file suffixes

I recall that at one point GHC came with "bundles", built in "ways", like profiling, parallel, tickyticky, etc.. There was also some filename-mangling scheme for distinguishing .hi interface and .o object files from the different bundles. My question is, what was that filename-mangling scheme? I ask because I'm about to do something similar for nhc98's "ways" (heap-profiling, time-profiling, tracing, etc.), and some consistency here might be useful. Regards, Malcolm