Re: [Haskell-cafe] Is it possible to get the information of instances of a type?
For TH look also at http://www.mail-archive.com/haskell-cafe@haskell.org/msg13057.html 2011/10/27 Magicloud Magiclouds > On Thu, Oct 27, 2011 at 1:57 AM, Brent Yorgey > wrote: > > On Wed, Oct 26, 2011 at 09:10:23PM +0400, MigMit wrote: > >> Can't be done. Even if this particular module doesn't contain > >> "instance Class Type", it's quite possible that the said instance > >> would be defined in another module, about which this one knows > >> nothing about. > > > > That doesn't mean it can't be done, only that you would have to be > > explicit about which modules to look in. > > > > -Brent > > > > ___ > > Haskell-Cafe mailing list > > Haskell-Cafe@haskell.org > > http://www.haskell.org/mailman/listinfo/haskell-cafe > > > > May I know more about this? Have not used TH on this subject. > > -- > 竹密岂妨流水过 > 山高哪阻野云飞 > > ___ > 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] Is it possible to get the information of instances of a type?
On Thu, Oct 27, 2011 at 1:57 AM, Brent Yorgey wrote: > On Wed, Oct 26, 2011 at 09:10:23PM +0400, MigMit wrote: >> Can't be done. Even if this particular module doesn't contain >> "instance Class Type", it's quite possible that the said instance >> would be defined in another module, about which this one knows >> nothing about. > > That doesn't mean it can't be done, only that you would have to be > explicit about which modules to look in. > > -Brent > > ___ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > May I know more about this? Have not used TH on this subject. -- 竹密岂妨流水过 山高哪阻野云飞 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Is it possible to get the information of instances of a type?
On Thu, Oct 27, 2011 at 7:04 AM, Evan Laforge wrote: >> No, this lists all the instances of a class. OP asked for the classes >> of which a given type is an instace. >> >> Presumably it is possible, since Haddock does it! In the >> documentation generated for a type it lists classes of which the type >> is an instance. So you might want to look at how Haddock does it. I >> suspect the only way is through the GHC API. > > ghci :info does it too. > > ___ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > Generally looked into GHC's source, seems like the :info (line 850 of compiler/main/InteractiveEval.hs) is internal function. At last, GHC parsed the code, it sure knew the type info. -- 竹密岂妨流水过 山高哪阻野云飞 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Is it possible to get the information of instances of a type?
> No, this lists all the instances of a class. OP asked for the classes > of which a given type is an instace. > > Presumably it is possible, since Haddock does it! In the > documentation generated for a type it lists classes of which the type > is an instance. So you might want to look at how Haddock does it. I > suspect the only way is through the GHC API. ghci :info does it too. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Is it possible to get the information of instances of a type?
On Wed, Oct 26, 2011 at 09:10:23PM +0400, MigMit wrote: > Can't be done. Even if this particular module doesn't contain > "instance Class Type", it's quite possible that the said instance > would be defined in another module, about which this one knows > nothing about. That doesn't mean it can't be done, only that you would have to be explicit about which modules to look in. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Is it possible to get the information of instances of a type?
On Wed, Oct 26, 2011 at 09:15:41AM -0700, Nathan Howell wrote: > On Wed, Oct 26, 2011 at 6:53 AM, Magicloud Magiclouds < > magicloud.magiclo...@gmail.com> wrote: > > > But in Haskell, could I write a code to list the classes that a type > > instanced? > > TemplateHaskell as well. > > > > It's possible with TemplateHaskell. Look at classInstances and the ClassI > data constructor. > > http://haskell.org/ghc/docs/7.0.4/html/libraries/template-haskell-2.5.0.0/Language-Haskell-TH.html#v:classInstances No, this lists all the instances of a class. OP asked for the classes of which a given type is an instace. Presumably it is possible, since Haddock does it! In the documentation generated for a type it lists classes of which the type is an instance. So you might want to look at how Haddock does it. I suspect the only way is through the GHC API. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Is it possible to get the information of instances of a type?
Can't be done. Even if this particular module doesn't contain "instance Class Type", it's quite possible that the said instance would be defined in another module, about which this one knows nothing about. On the other hand, what would you do with that information? Отправлено с iPad 26.10.2011, в 17:53, Magicloud Magiclouds написал(а): > Hi, > If this was in ruby or other languages that support reflection, it > won't be a question. > But in Haskell, could I write a code to list the classes that a type > instanced? > TemplateHaskell as well. > -- > 竹密岂妨流水过 > 山高哪阻野云飞 > > ___ > 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] Is it possible to get the information of instances of a type?
On Wed, Oct 26, 2011 at 6:53 AM, Magicloud Magiclouds < magicloud.magiclo...@gmail.com> wrote: > But in Haskell, could I write a code to list the classes that a type > instanced? > TemplateHaskell as well. > It's possible with TemplateHaskell. Look at classInstances and the ClassI data constructor. http://haskell.org/ghc/docs/7.0.4/html/libraries/template-haskell-2.5.0.0/Language-Haskell-TH.html#v:classInstances ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Is it possible to get the information of instances of a type?
Magicloud Magiclouds wrote: > If this was in ruby or other languages that support reflection, it > won't be a question. > But in Haskell, could I write a code to list the classes that a type > instanced? In regular Haskell, type information is completely lost after compilation, so you can't recover any of that. There is no run-time type information like in languages with OO inheritance. However, types can choose to provide type information through the Typeable type class (Data.Typeable). Generally you wouldn't want to use it, if you write Haskell properly (i.e. if you don't try to write Ruby in Haskell). > TemplateHaskell as well. I'm not sure about that one. Greets, Ertugrul -- nightmare = unsafePerformIO (getWrongWife >>= sex) http://ertes.de/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Is it possible to get the information of instances of a type?
Hi, If this was in ruby or other languages that support reflection, it won't be a question. But in Haskell, could I write a code to list the classes that a type instanced? TemplateHaskell as well. -- 竹密岂妨流水过 山高哪阻野云飞 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
