Brandon S. Allbery KF8NH wrote: > On May 8, 2009, at 13:08 , Sittampalam, Ganesh wrote: >> Brandon S. Allbery KF8NH wrote: >>> and therefore must be in IO. You may be thinking that it would >>> return a result for _|_, but as described if you fed it _|_ it could >>> only produce False (if the _|_ has been evaluated you would not be >>> able to reach the test). >> >> It could probably return True in GHC since you can catch exceptions. >> That still doesn't mean it solves the halting problem, of course. > > Unless it catches exceptions itself (which strikes me as a bad idea; > it becomes a trivial way to ignore exceptions, leading to bad > programming practices) either they're handled inside the _|_ (in > which case it isn't _|_ from the standpoint of our test) or in an > outer scope (in which case our test produces _|_ from the standpoint > of the exception handler).
Surely it just needs to inspect the thunk to decide whether it's _|_ or not, rather than entering it? Ganesh =============================================================================== Please access the attached hyperlink for an important electronic communications disclaimer: http://www.credit-suisse.com/legal/en/disclaimer_email_ib.html =============================================================================== _______________________________________________ Haskell-Cafe mailing list [email protected] http://www.haskell.org/mailman/listinfo/haskell-cafe
