I have a prelude-extras package that I use for 'bound' which contains those Eq1, Show1, etc classes.
(As an unrelated aside bound packages up the generalized de Bruijn indices you did with Hinze as a reusable Haskell 98 monad transformer, you may find it interesting.)
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On Dec 8, 2012, at 8:24 PM, Ross Paterson
On Sat, Dec 08, 2012 at 10:55:45PM +0000, Henning Thielemann wrote:
On Fri, 7 Dec 2012, Edward Kmett wrote:
I will be sad to see those instances go, but I'm also +1
How about:
import Prelude hiding (Show, showsPrec) import qualified Prelude as P
class Show m where showsPrec :: (P.Show e, P.Show a) => Int -> m (Either e a) -> ShowS
instance (Show m, P.Show e, P.Show a) => P.Show (EitherT e m a) where showsPrec d (EitherT m) = showParen (d > 10) $ showString "EitherT " . showsPrec 11 m
A more economical variation on this idea would be to lift these classes to functors, e.g.
class ShowF f where showsPrecF :: Show a => Int -> f a -> ShowS
instance (ShowF m, Show e, Show a) => Show (EitherT e m a) where showsPrec d (EitherT m) = showParen (d > 10) $ showString "EitherT " . showsPrecF 11 m
instance (ShowF m, Show e) => ShowF (EitherT e m) where showsPrecF = showsPrec
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