It's not as bad as you think. You can do this:
{-# OPTIONS -fglasgow-exts #-}
module Apply where
class Apply f a b | f -> a, f -> b where apply :: f -> a -> b
instance Apply (a -> b) a b where apply f a = f a
instance Apply (a1 -> b1, a2 -> b2) (a1, a2) (b1, b2) where apply (f1, f2) (a1, a2) = (f1 a1, f2 a2)
[snip]
Very nice. But in the scrap-your-boilerplate spirit, it would be nice if one could instead say
instance* Apply (T (a -> b)) a b where
apply (T f) a = T (f a)where instance* is an instance template, and T is a ``shape functor'' (in the sense of polynomial functors specifying an y of algebra/coalgebra/bialgebra/dialgebra). Or maybe even go for analytic functors (a la Joyal).
Well, I guess it's up to me to work out the theory... [based on the work of (at least) Jay, Hinze, Jeuring, Laemmel, Jansson and Peyton-Jones ! ]
Jacques _______________________________________________ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
