Re: [Haskell-cafe] Proposal to solve Haskell's MPTC dilemma

On Fri, May 21, 2010 at 3:56 AM, Max Bolingbroke wrote:

On 21 May 2010 01:58, Carlos Camarao wrote:

...

But this type-correct program would become not typeable if instances such as the ones referred to before (by Daniel Fischer)

I was thinking this through, and the situation is more complex than I had thought.

It seems that single param type classes enjoy a nice property: * Adding an instance to the module defining the class cannot conflict with any non-orphan instance defined elsewhere * Adding an instance for a type for a class *to the module defining that type* cannot conflict with any non-orphan instance defined elsewhere

This is only true in the absence of recursive imports. Otherwise, those points imply that I can put one instance in the module defining the type and another in the module defining the class without conflict. -- Dave Menendez http://www.eyrie.org/~zednenem/