On Feb 6, 2008 10:04 AM, Luke Palmer <lrpalmer@gmail.com> wrote:
How about:
inv m = do
success <- (m >> return True) `mplus` return False
if success then mzero else return ()
Prelude Control.Monad> inv []
[()]
Prelude Control.Monad> inv [10]
[()]
--
Felipe.
