Re: [Haskell-cafe] Dynamic and equality
You can define:
data EqDyn= forall a.(Typeable a, Eq a)= EqDyn a
instance Eq EqDyn where
(EqDyn x) == (EqDyn y)= typeOf x== typeOf y x== unsafeCoerce y
unsafeCoerce is safe synce the expression assures that types are equal
2013/7/20 adam vogt vogt.a...@gmail.com
On Sat, Jul 20, 2013 at 12:31 AM, Carter Schonwald
carter.schonw...@gmail.com wrote:
the tricky part then is to add support for other types.
another approach to existentially package type classes with the data
type!
eg
data HasEq = forall a . HasEq ( Eq a = a)
or its siblinng
data HasEq a = Haseq (Eq a = a )
note this requires more planning in how you structure your program, but
is a
much more pleasant approach than using dynamic when you can get it to
suite
your application needs.
note its also late, so I've not type checked these examples ;)
Hi Carter,
It doesn't seem like the existential one will work as-is, since ghc
rejects this:
{-# LANGUAGE ExistentialQuantification #-}
data HEQ = forall a. Eq a = HEQ a
usingHEQ :: HEQ - HEQ - Bool
usingHEQ (HEQ a) (HEQ b) = a == b
I think you were hinting at this option which is better than my first
suggestion:
{-# LANGUAGE ExistentialQuantification #-}
import Data.Typeable
data DYN = forall a. Typeable a = DYN (a, DYN - Bool)
mkDyn :: (Eq a, Typeable a) = a - DYN
mkDyn x = DYN (x, \(DYN (y, eq2)) - case cast y of
Just y' - x == y'
_ - False)
mkDyn' :: Typeable a = a - DYN
mkDyn' x = DYN (x, \_ - False)
eqDyn :: DYN - DYN - Bool
eqDyn x@(DYN (_, fx)) y@(DYN (_,fy)) = fx y || fy x
Maybe there's some way to get mkDyn' and mkDyn as the same function,
without having to re-write all of the Eq instances as a 2-parameter
class like http://www.haskell.org/haskellwiki/GHC/AdvancedOverlap.
--
Adam
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Alberto.
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[Haskell-cafe] Choosing an xml parser
Hello Cafe, I am trying to write a library to parse (and process) the OpenGL xml spec into haskell values. The problem is that I don't know what xml library to choose. So far I can think of the following requirements: - Some error reporting, possibly warning for unparsed elements (as that signals that the parser needs updating). - Not too bulky for the not so simple registry schema [1]. - Preferably some way to preprocess some nodes (this could probably be done by any xml library). - Preferably not too memory hungry (the current spec is about 2MB) Does somebody have a recommendation for a xml library to use for this? Regards, Lars [1]: https://cvs.khronos.org/svn/repos/ogl/trunk/doc/registry/public/api/registry.rnc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] catching IO errors in a monad transformer stack
On Thursday 18 July 2013 23:05:33 Eric Rasmussen wrote: […] Would there be any interest in cleaning that up and adding it (or something similar) to Control.Monad.CatchIO? […] MonadCatchIO-transformers is being deprecated, as recently GHC has removed the 'block' and 'unblock' functions, rendering the api provided by Control.Monad.CatchIO obsolete. Regards, Arie ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Choosing an xml parser
Hi L, I have used TagSoup, it is fine and simple. http://community.haskell.org/~ndm/tagsoup/ 2013/7/21 L Corbijn aspergesoe...@gmail.com Hello Cafe, I am trying to write a library to parse (and process) the OpenGL xml spec into haskell values. The problem is that I don't know what xml library to choose. So far I can think of the following requirements: - Some error reporting, possibly warning for unparsed elements (as that signals that the parser needs updating). - Not too bulky for the not so simple registry schema [1]. - Preferably some way to preprocess some nodes (this could probably be done by any xml library). - Preferably not too memory hungry (the current spec is about 2MB) Does somebody have a recommendation for a xml library to use for this? Regards, Lars [1]: https://cvs.khronos.org/svn/repos/ogl/trunk/doc/registry/public/api/registry.rnc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Haskell] [ANN] Initial release of the threepenny-gui library, version 0.1.0.0
Hi, I have a Path problem when installing threepenny-gui from Hackage. Probably somtething trivial. Sergey src/BarTab.hs:9:8: Could not find module `Paths' Use -v to see a list of the files searched for. Failed to install threepenny-gui-0.1.0.0 cabal: Error: some packages failed to install: threepenny-gui-0.1.0.0 failed during the building phase. The exception was: ExitFailure 1 2013/7/21 Heinrich Apfelmus apfel...@quantentunnel.de: Dear Haskellers, And the shark, he has teeth, And he wears them in (his) face. And Macheath, he has a knife, (But) yes the knife, no-one sees. After an obligatory cryptical quotation from a famous writer, I am pleased to announce the first public release of *threepenny-gui*, a cheap and simple library to satisfy your immediate GUI needs in Haskell. Want to write a small GUI thing but forgot to sacrifice to the giant rubber duck in the sky before trying to install wxHaskell or Gtk2Hs? Then this library is for you! Threepenny-gui is easy to install (!!) because it uses the web browser as a display. Internally, we implement a small web server that communicates with the browser to display GUI elements. Consequently, you can use HTML and CSS to design the user interface. You can freely manipulate the HTML DOM and handle browser events by writing Haskell code. hackage - http://hackage.haskell.org/package/threepenny-gui examples - https://github.com/HeinrichApfelmus/threepenny-gui#examples source - https://github.com/HeinrichApfelmus/threepenny-gui Many thanks to Daniel Austin for collaborating with me on this project and to Chris Done for implementing the Ji library which is the basis for this effort. On that note, the threepenny API for creating and manipulating GUI elements departs from earlier traditions. Do you like the new look and feel of the API? What do you think could be improved? Try it out and send us your feedback! Best regards, Heinrich Apfelmus -- http://apfelmus.nfshost.com ___ Haskell mailing list hask...@haskell.org http://www.haskell.org/mailman/listinfo/haskell ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] catching IO errors in a monad transformer stack
Arie, Thanks for calling that out. The most useful part for my case is the MonadCatchIO implementation of catch: catch :: Exception e = m a - (e - m a) - m a Hoogle shows a few similar functions for that type signature, but they won't work for the case of catching an IOException in an arbitrary monad. Do you happen to know of another approach for catching IOExceptions and throwing them in ErrorT? Thanks, Eric On Sun, Jul 21, 2013 at 7:00 AM, Arie Peterson ar...@xs4all.nl wrote: On Thursday 18 July 2013 23:05:33 Eric Rasmussen wrote: […] Would there be any interest in cleaning that up and adding it (or something similar) to Control.Monad.CatchIO? […] MonadCatchIO-transformers is being deprecated, as recently GHC has removed the 'block' and 'unblock' functions, rendering the api provided by Control.Monad.CatchIO obsolete. Regards, Arie ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Haskell] [ANN] Initial release of the threepenny-gui library, version 0.1.0.0
On Sun, 21 Jul 2013, Sergey Mironov wrote: Hi, I have a Path problem when installing threepenny-gui from Hackage. Probably somtething trivial. I have written a small script cabal-upload that tries to compile a package before uploading it to Hackage. That helps to assert that all required files are registered in the cabal file. http://hackage.haskell.org/package/cabal-scripts ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Haskell] [ANN] Initial release of the threepenny-gui library, version 0.1.0.0
Henning Thielemann wrote: On Sun, 21 Jul 2013, Sergey Mironov wrote: Hi, I have a Path problem when installing threepenny-gui from Hackage. Probably somtething trivial. I have written a small script cabal-upload that tries to compile a package before uploading it to Hackage. That helps to assert that all required files are registered in the cabal file. http://hackage.haskell.org/package/cabal-scripts Nice! However, I can't find the cabal-test executable after installing your package? Best regards, Heinrich Apfelmus -- http://apfelmus.nfshost.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wrapping all fields of a data type in e.g. Maybe
On 07/20/2013 04:49 PM, adam vogt wrote: Hi Michael, It's fairly straightforward to generate the new data with template haskell [1], and on the same page, section 10.7 'generic' zipWith is likely to be similar to your merging code. [1] http://www.haskell.org/haskellwiki/Template_Haskell#Generating_records_which_are_variations_of_existing_records I don't know any TH yet, but this looks like it just might work. Thanks for the suggestion! ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] catching IO errors in a monad transformer stack
I think most people use monad-control these days for catching exceptions in monad stacks (http://hackage.haskell.org/package/monad-control-0.3.2.1). The very convenient lifted-base package ( http://hackage.haskell.org/package/lifted-base) depends on it and exports a function Control.Exception.Lifted.catch: Control.Exception.Lifted.catch :: (MonadBaseControl IO m, Exception e) = m a - (e - m a) - m a I'd recommend you use that instead of MonadCatchIO. On Mon, Jul 22, 2013 at 4:13 AM, Eric Rasmussen ericrasmus...@gmail.comwrote: Arie, Thanks for calling that out. The most useful part for my case is the MonadCatchIO implementation of catch: catch :: Exception e = m a - (e - m a) - m a Hoogle shows a few similar functions for that type signature, but they won't work for the case of catching an IOException in an arbitrary monad. Do you happen to know of another approach for catching IOExceptions and throwing them in ErrorT? Thanks, Eric On Sun, Jul 21, 2013 at 7:00 AM, Arie Peterson ar...@xs4all.nl wrote: On Thursday 18 July 2013 23:05:33 Eric Rasmussen wrote: […] Would there be any interest in cleaning that up and adding it (or something similar) to Control.Monad.CatchIO? […] MonadCatchIO-transformers is being deprecated, as recently GHC has removed the 'block' and 'unblock' functions, rendering the api provided by Control.Monad.CatchIO obsolete. Regards, Arie ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
