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

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