[Haskell-cafe] MPTC inheritance

[Derek Gladding]

Please forgive me if I'm still mentally contaminated by the OO way of 
seeing (and discussing) the universe, but I'm trying to figure out how 
to "inherit an interface" from a multi-parameter type class.

I have a Graph class that's parameterisable by Node and Edge type:

class (Node a, Edge b) => Graph a b where
     (lots of stuff that you can do with Graph a b)

Now, I'd like to build a FooGraph on top of this that adds additional 
capabilities:

class (Graph a b) => FooGraph a b where
     (lots of additional stuff)

but this isn't allowed (kind mismatch).

Of couse, I can do:

class (Node a, Edge b) => FooGraph a b

but this means that I have to manually replicate the Graph a b 
operations in the FooGraph a b class definition, which is (a) work that 
the machine should (?) be able to do for me, and (b) fragile.

Any pointers / wisdom would be very much appreciated.

- Derek