No. You'll have to use a newtype. Type parameter order is a huge deal for some types, e.g. monad transformers, you'd better think about it beforehand. On Thu, 09 May 2013 19:39:12 -0800 Christopher Howard wrote:

Hi. Does Haskell allow you to flip around type parameters somehow? I was playing around with toy code (still learning the fundamentals) and I came up with a class like this:

code: -------- class Rotatable2D a where

rotate :: (Num b) => (a b) -> b -> (a b) --------

It was easy to make an instance of a generic single-parameter type:

code: -------- data Angle a = Angle a deriving (Show)

instance Rotatable2D Angle where

rotate (Angle a) b = Angle (a + b) --------

But let's say I have something a little more complicated:

code: -------- data CircAppr a b = CircAppr a a b -- radius, rotation angle, number of points --------

I think I need something like so: -------- instance Rotatable2D (\x -> CircAppr x a) where

rotate (CircAppr a b c) d = CircAppr a (b + d) c --------

But I tried that and it isn't valid syntax.