Runtime caught in an infinite loop
Triggering this bug seems a little fragile; but the program and method I've attached triggers the bug every time for me. It is minimal-ish, I certainly have cut it down a lot, and it perhaps could be made even smaller, but a lot of seemingly irrelevant changes to the file will fail to trigger the bug.
$ cabal configure && cabal build $ ./dist/build/deadlock/deadlock
And then edit the file and change the 1 to some other value, like 2. Configurator will reload the file within a second, and then I see that the thread that periodically writes something to standard out stops working, and that CPU usage goes to 100%, and that I can no longer type something in and have the program echo it back to me.
GHC-7.0.3 has no problem running this program.