November 2005 - Haskell-Cafe

RE: [Haskell-cafe] GHCi always optimizes?
by Simon Marlow 24 Nov '05

24 Nov '05

On 22 November 2005 10:07, Dusan Kolar wrote: > My question is rather strange, maybe, even if simple: > Does ghci always translates with "-O" option set on? I didn't see anyone answer this specific question: the answer is "no", GHCi does not optimise. Optimisation cannot be used when interpreting, except that you're allowed to load in compiled optimised modules. Cheers, Simon

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RE: [Haskell-cafe] Re: Re[2]: Uses forkOS all CPUS on-board?
by Simon Marlow 24 Nov '05

24 Nov '05

On 24 November 2005 01:35, Shae Matijs Erisson wrote: > Bulat Ziganshin <bulatz(a)HotPOP.com> writes: > >>>> They work, even in a context switching regime, but I can't >>>> exploit all the CPU's on my computer. Always is "active" >>>> just one thread >> this will not help. multi-processing support will be added in GHC >> 6.6, which must roll out due 6 months, as HCAR says > > In the meantime, you can try it yourself by grabbing ghc 6.5 from cvs > and reading http://www.haskell.org/~simonmar/papers/multiproc.pdf The code is still a bit green, but it's improving. I'm tracking down various crashes at the moment. By all means try it out though, and I'm interested in any test programs and benchmarks that folk have. To compile a program for SMP: - Add "GhcLibWays += s" to mk/build.mk when building GHC - Add -smp when compiling your code - +RTS -N2 -RTS to use 2 CPUs (for example) BTW you don't need to use forkOS to get parallelism, forkIO will do. Also we have now implemented par (as in Control.Parallel.par). Cheers, Simon

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Re: [Haskell-cafe] Records (was Re: [Haskell] Improvements to GHC)
by David Menendez 24 Nov '05

24 Nov '05

Chris Kuklewicz writes: > Would the record system describe at > http://lambda-the-ultimate.org/node/view/1119 > also be convertable "into System Fw, GHC's existing, strongly-typeed > intermediate language." ? Probably. Daan's current implementation uses MLF, which I believe is system F implemented for ML. (We're talking about the system in Daan Leijen's paper, "Extensible Records With Scoped Labels". Good stuff.) -- David Menendez <zednenem(a)psualum.com> | "In this house, we obey the laws <http://www.eyrie.org/~zednenem> | of thermodynamics!"

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Uses forkOS all CPUS on-board?
by Dusan Kolar 24 Nov '05

24 Nov '05

Hello haskellers, in past few days, a lot of stuff on concurrency went through the conference. I'm trying to use posted things and my own. They work, even in a context switching regime, but I can't exploit all the CPU's on my computer. Always is "active" just one thread and, thus, the computation is even slower than having a sequential version. Below, you can find my code - it computes nothing useful, it's been simplified to test parallelism, nothing else. Where's my error? Regards Dusan import Control.Concurrent -- computes nothing too much useful, but takes a long time ;-) sumAllSums [] = 0 sumAllSums l@(_:xs) = sumlist 0 l + sumAllSums xs where sumlist res [] = res sumlist sr (v:vs) = sumlist (sr+v) vs main = do putStrLn "Starting..." mv1 <- newEmptyMVar mv2 <- newEmptyMVar t1 <- forkOS $ mkSum1 mv1 t2 <- forkOS $ mkSum2 mv2 tt mv1 mv2 forkOS $ do killThread t1 killThread t2 putStrLn "Done!" where mkSum1 mv = do let res = sumAllSums [1..10000] let ms1 = "Sum1: " ++ show res seq (length ms1) (putMVar mv ms1) mkSum2 mv = do let res = sumAllSums [1..10001] let ms2 = "Sum2: " ++ show res seq (length ms2) (putMVar mv ms2) tt mv1 mv2 = do yield mr1 <- tryTakeMVar mv1 case mr1 of Just r1 -> do yield putStrLn r1 yield r2 <- takeMVar mv2 putStrLn r2 Nothing -> do mr2 <- tryTakeMVar mv2 case mr2 of Just r2 -> do yield putStrLn r2 yield r1 <- takeMVar mv1 putStrLn r1 Nothing -> tt mv1 mv2

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RE: [Haskell-cafe] Function application like a Unix pipe
by Scherrer, Chad 24 Nov '05

24 Nov '05

Bill Wood <william.wood3(a)comcast.net> writes: > Interesting note: in Richard Bird and Oege de Moor, _Algebra > of Programming_, pp. 2-3, the authors write > > As a departure from tradition, we write "f : A <- B" rather than > "f : B -> A" to indicate the source and target types associated > with a function "f". ... The reason for this choice has to do with > functional composition, whose definition now takes the smooth > form: if f : A <- B and g : B <- C, then f . g : A <- C is defined > by (f . g) x = f(g x). > > Further along the same paragraph they write: > > In the alternative, so-called diagrammatic forms, one writes > "x f" for application and "f ; g" for composition, where > x (f ; g) = (x f) g. > > I know I've read about the latter notation as one used by > some algebraists, but I can't put my hands on a source right now. > > I guess it's not even entirely clear what constitutes > "mathematical notation". :-) > > -- Bill Wood Good point. One of my undergrad algebra books ("Contemporary Abstract Algebra", by Gallian) actually used notation like this. Function application was written (x f). Some people even write the function as an exponential. But (f x) is still far more common. Chad Scherrer Computational Mathematics Group Pacific Northwest National Laboratory "Time flies like an arrow; fruit flies like a banana." -- Groucho Marx

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Problem over Context Free Grammar Transitive Closure Algorithm
by Victor Silva 24 Nov '05

24 Nov '05

Folks this is a parser for Context Free Grammars, for some reason when I go simplify the grammar trying to remove productions that substitute variables like in the case: S -> A, A -> B, B -> a, it works perfectly and returns S -> a, the problem is when the root symbol is on the listthat must be replaced as in: S -> aXa | bXb , X -> a | b | S | £(empty) instead of returning S -> aXa | bXb, X -> a | b | £ | aXa | bXb it ruturns X as X -> a | b | £ | S <- this S is wrong! it should return X -> a | b | £ | aXa | bXb! Im not sure about where is the mistake. If you can give me hints it would be grat. I will be checking the mail and also hanging over #haskell at freenode ifyou want to contact me directly. Thanks in advance for the help! Victor

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RE: [Haskell-cafe] Function application like a Unix pipe
by Scherrer, Chad 23 Nov '05

23 Nov '05

Henning Thielemann <lemming(a)henning-thielmann.de> writes: > Since > (a . b) x > a $ b x > a (b x) > > are equivalent, do you also want to reverse function and > argument in order to match argument order of . and $ ? > > That is > x (b . a) > x b $ a > (x b) a > ? I'm sorry, I'm not sure I understand your question. Are you asking whether one should be allowed to write x f instead of f x? I don't think anyone is advocating this, but is can be convenient to have an infix operator for this purpose. Chad Scherrer Computational Mathematics Group Pacific Northwest National Laboratory "Time flies like an arrow; fruit flies like a banana." -- Groucho Marx

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RE: [Haskell-cafe] Function application like a Unix pipe
by Scherrer, Chad 23 Nov '05

23 Nov '05

Henning Thielemann <lemming(a)henning-thielmann.de> writes: > I want to say, that the order of symbols for ($), (.) and > function application is consistent. This is a fine thing. I > think that shall not be distroyed by giving ($) and (.) > reversed argument order. I see. I like the argument order also, since it so nicely reflects mathematical notation. But I do think there's a place for (flip ($)) and (flip (.)). The problem is that the assignment of fixities is much more subtle and requires a consideration of what should be considered "proper style". Chad Scherrer Computational Mathematics Group Pacific Northwest National Laboratory "Time flies like an arrow; fruit flies like a banana." -- Groucho Marx

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RE: [Haskell-cafe] GHCi always optimizes?
by Simon Peyton-Jones 23 Nov '05

23 Nov '05

| Anyway, it's strange that you are experiencing crashes. IIRC, there | were problems if you mixed modules compiled with different levels of | optimisation in the same program, but I am not sure it still happens. If you can make a reproducible crash, please tar it up and send it to us. It shouldn't happen. Ever. Simon

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RE: [Haskell-cafe] Function application like a Unix pipe
by Scherrer, Chad 23 Nov '05

23 Nov '05

Udo Stenzel <u.stenzel(a)web.de> writes: > The unix pipe is actually function composition. Its argument > (standard > input) isn't explicitly mentioned Then it seems Unix must overload the "|" operator. I typically use it to do things like grep "." *.hs | wc So I think of the types as being grep "." *.hs :: String wc :: String -> Int -- ok, not really, but it shows the point better. So we'd have to have (|) :: a -> (a -> b) -> b And (flip ($)) is the only thing that makes sense. Is it the case that a Unix pipe is analagous to (flip ($)) or (flip (.)) depending on the context? Chad Scherrer Computational Mathematics Group Pacific Northwest National Laboratory "Time flies like an arrow; fruit flies like a banana." -- Groucho Marx

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