[Haskell-cafe] Re: what is inverse of mzero and return?

In article <200501231934.01764.daniel.is.fischer@web.de>, Daniel Fischer wrote:

from an earlier message of Keean:

...

1. |mzero >>= f == mzero| 2. |m >>= (\x -> mzero) == mzero| 3. |mzero `mplus` m == m| 4. |m `mplus` mzero == m|

What exactly does 2. mean in the IO-case? a) the results of both calculations are equal -- then it also holds for IO. b) both produce the same output and the same result -- then it doesn't hold for IO. I think, a) is the correct interpretation.

I disagree. Clearly (putStrLn "Hello" >> mzero) is not the same as mzero. -- Ashley Yakeley, Seattle WA