[Haskell-cafe] A question about "monad laws"

David Benbennick dbenbenn at gmail.com
Tue Feb 12 01:50:44 EST 2008

On Feb 11, 2008 10:18 PM, Uwe Hollerbach <uhollerbach at gmail.com> 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?

I'm doing Science and I'm still alive.

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