how to use ghci-debugger with packages

Hello, I have a program which uses some code in a package, and I would like to be able to find out the source of an error which is occuring inside that package. Can I use the ghci-debugger to do this? If I try to set a breakpoint inside the package, it says: "cannot set breakpoint on Vector.Sparse.Wrappers.vmergeOp: module Vector.Sparse.Wrappers is not interpreted" But this page: http://www.haskell.org/ghc/dist/current/docs/users_guide/ghci-debugger.html has no use of the word "package", so I assume that reading that (long) document won't ansnwer my question... Thank you, Frederik -- http://ofb.net/~frederik/