Wumpus

Copperbox revision 722.

I've sorted out the Frame module and made a type class that encompasses most of the relevant operations on frames. I suspect there will never be a lot of operations on frames in Wumpus. The most important one is coord which extracts the coordinates of a point in a frame into the standard Cartesian frame.


Something that I didn't really appreciate until today is that in points and coordinates are not synonymous in coordinate-free geometry (i.e the work of Tony DeRose and others at the University of Waterloo). This is a parallel of how vectors and points are different in affine geometry. One is free to use points as one likes in the coordinate-free approach but until they are extracted relative to a fixed frame they are considered "arbitrary".

For Wumpus this means I'm now happy with the types for creating lines that are Point -> Line. After I'd changed the Picture type to have Frame as the domain rather than Point, I was wondering what to do about the other types with Point as the domain (but where it seemed more natural) - I've concluded that they are fine.