On Thu, Mar 5, 2009 at 2:08 PM, Simon Marlow wrote:

So the argument is something like: we can think of the result of a call to unsafeInterleaveIO as having been chosen at the time we called unsafeInterleaveIO, rather than when its result is actually evaluated. This is on dodgy ground, IMO: either you admit that the IO monad contains an Oracle, or you admit it can time-travel.   I don't believe in either of those things :-)

As it turns out, time-travel as a vehicle for computation has a long tradition in the more advanced systems; see http://www.frc.ri.cmu.edu/~hpm/project.archive/general.articles/1991/TempCom... for an example.