val return : 'a -> 'a t
val (>>=) : 'a t -> ('a -> 'a t) -> 'a tt >>= f returns a computation that sequences the computations represented by two monad elements. The resulting computation first does t to yield a value v, and then runs the computation returned by f v.
val (>>|) : 'a t -> ('a -> 'b) -> 'a tt >>| f is t >>= (fun a -> return (f a)).