If you can't change the definition you can use the syntax Björn Bringert
added back in 2006 or so for StandaloneDeriving.
Just turn on
{-# LANGUAGE StandaloneDeriving, DeriveDataTypeable #-}
and then you can use
deriving instance Typeable Foo
-Edward
On Tue, Aug 5, 2014 at 1:47 PM, Volker Wysk
Am Dienstag, 5. August 2014, 12:46:23 schrieb Carter Schonwald:
i assume 7.6 and 7.8, if we're talking GHC rather than GCC :)
in 7.8 you can't define userland typeable instances, you need only write deriving (Typeable) and you're all set. add some CPP to select the instances suitable
So you need to be able to change the definition of the data type, in order to add deriving (Typeable). It's not possible to add a Typeable instance declaration later.
When you can't change the definition, you're out of luck.
Okay, V.W. _______________________________________________ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users