What is needed is a distribution, one for every composition rule, that assigns a likelihood to every allowable combination of constituents. There are many issues to attend to. And there is the very practical issue of computation. Provably, very hard by standard computation theory, at least in the case of vision. But maybe we are asking for too much.
Detail comes later.
A line is seen quickly and coarsely as a line, but the details of its width, intensity, straightness, position and so on are seen more slowly. Composition rules are constructed simultaneously and invariantly at each of multiple scales. The more you look the more you see. We should perhaps think instead about a process that is finite only in theory. The discernable detail and compositional complexity of even a single scene are nearly infinite.