Hi,

I've defined the datatype:

data Graph a b = Empty | Context a b :& Graph a b

and the function

 isEmpty     :: Graph a b -> Bool
 isEmpty Empty = True
 isEmpty _     = False

and when I do a test run with the graph,
( [ ],2,'c',[("down",3)]) :& Empty

Haskell is bringing the message "  Not in scope: data constructor `:&' "
Why is that so?

Kind regards