It looks, there remains a questions on memory distribution in ghc-5.00 -interpreted :

can ghci provide a command measuring the part of heap taken by interpreted programs, by interfaces? (or, at least, their sum)

Ah, I see now. You'd like to know how much memory your program is using, compared to GHCi itself? Hmm. Unfortunately I can't see a good way to do this I'm afraid. However, you can always compile the program and use profiling...

For, with -O and much in-lining, the interfaces may be very large.

You really don't want to use -O with GHCi (in fact, at the moment you can't). Cheers, Simon