[Haskell-cafe] Template Haskell: Generate annotated function of a typeclass
Ismael Figueroa Palet
ifigueroap at gmail.com
Fri Apr 13 22:12:50 CEST 2012
Thanks for your reply, in particular the reference to subsT!
I will work more on this next monday, and report my progress
2012/4/13 Michael Sloan <mgsloan at gmail.com>
> 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:
> 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
> <ifigueroap at 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
> > 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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> > Haskell-Cafe at haskell.org
> > http://www.haskell.org/mailman/listinfo/haskell-cafe
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