On Wed, 2011-09-14 at 13:56 +1200, Richard O'Keefe wrote:
> I don't *expect* to implement anything just once. I am perfectly
> happy writing as many instance declarations as I have tuple sizes
> that I care about.
Ah, okay... then sure, you can do this:
class Tuple a b c | a b -> c where
tuple :: a -> b -> c
instance Tuple (a -> b, a -> c) a (b,c) where
tuple (f,g) x = (f x, g x)
and so on... You'll need fundeps (or type families if you prefer to
write it that way), and probably at least flexible and/or overlapping
instances, too, but of course GHC will tell you about those.
--
Chris Smith
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