On Wed, Oct 26, 2011 at 6:53 AM, Magicloud Magiclouds <magicloud.magiclouds@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