshin 05 Jan '06

05 Jan '06

Hello Simon, Wednesday, January 04, 2006, 7:33:22 PM, you wrote: >>>>The minimum time between context switches is 20 milliseconds. >> SM> Sure, there's no reason why we couldn't do this. Of course, even >> SM> idle Haskell processes will be ticking away in the background, so >> SM> there's a reason not to make the interval too short. What do >> SM> you think is reasonable? >> >> Simon, the talk is about changing GHC _tick_, which is a _minimal_ >> possible context switch interval SM> Yes, I know. in this case, why you say that idle processes will be ticking in background? it's entirely up to program writers/users if they wants to decrease this interval. by default switches will occur in the same 20 ms, lesser tick will have no impact on ordinary programs as long as default switching time will be not changed -- Best regards, Bulat mailto:bulatz@HotPOP.com

2 2

RE: [Haskell-cafe] RE: Haskell vs. Clean
by Scherrer, Chad 05 Jan '06

05 Jan '06

Interesting. Have there been any performance comparisons vs GHC et al? Chad Scherrer Computational Mathematics Group Pacific Northwest National Laboratory "Time flies like an arrow; fruit flies like a banana." -- Groucho Marx > -----Original Message----- > From: Neil Mitchell [mailto:ndmitchell@gmail.com] > Sent: Thursday, January 05, 2006 1:58 PM > To: Scherrer, Chad > Cc: daniel.carrera(a)zmsl.com; haskell-cafe(a)haskell.org > Subject: Re: [Haskell-cafe] RE: Haskell vs. Clean > > Hi > > > My knowledge of Clean is fairly limited > Mine too, but one of the biggest differences is that Clean > has uniqueness types instead of Monads. > > They are in fact so similar that you can convert between them, using > Hacle: http://www-users.cs.york.ac.uk/~mfn/hacle/ > > I believe also that Clean has a lot more facilities for > strictness annotations, which may help with the speed. > > Thanks > > Neil >

2 1

RE: Haskell vs. Clean
by Scherrer, Chad 05 Jan '06

05 Jan '06

Daniel, My knowledge of Clean is fairly limited (even more so than my knowledge of Haskell), but no one seems to be responding to this, so I'll take a crack at it. Here is why I've stuck with Haskell instead of Clean: 1. It runs well on Linux 2. The license is more open 3. There is a (comparatively) large, active research community 4. Mailing list support is very good (haven't looked at Clean's for this) 5. It strikes me as more elegant Clean does seem to have a claim to speed. But given (3) and the fact that the languages are, after all, fairly similar, I wonder if (and hope that) Haskell may be able to make similar claims before long. Actually, this makes me wonder... Is Clean's claim to speed due to raw performance being a very high priority for its implementers, or is there something inherent in its semantics that will always give it an edge? Will Haskell be able to catch up? Chad ---------------------------------------------------- Daniel Carrera daniel.carrera at zmsl.com wrote: Hi all, How would you compare Haskell and Clean? It looks like they are both pure functional languages with very similar syntax. It also appears that Clean is faster than Haskell, it appears to be fairly fast. I'm curious to learn about relative advantages and disadvantages of each. ----------------------------------------------------

2 1

Re: [Haskell-cafe] Shootout favoring imperative code
by Chris Kuklewicz 05 Jan '06

05 Jan '06

This uses getLine instead of getContents and is 3.8 times slower. {-# OPTIONS -fglasgow-exts -O2 #-} -- -- The Computer Language Shootout -- http://shootout.alioth.debian.org/ -- -- compile with : ghc -O2 -o SumF SumF.hs -- To get better performance set default heap size to 10MB -- i.e. invoke as : ./SumF +RTS -H10M <input_file.txt -- contributed by Greg Buchholz -- modified by Mirko Rahn -- modified by Chris Kuklewicz, 5 Jan 2006 -- import Data.Char(ord) import GHC.Base {-# INLINE d2i #-} d2i :: Char -> Int# d2i c = let (I# x) = ord c (I# z) = ord '0' in x -# z main :: IO () main = do let next rt = do line <- catch getLine (\_ -> return []) if (null line) then return (I# rt) else next (rt +# aLine line) aLine ('-':rest) = nLine rest 0# where nLine [] soFar = (-1#) *# soFar nLine ( x :rest) soFar = nLine rest (d2i x +# (10# *# soFar)) aLine (x:rest) = pLine rest (d2i x) where pLine [] soFar = soFar pLine ( x :rest) soFar = pLine rest (d2i x +# (10# *# soFar)) total <- next 0# print total Sebastian Sylvan wrote: > On 1/5/06, Chris Kuklewicz <haskell(a)list.mightyreason.com> wrote: > >>I did manage to tweak SumFile to use unboxed Int# and go 10% faster. >> >>http://haskell.org/hawiki/SumFile > > > Interestingly, it's actually faster to do it this way than to call the > C functions fgets and atoi... > > However, I'm not sure it's "legal" since it's not using built-in > line-based IO functions (which the spec states, for no apparent reason > other than to favor languages whose IO convenience functions are > low-level :-)) > > /S > > -- > Sebastian Sylvan > +46(0)736-818655 > UIN: 44640862 >

1 0

Re: [Haskell-cafe] Frag/OSX
by Joel Reymont 05 Jan '06

05 Jan '06

On Jan 5, 2006, at 7:50 PM, Jason Dagit wrote: > I'm pretty sure I was on OSX when I tried it out a couple weeks > ago. There was at least one bot. I was able to kill it. > > Game play was buggy and awkward, bots didn't seem to have any > intelligence. Well, I would like to make extremely intelligent monsters (within my abilities of course) but I'm stumped at the moment. (gdb) r leveleg Starting program: /Users/joelr/Haskell/frag/a.out leveleg Reading symbols for shared libraries ... +.............................................................. done Program received signal EXC_BAD_ACCESS, Could not access memory. Reason: KERN_PROTECTION_FAILURE at address: 0x00000ab0 0x90ece5e8 in glDrawBuffer () (gdb) where #0 0x90ece5e8 in glDrawBuffer () #1 0x00011f5c in s1Iym_info () #2 0x0017e4a0 in schedule (mainThread=0x11c1748, initialCapability=0x9093000c) at Schedule.c:932 #3 0x0017f448 in waitThread_ (m=0x6066f0, initialCapability=0x0) at Schedule.c:2156 #4 0x0017f32c in scheduleWaitThread (tso=0x11c0000, ret=0x0, initialCapability=0x0) at Schedule.c:2050 #5 0x0019a120 in rts_evalLazyIO (p=0x22b874, ret=0x0) at RtsAPI.c:459 #6 0x0016929c in main (argc=1029, argv=0x9093000c) at Main.c:104 -- http://wagerlabs.com/

1 0

Frag/OSX
by Joel Reymont 05 Jan '06

05 Jan '06

Folks, Has anyone tried to run Frag on Mac OSX? Also, since I can't get it to run (glDrawBuffer crash), can someone tell me if it includes monsters? It looks to me like it's just a player with a gun running around. Thanks, Joel -- http://wagerlabs.com/

2 1

Re: Progress on shootout entries
by dons＠cse.unsw.edu.au 05 Jan '06

05 Jan '06

I've added an entry on the hawiki[1] for the regex-dna benchmark, and posted a smaller (down to 15 lines), faster entry for [2]reverse-complement, using string indexing from Alex. Cheers, Don [1] http://haskell.org/hawiki/ShootoutEntry [2] http://haskell.org/hawiki/ReverseComplementEntry

2 1

Re: Chaneneos
by Chris Kuklewicz 05 Jan '06

05 Jan '06

Josh Goldfoot wrote: > By the way, your version is already on the GP4 shootout, and has rated the fastest. > It also has the 3rd fewest lines of code, and uses a hell of a lot less memory than my version does. > Pretty cool! See the results here: > > http://shootout.alioth.debian.org/gp4/benchmark.php?test=chameneos&lang=all > > Thanks for the pointer, I had not seen the resuslts yet. Way cool. And thanks to Einar Karttunen for finind the Ch channel trick. Haskell is clearly good at their concurrency benchmark. Though there are many languages without entries, Haskell is the one to beat. -- Chris > > ----- Original Message ---- > From: Chris Kuklewicz <chris(a)mightyreason.com> > To: Josh Goldfoot <j_goldfoot(a)yahoo.com> > Sent: Wednesday, January 04, 2006 5:53:54 AM > Subject: Chaneneos > > > Hi, > > When I went to submit a Haskell entry for Chaneneos yesterday, I saw > yours for the first time but I did not know your address. I have copied > your entry's code to the wiki http://haskell.org/hawiki/ChameneosEntry. > The version Einar and I made has also been submitted to the shootout, > and should show up on the results list soon. > > Cheers, > Chris >

1 0

RE: [Haskell-cafe] Optimizing a high-traffic network architecture
by Simon Marlow 05 Jan '06

05 Jan '06

On 15 December 2005 10:21, Joel Reymont wrote: > Here are statistics that I gathered. I'm almost done modifying the > program to use 1 timer thread instead of 1 per bot as well as writing > to the socket from the writer thread. This should reduce the number > of threads from 6k (2k x 3) to 2k plus change. > > It appears that +RTS -k3k does make a difference. As per Simon, 2-4k > avoids the thread being garbage collected because each thread gets > its own block in the storage manager. Simon, did I get that right? The 3k threads are still GC'd, but they are not actually *copied* during GC. It'll increase the memory overhead per thread from 2k (1k * 2 for copying) to 4k (4k block, no overhead for copying). Cheers, Simon

3 4

RE: [Haskell-cafe] Re: [Haskell] Re: Boxing (Day) Question
by Simon Peyton-Jones 04 Jan '06

04 Jan '06

| > You'd still need several versions of the code for a polymorphic function, one | > for pointer values, one for 4-byte non-pointers, one for 8-byte non-pointers | > etc. | | Yes, but that's up to the user. A type variable always has a particular | kind, so for instance one might want an array over any 4-byte | non-pointer value: | | data Array4 (a :: #4) | | Functions on Array4 only need one version of code. This makes | polymorphism less useful, of course, but the goal here is to be closer | to the machine. Ah, now I see what you mean. I had not thought of doing that, but it'd make sense, esp if there were lots of 4-byte-non-pointer types. But there are only a couple (Int# and Word32#) so I'm not sure it's worth the effort. But (without thinking about it too hard) it looks like a very sensible idea. The trickiness is in the fact that some type constructors (notably (->)) are somewhat kind-polymorphic, which gives rise to some awkwardness in the type checker. So the details might not be entirely straightforward. Simon

2 1

Haskell vs Clean
by Daniel Carrera 04 Jan '06

04 Jan '06

Hi all, How would you compare Haskell and Clean? It looks like they are both pure functional languages with very similar syntax. It also appears that Clean is faster than Haskell, it appears to be fairly fast. I'm curious to learn about relative advantages and disadvantages of each. Thanks for the help! Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/ I am not over-weight, I am under-tall. /

1 0

RE: [Haskell-cafe] Shootout favoring imperative code
by Scherrer, Chad 04 Jan '06

04 Jan '06

> --- Sebastian Sylvan <sebastian.sylvan(a)gmail.com> > wrote: > Some of the problems seem to be heavily geared towards an > imperative *implementation*, meaning that a Haskell version > is hardly idiomatic Haskell (and as such I , and I suspect > otehrs, really have no inclination to work on it). This may be correct, but it still doesn't address the question. Why does Clean fare so much better? Clean is purely functional, right? Chad Scherrer Computational Mathematics Group Pacific Northwest National Laboratory "Time flies like an arrow; fruit flies like a banana." -- Groucho Marx

2 1

RE: [Haskell-cafe] Re: Joels Time Leak
by Simon Marlow 04 Jan '06

04 Jan '06

On 03 January 2006 15:37, Sebastian Sylvan wrote: > On 1/3/06, Simon Marlow <simonmar(a)haskell.org> wrote: >> Tomasz Zielonka wrote: >>> On Thu, Dec 29, 2005 at 01:20:41PM +0000, Joel Reymont wrote: >>> >>>> Why does it take a fraction of a second for 1 thread to unpickle >>>> and several seconds per thread for several threads to do it at the >>>> same time? I think this is where the mistery lies. >>> >>> >>> Have you considered any of this: >>> >>> - too big memory pressure: more memory means more frequent and more >>> expensive GCs, 1000 threads using so much memory means bad cache >>> performance - a deficiency of GHC's thread scheduler - giving too >>> much time one thread steals it from others (Simons, don't get >>> angry at me - I am probably wrong here ;-) >> >> I don't think there's anything really strange going on here. >> >> The default context switch interval in GHC is 0.02 seconds, measured >> in CPU time by default. GHC's scheduler is stricly round-robin, so >> therefore with 100 threads in the system it can be 2 seconds between >> a thread being descheduled and scheduled again. > > According to this: > http://www.haskell.org/ghc/docs/latest/html/users_guide/sec-using-parallel.… > > The minimum time between context switches is 20 milliseconds. > > Is there any good reason why 0.02 seconds is the best that you can get > here? Couldn't GHC's internal timer tick at a _much_ faster rate (like > 50-100µs or so)? Sure, there's no reason why we couldn't do this. Of course, even idle Haskell processes will be ticking away in the background, so there's a reason not to make the interval too short. What do you think is reasonable? > Apart from meaning big trouble for applications with a large number of > threads (such as Joels) it'll also make life difficult for any sort of > real-time application. For instance if you want to use HOpenGL to > render a simulation engine and you split it up into tons of concurrent > processes (say one for each dynamic entity in the engine), the 20ms > granularity would make it quite hard to achieve 60 frames per second > in that case... The reason things are the way they are is that a large number of *running* threads is not a workload we've optimised for. In fact, Joel's program is the first one I've seen with a lot of running threads, apart from our testsuite. And I suspect that when Joel uses a better binary I/O implementation a lot of that CPU usage will disappear. Cheers, Simon

5 10

Progress on shootout entries
by Chris Kuklewicz 04 Jan '06

04 Jan '06

Hello, Where there were no entries to the http://shootout.alioth.debian.org/benchmark.php?test=chameneos&lang=all benchmark, there are now two. The one by Josh Goldfoot is already posted, the one Einar Karttunen and I optimized has been submitted and will run faster/smaller. Our code is at http://haskell.org/hawiki/ChameneosEntry Now for improving the fasta benchmark, http://shootout.alioth.debian.org/benchmark.php?test=fasta&lang=all , which currently has a space leak in the Haskell entry. A non-leaking version which has been optimized to run 3.5 times faster is now up at http://haskell.org/hawiki/FastaEntra (ooops..my spelling mistake). It could still be made to run about 3 times faster, if the other languages are any guide. Anyone want to help polish this one? Also, two other existing entries have space leaks, as can be seen at http://shootout.alioth.debian.org/benchmark.php?test=all&lang=ghc&lang2=ghc And finially, the haskel entry for http://shootout.alioth.debian.org/benchmark.php?test=fannkuch&lang=all is currently the *slowest* entry out of 28 languages. It is 813x slower than the c-code, 500x slower than OCaml. Should be easy to make it faster... Cheers, Chris Kuklewicz

9 17

RE: [Haskell-cafe] Re: Haskell Speed
by Simon Marlow 04 Jan '06

04 Jan '06

On 30 December 2005 01:23, Jan-Willem Maessen wrote: > Probably. The minimum table chunk size was rather large. I have > been experimenting (tests are running even as I type) with alternate > implementations of Data.HashTable. So far the winning implementation > is one based on multiplicative hashing and simple table doubling. > This seems to be consistently competitive with / faster than > Data.Map. At this point my inclination is to make the whole suite > available: > > Data.HashTable.Class > Data.HashTable.DataMap > Data.HashTable.Doubling > Data.HashTable.Flat > Data.HashTable.Freeze > Data.HashTable.Modulus > Data.HashTable.Multiplicative > Data.HashTable.Original > Data.HashTable.Test > Data.HashTable > > I've separated out the hashing technique (Modulus, Multiplicative) > from the hash table implementation. Note that a few of the above are > bogus, and this is only a fraction of the implementations tried thus > far. > > I need to get distribution clearance for a bunch of this code from my > employer, and figure out how to package it. The latter may be > tricky, as Data.Hashtable is currently rather intimately tied to a > bunch of rather tricky bits of GHC. I wonder if you could put together a drop-in replacement for Data.HashTable that we can incorporate? There's not much point in us still providing the inefficient version as standard after you've done all this work to figure out how to do it better. Cheers, Simon

2 1

Re: Progress on shootout entries
by Josh Goldfoot 04 Jan '06

04 Jan '06

Keep in mind that the shootout requires that the first 30 permutations printed out by the Fannkuch benchmark to be exactly those given in the "example." Any other order of permutations gets your code labeled "Error" by the shootout administrators. See the discussion here: http://alioth.debian.org/tracker/index.php?func=detail&aid=302527&group_id=… The version of Fannkuch on the site before I got there used a permutation function that did not comply with this requirement. My only contribution was to translate the acceptable algorithm into Haskell. (The inefficient flop stuff and the other errors were not my fault, I swear!) The resulting (slow) code can definitely be sped up, but unfortunately the shootout benchmark favors imperative languages (and impure functional languages, I guess). I suppose we could have two permutation-generating functions: One used only to generate the first 30 required by the benchmark, and another that is actually used to calculate the fannkuch value. It's not clear how the shootout rule-lawyers would look that. It seems to violate the "same way" rule. I was able to significantly speed up the code by replacing the flip function with a function that relies entirely on pattern matching (no splitAts or reverses). It looks ugly, though: mangle list@(1:xs) = list mangle (2:x2:xs) = x2:2:xs mangle (3:x2:x3:xs) = x3:x2:3:xs ... and so on.

4 5

data vs type
by Daniel Carrera 04 Jan '06

04 Jan '06

Hello all, I'm trying to figure out how 'data' and 'type'. I haven't read any documentation because I can't find any. Could someone point me to a document explaining these? I'm happy to RTFM, I just need to know where the FM is :) Cheers, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/ I am not over-weight, I am under-tall. /

3 4

Controlling scheduling in Concurrent Haskell
by Simon Peyton-Jones 04 Jan '06

04 Jan '06

| Given that actually controlling priorities is not an option, adding | blocking like that makes sense. One can make a ring buffer instead of a Concerning priorities and scheduling (which affect both this shootout thread, and perhaps Joel's timeleak program), one can take two approaches 1. Ask more of the runtime system; e.g. add thread priorities 2. Program up a solution The merit of (1) is that you get an "automatic" solution. The problem is that it might not be the right solution for your problem. Whereas (2) will fit your problem, but is less convenient. Even the first paper on Concurrent Haskell discussed (2), in Section 4 "Control over scheduling". http://research.microsoft.com/copyright/accept.asp?path=/users/simonpj/p apers/concurrent-haskell.ps.gz Just to give an example, suppose you have zillions of threads, but you want to ensure that at most 10 of them are running simultaneously else their time slices are too spread out. Just use a quantity semaphore (QSem, discussed in the "Concurrent Haskell" paper). Each thread grabs permission from the semaphore before doing its work, and puts it back when done. How about fairness? As Simon mentioned, MVars *do* have an undocumented fairness property; waiting threads are serviced in first-come-first-served order. You'd have to check the QSem code, but I believe that means that threads will be dealt with first-come-first-served order for the quantity semaphore. We should probably document this property of MVars, and document fairness guarantees of abstractions such as QSem. | If 4 threads block trying to take an MVar, and a 5th thread puts a value | in the MVar, then *exactly one* of the 4 blocked threads is woken up and | scheduled to run. | | If 4 threads retry while in STM (e.g. takeTMVar), and a 5th thread | commits a change to that TMVar, then *all 4 threads* are woken up and | rescheduled. This is what the Apache httpd server folks called the | "thundering herd" problem when many processes are blocked waiting on | socket 80. Yes, that's precisely correct. MVars guarantee a single wake-up, whereas STM does not. Again, this is a property that it'd be good to document. Of course none of this helps if you simply have too much work to do. If you have 100 threads, each with 1s of processing to do, then no amount of fancy scheduling will get this done in less than 100s. But I thought I'd mention the possibility of doing scheduling explicitly. It's often not hard, and has the property that it's more robust to variations in the implementation. Simon

2 1

RE: [Haskell-cafe] Re: Joels Time Leak
by Simon Marlow 04 Jan '06

04 Jan '06

On 03 January 2006 17:32, Chris Kuklewicz wrote: > Thanks for the answer, but I should I written a longer comment. I have > added such a longer comment below: > > Simon Marlow wrote: >> Chris Kuklewicz wrote: >> >>> Another comment: between 1000's of threads and writing a custom >>> continuation based scheduler, what about using a thread pool? Does >>> anyone have a library with a "fork-IO-Pool" command? >> >> >> You don't need a thread pool, because threads are so cheap. Thread >> pools are just a workaround for lack of lightweight concurrency. >> >> Cheers, >> Simon >> > > Since the round-robin scheduler has (0.02 * N) seconds of delay for N > therads, then one could trade off latency between time spent waiting > for the thread pool to start a job and time spend running the job and > getting interrupted. > > In the limit of 1 worker thread, all the latency is waiting to get > run, and there are no interruptions, so the time taken *while > running* is very short. With 10 threads, there can be a delay to > start, and each interruption adds 0.2 seconds to the job's run time > once it has started. > > For a server, the client requests queue up and wait for room in the > thread pool, and the pool is kept small enough that the > round-robin-schedular-delay keeps requests from timing out while being > serviced. Otherwise 1000 client requests would cause 20 seconds of > reschedule penalty for all threads and they could all timeout. With a > thread pool, one can drop threads that have been waiting for too long > instead of running them, so those threads will timeout. But the pool > keeps servicing at least some of the client requests on time. > > All hypothetical to me, of course. I see - you want to use a thread pool as a way of restricting parallelism, so as to control latency. Good idea, it would make a useful library. Cheers, Simon

1 0

RE: [Haskell-cafe] Help with "shootout"
by Simon Marlow 04 Jan '06

04 Jan '06

On 03 January 2006 12:03, Chris Kuklewicz wrote: > STM* is usually slower than IO/MVar. STM has to do the transactional > record keeping and throws away work (i.e. CPU cycles and speed) when > it aborts. The Chameneos benchmark has 4 writers working *very* > quickly, so the contention is high. Taking the MVar acts like a > mutex to serialize access without throwing away work. We found that once you add exception safety to your MVar code, i.e. using withMVar and modifyMVar rather than raw takeMVar/putMVar, then MVar code is comparable in speed to STM. For example, Chan and TChan perform about the same. Of course, for a benchmark, you can forget about the exception safety, as the Ch implementation does (plus it is tweaked in various other ways). > Also, I suspect the following may be true: > > If 4 threads block trying to take an MVar, and a 5th thread puts a > value in the MVar, then *exactly one* of the 4 blocked threads is > woken up and scheduled to run. Yes, that's true. We haven't documented this as a property of MVars, but we don't intend to change this behaviour, so I think we probably should document it. Furthermore, the thread to be woken up is always the first thread to block on the MVar. That is, there's a kind of fairness built into MVars which isn't present in STM and TMVars. > If 4 threads retry while in STM (e.g. takeTMVar), and a 5th thread > commits a change to that TMVar, then *all 4 threads* are woken up and > rescheduled. This is what the Apache httpd server folks called the > "thundering herd" problem when many processes are blocked waiting on > socket 80. > > If 4000 threads were getting woken up when only 1 was needed, then > performance would be poor. Certainly I found 4 writer thread and STM > to be much slower for this shootout problem than the Einar's custom > MVar channel. > > Could someone who knows the STM implementation comment on this? Hope this helps... Simon PJ and I talked about this briefly this morning, and agreed that it might be possible to provide more primitive MVar-like objects in STM to recover single-wakeup and some of the speed that MVars currently have. We haven't worked through the details though. >> This is the CVS code. newTChanIO is exported but undocumented in GHC >> 6.4.1. I'm not sure what purpose it serves. > > I get tired of writing "do tv <- atomically $ newTVar foo" > > I bet this is just shorthand: "do tv <- newTVarIO foo" > > Same for newTChanIO. It's not just shorthand: you can use newTVarIO and friends inside unsafePerformIO, which doesn't always work for the longhand atomically version. Cheers, Simon

1 0

RE: [Haskell] Re: Boxing (Day) Question
by Simon Peyton-Jones 04 Jan '06

04 Jan '06

[Moving to haskell-café] You'd still need several versions of the code for a polymorphic function, one for pointer values, one for 4-byte non-pointers, one for 8-byte non-pointers etc. That's what .net does, I believe, but via runtime code generation. Simon | -----Original Message----- | From: haskell-bounces(a)haskell.org [mailto:haskell-bounces@haskell.org] On Behalf Of Ashley Yakeley | Sent: 29 December 2005 17:56 | To: haskell(a)haskell.org | Subject: [Haskell] Re: Boxing (Day) Question | | In article | <036EAC76E7F5EC4996A3B3C3657D411604105AB8(a)EUR-MSG-21.europe.corp.microso | ft.com>, | "Simon Peyton-Jones" <simonpj(a)microsoft.com> wrote: | | > The .NET CLR lifts the restriction by specialising code, so that it can | > adapt to whether it is moving Int# or Double# values around. In | > Haskell, though, it's not possible to statically generate all the | > instances you need, so you'd need run-time code generation to do this. | > | > It's a real restriction, and sometimes very tiresome, but I'm not | > planning to fix it soon, unless I have a brilliant idea for how to do it | > easily. | | So you don't think having a different kind for each kind of storage | (e.g. #4 for 4-byte values, etc.) would help you here? | | -- | Ashley Yakeley, Seattle WA | | _______________________________________________ | Haskell mailing list | Haskell(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell

2 1

How to print a string (lazily)
by Daniel Carrera 04 Jan '06

04 Jan '06

Hello, I've been studying more Haskell and I've improved a lot. But I just hit a small problem. I want to print all the elements of a linst (putStr). I'd like to write something like this: print_list [] = do putStr "" print_list (x:xs) = (do putStr x) && print_list xs I know this is wrong, but I hope you can see what I'm trying to do. I know of other ways I could print a list. For example: print_list xs = do putStr(join xs) where join [] = "" join (x:xs) = (show x) ++ "\n" ++ join xs But the thing is, I want to write a lazy version of this function. It's not that I need such a function, I'm just trying to learn Haskell. Any suggestions? Question: What do you call a function that has side-effects? (like putStr) I know that "function" is the wrong term. Cheers, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/ I am not over-weight, I am under-tall. /

13 18

Re: Progress on shootout entries
by Kimberley Burchett 04 Jan '06

04 Jan '06

I took a quick crack at optimizing fannkuch.hs. I got it down from 33s to 1.25s on my machine, with N=9. That should put it between forth and ocaml(bytecode) in the shootout page. The main changes I made were using Int instead of Int8, foldl' to accumulate the max number of folds, a custom flop function rather than a combination of reverse and splitAt, and a simpler definition for permutations. http://kimbly.com/code/fannkuch.hs Kimberley Burchett

2 1

RE: Haskell vs. Erlang: The scheduler
by Simon Marlow 03 Jan '06

03 Jan '06

On 03 January 2006 15:13, Joel Reymont wrote: > On Jan 3, 2006, at 2:30 PM, Simon Marlow wrote: >> The default context switch interval in GHC is 0.02 seconds, >> measured in CPU time by default. GHC's scheduler is stricly round- >> robin, so therefore with 100 threads in the system it can be 2 >> seconds between a thread being descheduled and scheduled again. >> >> I measured the time taken to unpickle those large 50k packets as >> 0.3 seconds on my amd64 box (program compiled *without* >> optimisation), so the thread can get descheduled twice during while >> unpickling a large packet, giving a >4s delay with 100 threads >> running. > > Is it impractical then to implement this type of app in Haskell? > Based on the nature of Haskell scheduling I would be inclined to say > yes. Absolutely not! Apart from the problem you have with a space leak caused by the input buffer of the logging thread overflowing, which is easily fixed by using a bounded channel, I don't know why you want priorities. Is there something else? We could easily add Erlang-style priorities (though without the overhead of counting function calls, I'd do it by counting allocations), but I'd rather not if we can avoid it. Cheers, Simon

2 1

file i/o
by Robert Heffernan 03 Jan '06

03 Jan '06

Hi, I am relatively new to Haskell and am finding i/o difficult to work with. I am trying to do something like the following: I have a file of data, each line of which looks like this: <STRING>, INTEGER SEQUENCE for example: FOO ,2,1,4,3,6,7,5,9,10,11,8,13,12, I would like to write a function the reads this file and returns arrays like this: ["FOO",[2,1,4,3,6,7,5,9,10,11,8,13,12]] Ideally, the function would return the first line when initially called, the second the next time it is called and so on. I would settle for something that returned a big array comprising arrays of the above type containing all the information in the file. The file is big, however. I can not figure out how to do this from any of the tutorials so I thought I might ask here. Thank you for your help, Robert.

3 3

Joels Time Leak
by Adrian Hey 03 Jan '06

03 Jan '06

Hello, I haven't followed everything that's happened on the Binary IO thread, but has anybody else actually tried Joels code? .. http://wagerlabs.com/timeleak.tgz I can reproduce the problem (ghc/Linux), but can't explain it. It seems very strange that friggin about with an otherwise irrelevant (AFAICT) MVar fixes the problem. Regards -- Adrian Hey

6 9

Re: Joels Time Leak
by Chris Kuklewicz 03 Jan '06

03 Jan '06

Thanks for the answer, but I should I written a longer comment. I have added such a longer comment below: Simon Marlow wrote: > Chris Kuklewicz wrote: > >> Another comment: between 1000's of threads and writing a custom >> continuation based scheduler, what about using a thread pool? Does >> anyone have a library with a "fork-IO-Pool" command? > > > You don't need a thread pool, because threads are so cheap. Thread > pools are just a workaround for lack of lightweight concurrency. > > Cheers, > Simon > Since the round-robin scheduler has (0.02 * N) seconds of delay for N therads, then one could trade off latency between time spent waiting for the thread pool to start a job and time spend running the job and getting interrupted. In the limit of 1 worker thread, all the latency is waiting to get run, and there are no interruptions, so the time taken *while running* is very short. With 10 threads, there can be a delay to start, and each interruption adds 0.2 seconds to the job's run time once it has started. For a server, the client requests queue up and wait for room in the thread pool, and the pool is kept small enough that the round-robin-schedular-delay keeps requests from timing out while being serviced. Otherwise 1000 client requests would cause 20 seconds of reschedule penalty for all threads and they could all timeout. With a thread pool, one can drop threads that have been waiting for too long instead of running them, so those threads will timeout. But the pool keeps servicing at least some of the client requests on time. All hypothetical to me, of course. -- Chris

1 0

Haskell vs. Erlang: Logging to one thread from thousands /Answer/
by Joel Reymont 03 Jan '06

03 Jan '06

I asked the Erlang guys why I can log to a single process in Erlang without any problems. The scheduler could well be round-robin but since the message queue is hard-wired to each Erlang process they found an elegant way out. -- There is a small fix in the scheduler for the standard producer/consumer problem: A process that sends to a receiver having a large receive queue gets punished with a large reduction (number of function calls) count for the send operation, and will therefore get smaller scheduling slots. -- Thanks, Joel -- http://wagerlabs.com/

1 0

Help with "shootout"
by Chris Kuklewicz 03 Jan '06

03 Jan '06

Hello all, I decided to put together an entry for one of the shooutout categories: http://haskell.org/hawiki/ChameneosEntry It involves 4 threads. There is no current Haskell entry. Anyone have comments? Alterations? I can't have created the best code yet. I don't have the compilers for the other entries, so I can't compare speed on my powerbook (which is the wrong kind of CPU anyway -- they test on an AMD system). -- Chris

5 10

RE: [Haskell-cafe] ST monad
by Ralf Lammel 03 Jan '06

03 Jan '06

... for the same reason as this one doesn't get through: import Control.Monad.ST import Data.Array.ST main = print $ runST $ do return () ... but this one does: import Control.Monad.ST import Data.Array.ST main = print $ runST ( do return ()) it's all about rank-2 types; see SPJ's et al. paper on type inference for these types. However, I guess that the jury is still out, say this specific rank-2 behavior may be revised (and I also hope so). HTH Ralf > -----Original Message----- > From: haskell-cafe-bounces(a)haskell.org [mailto:haskell-cafe- > bounces(a)haskell.org] On Behalf Of Bulat Ziganshin > Sent: Tuesday, January 03, 2006 2:28 AM > To: haskell-cafe(a)haskell.org > Subject: [Haskell-cafe] ST monad > > Hello > > the following code can't go through typechecking. can anyone help me > to fix it or, better, let me know what i need to read to fix it myself? :) > > import Control.Monad.ST > import Data.Array.ST > main = print $ runST $ > do arr <- newArray (1,10) 127 > a <- readArray arr 1 > writeArray arr 1 216 > b <- readArray arr 1 > return (a,b) > > > PS: error message is > > b.hs:4:15: > Inferred type is less polymorphic than expected > Quantified type variable `s' escapes > Expected type: ST s a -> b > Inferred type: (forall s1. ST s1 a) -> a > In the first argument of `($)', namely `runST' > In the second argument of `($)', namely > `runST > $ (do > arr <- newArray (1, 10) 127 > a <- readArray arr 1 > writeArray arr 1 216 > b <- readArray arr 1 > return (a, b))' > > > > -- > Best regards, > Bulat mailto:bulatz@HotPOP.com > > > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe

1 0

ST monad
by oleg＠pobox.com 03 Jan '06

03 Jan '06

Bulat Ziganshin wrote: the following code can't go through typechecking > import Control.Monad.ST > import Data.Array.ST > main = print $ runST $ > do arr <- newArray (1,10) 127 > a <- readArray arr 1 > writeArray arr 1 216 > b <- readArray arr 1 > return (a,b) Indeed. The short answer: use runST (long expression) rather than runST $ long expression when it comes to higher-ranked functions such as runST. A longer answer: http://www.haskell.org/pipermail/haskell-cafe/2004-December/008062.html > let me know what i need to read to fix it myself MLF (see Daan Leijen, A. Loeh, `Qualified types for MLF', ICFP05)

1 0

ST monad
by Bulat Ziganshin 03 Jan '06

03 Jan '06

Hello the following code can't go through typechecking. can anyone help me to fix it or, better, let me know what i need to read to fix it myself? :) import Control.Monad.ST import Data.Array.ST main = print $ runST $ do arr <- newArray (1,10) 127 a <- readArray arr 1 writeArray arr 1 216 b <- readArray arr 1 return (a,b) PS: error message is b.hs:4:15: Inferred type is less polymorphic than expected Quantified type variable `s' escapes Expected type: ST s a -> b Inferred type: (forall s1. ST s1 a) -> a In the first argument of `($)', namely `runST' In the second argument of `($)', namely `runST $ (do arr <- newArray (1, 10) 127 a <- readArray arr 1 writeArray arr 1 216 b <- readArray arr 1 return (a, b))' -- Best regards, Bulat mailto:bulatz@HotPOP.com

1 0

Catching string from error function with GHC Control.Exception
by Andrew Savige 03 Jan '06

03 Jan '06

I am a Haskell beginner, using GHC 6.4.1. Suppose I have a function, tt, say, which may call error. For the purposes of testing tt, I'd like to be able to catch the error string and assert that it matches the expected error string. Is HUnit or QuickCheck (or either) the appropriate tool for this sort of testing? I managed to get it working with HUnit, but it's horribly kludgy mainly because I'm yet to grok monads. The little test program below demonstrates my question outside of HUnit: import Control.Exception tt :: String -> Int tt s = error ("hi error '" ++ s ++ "'") -- tt s = read s ttWrap :: String -> IO String ttWrap x = do let r = tt x -- comment out next line, error string not caught putStr (show r) return (show r) ttWrap2 :: IO String ttWrap2 = do res <- tryJust errorCalls (ttWrap "123") case res of Right r -> return (show r) Left r -> return r main = do x <- ttWrap2 putStrLn ("caught:" ++ x) y <- ttWrap2 putStrLn ("caught:" ++ y) When you run the above test program, it does indeed catch the error string thrown by the tt function (and prints it out in main). However, if you comment out the putStr line as shown in the comment above, it no longer catches the error string, but dies instead. Why? I'm sure there is a cleaner way to achieve what I'm trying to do and I'd appreciate advice on the best way to do this. Thanks, /-\ Send instant messages to your online friends http://au.messenger.yahoo.com

3 2

Re: Haskell Speed
by Brent Fulgham 02 Jan '06

02 Jan '06

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 > I recently stumbled across this thread, related to the Shootout > (which I run) and wanted to add a few comments. > > First, I agree that I am a Haskell novice; however, I rely on > people like yourselves to show me where I am doing things wrong. > If our solutions are horribly inefficient, please tell us what we > can do to resolve the problem. But note that in some cases, we are > purposely being inefficient so that we can measure the cost of > certain basic operations. > > Doug Bagely started the Shootout as a comparison of scripting > languages. After I revived it, I started focussing more on > functional and logic languages, since I was curious how these > languages would fare in comparison with the more typically-used > languages like C/C++. Consequently, many of the tests show this > heritage and are highly imperative. We have been working to relax > some of these rules, and have added many new tests that try to be > more amenable to comparison of lazy and 'strict' languages. > > In our defense I would like to plead that it is not easy to devise > short problems (e.g., that can be expressed in a page or so of code > - -- we try to limit it to 100 lines of C++ code as a rough > benchmark), and that also take enough run time for a meaningful > measurement. So, many of the tests initially suffered from foolish > looping and repetition as a means of extending the run times > sufficiently to allow measurement. We have been changing tests so > that fewer of them rely on these kinds of activities to generate > results. We are always interested in new ideas, and would consider > any benchmark ideas you have. > > Finally, I don't agree at all that Haskell's scores show poorly. > The GHC compiler is one of the better performers, and regularly > trounces other languages when we let it do its job. For example, > we had to jump through many hoops to convince the compiler to > actually invoke all the loops required to do the "same way" tests > on methodcall and similar benchmarks, because the compiler was so > sharp at identifying wasted effort and optimizing it away. Perhaps > we don't say this strongly enough on the site, but I was truly > impressed at its ability to toss aside wasted calculations and > focus on the core problem. I'll admit it was frustrating because > we wanted to see how long it would take for Haskell to make N > recursive calls, or what have you, but the fact that the compiler > saw that there was no need to do the recursion to get the result is > quite amazing! I'm sure this would be extremely useful when > compiling real-world programs. > > There have been many cases where the "obvious" solution in Haskell > is a great performer, but we discover that it's so fast because it > has tossed aside wasted cycles and just done the work necessary to > arrive at a solution. It's unfortunate, since we then have to > dirty the program with wasted steps to force it to exercise the > tasks required. But in a "real world" test I think Haskell would > show quite well. > > As we evolve into the newer tests, I think you will see Haskell > make a better showing. Simon Marlow (and others) have been a huge > help in optimizing the existing tests in a "fair" fashion, and as > we provide more "same thing" type tests, I think Haskell will pull > further ahead. > > Thanks, > > - -Brent > > P.S. I must say that I find Haskell to be the most esthetically > pleasing language -- it's quite beautiful when printed! -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.2 (Darwin) iD8DBQFDuWIlzGDdrzfvUpURAnJuAJ90G9ltXH5m+jsz6D0QoucoY6anNACfcfkQ Mg2K0NO0kbBYLy4ZX7LCoeM= =uGnw -----END PGP SIGNATURE-----

1 0

Typechecking Help
by Dominic Steinitz 02 Jan '06

02 Jan '06

I have a function which, without a type annotation, types as: *Codec.ASN1.BER> :t choiceAux choiceAux :: forall (m :: * -> *) e e1. (MonadState [Maybe Encoding] m, MonadState [Maybe Encoding] (StateT [Maybe Encoding] m), MonadError e (StateT [Maybe Encoding] m), MonadError e1 m) => (TagPlicity, NamedType) -> Encoding -> m Defaulted But if I try to give it a type annotation of choiceAux :: (MonadState [Maybe Encoding] m, MonadState [Maybe Encoding] (StateT [Maybe Encoding] m), MonadError e (StateT [Maybe Encoding] m), MonadError e1 m) => (TagPlicity, NamedType) -> Encoding -> m Defaulted I get Codec/ASN1/BER.hs:66:0: Quantified type variable `e1' is unified with another quantified type variable e When trying to generalise the type inferred for `choiceAux' Signature type: forall (m :: * -> *) e e1. (MonadState [Maybe Encoding] m, MonadState [Maybe Encoding] (StateT [Maybe Encoding] m), MonadError e (StateT [Maybe Encoding] m), MonadError e1 m) => (TagPlicity, NamedType) -> Encoding -> m Defaulted Type to generalise: (TagPlicity, NamedType) -> Encoding -> m Defaulted In the type signature for `choiceAux' When generalising the type(s) for tc, choiceAux, k Changing e1 to e makes it typecheck. 1. Can anyone explain why the typechecker rejects the type it had inferred for itself? 2. I thought StateT guaranteed that the lifted monad was a state monad so why is the typechecker adding MonadState ... (StateT ... ) to the list of constraints? Ditto for MonadError ... (StateT ... )? Thanks, Dominic. PS What I thought I was going to get was choiceAux :: forall (m :: * -> *) e. (MonadError e m, MonadState [Maybe Encoding] m) => (TagPlicity, NamedType) -> Encoding -> m Defaulted and this is what I have now specified.

3 4

Bug in "Haskell for C programmers" tutorial?
by Erik de Castro Lopo 02 Jan '06

02 Jan '06

Hi all, I'm working through the "Haskell for C programmers" tutorial and in this section": http://www.haskell.org/~pairwise/intro/section2.html#part3 it has: fib :: Num a, Num b => a -> b fib n = fibGen 0 1 n fibGen :: Num a, Num b => b -> b -> a -> b fibGen a b n = case n of 0 -> a n -> fibGen b (a + b) (n - 1) which doesn't work with GHC, but it does if I add parentheses around both instances of "Num a, Num b". Is this a bug in the tutorial or is there another explanation? Cheers, Erik -- +-----------------------------------------------------------+ Erik de Castro Lopo +-----------------------------------------------------------+ "Anyone who considers arithmetical methods of producing random digits is, of course, in a state of sin." - John Von Neumann (1951)

4 11

Project postmortem II /Haskell vs. Erlang/
by Dominic Steinitz 02 Jan '06

02 Jan '06

I'd like to second Joel's comments on records very strongly. In an application where you need lots of big records (such as supporting X.509), you end up with very unnatural names for components. It works but it's not pretty. Dominic.

1 0

(no subject)
by Henk-Jan van Tuyl 01 Jan '06

01 Jan '06

L.S., I used the link checker of the World Wide Web Consortium to check the links on haskell.org; there are several links broken. As the checks take a long time, I have put the results on my website: http://members.chello.nl/hjgtuyl/computing/Haskell/checklinks/checklink.htm The check is a recursive check with depth 3, starting from the home page; this will probably not cover all of the website. To repeat this check, go to: http://validator.w3.org/checklink -- Best wishes for the new year, Henk-Jan van Tuyl -- http://members.chello.nl/hjgtuyl -- Using Opera's revolutionary e-mail client: https://secure.bmtmicro.com/opera/buy-opera.html?AID=789433

1 0

expanding do notation / StateMonad example from tutorial all about monads
by Marc Weber 31 Dec '05

31 Dec '05

Hi.. I'm still struggling with monads ;-) In the tutorial "All about monads" there is the function getOne used: getOne:: (Random a) => (a,a) -> State StdGen a getOne bound = do g <-get (x,g')= return $ randomR bounds g put g' return x In the haskell "Yet another Haskell tutorial" by Hal Daume it is said that do {fp <- e; es} is translated to: let ok p = do {es} ; ok _ = fail "..." in e >>= ok Using this rule I was able to expand the first "<-" of getOne: getOne2 :: (Random a) => (a,a) -> State StdGen a getOne2 bounds = let ok g = do (x,g') <- return $ randomR bounds g put g' return x ok _ = fail "asd" in get >>= ok but I couldn't manage to also expand the second. My attempt is: getOne3 :: (Random a) => (a,a) -> State StdGen a getOne3 bounds = let ok g = do let ok2 (x,g') = do { put g'; return x } -- ok2 _ = fail "2" in (return $ randomR bounds g >>= ok2 ok _ = fail "1" in get >>= ok But I get this compile error in at the line marked by a trailing --: "The last statement in a 'do' construct must be an expression" Can you help me? Sincerly Marc

2 1

OpenAL bindings / compiling ghc 6.5
by Michael Benfield 31 Dec '05

31 Dec '05

I see here: http://www.haskell.org/HOpenGL/newAPI/ OpenAL bindings listed as part of the Hierachical Libraries. And when I download the source to a development snapshot of GHC, there they are. Is there a way to install this on GHC 6.4? Alternatively... I can't get GHC 6.5 to compile. I do ./configure && make and it gets to this step: ------------------------------------------------------------------------ ==fptools== make all -r; in /Users/mike/source/ghc-6.5.20051221/ghc/compiler ------------------------------------------------------------------------ and sits forever (well, I only let it sit a day and a half, actually...). And the only relevant process that seems to be running is gmake (no ghc or gcc or anything). I've tried a few different versions of 6.5, including HEAD and STABLE branch. I'm on Mac OS 10.3.9. Thanks. Mike Benfield

4 7

Testing serialization/deserialization.
by Pupeno 31 Dec '05

31 Dec '05

Hello, I am working with NewBinary, I have made a lot of datatypes which are Binary instances. Now I want to write some testing for the serialization/de-serialization. I've started with QuickCheck but it seems I can't do IO inside a property of QuickCheck, am I right ? If not, how is it done ? Not being able to work with QuickCheck, I tried HUnit only to find another problem (which I would have found with QuickCheck anyway). How do I generate a BinHandle where I can write and read what I written ? Tring to do that I wrote a test for Int: intSerialization = TestCase (do bh <- openBinMem 1024 [] let i :: Int i = 3 put_ bh i i2 <- (get bh) :: IO Int assertEqual "i == i2" i i2) it didn't work: *Network.Server.DNS> runTestTT tests ### Error in: 1 user error (HUnit:i == i2 expected: 3 but got: 209944584) In general, what method/way do you recommend to test serialization/de-serialization (note: I'd like to use QuickCheck if possible)? Thank you. -- Pupeno <pupeno(a)pupeno.com> (http://pupeno.com)

1 0

Re: Haskell Speed
by Isaac Gouy 31 Dec '05

31 Dec '05

--- Isaac Gouy <igouy(a)yahoo.com> wrote: > We'll be happy to also show a Haskell program that > uses Data.HashTable - first, someone needs to > contribute that program. Someone did: k-nucleotide Haskell GHC #2 http://shootout.alioth.debian.org/gp4/benchmark.php?test=knucleotide&lang=a… __________________________________ Yahoo! for Good - Make a difference this year. http://brand.yahoo.com/cybergivingweek2005/

4 5

Can this be improved?
by Chris Kuklewicz 30 Dec '05

30 Dec '05

Happy Holidays, I was wondering if it this small snippet of code could be altered to require fewer OPTIONS -fallow-... switches. It creates a show-what-i-mean function called "swim" that takes a variable number of arguments, and treats strings as-is, calling show on the other arguments. > {-# OPTIONS -fglasgow-exts #-} > {-# OPTIONS -fallow-undecidable-instances #-} > {-# OPTIONS -fallow-incoherent-instances #-} > {-# OPTIONS -fallow-overlapping-instances #-} > > -- Want to show strings "as-is" > > class (Show a) => MyShow a where > myShow :: a -> String > myShow = show > > instance MyShow String where > myShow = id > > instance (Show b) => MyShow b > > -- Want to take variable number of arguments > > class PVShow a r where > pvShow :: String -> a -> r > > instance (MyShow b) => PVShow b String where > pvShow oldString b = oldString ++ (myShow b) > > instance (MyShow b,PVShow a r) => PVShow b (a->r) where > pvShow oldString b = pvShow (oldString ++ (myShow b)) > > -- swim is short for Show What I Mean > > swim :: (PVShow a r) => a -> r > swim = pvShow "" > > -- Demonstates of polymorphic and first class nature of swim > > test foo = foo " and " 7 " are " > > -- Tests > > main = do putStrLn $ swim "Hello" " " "World #" [17,18,19] "!" > putStrLn $ test (swim "I also think " [4,5,6]) "cool" "." GHCI session: Main> main Hello World #[17,18,19]! I also think [4,5,6] and 7 are cool. *Main> Could this be improved by TypeEq machinery? Is there a Haskell 98 way to make myShow work this way? -- Chris Kuklewicz

4 6

binary IO
by Pupeno 30 Dec '05

30 Dec '05

It seems I have found a hole in Haskell... :( Before I start to develop a library with functions such us those on http://haskell.org/hawiki/BinaryIo (hGetWord8, hGetWord16le, hGetWord16be, etc), is there some reliable library that can help me ? I basically need a set of functions to read binary data out of a Handle (a higher lever of hGetBuf and hPutBuf). What I am doing is implementing a DNS server, so, my typical need is: First two bytes are an integer. The next bit is a boolean. So are the following three bits. Then I have 4 bits which is also an integer. Etc. Any help is greatly appreciated. Thank you. -- Pupeno <pupeno(a)pupeno.com> (http://pupeno.com)

13 39

module names
by Scherrer, Chad 30 Dec '05

30 Dec '05

Something about the way module names are specified in a file seems really strange to me. When I first started learning Haskell (I had used OCaml previously), I tried things like module Main where import A import B main = A.f >> B.f module A where f = ... module B where f = ... in a single file. This example is straight from chapter 5 of the Report, and no mention is made (that I could find) about modules needing to be in separate files. But this won't load in ghci! (Even if ... is changed to putStr "hi"). Eventually I figured out that it works fine if it's split over three separate files. So here's what I'm trying to figure out: If every file corresponds to exactly one module (is that true?), then why must the module name be given again in the text of the file? When I'm using ghci, I have lots of modules that I sometimes want to load "as Main", and sometimes I only want them loaded as a dependency from another module. Currently, I have to go into each file to change the "module Foo where" line to do this. Chad Scherrer

6 7

Re: [Haskell-cafe] Arrows for invertible programming: Notation, question
by Arjen 30 Dec '05

30 Dec '05

On Fri, 23 Dec 2005, Joel Reymont wrote: > Folks, > > I have been looking at the code for the "Arrows for invertible > programming" paper (http://www.cs.ru.nl/A.vanWeelden/bi-arrows/) and > I have a question about syntax. ghci surely does not like it. > I've updated the web page to say that is does not work with Hugs, GHCi or GHC -fgenerics, sorry for the confusion. It really requires Generic Haskell (GH) 1.42. I never got GH working with GHC 6.4, so you also really need GHC 6.2.2. I think you can run the result of the GH preprocessor (using the right command line options) in GHCi or Hugs, but I'm not sure. If anyone got GH working with GHC 6.4(+), please tell me how you did it. > What does this mean and how do I make it compile? > > mapl{|a, b|arr|} :: (mapl{|a, b|arr|}, ArrowChoice arr, BiArrow arr) > => arr a b > In GH this means: mapl is a polytypic (type-indexed in a and b) function that yields an arr(ow) from a to b. It is overloaded in ArrowChoice and BiArrow on the arr(ow). Because it is polytypic, it is also overloaded `in itself'. Most of the time GH does not require the last part explicitly, but sometimes it triggers a bug if you don't specify it. The semantics of mapl can be found in the paper. regards, Arjen > Thanks, Joel > > -- > http://wagerlabs.com/ >

2 1

Mixing IO and STM
by Quan Ta 29 Dec '05

29 Dec '05

Hello folks, Newbie question: how can I do something like the following? mixing IO and STM. module Test where import System.Random import Control.Concurrent import Control.Concurrent.STM test_Cubby = do tv <- newTVar 0 forkIO (producer tv) >> (consumer tv) where producer tv = do r <- randomRIO (1,10) atomically (do { v <- readTVar tv ; writeTVar tv (v+r) }) print ("insert " ++ show r) producer tv return () consumer tv = do r <- randomRIO (1,10) atomically (do { v <- readTVar tv ; if (v < r) then retry else writeTVar tv (v-r) }) print ("consume " ++ show r) consumer tv return () Thanks.

4 5