I'm sorry this was a typo. Here's the correct one: {-# LANGUAGE FlexibleInstances, MultiParamTypeClasses #-} class Add a b where add :: a -> b instance Num a => Add a a where add = id instance (Num a, Add a b) => Add a (a -> b) where add x y = add (x + y) I'm trying to use the printf trick to achieve this. On Tue, Mar 13, 2012 at 9:30 PM, Johannes Waldmann < waldmann@imn.htwk-leipzig.de> wrote:
Can someone tell me why this is not working
that "someone" is actually ghci:
Prelude> instance (Num a, Add a b) => Add (a -> b) where add x y = add (x + y)
<interactive>:8:30: Expecting one more argument to `Add (a -> b)' In the instance declaration for `Add (a -> b)'
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