Re: [Haskell-cafe] Re: Problems with Haskell Platform
On Jun 3, 2010, at 20:27 , Jens Petersen wrote: I often find myself hitting Ctrl-C at cabal install HACKAGE to run yum install ghc-DEPENDENCY-devel and before returning to run cabal install again. It would be nice to automate this in some way - cabal-install plugins, anyone?? Supposedly a future Cabal extension will be to, instead of installing, write out a package for a vendor packaging system (yum, apt, yast, what have you). Consider contributing to that effort. -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allb...@kf8nh.com system administrator [openafs,heimdal,too many hats] allb...@ece.cmu.edu electrical and computer engineering, carnegie mellon universityKF8NH PGP.sig Description: This is a digitally signed message part ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Efficient string construction
Daniel Fischer daniel.is.fisc...@web.de writes: So why is there a UTF8 implementation for bytestrings? Does that not duplicate what Text is trying to do? If so, why the duplication? I think Data.ByteString.UTF8 predates Data.Text. One difference is that Data.Text uses UTF-16 internally, not UTF-8. When is each library more appropriate? Much data is overwhelmingly ASCII, but with an option for non-ASCII in comments, labels, or similar. E.g., for biological sequence data, files can be large (the human genome is about 3GB) and non-ascii characters can only occur in sequence headers which constitute a miniscule fraction of the total data. So I use ByteString for this. -k -- If I haven't seen further, it is by standing in the footprints of giants ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ICFP Programming Contest
This year's ICFP Programming Contest will begin on June 18th (12:00 Noon GMT) and will run till June 21st (12:00 Noon GMT). As in the previous editions, this is your chance to show that your favorite programming language is better than all others! The problem statement and further information will become available at: http://icfpcontest.org/2010/ Feel free to contact ifcpcont at imn dot htwk-leipzig dot de for further questions. Good luck! Wouter ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Problems with Haskell Platform
allbery: On Jun 3, 2010, at 20:27 , Jens Petersen wrote: I often find myself hitting Ctrl-C at cabal install HACKAGE to run yum install ghc-DEPENDENCY-devel and before returning to run cabal install again. It would be nice to automate this in some way - cabal-install plugins, anyone?? Supposedly a future Cabal extension will be to, instead of installing, write out a package for a vendor packaging system (yum, apt, yast, what have you). Consider contributing to that effort. However, we have tools for some distros that do this, and some distro tools support it directly (e.g. bauerbill --hackage on Arch Linux knows how to ask cabal2arch to translate the .cabal file). Contribut to yum to allow pulling from hackage, by calling cabal2yum? -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell opportunity at investment bank
Hello, I'm looking for a developer with expertise in Haskell for an investment bank in London. The role will involve working on a multi-asset, multi-region, pricing, risk and trade lifecycle solution for the wholesale banking division. Solutions are developed using Java, C#/WPF, C++ and make heavy use of Haskell. The requirement is for an experienced developer with in-depth knowledge of functional programming in Haskell - ideally in a commercial environment. If interested, please feel free to send your CV through or call me to discuss. Thanks, Chris Pearse 0207 469 5050 http://www.linkedin.com/pub/3/9a1/142 --- Huxley Associates - Professional Recruitment Solutions Established in 1995, Huxley Associates is an international recruitment consultancy. We provide bespoke recruitment services to the Accountancy Finance, Banking Technology, Energy, Engineering, Global Markets, Human Resources, IT, Oil Gas, Sales Marketing, and Supply Chain sectors. With over 400 specialist recruitment professionals, we are consistently able to meet the high recruitment needs of a diverse range of companies across the UK, Europe, Asia and the United States. This email message may contain confidential and/or privileged information, and is intended solely for the addressee(s). If you have received this email in error, please notify Huxley Associates immediately. Unauthorised copying, disclosure or distribution of the material in this email is forbidden. If you do not want to receive emails from us about our services in future, or if you want to query or qualify how your personal data is held by us (for details on this see our privacy statement http://www.huxley.co.uk/privacy_policy.html ) please e-mail audit.d...@huxley.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Efficient string construction
On Friday 04 June 2010 00:41:58, Bryan O'Sullivan wrote:
On Thu, Jun 3, 2010 at 9:16 AM, Daniel Fischer
daniel.is.fisc...@web.dewrote:
String can be quite memory efficient. As a stupid example,
length (replicate 1000 'a')
will need less memory than the equivalents using ByteString or Text.
Actually, this will be fused with Data.Text, and should execute more
quickly and in less space than String.
Right, forgot about fusion. However, that requires the code to be compiled
with optimisations, I think (well, one should never compile ByteString or
Text code without).
In which case
{-# RULES
length/replicate forall n x. length (replicate n x) = max 0 n
#-}
would be at least as good as the Data.Text thing ;)
Or, to be more fair, if you use Data.List.Stream, it should be fused too
and be equally efficient as Data.Text.
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Fwd: [Haskell-cafe] Weird socket problem on Mac OS X
-- Forwarded message --
From: Arnaud Bailly arnaud.oq...@gmail.com
Date: Fri, Jun 4, 2010 at 11:59 AM
Subject: Re: [Haskell-cafe] Weird socket problem on Mac OS X
To: Antoine Latter aslat...@gmail.com
Hello,
I managed to solve the problem using Network.Socket instead of
Network. Is this a bug or a feature ?
Arnaud
On Fri, Jun 4, 2010 at 7:11 AM, Arnaud Bailly arnaud.oq...@gmail.com wrote:
Yes, I have also seen the other post on the same topic, but it seemed
to refer to the PortNumber in Network.Socket with a PortNum
constructor I think, not the one in Network (but I am probably
misleading myself as one is a reexportation of the other...).
But then I got.
Slim\SlimClientIO.hs:26:51:
No instance for (Num PortID)
arising from a use of `fromInteger'
at Slim\SlimClientIO.hs:26:51-61
Possible fix: add an instance declaration for (Num PortID)
In the first argument of `($)', namely `fromInteger'
In the expression: fromInteger $ slimport $ slimConfig st
In the definition of `port':
port = fromInteger $ slimport $ slimConfig st
:-(
Thanks
Arnaud
On Fri, Jun 4, 2010 at 1:46 AM, Antoine Latter aslat...@gmail.com wrote:
Hi Arnaud,
One thing you might want to try is to stop using the PortNumber data
constructor, and instead rely on 'fromInteger' to do the right thing.
The data constructor assumes that it's argument is in network byte order,
which won't always be the case.
It's not obvious that the constructor should be avoided - this is the second
time today I've seen this!
Take care,
Antoine
On Jun 3, 2010 5:13 PM, Arnaud Bailly arnaud.oq...@gmail.com wrote:
Hello,
I have the following code which works ok on Linux and Windows XP, but
fails on Mac OS X with error message:
Connect: does not exist (connection refused)
The server:
doStartstate = do pr - liftIO $ runProcess ...
liftIO $ threadDelay 50
st - get
put st { slimHandle = Just pr }
The client:
fetchAnswers st msgs = liftIO $! do let port = PortNumber $
fromInteger $ port $ config st
cnx - connectTo localhost port
Help most welcome, thanks
Arnaud
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Re: [Haskell-cafe] Re: Problems with Haskell Platform
Don Stewart d...@galois.com writes: allbery: Supposedly a future Cabal extension will be to, instead of installing, write out a package for a vendor packaging system (yum, apt, yast, what have you). Consider contributing to that effort. However, we have tools for some distros that do this, and some distro tools support it directly (e.g. bauerbill --hackage on Arch Linux knows how to ask cabal2arch to translate the .cabal file). Contribut to yum to allow pulling from hackage, by calling cabal2yum? In general, I think this is a bad idea. I don't know how it is in Arch, but for Gentoo we need to do a lot of QA'ing to make sure our ebuilds generated with hackport work properly (which is one reason why we don't churn ebuilds out as fast as you generate PKBUILDs). Part of the problem is probably that hackport isn't as polished as cabal2arch, but a few other concerns we need to take care of are: 1) Gentoo has categories for packages; whilst for Haskell stuff we can usually correctly guess dev-haskell/ as the category, there are a few exceptions (e.g. pandoc is in app-text/). This is an even bigger problem when dealing with C deps, etc. 2) Dealing with flags: in most cases, we expose the Cabal flags as USE flags, so we need to take care of getting all those dependencies right. 3) Multiple versions: we have to take care of supporting multiple versions of GHC, as well as different versions of QuickCheck, etc. It doesn't help that due to the limitations of portage, Gentoo ebuilds do not support proper ranged dependencies. However, this is most probably not an issue for most distributions where users get given one version of a specific package and they'll shut up and accept it. 4) It has to build always: related to the above, because we don't provide binaries, we have to ensure that packages are built reliably in a multitude of situations. We recently had the situation where for some reason GHC 6.12.2 would build for someone but then wouldn't actually run; we eventually tracked down the problem to his usage of ccache: as of 6.12.2, the GHC wrapper script hardcodes which C compiler it was built with, and as ccache was only used when building packages the path to the C compiler in the GHC wrapper script was incorrect (so all our hacks to get this new feature of GHC working properly when users bootstrap had to be scrapped as they made the situation even worse in this case). Again, these situations are mainly Gentoo-specific due to the unique nature of the distribution (though distributions without categories still have to ensure the Cabal-package-name-to-distribution-package-name mapping is consistent and correct). I would, however, imagine that in general having end users use their package manager attempt to automagically integrate Hackage packages into system packages would be fraught with peril. -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: random-fu 0.1.0.0
On Jun 3, 2010, at 10:03 PM, wren ng thornton wrote: Though, since RVar is a synonym for RVarT, I can't imagine why rvar is a method instead of a shorthand defined outside of the class. (If RVar were primitive then I could imagine performance reasons, but since it isn't...) The reason for this is purely a matter of convenience combined with a bit of historical accident and/or laziness. The RVar type predates the RVarT type, and thus rvar predates rvarT as well. My personal idioms for defining distributions were invented before RVarT and have been slow to change. These idioms involve defining the 'rvar' implementations in terms of the public interface of simpler distributions, which are mostly exporting plain 'RVar's in order to reduce the need for type annotations fixing 'n' elsewhere. In particular, functions such as 'uniform' and 'normal' which directly construct RVars are very useful in defining the rvar implementation of other types. I have been reluctant to drop the rvar function from the Distribution class because it is very useful to be able to define other Distribution instances in terms of these functions instead of the uglier explicit use of rvarT - e.g. rvarT StdUniform in place of just 'stdUniform'. Eventually I'll probably give up this particular objection – probably sooner rather than later now that you've made me think about it – but I'm presently in the state where I know it isn't right to have both (for some value of right) but I don't know yet what a better solution is, given my conflicting objectives (one of which is to refrain from changing everything at once, so users have a chance to keep up with the library's evolution). Making the convenience functions mentioned above return RVarT seems natural, but when I tried it I found it made their usage require type annotations in many other places to fix the type of the underlying monad, and I have not yet decided whether it is worth all that. I may yet introduce separate RVarT-typed convenience functions as well, but I'm not sure I want to do that either. Suggestions are welcome :) -- James___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] alphanum in infix constructors (and possibly functions as well) - why not?
Hi all, The constructor names in Haskell need to obey one of the two following rules: - either starts with a capital letter and contains alphanumeric characters afterwards, (including _ I guess) - or starts with a colon (:) and only contains symbols afterwards The first one is used Prefix by default, and the second ose is used infix by default. What stops us from allowing alphanum characters appear in the Infix version (after the colon)? Can't it be relaxed to only start woth a colon? So I want to be able to say something like: data Expr = Expr : Expr -- checks for LT betwen two Expr's | Expr :2 Expr -- a different implementation of the same thing maybe | Expr :veryfast Expr-- and the veryfast implementation of it (just a silly example I could think of now.) Best, Ozgur Akgun ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: random-fu 0.1.0.0
On Jun 4, 2010, at 1:19 AM, Alexander Solla wrote:
We don't necessarily have to compute the inverse of the distribution via
sampling to do it. It can be done algebraically, in terms of the convolution
operator. Since the types are enumerated, wouldn't something like... work?
-- A set and binary operation. We have an algebra. I like the J for 'join'.
-- With this algebra, we can use the real-complex analytical methods to
-- interpret the terms later, if we want to actually reify a Distribution
-- instance as a Real (Float, Double) function.
data DistributionJ a = UniformDistribution Uniform a
| ...
| ExponentialDistribution Exponential a
| DistributionJ a `Convolve` (DistributionJ a)
-- I hope I understand the semantics for the PromptT monad.
newtype RVarT m a = RVarT { unRVarT :: PromptT (Prim, DistributionJ) m a }
I guess threading fst and snd in all the low level computations is inelegant,
but it's a step closer.
An algebraic solution would work as long as the user only made use of a very
small set of supported operations. Unfortunately, even detecting whether they
have done so in any implementation supporting Monad is not really feasible.
The Functor/Applicative/Monad classes allow inclusion of arbitrary functions in
the construction of an RVar, which is a very big part of the usefulness of the
system. Even in a simple no-op defininion such as fmap id x, fmap has no way
of discovering whether the function is id, negate, primes !!, or worse,
so the only way (I believe) to effectively propagate the algebraic part would
be to drop the Functor, Applicative and Monad instances and work with RVars
solely via some combinator library. At that point, why not just work with the
symbolic form directly and choose at the end whether to sample or compute a
pdf? You could make DistributionJ an instance of Distribution to make it
sampleable, and do precisely that. In fact, that would probably be a pretty
nifty thing to do.
-- James
PS - the usage of DistributionJ in the prompt wouldn't quite work, because a
DistributionJ a would just be a standin for a computation of type m a where
m is the monad in which the variable is eventually sampled. There is no way
to rediscover the particular constructor that was used for the prompt, for
approximately the same reasons as above.___
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Re: [Haskell-cafe] alphanum in infix constructors (and possibly functions as well) - why not?
Ozgur Akgun ozgurak...@gmail.com writes: Hi all, The constructor names in Haskell need to obey one of the two following rules: - either starts with a capital letter and contains alphanumeric characters afterwards, (including _ I guess) - or starts with a colon (:) and only contains symbols afterwards The first one is used Prefix by default, and the second ose is used infix by default. What stops us from allowing alphanum characters appear in the Infix version (after the colon)? Can't it be relaxed to only start woth a colon? The definition. I believe this is probably to make parsing of foo:bar (using your example below) unambiguous, the same as how symbolic operators can't contain alphanumeric characters, etc. So I want to be able to say something like: data Expr = Expr : Expr -- checks for LT betwen two Expr's | Expr :2 Expr -- a different implementation of the same thing maybe | Expr :veryfast Expr-- and the veryfast implementation of it How does a data structure have a faster implementation? _ -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Weird socket problem on Mac OS X
On Fri, Jun 4, 2010 at 12:11 AM, Arnaud Bailly arnaud.oq...@gmail.com wrote: Yes, I have also seen the other post on the same topic, but it seemed to refer to the PortNumber in Network.Socket with a PortNum constructor I think, not the one in Network (but I am probably misleading myself as one is a reexportation of the other...). But then I got. Slim\SlimClientIO.hs:26:51: No instance for (Num PortID) arising from a use of `fromInteger' at Slim\SlimClientIO.hs:26:51-61 Possible fix: add an instance declaration for (Num PortID) In the first argument of `($)', namely `fromInteger' In the expression: fromInteger $ slimport $ slimConfig st In the definition of `port': port = fromInteger $ slimport $ slimConfig st Oops! I didn't read carefully enough. That's what I get for trying to program without haddocks or GHCi in front of me. I am glad you have something that works. Antoine ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Proposal: Sum type branches as extended types (as Type!Constructor)
Jason Dagit dagit at codersbase.com writes:
How will this proposal scale with data types that have multiple
alternatives that make sense? No natural examples come to mind
so how about a contrived example:
data List2 a = Nil | Cons a (List2 a) | Cons2 a a (List2 a)
Now I want to define hd for both Cons and Cons2, but not Nil.
Do I use an either type like this?
hd :: Either (List2!Cons a) (List2!Cons2 a) - a
It seems like some other syntax would be desirable here, maybe:
hd :: List2!{Cons, Cons2} a - a
How should it work for functions where no type signature is supplied?
Shouldit infer the type we would now and only enable the
subset of constructors when the type is explicit as above?
Jason
I agree with your syntax proposal.
hd :: List2!{Cons, Cons2} a - a
in functions where no type signature, type inference could work as usual.
After normal types passes typechecker with type inference,
then Constructor matching could be checked.
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Re: [Haskell-cafe] alphanum in infix constructors (and possibly functions as well) - why not?
On 4 June 2010 12:33, Ivan Lazar Miljenovic ivan.miljeno...@gmail.comwrote: Ozgur Akgun ozgurak...@gmail.com writes: [...] What stops us from allowing alphanum characters appear in the Infix version (after the colon)? Can't it be relaxed to only start woth a colon? The definition. I believe this is probably to make parsing of foo:bar (using your example below) unambiguous, the same as how symbolic operators can't contain alphanumeric characters, etc. I see. Then people would need to put spaces between those things, right? What a horrible consequence! So I want to be able to say something like: data Expr = Expr : Expr -- checks for LT betwen two Expr's | Expr :2 Expr -- a different implementation of the same thing maybe | Expr :veryfast Expr-- and the veryfast implementation of it How does a data structure have a faster implementation? _ Well it might indicate to use a different function while evaluating the expression. Still not a good example, I know. Best, Ozgur ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Strange GHC messages?
Hi all, I've got some strange GHC output that doesn't seem to be
affecting my program adversely but I thought I should post about it
cos it's disquieting
mkUsageInfo: internal name? r{tv aIR}
mkUsageInfo: internal name? s{tv aIS}
It seems to be complaining about this newtype declaration:
newtype ThreadStateM r s v = ThreadState { unbox :: StateT s (ReaderT r IO) v
}
deriving (Monad, Functor, MonadIO, MonadState s, MonadReader r)
(uses newtype deriving)
I'm not sure what the problem here is?
Cheers.
~Liam
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Re: [Haskell-cafe] alphanum in infix constructors (and possibly functions as well) - why not?
Ozgur Akgun ozgurak...@gmail.com writes: Then people would need to put spaces between those things, right? What a horrible consequence! I like to think that Haskell is a language where aesthetics matter. So, in my opinion this is indeed a horrible consequence. I find mixing of symbols and letters in identfiers to be in itself aesthetically inferior, and there's already more than enough whitespace-dependent parsing warts in Haskell. -k -- If I haven't seen further, it is by standing in the footprints of giants ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] alphanum in infix constructors (and possibly functions as well) - why not?
OK I back up. I justed wanted it to happen for a moment :) You're right, ambiguity in parsing and a lot of whitespace-dependency are things to avoid. Best, On 4 June 2010 14:25, Ketil Malde ke...@malde.org wrote: Ozgur Akgun ozgurak...@gmail.com writes: Then people would need to put spaces between those things, right? What a horrible consequence! I like to think that Haskell is a language where aesthetics matter. So, in my opinion this is indeed a horrible consequence. I find mixing of symbols and letters in identfiers to be in itself aesthetically inferior, and there's already more than enough whitespace-dependent parsing warts in Haskell. -k -- If I haven't seen further, it is by standing in the footprints of giants ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Ozgur Akgun ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] How to Show an Operation?
Dear all, If I have a problem where I have to select from a set of operations, how would I print the result? Example: If I can chose from (x+y), (x*y), (x^2+y)... and I feed them all into my problem solver and it finds that (x*y) is right, how can I print that string? -- Martin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to Show an Operation?
One way woul be to represent them usnig a data structure. If it's only artihmetic operations, it should be pretty easy. data Arith = Var String | Plus Artih Arith | Mult Arith Arith | Pow Arith Arith x + y would be Plus (Var x) (Var y), so on so forth.. You can even use infix constructors like :+:, :*:, :^: On 4 June 2010 16:37, Martin Drautzburg martin.drautzb...@web.de wrote: Dear all, If I have a problem where I have to select from a set of operations, how would I print the result? Example: If I can chose from (x+y), (x*y), (x^2+y)... and I feed them all into my problem solver and it finds that (x*y) is right, how can I print that string? -- Martin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Ozgur Akgun ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to Show an Operation?
On Friday 04 June 2010 17:37:16, Martin Drautzburg wrote: Dear all, If I have a problem where I have to select from a set of operations, how would I print the result? Example: If I can chose from (x+y), (x*y), (x^2+y)... and I feed them all into my problem solver and it finds that (x*y) is right, how can I print that string? You'd have to pass the description string to the problem solver too. If it was previously solver :: Num a = Whatever - [a - a - a] - Result it would become for example solver :: Num a = Whatever - [(a - a - a, String)] - Result ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Reporting a problem with binary-0.5
I've been trying to get in touch with the maintainers of the Binary package, to report an issue. When I emailed the addresses given on Hackage, I got an automated response saying I had used an address that was no longer current. I don't want to put pressure on anyone to fix my bug -- I didn't pay anything for Binary, so it wouldn't be fair for me to have that kind of expectation. At the same time, I don't really want my bug report to go missing just because someone's email address has changed. Does anyone know who I should be talking to? Or is there a bug tracker for the Hackage packages somewhere? I noticed this problem when I ran into some trouble with the network-dns package. It would hang up as soon as I tried to send a query. Eventually I traced the problem to the binary module, and reduced it to this short test case: module Main where import qualified Data.Binary.Get as G import qualified Data.ByteString.Lazy as B main = do urandom - B.readFile /dev/urandom let urandomParser :: G.Get [Int] urandomParser = do v - G.getWord32be rest - urandomParser return $ fromIntegral v : rest seeds = G.runGet urandomParser urandom print $ take 4 seeds This code attempts to create an infinite list of random numbers -- a technique also used by network-dns. It turns out that this code works with binary-0.4.4 but not with binary-0.5.0.2. Both were built with ghc-6.12.1 on Ubuntu. (I haven't tested with the intermediate versions of the binary module.) It seems that with binary-0.5.0.2 there is some unwanted strictness; something is evaluated for the whole list, even though it is only the first few elements that are required. Incidentally, if the test case is changed like this: --- get_monad.hs2010-05-28 11:31:02.399202535 +0100 +++ get_monad2.hs 2010-05-28 13:44:25.515486013 +0100 @@ -1,10 +1,12 @@ module Main where +import Control.Monad + import qualified Data.Binary.Get as G import qualified Data.ByteString.Lazy as B main = do - urandom - B.readFile /dev/urandom + urandom - liftM (B.take 64) $ B.readFile /dev/urandom let urandomParser :: G.Get [Int] urandomParser = do v - G.getWord32be the program exits with an error: get_monad2.hs: too few bytes. Failed reading at byte position 68 This seems to demonstrate that the program is reading more data than it needs to. Thanks, Pete ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Proposal: Sum type branches as extended types (as Type!Constructor)
Edward Kmett suggests the use of @ instead of !
Edward Kmett wrote:
This is just a form of refinement type. Googling the term should turn up a
couple dozen papers on the topic.
You can emulate them (and more) with phantom types in the existing
type system, though admittedly the encoding is occasionally uncomfortable.
As a result there hasn't been much interest in them from on high.
And a minor technical issue with the use of ! there is that it would be
awkward from a grammar perspective because it would require that ! bind
more tightly than juxtaposition, but only when parsing a type.
Another syntactic operator like @ that already binds very tightly
might be more appropriate.
-Edward Kmett
New proposal draft:
Proposal: Type supplement for constructor specific uses of sum types
Purpose: Avoid error clauses (runtime errors), exception control or Maybe
types in partially defined (constructor specific) functions on sum types.
As an example, with
data List a = Nil | Cons a (List a)
* Actual system, with runtime errors (as in GHC Data.List head) or
exception throwing or optional Maybe results.
hd :: List a - a
hd (Cons x _) - x
hd Nil - error error: hd: empty list -- error or exception throwing
* Proposed system extending types with a suffix @ Constructor or @
{Constructor1, Constructor2, ..}
hd :: List @ Cons a - a
hd (Cons x _) = x
The caller must do pattern matching before applying the constructor-specific
function.
In ''var @ (Constructor {})'' the compiler should set a type supplement
property for ''var'' to the specified pattern constructor and check
the supplement when used in a constructor specific parameter position.
using it:
accumHead :: (a-b) - a - List a - b
accumHead f accum list = case list of
li @ Cons {} - f accum $ hd li -- typeSupplementOf li == 'Cons'
-- should pass typechecker at ''hd'' for
List!Cons
li @ Nil - f accum $ hd li -- compiler error !!
-- typeSupplementOf li == 'Nil' ; no match
_ - f accum $ hd list -- compiler error !!
-- typeSupplementOf list == Nothing ; no match
_ - accum -- default closing pattern matching exhaustivity.
(from Jason Dagit contribution) For more than one constructor say
data List2 a = Nil | Cons a (List2 a) | Cons2 a a (List2 a)
hd :: List2 @ {Cons, Cons2} a - a
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Re: [Haskell-cafe] Reporting a problem with binary-0.5
Pete Chown 1...@234.cx writes: This code attempts to create an infinite list of random numbers -- a technique also used by network-dns. It turns out that this code works with binary-0.4.4 but not with binary-0.5.0.2. There was a deliberate change in strictness in 0.5 making binary strict, which apparently speeds up GHC. I ran into the same problem, but have no better workaround than to require binary 0.5 in my .cabal. -k (I made a note about this at http://blog.malde.org/index.php/2010/05/22/snagged/) -- If I haven't seen further, it is by standing in the footprints of giants ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Reporting a problem with binary-0.5
On Fri, Jun 4, 2010 at 8:02 PM, Pete Chown 1...@234.cx wrote: I've been trying to get in touch with the maintainers of the Binary package, to report an issue. When I emailed the addresses given on Hackage, I got an automated response saying I had used an address that was no longer current. I don't want to put pressure on anyone to fix my bug -- I didn't pay anything for Binary, so it wouldn't be fair for me to have that kind of expectation. At the same time, I don't really want my bug report to go missing just because someone's email address has changed. Does anyone know who I should be talking to? Or is there a bug tracker for the Hackage packages somewhere? I noticed this problem when I ran into some trouble with the network-dns package. It would hang up as soon as I tried to send a query. Eventually I traced the problem to the binary module, and reduced it to this short test case: module Main where import qualified Data.Binary.Get as G import qualified Data.ByteString.Lazy as B main = do urandom - B.readFile /dev/urandom let urandomParser :: G.Get [Int] urandomParser = do v - G.getWord32be rest - urandomParser return $ fromIntegral v : rest seeds = G.runGet urandomParser urandom print $ take 4 seeds This issue was discussed on the list before. Get monad definition was changed in binary 0.5.0.2. It was made strict and evaluation of result of runGet is forced. This increased performance but broke programs which relies on lazyness to work. Here is code I use to work around this issue: runGetStream :: Get a - ByteString - [a] runGetStream getter bs = unfoldr step bs where step bs = case runGetState getOne bs 0 of (Nothing, _, _ ) - Nothing (Just x, bs', off') - Just (x, bs') getOne = do empty - isEmpty if empty then return Nothing else Just $ getter ... seeds = runGetStream (fromInteger $ getWord64be) urandom ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Reporting a problem with binary-0.5
On Fri, Jun 4, 2010 at 8:31 PM, Alexey Khudyakov alexey.sklad...@gmail.com wrote: Here is code I use to work around this issue: Forgot to mention. This code checks for end of input. Your data is infinite so you simplify definition if you like ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Tricks with GMap -- question about conflicts w/ indexed type families
GMaps -- families of map implementations indexed by the key type -- are an example on the wiki: http://www.haskell.org/haskellwiki/GHC/Type_families I've been using something like this myself. It sure would be nice to have a fully developed version on Hackage, and I may try to submit this myself if no one else has already done it. But I'm running into a problem in achieving a particular optimization that I want -- namely, small tuple keys packed into Ints. For example, with a key type (Int16,Int16) it's possible to pack the key into a plain Int and use Data.IntMap. In fact, in the rough/partial implementation here (http://people.csail.mit.edu/newton/gmap/GMap.hs) I have a class for things that fit in a word: class FitInWord v where toWord :: v - Word fromWord :: Word - v (Or fitInInt for that matter.) Which includes things like small tuples: instance FitInWord (Int16,Int16) where toWord (a,b) = shiftL (fromIntegral a) 16 + (fromIntegral b) fromWord n = (fromIntegral$ shiftR n 16, fromIntegral$ n .. 0x) (If you know a better idea than using templates/program generation to generate every combination of small scalar tuples that fit in a word let me know.) What I would next *like* to do is something like the following: import qualified Data.IntMap as DI instance FitInWord t = GMapKey t where data GMap t v = GMapInt (DI.IntMap v) deriving Show empty = GMapInt DI.empty lookup k (GMapInt m) = DI.lookup (wordToInt$ toWord k) m insert k v (GMapInt m) = GMapInt (DI.insert (wordToInt$ toWord k) v m) alter fn k (GMapInt m) = GMapInt (DI.alter fn (wordToInt$ toWord k) m) toList (GMapInt m) = map (\ (i,v) - (fromWord$ intToWord i, v)) $ DI.toList m The problem is that there's already a more general instance of GMapKey that handles pairs by representing them as nested GMaps: instance (GMapKey a, GMapKey b) = GMapKey (a, b) where data GMap (a, b) v= GMapPair (GMap a (GMap b v)) Ideally, I want both of these to coexist (and to prioritize the more specific one). With normal type classes, OverlappingInstances can handle this, but with type families I get an error like the following: Conflicting family instance declarations: data instance GMap t v -- Defined at Intel/GMap.hs:108:7-10 data instance GMap (a, b) v -- Defined at Intel/GMap.hs:225:7-10 Any fixes? Thanks, -Ryan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Issue with connectTo function in network package
* aditya siram aditya.si...@gmail.com [2010-06-03 22:30:33-0500] Hi all, I had an issue where using the connectTo [1] function would fail to connect to localhost if my wireless card was turned off. The moment I turned on my wireless connection it worked. But if I use connectTo with 127.0.0.1 [2] with my network off it works. I confirmed that localhost' resolves to 127.0.0.1 by pinging localhost from command line with the Internet off. Is this a bug in connectTo? -deech [1] connectTo localhost (PortNumber some_number) [2] connectTo 127.0.0.1 (PortNumber some_number) How exactly did it fail? Did it throw an exception? If so, what was the exception? Which operating system did you observe that under? If that was Linux, can you show the contents of the following files on that system: /etc/nsswitch.conf /etc/hosts -- Roman I. Cheplyaka :: http://ro-che.info/ Don't let school get in the way of your education. - Mark Twain ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
