Using fundeps I came up with this: class T funs arg res | funs -> arg res, arg res -> funs where tuple :: funs -> arg -> res
instance (a ~ a0, a0 ~ a1) => T (a0 -> b, a1 -> c) a (b, c) where tuple (f, g) a = (f a, g a) instance (a ~ a0, a0 ~ a1, a1 ~ a2) => T (a0 -> b, a1 -> c, a2 -> d) a (b, c, d) where tuple (f, g, h) a = (f a, g a, h a) Intuitively it seems to be exactly the same as the type families' aproach, and looks quite clear too. On 9/15/11, Richard O'Keefe <o...@cs.otago.ac.nz> wrote: > > On 14/09/2011, at 2:45 PM, Casey McCann wrote: > >> >> class Tuple t where >> type Arg t :: * >> type Result t :: * >> tuple :: t -> Arg t -> Result t >> >> instance (x1 ~ x2) => Tuple (x1 -> a, x2 -> b) where >> type Arg (x1 -> a, x2 -> b) = x1 >> type Result (x1 -> a, x2 -> b) = (a, b) >> tuple (f, g) x = (f x, g x) > > That's it, that's what I was after. Thanks. > > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > -- Markus Läll _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
