Mysterious slowness/crashing in GHCi

[Simon Marlow]

Hi folks,

GHCi has some weird behaviour sometimes with one or more of these symptoms:

  - becoming very slow and/or unresponsive
  - gobbling up memory
  - crashing with "thread blocked indefinitely on MVar"

Some people have reported this happening when they weren't even doing 
anything, GHCi was just sitting at the prompt.

e.g. this ticket:

   http://hackage.haskell.org/trac/ghc/ticket/4245

All the reports were Windows, but I've seen it happen on Mac too (but 
not Linux).

I really need a way to reproduce this.  If anyone has any clues, or can 
offer any more information (even if it's just a "me too, on platform 
X"), please let us know.

Cheers,
	Simon