SJT's book has a limited definition of relation... why?
In 16.9 of SJT's book "Craft of Functional Programming" he says "A binary relation relates together certain elements of a set"
My problem with this is that the elements do not have to be in the same set. A relation is a subset of the cross product of sets A and B, where A and B are not of the same type.
Next he gives a type definition
type Relation a = Set (a,a)
And I think it should be:
type Relation a,b = Set (a,b)