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Haskell and OS X
by Patrick Collison 21 Oct '05

21 Oct '05

Hi, I'm looking to get started developing Haskell under OS X, and I'm wondering what sort of IDE/implementation combinations people find productive. I've got haskell mode working with Emacs and ghc, this works okay, though the mode seems a little rough-edged, and the indentation appears slightly wonky at times. I didn't immediately stumble across any native OS X IDEs. What do OS X-based Hasellers tend to use? Thanks, Patrick

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Re: [Haskell-cafe] Re: Haskell and OS X
by Joel Reymont 21 Oct '05

21 Oct '05

On Oct 21, 2005, at 5:54 PM, J. Garrett Morris wrote: > Can I throw a vote in for handling > > data T = T { granularity :: (Int, Int, Int, Int) > , items :: Map (Int, Int, Int, Int) [Item] } How is this supposed to align? It aligns like this for me. Thanks, Joel -- http://wagerlabs.com/

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RE: [Haskell-cafe] Template Haskell -- Bug?
by Simon Peyton-Jones 21 Oct '05

21 Oct '05

| $ ghc --make THTest1.hs | Chasing modules from: THTest1.hs | Compiling THTest1TH ( ./THTest1TH.hs, ./THTest1TH.o ) | Compiling THTest1 ( THTest1.hs, THTest1.o ) | | THTest1.hs:10:4: `incrSelf' is not a (visible) method of class `IncrSelf' This is definitely a bug. I'll look into it. Thanks! Simon

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RE: [Haskell-cafe] Re: "getServiceEntry: does not exist" on Windows
by Simon Marlow 21 Oct '05

21 Oct '05

Nope, actually it also happens for me with the updated installer. Sigbjorn - any ideas? It doesn't happen with my local STABLE build, but I'm still using gcc 3.2.x. Cheers, Simon On 21 October 2005 13:33, Simon Marlow wrote: > Please try the updated installer for 6.4.1. I believe this is caused > by the same bug in the dynamic linker that was fixed in the update. > At least, I can reproduce your bug with the 6.4.1 installation I > have, but not with a fresh build. > > Cheers, > Simon > > On 21 October 2005 13:20, Joel Reymont wrote: > >> Folks, ideas on this? It's a major showstopper for me since it >> prevents me from deploying the Haskell app for my customer :(. >> >> Thanks, Joel >> >> On Oct 19, 2005, at 5:06 PM, Joel Reymont wrote: >> >>> This fails also but the C call to getprotobyname succeeds. >>> >>> Prelude> Network.BSD.getProtocolByName "tcp" >>> *** Exception: getServiceEntry: does not exist (no such service >>> entry) >>> >>> On Oct 19, 2005, at 4:51 PM, Joel Reymont wrote: >>> >>> >>>> I checked my Windows protocol file in system32/drivers/etc and it >>>> has >>>> >>>> tcp 6 TCP # Transmission control protocol >>>> >>>> Still, I get the following: >>>> >>>> Prelude> Network.BSD.getProtocolNumber "tcp" >>>> *** Exception: getServiceEntry: does not exist (no such service >>>> entry) >>>> >>> >>> -- >>> http://wagerlabs.com/ > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe

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FFI and modifying haskell memory
by Joel Reymont 21 Oct '05

21 Oct '05

Folks, I stumbled upon this when binding the Zlib library and want to make sure I'm doing this right. foreign import ccall unsafe "uncompress" uncompress_ :: Ptr Word8 -> Ptr CULong -> Ptr Word8 -> CULong -> IO CInt You give this function the address of your size as second argument and it updates size for you. basic uncompress(char* buf, unsigned long *size, ...) for you. Is it correct that I need to allocate a chunk of 4 bytes to be passed into C and updated there and then need to peek my value from that chunk of memory? I thought StablePtr would give me the address of a Haskell value but it gives me an offset into some table instead. Thanks, Joel -- http://wagerlabs.com/

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Re: [Haskell-cafe] Regular Expressions without GADTs
by oleg＠pobox.com 21 Oct '05

21 Oct '05

Conor McBride wrote: > Neither Oleg nor Bruno translated my code; they threw away my > structurally recursive on-the-fly automaton and wrote combinator parsers > instead. That's why there's no existential, etc. The suggestion that > removing the GADT simplifies the code would be better substantiated if > like was compared with like. ... > I'm sure the program I actually wrote can be expressed with the type > class trick, just by cutting up my functions and pasting the bits into > individual instances; the use of the existential is still available. I > don't immediately see how to code this up in Bruno's style, but that > doesn't mean it can't be done. Still, it might be worth comparing like > with like. Please see the enclosed code. It is still in Haskell98 -- and works in Hugs. > I suspect that once you start producing values with the > relevant properties (as I do) rather than just consuming them (as Oleg > and Bruno do), the GADT method might work out a little neater. Actually, the code is pretty much your original code, with downcased identifiers. It faithfully implements that parser division approach. Still, there are no existentials. I wouldn't say that GADT code is so much different. Perhaps the code below is a bit neater due to the absence of existentials, `case' statements, and local type annotations. {-- Haskell98! --} module RegExps where import Monad newtype Zero = Zero Zero -- Zero type in Haskell 98 -- Bruno.Oliveira's type class class RegExp g where zero :: g tok Zero one :: g tok () check :: (tok -> Bool) -> g tok tok plus :: g tok a -> g tok b -> g tok (Either a b) mult :: g tok a -> g tok b -> g tok (a,b) star :: g tok a -> g tok [a] data Parse tok t = Parse { empty :: Maybe t , divide :: tok -> Parse tok t} parse :: Parse tok a -> [tok] -> Maybe a parse p [] = empty p parse p (t:ts) = parse (divide p t) ts liftP f p = Parse{empty = liftM f (empty p), divide = \tok -> liftP f (divide p tok)} liftP2 mf p1 p2 = Parse{empty = mf (empty p1) (empty p2), divide = \tok -> liftP2 mf (divide p1 tok) (divide p2 tok)} lsum x y = (liftM Left x) `mplus` (liftM Right y) lprod x y = liftM2 (,) x y -- Conor McBride's parser division algorithm instance RegExp Parse where zero = Parse mzero (\_ -> zero) one = Parse (return ()) (\_ -> liftP (const ()) zero) check p = Parse mzero (\t -> if p t then liftP (const t) one else liftP (const t) zero) plus r1 r2 = Parse (lsum (empty r1) (empty r2)) (\t -> plus (divide r1 t) (divide r2 t)) mult r1 r2 = Parse (lprod (empty r1) (empty r2)) (\t -> let (q1,q2) = (divide r1 t, divide r2 t) lp x1 = liftP (either id ((,) x1)) in maybe (mult q1 r2) (\x1 -> lp x1 (plus (mult q1 r2) q2)) (empty r1)) star r = Parse (return []) (\t-> liftP (uncurry (:)) (mult (divide r t) (star r))) p1 :: RegExp g => g Char ([Char], [Char]) p1 = mult (star (check (== 'a'))) (star (check (== 'b'))) testp = parse (star (mult (star (check (== 'a'))) (star (check (== 'b'))))) "abaabaaabbbb" {- *RX> testp Just [("a","b"),("aa","b"),("aaa","bbbb")] -} testc = parse (star one) "abracadabra" -- Parsing the list of integers ieven = even :: Int->Bool iodd = odd :: Int->Bool p2 :: RegExp g => g Int (Either (Int, (Int, [Int])) (Int, [Int])) p2 = plus (mult (check iodd) (mult (check iodd) (star (check ieven)))) (mult (check ieven) (star (check iodd))) test2 = parse (star p2) [1::Int,1,2,3,3,4]

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RE: [Haskell-cafe] Re: "getServiceEntry: does not exist" on Windows
by Simon Marlow 21 Oct '05

21 Oct '05

Please try the updated installer for 6.4.1. I believe this is caused by the same bug in the dynamic linker that was fixed in the update. At least, I can reproduce your bug with the 6.4.1 installation I have, but not with a fresh build. Cheers, Simon On 21 October 2005 13:20, Joel Reymont wrote: > Folks, ideas on this? It's a major showstopper for me since it > prevents me from deploying the Haskell app for my customer :(. > > Thanks, Joel > > On Oct 19, 2005, at 5:06 PM, Joel Reymont wrote: > >> This fails also but the C call to getprotobyname succeeds. >> >> Prelude> Network.BSD.getProtocolByName "tcp" >> *** Exception: getServiceEntry: does not exist (no such service >> entry) >> >> On Oct 19, 2005, at 4:51 PM, Joel Reymont wrote: >> >> >>> I checked my Windows protocol file in system32/drivers/etc and it >>> has >>> >>> tcp 6 TCP # Transmission control protocol >>> >>> Still, I get the following: >>> >>> Prelude> Network.BSD.getProtocolNumber "tcp" >>> *** Exception: getServiceEntry: does not exist (no such service >>> entry) >>> >> >> -- >> http://wagerlabs.com/

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"getServiceEntry: does not exist" on Windows
by Joel Reymont 21 Oct '05

21 Oct '05

Folks, I have a silly Windows issue: *** Exception: getServiceEntry: does not exist (no such service entry) I connect thusly and don't see myself using any services. I also do not have this issue on Mac OSX. Any ideas? I googled for this issue but don't even know if there's a protocols file on Windows, much less where it is and why "tcp" might not be there :-). connect :: HostName -> Int -> IO Handle connect h p = connectTo h $ PortNumber $ fromIntegral p main = withSocketsDo $ do connect "10.0.0.1" 15667 Thanks, Joel -- http://wagerlabs.com/

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RE: [Haskell-cafe] FPS lib
by Simon Marlow 21 Oct '05

21 Oct '05

On 21 October 2005 02:36, John Meacham wrote: > I think a lot of benefit can be had by making ForeignPtr a product > type rather than a union one. being able to unbox it in constructors > and opening it to CPR analysis is key for tight inner loop code which > pointers will most definitly be involved in. Actually this is what we did, and why the benchmarks go a lot faster with GHC 6.5 compared to 6.4.x. Cheers, Simon

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Re[2]: [Haskell] Read Instances for Data.Map and Data.Set
by Bulat Ziganshin 21 Oct '05

21 Oct '05

Hello Johannes, Friday, October 21, 2005, 11:42:55 AM, you wrote: JW> I'd like to repeat my earlier point that it would be better JW> if the user of the type can decide whether he wants JW> some predefined Show/Read instances or roll his own. JW> http://www.haskell.org/pipermail/libraries/2005-March/003496.html long standing sight...... parameterized modules will be a good solution for all those problems. or ability to hide/import class instances, not only plain functions: import Data.Map hiding (Show(Map)) -- Best regards, Bulat mailto:bulatz@HotPOP.com

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RE: [Haskell-cafe] FPS lib
by Simon Marlow 21 Oct '05

21 Oct '05

[ oops, I meant to send this yesterday but it didn't go out for some reason ] On 18 October 2005 12:40, Krasimir Angelov wrote: > ForeignPtr requires more memory. Each ForeignPtr has > ForeignPtrContents structure attached. In the ForeignPtrContents there > is one IORef. Each finalizer adds one Weak# object in the heap. The > IORef is a reference to a list of finalizers, so each new finalizer > adds a new CONS cell. The finalizers require additional steps in GC > time. I haven't tried to measure the difference between ForeignPtr and > ByteArray# based implementations but it seems to me that the latter > might be better. Of course it will be GHC specific. > mmap is valuable only for large string. Typically only when someone > wants to read the entire file in the memory. For this case a special > data structure might be provided. We can assume that in the packed string case, most of the packed strings will be allocated in Haskell, and will therefore be represented by a ForeignPtr with a ByteArray# inside - therefore no finalizer, no Weak# object, and no cons cells. It is a shame that we need the IORef, but I'm wondering whether we should have a special kind of ForeignPtr to which you can't add any more finalizers (ie. addForeignPtrFinalizer would fail) to optimise this case. We never need to add any finalizers to packed strings created in Haskell. Also, the IORefs will interact badly with generational GC, so we should really get rid of them. If we eliminated the IORef, then the difference between ByteArray and ForeignPtr would be one word, i.e. negligible. I think the flexibility is worth it. Also, I bet that you won't find any useful benchmarks in which the difference is significant Cheers, Simon

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Template Haskell -- Bug?
by Gracjan Polak 20 Oct '05

20 Oct '05

Hi, Could somebody try to compile these two files *TWICE*? GHC dumps core at me. I don't know if it is something about me, or something more general :) I'd like to know a bit more, before I bother anybody from devel team. Log: $ ghc --make THTest1.hs Chasing modules from: THTest1.hs Compiling THTest1TH ( ./THTest1TH.hs, ./THTest1TH.o ) Compiling THTest1 ( THTest1.hs, THTest1.o ) THTest1.hs:10:4: `incrSelf' is not a (visible) method of class `IncrSelf' $ ghc --make THTest1.hs Chasing modules from: THTest1.hs Skipping THTest1TH ( ./THTest1TH.hs, ./THTest1TH.o ) Compiling THTest1 ( THTest1.hs, THTest1.o ) Loading package base-1.0 ... linking ... done. Loading package haskell98-1.0 ... linking ... done. Loading package template-haskell-1.0 ... linking ... done. (here core dump, aka 0xc00000001) First of all, I do not understand the error in first compilation. Second, core dump is not nice :) My config: Windows XP Home, $ ghc -v Glasgow Haskell Compiler, Version 6.4, for Haskell 98, compiled by GHC version 6.2.2 Using package config file: c:\ghc\ghc-6.4\package.conf Using package config file: C:\Documents and Settings\gracjan\Application Data\ghc/i386-mingw32-6.4/package.conf Default windows package as taken from www.haskell.org. -- Gracjan {-# OPTIONS -fglasgow-exts -fth -fallow-undecidable-instances #-} module THTest1TH ( instanceIncrSelfTuple, IncrSelf(..) ) where import Control.Monad import Data.Maybe import Language.Haskell.TH class IncrSelf a where incrSelf :: a -> a instance Num a => IncrSelf a where incrSelf x = x + 1 sel' :: Int -> Int -> ExpQ sel' i n = lamE [pat] rhs where pat = tupP (map varP as) rhs = varE (as !! (i - 1)) as = map mkName [ ("a__" ++ show j) | j <- [1..n] ] instanceIncrSelfTuple :: Int -> Q [Dec] instanceIncrSelfTuple n = do decs <- qOfDecs let listOfDecQ = map return decs conIncrSelf = conT ''IncrSelf name_a = mkName "a" name_b = mkName "b" name_c = mkName "c" var_a = varT name_a var_b = varT name_b var_c = varT name_c dec <- instanceD (sequence [appT conIncrSelf var_a,appT conIncrSelf var_b]) (appT conIncrSelf (appT (appT (tupleT 2) var_a ) var_b ) ) listOfDecQ return [dec] where qOfDecs = [d| incrSelf value = let value1 = maybe Nothing (Just . fst) value value2 = maybe Nothing (Just . snd) value in error "adfasf" -- (incrSelf value1, incrSelf value2) |] {-# OPTIONS -fglasgow-exts -fth -fallow-undecidable-instances #-} module THTest1 where import THTest1TH instance IncrSelf String where incrSelf x = x ++ "x" $(instanceIncrSelfTuple 2)

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Zlib bindings
by Joel Reymont 20 Oct '05

20 Oct '05

Folks, Are there any zlib bindings for Haskell? The docs for HDirect mention the examples directory with the bindings but I cannot find the examples directory in the source distro. The MissingH code works with gzipped files apparently but not with memory buffers. Thanks, Joel -- http://wagerlabs.com/

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RE: [Haskell-cafe] FPS lib
by Simon Marlow 20 Oct '05

20 Oct '05

On 18 October 2005 10:08, Krasimir Angelov wrote: > I am curious why FPS is implemented on top of ForeignPtr. ByteArray# > based implementation should be faster and more space efficient. Actually there's not much difference between ForeignPtr and ByteArray#, at least in GHC 6.5+ where we optimised the ForeignPtr implementation. Furthermore ForeignPtr is much more useful, because you can create a ForeignPtr from a Ptr, and you can pass a ForeignPtr to C code portably (i.e. not using GHC extensions). ForeignPtr is essential if you want to make packed strings from eg. mmap()'d memory. Also, a ForeignPtr allocated using mallocForeignPtr *is* a ByteArray#. My PackedString library (which DonS is currently merging with FPS) uses ForeignPtr and gets pretty good performance. withForeignPtr compiles to almost nothing at all: the touch# becomes visible to GHC and compiles to no code. I needed to inline unsafePerformIO to get the best results, though (not always safe, but in this case it's ok). Cheers, Simon

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Re: [Haskell] Read Instances for Data.Map and Data.Set
by dons＠cse.unsw.edu.au 20 Oct '05

20 Oct '05

mai99dgf: > Hi folks, > > I was really annoyed by the fact that for Data.Map and Data.Set are no Read > instances declared, but Show instances are! I believe there should be some > kind of unwritten rule that in the standart lib the Show and Read instances > come pairwise and are fully compatible. There are some things that are Showable, but would be wrong to be Readable. Dynamics come to mind. That's not the case with Map, though :) (moved to haskell-cafe@ just in case :) -- Don

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RE: [Haskell-cafe] FPS lib
by Simon Marlow 20 Oct '05

20 Oct '05

On 18 October 2005 21:04, John Meacham wrote: > On Tue, Oct 18, 2005 at 10:39:24AM +0300, Einar Karttunen wrote: >> On 18.10 10:44, Bulat Ziganshin wrote: >>> 2) as i say you before, i need to sort filenames in windows fashion >>> (case-ignoring), so if you will include case-ignoring comparision >>> operators - i will be glad >> >> Case ignoring comparisons make only sense on characters - not on >> bytes. And fps is ignoring character set conversion issues. I think >> the proper way is to provide a layer on top of (and separate from) >> fps that does conversion into character strings where things like >> case make sense. > > My FastString library always stores everything as UTF8 to good effect. > I have some nice fast unboxed UTF8 character folding routines in there > too which you might want to grab if you go the UTF8 route. (which I > recommend highly). > > http://repetae.net/john/repos/jhc/PackedString.hs I believe I stole your UTF-8 code for my Data.PackedString.UTF8 version (which Don uploaded here http://www.cse.unsw.edu.au/~dons/packedstring.tar.gz) It might be slightly modified though; in my version I wanted to support foldr/build optimisation of things like (pack (map f xs)) and (unpack s ++ t). IIRC I got it working for unpack, but not for pack. Cheers, Simon

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Parsec vs ReadP
by Sebastian Sylvan 20 Oct '05

20 Oct '05

Can anyone briefly compare these two parsing-libraries? In short, which one is better? /S -- Sebastian Sylvan +46(0)736-818655 UIN: 44640862

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RE: [Haskell-cafe] Prebuilt FPS for Windows
by Simon Marlow 19 Oct '05

19 Oct '05

On 18 October 2005 17:01, Joel Reymont wrote: > Since I cannot build Data.FastPackedString on Windows (ghc crashes) > and it's the only library I really depend on, would someone have a > pre-built version or let me know how I can build it without Cabal? A workaround for that crashing problem is to compile the Setup.lhs script using GHC first, and then run it: $ ghc --make Setup.lhs -o setup $ ./setup configure etc. > On a related note, Haskell tools for Windows (happy, alex) come with > extra files (templates). Where are these to be placed? On Windows, they are placed in the same folder as the executable. Cheers, Simon

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RE: [Haskell] reader-like IO, parents of threads
by Simon Marlow 19 Oct '05

19 Oct '05

Certainly, adding hooks to forkIO is possible. Also, providing thread local data directly is something we could do quite easily (and efficiently) in GHC. Cheers, Simon On 18 October 2005 19:12, Frederik Eaton wrote: > What about adding support for hooks in forkIO? These could be useful > for other things as well. Pthreads could be said to have this > functionality: > > -- Function: int pthread_atfork (void (*PREPARE)(void), void > (*PARENT)(void), void (*CHILD)(void)) > `pthread_atfork' registers handler functions to be called just > before and just after a new process is created with `fork'. The > PREPARE handler will be called from the parent process, just > before the new process is created. The PARENT handler will be > called from the parent process, just before `fork' returns. The > CHILD handler will be called from the child process, just before > `fork' returns. > > As well as: > > -- Function: void pthread_cleanup_push (void (*ROUTINE) (void *), > void *ARG) > `pthread_cleanup_push' installs the ROUTINE function with > argument ARG as a cleanup handler. From this point on to the > matching `pthread_cleanup_pop', the function ROUTINE will be > called with arguments ARG when the thread terminates, either > through `pthread_exit' or by cancellation. If several cleanup > handlers are active at that point, they are called in LIFO > order: the most recently installed handler is called first. > > Of course, 'fork' has a bit of a different meaning in pthreads. I > don't know if there is support for handlers which are run when a new > thread is created. > > (Pthreads also has support for "thread-specific data": > > -- Function: int pthread_setspecific (pthread_key_t KEY, const > void *POINTER) > `pthread_setspecific' changes the value associated with KEY > in the calling thread, storing the given POINTER instead. > > If there is no such key KEY, it returns `EINVAL'. Otherwise > it returns 0. > > -- Function: void * pthread_getspecific (pthread_key_t KEY) > `pthread_getspecific' returns the value currently associated > with KEY in the calling thread. > > If there is no such key KEY, it returns `NULL'. > ) > > Regards, > > Frederik > > On Tue, Oct 18, 2005 at 11:47:29AM +0100, Simon Marlow wrote: >> It seems that you can do this as long as you provide your own >> version of forkIO, but not if you want to use the built-in forkIO. >> >> One could argue that getting the parent ThreadId is something that >> should be supported natively by forkIO, and I might be inlined to >> agree. Unfortunately there are some subtleties: currently a ThreadId >> is represented by a pointer to the thread itself, which causes the >> thread to be kept alive. This has implications not only for space >> leaks, but also for reporting deadlock: if you have a ThreadId for a >> thread, you can send it an exception with throwTo at any time, and >> hence the runtime can never determine that the thread is deadlocked >> so it will never get the NonTermination exception. Perhaps we need >> two kinds of ThreadId: a weak one for use in Maps, and a strong one >> that you can use with throwTo. But then building a Map in which >> some elements can be garbage collected is a bit tricky (it can be >> done though; see our old Memo table implementation in >> fptools/hslibs/util/Memo.hs). >> >> Cheers, >> Simon >> >> On 16 October 2005 20:53, Frederik Eaton wrote: >> >>> John Meacham suggested that I should be a little more clear about >>> the semantics I'm seeking. Also, apparently it isn't possible to >>> implement writeTLRef/modifyTLRef with the data structure I gave: >>> >>>> data TLRef a = TLR a (MVar (Map ThreadId a)) >>> (the first argument is a default value, the second is a map storing >>> the values in each thread. The MVar is for safe concurrent access) >>> >>> Without those functions, it looks a little more like the Reader >>> monad I'm comparing it to. >>> >>> - What happens on fork? The child thread effectively gets a "copy" >>> of each TLRef in its parent. They have the same values, but >>> modifying them using withTLRef has no effect on the values in other >>> threads. >>> >>> - Can you pass a TLRef to a different thread? Yes, but the value it >>> holds will not be the same when it is dereferenced in a different >>> thread. >>> >>> The problem with writeTLRef is that if a child thread looks up the >>> default value for an unbound reference by looking up the value in >>> its parent, but after calling forkIO the parent changes the value >>> with writeTLRef, then the child thread will get the wrong value. It >>> is supposed to only see the value which was stored in the reference >>> at the point where forkIO was called. >>> >>> Also, for this reason, I think withTLRef would have to be >>> implemented by creating a separate thread with forkIO and waiting >>> for it to finish. This would avoid overwriting a value which other >>> child threads might still need to access. >>> >>> Note that an e.g. "myParentThreadId" function isn't enough - what >>> is needed is a >>> >>> parentThreadId :: ThreadId -> IO (Maybe ThreadId) >>> >>> which can look up the parent of an arbitrary thread. >>> >>> Alternatively, if 'forkIO' supported hooks to run before and/or >>> after forking, then a 'parentThreadId' function could be >>> implemented from that. >>> >>> Frederik >>> >>> On Sun, Oct 16, 2005 at 04:40:40AM -0700, Frederik Eaton wrote: >>>> Hi, >>>> >>>> I'm trying to get MonadReader-like functionality in the IO monad. >>>> It doesn't appear possible implement it with the interfaces that >>>> Haskell98 or GHC provide. I'm looking for something like >>>> "thread-local variables". The interface could be something like >>>> this: >>>> >>>> newTLRef :: a -> IO (TLRef a) >>>> withTLRef :: TLRef a -> a -> IO b -> IO b >>>> readTLRef :: TLRef a -> IO a >>>> writeTLRef :: TLRef a -> a -> IO () >>>> modifyTLRef :: TLRef a -> (a -> a) -> IO () >>>> >>>> This would have a lot of uses. I am aware of the "Implicit >>>> Configurations" paper by Kiselyov and Shan, but a solution such as >>>> theirs which requires modifying the type signatures of all >>>> intermediate function calls is not suitable. I want to be able to >>>> say "run algorithm A using database D" without requiring all of the >>>> functions in algorithm A to know that databases are somehow >>>> involved. One way to look at it is that I am seeking something >>>> like the type-based approach, but easier and with less explicit >>>> syntax; another way to look at it is that I am seeking something >>>> like a global IORef based approach, but more safe. >>>> >>>> An implementation based on ThreadId-keyed maps is almost workable: >>>> >>>> data TLRef a = TLR a (MVar (Map ThreadId a)) >>>> >>>> The problem with this is that while it is possible to find out the >>>> ThreadId of the current thread, it doesn't appear to be possible to >>>> get the ThreadId of the parent thread, which would be needed for >>>> values to be properly inherited. >>>> >>>> Is there a way around this? Will there ever be standard support for >>>> either finding the thread id of the parent of the current thread, >>>> or for something like the thread-local references I have proposed? >>>> >>>> Thanks, >>>> >>>> Frederik >>>> _______________________________________________ >>>> Haskell mailing list >>>> Haskell(a)haskell.org >>>> http://www.haskell.org/mailman/listinfo/haskell >>>> >>> _______________________________________________ >>> Haskell mailing list >>> Haskell(a)haskell.org >>> http://www.haskell.org/mailman/listinfo/haskell >> >> _______________________________________________ >> Haskell mailing list >> Haskell(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell

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pre-built ghc 6.4.1 crashes building FPS
by Joel Reymont 19 Oct '05

19 Oct '05

Folks, I downloaded and installed the pre-built ghc 6.4.1 on Windows XP and Win2k. I tried building FastPackedStrings but ghc crashes soon after starting. Any tips? I'm gonna try with a hand-built ghc but somehow doubt it will help. Thanks, Joel -- http://wagerlabs.com/

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Re: [Haskell-cafe] Regular Expressions without GADTs
by oleg＠pobox.com 19 Oct '05

19 Oct '05

Conor McBride wrote: > Neither Oleg nor Bruno translated my code; they threw away my > structurally recursive on-the-fly automaton and wrote combinator parsers > instead. That's why there's no existential, etc. The suggestion that > removing the GADT simplifies the code would be better substantiated if > like was compared with like. The following code specifically tries to be as close to the original Conor McBride's code as possible. I only removed local type annotations (turn out unnecessary) and replaced `ap' with `liftM' as a matter of personal preference. > Where we came in, if you recall, was the use of a datatype to define > regular expressions. I used a GADT to equip this type with some useful > semantic information (namely a type of parsed objects), and I wrote a > program (divide) which exploited this representation to compute the > regexp the tail of the input must match from the regexp the whole input > must match. This may be a bit of a weird way to write a parser, but it's > a useful sort of thing to be able to do... That particular feature is fully preserved. Data types are used to define regular expression: > p = (Star (Mult (Star (Check (== 'a'))) (Star (Check (== 'b'))))) > > testp = parse p "abaabaaabbbb" Moreover, *RX> :t p p :: Star (Mult (Star (Check Char)) (Star (Check Char))) the regular expression is apparent in the type of the `parser' (or its representation, to be precise). One can easily define data types Digit, Alphanumeric, WhiteSpace, etc. and so type will look more informative. Here's one step to regular types... Instead of GADT, a type class is used to associate semantic information with the data type (with labels). Typing is more explicit now. > And that's the point: not only does the GADT have all the disadvantages > of a closed datatype, it has all the advantages too! A type class can be closed too, thanks to functional dependencies. You were right: the code below is just the mechanical reshuffling of the original code, using the translation I come across a year ago. `empty' and `division' are now grouped by the parser type, which I personally like. It is hard to see any loss of expressiveness by getting rid of GADTs in this case. More explicit type is an advantage. Also an advantage is the fact that `pattern match' is guaranteed exhaustive. If I forgot to implement some particular parser, that would be a type error (rather than a pattern-match run-time error, as is the case with ADT/GADT). > Moreover, once you have to start messing about with equality > constraints, the coding to eliminate GADTs becomes a lot hairier. I > implemented it back in '95 (when all these things had different names) > and I was very glad not to have to do it by hand any more. The discovery of the presence of type equality in Haskell changes things a great deal. It would be interesting to see how your code of '95 will look now. Writing an equality and even _dis-equality_ constraint is just as simple as |TypeEq a b HTrue| or |TypeEq a b HFalse|. {-# OPTIONS -fglasgow-exts #-} module RX where import Control.Monad class RegExp r tok a | r tok -> a where empty :: r -> [tok] -> Maybe a divide :: tok -> r -> Division tok a data Zero = Zero data One = One newtype Check tok = Check (tok -> Bool) data Plus r1 r2 = Plus r1 r2 data Mult r1 r2 = Mult r1 r2 newtype Star r = Star r data Empty = Empty data Division tok x = forall r y. RegExp r tok y => Div r (y -> x) parse :: (RegExp r tok x) => r -> [tok] -> Maybe x parse r t@[] = empty r t parse r (t : ts) = case divide t r of Div q f -> liftM f $ parse q ts nullt :: tok -> [tok] nullt _ = [] instance RegExp Zero tok Empty where empty _ _ = mzero divide _ _ = Div Zero naughtE instance RegExp One tok () where empty _ _ = return () divide _ _ = Div Zero naughtE instance RegExp (Check tok) tok tok where empty _ _ = mzero divide t (Check p) | p t = Div One (const t) divide _ _ = Div Zero naughtE instance (RegExp r1 tok a, RegExp r2 tok b) => RegExp (Plus r1 r2) tok (Either a b) where empty (Plus r1 r2) t = (liftM Left $ empty r1 t) `mplus` (liftM Right $ empty r2 t) divide t (Plus r1 r2) = case (divide t r1, divide t r2) of (Div q1 f1, Div q2 f2) -> Div (Plus q1 q2) (f1 +++ f2) instance (RegExp r1 tok a, RegExp r2 tok b) => RegExp (Mult r1 r2) tok (a,b) where empty (Mult r1 r2) t = liftM2 (,) (empty r1 t) (empty r2 t) divide t (Mult r1 r2) = case (empty r1 (nullt t), divide t r1, divide t r2) of (Nothing, Div q1 f1, _) -> Div (Mult q1 r2) (f1 *** id) (Just x1, Div q1 f1, Div q2 f2) -> Div (Plus (Mult q1 r2) q2) (either (f1 *** id) (((,) x1) . f2)) instance RegExp r tok a => RegExp (Star r) tok [a] where empty _ _ = return [] divide t (Star r) = case (divide t r) of Div q f -> Div (Mult q (Star r)) (\ (y, xs) -> (f y : xs)) (***) :: (a -> b) -> (c -> d) -> (a, c) -> (b, d) (f *** g) (a, c) = (f a, g c) (+++) :: (a -> b) -> (c -> d) -> Either a c -> Either b d (f +++ g) (Left a) = Left (f a) (f +++ g) (Right c) = Right (g c) naughtE :: Empty -> x naughtE = undefined p = (Star (Mult (Star (Check (== 'a'))) (Star (Check (== 'b'))))) testp = parse p "abaabaaabbbb"

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Parsing in Practice
by Tom Hawkins 18 Oct '05

18 Oct '05

I am writing a parser for a big, ugly, standard language and I need to decide between using either Happy or Parsec. I currently have a priliminary LALR(1) grammar, so a port to Happy would be relatively easy. But, I'm wondering if life would be easier if I chose Parsec's combinator parsing instead. It's error reporting seems to be top notch and it's "optional", "many", and "sepBy1" combinators are very elegant. However, I have a few concerns with Parsec. First is performance; what factor of slow-down should I expect? Second is bug prevention. I don't have much experience writing LL(n) grammars, so how easy is it to introduce bugs in a Parsec grammar? Even though I hate debugging LALR(1) parsing ambiguities, it prevents problems. Also, it appears the GHC developers chose Happy for Haskell. What was their rational? Thanks for your recommendations, one way or another. -Tom

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Prebuilt FPS for Windows
by Joel Reymont 18 Oct '05

18 Oct '05

Folks, Since I cannot build Data.FastPackedString on Windows (ghc crashes) and it's the only library I really depend on, would someone have a pre-built version or let me know how I can build it without Cabal? On a related note, Haskell tools for Windows (happy, alex) come with extra files (templates). Where are these to be placed? Thanks, Joel -- http://wagerlabs.com/

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Re: [Haskell-cafe] Regular Expressions, was Re: Interest in helping w/ Haskell standard
by Martin Sulzmann 18 Oct '05

18 Oct '05

Semantic subtyping issue: Assume we have a function f of type f :: Reg (r*) -> ... to which we pass a value x of type Reg (r,r*). We have that (r,r*) is a semantic subtype of r*, hence, the code f x is accepted in languages such as XDuce/CDuce. I'm just saying that the fact regexp can be represented via GADTs doesn't imply that we get the same expressive power of languages such as XDuce/CDuce. Martin Hongwei Xi writes: > Hi Martin: > > Thanks for the message. > > No, I am not on the list. > > Back then, we did something similar but for a different > purpose. The idea is like this: > > We wanted to represent an XML document as a pair: > > XML (r) * Reg (r) > > where r stands for some regexp and Reg(r) is a > singleton type. When performing search over XML(r), > we can use Reg(r) as some kind of pilot value > (which is a lot smaller than XML(r)) to guide the > search. For instance, it is often easy to tell from > Reg(r) that an item to be found is not in XML(r) and > thus we can skip searching XML(r) entirely. > This is sort of like indexing scheme in database. > > BTW, I am not sure what kind of 'semantic typing' > you have in mind. An example? > > --Hongwei > > Computer Science Department > Boston University > 111 Cummington Street > Boston, MA 02215 > > Email: hwxi(a)cs.bu.edu > Url: http://www.cs.bu.edu/~hwxi > Tel: +1 617 358 2511 (office) > Fax: +1 617 353 6457 (department) > > > > On Mon, 17 Oct 2005, Martin Sulzmann wrote: > > >> > >>Very interesting Conor. Do you know Xi et al's APLAS'03 paper? > >>(Hongwei, I'm not sure whether you're on this list). > >>Xi et al. use GRDTs (aka GADTs aka first-class phantom types) > >>to represent XML documents. There're may be some connections > >>between what you're doing and Xi et al's work. > >> > >>I believe that there's an awful lot you can do with GADTs > >>(in the context of regular expressions). But there're two things > >>you can't accomplish: > >>semantic subtyping and regular expression pattern matching > >>a la XDuce/CDuce. Unless somebody out there proves me wrong. > >> > >>Martin > >> > >> > >> > >>Hi folks, > >> > >>Inspired by Ralf's post, I thought I'd just GADTize a dependently typed=20 > >>program I wrote in 2001. > >> > >>Wolfgang Jeltsch wrote: > >> > >>> Now lets consider using an algebraic datatype for regexps: > >>> > >>> data RegExp > >>> =3D Empty | Single Char | RegExp :+: RegExp | RegExp :|: RegExpt | Ite= > >>r RegExp > >>> > >>>Manipulating regular expressions now becomes easy and safe =E2=80=93 you= > >> are just not=20 > >>>able to create "syntactically incorrect regular expressions" since durin= > >>g=20 > >>>runtime you don't deal with syntax at all. > >>> =20 > >>> > >> > >>A fancier variation on the same theme... > >> > >> > data RegExp :: * -> * -> * where > >> > Zero :: RegExp tok Empty > >> > One :: RegExp tok () > >> > Check :: (tok -> Bool) -> RegExp tok tok > >> > Plus :: RegExp tok a -> RegExp tok b -> RegExp tok (Either a b) > >> > Mult :: RegExp tok a -> RegExp tok b -> RegExp tok (a, b) > >> > Star :: RegExp tok a -> RegExp tok [a] > >> > >> > data Empty > >> > >>The intuition is that a RegExp tok output is a regular expression=20 > >>explaining how to parse a list of tok as an output. Here, Zero is the=20 > >>regexp which does not accept anything, One accepts just the empty=20 > >>string, Plus is choice and Mult is sequential composition; Check lets=20 > >>you decide whether you like a single token. > >> > >>Regular expressions may be seen as an extended language of polynomials=20 > >>with tokens for variables; this parser works by repeated application of=20 > >>the remainder theorem. > >> > >> > parse :: RegExp tok x -> [tok] -> Maybe x > >> > parse r [] =3D empty r > >> > parse r (t : ts) =3D case divide t r of > >> > Div q f -> return f `ap` parse q ts > >> > >>Example > >> > >>*RegExp> parse (Star (Mult (Star (Check (=3D=3D 'a'))) (Star (Check (=3D=3D= > >>=20 > >>'b'))))) "abaabaaabbbb" > >>Just [("a","b"),("aa","b"),("aaa","bbbb")] > >> > >>The 'remainder' explains if a regular expression accepts the empty=20 > >>string, and if so, how. The Star case is a convenient=20 > >>underapproximation, ruling out repeated empty values. > >>=20 > >> > empty :: RegExp tok a -> Maybe a > >> > empty Zero =3D mzero > >> > empty One =3D return () > >> > empty (Check _) =3D mzero > >> > empty (Plus r1 r2) =3D (return Left `ap` empty r1) `mplus` > >> > (return Right `ap` empty r2) > >> > empty (Mult r1 r2) =3D return (,) `ap` empty r1 `ap` empty r2 > >> > empty (Star _) =3D return [] > >> > >>The 'quotient' explains how to parse the tail of the list, and how to=20 > >>recover the meaning of the whole list from the meaning of the tail. > >> > >> > data Division tok x =3D forall y. Div (RegExp tok y) (y -> x) > >> > >>Here's how it's done. I didn't expect to need scoped type variables, but=20 > >>I did... > >> > >> > divide :: tok -> RegExp tok x -> Division tok x > >> > divide t Zero =3D Div Zero naughtE > >> > divide t One =3D Div Zero naughtE > >> > divide t (Check p) | p t =3D Div One (const t) > >> > | otherwise =3D Div Zero naughtE > >> > divide t (Plus (r1 :: RegExp tok a) (r2 :: RegExp tok b)) =3D > >> > case (divide t r1, divide t r2) of > >> > (Div (q1 :: RegExp tok a') (f1 :: a' -> a), > >> > Div (q2 :: RegExp tok b') (f2 :: b' -> b)) -> > >> > Div (Plus q1 q2) (f1 +++ f2) > >> > divide t (Mult r1 r2) =3D case (empty r1, divide t r1, divide t r2) of > >> > (Nothing, Div q1 f1, _) -> Div (Mult q1 r2) (f1 *** id) > >> > (Just x1, Div q1 f1, Div q2 f2) -> > >> > Div (Plus (Mult q1 r2) q2) (either (f1 *** id) (((,) x1) . f2)) > >> > divide t (Star r) =3D case (divide t r) of > >> > Div q f -> Div (Mult q (Star r)) (\ (y, xs) -> (f y : xs)) > >> > >>Bureaucracy. > >> > >> > (***) :: (a -> b) -> (c -> d) -> (a, c) -> (b, d) > >> > (f *** g) (a, c) =3D (f a, g c) > >> > >> > (+++) :: (a -> b) -> (c -> d) -> Either a c -> Either b d > >> > (f +++ g) (Left a) =3D Left (f a) > >> > (f +++ g) (Right c) =3D Right (g c) > >> > >> > naughtE :: Empty -> x > >> > naughtE =3D undefined > >> > >>It's not the most efficient parser in the world (doing some algebraic=20 > >>simplification on the fly wouldn't hurt), but it shows the sort of stuff=20 > >>you can do. > >> > >>Have fun > >> > >>Conor > >>_______________________________________________ > >>Haskell-Cafe mailing list > >>Haskell-Cafe(a)haskell.org > >>http://www.haskell.org/mailman/listinfo/haskell-cafe > >>

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RE: [Haskell-cafe] pre-built ghc 6.4.1 crashes building FPS
by Simon Peyton-Jones 18 Oct '05

18 Oct '05

OK we can reproduce it now. It's a bad bug.. we're investigating. S | -----Original Message----- | From: haskell-cafe-bounces(a)haskell.org [mailto:haskell-cafe-bounces@haskell.org] On Behalf Of Joel | Reymont | Sent: 18 October 2005 14:01 | To: Donald Bruce Stewart | Cc: Haskell Cafe | Subject: Re: [Haskell-cafe] pre-built ghc 6.4.1 crashes building FPS | | Just the latest darcs repo. It's a memory access error 0x0:0x0 I | think (null pointer reference?) at the "setup build" stage. | | On Oct 18, 2005, at 2:01 AM, Donald Bruce Stewart wrote: | | > Oh, now that's interesting. Do you have a log of where it crashes? It | > could be some Cabal code, or perhaps something strange in FPS that's | > tricking GHC. | > | > Which version of the FPS code is this? Just the one in the darcs repo? | | -- | http://wagerlabs.com/ | | | | | | _______________________________________________ | Haskell-Cafe mailing list | Haskell-Cafe(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe

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Parsec, state and/of my cluelessness
by Niklas 18 Oct '05

18 Oct '05

Hi everybody, for my first real 'learn some haskell'-project I decided upon a parser. The resulting application would be somewhat useful to me and armed with such a cool library as Parsec, how could I fail? I was going to be a haskell hacker in notime. Oh, the wine, the women and the fame. Didn't work out though. I'm going to parse a tree of controls. Each control can have values, (a tree of) properties and more controls as children: type Guid = String type Value = (String, String) data Property = MkProperty String (Maybe Guid) [Value] [Property] data Control = MkControl String String [Value] [Property] [Control] The top parser is along the lines of: ctrlParser :: Parser Control ctrlParser = do { reserved "Begin" ; ctrl <- identifier ; name <- identifier ; (vs, ps, cs) <- ctrlBodyParser ; reserved "End" ; return (MkControl ctrl name vs ps cs) } Now comes the tricky part for me. Since the control can have three different types of children I use a helper that parses the body of the control using other parsers, collecting their results in three lists: ctrlBodyParser :: CharParser ([Value], [Property], [Control]) ([Value], [Property], [Control]) ctrlBodyParser = do { c <- ctrlParser -- parse child control ; (vs, ps, cs) <- getState ; setState (vs, ps, (c : cs)) ; ctrlBodyParser } <|> do { p <- propParser -- parse child property ; (vs, ps, cs) <- getState ; setState (vs, (p : ps), cs) ; ctrlBodyParser } <|> do { v <- valueParser -- parse value ; (vs, ps, cs) <- getState ; setState ((v : vs), ps, cs) ; ctrlBodyParser } <|> do { getState } -- we're finished, return children GHC error: ---8<--- Couldn't match `()' against `(a, b, c)' Expected type: () Inferred type: (a, b, c) When checking the pattern: (vs, ps, cs) In a 'do' expression: (vs, ps, cs) <- getState --->8--- So, I have a problem with the state handling. Any hints? Some other questions: Do I need to supply the ctrlBodyParser with an initial state when I call it from the ctrlParser? Should I modify the last alternative in the ctrlBodyParser so that it resets the state before calling return with the collected results? Thanks, Niklas

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RE: [Haskell-cafe] pre-built ghc 6.4.1 crashes building FPS
by Bayley, Alistair 18 Oct '05

18 Oct '05

> From: dons(a)cse.unsw.edu.au [mailto:dons@cse.unsw.edu.au] > > joelr1: > > Folks, > > > > I downloaded and installed the pre-built ghc 6.4.1 on > Windows XP and > > Win2k. I tried building FastPackedStrings but ghc crashes > soon after > > starting. Any tips? > > > > I'm gonna try with a hand-built ghc but somehow doubt it will help. > > Oh, now that's interesting. Do you have a log of where it crashes? It > could be some Cabal code, or perhaps something strange in FPS that's > tricking GHC. > > Which version of the FPS code is this? Just the one in the darcs repo? (from the libraries list) -----Original Message----- From: Simon Peyton-Jones [mailto:simonpj@microsoft.com] Subject: RE: Cabal doesn't echo commands with -v on Windows Windows GHC 6.4.1 is definitely seg-faulting when it runs Cabal. (Cabal outputs less trace stuff than it should, but that's a separate and less urgent matter.) We're investigating. Simon

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Interactively used EDSLs
by Lauri Alanko 18 Oct '05

18 Oct '05

Hello. Are there any embedded domain specific languages that are meant to be used interactively from a Hugs or GHCi prompt without requiring the user to be acquainted with Haskell in general, only the DSL library? For instance, a Haskell shell DSL that provided combinators for creating and piping processes would fill this description, but I don't think such a thing exists. Yet I do have a vague recollection that there are some existing DSLs that can be used in such a way. Does anyone have suggestions? Thanks. Lauri Alanko la(a)iki.fi

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Announce: Decimal arithmetic library (questions inside)
by Jeremy Shaw 17 Oct '05

17 Oct '05

Announcment: ------------ I am proud to announce the *premature* release of my Decimal arithmetic library: darcs get http://www.n-heptane.com/nhlab/repos/Decimal It implements real decimal arithmetic, for cases where the binary floating point is not acceptable (money, etc). Need Advice: ----------- I am currently stuck trying to figure out how to implement contexts. The decimal operations are supposed to be executed in a context that determines things such as, type of rounding, how many digits of precision, what signals should be considered exceptions, etc. More details at the end of this page: http://www2.hursley.ibm.com/decimal/damodel.html Ideally, the user should be able to have multiple contexts in the same program. So far the best solution I have seen is the solution presented in 'Functional Pearl: Implicit Configurations' to deal with modular arithmetic. http://www.eecs.harvard.edu/~ccshan/prepose/prepose.pdf However, this solution seems a bit over the top -- I would like to implement things such that the finished product could be included in fptools. One option would be to define a unique type for each context. So by default I could provide DecimalFloat, and DecimalDouble. If the user wants a different context then they create a new type. This is a bit annoying however, because the user will have to create a bunch of boilerplate code to add the new type to all the right classes. I could probably automate that with TH however... Another option might be to include the context in each Decimal value. However, to check for context mismatches at compile time will probably require encoding the context into a phantom type, or something of that nature... I have not done a lot of numeric programming, so I am don't really know what people are even expecting or used to. Background: ---------- I plan to use this library as the basis of a Money library. The python folks have done a fine job of decribing why I am doing this which you can read here: http://www.python.org/peps/pep-0327.html I have been working from this spec so far: http://www2.hursley.ibm.com/decimal/decarith.html What's Done So Far: ------------------ I have created instances for Decimal for the type classes: ~ Eq ~ Ord ~ Num (precision/rounding not enforced correctly) ~ Fractional I am also going to investigate adding instances for: ~ Real ~ RealFrac ~ RealFloat ~ Floating The Future: ----------- There is still a fair bit of work to do long term: ~ Handle contexts ~ Enforce precision limits ~ Finish test suite ~ Add additional class instances ~ Optimize for speed But, I want to get the context stuff figured out first, so I don't have to rewrite everything later. Thanks! Jeremy Shaw.

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RE: [Haskell-cafe] pre-built ghc 6.4.1 crashes building FPS
by Simon Peyton-Jones 17 Oct '05

17 Oct '05

Joel A released GHC should never crash. Can you submit a bug report please (see "Report a bug" on GHC's home page)? In doing so, please attach the source code that provokes the crash. Thanks Simon | -----Original Message----- | From: haskell-cafe-bounces(a)haskell.org [mailto:haskell-cafe-bounces@haskell.org] On Behalf Of Joel | Reymont | Sent: 17 October 2005 14:54 | To: Haskell Cafe | Subject: [Haskell-cafe] pre-built ghc 6.4.1 crashes building FPS | | Folks, | | I downloaded and installed the pre-built ghc 6.4.1 on Windows XP and | Win2k. I tried building FastPackedStrings but ghc crashes soon after | starting. Any tips? | | I'm gonna try with a hand-built ghc but somehow doubt it will help. | | Thanks, Joel | | -- | http://wagerlabs.com/ | | | | | | _______________________________________________ | Haskell-Cafe mailing list | Haskell-Cafe(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe

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RE: [Haskell-cafe] Interest in helping w/ Haskell standard
by Simon Marlow 17 Oct '05

17 Oct '05

On 12 October 2005 23:50, Sebastian Sylvan wrote: > (I'm specifically interested in seeing SPJ's records proposal > included, and a new module system). Highly unlikely, IMHO. A new revision of the Haskell standard is not the place for testing new research, rather it's a clear specification of existing well-understood language features. If you want a new record system, or a new module system, now is the time to start designing and implementing them ready for the next standardisation process. Cheers, Simon

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RE: Re[2]: [Haskell-cafe] newtype is superfluous
by Simon Marlow 17 Oct '05

17 Oct '05

On 15 October 2005 19:08, Bulat Ziganshin wrote: > Hello Lennart, > > Saturday, October 15, 2005, 5:03:50 PM, you wrote: > >> Alas, Haskell is more subtle than that. Which is why newtype exists. > >> Try >> case A _|_ of A _ -> 1 >> with the two versions of A to see the difference. > > this have practical usage?? may be for such very special things > strictness annotation will be enough?? The semantics of newtype are really decided by its implementation. The basic idea is that a newtype of T can be represented in the same way as T. Once you know this, it pretty much fixes what semantics you can expect - the semantics of a newtype of T must be the same as T, because the runtime cannot distinguish the two. Cheers, Simon

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Newbie question on Haskell type
by Huong Nguyen 17 Oct '05

17 Oct '05

Hi all, I want to write a small functionto test whether an input is a String or not. For example, isString::(Show a) =>a ->Bool This function will return True if the input is a string and return False if not Any of you have idea about that? Thanks in advance

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Re: [Haskell-cafe] Generic parser without GADTs
by Huong Nguyen 17 Oct '05

17 Oct '05

Hi all, You are talking about parsing and data type, so I want to ask you a question relating to my data type. I have a data types and a function as follows: \begin{code} data Type a = C1 { x :: [String] ,y :: Type a} | C2 {x1 :: String} | C3 {y1 :: Bool} deriving Show showType :: Type a -> String showType (C2 a) = show a showType (C3 a) = show a showType (C1 a b) = show "(" ++ (show a) ++ (showType b) ++ (show ")") r1 = C1 { x = ["x","y"] , y = C2{x1 = "x^2 + y^2 < 20"} } r2=C3{y1=False} r3=C2{x1="x+y=z"} \end{code} --Result: Main>showType r1 "\"(\"[\"x\",\"y\"]\"x^2 + y^2 < 20\"\")\"" Main>showType r2 "False" Main>showType r3 "\"x+y=z\"" Now, I want to write a function to see the result in its original type, for example : input: "False" output: False input:"\"x+y=z\"" output:"x+y=z" input:"\"(\"[\"x\",\"y\"]\"x^2 + y^2 < 20\"\")\"" output:(["x","y"]x^2 + y^2 < 20") So, how I should write the function ? Do you have any idea about this ? Thanks. From: oleg(a)pobox.com <oleg(a)pobox.com > Date: Oct 16, 2005 8:50 PM Subject: [Haskell-cafe] Generic parser without GADTs To: haskell-cafe(a)haskell.org Cc: ralf(a)informatik.uni-bonn.de Also inspired by Ralf Hinze's post, I thought of removing GADTs from that code. The result is Haskell98! code, which works well in Hugs. The code seems to be a bit simpler too. Like the original code, the function 'parseAny' correctly discriminates between the list of characters (i.e., strings) and the list of other things. {-- Haskell98! --} class Type a where parse :: ReadS a > hugs /tmp/h.hs Haskell 98 mode: Restart with command line option -98 to enable extensions Main> parseAny "4711" [(ValInt 4711,"")] Main> parseAny "\"4711\"" [(ValString "4711","")] Main> parseAny "[4711, 0]" [(ValList [ValInt 4711,ValInt 0],"")] Main> parseAny "[4711, 'a']" [(ValList [ValInt 4711,ValChar 'a'],"")] Main> parseAny "[\"hello world\"] x" [(ValList [ValString "hello world"]," x")] ______________________________ _________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

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Generic parser without GADTs
by oleg＠pobox.com 17 Oct '05

17 Oct '05

Also inspired by Ralf Hinze's post, I thought of removing GADTs from that code. The result is Haskell98! code, which works well in Hugs. The code seems to be a bit simpler too. Like the original code, the function 'parseAny' correctly discriminates between the list of characters (i.e., strings) and the list of other things. {-- Haskell98! --} class Type a where parse :: ReadS a newtype Str = Str{unStr :: String} instance Type Char where parse = reads instance Type Int where parse = reads instance Type Str where parse = Str <$> reads instance Type a => Type [a] where parse = parseList parse instance Type Value where parse = parseAny data Value = ValChar Char | ValInt Int | ValString String | ValList [Value] deriving (Show) parseAny = ValChar <$> parse <+> ValInt <$> parse <+> ValString <$> (unStr <$> parse) <+> ValList <$> parse -- The following is Ralf Hinze's code verbatim parseList parsea = readParen False (\ s -> [ xs | ("[", t) <- lex s, xs <- parsel t ]) where parsel s = [ ([], t) | ("]", t) <- lex s ] ++ [ (x : xs, u) | (x, t) <- parsea s, (xs, u) <- parsel' t ] parsel' s = [ ([], t) | ("]", t) <- lex s ] ++ [ (x : xs, v) | (",", t) <- lex s, (x, u) <- parsea t, (xs, v) <- parsel' u] infix 8 <$> infixr 6 <+> (f <$> p) s = [ (f a, t) | (a, t) <- p s ] (p <+> q) s = p s ++ q s Tests: > hugs /tmp/h.hs Haskell 98 mode: Restart with command line option -98 to enable extensions Main> parseAny "4711" [(ValInt 4711,"")] Main> parseAny "\"4711\"" [(ValString "4711","")] Main> parseAny "[4711, 0]" [(ValList [ValInt 4711,ValInt 0],"")] Main> parseAny "[4711, 'a']" [(ValList [ValInt 4711,ValChar 'a'],"")] Main> parseAny "[\"hello world\"] x" [(ValList [ValString "hello world"]," x")]

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Estonia and GADT
by Bulat Ziganshin 16 Oct '05

16 Oct '05

Hello Haskell, 1) where can i find articles from Estonia conference? 2) they all say that GADT is great, but i personally don't "feel" GADTs. can anyone write a paper about it for beginners like me, or may be just collect examples of using GADT in real programs? -- Best regards, Bulat mailto:bulatz@HotPOP.com

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newtype is superfluous
by Bulat Ziganshin 15 Oct '05

15 Oct '05

Hello Haskell, number of type definition statements in Haskell (data, type, newtype) is a bit too large. at least, newtype definition seems to be superfluous - it can be replaced by the same `data` definition: newtype A = A Int and data A = A Int is equal, excluding for internal representation. we can exclude newtype definition and rely on the assumption that compiler is smart enough to optimize `data` definitions with just one constructor containing one field (moreover, i prefer something like `alias` to defining aliases for existing types, and `type` for defining new types, but i think it's a bit too late to complain about it :) ) -- Best regards, Bulat mailto:bulatz@HotPOP.com

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Emptying a list
by poogle＠netspace.net.au 15 Oct '05

15 Oct '05

Before you read any more, let me just say I'm fairly new to Haskell, so forgive me if this is really basic stuff. Hi there, I'm just wondering if there is a command for emptying a list? Also, is there any way to incorporate list operations (concatenation in particular) in a do-statement on lists? Every time I try it gives a type error. Thanks Jeremy Frech ------------------------------------------------------------ This email was sent from Netspace Webmail: http://www.netspace.net.au

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Examples of using STUArray + help with converting code
by joel reymont 14 Oct '05

14 Oct '05

Folks, Are there any examples on using STUArray and friends? I'm trying to convert the following bit of code which uses deprecated features. I don't understand the syntax needed to create a new double or float array with newArray from Data.Array.MArray. I also don't yet understand how to cast that double array to read ints from it. doubleToInts d = runST ( do arr <- newDoubleArray (1,2) writeDoubleArray arr 1 d i1 <- readIntArray arr 1 i2 <- readIntArray arr 2 return (i1,i2)) Thanks, Joel -- http://wagerlabs.com/ -- http://wagerlabs.com/

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RE: [Haskell-cafe] Re: Interest in helping w/ Haskell standard
by Bayley, Alistair 14 Oct '05

14 Oct '05

> From: Marco Tulio Gontijo e Silva [mailto:marcot@minaslivre.org] > > Em Qui, 2005-10-13 às 09:47 +0100, Bayley, Alistair escreveu: > > ***************************************************************** > Confidentiality Note: The information contained in this message blah blah blah > > Is this kind of notice legal in the context of Haskell-Cafe? Sorry, but it's not under my control. My employer's email system is configured to append this to every message, and I suspect that it's not worth the hassle to try to get it removed. Alistair.

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Re: [Haskell-cafe] Newbie question on Haskell type
by robert dockins 14 Oct '05

14 Oct '05

So this is essentially a parsing problem. You want a user to be able input a string and have it interpreted as an appropriate data value. I think you may want to look at the Parsec library (http://www.cs.uu.nl/~daan/parsec.html) I don't think the direction you are heading will get the results you want. As to typeable, the basic types are mostly all members of Typeable. You can find a pretty good list here: http://www.haskell.org/ghc/docs/latest/html/libraries/base/Data.Typeable.ht… Additionally, GHC can create Typeable instances automaticly for user defined datatypes; just add a deriving Typeable clause. data SomeType = C1 | C2 deriving (Show,Eq,Typeable) The restriction is that all types which appear in constructors must also be in Typeable. I believe the DrIFT preprocessor can also create Typeable instances if you are not using GHC. Huong Nguyen wrote: > Hello, > > Thanks for your solution. > > My main purpose is that I want to input a value and check whether this > value is belong to some specific types or not. These types can be some > popular types (such as: String, Char, Int, etc) or some more complex > data structures defined by user. Thus, at first, I try with type String > (even with that simple type, I still face difficulty ;-)) > > I want to ask you which types can be used with Data.Typeable. I read for > over 15 minutes but it is still not clear with me. > For some other complex data types defined by user, what I should do to > use Data.Typeable ? > > Thank you very much. > > On 10/13/05, *robert dockins* <robdockins(a)fastmail.fm > <mailto:robdockins@fastmail.fm>> wrote: > > In GHC you can do this: > > > import Data.Typeable > > > isString :: (Typeable a) => a -> Bool > > isString x = typeOf x == typeOf (undefined::String) > > Why do you want this? It's not the kind of operation one does very > often in Haskell. > > > Huong Nguyen wrote: > > > Hi all, > > > > I want to write a small functionto test whether an input is a > String or > > not. For example, > > > > isString::(Show a) =>a ->Bool > > This function will return True if the input is a string and > return False > > if not > > > > Any of you have idea about that? Thanks in advance > > > > > > > ------------------------------------------------------------------------ > > > > > _______________________________________________ > > Haskell-Cafe mailing list > > Haskell-Cafe(a)haskell.org <mailto:Haskell-Cafe@haskell.org> > > http://www.haskell.org/mailman/listinfo/haskell-cafe > >

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RE: [Haskell-cafe] Re: Interest in helping w/ Haskell standard
by Bayley, Alistair 14 Oct '05

14 Oct '05

> From: Stephane Bortzmeyer [mailto:bortzmeyer@nic.fr] > > As someone who is not an academic researcher and not a student in CS, > I would like to express a personal opinion; we don't need a new > standard. To me, Haskell needs more libraries, more users (which means > more debugging and more documentations), more implementations, of > course more real applications (darcs did a lot of the success of > Haskell), so we can read their code, push sysadmins to install > Haskell, etc. A significant number of Haskell libraries, both user-contributed and compiler-bundled (in the "standard" library hierarchy), are not written in Haskell98, and rely on a number of (typically well supported) language extensions like multi-parameter type classes + functional dependencies, existential types, hierarchical modules, etc. Some libraries target a specific compiler (often GHC). It should be clear that standardising the popular extensions would make a greater number of compiler-bundled and user-contributed libraries standards compliant, which has the obvious benefit that they can be used with any standardised compiler/interpreter i.e. they become more portable. Alistair. ----------------------------------------- ***************************************************************** Confidentiality Note: The information contained in this message, and any attachments, may contain confidential and/or privileged material. It is intended solely for the person(s) or entity to which it is addressed. Any review, retransmission, dissemination, or taking of any action in reliance upon this information by persons or entities other than the intended recipient(s) is prohibited. If you received this in error, please contact the sender and delete the material from any computer. *****************************************************************

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Re: [Haskell-cafe] Newbie question on Haskell type
by voigt.16734551＠bloglines.com 14 Oct '05

14 Oct '05

--- Cale Gibbard <cgibbard(a)gmail.com wrote: > As an example of this sort of thing, I know that there are only 4 > values of type a -> Bool (without the class context). They are the > constant functions (\x -> True), (\x -> False), and two kinds of > failure (\x -> _|_), and _|_, where _|_ is pronounced "bottom" and > represents something along the lines of nontermination (aborting the > program also counts). Not exactly. There are also (\x -> seq x True) and (\x -> seq x False), neither of which is equivalent to any of the four functions above. Regards, Janis Voigtlaender.

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Interest in helping w/ Haskell standard
by Isaac Jones 14 Oct '05

14 Oct '05

At the end of the Haskell Workshop at ICFP, we had the traditional "Future of Haskell" discussion (chaired by Andres Loeh). One of the main topics was the perceived need of a new standard, because the Haskell 98 standard is quite old already, and Haskell has evolved in the meantime, leading to a situation where almost none of the actually existing Haskell programs is according to the 98 standard. No clear opinion was visible on what form a new standard would take. There was, however, considerable support for the idea to standardize an incremental and moderate extension to Haskell 98 (working name "Haskell 06" or "Industrial Haskell"). This effort would then be separate from discussion about the Real Next Version (dubbed "Haskell 2"). John Launchbury asked for a show of hands of those who would be interested in helping out with the "Haskell 06" standard. I think "helping" means "willing to spend a non-trivial amount of time". That is, it's pretty well expected that most Haskellers will be willing to contribute to discussion on the mailing lists, but we're trying to get a list of those who want to take it to the next level. If you raised your hand, or if you think this describes you, please email John Launchbury at john(a)galois.com. peace, Isaac Jones & Andres Loeh

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newbe/ hdirect/ windows/ com how to compile?
by Marc Weber 13 Oct '05

13 Oct '05

Hi. I now get the errror that the module NativeInfo is in the project hdirect and in the library lang of ghc. Removing the files from the hdirect project resulted in a ld error Main_16 not found (don't remember exactly).. If you use hdirect on win succesfully, can you tell me which ghc/ hdirect version you're using? I can't compile cvs version, either. I get file not found errors in mk/target.mk and another mk/*.mk file. After adjusting the TOP directory there make core dumps (I think I get a recursive loop)... Any ideas what to try next? Marc

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Re: [Haskell-cafe] Papers from the 2005 Haskell Workshop (Tallinn)?
by Antonio Regidor García 13 Oct '05

13 Oct '05

> > De: John Meacham > > On Wed, Oct 05, 2005 at 10:53:01PM +0200, Nils Anders Danielsson wrote: > > Most authors do put their papers on their web pages nowadays. > > > > On a side note, it is a little strange that the research community > > does the research, writes and typesets the papers, and does most (?) > > of the arrangements for the conferences, and still someone else gets > > the copyright. University libraries have to pay lots of money for > > access to publications. I may have missed some term in the equation, > > though. > > knuth wrote an open letter on just this subject that was very > interesting.. > http://www-cs-faculty.stanford.edu/~knuth/joalet.pdf > > > I wonder if it would be okay to make a meta-web page that points to > each authors homepage where they have their papers for each person that > presented at a conference. > > I certainly think we should somehow centralize an index to papers on > haskell. I have found it extremely difficult to track down papers for > authors that have since moved out of academia or have passed on and > don't have their personal homepages with their papers anymore. > > John There are already some free repositories of papers: http://arxiv.org/ http://citeseer.ist.psu.edu/ http://www.publiclibraryofscience.org/ http://www.sciencedirect.com/ But a "Haskell-only" repository will be interesting. Antonio Regidor García ______________________________________________ Renovamos el Correo Yahoo! Nuevos servicios, más seguridad http://correo.yahoo.es

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Hi, I'm a Bolivian student working in my proyect of grade...
by Soujiro Seta 12 Oct '05

12 Oct '05

Hello, sorry for this bother, I'm a student of computer science of one university of Bolivia (UMSS, Cochabamba - Bolivia http://www.umss.edu.bo/) In my university the principal tool is Java and the OO paradigm, but for the area of programming languages we use the functional programming paradigm and Haskell. I´m working in my project of grade, and one teacher suggest me to use something new, in this case "Hugs98 for .NET" for develop something interesant. At this time I have learned about ASP.NET and C# and I think to develop a Web Service, but I'm not so happy with the idea of my project, please, can you suggest me something interesant to develop with Hugs98 for .NET?, in other words, I'm asking you about a something interesant thing to develop using the .NET framework and haskell, something interesant to apply the functional paradigm and a intelligent architecture to implement it. Thanks, and sorry for my bad english :( Best regards. _________________________________________________________________ Horóscopo, tarot, numerología... Escucha lo que te dicen los astros. http://astrocentro.msn.es/

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Papers from the 2005 Haskell Workshop (Tallinn)?
by Dimitry Golubovsky 12 Oct '05

12 Oct '05

The papers presented at the Workshop are already available in the ACM library which requires membership/subscription to read full text PDFs. Are there any plans to make those papers available anywhere else on the Web without subscription? -- Dimitry Golubovsky Anywhere on the Web

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puzzling memory leak? (GHC)
by Young Hyun 11 Oct '05

11 Oct '05

I'm seeing a very puzzling behavior that would be considered a memory leak, or unwanted retention of objects, in other languages. If I've made a newbie mistake, could someone point out what I am doing wrong? The process size (resident size and not just virtual size) of my program just grows and grows, passing a few hundred MB's in just 30 seconds, until I'm forced to kill the process. I get the same problem with GHC 6.4 and 6.4.1 on Solaris 2.8 and MacOS X 10.4.2, and GHC 6.2.2 on Solaris 2.8. Here's what the program does. It reads a binary file containing a large number of varying-length structured records. Some of these records are corrupt (e.g., truncated), and it is the job of my program to write out a new file with corrupted records filtered out. I decided to take advantage of Haskell's lazy evaluation to separate out the task of input parsing from the task of filtering as follows: import qualified Data.Map as Map main = do contents <- getContents fixArts $ parseArts contents [] (Map.singleton "offset" 0) The invoked functions have the following signatures: parseArts :: [Char] -> [Char] -> HeaderMap -> [Either ParseError Arts] fixArts :: [Either ParseError Arts] -> IO () where type HeaderMap = Map.Map String Word data Arts = Arts { ar_version::Int, ar_flags::Word, ar_data_length::Int, ar_timestamp::Word, ar_src_ip::Word, ar_dst_ip::Word, ar_list_id::Word, ar_cycle_id::Word, ar_rtt::Word, ar_rtt_mod::Word, ar_hop_distance::Int, ar_dst_replied::Bool, ar_halt_reason::Int, ar_halt_data::Int, ar_reply_ttl::Int, ar_hops::[ArtsHop], ar_offset::Int, ar_bytes:: [Char] } data ArtsHop = ArtsHop { ar_hop_num::Int, ar_hop_addr::Word, ar_irtt::Word, ar_num_tries::Int } data ParseError = ParseError { pe_message::String, pe_offset::Int, pe_bytes::[Char] } Here's the body of fixArts: fixArts ((Left x):xs) = do hPutChar stderr '\n' hPutStrLn stderr $ "Parse error: " ++ pe_message x hPutHexDump stderr bytes offset fixArts xs where bytes = pe_bytes x offset = pe_offset x {-- XXX normally: do putStr (ar_bytes x); fixArts xs --} fixArts ((Right x):xs) = fixArts xs fixArts [] = return () -------------------------------- The function hPutHexDump simply prints out a hex dump of a [Char] (and commenting out the call makes no difference). Unless I'm badly mistaken, nothing about fixArts suggests that it would leak memory. So, it would appear parseArts is somehow to blame for the memory leak, but this is where it gets weird. If I just slightly change fixArts (see below), then I no longer get a memory leak (the process size stays at just over 3MB): fixArts ((Right x):xs) = do hPutArts stderr x fixArts xs The function hPutArts :: Handle -> Arts -> IO () simply prints out the fields of the Arts object. So why should this change fix the memory leak if parseArts is truly at fault? The function parseArts has the following basic form (though the actual implementation is much more involved): parseArts (x:xs) ... = (createArts x) : parseArts xs So, even without seeing all of the code, does anyone have any clues about what may be wrong? --Young

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RE: [Haskell-cafe] puzzling memory leak? (GHC)
by Simon Marlow 11 Oct '05

11 Oct '05

On 11 October 2005 07:34, Young Hyun wrote: > What intuition should be my guide about the "proper way" of employing > lazy evaluation? It's not yet clear to me what you mean by "the > system needs to hang onto all the input data ...". It seems > counterintuitive for the evaluator to hang onto partially evaluated > functions and input data when it can be proven (through static > analysis) that references to that data can no longer exist in the > remainder of the program execution; for example, consider > > case head $ drop 500000 $ parseArts ... of > Right x -> hPutArts stderr x This example should not have a space leak (try it). Space leaks arise when large unevaluated expressions build up, or there are unevaluated expressions that refer to large amounts of data. The solution is usually to insert some strictness, to force evaluation of the offending expressions, assuming the evaluated representation is smaller than the unevaluated one. I suggest you try out space profiling (with GHC or nhc98), and try various modifications to your code to get a handle on what's happening. It's hard to tell exactly where the space leak is in your original code, because it depends on the actual definition of parseArts. Ben's analysis is definitely plausible. Take a look at the code and ask yourself: does each element of the list refer to previous elements, or to an expression accumulated while traversing the list? If this is the case, and you never actually evaluate the head of the list, then the entire list will be retained. A good way to begin to understand space leaks is to study foldl (see many previous threads on this list). Cheers, Simon

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