Brandon S Allbery KF8NH
On 8/15/10 11:40 , Tillmann Rendel wrote:
But in a world passing interpretation of IO, print is supposed to be a pure Haskell function. So the value world2 can only depend on the values of print and world1, but not on the actions of some concurrent thread.
If print is not restricted to be a pure Haskell function, we don't need the world passing in the first place.
I am confused by this discussion. I originally thought some time back that IO was about "world passing", but in fact it's just handing off a baton to insure that a particular sequence of IO functions is executed in the specified sequence and not reordered. Nothing in the "baton" is intended to represent the actual "state of the world", nor is anything said about concurrent actions either in another thread of the current program or elsewhere outside the program; only ordering of calls in the *current* thread of execution. (Which, hmm, implies that unsafePerformIO and unsafeInterleaveIO are conceptually similar to forkIO.)
IO is just a simple language to express impure operations. What we discuss is how to /interpret/ IO, or more specifically how to translate IO computations into pure ones mentally. Greets, Ertugrul -- nightmare = unsafePerformIO (getWrongWife >>= sex) http://ertes.de/