Re: [Haskell-cafe] template haskell for typeclass synonyms

It's first time I use TH. It would be nice to point out the motivations for using it. If everything TH does is doable without it, the point of using it is write less code, eliminating some necessary and automatically computable code. But I guess there is some more ..... paolino 2010/11/2 Antoine Latter

2010/11/1 Paolino :

...

I think I've got something nice in the end.

http://hpaste.org/41042/classsynonymhs

example:

class ( ParteDi (Servizio a) s , Read a , Eq a , Show a , Integer `ParteDi` s ) => SClass s a

$(classSynonym ''SClass)

ghci ":i SClass" command is printing some strange type variables but it compiles

Template Haskell might be overkill for this. In the past, I've done:

...

class (Eq b, Show b, MyClass b, MyOtherClass b) => MySynonym b instance (Eq b, Show b, MyClass b, MyOtherClass b) => MySynonym b

I think this requires a couple of GHC extensions, but TemplateHaskell is an extension as well. Maybe there are pitfalls with this approach.

Antoine