14 May
2002
14 May
'02
12:42 p.m.
On Tue, May 14, 2002 at 12:14:02PM +0100, Simon Marlow wrote:
The question we were considering was whether the following should hold in the IO monad:
(return () >>= \_ -> undefined) `seq` 42 == undefined
[as implied by the left-identity monad law]
This discrepancy applies to any state monad.
It also fails for the reader, writer and continuation monads, also thanks to lifted functions and tuples. The right-identity law also fails for these monads: (undefined >>= return) `seq` 42 /= undefined `seq` 42