Hugs-Bugs

Download

hugs-bugs@haskell.org

November 2001

25 participants
32 discussions

RE: Not lazy/smart enough
by Simon Marlow 02 Nov '01

02 Nov '01

> >>>>> "Sohrab" == Sohrab Saran <sohrabsaran(a)hotmail.com> writes: > > > If at the Hugs interpreter prompt I type: > > 3/4 == 3/4 > > ...I get "True" > > If I now type: > > 3/0 == 3/0 > > ...I should get "True" but I get a divide-by-zero error > > instead. Anyone ready to fix this, or should I fix this myself? > > I don't believe this is a bug. > > Suppose we adopt your proposal, I think we'd also want to add the > following equalities too: > > 1. f 3 == f 3 = True > > 2. f 3 == g 3 = True where g x = f x > > 3. f 3 == g 3 = True where g x = x / 0; f x = x / 0 > > 4. f 3 == g 3 = True where g is semantically equivalent to f > > The problem with this is that it's hard to say why we'd accept 1-3 but > not accept 4 and accepting 4 requires us to solve the halting problem. I think you're missing the point - the original poster wants 3/0 to have a non-bottom value, namely Infinity, which would make the equality hold. This works in GHCi, because we choose to represent floating point exceptions with the special values Infinity and NaN, but a Haskell implementation isn't required to do this (see section 6.4 in the report). Personally I think GHC's behaviour is preferrable because it more closely matches the IEEE standard and other languages. Cheers, Simon

1 0

Not lazy/smart enough
by Sohrab Saran 01 Nov '01

01 Nov '01

If at the Hugs interpreter prompt I type: 3/4 == 3/4 ...I get "True" If I now type: 3/0 == 3/0 ...I should get "True" but I get a divide-by-zero error instead. Anyone ready to fix this, or should I fix this myself? _________________________________________________________________ Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp

3 2