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Showing >100% CPU usage of parallel code
by Jim Burton 21 Feb '09

21 Feb '09

Hi, I copied the program below from a reddit post of dons'. I have a dual core laptop with ubuntu hardy and ghc 6.10.1. I can see the difference when I run the program with +RTS -N2 but CPU always says 100%. I'd like an example that shows >100 -- is it not showing >100 because of my timeformat or because of the program? If it's the latter can you point me to an example that will use more cpu? Here's the output: $ cat /proc/cpuinfo | grep processor | wc -l 2 $ export TIMEFORMAT="%E real,%U user,%S sys, %P cpu" $ ghc -O2 --make Par.hs -threaded $ time ./Par 1405006117752879898543142606244511569936384005711076 2.330 real,2.328 user,0.000 sys, 99.92 cpu $ time ./Par +RTS -N2 1405006117752879898543142606244511569936384005711076 1.504 real,2.316 user,0.016 sys, 100.00 cpu Here's the program: ---------------- import Control.Parallel main = a `par` b `par` c `pseq` print (a + b + c) where a = ack 3 10 b = fac 42 c = fib 34 fac 0 = 1 fac n = n * fac (n-1) ack 0 n = n+1 ack m 0 = ack (m-1) 1 ack m n = ack (m-1) (ack m (n-1)) fib 0 = 0 fib 1 = 1 fib n = fib (n-1) + fib (n-2) -------------------- Thanks, Jim -- View this message in context: http://www.nabble.com/Showing-%3E100--CPU-usage-of-parallel-code-tp22137081… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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A typeclass for Data.Map etc?
by Eugene Kirpichov 21 Feb '09

21 Feb '09

Greetings, Is there a typeclass for mappings with a Data.Map-like interface, with stuff like: empty, insert, insertWithKey, unionWith etc. ? And, probably, a similar typeclass for mutable mappings like Data.Hashtable. Looks like such a thing would be useful; as for now, I see at least two applications: Data.Map and Data.Trie (bytestring-trie) - it's a pity that they have rather similar interfaces, but the latter lacks many methods and some are named in a different way. Also, Data.Map has some inconsistensies, too: for instance, it has an insertWith' but lacks a unionWith'. "One typeclass for all" would eliminate these inconsistencies. I'm asking mainly because I've been wondering why noone has yet written a mutable hashtable package with a MArray-like interface, I wrote a small thing myself and I am unsure as to what interface it should have. -- Eugene Kirpichov

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RE: "first class" tuples?
by Brian Bloniarz 21 Feb '09

21 Feb '09

Wolfgang Jeltsch wrote: > Make , an infix operator. Then even the syntax (,) works without further ado. > Make , right-associative, for example. Then you can write (a1,...,an) which > means (a1,(a2,(...,an))). You just need one data declaration: > > data (a,b) = (a,b) > > However, this has the problem that it leads to more partially-defined values > than with today's tuples. For example, you could have a *triple* (a,_|_). > > So maybe we should treat tuple syntax completely as special syntax (as it is > today) and define our tuple types so that tuples don't end with the last > element (as above) but with an explicit empty tuple (like lists end in a > nil). This would also give use 1-tuples. We would need the unit type () for > empty tuples. Then we define a cons type which has a strictness annotation: > > data head :# tail = head :# !tail Lennart Augustsson wrote: > Look at the HList stuff by Oleg and others and you'll find the kind of > tuples you suggest. One thing about HList: the HCons type is lazy in its second element, so HList tuples can be more partially-defined than normal tuples. Anybody know the rationale for this? I'm curious whether it could be changed, or if any code depends on it. -Brian _________________________________________________________________ Access your email online and on the go with Windows Live Hotmail. http://windowslive.com/online/hotmail?ocid=TXT_TAGLM_WL_HM_AE_Access_022009

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Trying to install Cabal
by David 21 Feb '09

21 Feb '09

Hi! I've just installed ghc (v 6.10.1) for Windows, and it seems to be installed correctly, and now I'm trying to install Cabal (v1.6.0.2), but I'm getting the following error message (along with a lot of warnings about a deprecated something-or-other, which I assume I can ignore): C:\Temp>runghc Setup configure -p Distribution\Simple\Utils.hs:1:11: Warning: -fffi is deprecated: use -XForeignFunctionInterface or pragma {-# LANGUAGE ForeignFunctionInterface#-} instead Distribution\Simple\Utils.hs:4:15: Warning: -fffi is deprecated: use -XForeignFunctionInterface or pragma {-# LANGUAGE ForeignFunctionInterface#-} instead Distribution\Simple\InstallDirs.hs:1:11: Warning: -fffi is deprecated: use -XForeignFunctionInterface or pragma {-# LANGUAGE ForeignFunctionInterface#-} instead Distribution\Simple\InstallDirs.hs:4:15: Warning: -fffi is deprecated: use -XForeignFunctionInterface or pragma {-# LANGUAGE ForeignFunctionInterface#-} instead During interactive linking, GHCi couldn't find the following symbol: SHGetFolderPathA@20 This may be due to you not asking GHCi to load extra object files, archives or DLLs needed by your current session. Restart GHCi, specifying the missing library using the -L/path/to/object/dir and -lmissinglibname flags, or simply by naming the relevant files on the GHCi command line. Alternatively, this link failure might indicate a bug in GHCi. If you suspect the latter, please send a bug report to: glasgow-haskell-bugs(a)haskell.org Am I missing a dependency, or is ghc not installed properly, or am I doing something else wrong? Thanks, David.

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Error installing pkg 'HDBC-sqlite3'
by David 21 Feb '09

21 Feb '09

I've encountered another problem while trying to install 'HDBC-sqlite3'. I did the install "manually", instead of using Cabal, and during the build phase, received the following error message: D:\Apps\ghc\ghc-6.10.1\HDBC-sqlite3-2.1.0.0>runghc Setup build Preprocessing library HDBC-sqlite3-2.1.0.0... Database\HDBC\Sqlite3\Statement.hsc:41:21: sqlite3.h: No such file or directory Database\HDBC\Sqlite3\Statement.hsc: In function `main': Database\HDBC\Sqlite3\Statement.hsc:137: error: `SQLITE_NULL' undeclared (first use in this function) Database\HDBC\Sqlite3\Statement.hsc:137: error: (Each undeclared identifier is reported only once Database\HDBC\Sqlite3\Statement.hsc:137: error: for each function it appears in.) Database\HDBC\Sqlite3\Statement.hsc:148: error: `SQLITE_ROW' undeclared (first use in this function) Database\HDBC\Sqlite3\Statement.hsc:149: error: `SQLITE_DONE' undeclared (first use in this function) Database\HDBC\Sqlite3\Statement.hsc:150: error: `SQLITE_ERROR' undeclared (first use in this function) compiling dist\build\Database\HDBC\Sqlite3\Statement_hsc_make.c failed Is the file 'sqlite3.h' missing? Or am I doing something wrong? Thanks, David.

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foreign export space-leaks?
by James Ge 21 Feb '09

21 Feb '09

first I wrote a silly haskell program: --- a program to walk through very long list ---- data Silly = A !Int | B !Int deriving (Show) main = go [a + b | a <- [0..10000], b <- [0..10000]] where go [] = do putStrLn $ "completed." go (x:xs) = do case even x of True -> putStrLn $ show (A x) False -> putStrLn $ show (B x) go xs ---------- end of the program ----------- upper program ran well, and consumed fixed memory (2.8M watched by top). but when I exported the main to C and host the whole haskell program in C, memory consumption increased CONSTANTLY. what I did are: 1) explicit name the module to `Silly' and rename `main' to `call_me_back' 2) write a c wrapper following guildlines here(http://www.haskell.org/ ghc/docs/latest/html/users_guide/ffi-ghc.html#hs-exit): --- c wrapper code begins ---- #include <stdio.h> #include "HsFFI.h" #ifdef __GLASGOW_HASKELL__ #include "Silly_stub.h" #endif #ifdef __GLASGOW_HASKELL__ extern void __stginit_Silly ( void ); #endif int main() { hs_init(0, 0); #ifdef __GLASGOW_HASKELL__ hs_add_root(__stginit_Silly); #endif call_me_back(); hs_exit(); return 0; } ---- wrapper code ends ----- then I compiled them together: ---- Makefile section begins ----- ghc -O2 --make Silly.hs ghc -O2 --make Silly_wrapper.c ghc -O2 -o Silly.out *.o ./Silly -----Makefile sect ends ----------- this program consumed memory constantly until the process being terminated by OS because of `out of memory'. I guess this must have something to do with GC (although i tried import hs_perform_gc declared in HsFFI.h and called the function, but i didn't see any change), do you have ideas? Thanks in advance, jge

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Fwd: [Haskell-cafe] speed: ghc vs gcc
by Alberto G. Corona 21 Feb '09

21 Feb '09

I think that a higuer level language has better opportunities to optimize, specially if the compiler is coded in its own language. for example I guess that a good type dependent implementation would evaluate the sum[1..10^9::Int] at compilation time. I reality haskell is much much faster than c in some cases that now are not considered, but it is fair to remember that haskell outperfromed all the rest in those old benchmarks with did´t care to print the results. This may seem trivial now, but at the time surprised the benchmark people. 2009/2/21 Khudyakov Alexey <alexey.skladnoy(a)gmail.com> On Friday 20 February 2009 16:29:29 Bulat Ziganshin wrote: > > Hello haskell-cafe, > > > > since there are no objective tests comparing ghc to gcc, i made my own > > one. these are 3 programs, calculating sum in c++ and haskell: > > > > main = print $ sum[1..10^9::Int] > > > > ... skipped ... > > The discussion is mostly about low level optimizations such as loop > unrolling > etc. > > I have another question. Why shouldn't compiler realize that `sum > [1..10^9]' > is constant and thus evaluate it at compile time? > > -- > Khudakov Alexey > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

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Paper draft: "Denotational design with type class morphisms"
by Conal Elliott 20 Feb '09

20 Feb '09

I have a draft paper some of you might enjoy, called "Denotational design with type class morphisms". Abstract: Type classes provide a mechanism for varied implementations of standard interfaces. Many of these interfaces are founded in mathematical tradition and so have regularity not only of *types* but also of *properties* (laws) that must hold. Types and properties give strong guidance to the library implementor, while leaving freedom as well. Some of the remaining freedom is in *how* the implementation works, and some is in *what* it accomplishes. To give additional guidance to the *what*, without impinging on the *how*, this paper proposes a principle of *type class morphisms* (TCMs), which further refines the compositional style of denotational semantics. The TCM idea is simply that *the instance's meaning is the meaning's instance*. This principle determines the meaning of each type class instance, and hence defines correctness of implementation. In some cases, it also provides a systematic guide to implementation, and in some cases, valuable design feedback. The paper is illustrated with several examples of type, meanings, and morphisms. You'll find the paper at http://conal.net/papers/type-class-morphisms/ . I'd sure appreciate feedback on it, especially if in time for the *March 2* ICFP deadline. Pointers to related work would be particularly appreciated, as well as what's unclear and what could be cut. This draft is an entire page over the limit, so I'll have to do some trimming before submitting. Enjoy, and thanks! - Conal

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parallelism or concurrency ? if they are different
by Paolino 20 Feb '09

20 Feb '09

When I came to haskell, I arrived with a small and only evolutionary background in programming. First monad I met was MonadState StdGen m. Everything was in someway acceptable, I had no problem in explicitating the need for the generator. The lesson was referential transparency. To me referential tranparency is still obscure as a feature. Not using the monad , my functions pass around a generator, then they are repeatable, same generator , same computation. Years pass by, now evolutionary algorithms need to scale multicores. But multicore can be used with threads or par, the difference is that par is pure, because it respects referential transparency. But threads not. They are always unrespectful ? Or it's an implementation issue of preemptive choice? Can I have a baton to pass around like I had for random generator, so that the computation ends without IO (unsafe performed) , without breaking tranparency, something like (runIOThreads :: ThreadsIO a -> ThreadsBaton -> a) ? >From Real World Haskell my algorithm have to be parallelized as they don't do some kind of IO, they don't deal with the world, but where is it stated that it is possible to write them with par (I couldn't) ? More , I'm not caring that my computation is unrepeatable, for me it's fine that the runtime system gives me the cached results for same arguments computation. The fact that it doesn't ,and recompute the function giving out something fuzzily different from before, is enough to coerce me to spit out IO values ? Finally, why and where the optimizer will substitute a value with its definition, so that it possibly get computed twice ? Thanks paolino

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Haskell.org GSoC
by Daniel Kraft 20 Feb '09

20 Feb '09

Hi, I noticed last year Haskell.org was a mentoring organization for Google's Summer of Code, and I barely noticed some discussion about it applying again this year :) I participated for GCC in 2008 and would like to try again this year; while I'm still active for GCC and will surely stay so, I'd like to see something new at least for GSoC. And Haskell.org would surely be a very, very nice organization. Since I discovered there's more than just a lot of imperative languages that are nearly all the same, I love to do some programming in Prolog, Scheme and of course Haskell. However, so far this was only some toy programs and nothing "really useful"; I'd like to change this (as well as learning more about Haskell during the projects). Here are some ideas for developing Haskell packages (that would hopefully be of general use to the community) as possible projects: - Numerics, like basic linear algebra routines, numeric integration and other basic algorithms of numeric mathematics. - A basic symbolic maths package; I've no idea how far one could do this as a single GSoC project, but it would surely be a very interesting task. Alternatively or in combination, one could try to use an existing free CAS package as engine. - Graphs. - Some simulation routines from physics, though I've not really an idea what exactly one should implement here best. - A logic programming framework. I know there's something like that for Scheme; in my experience, there are some problems best expressed logically with Prolog-style backtracking/predicates and unification. This could help use such formulations from inside a Haskell program. This is surely also a very interesting project. What do you think about these ideas? I'm pretty sure there are already some of those implemented, but I also hope some would be new and really of some use to the community. Do you think something would be especially nice to have and is currently missing? Thanks for your comments, Daniel

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