Monad 二三念

Monad is type contractor.

1. make the evaluation by order.

2. Mark you touch a Monad. Once you touch Monad, you are in this Monad forever, otherwise you may be in danger.

3. function combination. In other words, a monad is a box- you can put things into the box (withreturn) and manipulate things inside of the box (with bind).