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

[Jules Bean]

On 25 Jan 2005, at 09:30, Daniel Fischer wrote:

> putStrLn "hello" >>= (\_ -> mzero)
>  ===
> (\_ -> mzero) ()

...no. That last identity holds for 'return ()' but not for 'putStrLn 
"hello"'.

The monad law is a law for 'return'  not for arbitrary things.

Jules