On 11/6/05, Klaus Ostermann
instance Node Person where isConnectedTo g n (p1,p2) = (p1 == n) || (p2 == n)
At this point, isConnectedTo knows nothing about the third argument except that it is an edge, and there's no reason to think that an Edge is a tuple. All you can say is that there are two functions, n1 and n2, which extract the nodes of the edge. Use those instead, for example isConnectedTo g n p = n == n1 p || n == n2 p Couldn't match the rigid variable `e' against `(a, b)'
`e' is bound by the type signature for `isConnectedTo' Expected type: e Inferred type: (a, b) When checking the pattern: (p1, p2) In the definition of `isConnectedTo': isConnectedTo g n (p1, p2) = (p1 == n) || (p2 == n)
Hopefully this error makes more sense now. It's saying that it expected something of type 'e', but it found a tuple. regards, Fraser.