"instrumenting" functions

Hi all, Given a module with top-level (functions) f1 ... fn, I would like to generate/compile an "instrumented" version where, say, each function prints the string "hello", every time it is called. Can anyone suggest some ways of doing this? One option is a core-to-core transform with an unsafePerformIO (print "hello") stuck into the appropriate places. But perhaps there are better ways? Ideally I'd like to instrument each "App" to log every function application. Are other libraries or tools that use the GHC API to do this sort of thing? Thanks in advance! Ranjit.