[Haskell-cafe] Template Haskell: Generate annotated function of a typeclass
Ismael Figueroa Palet
ifigueroap at gmail.com
Thu May 10 14:18:05 CEST 2012
Hi Michael, I was able to do what I wanted using reify instead of
reifyInstances, and also I used applyT instead of substT.
2012/4/13 Ismael Figueroa Palet <ifigueroap at gmail.com>
> 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
>> > thank beforehand for your answers :-)
>> > I'm experimenting with typeclasses and TH, and I want to define a
>> > 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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