On Sun, May 02, 2010 at 01:10:17PM +0200, Sebastian Fischer wrote:
What makes me wary is that GHC distinguishes between different kinds of non-terminating computations (those it can detect as black holes and those it can't). As a consequence, the semantics of my program depends on how I define the infinite loop don't_launch_first (the program either writes to stdout or doesn't).
For me, it is interesting to notice (and slightly disturbing) that this is intended and that the Control.Exception module defines the NonTermination exception to explicitly handle black holes.
If you think about it, there aren't a lot of options: (a) Don't provide a way of catching *any* kind of non-terminating computations. (b) Provide a way to catch some of them. (c) Solve the halting problem and catch'em all. =) Considering that someone who wants (a) can live with (b) or (c) just by ignoring the extra functionality, and that (c) is impossible, GHC provides (b). Cheers, -- Felipe.