Ambiguous defaults

[Andrew J Bromage]

G'day all.

On Thu, Jan 02, 2003 at 05:49:41PM +0100, Ferenc Wagner wrote:

> What's the way to express the following: a compound object
> is generally made up of two components with identical type.

This should work:

\begin{code}
module Test where

class Component b where
    property :: b -> Int

class (Component b) => Compound a b | a -> b where
    decompose :: a -> (b,b)
    additive :: a -> Int
    additive x = property l + property r
        where (l,r) = decompose x
\end{code}

Cheers,
Andrew Bromage