Hello! It seems like you would want to use "reifyInstances" in order to get all of the instances associated with a class. Then, you can match up the variables in each instance with the variables in the class declaration, and create a mapping from the class variables to the instance parameters. Then, you can apply these mappings with substT: http://hackage.haskell.org/packages/archive/haskell-src-meta/0.5.1.2/doc/html/Language-Haskell-Meta-Utils.html#v:substT
The result would also need to have the context of the instance, perhaps reduced to just the constraints that mention the type variables used in the selected function. -Michael Sloan On Fri, Apr 13, 2012 at 11:37 AM, Ismael Figueroa Palet <ifiguer...@gmail.com> wrote: > Hi all, I think this is the right place for the following questions and I > thank beforehand for your answers :-) > > > I'm experimenting with typeclasses and TH, and I want to define a 'macro' > that works more or less like this: > > Given the name of a typeclass and a function, return the expressions > corresponding to the type-annotated instances, for instance > > $(foo Show show) > > should translate to: > > ["(show :: Int -> String)", "(show :: Bool -> String)", ....] > > for all instances currently in scope. > > I'm currently playing with the isInstance function (I'm running GHC 7.4.1) > and can get a list of instances, and check if a given type is part of a > typeclass or not. But I don't know how to create the expression > corresponding to "instantiated function", as above. > > Thanks! > -- > Ismael > > > _______________________________________________ > 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