Concisely specify which classes to derive for your datatypes.
As well as the standard derivable classes, it can also
New.Data class and Happstack.Data.Default's
deriveAll function takes a list of classes to derive and
a block of declarations. It will additionally derive instances for
Typeable, Old.Data and New.Data.
$( deriveAll [''Show, ''Eq, ''Default] [d| data Foo a = Foo a data Bar = Baz | Quux |] )
Derives instances for syb-with-class's Data class and Happstack.Data.Default's Default class. The list of names should be of the form [''Foo,''Bar,..]