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/htm...
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
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
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