On Feb 12, 2008 6:12 AM, Jan-Willem Maessen <[EMAIL PROTECTED]> wrote:
> > On Feb 12, 2008, at 1:50 AM, David Benbennick wrote: > > > On Feb 11, 2008 10:18 PM, Uwe Hollerbach <[EMAIL PROTECTED]> > > wrote: > >> If I fire up ghci, import > >> Data.Ratio and GHC.Real, and then ask about the type of "infinity", > >> it > >> tells me Rational, which as far as I can tell is Ratio Integer...? > > > > Yes, Rational is Ratio Integer. It might not be a good idea to import > > GHC.Real, since it doesn't seem to be documented at > > http://www.haskell.org/ghc/docs/latest/html/libraries/. If you just > > import Data.Ratio, and define > > > >> pinf :: Integer > >> pinf = 1 % 0 > > > >> ninf :: Integer > >> ninf = (-1) % 0 > > > > Then things fail the way you expect (basically, Data.Ratio isn't > > written to support infinity). But it's really odd the way the > > infinity from GHC.Real works. Anyone have an explanation? > > An educated guess here: the value in GHC.Real is designed to permit > fromRational to yield the appropriate high-precision floating value > for infinity (exploiting IEEE arithmetic in a simple, easily- > understood way). If I'm right, it probably wasn't intended to be used > as a Rational at all, nor to be exploited by user code. > > -Jan-Willem Maessen > > Well... I dunno. Looking at the source to GHC.Real, I see infinity, notANumber :: Rationalinfinity = 1 :% 0notANumber = 0 :% 0 This is actually the reason I imported GHC.Real, because just plain % normalizes the rational number it creates, and that barfs very quickly when the denominator is 0. But the values themselves look perfectly reasonable... no? Uwe
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