If you have GHC-6.6 or greater, try: let n = 2 in GHC.Base.breakpoint ()
GHC.Base.breakpoint doesn't work in the HEAD at the moment. We might want to restore it; I'm not sure. Since breakpoints are almost everywhere, it didn't seem necessary.
I don't understand the last sentence. Breakpoints didn't seem necessary since they are almost everywhere? Thanks, Frederik
I don't currently have breakpoints in either compiled code or expressions typed at the prompt, so you can't do exactly what Frederik was asking for, although if the code is in a source file then it works fine.
Instrumenting expressions typed at the prompt wouldn't be hard, I'll add that to the list.
The documentation for the GHCi debugger is here, FYI:
http://www.haskell.org/ghc/dist/current/docs/users_guide/ghci-debugger.html
Cheers, Simon