helper-function for imperative

exmaple : "Shut the door."
If the subjects of the Imperative sentences are always "you", then I don't think it's necessary to set a marker. As all the pronouns are required for anaphore resolution anyway. On the other hand, if we don't have the "imperative" marker, then the above representation for the imperative sentences will look the same as "statements", i.e. "You shut the door."