Lennart Augustsson wrote:
I don't see any breaking of referential transparence in your code. Every time you do an IO operation the result is basically non-deterministic since you are talking to the outside world. You're assuming the IO has some kind of semantics that Haskell makes no promises about.
I'm not saying that this isn't a problem, because it is. But it doesn't break referential transparency, it just makes the semantics of IO even more complicated.
+1 If we are in a situation where really have to take this seriously, we already have a well-known standard trick for this kind of problem: refine the monad! We can always define NonInterlavedIO monad for the operations that does not use unsafeInterleaveIO. We have been doing this all the time including the recent STM stuff.
(I don't have a formal proof that unsafeInterleaveIO cannot break RT, but I've not seen an example where it does yet.)
-- Lennart