Would you mind illustrating the source-to-source transformation on a small example? Suppose there's a package foo with a module
module C where f = 'a'
that this package is grafted in at both A.B and X, and there's a module
module Foo (f) where import A.B.C (f) import X.C (f)
One possible transformation is this: module A.B.C where f = 'a' module X.C (module A.B.C) where import A.B.C
I also can't see much to gain from local graftings. But that leaves us wanting each combination of
default root for package + local module name
unique across all packages, doesn't it?
No - we don't want globally-unique module names (that's what we were trying to solve in the first place). We therefore do want local grafting. There are good uses for packages which overlap in their default installation - versioning is one example. Cheers, Simon