class virtual[['i, 'o]]start :object..end
Use inherit ['i, 'o] start to derive a class to represent the
initial state of a machine. It's start method initiates the machine
with the virtual private guard method.
method private virtual guard : ('i, 'o, unit) guardThe first guard evaluationed by the machine after starting.
method start : ('i, 'o, unit) tStarts a new gadget, i.e. start (guard self#guard).