- Haskell-Cafe - Haskell.org

`typeof' is not a (visible) method of class `Typeable' ?
by WANG Meng 12 Nov '05

12 Nov '05

Hi All, While I was trying to declare Language.Haskell.TH.Exp as an instance of "Typeable", ghci 6.4 yields this error. It does not allow me to define an instance of "typeof". Does anybody know what should be the right way of doing this? Thanks. -W-M- @ @ | \_/

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Re: Making Haskell more open
by Nils Anders Danielsson 11 Nov '05

11 Nov '05

On Fri, 11 Nov 2005, Tomasz Zielonka <tomasz.zielonka(a)gmail.com> wrote: [Moved to cafe.] > How about an integrated newsgroup+mailinglist+forum. If we had a > two-way newsgroup+mailinglist integration, people could use it also > as a forum, for example through gmail.google.com. But I don't use > fora, so I probably talk nonsense. I think Gmane has everything you're looking for (bidirectional mail-to-news gateway, you can read and post via a web page, and quite a few Haskell mailing lists are already archived there; see http://dir.gmane.org/gmane.comp.lang.haskell.general, for instance). I've hardly used it, though, so I can't tell whether it works well. -- /NAD

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throwDyn typing "fun"
by Einar Karttunen 11 Nov '05

11 Nov '05

Hello It seems that the type of throwDyn and throwDynTo are dangerously close. ThrowDyn works in with any of the arguments of throwDynTo, which can cause evil situations. throwDyn :: Typeable exception => exception -> b Which means e.g. "throwDyn someThreadId SomeException" will work when you wanted to say "throwDynTo someThreadId SomeException" and they both have types which unify with IO (). I think using a class Typeable => DynamicException a where ... and throwDyn :: DynamicException a => a -> b could make more sense. - Einar Karttunen

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RE: [Haskell-cafe] Re: FPS: Finalizers not running (wasMemoryusageoutside of the Haskell heap)
by Simon Marlow 10 Nov '05

10 Nov '05

On 10 November 2005 14:56, Jan-Willem Maessen wrote: > On Nov 9, 2005, at 4:46 AM, Ketil Malde wrote: > >> Sebastian Sylvan wrote: >> >>> On 11/8/05, Jan-Willem Maessen <jmaessen(a)alum.mit.edu> wrote: >>> >>>> Just wanted to let people know that I've been working on improving >>>> Data.HashTable, with the help of Ketil Malde's badly performing >>>> code >>>> >>>> >> Always happy to help, of course - bad performance R us:-) > > I think that if I can get unsafeFreeze/unsafeThaw to work reliably, > it'll finally outperform Data.Map on your example. I haven't yet > played with the hash function, which looks kind of bad; there may be > hope for improvement there as well. > >>> Request: Data.HashTable.Immutable >>> >> I'm not sure you really want that - do you wish to copy a large >> array each time you do an update? >> Freezing and thawing might be a good idea, though. > > A true read-only hash table, with a freeze for the mutable version, > but NO THAW, could potentially be useful. I seem to recall that hbc > had an immutable hash table (along with a derivable Hashable class), > where the content was specified as in an array comprehension. The unsafeFreeze/unsafeThaw trick can be used to speed up DiffArrays, which in turn could be used to provide a good immutable HashTable implementation. I'm pretty sure this would be a profitable approach. It's possible that DiffArrays need more work than just unsafeFreeze/unsafeThaw to make them efficient, though. Cheers, Simon

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Parameterizing on type
by Joel Reymont 10 Nov '05

10 Nov '05

Folks, How can I create a generic pickler that's parameterized on type and constructor? I define types like this: newtype AvgPot = AvgPot Word64 deriving (Show, Typeable) newtype NumberOfPlayers = NumberOfPlayers Word16 deriving (Show, Typeable) and then have a lot of boiler-plate code like this, a pickler for each type: puAvgPot :: PU AvgPot puAvgPot = wrap (\a -> AvgPot a, \(AvgPot b) -> b) endian where data PU a = PU { appP :: (a, [Word8]) -> [Word8], appU :: [Word8] -> (a, [Word8]) } wrap :: (a -> b, b -> a) -> PU a -> PU b What I would like to have is a generic pickler that's parameterized on constructor and type. These can and will be the same, though. I want something like this, how can it be done in Template Haskell or otherwise? pickler :: PU T pickler Con pa = wrap (\a -> Con a, \(Con b) -> b) pa Thanks, Joel -- http://wagerlabs.com/

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GHC cannot compile my code
by Joel Reymont 09 Nov '05

09 Nov '05

Folks, I'm on Mac OSX 10.4.3 with 1Gb of memory and GHC 6.4.1. I'm using HList to define 92 structures in a module. I'm not using classes. There's some nesting going on (see below). Few datypes above are data, mostly they are newtypes around Word32s, Strings, and lists of those. I have 40 newtypes that wrap HLists and homogeneous lists of HList types, 52 are type aliases around HLists. Both with and without -O ghc cannot compile my module. I run out of physical memory within 2-3 minutes and then it's just swapping (I think) and the system becomes totally unresponsive. Any ideas how to remedy this? I shudder at thinking about compiling this on Windows with 256Mb of memory. I will try to split the module into smaller modules and will report my findings. Thanks, Joel P.S. Some example types: newtype Tables = Tables [TableInfo] deriving (Show, Typeable) type TableInfo = AvgPot :*: NumPlayers :*: Waiting :*: PlayersFlop :*: TableName :*: TableID :*: GameType :*: InfoMaxPlayers :*: RealMoneyTable :*: LowBet :*: HighBet :*: MinStartMoney :*: MaxStartMoney :*: GamesPerHour :*: TourType :*: TourID :*: BetType :*: CantReturnLess :*: AffiliateID :*: NIsResurrecting :*: MinutesForTimeout :*: SeatsToResurrect :*: LangID :*: HNil -- http://wagerlabs.com/

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Request for subject suggestions for a series of informal top 10 Haskell articles
by Kenneth Hoste 08 Nov '05

08 Nov '05

Greetings, As you all might know, the Haskell community has it's own informal magazine, The Monad.Reader (http://haskell.org/tmrwiki) I'm planning to write (with some support from the frequent users of #haskell @ irc.freenode.net) a series of articles for TMR, which describe some aspect of Haskell. Because of the informal (but serious and thorough) style of TMR, I'd like to do this using a top 10 list regarding some subject. Every article will list 10 of most famous, most frequently used or most usefull things regarding that subject. I'd like to ask for suggestions on each subject when I'm writing the article on this mailing list, because I don't know the Haskell world very well (I've only been working with it for a year know, in my spare time). This first mail is intented to ask for suggestions regarding future subjects for the articles. Suggestions are welcome by replying, or by adding them to the 'take 10 [1..]'-wiki at http://haskell.org/tmrwiki/TopTenHaskell . Also other suggestions or remarks are very welcome. I hope this series of articles can provide a source of information for both new and experienced users, because you there's always room to discover new aspects of your favourite language. Kenneth a.k.a. boegel

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Inferred type less polymorphic than expected
by Joel Reymont 08 Nov '05

08 Nov '05

Folks, How do I fix this? data Prop = forall a b.(Eq a, Show a) => Attr a := a data Attr a = Attr String (a -> Dynamic, Dynamic -> Maybe a) (PU a) type Props = M.Map String (Int, Prop) instance Ord (Int, Prop) where compare (a, _) (b, _) | a == b = EQ | a > b = GT | otherwise = LT makeAttr :: Typeable a => String -> PU a -> Attr a makeAttr name pickler = Attr name (toDyn, fromDynamic) pickler ... props :: Props -> PU Props props m = props' $ sort $ M.toList m where props' [] = lift [] props' ((_, (Attr _ _ pp := _)):xs) = wrap (\(a, b) -> a : b, \(a : b) -> (a, b)) (pair pp (props' xs)) ./Script/Prop.hs:80:10: Inferred type is less polymorphic than expected Quantified type variable `a' is mentioned in the environment: props' :: [(a1, Prop)] -> PU [a] (bound at ./Script/Prop.hs: 79:10) When checking an existential match that binds $dEq :: {Eq a} $dShow :: {Show a} pp :: PU a The pattern(s) have type(s): [(a1, Prop)] The body has type: PU [a] In the definition of `props'': props' ((_, (Attr _ _ pp := _)) : xs) = wrap (\ (a, b) -> a : b, \ (a : b) -> (a, b)) (pair pp (props' xs)) In the definition of `props': props m = props' $ (sort $ (Data.Map.toList m)) where props' [] = lift [] props' ((_, (Attr _ _ pp := _)) : xs) = wrap (\ (a, b) -> a : b, \ (a : b) -> (a, b)) (pair pp (props' xs)) Thanks, Joel -- http://wagerlabs.com/

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Re: [Haskell-cafe] Inferred type less polymorphic than expected
by Joel Reymont 08 Nov '05

08 Nov '05

This gets me pretty close. I now have to figure out how to return a PU Props instead of a PU [Prop] which is what it's returning. Still, it's a huge step forward. props :: Props -> PU Props props m = props' $ sort $ M.toList m where props' [] = lift [] props' ((_, (_, x)):xs) = wrap (\(a, b) -> a : b, \(a : b) -> (a, b)) (pair (prop x) (props' xs)) ./Script/Prop.hs:82:10: Couldn't match `Props' against `[Prop]' Expected type: PU Props Inferred type: PU [Prop] In the expression: props' $ (sort $ (Data.Map.toList m)) In the definition of `props': props m = props' $ (sort $ (Data.Map.toList m)) where props' [] = lift [] props' ((_, (_, x)) : xs) = wrap (\ (a, b) -> a : b, \ (a : b) -> (a, b)) (pair (prop x) (props' xs)) Big thanks to Andrew and Malcolm on #haskell for pointing me in the right direction! Thanks, Joel On Nov 8, 2005, at 5:23 PM, Andrew Pimlott wrote: > You might have better luck getting if you send a complete example, > since > it's hard for me to figure out exactly what this code is supposed > to do. > However, I'll take a quick stab. > > On Tue, Nov 08, 2005 at 04:46:56PM +0000, Joel Reymont wrote: >> props :: Props -> PU Props >> props m = props' $ sort $ M.toList m >> where props' [] = lift [] >> props' ((_, (Attr _ _ pp := _)):xs) = >> wrap (\(a, b) -> a : b, >> \(a : b) -> (a, b)) >> (pair pp (props' xs)) >> >> >> ./Script/Prop.hs:80:10: >> Inferred type is less polymorphic than expected >> Quantified type variable `a' is mentioned in the environment: >> props' :: [(a1, Prop)] -> PU [a] (bound at ./Script/Prop.hs: >> 79:10) > > Recall that pp is a (PU a) for some a. However, the inferred type for > props' is fully polymorphic in a. It might help first of all to write > down the type you expect for props', and then add type annotations to > different pieces until you find the one that's going awry. > > Andrew -- http://wagerlabs.com/

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\Parsec\Token.hs
by Sara Kenedy 08 Nov '05

08 Nov '05

Dear all, I run file Token.hs in hugs98\libraries\Text\ParserCombinator\Parsec\Token.hs, but it displays this error ERROR : 64 - Syntax error in data type definition (unexpected '.') Anyone know how to fix this? Thanks.

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