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
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