On 26 April 2006 01:42, John Meacham wrote:
It was pointed out that you can't necessarily know what routines to avoid in unsafePerformIO without mandating certain things _don't_ use concurrency, rather than that, how about the following:
"Whether an implementation can yield to another thread inside an unsafePerformIO action is implementation dependent, however an implementation should not 'go wrong'"
Better, certainly. I agree that rather than taling about "going wrong" we should say "may not yield". And concurrent foreign calls may not behave concurrently, reentrant foreign calls may fail if they call back to Haskell. One common case (perhaps the only common case) where this happens is hGetContents. The lazy stream returned by hGetContents will not behave in a non-blocking way in a cooperative implementation. I can't decide which demon to blame here: lazy I/O or cooperative concurrency :-) Cheers, Simon