- Haskell-Cafe - Haskell.org

Maximum number of sockets
by Joel Reymont 03 Nov '05

03 Nov '05

Is there a limit on the maximum number of sockets that's possible to open in GHC? I'm concerned with Mac OSX and Windows. Thanks, Joel -- http://wagerlabs.com/

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Socket finalizers
by Joel Reymont 03 Nov '05

03 Nov '05

Folks, I remember a message about this recently and tried googling for it but came up empty. I'm running a bunch of "poker bots" from ghci and although I'm calling hClose on the socket handle, it does not seem to actually close when my bots finish. I need to exit ghci for the sockets to close. How can I tackle this problem? It's important for me that the sockets close when I call hClose . Thanks, Joel -- http://wagerlabs.com/

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Compiled hugs - on "overload" crashes
by Dusan Kolar 03 Nov '05

03 Nov '05

Hello again, without the --enable-timer option, I have managed to compile hugs. Nevertheless, I was not successful with doc. OK, I don't care about it, but anyway... I've run several tests. One of them is appended - for trial just type: cesty (1,1) /(It's a kind of state-space search implementation (horse problem) made by a student long time ago, without any optimization, for testing very good.)/ My older hugs interpreter stops with error: ERROR - Control stack overflow GHCi stops with the same error: *** Exception: stack overflow That's OK, really, that's correct behavior after printing some results. Nevertheless, the new hugs compilation stops with this: Segmentation Fault(coredump) And that's probably not the correct end. May I do something wrong? I've thought that configure + make + make install_all_but_docs (no doc compiled) should work. Sorry for bothering if this is trivial or off topic. Regards, hoping for help, Dusan -- Dusan Kolar tel: +420 54 114 1238 UIFS FIT VUT Brno fax: +420 54 114 1270 Bozetechova 2 e-mail: kolar(a)fit.vutbr.cz Brno 612 66 Czech Republic --

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Compiled hugs - on "overload" crashes
by Dusan Kolar 03 Nov '05

03 Nov '05

Hello again, without the --endable-timer option, I have managed to compile hugs. Nevertheless, I was not successfull with doc. OK, I don't care about it, but anyway... I've run serveral tests. One of them is appended - for trial just type cesty (1,1) - it's a kind of state-space search implementation (horse problem) made by a student long time ago, without any optimization, for testing very good. My older hugs interpreter stops with error: ERROR - Control stack overflow GHCi stops with the same error: *** Exception: stack overflow That's OK, really, that's correct behavior after printing some results. Nevertheless, the new hugs compilation stops with this: Segmentation Fault(coredump) And that's probably not the correct end. May I do something wrong? I've thought that configure + make + make install_all_but_docs (no doc compiled) should work. Sorry for bothering if this is trivial or off topic. Regards, hoping for help, Dusan -- Dusan Kolar tel: +420 54 114 1238 UIFS FIT VUT Brno fax: +420 54 114 1270 Bozetechova 2 e-mail: kolar(a)fit.vutbr.cz Brno 612 66 Czech Republic --

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Vector/matrix arithmetic
by James McNeill 03 Nov '05

03 Nov '05

I'm attempting to learn Haskell by writing some orbital mechanics code. I'd like to use vector and matrix arithmetic to simplify it. The Haskell book I've got, Simon Thompson's "Haskell: The Craft of Functional Programming," has one approach, which is to alias a list of numbers to Vector, and a list of vectors to Matrix, and then define functions to perform inner and outer products (dot/cross products) and so forth. On http://haskell.org/hawiki/FunDeps another approach is sketched out that looks far more appealing to me. This is to create Vector and Matrix types that can use overloaded arithmetic operators. It uses functional dependencies, and the resulting syntax looks a lot like what you can do using C++ or Matlab. I don't know enough Haskell to finish out the code that is started there, and I haven't been able to find any vector/matrix libraries for Haskell that look like this. I did find a port of a linear algebra library (BLAS) to Haskell, but it looked like it did everything in imperative style. Performance is not a major concern for me at this point so I'd prefer to do things functionally. Does anyone know what the best way to do vector/matrix arithmetic in Haskell might be? I don't need arbitrary dimension; all my work will be confined to 2D and 3D space. Thanks!

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Compiling hugs - stop on missing symbol
by Dusan Kolar 03 Nov '05

03 Nov '05

Hello all, I don't know if this is the right place to ask about how to compile hugs, but I'll try. :-) My machine identifies this way: Linux mymachine 2.6.14 #1 SMP Mon Oct 31 10:55:16 CET 2005 i686 athlon i386 GNU/Linux I've downloaded this SRC package of hugs: hugs98-Mar2005-patched.tar.gz Download, unpack - OK ./configure --prefix=/mnt/data/FLP --enable-timer does not complain, suggests to perform make; make install Unfortunately, make stops with this error: gcc runhugs.o server.o builtin.o char.o compiler.o errors.o evaluator.o ffi.o goal.o input.o machdep.o machine.o module.o opts.o output.o plugin.o script.o static.o storage.o strutil.o subst.o type.o version.o -lreadline -lncurses -lm -ldl -o runhugs evaluator.o(.text+0x137): In function `evaluator': /mnt/data/FLP/Downloads/hugs98-Mar2005-patched/src/evaluator.c:98: undefined reference to `updateTimers' collect2: ld returned 1 exit status make: *** [runhugs] Error 1 Well, yes, the symbol is definitely missing, as timer.c, which defines the symbol, is included in hugs.c, which is not in the list of linked files. Nevertheless, I don't think including the file manually would help. Moreover, probably configure has produced a wrong Makefile. Any suggestions how to make it work? Dusan -- Dusan Kolar tel: +420 54 114 1238 UIFS FIT VUT Brno fax: +420 54 114 1270 Bozetechova 2 e-mail: kolar(a)fit.vutbr.cz Brno 612 66 Czech Republic --

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Haskell Workshop Steering Committee
by Johan Jeuring 02 Nov '05

02 Nov '05

At the Haskell workshop in Tallinn in September it was decided to set up a Haskell Workshop Steering Committee. The main purpose of the Haskell Workshop Steering Committee is to provide continuity of the workshop and to offer help and advice to the current organizer(s) of the workshop. I'm pleased to announce the Haskell Workshop Steering Committee, which has been approved by ACM SIGPLAN. You can find more information about the Haskell Workshop and its Steering Committee on http://www.haskell.org/haskell-workshop/ -- Johan Jeuring

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MaybeT, guards and run-time pattern matching failure
by Joel Reymont 01 Nov '05

01 Nov '05

I'm trying to optimize this and I thought that things that return Nothing in the Maybe monad should fail the whole computation sequence. Something subtle is going wrong, I think. MaybeT is at the end of this message. ---- timeout :: forall a.Int -> IO a -> IO (Maybe a) connect_ :: HostName -> Int -> IO Handle startSSL :: IO (SSL, BIO, BIO) type EngineState = MaybeT (WriterT [Log] (StateT World IO)) connect :: [Prop] -> HostName -> Int -> EngineState () connect env h p = do h <- liftIO $ timeout 0 $ connect_ h p -- no complains about this (ssl', tob, fromb) <- liftIO $ timeout 0 startSSL -- bummer, see below ./Script/Engine.hs:101:7: Couldn't match `Maybe (SSL, BIO, BIO)' against `(a, b, c)' Expected type: Maybe (SSL, BIO, BIO) Inferred type: (a, b, c) When checking the pattern: (ssl', tob, fromb) In a 'do' expression: (ssl', tob, fromb) <- liftIO $ (timeout 0 startSSL) ---- I thought I would change it like this: ---- connect env h p = do (Just h) <- liftIO $ timeout 0 $ connect_ h p -- no complains about this ---- but when the connection times out (i'm making it with a delay of 0) I get the following runtime error: *** Exception: Pattern match failure in do expression at ./Script/ Engine.hs:103: So am I stuck with this? ---- connect :: [Prop] -> HostName -> Int -> EngineState () connect env h p = do m'h <- liftIO $ timeout 0 $ connect_ h p m'ssl <- liftIO $ timeout 0 startSSL guard (m'h /= Nothing && m'ssl /= Nothing) -- do I need this?! let h = case m'h of (Just h) -> h let (ssl', tob, fromb) = case m'ssl of a -> a ---- And this is MaybeT: newtype MaybeT m a = MaybeT { runMaybeT :: m (Maybe a) } instance (Monad m) => Monad (MaybeT m) where (MaybeT mon) >>= f = MaybeT (mon >>= maybe (return Nothing) (runMaybeT . f)) return = MaybeT . return . Just instance MonadTrans MaybeT where lift mon = MaybeT (mon >>= return . Just) instance (Monad m) => MonadPlus (MaybeT m) where mzero = MaybeT (return Nothing) mplus (MaybeT a) (MaybeT b) = MaybeT $ do ma <- a mb <- b return $ ma `mplus` mb instance MonadState s m => MonadState s (MaybeT m) where get = lift get put s = lift $ put s instance (MonadIO m) => MonadIO (MaybeT m) where liftIO = lift . liftIO Thanks, Joel -- http://wagerlabs.com/

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Interactive Haskell and hs-plugins
by Fraser Wilson 01 Nov '05

01 Nov '05

Hi there, I would like to use evaluate arbitrary expressions in the context of a mixed-language (Ada, Haskell and about twelve lines of C glue) applications. Is it possible to use dynload from hs-plugins to load a module that references symbols in the loading program? For example, the application contains a Haskell module that looks a bit like this: > module TestKeys.NamedObject where > tt :: Int > tt = 2 I want the application to be able to offer the following sort of interaction: haskell> tt 2 haskell> But what actually happens is this: haskell> tt test_haskell3: /tmp/MDnum15633.o: unknown symbol `TestKeysziNamedObject_tt_closure' test_haskell3: user error (resolveObjs failed with <<False>>) Compiling Haskell code in advance works (i.e. if I create and compile a module that evalutes tt and link it in, everything runs fine). This is how I try to evaluate the expression: > evaluate :: String -> IO () > evaluate "" = return () > evaluate e = do writeFile "temp.hs" fileContents > status <- makeWith "LeanderStub.hs" "temp.hs" ["-c"] > case status of MakeSuccess code path -> loadAndEval path > MakeFailure error -> print error > where fileContents = "module Temp where\n\ > \ result = " ++ e ++ "\n" > > loadAndEval :: FilePath -> IO () > loadAndEval path = do mv <- dynload path [] [] "result" > case mv of > LoadFailure msg -> print msg > LoadSuccess _ v -> putStrLn v LeanderStub.hs is a module containing the necessary imports for the expression to evaluate in the right context. I was hoping that passing "-c" to makeWith would create an object file whose missing dependencies would be resolved when it was loaded into an application which contained them. Is this a dumb expectation? The alternative -- linking to the entire application for each expression evaluated -- seems a bit over the top, and I can't see how state would be maintained. I originally used unsafeEval_, but this has the same problem. I can't help but think that this must have been done before. Any advice? If you know Guile, then the equivalent of gh_repl is what I'm really after. cheers, Fraser.

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DARCS and case of file name letters
by Dimitry Golubovsky 01 Nov '05

01 Nov '05

I have a file in my repo (HSX11/Xauthority.hs) and I want to rename it changing just case of one letter: bash$ darcs mv HSX11/Xauthority.hs HSX11/XAuthority.hs darcs failed: A file or dir named HSX11/XAuthority.hs already exists in working directory. bash$ ls HSX11/X[aA]*.hs HSX11/Xauthority.hs bash$ darcs --version 1.0.3 (release) DARCS was compiled by GHC 6.2.2. bash$ uname -a Linux dmghome 2.2.16 #9 Mon Sep 16 22:43:25 EDT 2002 i686 unknown Is it DARCS that ignores the case of letters in filenames, or the Haskell runtime? Dimitry Golubovsky Middletown, CT

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Computations that can time out + gathering feedback from threads
by Joel Reymont 31 Oct '05

31 Oct '05

Folks, I need to implement computations that can time out (connecting to a server, reading from socket, etc.), plus gather feedback from a few thousands of threads. What is the best way to implement this? Do I launch a thread to sleep and a thread to connect/read from socket and use something like Shared Transaction Memory to wait for either of the two to finish? Also, my "simple scripting engine" launches a few thousands of scripts that connect to a server, exchange commands and update their internal state. I need to wait for all these to finish and get the results of their execution. My scripts are a combination of monads and I run them with runXXX( ... ) from the IO monad so that I can inspect the resulting state. Is there an elegant solution for waiting for all the threads to complete and then figuring out how many of these are in good share according to their end state? Thanks, Joel -- http://wagerlabs.com/

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Value-weak hash tables for GHC?
by Juliusz Chroboczek 31 Oct '05

31 Oct '05

Hi, Does anyone have an implementation of value-weak hash tables for GHC he'd be willing to share? (Hash tables where an entry is removed when the value, not the key, is collected.) Since GHC has (usable) weak pointers, finalisers and hash tables, I could in principle roll my own, but I'd rather get an efficient implementation off someone competent. Oh, and it needs to be under a license that makes it suitable for inclusion in Darcs. Thanks a lot, Juliusz P.S. I am not subscribed to the list -- I'd be grateful if you could CC me with any replies.

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RE: [Haskell-cafe] Silly question
by Bayley, Alistair 31 Oct '05

31 Oct '05

> From: Joel Reymont [mailto:joelr1@gmail.com] > > I didn't know about "it" in ghci, thanks. Are there multiple levels > of it? > > I wanted z "a" :: Maybe Int which I understand now. > > Thanks, Joel What do you mean by multiple levels? "It" just stores the most recent expression/value. If you type "print it" then the result of the print becomes the most recent value e.g. *Foo> "boo" "boo" *Foo> :t it it :: [Char] *Foo> print it "boo" *Foo> :t it it :: () *Foo> print it () *Foo> The docs probably explain it better: http://www.haskell.org/ghc/docs/latest/html/users_guide/ch03s04.html#id31036 40 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] Silly question
by Bayley, Alistair 31 Oct '05

31 Oct '05

s> From: Joel Reymont [mailto:joelr1@gmail.com] > > How do I run z "a" from ghci or the IO monad? > > module Foo where > > import qualified Data.Map as M > import Control.Monad > import Control.Monad.List > import Prelude hiding ((!!)) > > (!!) :: (Ord k, MonadPlus m) => [M.Map k v] -> k -> m v > (!!) maps key = msum $ map (M.lookup key) maps > x :: M.Map String Int = M.empty > y :: M.Map String Int = M.fromList [("a", 1)] > z m = [x, y] !! m There are a couple of ways, depending on how you want to run it through MonadPlus, I think (although I don't understand your code much): main = do let a :: [Int]; a = z "a" print a b <- z "a" print b *Foo> main <<- running main from ghci [1] 1 Or directly the the ghci prompt: *Foo> z "a" *Foo> :t it it :: Int *Foo> print it 1 *Foo> z "a" :: [Int] [1] Did you know about the "it" variable in ghci? It holds the last expression typed at the prompt. 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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Silly question
by Joel Reymont 31 Oct '05

31 Oct '05

How do I run z "a" from ghci or the IO monad? module Foo where import qualified Data.Map as M import Control.Monad import Control.Monad.List import Prelude hiding ((!!)) (!!) :: (Ord k, MonadPlus m) => [M.Map k v] -> k -> m v (!!) maps key = msum $ map (M.lookup key) maps x :: M.Map String Int = M.empty y :: M.Map String Int = M.fromList [("a", 1)] z m = [x, y] !! m Thanks, Joel -- http://wagerlabs.com/

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RE: [Haskell-cafe] FFI and modifying haskell memory
by Simon Marlow 29 Oct '05

29 Oct '05

On 21 October 2005 14:40, Joel Reymont wrote: > 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? yes, something like with $ \pculong -> r <- uncompress_ buf pculong ... size <- peek pculong > I thought StablePtr would give me the address of a Haskell value but > it gives me an offset into some table instead. That's right, the reason being that Haskell values move around when GC happens. Cheers, Simon

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hugs maintenance
by Iavor Diatchki 28 Oct '05

28 Oct '05

hello, i was wondering if anyone is maintaining hugs. in particular is the hugs-bugs list still operational? i tried to post a bug-report, but it seems that it never got there, but it also didn't bounce back... and the last post in the archive is from 10 sept 2005. -iavor

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RE: [Haskell-cafe] lockFile: fd out of range
by Simon Marlow 28 Oct '05

28 Oct '05

Yes, it's hardcoded. FD_SETSIZE should be the maximum number of file descriptors you can ever have open. On my Linux box here, FD_SETSIZE is 1024, and I can't ulimit -n any more than this. Cheers, Simon On 27 October 2005 15:18, Joel Reymont wrote: > Actually, I think I was just hitting the top range of FD_SETSIZE, > about 8000 on that machine. > > Does FD_SETSIZE get hardcoded into ghc-built binaries? That is if I > increase the available descriptors per process with uname -n, will it > be taken into account? > > Thanks, Joel > > On Oct 26, 2005, at 10:04 AM, Simon Marlow wrote: > >> lockFile uses FD_SETSIZE as its idea of the maximum value of a file >> descriptor. If you can get file descriptors outside this range, then >> the above error would ensue. Not sure if this is the case on >> FreeBSD... seems odd if it is. Can you try a truss/ktrace and see >> the values of your file descriptors?

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LINQ
by Niklas Broberg 28 Oct '05

28 Oct '05

Why is it that everything that OO "steals" from the functional paradigm is always marketed as something new that will revolution the way we program? Can't they at least give some credit where credit is due? :-p http://msdn.microsoft.com/netframework/future/linq/default.aspx?pull=/libra… /Niklas

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Quickcheck examples and Data.Word32
by Joel Reymont 28 Oct '05

28 Oct '05

Folks, Does anyone have QuickCheck examples they could send me? Also, how can I check Word32, Word64, etc. properties? It looks like the built-in random generator only works with Int values and for the life of me I cannot figure out how to extend it. Last but not least, I'm trying to figure out how I can use QuickCheck with tests against a network server. I would want to make sure that a certain packet sequence always produces a particular packet sequence in response. Is this a good area to apply QC? Thanks, Joel -- http://wagerlabs.com/

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hugs type inference
by Christian Maeder 27 Oct '05

27 Oct '05

Hi, Hugs leaves an odd context when showing the type of the following expression. Is this a bug or just a harmless flaw? Christian Hugs.Base> :t toRational 1 / 2 toRational 1 / 2 :: Real a => Ratio Integer ghci yields: Prelude> :t toRational 1 / 2 <interactive>:1:0: Warning: Defaulting the following constraint(s) to type `Integer' `Real a' arising from use of `toRational' at <interactive>:1:0-9 In the first argument of `(/)', namely `toRational 1' toRational 1 / 2 :: Rational

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Nice way to calculate character frequency in a string
by Scherrer, Chad 27 Oct '05

27 Oct '05

Sorry to drag this thread out, but here's one more thing you might try... I was thinking, if we just wanted something like intTable :: [Int] -> [(Int, Int)] we could just replace Map with IntMap in the previous solution: intTable xs = IntMap.assocs $! foldl' f IntMap.empty xs where f m x = let m' = IntMap.insertWith (+) x 1 m Just v = IntMap.lookup x m' in v `seq` m' To get another polymorphic version, we could just write this wrapper: freq :: (Enum a) => [a] -> [(a,Int)] freq = map fstToEnum . intTable . map fromEnum where fstToEnum (x,y) = (toEnum x, y) This seems to run faster than the other polymorphic version on my machine. Chad Scherrer Computational Mathematics Group Pacific Northwest National Laboratory "Time flies like an arrow; fruit flies like a banana." -- Groucho Marx

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Monads as control structures?
by Creighton Hogg 27 Oct '05

27 Oct '05

Hi, so I'm a newbie getting used to Haskell. I'm writing some simple things like genetic algorithms in it for practice, and I keep coming across something that really bugs me: are there any standard libraries that allow you to do imperative style for or while loops using monads to keep track of state? I know there's things like "until", but honestly that's not quite what I'm looking for. I just think there should be a simple way to say "execute this block of code 10 times" without having to wrap it up in recursion. Haskell seems to me to be a very powerful language, and it looks like it should be possible to define control structures such as for loops using monads.

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Re: [Haskell-cafe] Monads as control structures?
by Creighton Hogg 27 Oct '05

27 Oct '05

On Thu, 27 Oct 2005, Creighton Hogg wrote: > On Thu, 27 Oct 2005, Robert Dockins wrote: > > > > > On Oct 27, 2005, at 11:54 AM, Creighton Hogg wrote: > > > > > Hi, > > > so I'm a newbie getting used to Haskell. I'm writing some > > > simple things like genetic algorithms in it for practice, > > > and I keep coming across something that really bugs me: > > > are there any standard libraries that allow you to > > > do imperative style for or while loops using monads to keep > > > track of state? > > > One way is to create a list of the actions you want to execute, and > > then use one of the sequence family of functions. > > The actions can share state with an IORef or STRef or whatever. > > Another option is to use a fold with >>= to allow > > actions to pass their results directly to the next action. This > > works even in "stateless" monads like the list monad. > > > > Some examples using sequence: > > > > > > forMonad :: Monad m => a -> (a -> Bool) -> (a -> a) -> (a -> m ()) -> > > m () > > forMonad init cond inc f = sequence_ $ map f $ takeWhile cond $ > > iterate inc init > > > > xTimes :: Monad m => Int -> (Int -> m ()) -> m () > > xTimes x f = sequence_ $ map f [0..(x-1)] > > > > main = do { forMonad 0 (<10) (+1) (putStrLn . show); xTimes 10 (\_ -> > > putStrLn "hi") } > > Thanks to all who answered, this gives me a lot to chew on. > I especially like these examples, because it makes me > realize that I've been thinking about monads and evaluation > wrong. > I think doing genetic programming in Haskell is going to be > easier than I thought. >

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Haskell scripting system (please help me simplify the design)
by Joel Reymont 27 Oct '05

27 Oct '05

Folks, With lots of help from #haskell and haskell-cafe I came up with the following setup. It's working fine but requires quite a bit of boilerplate code. Could you please help me simplify it? I apologize for the very long message and will describe any parts that are unclear. Please ask away. This is my first Haskell code, written over the course of 3 weeks (1 week to learn Haskell) so I'm bound to get some things wrong or unoptimal. Still, I'm quite amazed that I have been able to get this to work and to work correctly in such a short time span. The system is basically a scripting engine to test a poker server that lets you write simple scripts. I went out of my way to enable QA techs to use as little Haskell as possible, thus I'm treating all poker commands/packets as a list of properties. What I found is that I'm writing a lot of boiler-plate code to handle the convertion of property values into "storables". I think this dovetails into the recent GADT discussion. I wonder if my design and interaction between Packet, Convertible, Prop and Attr can be simplified. These are a couple of sample scripts (incomplete): --- module Test where import Script import Handshake as H script env = do setDebugLevel 100 dotimes 1 $ launch $ H.script [] waitForChildren --- module Handshake where import Script script env = -- connect to server do world <- connect env "192.168.0.197" 15667 -- setup callbacks world <- add world [ [ onCmd := CmdHandshake Server, call := onServerHandshake ], [ onCmd := CmdConnectGame Server, call := onConnectGame ], [ onCmd := CmdServerInfo Server, call := onServerInfo ], [ onCmd := CmdLogon Server, call := onLogon ], [ onCmd := CmdGameInfo Server, call := onGameInfo ], [ onCmd := CmdMoney Server, call := onMoney ] ] -- start handshake send world $ make (CmdHandshake Invalid) [] run world onServerHandshake cmd world = do send world $ make (CmdConnectGame Client) [ localIP := "10.0.0.2", affiliateID := [28] ] return world onServerInfo cmd world = do send world $ make (CmdLogon Client) [ name := "foo", password := "bar", affiliateID := [28] ] -- retrieve table id tables' <- get tables cmd debug 99 $ "Tables: " ++ show tables' tableID' <- get tableID $ head tables' debug 99 $ "TableID: " ++ show tableID' debug 99 $ "World: " ++ show world -- save it for later use world <- set (tableID := tableID') world -- return updated info return world onGameInfo cmd world = do debug 99 "Got game!" stop world --- I'm describing binary packets using properties (from WxHaskell) with the added twist that when you say attr := value you can specify what value will be converted to for storage. This is how I would use the system... This describes the properties for the admin message and wait list init commands. I would use the properties to serialize the commmands. cmdProps (CmdAdminMessage Server) = [ title := "", message := "", postAction := 0 ] cmdProps (CmdSrvWaitListInit Server) = [ waitListTables := [] ] I also have a "dictionary" that describes the attributes such as title, message, postAction, etc. I'm allowing deeply nested lists of properties. title :: Attr String WString = makeAttr "title" message :: Attr String WString = makeAttr "message" postAction :: Attr Word8 Word8 = makeAttr "postAction" waitListTables :: Attr [TableID] (FixedList Word8 (LE TableID)) = makeAttr "waitListTables" Attr String WString means that a String is accepted on the right-hand side and the string will be converted into a wide string for storage. Same thing with a list of table ids that is converted into a list of little-endian table ids (word32s) prefixed by a Word8 length for storage. The conversion/casting is done with code like this: class Convertible a b where convert_AB :: a -> b convert_BA :: b -> a instance Convertible [Word8] FastString where convert_AB a = packWords a convert_BA b = unpackWords b instance Convertible Bool Bool where convert_AB a = a convert_BA b = b instance Convertible Bool Word8 where convert_AB True = 1 convert_AB False = 0 convert_BA 1 = True convert_BA 0 = False instance Convertible String WString where convert_AB a = WString $ FS.pack a convert_BA (WString b) = FS.unpack b instance Convertible (String, String) (WString, WString) where convert_AB (a1, a2) = (convert_AB a1, convert_AB a2) convert_BA (b1, b2) = (convert_BA b1, convert_BA b2) instance Convertible [String] (FixedList (LE Word32) WString) where convert_AB a = FixedList $ map convert_AB a convert_BA (FixedList b) = map convert_BA b My concern is mostly with a lot of similar boilerplate code required for casting, specially in very alike cases like the following: data Pot = Pot [Prop] deriving (Eq, Show, Typeable) data BaseTableState = BaseTableState [Prop] deriving (Eq, Show, Typeable) instance Packet Pot where unstuff xs = case props of Just props -> (Just $ Pot props, xs') Nothing -> (Nothing, xs) where (props, xs') = unstuffprops xs potProps <<< this is the only difference stuff (Pot a) = stuffprops a size (Pot a) = sizeprops a instance Convertible [Prop] Pot where convert_AB a = Pot $ mergeprops a potProps convert_BA (Pot b) = b instance Packet BaseTableState where unstuff xs = case props of Just props -> (Just $ BaseTableState props, xs') Nothing -> (Nothing, xs) where (props, xs') = unstuffprops xs baseTableStateProps stuff (BaseTableState a) = stuffprops a size (BaseTableState a) = sizeprops a instance Convertible [Prop] BaseTableState where convert_AB a = BaseTableState $ mergeprops a baseTableStateProps convert_BA (BaseTableState b) = b Notice that the differences are only in the list of properties required for conversion. I'm wondering if this can be simplified somehow. This is how I describe serialization: class (Eq a) => Packet a where unstuff :: P.FastString -> (Maybe a, P.FastString) stuff :: a -> P.FastString size :: a -> Int instance Packet Word8 where unstuff xs | P.null xs = (Nothing, xs) | otherwise = let (ys, zs) = P.splitAt 1 xs in (Just $ concatBits ys, zs) stuff a = P.packWords $ unpackBits a size a = 1 instance Packet Bool where unstuff xs | P.null xs = (Nothing, xs) | otherwise = (b, xs') where (a :: Maybe Word8, xs') = unstuff xs b = case a of Just a -> if a == 0 then Just False else Just True Nothing -> Nothing stuff True = stuff (1 :: Word8) stuff False = stuff (0 :: Word8) size a = 1 This is the foundation for properties, with the idea taken from WxHaskell and the Convertible twist added on top: infixr 0 := data Prop = forall a b. (Eq a, Eq b, Show a, Packet b, Convertible a b) => Attr a b := a deriving (Typeable) instance Show Prop where show (Attr name _ _ := x) = name ++ " := " ++ show x instance Eq Prop where (Attr name1 (todyn1, fromdyn1) _ := x1) == (Attr name2 (todyn2, fromdyn2) _ := x2) | name1 == name1 = case fromdyn1 $ todyn2 x2 of Just x2 -> x2 == x1 Nothing -> False | otherwise = False data Attr a b = Attr String (a -> Dynamic, Dynamic -> Maybe a) (a -> b, b -> a) instance Show (Attr a b) where show (Attr name _ _) = name makeAttr :: (Typeable a, Convertible a b) => String -> Attr a b makeAttr name = Attr name (toDyn, fromDynamic) (convert_AB, convert_BA) setprop :: Prop -> [Prop] -> [Prop] setprop _ [] = [] setprop (Attr name (todyn, fromdyn) _ := x) props = map setprop' props where setprop' prop@(attr@(Attr name' (todyn', fromdyn') _) := x') | name == name' = case fromdyn' $ todyn x of Just y -> attr := y Nothing -> prop | otherwise = prop mergeprops :: [Prop] -> [Prop] -> [Prop] mergeprops [] props = props mergeprops (x:xs) props = mergeprops xs (setprop x props) get :: Typeable a => Attr a b -> [Prop] -> IO a get a b = return $ getprop a b getprop :: Typeable a => Attr a b -> [Prop] -> a getprop attr props = case findprop attr props of Just x -> x Nothing -> error $ "Could not retrieve " ++ show attr ++ " from " ++ show props -- http://wagerlabs.com/

3 4

hs-plugins runtime loading issue
by Joel Reymont 27 Oct '05

27 Oct '05

Folks, I'm using hs-plugins to compile and load haskell code on Mac OSX. This works perfectly. Once I try this on Windows, though, I'm getting an error when it tries to load HSBase again. This happens when calling a function from within ghci. Any ideas? --- GHCi runtime linker: fatal error: I found a duplicate definition for symbol _GHCziWord_fromEnum1_closure whilst processing object file d ghc/ghc-6.4.1/HSbase1.o This could be caused by: * Loading two different object files which export the same symbol * Specifying the same object file twice on the GHCi command line * An incorrect `package.conf' entry, causing some object to be loaded twice. GHCi cannot safely continue in this situation. Exiting now. Sorry. -- Thanks, Joel -- http://wagerlabs.com/

2 2

RE: [Haskell-cafe] lockFile: fd out of range
by Simon Marlow 27 Oct '05

27 Oct '05

On 25 October 2005 17:02, Joel Reymont wrote: > Is there a set limit on the number of file descriptors that a Haskell > program can open? > > I'm using hs-plugins on FreeBSD to transparently compile, load and > launch scripts that establish a connection to a server. I'm getting > this error: > > internal error: lockFile: fd out of range > Please report this as a bug to glasgow-haskell-bugs(a)haskell.org, > or http://www.sourceforge.net/projects/ghc/ lockFile uses FD_SETSIZE as its idea of the maximum value of a file descriptor. If you can get file descriptors outside this range, then the above error would ensue. Not sure if this is the case on FreeBSD... seems odd if it is. Can you try a truss/ktrace and see the values of your file descriptors? Cheers, Simon

2 1

RE: Instances That Ignore Type Constraints? (HList-related)
by Ralf Lammel 27 Oct '05

27 Oct '05

Yeah, I was also thinking of impredicative types and that they would make this problem go away. First of all, we may need to wait a while for such types to become available in Haskell, but Daan has good stuff at avail. Also, for clarity, let me just point out that this is really about an *interaction* of impredicativeness *and* type classes. Hence, I really think that an argument in favor of impredicative types is slightly overrated unless a Haskell approach to impredicativeness is fully conclusive for the type-class story. The following queries make it clear: Prelude> null [fromEnum] <interactive>:1:6: Ambiguous type variable `a' in the constraint: `Enum a' arising from use of `fromEnum' at <interactive>:1:6-13 Probable fix: add a type signature that fixes these type variable(s) Prelude> null [id] False More importantly, I need more input to fully endorse the appropriateness of impredicative types in this sort of context. That is, the question is ... what does it *mean* to wrap (or to box or to cartoon) an expression with non-escaping type variables that locally occur in type-class constraints? GHC/Haskell, as of today: - it means nothing; type error. Some sort of impredicative type: - it means universal quantification Potentially elsewhere: - it means existential quantification In Ghc with incoherent instances: - see above; except that the instance is actually selected. In addition to this scary diversity, all the three last choices are bogus in some sense because the quantified variables are totally inaccessible; so why would a type system honor such potentially accidental opaqueness. In summary, this makes me conclude that null [fromEnum] is just a really loose question to ask, which is perhaps just better rejected by a strong type system, no? Please, prove that I am wrong. :-) Ralf Oleg wrote: > When GHC does implement > MLF and start explicitly supporting impredicative types, the problem > would be fixed indeed... Currently, the only way to achieve the same > effect is to do this manually: > > newtype W = W (forall a. (Enum a) => a -> Int) > > *Main> null [W fromEnum] > False > > Perhaps indeed we should move to Cafe...

1 0

Nice way to calculate character frequency in a string
by Charles SDudu 27 Oct '05

27 Oct '05

Hello, I need to calculate the frequency of each character in a String. And if I can do this really well in C, I dont find a nice (and fast) answer in haskell. I tried several functions, listed below, and even the fastest do a lot of unnecessary things : calc :: String -> [ (Char, Int) ] -- 3.0s normally (without profiling) -- time 10-12% alloc 59% (info from profiling) -- so it's the fastest when I profile but not when I compile normally -- mutable array may be better but it's to complicated for me calc = filter (\p -> snd p > 0) . assocs . foldl (\k c -> unsafeReplace k [(fromEnum c, (unsafeAt k (fromEnum c))+1)] ) k where k = array (toEnum 0, toEnum 255) [(toEnum i, 0) | i <- [0 .. 255]] :: UArray Char Int -- 2.1s normally -- time 15-19% alloc 40% (info from profiling) -- so for true, it's the best but the sort and group probably do unnecessary things calc s = map (\l -> (head l, length l)) $ group $ sort s -- 3.4s normally -- time 58% alloc 0% (info from profiling) -- this one dont do unnecessary things but has to read the file again for each character -- calc s = map (\c -> (c, foldl (\a b -> if b==c then a+1 else a) 0 s)) $ nub s -- 22s normally -- time 85% alloc 92% (info from profiling) -- this one read the file only one time but is really slow calc = foldl (addfreq) [] where addfreq f c = let xs1 = takeWhile (\f -> fst f /= c) f xs2 = dropWhile (\f -> fst f /= c) f xs = if null xs2 then [(c,1)] else ((fst . head) xs2, (snd . head) xs2 + 1) : tail xs2 in xs1 ++ xs -- I have a lot of even slower version but I wont include them -- each compilation was done with GHC 6.4.1 with the -O flag and with -O -prof -auto-all for profiling Thanks for your answer, Charles PS : Yes, english is not my mother language... :-(

7 6

Re: Typeclasses and GADT [Was: Regular Expressions without GADTs]
by oleg＠pobox.com 27 Oct '05

27 Oct '05

Tomasz Zielonka wrote: > Speaking about casts, I was playing with using GADTs to create a > non-extensible version of Data.Typeable and Data.Dynamic. > I wonder if it's possible to write such a thing without GADTs (and > unsafeCoerce, which is used in Data.Dynamic, IIRC). Absolutely. Stephanie Weirich did that back in 2000 (actually, earlier: her paper, TypeSafe cast was presented at ICFP'00). The code does not use existentials -- only universals. BTW, if you don't plan to store your dynamics in a data structure (or plan to cast them to the same thing), then no explicit quantification is needed and the code becomes Haskell98. Here's her code for the cast, with slight embellishments. It should be pointed out that we can cast polymorphic lists and polymorphic functions. There is a different way to perform casting within a closed universe, see http://www.mail-archive.com/haskell@haskell.org/msg13089.html {-# OPTIONS -fglasgow-exts #-} module CWeirich where class CF a where cast :: CT b => a -> Maybe b class CT b where cBool :: Bool -> Maybe b cBool = const Nothing cInt :: Int -> Maybe b cInt = const Nothing cList :: CF a => [a] -> Maybe b cList = const Nothing cFun :: (CT b1, CF a2) => (b1->a2) -> Maybe b cFun = const Nothing instance CF Bool where cast = cBool instance CF Int where cast = cInt instance CF a => CF [a] where cast = cList instance (CT b1, CF a2) => CF (b1->a2) where cast = cFun instance CT Bool where cBool = Just instance CT Int where cInt = Just instance CT b => CT [b] where cList x = mapM cast x instance (CT b2, CF a1) => CT (a1->b2) where cFun f = let f' :: a1 -> Maybe b2 f' x = maybe Nothing (cast . f) (cast x) f'' x = maybe undefined id (f' x) in maybe Nothing (const $ Just f'') (f' undefined) -- This is a universal rather than existential type! data Dyn = Dyn {fromDyn :: forall b. CT b => Maybe b} toDyn :: CF a => a -> Dyn toDyn a = Dyn (cast a) td1 = toDyn True td2 = toDyn [1::Int, 2,3] td3 = toDyn not tf1 = fromDyn td1 :: Maybe Bool tf2 = fromDyn td1 :: Maybe Int tf3 = fromDyn td2 :: Maybe [Int] tf4 :: Maybe Bool = maybe Nothing (\f -> Just $ f True) (fromDyn td2) tf5 :: Maybe Bool = maybe Nothing (\f -> Just $ f True) (fromDyn td3) tf6 :: Maybe Int = maybe Nothing (\f -> Just $ f True) (fromDyn td3)

2 1

Regular Expressions without GADTs
by oleg＠pobox.com 26 Oct '05

26 Oct '05

Conor McBride wrote: > Inspired by Ralf's post, I thought I'd just GADTize a dependently typed > program I wrote in 2001. Equally inspired, I thought of deGADTizing that code. The code below also uses no existentials, and no local type annotations. The code is more general in that the parser works in an arbitrary MonadPlus. If that happens to be the List monad, we can see alternative parses. The tests illustrate alternative parses and parsing of a list of integers, for example. The code seems a bit simpler, too. {-# OPTIONS -fglasgow-exts #-} module RX where import Control.Monad -- If monadPlus is List, we can get alternative parses class RegExp t tok a | t tok -> a where parse :: MonadPlus m => t -> [tok] -> m 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 data Push tok r = Push tok r newtype Star r = Star r data Void = Void -- Parser Zero fails everywhere instance RegExp Zero tok Void where parse _ _ = mzero -- Parser One recognizes the empty string instance RegExp One tok () where parse _ [] = return () parse _ _ = mzero -- Parser (Check p) recognizes a single-element stream [tok] -- provided tok satisfies the predicate p instance RegExp (Check tok) tok tok where parse (Check p) [t] | p t = return t parse _ _ = mzero -- Parser (Push tok r) prepends tok to the stream and gets parser -- r to recognize the result instance RegExp r tok a => RegExp (Push tok r) tok a where parse (Push tok r) ts = parse r (tok:ts) -- Non-deterministic choice of parsers r1 and r2, applied to the same stream instance (RegExp r1 tok a, RegExp r2 tok b) => RegExp (Plus r1 r2) tok (Either a b) where parse (Plus r1 r2) ts = (liftM Left $ parse r1 ts) `mplus` (liftM Right $ parse r2 ts) -- Mult r1 r2: A sequence of parsers r1 and r2. -- Note the order: we search for the longest prefix of the input stream -- that satisfies the parser r1 instance (RegExp r1 tok a, RegExp r2 tok b) => RegExp (Mult r1 r2) tok (a, b) where parse (Mult r1 r2) ts@[] = liftM2 (,) (parse r1 ts) (parse r2 ts) parse (Mult r1 r2) (t:ts) = parse (Mult (Push t r1) r2) ts `mplus` liftM2 (,) (parse r1 ([] `asTypeOf` ts)) (parse r2 (t:ts)) -- Kleene's star instance RegExp r tok a => RegExp (Star r) tok [a] where parse (Star r) [] = return [] parse (Star r) ts = parse (Mult r (Star r)) ts >>= (\ (x,xs) -> return $ x:xs) p1 = (Mult (Star (Check (== 'a'))) (Star (Check (== 'b')))) asMayBe :: Maybe a -> Maybe a asMayBe = id asList :: [a] -> [a] asList = id testp = asMayBe $ parse (Star (Mult (Star (Check (== 'a'))) (Star (Check (== 'b'))))) "abaabaaabbbb" -- *RX> testp -- Just [("a","b"),("aa","b"),("aaa","bbbb")] -- see alternative parses testp1 = take 3 $ asList $ parse (Star (Mult (Star (Check (== 'a'))) (Star (Check (== 'b'))))) "abaabaaabbbb" -- Parsing the list of integers ieven = even :: Int->Bool iodd = odd :: Int->Bool p2 = Plus (Mult (Check iodd) (Mult (Check iodd) (Star (Check ieven)))) (Mult (Check ieven) (Star (Check iodd))) -- the parser is ambiguous. We can see the alternatives test2 = take 3 $ asList $ parse (Star p2) [1::Int,1,2,3,3,4]

8 10

Re: [Fwd: Re: [Haskell-cafe] Typeclasses and GADT [Was: Regular Expressions without GADTs]]
by kahl＠cas.mcmaster.ca 26 Oct '05

26 Oct '05

Tomasz Zielonka <tomasz.zielonka(a)gmail.com> wrote Wed, 26 Oct 2005 13:37:29 +0200: > > Speaking about casts, I was playing with using GADTs to create a > non-extensible version of Data.Typeable and Data.Dynamic. > I wonder if it's possible to write such a thing without GADTs (and > unsafeCoerce, which is used in Data.Dynamic, IIRC). It is possible to get even closer to Typeable by using the same interface --- which is sufficient for some applications. Otherwise, what I did recently is essentially equivalent to the ``non-Dynamic part'' of Tomasz code (and adding Dyn would of course work in the same way): Thomasz' --> attached modules ------------------------------------------------------- data Type --> data TI.TI* class Typed --> class Typeable.Typeable* newtype Wrapper* --> replaced by the ``*''s above ;-) Wolfram --[[application/octet-stream Content-Disposition: attachment; filename="TI.lhs"][quoted-printable]] %include lhs2TeX.fmt %include WKlhs.sty \section{Type Indices} %{-# OPTIONS_GHC -fglasgow-exts #-} taken out for lhs2tex \begin{code} module TI where import NatNum \end{code} For each ground type |a| constructed only from supported type constructors, there is exactly one \emph{type index} in |TI a|. In that respect, an element of |TI a| is similar to the satisfaction of the constraint |Typeable a|. The important difference between |TI a| and |Typeable a| is that structural induction over the structure of a type documented by a |TI a| contains references to the constituent types \emph{at the type level}, while structural induction over |TypeRep| representations of type structure made accessible by |Typeable a| has no connection to the type level at all. \begin{code} data TI :: * -> * where Triv :: TI () Bool :: TI Bool Char :: TI Char Nat :: TI Nat Int :: TI Int Integer :: TI Integer Float :: TI Float Double :: TI Double Apply_0 :: TI_0 t -> TI a -> TI (t a) Apply_1 :: TI_1 t -> TI_0 a -> TI (t a) \end{code} Since one of the limitations of |Data.Typeable| is its naming scheme that does not accommodate higher-kinded type constructors, we use a naming scheme that is at least somewhat open in that direction, and provide alternative names following the scheme of |Data.Typeable| as type synonyms. \begin{code} type TI1 = TI_0 type TI2 = TI_0_0 type TI3 = TI_0_0_0 \end{code} \begin{code} data TI_0 :: (* -> *) -> * where Maybe :: TI_0 Maybe List :: TI_0 [] Apply_0_0 :: TI_0_0 t -> TI a -> TI_0 (t a) \end{code} \begin{code} data TI_0_0 :: (* -> * -> *) -> * where Either :: TI_0_0 Either Pair :: TI_0_0 (,) Fct :: TI_0_0 (->) Apply_0_0_0 :: TI_0_0_0 t -> TI a -> TI_0_0 (t a) \end{code} \begin{code} data TI_0_0_0 :: (* -> * -> * -> *) -> * where Tup3 :: TI_0_0_0 (,,) \end{code} Just to demonstrate a higher-order kind in this context, we define the datatype recursion type constructor. \begin{code} data TI_1 :: ((* -> *) -> *) -> * where Fix :: TI_1 DFix data DFix f = DFix (f (DFix f)) \end{code} Defining type index equality without requiring identical types makes the implementation of the cast functions much easier. \begin{code} eqTI :: TI a -> TI b -> Bool eqTI Triv Triv = True eqTI Bool Bool = True eqTI Char Char = True eqTI Nat Nat = True eqTI Int Int = True eqTI Integer Integer = True eqTI Float Float = True eqTI Double Double = True eqTI (Apply_0 t a) (Apply_0 t' a') = eqTI_0 t t' && eqTI a a' eqTI (Apply_1 t a) (Apply_1 t' a') = eqTI_1 t t' && eqTI_0 a a' eqTI _ _ = False \end{code} \begin{code} eqTI_0 :: TI_0 t -> TI_0 t' -> Bool eqTI_0 Maybe Maybe = True eqTI_0 List List = True eqTI_0 (Apply_0_0 t a) (Apply_0_0 t' a') = eqTI_0_0 t t' && eqTI a a' eqTI_0 _ _ = False \end{code} \begin{code} eqTI_1 :: TI_1 t -> TI_1 t' -> Bool eqTI_1 Fix Fix = True eqTI_1 _ _ = False \end{code} \begin{code} eqTI_0_0 :: TI_0_0 t -> TI_0_0 t' -> Bool eqTI_0_0 Either Either = True eqTI_0_0 Pair Pair = True eqTI_0_0 Fct Fct = True eqTI_0_0 _ _ = False \end{code} %{{{ EMACS lv % Local Variables: % folded-file: t % fold-internal-margins: 0 % eval: (fold-set-marks "%{{{ " "%}}}") % eval: (fold-whole-buffer) % end: %}}} --[[application/octet-stream Content-Disposition: attachment; filename="Typeable.lhs"][quoted-printable]] %include lhs2TeX.fmt %include WKlhs.sty \section{Home-made |Typeable|} %{-# OPTIONS_GHC -fglasgow-exts #-} taken out for lhs2tex \begin{code} module Typeable where import NatNum import TI import GHC.Base ( unsafeCoerce# ) \end{code} This module is currently happily restricting itself to Glasgow Haskell. Many things that are done in a more portable way in |Data.Typeable| are done in a more concise, but GHC-specific way here. The following function is GHC-specific: \begin{code} unsafeCoerce :: a -> b unsafeCoerce = unsafeCoerce# \end{code} For the tyme being, we only go to |Typeable3|, while |Data.Typeable| goes all the way to |Typeable7|. \begin{code} class Typeable a where typeIndex :: a -> TI a class Typeable1 t where typeIndex1 :: t a -> TI1 t class Typeable2 t where typeIndex2 :: t a b -> TI2 t class Typeable3 t where typeIndex3 :: t a b c -> TI3 t \end{code} We shamelessly use scoped type variables to abbreviate the |cast| and |gcast| definitions, which otherwise correspond directly to those from |Data.Typeable|. \begin{code} cast :: (Typeable a, Typeable b) => a -> Maybe b cast x :: Maybe b = if typeIndex x `eqTI` typeIndex (undefined :: b) then Just $ unsafeCoerce x else Nothing \end{code} \begin{code} gcast :: (Typeable a, Typeable b) => c a -> Maybe (c b) gcast (x :: c a) :: Maybe (c' b) = if typeIndex (undefined :: a) `eqTI` typeIndex (undefined :: b) then Just $ unsafeCoerce x else Nothing \end{code} \begin{code} gcast1 :: (Typeable1 t, Typeable1 t') => c (t a) -> Maybe (c (t' a)) gcast1 (x :: c (t a)) :: Maybe (c' (t' a')) = if typeIndex1 (undefined :: t a) `eqTI_0` typeIndex1 (undefined :: t' a) then Just $ unsafeCoerce x else Nothing \end{code} \begin{code} gcast2 :: (Typeable2 t, Typeable2 t') => c (t a b) -> Maybe (c (t' a b)) gcast2 (x :: c (t a b)) :: Maybe (c' (t' a' b')) = if typeIndex2 (undefined :: t a b) `eqTI_0_0` typeIndex2 (undefined :: t' a b) then Just $ unsafeCoerce x else Nothing \end{code} %{{{ automatic instances For the automatic instances, the machinery from |Data.Typeable| can easily be adapted. \begin{code} instance (Typeable1 s, Typeable a) => Typeable (s a) where typeIndex = typeIndexDefault instance (Typeable2 s, Typeable a) => Typeable1 (s a) where typeIndex1 = typeIndex1Default instance (Typeable3 s, Typeable a) => Typeable2 (s a) where typeIndex2 = typeIndex2Default \end{code} \begin{code} -- | For defining a 'Typeable' instance from any 'Typeable1' instance. typeIndexDefault :: (Typeable1 t, Typeable a) => t a -> TI (t a) typeIndexDefault (x :: t a) = typeIndex1 x `Apply_0` typeIndex (undefined :: a) -- | For defining a 'Typeable1' instance from any 'Typeable2' instance. typeIndex1Default :: (Typeable2 t, Typeable a) => t a b -> TI_0 (t a) typeIndex1Default (x :: t a b) = typeIndex2 x `Apply_0_0` typeIndex (undefined :: a) -- | For defining a 'Typeable2' instance from any 'Typeable3' instance. typeIndex2Default :: (Typeable3 t, Typeable a) => t a b c -> (TI_0_0 (t a)) typeIndex2Default (x :: t a b c) = typeIndex3 x `Apply_0_0_0` typeIndex (undefined :: a) \end{code} %}}} %{{{ standard library instances With our standard library instances we are obviously restricted to the types covered by |TI|. \begin{code} instance Typeable () where typeIndex _ = Triv instance Typeable Bool where typeIndex _ = Bool instance Typeable Char where typeIndex _ = Char instance Typeable Nat where typeIndex _ = Nat instance Typeable Int where typeIndex _ = Int instance Typeable Integer where typeIndex _ = Integer instance Typeable Float where typeIndex _ = Float instance Typeable Double where typeIndex _ = Double instance Typeable1 Maybe where typeIndex1 _ = Maybe instance Typeable1 [] where typeIndex1 _ = List instance Typeable2 Either where typeIndex2 _ = Either instance Typeable2 (,) where typeIndex2 _ = Pair instance Typeable2 (->) where typeIndex2 _ = Fct \end{code} %}}} %{{{ EMACS lv % Local Variables: % folded-file: t % fold-internal-margins: 0 % eval: (fold-set-marks "%{{{ " "%}}}") % eval: (fold-whole-buffer) % end: %}}} --[[application/octet-stream Content-Disposition: attachment; filename="GCast.lhs"][quoted-printable]] %include lhs2TeX.fmt %include WKlhs.sty \section{Minimal Interface Providing Generic Cast} This module provides a minimal interface to |gcast| since this is all that is really required by many applications of |Typeable| and friends. Isolating this interface makes it easier to switch between different implementations. %{-# OPTIONS_GHC -fglasgow-exts #-} taken out for lhs2tex \begin{code} module GCast ( Typeable() , Typeable1() , Typeable2() , Typeable3() , cast , gcast , gcast1 , gcast2 ) where -- import Data.Typeable import Typeable \end{code} %{{{ EMACS lv % Local Variables: % folded-file: t % fold-internal-margins: 0 % eval: (fold-set-marks "%{{{ " "%}}}") % eval: (fold-whole-buffer) % end: %}}} --[[application/octet-stream Content-Disposition: attachment; filename="NatNum.lhs"][quoted-printable]] \section{Inductive Definition of Natural Numbers} \begin{code} module NatNum where import Data.Typeable data Nat = Zero | Succ deriving Typeable \end{code}

2 2

RE: [Haskell-cafe] Help using QuickCheck
by Simon Peyton-Jones 26 Oct '05

26 Oct '05

I'm afraid this fix didn't make it into the 6.4 branch, but the double error (which is bad) is certainly fixed in the HEAD Simon | -----Original Message----- | From: haskell-cafe-bounces(a)haskell.org [mailto:haskell-cafe-bounces@haskell.org] On Behalf Of | Andrew Pimlott | Sent: 21 October 2005 20:45 | To: haskell-cafe(a)haskell.org | Subject: Re: [Haskell-cafe] Help using QuickCheck | | On Fri, Oct 21, 2005 at 09:09:41PM +0200, Benjamin Franksen wrote: | > Many thanks! I wish I had remembered that I had this kind of problem | > before: ghc reports two errors, of which the /second/ one is the 'real' | > problem and the first one is just a by-product. | | The case in your original message is particularly annoying, but at least | it only affects ghci. I thought it had been fixed[1], but it is still | present in 6.4.1, so perhaps it's waiting for 6.5? | | > This practically never | > happens with C compilers which I (must, sadly) use every day and thus I | > always tend to disregard all error messages but the first. | | I generally find that most of GHC's errors are real, ie they don't | change much when I fix earlier errors. (It seems to report only one | error per function to achieve that?) It's fun to work through the dozen | reported mistakes, then compile again to see how many I actually fixed. | :-) | | Andrew | | [1] | http://sourceforge.net/tracker/index.php?func=detail&aid=1156554&group_i d=8032&atid=108032 | _______________________________________________ | Haskell-Cafe mailing list | Haskell-Cafe(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe

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RE: [Haskell-cafe] Template Haskell -- Bug?
by Simon Peyton-Jones 26 Oct '05

26 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' I've now fixed this bug, in the HEAD. The fix will appear in 6.4.2 (if we release that). Thanks for reporting it. Simon

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Fwd: [Haskell-cafe] Parsing in Practice
by Tomasz Zielonka 26 Oct '05

26 Oct '05

[Sending it again to haskell-cafe] On 10/18/05, Tom Hawkins <tom(a)confluent.org> wrote: > I am writing a parser for a big, ugly, standard language and I need to > decide between using either Happy or Parsec. I wrote a parser for a big, ugly, non-standard language - Transact-SQL from MSSQL. > I currently have a priliminary LALR(1) grammar, so a port to Happy would > be relatively easy. In such situation I would try Happy first, but with some cautiousness. I also started with LALR(1) parsing in ocamlyacc, but I didn't manage to cover the whole language with this approach. The more productions I added the more conflicts I had. Of course I tried to remove the conflicts, but often when I added new productions I had to repeat the work. It is possible that my understanding of LALR parsing was insufficient, but the problem is that the set of LALR grammars is not closed under composition (as I've read in some paper on GLR parsing). Do you know that Happy supports GLR parsing? > But, I'm wondering if life would be easier if I chose Parsec's combinator > parsing instead. >From my experience it was indeed quite nice. However, there were some parts of the grammer that I didn't know how to handle without using "try", which could result in worse efficiency and error reporting. > It's error reporting seems to be top notch So long as you can avoid using "try" for non-terminals. > and it's "optional", "many", and "sepBy1" combinators are very elegant. Indeed they are, as they correspond nicely to E in EBNF ;-) > However, I have a few concerns with Parsec. First is performance; what > factor of slow-down should I expect? I only have a Parsec parser, so I can't compare. I dimly remember that my parser had an average efficiency, ie. it could parse about 100kB per second on P3 850. There is a parser-combinator version of a parser for Haskell which you could compare to the one from GHC. > 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? I always feared that this would be a problem, but it wasn't. I used a sample of about 1MB of application code to test, and I didn't get to using QuickCheck. > Even though I hate debugging LALR(1) parsing ambiguities, > it prevents problems. Yes, when you fight the conflicts, you get static guarantees in return. I wonder how it is with GLR? Best regards Tomasz

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Re: [Haskell-cafe] Nice way to calculate character frequency in a string
by Charles SDudu 25 Oct '05

25 Oct '05

It seems like the fastest way to build a list of frequency from a string is this : import Data.Array (assocs, accumArray, Array) frequency :: String -> [(Char,Int)] frequency = filter (\f -> snd f>0) . assocs . accumArray (+) 0 ('\0', '\255') . map (\x->(x,1)) -- (~1.3 sec on a string of 700ko) But if we want to make this polymorphic we have to do this : import Data.Ix (Ix) frequency :: (Ix a, Bounded a) => [a] -> [(a,Int)] frequency = filter (\f -> snd f>0) . assocs . accumArray (+) 0 (minBound, maxBound) . map (\x->(x,1)) -- (>5 sec on a string of 700ko) but it's really much slower, it seems like min/maxBound are check each time or I dont know, and it's restrictive on the type of the elements of the list. The best polymorphic version seems to be : import Data.Map as Map (lookup, assocs, empty, insertWith) frequency :: (Ord a) => [a] -> [(a,Int)] frequency xs = Map.assocs $ foldl f Map.empty xs where f m x = let m' = Map.insertWith (+) x 1 m Just v = Map.lookup x m' in seq v m' -- (~2.1 sec on a string of 700ko) Which is not as fast as the specialized version on string, but really faster and less restrictive than the second. Thanks everyone for all your answers ! Charles

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REMINDER: Contributions to the HC&A Report (November 2005 edition)
by Andres Loeh 25 Oct '05

25 Oct '05

Dear Haskellers, the deadline for the November 2006 edition of the Haskell Communities and Activities Report is only a few days away -- but this is still enough time to make sure that the report contains a section on *your* project, on the interesting stuff that you've been doing; using or affecting Haskell in some way. Many projects that have been included in former reports have not yet updated their entries. Please have a look at http://haskell.org/communities/topics.html and at the May 2005 edition for reference. * Has your project been listed in previous Reports, but is not yet updated? Please write a short update! * Are you no longer working on a project that was included in the Report? Write up what you are working on instead, and tell me if someone else has picked up the project. * Is some project you have heard about not included in any previous Report? Please let me know ... There is still time to write a completely new entry, on a new compiler, tool, library, company, user group, idea, ... -- as long as there is a connection to the Haskell language, there is a place for it in the Report! Submissions are due by next Tuesday, that is Tuesday, 01 November 2005. Please mail your entries to <hcar at haskell dot org>, in plain text or pseudo-(La)TeX format. More information can be found in the original Call for Contributions at http://www.haskell.org/pipermail/haskell/2005-October/016575.html I look forward to receiving your contributions. Thanks a lot, Andres (current editor) -- Haskell Communities and Activities Report (http://haskell.org/communities) 11/2005 edition submission deadline: 01 November 2005 <hcar(a)haskell.org>

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lockFile: fd out of range
by Joel Reymont 25 Oct '05

25 Oct '05

Folks, Is there a set limit on the number of file descriptors that a Haskell program can open? I'm using hs-plugins on FreeBSD to transparently compile, load and launch scripts that establish a connection to a server. I'm getting this error: internal error: lockFile: fd out of range Please report this as a bug to glasgow-haskell-bugs(a)haskell.org, or http://www.sourceforge.net/projects/ghc/ Thanks, Joel -- http://wagerlabs.com/

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Re: Nice way to calculate character frequency in a string
by Scherrer, Chad 25 Oct '05

25 Oct '05

> Hello, I need to calculate the frequency of each character in a > String. And if I can do this really well in C, I don't find a nice (and > fast) answer in haskell. I tried several functions, listed below, and > even the fastest do a lot of unnecessary things : A while back, I was trying to build a "table" function similar to what you describe, and Dean Herrington helped me speed it up and stop the stack overflows I had been getting. Here it is, in case this is useful to you... table :: (Ord a) => [a] -> [(a,Int)] table xs = Map.assocs $! foldl' f Map.empty xs where f m x = let m' = Map.insertWith (+) x 1 m Just v = Map.lookup x m' in v `seq` m' I would be interested in whether this is much slower than the other approaches you've tried. If a faster approach could be made polymorphic, I'd have a faster way to build tables! Chad Scherrer Computational Mathematics Group Pacific Northwest National Laboratory "Time flies like an arrow; fruit flies like a banana." -- Groucho Marx

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RE: [Haskell-cafe] Nice way to calculate character frequency inastring
by Simon Peyton-Jones 25 Oct '05

25 Oct '05

| > Better still, help us make it faster! | > | > Simon | | What can your average Haskell user do to help other than | point out things they don't like? Well-characterised test cases are always motivating: small programs that should go fast, and don't. Why does the brain-twisting version work fast, and the obvious code go slow. Ian Lynagh's recent message was a good example [although I'm afraid we have still not done anything about it] http://urchin.earth.li/~ian/bench/bench-0.2/ghc-6.4.1.html. The next step is to look at the intermediate code that GHC produces, and try to see what's different about the good and bad version. Sometimes, as Simon M's recent message mentioned, there are things that aren't easy to change, like auto-unboxing of arrays. Other times there are just missing SPECIALISE pragmas and the like. The more the problem is characterised, the more likely we are to do something about it. Simon

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Re: [Haskell-cafe] Nice way to calculate character frequency in a string
by Jon Fairbairn 25 Oct '05

25 Oct '05

On 2005-10-25 at 13:42+0200 "Charles SDudu" wrote: > > okay, it took me some time to make your solution work, but it's as fast as > the precedent solution, and really more elegant. Thank you, but I dont know > how to structure the function, see yourself : > > calc str = filter (\p -> snd p > 0) $ assocs $ ((accumArray (+) 0 (toEnum 0, > toEnum 255) (map (\x->(x,1)) str)) :: UArray Char Int) > > It's not so nice but it works, isn't there a solution to put the type > elsewhere, and another type than UArray ? Well, you can do this: import Array calc::String->[(Char, Int)] calc = filter (\p-> snd p > 0) . assocs . accumArray (+) 0 (minBound, maxBound) . (map (\x->(x,1))) You can import whatever sort of array you want, so long as it has assocs and accumArray. You don't want to change minBound and maxBound to toEnum x, since they are the bounds of Char, which might or might not be 0 and 255. Jón -- Jón Fairbairn Jon.Fairbairn at cl.cam.ac.uk

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RE: [Haskell-cafe] Nice way to calculate character frequency in astring
by Simon Marlow 25 Oct '05

25 Oct '05

On 25 October 2005 11:59, Jon Fairbairn wrote: > On 2005-10-25 at 12:20+0200 Lemmih wrote: >> On 10/25/05, Charles SDudu <iwin_1(a)hotmail.com> wrote: >>> Hello, I need to calculate the frequency of each >>> character in a String. And if I can do this really well >>> in C, I dont find a nice (and fast) answer in haskell. I >>> tried several functions, listed below, and even the >>> fastest do a lot of unnecessary things : >>> >>> calc :: String -> [ (Char, Int) ] >>> calc = filter (\p -> snd p > 0) . assocs . >>> foldl (\k c -> unsafeReplace k [(fromEnum c, >>> (unsafeAt k (fromEnum c))+1)] ) k where k = array >>> (toEnum 0, toEnum 255) [(toEnum i, 0) | i <- [0 .. 255]] >>>>> UArray Char Int > > [snip even more disagreable code] > > Ugh! These are all horrid. If something on the lines of > >> calc = accumArray (+) 0 (minBound, maxBound) . (map (\x->(x,1))) > > isn't fast enough, complain to the implementors! What's the > point of functional programming if one has to twist into a > shape that allows inspection of one's own fundament to get > stuff to run in decent time? To make that go fast, you'd want to use a UArray. Could the compiler figure this out for itself? Not really, it might be able to figure out certain special cases where changing an Array to a UArray doesn't affect the semantics, but not in general (and GHC certainly makes no attempt to do it). Sometimes, you just need to give the compiler a bit of help. And you really want to read the file as a packed string, not a String. Or hope that GHC manages to deforest calc with whatever is generating the String. It's possible that calc deforests, but highly unlikely that hGetContents does, so I'm afraid you'll have to do the packed string conversion yourself. To make it go even faster, you need to inline & specialise accumArray. I'm not sure how much of this GHC currently does. Cheers, Simon

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RE: [Haskell-cafe] Nice way to calculate character frequency in astring
by Simon Peyton-Jones 25 Oct '05

25 Oct '05

| Ugh! These are all horrid. If something on the lines of | | > calc = accumArray (+) 0 (minBound, maxBound) . (map (\x->(x,1))) | | isn't fast enough, complain to the implementors! What's the | point of functional programming if one has to twist into a | shape that allows inspection of one's own fundament to get | stuff to run in decent time? I agree. Better still, help us make it faster! Simon

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RE: [Haskell-cafe] Safe FFI calls, -threaded and killThread
by Simon Marlow 25 Oct '05

25 Oct '05

On 25 October 2005 09:07, Einar Karttunen wrote: > I noticed that killThread in GHC behaves in a problematic fashion with > -threaded when the killed thread is in a midle of performing a safe > FFI call. If the behaviour (blocking until the call is done) is > intended adding documentation might be nice. > > The example below demonstrates the problem. Tthe program gets stuck > in the killThread call which is not very intuitive. Wrapping every > killThread in forkIO does not sound very nice either. > > - Einar Karttunen > > import Control.Concurrent > import Foreign.C > > foreign import ccall threadsafe "sleep" sleep :: CInt -> IO CInt > > main = do mv <- newEmptyMVar > tid <- forkIO $ sleep 100 >> putMVar mv () > threadDelay 10000 > e <- isEmptyMVar mv > if e then do putStrLn "killing sleeper" > killThread tid > putStrLn "done" > else do putStrLn "sleeper already done" This is correct, I'll document the behaviour. killThread/throwTo is currently synchronous - that is, it blocks until the exception has been delivered to the target thread (unlike the version in our PLDI paper which was non-blocking, IIRC). A non-blocking version can easily be constructed by using forkIO, as you noted. We can't kill a thread that is involved in a safe foreign call, because we have no control over the thread involved in the call. This is the really the only sensible behaviour. In the case of an unbound Haskell thread it would be possible to kill the Haskell thread while leaving the foreign call running, but this can't be done if the Haskell thread is bound (because the OS thread it is bound to is currently running foreign code). Cheers, Simon

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Safe FFI calls, -threaded and killThread
by Einar Karttunen 25 Oct '05

25 Oct '05

Hello I noticed that killThread in GHC behaves in a problematic fashion with -threaded when the killed thread is in a midle of performing a safe FFI call. If the behaviour (blocking until the call is done) is intended adding documentation might be nice. The example below demonstrates the problem. Tthe program gets stuck in the killThread call which is not very intuitive. Wrapping every killThread in forkIO does not sound very nice either. - Einar Karttunen import Control.Concurrent import Foreign.C foreign import ccall threadsafe "sleep" sleep :: CInt -> IO CInt main = do mv <- newEmptyMVar tid <- forkIO $ sleep 100 >> putMVar mv () threadDelay 10000 e <- isEmptyMVar mv if e then do putStrLn "killing sleeper" killThread tid putStrLn "done" else do putStrLn "sleeper already done"

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RE: [Haskell-cafe] Template Haskell -- Bug?
by Simon Marlow 24 Oct '05

24 Oct '05

On 20 October 2005 14:03, Gracjan Polak wrote: > $ 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 Please try again with 6.4.1; lots of bugs were fixed. Cheers, Simon

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Help using QuickCheck
by Benjamin Franksen 23 Oct '05

23 Oct '05

Hello All, I am asking help with using QuickCheck. I tried everything I could think of, but invariably as soon as I start invoking the quickCheck function on my property it fails with *Data.FingerSearchTreeUtil> Top level: No instance for (Show (IO ())) arising from use of `print' at Top level Probable fix: add an instance declaration for (Show (IO ())) In a 'do' expression: print it <interactive>:1:0: No instances for (Arbitrary (OrdSeq Int), Show (OrdSeq Int)) arising from use of `quickCheck' at <interactive>:1:0-20 Probable fix: add an instance declaration for (Arbitrary (OrdSeq Int), Show (OrdSeq Int)) In the definition of `it': it = quickCheck prop_DeleteInsert The property is quite a simple one: prop_DeleteInsert x xs = delete x (insert x xs) == xs where types = xs :: OrdSeq Int My code compiles just fine with ghc. I tried some examples from the QuickCheck manual and these seem to work; at least I get the expected "OK, passed 100 tests.". What am I doing wrong? Besides, there are some really non-obvious quirks with QuickCheck. For instance, the following one caused me some headache: I downloaded the haskell script 'quickCheck' and modified the line where ghci is executed like this: system ("/usr/bin/ghci -cpp -package QuickCheck "++options opts'++" <hugsin") (I am using ghc 6.4.1, btw). Running 'quickCheck Data/FingerSearchTreeUtil.hs' gives me: <interactive>:1:0: Failed to load interface for `QuickCheck': Could not find module `QuickCheck': it is a member of package util-1.0, which is hidden Strange. Replacing 'ChickCheck' with 'util' gives me the above error message about "No instance for (Show (IO ()))..." Ben

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RE: [Haskell-cafe] FastString a misnomer
by Simon Marlow 22 Oct '05

22 Oct '05

On 21 October 2005 02:53, Donald Bruce Stewart wrote: > john: >> On Thu, Oct 20, 2005 at 10:45:28AM +0100, Simon Marlow wrote: >>> I think when this is ready it should replace Data.PackedString. >>> >>> I don't necessarily mean put it into fptools/libraries/base - we >>> could just remove the existing Data.PackedString from there and >>> your separate package can provide Data.PackedString. That is, >>> unless we decide to use it in GHC in some way, in which case we'll >>> have to pull (a copy of) it into fptools/libraries. >> >> We should make 'PackedString' the UTF8 wrapper though and provide >> Data.ByteArray as a separate library. If it has string in the name, >> one should be able to replace strings with it everywhere and expect >> the right thing to happen as enforced by the type system. that and >> C's conflation of characters and bytes and Haskell 98s lack of >> clearing up the issue has been a huge pet peeve of mine. > > Ok, so a rough structure of the final lib would be: > > Data Data System > | | | > ByteArray (?) PackedString Posix > | | | > UTF8 Latin1 ... MMap (providing > mmapFile :: FilePath -> ByteArray) Remind me what Data.ByteArray is for? Seems like it would overlap a lot with Data.PackedString.Latin1 and UArray Word8. We should have Data.PackedString.UTF16 too; it'll make interoperating with Win32 APIs easier as Bulat pointed out. I like John Meacham's suggestion of changing the UTF8 representation to include a count of characters as well as bytes. I'm not volunteering to do it, just adding my "+1" in case anyone else wanted to :-) Cheers, Simon

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RE: [Haskell-cafe] FPS lib
by Simon Marlow 22 Oct '05

22 Oct '05

On 19 October 2005 01:08, Donald Bruce Stewart wrote: > However, on my machine: > > OpenBSD/Pentium-M 1.6G/ghc-6.5 -O > Elapsed time: FPS Simon's PackedString > Krasimir's test1 1.966s (40M) 2.151s (36M) > 2.235s (36M) test2 6.048s (24M) 3.160s (73M) > 2.318s (39M) > > Which is basically what I expected. Though perhaps I need to improve > concat (we currently do things a little strangely in concat, due to > the darcs legacy), but pack itself is nice and fast. > > Linux/Pentium 4 3.6G/ghc-6.4.1 -O > test1 35.37s 30.97s 2.180s > test2 90.93s 60.55s 1.916s > > Ah!! So what's going on on Linux, I wonder. Could it be something > about > 6.4.1? Are we seeing the difference between ForeignPtrs from 6.4 to > 6.5? I will investigate. I bet that's the difference between ForeignPtrs in 6.4.1 and 6.5. I'm very tempted to merge the ForeignPtr optimisations into 6.4.2, so we can benefit from this earlier. The changes are all confined to one module (GHC/ForeignPtr.hs). BTW, concat isn't optimised in my library. It's defined like this: concat pss = pack $ Prelude.concat $ Prelude.map unpack pss which is why I'm not winning this benchmark :) > I'd be very wary of switching entirely to non-portable ghc > primop-based code, as FPS already run ons hugs and I think nhc. Yes, I think the benchmarks will ultimately show that using ByteArray# isn't worth much, if any, performance gain. Cheers, Simon

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RE: [Haskell-cafe] FastString a misnomer
by Simon Marlow 21 Oct '05

21 Oct '05

On 20 October 2005 09:48, Donald Bruce Stewart wrote: > bulatz: >> Hello John, >> >> Thursday, October 20, 2005, 4:12:36 AM, you wrote: >> >>> FastString seems to be a misnomer for this library. >> >>> what it provides is a fast _byte array_ with a lot of useful >>> operations, but it does not provide strings since it does not >>> enforce character encodings in the type system, which would be >>> vital for a real FastString library. In any case, just had to get >>> that off my chest :) >> >> may be it can be named ByteArray? and then FastString.Latin1, >> FastString.UTF8... will use its utilities >> >> also, all UTF8 utilities may be placed outside of FastString.UTF8 >> module, because it can be used for something else >> >> btw, FastString is also a bit misnamed. it's really a CompactString. >> ghc's FastString was named so, imho, just because they provided >> hashes for fast string comparision > > Well, it's a PackedString really, isn't it? I changed it to FastString > after too many people grumbled about colliding with the existing > PackedString. I think when this is ready it should replace Data.PackedString. I don't necessarily mean put it into fptools/libraries/base - we could just remove the existing Data.PackedString from there and your separate package can provide Data.PackedString. That is, unless we decide to use it in GHC in some way, in which case we'll have to pull (a copy of) it into fptools/libraries. Cheers, Simon

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