[Haskell-cafe] Fwd: incorrect MonadPlus law "v >> mzero = mzero"?

Brandon Allbery allbery.b at gmail.com
Mon Feb 3 23:00:36 UTC 2014

On Mon, Feb 3, 2014 at 5:51 PM, Dan Burton <danburton.email at gmail.com>wrote:

> Indeed this issue is not limited merely to multiple failure values.
>     >>> runMaybeT $ lift (putStrLn "effect") >> mzero
>     effect
>     >>> runMaybeT mzero
> So you're right. This law is being violated

I thought it was fairly well known that IO violates one of the monad laws,
in a way that would lead to this?

brandon s allbery kf8nh                               sine nomine associates
allbery.b at gmail.com                                  ballbery at sinenomine.net
unix, openafs, kerberos, infrastructure, xmonad        http://sinenomine.net
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