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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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RE: [Haskell-cafe] Spurious program crashes
by Simon Marlow 23 Nov '05

23 Nov '05

On 23 November 2005 13:29, Joel Reymont wrote: > On Nov 23, 2005, at 1:18 PM, Simon Marlow wrote: > >> After subsequent dicsussion, do you still think something strange was >> going on here? > > Yes, but in a different thread. The "Postmortem" one. > >> so this basically loops until there are no messages in the channel, >> and then exits. Is that what you wanted, or did you want it to keep >> reading from the channel until told to die? > > I probably made a mistake someplace as I wanted to read until told to > die but ONLY if the channel was empty. I replaced that code with > Tomasz's elegant solution so now I read until Nothing is read from > the channel. > > logger :: Handle -> IO () > logger h = > do ss <- getChanContents parent > logger' ss > where logger' [] = return () > logger' (Nothing:_) = return () > logger' ((Just x):xs) = > do putStrLn x > hPutStrLn h x > logger' xs > yield The yield is unnecessary. Also, getChanContents is considered by some (me included) to be poor style, because it relies on lazy I/O. This should work just as well: logger h = do m <- readChan parent case m of Nothing -> return () Just x -> do hPutStrLn h x; logger h Cheers, Simon

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RE: [Haskell-cafe] Spurious program crashes
by Simon Marlow 23 Nov '05

23 Nov '05

On 21 November 2005 16:43, Joel Reymont wrote: > I'm being quite careful with resources these days. The outstanding > issues are > > 1) Crashes on Mac OSX that are not reproduced on Linux, Windows, etc. > > 2) Some kind of a problem with Chan. getChanContents retrieves things > smoothly, readChan only does it for the first few lines. Simon? > Anyone? After subsequent dicsussion, do you still think something strange was going on here? The code does look strange: logger :: MVar () -> IO () logger die = do empty <- isEmptyChan parent unless empty $ do x <- readChan parent putStrLn x alive <- isEmptyMVar die when (alive || not empty) $ logger die so this basically loops until there are no messages in the channel, and then exits. Is that what you wanted, or did you want it to keep reading from the channel until told to die? STM is a better solution, as already suggested. Without STM, the best way to do this is to multiplex everything into a single channel (i.e. send the die message down the channel). > 3) Different performance of the logger thread on Mac OSX and Windows. > > I'm having thousands of threads write their trace messages to a Chan. > The logger On Windows I only see the first few lines of output when > using isEmptyChan/readChan to retrieve values in a loop. On Mac OSX I > do see smooth output. Context switch behaviour might be different between MacOS X and Windows. With the above code, it might be that the logger thread found an empty channel at sp,e point and exited. Does that make sense? > On Windows I run out of memory because all the output sent to the > chan builds up and is never processed. I can process it by replacing > isEmptyChan/readChan with getChanContents but then my logger thread > hangs forever (right semantics) and hangs everything else that waits > for the logger thread to check an MVar and exit. yes, because the logger thread has exited. Cheers, SImon

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

23 Nov '05

"Albert Lai" <trebla(a)vex.net> writes: > I offer a simpler, more direct, and pre-existing correspondence between a functional > programming construct and unix pipes: Maybe my point wasn't clear. Of course this idea of comparing lazy evaluation to Unix pipes is very old (long before July 2004, I'm sure). The point I'm making is that there is an old idea that may be underused. We use ($) all over the place, but if there are a lot of them (and especially if they are spread over several lines) it becomes awkward to read the whole thing backward to trace through the function from beginning to end. In these cases, it's much simpler to use (\|) = flip ($) -- (#) seems to me too pretty for other purposes to use it here. infixl 0 \| -- Again, why can't this be negative or Fractional?? What I'm asking is really a question of pedagogy and style. This style seems reasonable to me. OTOH, there are some reasons not to do things in this way. Maybe any function big enough to benefit from writing it this way should be broken up anyway. Or maybe getting used to this style where the laziness is right in your face could make it more difficult for people to learn to reason through less obvious laziness. I'm really trying to figure out whether this approach is worth pursuing, rather than imply that this is a completely original idea. 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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Records (was Re: [Haskell] Improvements to GHC)
by Joel Reymont 23 Nov '05

23 Nov '05

I second this motion! I rather like Simon's proposal. On Nov 17, 2005, at 5:00 PM, Fraser Wilson wrote: > Yeah, I thought you might have tried that at some point :-) > > I like http://research.microsoft.com/~simonpj/Haskell/records.html > > cheers, > Fraser. > > On 11/17/05, Joel Reymont <joelr1(a)gmail.com > wrote: Don't get me > started, please :-). I tried making each field a > separate class but then needed to compose records of difference field > instances which led to HList which led to GHC eating up all my memory > and crashing, etc. > > I can see where you are going but if I have 250 records with shared > fields then that's a whole lot of extra boiler plate code to marshall > between the functions with prefixes to the class method > implementations. The road to hell is paved with good intentions ;-). > > Thanks for the tip, though. > > On Nov 17, 2005, at 2:12 PM, Fraser Wilson wrote: > > > To solve this problem I just made them all instances of a class > > with a gameId function. Still, not ideal. -- http://wagerlabs.com/

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RE: Re[2]: [Haskell-cafe] using of data types as kinds
by Simon Peyton-Jones 23 Nov '05

23 Nov '05

Sorry should be fixed now (or shortly when the mirror does its stuff) Simon | -----Original Message----- | From: Bulat Ziganshin [mailto:bulatz@HotPOP.com] | Sent: 22 November 2005 19:28 | To: Simon Peyton-Jones | Cc: haskell-cafe(a)haskell.org | Subject: Re[2]: [Haskell-cafe] using of data types as kinds | | Hello Simon, | | Tuesday, November 22, 2005, 8:17:38 PM, you wrote: | | SPJ> I have not written anything about what I plan to do in GHC, but | SPJ> basically it amounts to allowing you to use a data type as a | SPJ> kind. Busy doing GADTs and impredicativity at the moment though | | Simon, i can't download file | | http://research.microsoft.com/~simonpj/papers/boxy/boxy-pldi.ps.gz | | reffered at http://research.microsoft.com/~simonpj/papers/boxy/ | | | -- | Best regards, | Bulat mailto:bulatz@HotPOP.com | |

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Shortening if-then-else
by Joel Reymont 23 Nov '05

23 Nov '05

Is there a shorter way to write the if-then-else part below? -- tryTakeSeat :: [Word8] -> Word8 -> ScriptState (Maybe Word8) tryTakeSeat _ _ = do ... if (cmdType cmd) /= (CmdSitError Server) then return $ Just seat_num else return Nothing -- Thanks, Joel -- http://wagerlabs.com/

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Re: Frag: a First Person Shooting game
by Joel Reymont 23 Nov '05

23 Nov '05

Mun, I hope this ushers the era of Haskell games! I, for one, was certainly looking for something like this. Did you encounter any difficulties in your development because of Haskell? Was lazy evaluation ever a problem? Why did you choose Yampa to program the game entities? Did this give you a particular advantage? Isn't your frame rate a bit low? Thanks, Joel On Nov 22, 2005, at 6:05 AM, Mun Hon Cheong wrote: > Frag is a 3D First Person Shooting game. > > Features: > > *Yampa, a domain-specific embedded language > for the programming of hybrid systems that > using the concepts of Functional Reactive > Programming (FRP) was used to program the > game entities. -- http://wagerlabs.com/

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re-definition of '.'
by Bulat Ziganshin 23 Nov '05

23 Nov '05

Hello haskell-cafe, if we will define "." as: a.b = b a then we can use "." for 1) field selection 2) sequential functions application in OOP style: [1..100] .map (2*) .sum 3) qualified identifiers - if we treat module name as the record containing all its exported functions: "import M (f,g,h)" defines record M with fields f, g and h The only problem is priority of this operation - for field selection it need to be greater than for application: infixl 11 . while for OOP-styled operations with arguments - its priority must be minimal. one possible solution is rather revolitionary: raise priority of "." if there is no spaces around it, so the following will be interpreted precisely as we want: record.field .List.map (2*) .sum -- Best regards, Bulat mailto:bulatz@HotPOP.com

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Monad Transformer question
by Fan Wu 23 Nov '05

23 Nov '05

Hi Haskell gurus, I'm learning Haskell now and here I'm quite puzzled over some code about Monad Transformers. The code is like: type NDS a = StateT ProblemState [] a getVar :: Var -> NDS (Maybe Value) getVar v = do vs <- gets vars return $ lookup v vs What puzzles me is that, I think the Monad of the do block shall be the "NDS (Maybe Value)" in declaration, but the type of gets is gets :: (MonadState s m) => (s -> a) -> m a So "gets" returns a Monad of type m ([] is this case), which seems to be different from "NDS (Maybe Value)", but GHC does not complain about it. If I comment out the type declaration of "getVar :: Var -> NDS (Maybe Value)" and let GHC interpret the type, then the type of getVar is like: getVar :: (MonadState ProblemState m) => Var -> m (Maybe Value) So does it mean "StateT ProblemState m" and the "m" as in "MonadState ProblemState m" is the same thing? I guess I must missed something when trying to understand the Monad Transformers. Please give me some insights. Thanks, Fan

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RE: [Haskell-cafe] using of data types as kinds
by Simon Peyton-Jones 22 Nov '05

22 Nov '05

Read about Omega! I have not written anything about what I plan to do in GHC, but basically it amounts to allowing you to use a data type as a kind. Busy doing GADTs and impredicativity at the moment though Simon | -----Original Message----- | From: haskell-cafe-bounces(a)haskell.org [mailto:haskell-cafe-bounces@haskell.org] On Behalf Of | Bulat Ziganshin | Sent: 22 November 2005 15:41 | To: haskell-cafe(a)haskell.org | Subject: [Haskell-cafe] using of data types as kinds | | Hello , | | in the HCAR GHC team wrote "On the type system front, we hope to ... | Allow you to use data types as kinds, in a manner similar to Tim | Sheard▓s Omega language". can someone point me where i can read about | this? | | -- | Best regards, | Bulat mailto:bulatz@HotPOP.com | | | | _______________________________________________ | Haskell-Cafe mailing list | Haskell-Cafe(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe

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Existential quantification of environments.
by Keean Schupke 22 Nov '05

22 Nov '05

If I have a function: f x y = add x y and I want to type the function in isolation, then the type of 'add' is essentially carried in the environment... Lets say I want to make this type explicit in the type signature (where f is valid for any a where there is an add function on a - ignoring the class that Haskell would require for the overloading): add :: Int -> Int -> Int add :: Float -> Float -> Float f :: forall a . exists (add :: a -> a -> a) => a -> a -> a or a step further: class Add a where add :: a -> a -> a instance Add Int where ... instance Add Float where ... f :: forall a . Add a => a -> a -> a This seems to suggest: Add a == exists (add :: a -> a -> a) Does this seem in any way right? It seems that the definition of 'f' does require the existance of 'add'. That is the definition is valid iff there exists a function called 'add' of the correct type. Also doesn't the existential quantifier stop you looking inside 'add' - obviously you cannot inspect the definition as it may not be defined (yet?), but presumably you can still apply 'add'. Regards, Keean.

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GHCi always optimizes?
by Dusan Kolar 22 Nov '05

22 Nov '05

Hello all, My question is rather strange, maybe, even if simple: Does ghci always translates with "-O" option set on? I've done some measurements on an application using ghc and ghci. ghc compiled with no opmitization => program running real 988m59.260s user 989m1.325s sys 0m0.704s ghc compiled with optimization set on => program running real 15m54.343s user 15m54.168s sys 0m0.172s ghci alaways: 951.97 secs, 7445117252 bytes (which is 15m51.97sec) To be honest, I don't mind ghci optimizes always but saying it uses the same options as ghc is not entirely true and, for optimization, it's quite painful because one searches error where it is not. (/Understand, I was wondering why program compiled by ghc crashes and/or evaluates so long while running correctly and fast in ghci./) Dusan

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Pickling HList
by Joel Reymont 22 Nov '05

22 Nov '05

Folks, I'm having trouble creating a pickler for HLists and would appreciate a solution. The code for (HCons e HNil) works fine but I get an error trying to implement puHList for (HCons e l) where l is supposed to be (HCons e ...), i.e. another HList. Bar.hs:21:37: Couldn't match the rigid variable e' against PU e' `e' is bound by the instance declaration at Bar.hs:17:0 Expected type: HCons (PU e) l Inferred type: HCons e l In the first argument of puHList', namely l' In the second argument of pair', namely (puHList l)' Failed, modules loaded: none. ---- module Bar where import Data.Word import OOHaskell main = print "We are here!" class HList l => HLPU l where puHList :: HCons (PU e) l -> PU (HCons e l) instance HLPU HNil where puHList (HCons pe HNil) = wrap (\e -> HCons e HNil, \(HCons e HNil) -> e) pe instance HList l => HLPU (HCons e l) where puHList (HCons pe l) = wrap (\(a, b) -> HCons a b, \(HCons a b) -> (a, b)) (pair pe (puHList l)) newtype TourType = TourType TourType_ deriving (Show{-, Typeable-}) newtype AvgPot = AvgPot Word64 deriving (Show{-, Typeable-}) data TourType_ = TourNone | TourSingle | TourMulti | TourHeadsUpMulti deriving (Enum, Show{-, Typeable-}) --- Pickling data PU a = PU { appP :: (a, [Word8]) -> [Word8], appU :: [Word8] -> (a, [Word8]) } pickle :: PU a -> a -> [Word8] pickle p value = appP p (value, []) unpickle :: PU a -> [Word8] -> a unpickle p stream = fst (appU p stream) lift :: a -> PU a lift x = PU snd (\s -> (x, s)) sequ :: (b -> a) -> PU a -> (a -> PU b) -> PU b sequ f pa k = PU (\ (b, s) -> let a = f b pb = k a in appP pb (b, appP pa (a, s))) (\ s -> let (a, s') = appU pa s pb = k a in appU pb s') pair :: PU a -> PU b -> PU (a,b) pair pa pb = sequ fst pa (\ a -> sequ snd pb (\ b -> lift (a,b))) wrap :: (a -> b, b -> a) -> PU a -> PU b wrap (i, j) pa = sequ j pa (lift . i) Thanks, Joel -- http://wagerlabs.com/

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using of data types as kinds
by Bulat Ziganshin 22 Nov '05

22 Nov '05

Hello , in the HCAR GHC team wrote "On the type system front, we hope to ... Allow you to use data types as kinds, in a manner similar to Tim Sheard▓s Omega language". can someone point me where i can read about this? -- Best regards, Bulat mailto:bulatz@HotPOP.com

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How to use notFollowedBy function in Parsec
by Sara Kenedy 22 Nov '05

22 Nov '05

Dear all, Using Parsec, I want to represent a string (of anyToken) not ended with symbol semi (;). I use the command notFollowedby as follows: module Parser where import Parsec import qualified ParsecToken as P import ParsecLanguage langDef::LanguageDef () langDef = emptyDef {reservedOpNames = []} lexer::P.TokenParser() lexer = P.makeTokenParser langDef semi = P.semi lexer str1 :: Parser String str1 = do {str <- many anyToken; notFollowedBy semi; return str} However, when I compile, there is an error. ERROR "Test.hs":17 - Type error in application *** Expression : notFollowedBy semi *** Term : semi *** Type : GenParser Char () String *** Does not match : GenParser [Char] () [Char] I do not know how to fix it. Help me. Thanks for your time.

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Re: [Haskell-cafe] records proposals list
by David Menendez 22 Nov '05

22 Nov '05

Keean Schupke writes: > Haskell already has static records (in H98) > > Dynamic records are addressed by the HList library, which uses > extensions already present in GHC and Hugs (namely Multi-parameter > type-classes and function-dependancies). Is this the case? Every implementation of HList that I've seen also uses overlapping and undecidable instances. -- David Menendez <zednenem(a)psualum.com> | "In this house, we obey the laws <http://www.eyrie.org/~zednenem> | of thermodynamics!"

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records proposals list
by Bulat Ziganshin 22 Nov '05

22 Nov '05

Hello Haskell, can anyone write at least the list of record proposals for Haskell? or, even better, comment about pros and contras for each proposal? -- Best regards, Bulat mailto:bulatz@HotPOP.com

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Re: [Haskell-cafe] Spurious program crashes
by Joel Reymont 22 Nov '05

22 Nov '05

On Nov 17, 2005, at 1:44 PM, Sebastian Sylvan wrote: > Are you sure it's safe to kill a thread which has already been killed? It seems so from the docs. > Why do you fork off the killing of the threads? Why not just run them > in sequence? Someone said that they read somewhere that killThread can block. I'm not gonna point any fingers at musasabi ;-). > Also, I'd recommend refactoring the code a bit, write a function > "parIO" which runs IO computations in parallell and then define > timeout in terms of that. I did this by stealing the timeout/either combinators from the Asynchronous Exceptions paper. It did not help a single bit. Joel -- http://wagerlabs.com/

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Function application like a Unix pipe
by Scherrer, Chad 21 Nov '05

21 Nov '05

I'm still trying to settle on a "feel" for good programming style in Haskell. One thing I've been making some use of lately is (\|) = flip ($) infixl 0 \| Then expressions like f4 $ f3 $ f2 $ f1 $ x become x \| f1 \| f2 \| f3 \| f4 I've seen something like this on haWiki using (#), but I prefer this notation because it looks like a Unix pipe, which is exactly how it's used. This style makes the sequential feel of monadic do notation available to non-monadic functions, and would seem to ease the initial confusion most people experience when they first program using lazy evaluation. Many newbies have experience with Unix pipes, and this notation makes that analogy explicit. I have a couple of questions about this... First, it would be convenient if ($) could appear in an fi without extra parentheses, but this would require "infixl (-1) \|". Is there a reason this isn't allowed? The current fixities don't seem to allow much room for expansion. Would it be possible to either (1) allow negative and/or fractional fixities, or (2) shift and spread out the current fixities to allow more flexibility in the introduction of new operators? I'm also trying to determine to what extent this style should really be used. Does anyone see this as "bad style"? Is there an argument why this might not be such a good way to ease someone into the language? 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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getCPUTime ??
by Michael Benfield 21 Nov '05

21 Nov '05

I'm new to Haskell. I'm apparently misunderstanding something here. When I run this program: --------- module Main where import System.Posix import System.CPUTime printTime = getCPUTime >>= putStrLn . show main = printTime >> sleep 5 >> printTime --------- It produces this output: 1430000000000 1430000000000 or similar. In any case, both the numbers are the same. Should the second number not reflect a time 5 seconds later than the first? I've tried this with both GHC and Hugs, and both give me the same thing. Thanks. Mike Benfield

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RE: [Haskell-cafe] records proposals list
by Ralf Lammel 21 Nov '05

21 Nov '05

I certainly agree with Keean. It's just that the given example is a bit misleading. As Bulat observed, the example is about a heterogeneous list, as opposed to a record. But there are of course tons of record examples to be found, if you follow the HList link. Ralf P.S.: The HList paper also has a reasonable related work section, which might hold more information of the kind that Bulat asked for. > -----Original Message----- > From: haskell-cafe-bounces(a)haskell.org [mailto:haskell-cafe- > bounces(a)haskell.org] On Behalf Of Keean Schupke > Sent: Monday, November 21, 2005 7:56 AM > To: Bulat Ziganshin > Cc: Haskell Cafe > Subject: Re: [Haskell-cafe] records proposals list > > Hi, > > Haskell already has static records (in H98) > > Dynamic records are addressed by the HList library, which uses > extensions already present in GHC and Hugs (namely Multi-parameter > type-classes and function-dependancies). > > So you can do this now... with reasonable syntax, for example to > create an extensible record > > ("some thing" .*. (27 :: Int) .*. True .*. HNil) > > is a statically typed anonymous record. > > > In other words there is no need for any more extensions to GHC or > Hugs to implement Records (although having a type-level type-equality > constaint would simplify the internal implementation of the library)... > > For details see the HList paper: http://homepages.cwi.nl/~ralf/HList/ > > Regards, > Keean. > > Bulat Ziganshin wrote: > > >Hello Haskell, > > > > can anyone write at least the list of record proposals for Haskell? > >or, even better, comment about pros and contras for each proposal? > > > > > > > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe

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Monad strictness
by Yitzchak Gale 21 Nov '05

21 Nov '05

In the following, why does testA work and testB diverge? Where is the strictness coming from? Thanks, Yitz module Test where import Control.Monad.State import Control.Monad.Identity repeatM :: Monad m => m a -> m [a] repeatM = sequence . repeat testA = take 5 $ flip evalState [1..10] $ repeatM $ do x <- gets head modify tail return x testB = take 5 $ runIdentity $ flip evalStateT [1..10] $ repeatM $ do x <- gets head modify tail return x

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RE: [Haskell-cafe] Project postmortem
by Simon Peyton-Jones 21 Nov '05

21 Nov '05

If it's MacOS specific, we're not going to be much help at GHC HQ, because we don't have any (Macs that is). Wolfgang Thaller is the MacOS expert, but maybe there are others now? Simon | -----Original Message----- | From: Joel Reymont [mailto:joelr1@gmail.com] | Sent: 19 November 2005 00:57 | To: Simon Marlow | Cc: Simon Peyton-Jones; Haskell Cafe | Subject: Re: [Haskell-cafe] Project postmortem | | I'm happy to report that the problem can be reproduced by running the | code from my darcs repo at http://test.wagerlabs.com/postmortem. See | the README file. I'm on Mac OSX 10.4.3. | | The server just sits there, goes through the SSL handshake and... | does nothing else. The clients go through the handshake with the | server and do nothing else. The handshake goes through X number of | times and then the client crashes. | | On Nov 18, 2005, at 1:55 PM, Simon Marlow wrote: | | > How we normally proceed for a crash like this is as follows: examine | > where the crash happened and determine whether it is a result of | > heap or | > stack corruption, and then attempt to trace backwards to find out | > where | > the corruption originated from. Tracing backwards means running the | > program from the beginning again, so it's essential to have a | > reproducible example. Without reproducibility, we have to use a | > combination of debugging printfs and staring really hard at the code, | > which is much more time consuming (and still requires being able to | > run | > the program to make it crash with debugging output turned on).

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RE: [Haskell-cafe] Records
by Simon Marlow 21 Nov '05

21 Nov '05

On 19 November 2005 20:53, Ketil Malde wrote: > Antti-Juhani Kaijanaho wrote: > >> Ketil Malde wrote: >> [about A.b and A . b potentially meaning different things:] >> >> >>> Syntax that changes depending on spacing is my number >>> one gripe with the Haskell syntax >>> >>> >> >> I've generally considered that one of the good ideas in most current >> languages (it's not specific to Haskell). ISTR there was a Basic >> dialect where IFX=0THENX=X+1 >> and >> IF X = 0 THEN X = X + 1 >> meant the same thing. >> >> > My point is that e.g. currently "foo? bar", "foo ?bar" and "foo ? bar" > have (at least two) different meanings. Hierarchical naming collides > with function composition (admittedly only rarely in practice). > Template haskell collides with list comprehensions. > > Do you really think that is such a great idea? I think many people agree that this is a bad thing. It occurs in two places in Haskell 98, I believe: - qualified identifiers (M.T is different from M . T) - single-line comments (--??? is not a comment, but -- ??? is) Both of these were late additions to Haskell, and if we were starting from scratch the syntax would probably not have such anomalies. The other odd cases that GHC has are all extensions too - you mentioned implicit parameters and template haskell, there is also GHC's unboxed values (1#, (#..#)), arrows, and parrays. I would argue against adding any of these syntactic anomalies to the standard language, and we should strive to remove those that we have (e.g. by deprecating the use of '.' as function composition in favour of something else, thus freeing it up for use as record/module selection). I'm assuming you don't consider the distinction between '::' and ': :' to be a problem - the justification for this is simple and logical: a double colon '::' is a reserved symbol, in the same way that 'then' is a reserved identifier. Cheers, Simon

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Two questions: lazy evaluation and Church-Rosser
by Gregory Woodhouse 19 Nov '05

19 Nov '05

This is surely a dumb question, but where can I find a proof of the Church-Rosser theorem? Now, a totally(?) separate question: I've been trying to do some background reading on lambda calculus, and have found discussions of strict evaluation strategies (call-by-value and call-by-name) but have yet to find an appropriate framework for modeling lazy evaluation (much less infinite lists and comprehensions). Can anyone point me in the right direction? === Gregory Woodhouse gregory.woodhouse(a)sbcglobal.net "Nothing is as powerful than an idea whose time has come." -- Victor Hugo

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Formalizing lazy lists?
by Greg Woodhouse 19 Nov '05

19 Nov '05

Maybe this is old hat, but the question about detecting loops in data structures got me thinking about this. I know you can encode the cons operator (and ordinary lists) in pure lambda calculus, but how could you possibly represent something like [0, 1..]? One thought that occurss to me is to treat it ass a kind of direct limit, but of course, the essence of a structure like this is that the ith entry is computable in a natural way, and it seems that an algebraic limit couldn't really capture this intuition unless we were to introduce some sort of higher order structure (which may be what we want, anyway). === Gregory Woodhouse <gregory.woodhouse(a)sbcglobal.net> "Interaction is the mind-body problem of computing." --Philip Wadler

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RE: [Haskell-cafe] Project postmortem
by Simon Marlow 19 Nov '05

19 Nov '05

On 18 November 2005 10:48, Joel Reymont wrote: > On Nov 18, 2005, at 10:17 AM, Simon Peyton-Jones wrote: > >> I hope you don't abandon Haskell altogether. Without steady, >> friendly pressure from applications-end folk like you, things won't >> improve. > > Nah, I'm just having a very frustrating Friday. I think I need some > direction in which to dig and a bit of patience over the weekend. For > example, > > What does this mean precisely? My take is that the GHC runtime is > trying to call a C function. this much I gathered from the source > code. It also seems that since I do not see another library at #0 > then the issue is within GHC. Is that the right take on it? The stack trace doesn't mean much at all I'm afraid - GHC doesn't use the C stack, so any stack trace generated for a crash inside the Haskell code is mostly useless. It does tell you the block in which the crash happened (s8j1_info), and it tells you that the crash was in Haskell and not C. The rest of the frames on the stack are from the GHC runtime, and you'll pretty much always see these same frames on the stack for any crash inside Haskell code. How we normally proceed for a crash like this is as follows: examine where the crash happened and determine whether it is a result of heap or stack corruption, and then attempt to trace backwards to find out where the corruption originated from. Tracing backwards means running the program from the beginning again, so it's essential to have a reproducible example. Without reproducibility, we have to use a combination of debugging printfs and staring really hard at the code, which is much more time consuming (and still requires being able to run the program to make it crash with debugging output turned on). You can get debugging output by compiling your program with -debug, and then running it with some of the -D<something> options (use +RTS -? for a list, +RTS -Ds is a good one to start with). Cheers, Simon

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Records (was Re: [Haskell] Improvements to GHC)
by Dimitry Golubovsky 18 Nov '05

18 Nov '05

Sebastian Sylvan wrote: >Personally I think that the dot is way to good of a symbol to be >"wasted" on function composition. I mean, how often do you really use >function composition in a way which doesn't obfuscate your code? I use >($) way more often than (.). Some people do use it more often than I I found it useful to use (mainly for debugging purposes) mapM (putStrLn . show) <some list> if I want to print its elements each on a new line. -- Dimitry Golubovsky Anywhere on the Web

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Re: [Haskell-cafe] Project postmortem
by Joel Reymont 18 Nov '05

18 Nov '05

The exception is actually from withTimeOut. Removing calls to that lets the handshake proceed. The server is using a client handshake, though, so the handshake of client vs. client goes on indefinitely. I'm fixing the server side and once that is done will clean up SSL at the end of the handshake and launch a few thousand clients. It's not a good repro case yet although I would love to know why withTimeOut is throwing that exception. Joel On Nov 18, 2005, at 5:02 PM, Christian Maeder wrote: > Sorry, I can only show you my output on > Linux turing 2.6.11.4-21.9, but I don't know what's going on and > will not have more time this week. > > Cheers Christian > > maeder@turing:/local/maeder/haskell/postmortem> ./server > 17:55:14: ThreadId 1: Accepted new connection: {handle: <socket: 4>} > 17:55:14: ThreadId 1: Verify locations: 1 > 17:55:14: ThreadId 1: sslGetError: 2 > 17:55:14: ThreadId 4: Starting SSL handshake... > 17:55:14: ThreadId 4: Reading from BIO... > 17:55:14: ThreadId 4: Waiting for BIO 0x080d10d8 > 17:55:14: ThreadId 4: waitForBio: gotta wait a bit... > server: unknown exception -- http://wagerlabs.com/

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RE: [Haskell-cafe] Project postmortem
by Simon Peyton-Jones 18 Nov '05

18 Nov '05

| Unless lightning strikes and tomorrow morning I figure out what's the | deal with the spurious Mac OSX crashes, I think this might be my last | network app in Haskell. I should really be spending time on the | business end of the app intead of figuring out platform differences | and the like. Joel, I think it's fantastic that you've been pushing on Haskell in the way you have. What I learn from your experience is that the *language* is pretty good for what you wanted to do (esp lightweight concurrency) but the *libraries* in the area of networking are lacking both functionality and (more particularly) robustness. I hope you don't abandon Haskell altogether. Without steady, friendly pressure from applications-end folk like you, things won't improve. It's incredibly valuable feedback. But I can see that when you have to deliver something next week you can't wait around for some someone to get around to fixing your problem. (They aren't paid either!) Maybe you can use Haskell for something less mission-critical, so that you can keep up the pressure? Meanwhile, let me utter my customary encouragement to the Haskell community out there: please pitch in and help! Haskell will only break into real applications, of the kind Joel has been writing, if we can offer robust libraries, and that depends utterly on you. Don't wait for someone else to do it. Simon

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RE: [Haskell-cafe] Project postmortem
by Simon Marlow 18 Nov '05

18 Nov '05

On 18 November 2005 14:42, Joel Reymont wrote: > On Nov 18, 2005, at 1:55 PM, Simon Marlow wrote: > >> You can get debugging output by compiling your program with -debug, >> and then running it with some of the -D<something> options (use +RTS >> -? for a list, +RTS -Ds is a good one to start with). > > I'm still working on a repro case but here's what I get... > > +RTS -Ds > ... > scheduler: checking for threads blocked on I/O > sched: -->> running thread 1103 ThreadRunGHC ... > sched: --<< thread 1103 (ThreadRunGHC) stopped: is blocked on an MVar > all threads: > thread 1225 @ 0x1539000 is not blocked > thread 1224 @ 0x1506aa4 is not blocked > thread 1223 @ 0x15066a4 is not blocked > ... > scheduler: checking for threads blocked on I/O > sched: -->> running thread 1107 ThreadRunGHC ... > Segmentation fault > > 1107 is not blocked in the list of all threads. What options should I > try next? That doesn't tell us much unfortunately. Can you send a disassembly of the block in which the crash happened? Is it always the same block, BTW? Does changing the heap size (+RTS -H<size>) have any effect? Cheers, Simon

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Re: [Haskell] Re: Making Haskell more open
by Malcolm Wallace 18 Nov '05

18 Nov '05

Ben Moseley <ben_moseley(a)mac.com> writes: > Simon Peyton-Jones <simonpj <at> microsoft.com> writes: > > > ... And avoid > > getting screwed up by malicious folk? > > ... but I believe there are a number of people who regularly > review all the "Recent Changes" and undertake to 'undo' any > malicious/inaccurate modifications. I suspect this would end up adding /more/ work to central maintainers, rather than less. In any case, there is already a Haskell wiki. If it becomes sufficiently rich as a source of information, it will naturally start to take over from the "fixed" webpages. This improved-documentation experiment has already begun some time ago... Regards, Malcolm

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Project postmortem
by Joel Reymont 17 Nov '05

17 Nov '05

Folks, I have done a lot of experiments over the past few weeks and came to a few interesting conclusions. First some background, then issues, solutions and conclusions. I wrote a test harness for a poker server that understands the different binary packets and can send and receive them. The harness launches each "script" in a separate unbound thread that connects to the server via TCP and does its work. The main goals of the project were: easy scripting, very high number of connections from the harness (a few thousand) and running on Windows. I develop on Mac OSX but have a Windows machine for testing and to run the poker server. Another key goal was to support the server encryption. SSL encryption is done in a wierd way that requires attaching read/write OpenSSL BIOs to the SSL descriptor so that SSL encrypts to/from memory. Encrypted chunks are then taken from the BIOs and sent as payload in servver packets. Overall, I probably spent about 4 weeks writing the server and about 2 more weeks grappling with the various issues. The issues centered around 1) the program trashing memory like no tomorrow, 2) intermittent crashes on Windows and 3) not being able to launch a high number of connections on Windows before crashing. I significantly improved trashing of memory by switching to plain Haskell structures from nested lists of wxHaskell-style properties (attr := value). Intermittent crashes were harder to troubleshoot, specially given that things were running smoothly on Mac OSX. Stack traces pointed into libcrypto (part of OpenSSL) and thus to the BIOs that I was allocating. I guesses that OpenSSL was maxing out some resources and closed the leak by explicitly freeing the SSL descriptor which freed the associated BIO structures. Then things got wierder as my program started crashing in a different place entirely with stack traces like this: Program received signal EXC_BAD_ACCESS, Could not access memory. Reason: KERN_INVALID_ADDRESS at address: 0x3139322e 0x0027c174 in s8j1_info () (gdb) where #0 0x0027c174 in s8j1_info () #1 0x0021c9f4 in StgRunIsImplementedInAssembler () at StgCRun.c:576 #2 0x0021cdc4 in schedule (mainThread=0x1100360, initialCapability=0x308548) at Schedule.c:932 #3 0x0021dd6c in waitThread_ (m=0x1100360, initialCapability=0x0) at Schedule.c:2156 #4 0x0021dc50 in scheduleWaitThread (tso=0x13c0000, ret=0x0, initialCapability=0x0) at Schedule.c:2050 #5 0x00219548 in rts_evalLazyIO (p=0x29b47c, ret=0x0) at RtsAPI.c:459 #6 0x001e4768 in main (argc=2262116, argv=0x308548) at Main.c:104 I took waitThread_ as a clue and started digging deeper. Whenever I connect to the server or send a command I wait for X seconds and if not connected or desired command is not received I throw an exception which fails the script. I implemented the timeout combinator a couple of different ways, including that in the Asynchronous Exceptions paper but it did not help. I think the issue has to do with killing threads that are using FFI. Although I'm killing threads that call the Haskell connectTo, hGetBuf, etc. I think it's still FFI. I disposed of timeouts entirely, leaving connectTo as it is and using hWaitForInput on my socket handle to simulate timeouts. This improved things tremendously and I'm now able to run a few thousands of unbound script threads on Windows with OpenSSL FFI and everything. Memory usage is still higher than I would have liked and crashes in OpenSSL still happen when the number of threads/memory usage is really high so there's still room for improvement. I should probably go back to using a foreign finalizer (SSL_free) on the SSL descriptors rather than freeing them explicitly as the freeing does not happen if a script fails mid-way. I'm quite satisfied with my first Haskell project. I love Haskell and will continue hacking away with it. This list is invaluable in the depth of offered help whereas #haskell (IRC) is invaluable when speed matters. I'm quite amazed at the things I have been able to do, the expressiveness of Haskell and the clean looks. Clean looks can be deceptive, though, as they can hide code of amazing complexity. Fundeps, existential types, HList take a while to grasp. Also, I feel somewhat like a pioneer and I definitely got more than a fair share of arrows in my back. I had GHC run out of memory during compilation (fixed by SPJ), had it quit midway during compilation with an error about generated extents being too large in assembler code. I had GHC crash at runtime with an error like "fromJust not returning Just, this could not be happening!". Yesterday's error topped them all: internal error: update_fwd: unknown/strange object 0 Please report this as a bug to glasgow-haskell-bugs(a)haskell.org, or http://www.sourceforge.net/projects/ghc/ I think I got this when using +RTS -C0 -c. Overall, the experience with Haskell has been exhilarating and I'm already preparing to use it on my next projects like detecting collusion in poker as well as rake optimization (Dazzle paper very helpful here!). Still, I think that GHC can be a bit rough around the edges and I would think twice about writing high-performance network apps with it. Thanks, Joel P.S. The Glasgow Distributed Haskell (GdH) people are supposed to have a mailing list and I would love to share my findings twith them but I could not find the mailing list itself. -- http://wagerlabs.com/

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RE: [Haskell-cafe] Re: IO exception not being caught
by Simon Peyton-Jones 17 Nov '05

17 Nov '05

Indeed! I always use braces and semicolons with do-notation. You are free to do so too! Nothing requires you to use layout. Indeed, you can freely mix the two. Simon | -----Original Message----- | From: haskell-cafe-bounces(a)haskell.org [mailto:haskell-cafe-bounces@haskell.org] On Behalf Of Joel | Reymont | Sent: 16 November 2005 15:37 | To: Haskell Cafe | Subject: [Haskell-cafe] Re: IO exception not being caught | | After almost two months with Haskell I'm starting to understand why | its use is not as widespread as... well pick a favorite language of | your own. My issue was that of indentation. | | Compare this working version: | | liftIOTrap io = | do mx <- liftIO (do x <- io | return (return x) | `catchError` | (\e -> do let x = fromIOError e | trace_ $ "Caught " ++ x | return $ throwError x | )) | mx | | With the one below | | On Nov 16, 2005, at 2:27 PM, Joel Reymont wrote: | | >> liftIOTrap io = | >> do mx <- liftIO (do x <- io | >> return (return x) | >> `catchError` | >> (\e -> return (throwError | >> (fromIOError e)))) | >> mx | | -- | http://wagerlabs.com/ | | | | | | _______________________________________________ | Haskell-Cafe mailing list | Haskell-Cafe(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe

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Darcs and the Google Base
by Dimitry Golubovsky 17 Nov '05

17 Nov '05

This may be just funny, but... As the Google Base went live yesterday (11/16/2005), I tried to add the information about my HSFFIG project to the Base. As the Base allows to define arbitrary attributes (labels) for each item, I added the two of "Web URL" type: CABAL and DARCS holding urls for the project Cabal file and the Darcs repo respectively. I was turned down on "excessive capitalization" of these labels. I made them into "Cabal" and "Darcs". The former was accepted. the latter was turned down again as "misspelled". I wrote an "exemption request" explaining that Darcs is not a misspelling. However, it's been more than a whole day since my attempt, it hasn't been resolved. Interestingly, my item was published after I removed the "Darcs" label, but shortly after I resubmitted the exemption request for Darcs the item disappeared. -- Dimitry Golubovsky Anywhere on the Web

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RE: [Haskell-cafe] Spurious program crashes
by Simon Marlow 17 Nov '05

17 Nov '05

On 16 November 2005 17:38, Joel Reymont wrote: > I'm getting crashes like this and I cannot figure out what the > problem is. I'm launching a bunch of threads that connect to a server > via TCP and exchange packets. > > I am running operations like connect and receive in a timeout > function that launches two threads and uses an MVar to figure out > who's done first. The timeout function then kills the two threads. > > Any ideas what could be causing this? I feel like a Haskell guinea > pig these days :-). I don't see any reason why you should be getting crashes here, but this is a delicate area (async exceptions + FFI). It's possible there's a bug, but as usual we need to reproduce the symptoms here. Can you help with a repro case? Regarding the behaviour of killThread, I believe the version in GHC is slightly different from the version described in the Asynchronous Exceptions paper, in particular the GHC version blocks until the exception has been delivered to the target thread (use another forkIO to get the fully async version). Cheers, Simon

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ReaderT and concurrency
by Kurt Hutchinson 17 Nov '05

17 Nov '05

I'm writing a program that will be using multiple threads to handle network activity on multiple ports in a responsive way. The treads will all need access to some shared data, so I'm using an MVar. So far so good. The problem is that passing the MVar around everywhere is kind of a pain, so I was hoping to use a ReaderT monad on top of the IO monad to handle that for me. I have that working, but one piece seemed a bit out of place so I wondered if there was a better way. Below is a small test program that presents my question. My program uses forkIO to create the separate threads (Set A), and some of *those* threads will need to create threads (Set B). In order for the ReaderT to handle the environment of the threads in Set B, do I have to perform another runReaderT when forking? Or is there a way to get the ReaderT environment automatically carried over to the newly created Set B thread? See the "NOTE" comment in the code below for the particular spot I'm asking about. > import Control.Monad.Reader > import Control.Concurrent > > type MyReader a = ReaderT (MVar Integer) IO a > > main = do > mv <- newMVar 1 > forkIO $ runReaderT (printAndFork "one" 5) mv > forkIO $ runReaderT (printAndFork "two" 5) mv > getChar -- Pause so the threads can print before program exit > > printAndFork :: String -> Integer -> MyReader () > printAndFork _ 0 = return () > printAndFork str n = do > mv <- ask > lift $ do > modifyMVar_ mv $ \i -> do > print $ str ++ show i > return (i + 1) > -- NOTE: Is this runReaderT necessary to carry the > -- environment to the new thread? Is there a better way? > forkIO $ runReaderT (justPrint $ "inner " ++ str) mv > printAndFork str (n - 1) > > justPrint :: String -> MyReader () > justPrint str = do > mv <- ask > lift $ do > modifyMVar_ mv $ \i -> do > print $ str ++ show i > return (i + 1) > return () Kurt Hutchinson

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RE: [Haskell-cafe] layout problem
by Simon Marlow 17 Nov '05

17 Nov '05

On 16 November 2005 17:15, Christian Maeder wrote: > Simon Peyton-Jones wrote: >> Indeed! I always use braces and semicolons with do-notation. You >> are free to do so too! Nothing requires you to use layout. Indeed, >> you can freely mix the two. > > I would not recommend braces and semicolons, because these allow a bad > layout (easy to parse for a compiler, but hard to read for a human), > unless you invest the time to make a tidy layout despite the braces > and semicolons. (So why not only make a tidy layout?) > > Surely, a different layout may change your semantics (in rare cases). > A missplaced "_ -> error ..." case usually causes a pattern warning. > >>>>> liftIOTrap io = >>>>> do mx <- liftIO (do x <- io >>>>> return (return x) >>>>> `catchError` >>>>> (\e -> return (throwError >>>>> (fromIOError >>>>> e)))) > > I'ld rather avoid the infix `catchError' and write: > > liftIO $ catchError > (do ... > ) $ \e -> I generally prefer to use the "handle" variants rather than "catch": liftIO $ handle my_handler $ do x <- io return (return x) where my_handler e = return (throwError (fromIOError e)) Don't be afraid to name things if it makes your code easier to read. Cheers, Simon

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RE: [Haskell-cafe] Reducing # of context switches
by Simon Marlow 17 Nov '05

17 Nov '05

On 17 November 2005 00:17, Joel Reymont wrote: > The latest GHC docs mention that the -C option takes a seconds value > whereas prior docs mention microseconds. Which is it? > > Also, do I pass +RTS -Cxxx or is it just -C? It is in seconds, eg. +RTS -C0.5 for switches every half a second. I've just fixed and cleaned up the docs a bit. Cheers, Simon

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updated_fwd: unknown/strange object 0
by Joel Reymont 17 Nov '05

17 Nov '05

internal error: update_fwd: unknown/strange object 0 Please report this as a bug to glasgow-haskell-bugs(a)haskell.org, or http://www.sourceforge.net/projects/ghc/ This happened when I tried running with +RTS -C0 -c I think. -- http://wagerlabs.com/

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Hackage or Where to Host Haskell projects, and simple darcsforge description was Re: Making Haskell more open
by Shae Matijs Erisson 17 Nov '05

17 Nov '05

Wolfgang Jeltsch <wolfgang(a)jeltsch.net> writes: > Would it be intended that every Haskell-related project is hosted under > haskell.org? This might be not so nice. And it might be not so nice if most > Haskell-related projects are hosted under haskell.org so that potential users > might only look under haskell.org for projects and miss those that are hosted > elsewhere. Hackage[1] is designed to be the freshmeat and apt-get of the Haskell world. I have a simple plan for a darcsforge as well: If Cabal includes a darcs-repository field, developers will be able to upload their project.cabal file to Hackage or to a darcsforge server. That server will run darcs pull on the repositories once a night or so. The developers can include an index.html in their repo that points to a doc/ subdirectory, or is the entire docs and description for simple projects. That way a single site can host the equivalent of cvs and webspace for darcs. That site could do http://host/projectname urls for each project. This is roughly a darcs equivalent to RSS aggregators. It does require that developers have a publically accessible repo, but anyone can get space from geocities or angelfire for that. Advantages of this include: * easy indexing and searching of projects and sources * easy references to other darcs/cabal projects * host needs nearly zero admin effort, notably zero user accounts required. Disadvantages are: * no bug tracker * no mailing lists Though maybe those could have darcs backends also? Still, this simple darcsforge has an excellent effort to results ratio. I hope to have time to add this sort of thing to cabal and hackage soon. [1] http://www.haskell.org/hawiki/Hackage -- Shae Matijs Erisson - http://www.ScannedInAvian.com/ - Sockmonster once said: You could switch out the unicycles for badgers, and the game would be the same.

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Reducing # of context switches
by Joel Reymont 17 Nov '05

17 Nov '05

Folks, The latest GHC docs mention that the -C option takes a seconds value whereas prior docs mention microseconds. Which is it? Also, do I pass +RTS -Cxxx or is it just -C? Thanks, Joel -- http://wagerlabs.com/

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IO exception not being caught
by Joel Reymont 16 Nov '05

16 Nov '05

Folks, I have a problem catching my IO exception with the code below. The intent is to catch either the IO exception from connectTo (connection refused, etc.) or the timeout. type EngineState = ErrorT String (StateT World IO) fromIOError err = ioeGetErrorString err liftIOTrap :: IO a -> EngineState a liftIOTrap io = do mx <- liftIO (do x <- io return (return x) `catchError` (\e -> return (throwError (fromIOError e)))) mx timeout secs fun = do resultVar <- newEmptyMVar threadId <- forkIO $ do result <- fun putMVar resultVar result forkIO $ do threadDelay (secs * 1000000) throwError $ userError "Timeout" maybeResult <- takeMVar resultVar killThread threadId return maybeResult connect_ :: HostName -> Int -> IO Handle connect_ h p = connectTo h $ PortNumber $ fromIntegral p connect :: HostName -> Int -> EngineState () connect host port = do w <- get let secs = timeout_seconds w h <- liftIOTrap $ timeout secs $ connect_ host port trace $ "Connection established, h: " ++ show h ... Thanks, Joel -- http://wagerlabs.com/

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Spurious program crashes
by Joel Reymont 16 Nov '05

16 Nov '05

I'm getting crashes like this and I cannot figure out what the problem is. I'm launching a bunch of threads that connect to a server via TCP and exchange packets. I am running operations like connect and receive in a timeout function that launches two threads and uses an MVar to figure out who's done first. The timeout function then kills the two threads. Any ideas what could be causing this? I feel like a Haskell guinea pig these days :-). My Cabal build options look like this ghc-options: -fglasgow-exts -Wall -O -debug And the stack trace: Program received signal EXC_BAD_ACCESS, Could not access memory. Reason: KERN_INVALID_ADDRESS at address: 0x3139322e 0x0027c174 in s8j1_info () (gdb) where #0 0x0027c174 in s8j1_info () #1 0x0021c9f4 in StgRunIsImplementedInAssembler () at StgCRun.c:576 #2 0x0021cdc4 in schedule (mainThread=0x1100360, initialCapability=0x308548) at Schedule.c:932 #3 0x0021dd6c in waitThread_ (m=0x1100360, initialCapability=0x0) at Schedule.c:2156 #4 0x0021dc50 in scheduleWaitThread (tso=0x13c0000, ret=0x0, initialCapability=0x0) at Schedule.c:2050 #5 0x00219548 in rts_evalLazyIO (p=0x29b47c, ret=0x0) at RtsAPI.c:459 #6 0x001e4768 in main (argc=2262116, argv=0x308548) at Main.c:104 Thanks, Joel -- http://wagerlabs.com/

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RE: [Haskell-cafe] Re: [Haskell] Making Haskell more open
by Simon Marlow 16 Nov '05

16 Nov '05

On 14 November 2005 08:32, Gour wrote: > Nobody said that DocBook does not work fine. However let me quote > SPJ's message: > > <quote> > However, I still wonder if there are things we could do that would > make > it easier for people to contribute. Here are two concrete > suggestions: ^^^^^^^ > - Make it possible for people to add comments, explanations, or > questions to > * The GHC user manual [currently generated using DocBook] > * The Haskell 98 Report > The idea would be that anyone could help improve these documents, > ^^^^^^^^^^^^^^^^^^^ > and that, at least in the case of the GHC user manual, we could > use the comments to help clarify the text. > </quote> > > So, the whole discussion, at least from my side, was to offer > suggestions to make it easier for more people to contribute to the > whole haskell community. With regard to the GHC user manual, I don't think the implication above was that we should change the markup technology (at least, I agree with Sven that DocBook XML is on the whole a reasonable solution). The idea was to make it easy for Joe Programmer to add his comments to the manual, whether by a wiki link or some other clever user-editable content mechanism. In a separate stage the comments could be incorporated into the manual proper by the developers, or just left in place for the edification of other users. Cheers, Simon

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RE: [Haskell-cafe] waitForProcess: sytem call interrupted
by Simon Marlow 16 Nov '05

16 Nov '05

On 16 November 2005 11:26, Joel Reymont wrote: > I think runhaskell reports that when the program has crashed > violently with a segmentation violation. It does, and that's a bug. I fixed it last week. Cheers, Simon > > On Nov 16, 2005, at 1:54 AM, Donald Bruce Stewart wrote: > >> I've been getting this in lambdabot with waitForProcess since 6.4.1 >> (I think). Seems harmless though (I think). Try catching the >> exception. >> >> Control.Exception.catch (waitForProcess pid) >> (\_ -> return ExitSuccess) -- so just >> fake success

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RE: [Haskell-cafe] GHC ignores RTS options
by Simon Marlow 16 Nov '05

16 Nov '05

On 16 November 2005 13:24, Tomasz Zielonka wrote: > On Wed, Nov 16, 2005 at 01:09:07PM -0000, Simon Marlow wrote: >>> BTW - it would be nice if it was easier to override the default RTS >>> options when compiling the program. Perhaps a nice task for a newbie >>> GHC developer? >> >> Already possible, see: >> >> http://www.haskell.org/ghc/docs/latest/html/users_guide/runtime-control. >> html#rts-hooks > > I was aware of this, and I should write about it. > >> Admittedly it's a bit more fiddly than a command-line flag to GHC, >> though. > > And because of this I wrote that it would be nice if it was easier :-) Sorry, I misread the message. > I've bitten several times by the default values of RTS options, > especially the stack size limit (-K). But it was always easier to > set GHCRTS or use +RTS -RTS, so I never used the rts-hooks. > > Do you think I could do this? I am not sure how difficult it would be. Sure, it shouldn't be too hard. You need to generate a .c file containing the ghc_rts_opts setting, and then compile & link it into the final binary. It's just a matter of plumbing the various bits together in GHC's front end. (it might be nicer to generate Cmm and then push this through the back end, to avoid the dependence on the C compiler, though). Cheers, Simon

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