Re: compare on Double

20 Mar 2007

      On Tue, Mar 20, 2007 at 03:53:58PM +0000, Malcolm Wallace wrote:
...
Ian Lynagh  wrote:
...
(D# x) `compare` (D# y) | x <## y   = LT
                            | x ==## y  = EQ
                            | otherwise = GT
becomes
(D# x) `compare` (D# y) | x <## y   = LT
                            | x ==## y  = EQ
                            | x >## y   = GT
                            | otherwise = error "Incomparable values"
I'm pretty uncomfortable with calling 'error' in this situation.  How
about throwing an imprecise exception instead?
Doesn't error throw an imprecise exception?

We already have things like

    remInteger ia ib
     | ib == 0 = error "Prelude.Integral.rem{Integer}: divide by 0"

We could

    throw (ArithException something)

instead if that's what you mean, but I think we'd need a new constructor
for something. I'm not sure if it should be an ArithException or not.

(should remInteger above throw (ArithException DivideByZero)? We'd give
a less useful message to the developer, but have something possibly more
useful to catch. I've wished for exceptions to have a stack of locations
in the past; perhaps that should be another proposal.)

Thanks
Ian