Re: [Haskell-cafe] Why cannot ghc find a existng module ?
`ghc-pkg list` finds two random packages. After `ghc-pkg unregsiter` the one installed by cabal in ~/.ghc/, all works normally now! %ghc-pkg list|grep -i random random-1.0.0.2 zaxis wrote: I have reinstall ghc, xmonad and xmonad-contrib but it still doesnot work! %ghc-pkg list|grep xmonad xmonad-0.9.1 xmonad-contrib-0.9.1 %cat /usr/lib/ghc-6.12.1/package.conf.d/xmonad-contrib-0.9.1-e073c906e3b29eb062e632e9bb989664.conf|grep LayoutHints XMonad.Layout.LayoutCombinators XMonad.Layout.LayoutHints %ls /usr/lib/ghc-6.12.1/site-local/xmonad-contrib-0.9.1/XMonad/Layout/LayoutHints.hi ../site-local/xmonad-contrib-0.9.1/XMonad/Layout/LayoutHints.hi LayoutHints is indeed there. But ghc still cannot find it ! Thanks for your suggestion. i will try #xmonad and xmond mailinglist later! Ivan Lazar Miljenovic wrote: zaxis z_a...@163.com writes: It seems that it is not a xmonad problem as xmond just call ghc directly. Well, yes, except that it might be something else to do with your config, etc. and as such the xmonad mailing list is probably more relevant. -- 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 - e^(π⋅i) + 1 = 0 -- View this message in context: http://old.nabble.com/Why-cannot-ghc-find-a-existng-module---tp28507704p28521179.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why cannot ghc find a existng module ?
On Tue, May 11, 2010 at 10:10 AM, zaxis z_a...@163.com wrote: `ghc-pkg list` finds two random packages. After `ghc-pkg unregsiter` the one installed by cabal in ~/.ghc/, all works normally now! I stopped counting the number of times I've reinstalled GHC because I forgot to tell cabal to install a package globally. I really should modify the config file. David. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why cannot ghc find a existng module ?
David Virebayre dav.vire+hask...@gmail.com writes: On Tue, May 11, 2010 at 10:10 AM, zaxis z_a...@163.com wrote: `ghc-pkg list` finds two random packages. After `ghc-pkg unregsiter` the one installed by cabal in ~/.ghc/, all works normally now! I stopped counting the number of times I've reinstalled GHC because I forgot to tell cabal to install a package globally. I really should modify the config file. No, this isn't the problem here. The problem is that zaxis should never have installed the second random library in the first place, because it is a boot library of GHC. -- 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
[Haskell-cafe] Haskell meeting in Leipzig, Germany, June 4
The Fifth Haskell in Leipzig meeting will be held on June 4, see http://www.iba-cg.de/hal5.html . You can still submit proposals (and wishes) for tutorials and talks (deadline: May 14). For instance, we'd love to hear about recent advances in Haskell IDEs (eclipsefp? leksah?), and parallel/multicore programming is always a hot topic as well. The primary language is German but we can switch to English if requested/agreed upon by audience and speaker. Best regards, Johannes Waldmann, HTWK Leipzig. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How efficient is read?
On Tue, May 11, 2010 at 12:16 AM, Tom Hawkins tomahawk...@gmail.com wrote:
The tarball was missing its Rules.hs; as it happens, GHC has a module
named Rules.hs as well, hence the confusing error. I've uploaded a
fresh one that should work.
Thanks. This builds and installs fine.
But I think there is something wrong with the generated parser. It
doesn't look for (..) groupings. For example:
data Something = Something Int (Maybe String)
deriving Show {-! derive : Parse !-}
There is nothing in the generated parser to look for parens around the
Maybe in case it is a (Just string).
Am I missing something?
I don't know. If you could check whether the original Drift has that
error as well, then I suspect Drift's author, Meachem, would be
interested to know. (I only maintain drift-cabalized as a packaging
fork; I tried not to change any actual functionality.)
--
gwern
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Re: [Haskell-cafe] How efficient is read?
data Something = Something Int (Maybe String)
deriving Show {-! derive : Parse !-}
There is nothing in the generated parser to look for parens around the
Maybe in case it is a (Just string).
Sorry, that will be my fault. I contributed the rules for deriving
Parse to DrIFT. I am on holiday right now, but will try to take a
look shortly.
Regards,
Malcolm
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[Haskell-cafe] Functions of type foo :: f a - g a
I would like to build a class that includes a method to move data from one arbitrary functor to another, a natural transformation. The structures might be more than just functors, but I can start with that. I ran into some practical issues with resolving the type variables for my multiparameter type class, which I can resolve with functional dependencies. I can also not isolate the natural transformation from my overall operation, muddling it with the element transformation. I was wondering if anyone had any words of advice, example or warning about this kind of function or method in general? Class (Functor f, Functor g) = Foo f g a where foo :: f a - g a bar :: (a-b) - g a - g b Thanks, Gordon J. Uszkay, McMaster University uszka...@mcmaster.ca ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Functions of type foo :: f a - g a
On Tue, May 11, 2010 at 02:01:05PM -0400, Gordon J. Uszkay wrote: I would like to build a class that includes a method to move data from one arbitrary functor to another, a natural transformation. The structures might be more than just functors, but I can start with that. I ran into some practical issues with resolving the type variables for my multiparameter type class, which I can resolve with functional dependencies. I can also not isolate the natural transformation from my overall operation, muddling it with the element transformation. I was wondering if anyone had any words of advice, example or warning about this kind of function or method in general? Class (Functor f, Functor g) = Foo f g a where foo :: f a - g a bar :: (a-b) - g a - g b A couple points, * why is 'a' a member of the type class head? Functors don't care about what is stored inside the type, so your class shouldn't either if it is a transformer from functor to functor. * isn't bar exactly the same as 'fmap' for g? A better way might be class (Functor f, Functor g) = FunctorPair f g where transformFunctor :: f a - g a though, I am not sure what your use is, there isn't an obvious instance to me, but I don't know what your motivating task is. John -- John Meacham - ⑆repetae.net⑆john⑈ - http://notanumber.net/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Functions of type foo :: f a - g a
On Tue, May 11, 2010 at 2:01 PM, Gordon J. Uszkay uszka...@mcmaster.cawrote: I would like to build a class that includes a method to move data from one arbitrary functor to another, a natural transformation. The structures might be more than just functors, but I can start with that. I ran into some practical issues with resolving the type variables for my multiparameter type class, which I can resolve with functional dependencies. I can also not isolate the natural transformation from my overall operation, muddling it with the element transformation. I was wondering if anyone had any words of advice, example or warning about this kind of function or method in general? Class (Functor f, Functor g) = Foo f g a where foo :: f a - g a bar :: (a-b) - g a - g b In general I would shy away from encoding natural transformations as a typeclass describing one family of morphisms of the form f a - g a. I would avoid it because the choice of function f a - g a isn't really canonical. There are many potentially valid such functions. foo :: Maybe a - [a] foo (Just a) = [a] foo Nothing = [] bar :: Maybe a - [a] bar (Just a) = repeat a bar Nothing = [] baz :: Maybe a - [a] baz _ = Nothing quux n :: Int - Maybe a - [a] quux (Just a) = replicate a n quux Nothing = Nothing With that in mind an arguably better approach would be to define a natural transformation as: type Nat f g = forall a. f a - g a or even type f :~ g = forall a. f a - g a and pass them around explicitly then you can encode things like: hylohttp://hackage.haskell.org/packages/archive/category-extras/0.53.5/doc/html/Control-Morphism-Hylo.html#v%3Ahylo:: Functorhttp://hackage.haskell.org/packages/archive/base/4.2.0.1/doc/html/Control-Monad.html#t%3AFunctorf = Algebrahttp://hackage.haskell.org/packages/archive/category-extras/0.53.5/doc/html/Control-Functor-Algebra.html#t%3AAlgebrag b - (f :~http://hackage.haskell.org/packages/archive/category-extras/0.53.5/doc/html/Control-Functor-Extras.html#t%3A%3A%7E%3Eg) - Coalgebrahttp://hackage.haskell.org/packages/archive/category-extras/0.53.5/doc/html/Control-Functor-Algebra.html#t%3ACoalgebraf a - a - b hylo f e g = f . e . fmap (hylo f e g). g This is important because there can exist such natural transformations that need data out of your current environment: i.e. the natural transformation ((,) x), the quux example above, etc. -Edward Kmett ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Functions of type foo :: f a - g a
On Tue, May 11, 2010 at 2:06 PM, John Meacham j...@repetae.net wrote: A better way might be class (Functor f, Functor g) = FunctorPair f g where transformFunctor :: f a - g a though, I am not sure what your use is, there isn't an obvious instance to me, but I don't know what your motivating task is. Furthermore, to select an instance at this point both Functors must be known in context of use, which exhausts pretty much the entire informational content of the instance--raising the question of what benefit is drawn from a type class at all, as opposed to simply passing around functions of type f a - g a as needed. Consider that fmap doesn't require a multi-parameter type class for each pair a, b, it just takes a function (a - b). The only way a type class would make sense here, I think, is with a fundep uniquely determining a particular natural transformation based on one of the Functors, at which point I'm not sure that the concept of natural transformation is what you're actually trying to model. - C. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] comprehending monad execution
All:
I've been analyzing monads for a while now and have a question on execution. I
suspect I've missed something basic.
In the snippet below the ghc debugger shows that in just one single step
Discriminate has been substituted for g.
Even with :trace turned on in the debugger there is no evidence of an execution
step to carry out the substitution.
This leads me to assume a compile time operation identifies Discriminate as a
substitute for g.
Could someone correct my assumption or explain how this works?
Note: this snippet was extracted from [1].
{-# LANGUAGE EmptyDataDecls, Rank2Types #-}
module LEM where
import Control.Monad.Identity
data F -- no constructors
data Discriminate a b = L a | R b
instance Monad (Discriminate e) where
return = R
R x = f = f x
L x = f = L x
h :: (forall m. Monad m = ((a - m F) - m F)) - a
h g = case g (\x - L x) of
R x - error Not reachable
L x - x
-- A proof term for a - NOT NOT a
lift :: forall a m. Monad m = a - ((a - m F) - m F)
lift x = \k - k x
t = h $ lift True
ghci trace ...
C:\haskell\lemghci lem.lhs
GHCi, version 6.8.3: http://www.haskell.org/ghc/ :? for help
Loading package base ... linking ... done.
[1 of 1] Compiling LEM ( lem.lhs, interpreted )
Ok, modules loaded: LEM.
*LEM :b h
Breakpoint 0 activated at lem.lhs:(14,2)-(16,17)
*LEM :trace t
Loading package mtl-1.1.0.1 ... linking ... done.
Stopped at lem.lhs:(14,2)-(16,17)
_result :: a = _
[lem.lhs:(14,2)-(16,17)] *LEM :step
Stopped at lem.lhs:(14,8)-(16,17)
_result :: a = _
g :: (a - Discriminate a F) - Discriminate a F = _
[lem.lhs:(14,8)-(16,17)] *LEM :hist
-1 : h (lem.lhs:(14,2)-(16,17))
-2 : t (lem.lhs:22:6-18)
end of history
[lem.lhs:(14,8)-(16,17)] *LEM
My previous analysis includes running single step execution on Wadler's I monad
here [2],
where I am able to observe execution of the I monad.
[essence.lhs:32:33-37] *Essence :hist
-1 : unitI (essence.lhs:7:34)
-2 : unitI (essence.lhs:7:2-34)
-3 : interp (essence.lhs:32:26-38)
-4 : interp (essence.lhs:(31,2)-(39,44))
-5 : test (essence.lhs:54:41-51)
-6 : showval (essence.lhs:(26,2)-(28,45))
-7 : showI (essence.lhs:9:34-42)
-8 : showI (essence.lhs:9:2-42)
-9 : test (essence.lhs:54:34-52)
-10 : test (essence.lhs:54:2-52)
end of history
[1] http://okmij.org/ftp/Computation/lem.html
[2] http://homepages.inf.ed.ac.uk/wadler/papers/essence/essence.ps
Thanks much in advance for your help.
Rick
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[Haskell-cafe] hSetEncoding on socket handles
Greetings, I am having trouble sending unicode characters as utf8 over a socket handle. Despite setting the encoding on the socket handle to utf8, it still seems to use some other encoding when writing to the socket. It works correctly when writing to stdout, but not to a socket handle. I am using ghc 6.12.1 and network-2.2.1.7. I can get it to work using System.IO.UTF8, but I was under the impression this was no longer necessary? I also don't seem to understand the interaction between hSetEncoding and hSetBinaryMode because if I set the binary mode to 'False' and the encoding to utf8 on the socket, then when writing to the socket the string seems to be truncated at the first non-ascii codepoint. Here is a test snippet, which can be used with netcat as a listening server (ie. nc -l 1234). import System.IO import Network main = do let a=λ s - connectTo 127.0.0.1 (PortNumber 1234) hSetEncoding s utf8 hSetEncoding stdout utf8 hPutStrLn s a putStrLn a hClose s Thanks, David ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Speed of Error handling with Continuations vs. Eithers
Max Cantor wrote:
Based on some discussions in #haskell, it seemed to be a consensus
that using a modified continuation monad for Error handling instead
of Eithers would be a significant optimization since it would
eliminate a lot of conditional branching (everytime = is called
in the Either monad, there is a conditional.
I implemented a ErrCPS monad which does exactly that, but the speed
has been disappointing. It runs almost exactly 3x slower than a
drop in replacement using the MonadError instance of Either from mtl.
I have noticed speedup in my CPS version of Maybe[1] (kidnapped from the
Wiki) so the difference is curious. Jan-Willem's comments about closures
are significant when doing CPS work, but I'd expect Maybe and Either to
perform similarly, whatever their performance is. It's been a while
since I've benchmarked MaybeCPS, so perhaps I now have the slowdown too.
Let's look at the code and see if we can find other differences...
[1]
http://community.haskell.org/~wren/wren-extras/src/Control/Monad/MaybeCPS.hs
Here's one big difference:
newtype ErrCPS e m a = ErrCPS { runErrCPS ::
forall r . (e - m r) -- error handler
- (a - m r) -- success handler
- m r }
The analogous version I use is:
newtype MaybeCPS a = MaybeCPS
(forall r. (a - Maybe r) - Maybe r)
While I also offer a transformer version of MaybeCPS, the transformer
*does* suffer from significant slowdown. Also, for MaybeCPS it's better
to leave the handlers inline in client code rather than to abstract them
out; that helps to keep things concrete. So perhaps you should first try
a direct CPS translation:
newtype ErrCPS e a = ErrCPS
(forall r. (a - Either e r) - Either e r)
runErrCPS :: ErrCPS e a - Either e a
runErrCPS (ErrCPS f) = f return
I'd be curious if this version suffers the same slowdown.
--
Live well,
~wren
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[Haskell-cafe] Tsuru Capital is hiring
We are looking to hire a programmer that has experience programming in a functional language, and is familiar with Haskell. There is a wide range of tools and applications that we want to build over time, including graphical interfaces and profiling tools for our trading system, parsers for new market feeds, and algorithms for trading strategies. If you have experience in any one of these areas it's a definite bonus. You will be working with a small team of developers, and from time to time will be working along side Traders to assist in tool development. Annual compensation will be in the region of USD150k with potential for growth. The team is based in Tokyo but there are projects that could be done remotely so feel free to apply for this type of work also. http://tsurucapital.com/en/jobs.html#programmer ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Speed of Error handling with Continuations vs. Eithers
wren ng thornton wrote:
Here's one big difference:
newtype ErrCPS e m a = ErrCPS { runErrCPS ::
forall r . (e - m r) -- error handler
- (a - m r) -- success handler
- m r }
The analogous version I use is:
newtype MaybeCPS a = MaybeCPS
(forall r. (a - Maybe r) - Maybe r)
While I also offer a transformer version of MaybeCPS, the transformer
*does* suffer from significant slowdown. Also, for MaybeCPS it's better
to leave the handlers inline in client code rather than to abstract them
out; that helps to keep things concrete. So perhaps you should first try
a direct CPS translation:
newtype ErrCPS e a = ErrCPS
(forall r. (a - Either e r) - Either e r)
runErrCPS :: ErrCPS e a - Either e a
runErrCPS (ErrCPS f) = f return
I'd be curious if this version suffers the same slowdown.
With this change [1] I can't notice any difference for your
benchmark[2]. Then again, all the runTest calls take 0 msec and I've had
no luck making the computation take much time; perhaps your computer can
detect a difference.
You may want to see what standard benchmarking tools like Microbench[3]
or the magnificent Criterion[4] have to say. I'd do it myself, but I
haven't had a chance to reinstall everything since getting my new
computer (due to the installation issues on newer versions of OSX).
[1]
http://community.haskell.org/~wren/wren-extras/src/Control/Monad/ErrCPS.hs
[2]
http://community.haskell.org/~wren/wren-extras/test/Control/Monad/ErrCPS/MaxCantorBenchmark.hs
[3] http://hackage.haskell.org/package/microbench
[4] http://hackage.haskell.org/package/criterion
--
Live well,
~wren
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