:: Monoid_a _ => _ a package:rio

O(1) Empty vector
Lifted version of "System.Exit.exitFailure". @since 0.1.9.0.
Lifted version of "System.Exit.exitSuccess". @since 0.1.9.0.
The identity of mplus. It should also satisfy the equations
mzero >>= f  =  mzero
v >> mzero   =  mzero
The default definition is
mzero = empty
Retrieves the monad environment.
Return the state from the internals of the monad.