November 2005 - Haskell-Cafe

Re: [Haskell] Making Haskell more open
by Gour 14 Nov '05

14 Nov '05

Wolfgang Jeltsch (wolfgang(a)jeltsch.net) wrote: > The font size is much smaller than the font size of other webpages. So if I > would change the default font size to give good results with the Haskell > website, all other websites would have their text in very large letters. Well, haskell.org has smaller font size for the links, but the my preferred portal site (www.iskon.hr) has even smaller. However, pressing 'Ctrl +' to increase font size is, imoho, not such a big task :-) > The question is if HTML is sufficient. In addition, HTML is at some points > not well thought-out. True, but considering the present situation, it is all what is required. Sincerely, Gour -- Registered Linux User | #278493 GPG Public Key | 8C44EDCD

4 3

Re: [Haskell] Making Haskell more open
by Gour 13 Nov '05

13 Nov '05

Wolfgang Jeltsch (wolfgang(a)jeltsch.net) wrote: > The most important question is: Does txt2tags use logical markup? A kind of, e.g. = title = == subtitle == === subsub...=== if this is logical ;) Sincerely, Gour -- Registered Linux User | #278493 GPG Public Key | 8C44EDCD

1 0

Re: [Haskell] Making Haskell more open
by Gour 13 Nov '05

13 Nov '05

Wolfgang Jeltsch (wolfgang(a)jeltsch.net) wrote: > In addition, one could argue that since newsgroups were specifically > designed for discussions, newsgroup software allows proper mangagement > of threads but, well, current e-mail programs might do this in similar > quality. >From the most plain mailers like pine & mutt, to the gui-mailers (kmail, evolution), all have threading support. Sincerely, Gour p.s. I am moving this reply to cafe. -- Registered Linux User | #278493 GPG Public Key | 8C44EDCD

1 0

Please explain behavior of setBit
by Murray Gross 13 Nov '05

13 Nov '05

Here is my trivial program: import Bits main = putStr (show(bit 0::Int)++" "++show (mybit 0)) mybit:: Int -> Int mybit x = setBit (bit 0) x The output (with GHC-5) is 1 1 My question: Why is (bit 0) equal to 1 and not 0? That first bit is set regardless of the value of x (I have tried several), although in each case, the bit I expect to be set is also set (e.g., mybit 4 yields 17). Thanks in advance for assistance. Murray Gross

2 2

RE: [Haskell-cafe] Re: FPS: Finalizers not running (was Memoryusageoutside of the Haskell heap)
by Simon Marlow 12 Nov '05

12 Nov '05

On 07 November 2005 12:07, Donald Bruce Stewart wrote: > simonmar: >> Finalizers aren't guaranteed to be run. In particular, if the main >> thread exits, then we don't run any outstanding finalizers. This >> change was made recently, but it turned out that even prior to 6.4 >> we couldn't guarantee to run all outstanding finalizers. >> >> Does this explain it, or is there something else going on? >> >> BTW, when you addForeignPtrConcFinalizer to a ForeignPtr created with >> mallocForeignPtr, you're *creating* a finalizer, it doesn't have one >> to start with. It's pretty expensive to do this. > > Ah, right, I see. It's: > > mallocForeignPtr = doMalloc undefined > where doMalloc :: Storable b => b -> IO (ForeignPtr b) > doMalloc a = do > IO $ \s -> > case newPinnedByteArray# size s of { (# s, mbarr# #) > -> (# s, ForeignPtr (byteArrayContents# > (unsafeCoerce# mbarr#)) > (MallocPtrNoFinalizer mbarr#) #) } > where (I# size) = sizeOf a > > So the GC will take care of these thingies? > Now, this probably means that the problem is somewhere else in > Joelr's code. Yes, mallocForeignPtr's are implemented using pinned GC'd memory, with no finalizer (unless you add one). That's why they're nice and fast. It looks like you have an old version of GHC.ForeignPtr there - it has a bug in it, please cvs update to the latest version. Cheers, Simon

5 7

`typeof' is not a (visible) method of class `Typeable' ?
by WANG Meng 11 Nov '05

11 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- @ @ | \_/

2 1

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

1 0

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

2 1

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

1 0

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/

2 2