I think I understand that, but without actually writing it out, it's going to be impossible to test. The types I was talking about go as: type Context a b

I think I understand that, but without actually writing it out, it's going to be impossible to test. The types I was talking about go as: type Context a b = (Adj b, Node, a, Adj b) type Adj b = [(b, Node)] It definitely allows traversal, and adding nodes seems to be possible, too (judging from the api, of course, it ought to be :)